magmatic precipitation as a possible origin of noachian clays on mars hydrous clay minerals detected on the surface of mars have been interpreted as indicators of the hydrologic and climatic evolution of the planet the iron and magnesium rich clays described in thick extensive outcrops of noachian crust have been proposed to originate from aqueous weathering this would imply that liquid water was stable at the surface of early mars presumably when the climate was warmer and wetter here we show that iron and magnesium rich clays can alternatively form by direct precipitation from residual water rich magma derived fluids infrared reflectance spectra from terrestrial lavas from the mururoa atoll french polynesia that underwent this precipitation process are similar to those measured for the noachian crust such an origin is also consistent with the d h ratio of iron and magnesium rich clays in some martian meteorites and the widespread presence of these clays in massive basaltic lavas breccias and regolith we propose that the progressive degassing of the martian interior over time and the resultant increasingly water poor magmatic fluids and not a cooling climate may explain the absence of clays in hesperian aged and more recent formations

thickness and grain size distribution of the 2004 indian ocean tsunami deposits in periya kalapuwa lagoon eastern sri lanka abstract in this paper we describe the sedimentary characteristics of the 2004 indian ocean tsunami deposits in and around periya kalapuwa lagoon sri lanka periya kalapuwa is a coastal lagoon of about 13 km 2 area and has an average depth of about 1 m it is separated from the indian ocean by coastal barrier sand dunes of up to 9 m elevation through which two inlet channels open the lagoon to the ocean this region was hit by three waves during the 2004 indian ocean tsunami the second wave was largest 4 6 m and entered the lagoon not only via the two inlet channels but also by flowing over the sand dunes erosive scars were found on the sand dunes adjacent to the two inlets twenty seven core samples along with trenching and hand auger data show that the tsunami deposits are 9 cm thick on average up to 35 cm in the lagoon and up to 66 cm on the shore and are composed mainly of medium sand mean grain size 1 06 with low mud content 0 61 wt which is similar to the composition of sand from near the erosive scars in the sand dunes mean grain size 0 94 but different from the lagoon deposits mean grain size 1 68 mud content 4 7 wt the distribution of the tsunami deposits was limited to within about 1 km from each inlet the tsunami deposits become thinner and finer grained with increasing distance from the inlets most of the tsunami deposits are massive but some show sedimentary structures single or multiple graded bedding structures parallel laminations defined by layers of heavy minerals and muddy laminations our observations and analyses suggest that the tsunami deposits were formed mainly from sand eroded from sand dunes near the two inlets we estimated the total volume of tsunami sediments to be 83 000 m 3 by assuming that the sediments of the tsunami deposits were supplied only by erosion of sand dunes from near the two inlets this is equivalent to erosion of 83 m 3 of sand per meter of sand dune traversed by the tsunami wave

the morphology and dynamics of low amplitude bedwaves upon upper stage plane beds and the preservation of planar laminae experimental studies of subcritical unidirectional flow over upper stage plane beds of medium grained sand reveal the ubiquitous presence of low amplitude bedwaves flow depth was 0 11 m mean flow velocities were 0 86 1 0 m s 1 shear velocities were 0 058 0 71 m s 1 and dimensionless shear stresses were 0 56 0 87 bedwaves are asymmetrical in profile and range from 0 75 to 11 mm in height mainly 2 6 mm from 0 7 to 1 3 m in wavelength and have mean celerities of 10 mm s 1 flow records suggest that the bedwaves are associated with accelerating flow over the bedwave crests and flow which decelerates and diverges laterally over the troughs high resolution bed profiling during aggradation of the bed combined with subsequent box coring illustrates that these bedwaves are responsible for the planar laminae characteristic of upper stage plane beds lamina preservation is dependent upon the mean aggradation rate and the sequence of bedwaves of different height crossing any point individual laminae are more readily preserved at higher aggradation rates where the possibility of reworking by later bedwaves is reduced laminae are recognized by small changes in grain size and commonly a fining upwards at the top of laminae which is generated by fine grained material infiltrating a lower lamina in the leeside of a bedwave

tsunami history of an oregon coastal lake reveals a 4600 yr record of great earthquakes on the cascadia subduction zone bradley lake on the southern oregon coastal plain records local tsunamis and seismic shaking on the cascadia subduction zone over the last 7000 yr thirteen marine incursions delivered landward thinning sheets of sand to the lake from nearshore beach and dune environments to the west following each incursion a slug of marine water near the bottom of the freshwater lake instigated a few year to several decade period of a brackish 4 salinity lake four additional disturbances without marine incursions destabilized sideslopes and bottom sediment producing a suspension deposit that blanketed the lake bottom considering the magnitude and duration of the disturbances necessary to produce bradley lake s marine incursions a local tsunami generated by a great earthquake on the cascadia subduction zone is the only accountable mechanism extreme ocean levels must have been at least 5 8 m above sea level and the cumulative duration of each marine incursion must have been at least 10 min disturbances without marine incursions require seismic shaking as well over the 4600 yr period when bradley lake was an optimum tsunami recorder tsunamis from cascadia plate boundary earthquakes came in clusters between 4600 and 2800 cal yr b p tsunamis occurred at the average frequency of 3 4 every 1000 yr then starting 2800 cal yr b p there was a 930 1260 yr interval with no tsunamis that gap was followed by a 1000 yr period with 4 tsunamis in the last millennium a 670 750 yr gap preceded the a d 1700 earthquake and tsunami the a d 1700 earthquake may be the fi rst of a new cluster of plate boundary earthquakes and accompanying tsunamis local tsunamis entered bradley lake an average of every 390 yr whereas the portion of the cascadia plate boundary that underlies bradley lake ruptured in a great earthquake less frequently about once every 500 yr therefore the entire length of the subduction zone does not rupture in every earthquake and bradley lake has recorded earthquakes caused by rupture along the entire length of the cascadia plate boundary as well as earthquakes caused by rupture of shorter segments of the boundary the tsunami record from bradley lake indicates that at times most recently 1700 yr b p overlapping or adjoining segments of the cascadia plate boundary ruptured within decades of each other

haughton impact structure structural and morphological aspects haughton is a complex meteorite impact structure of tertiary age on devon island in the canadian arctic the 20 5 km diameter site was formed in essentially flat lying paleozoic carbonates roughly 1700 m in thickness overlying precambrian gneisses the structure comprises three concentric rings surrounding a central basin with interior peaks the outer ring diameter 20 5 km is an annulus of peaks separating the allen bay dolomites of the regional plateau from the same unit that has been downdropped towards the crater interior along a series of circumferential faults the middle ring of peaks diameter 14 15 km comprises both faulted allen bay dolomites and blocks of the underlying bay fiord formation uplifted 250 m hills of the inner elliptical ring 3 5 5 5 km in diameter are also formed from bay fiord formation and the underlying eleanor river formation brought up 600 m an interconnected series of normal faults occupies most of the annulus between the inner and outer rings within the central b

anatomy of a pressure induced ferromagnetic to paramagnetic transition in pyrrhotite implications for the formation pressure of diamonds 1 meteorites and diamonds encounter high pressures during their formation or subsequent evolution these materials commonly contain magnetic inclusions of pyrrhotite because magnetic properties are sensitive to strain pyrrhotite can potentially record the shock or formation pressures of its host moreover pyrrhotite undergoes a pressure induced phase transition between 1 6 and 6 2 gpa but the magnetic signature of this transition is poorly known here we report room temperature magnetic measurements on multidomain and single domain pyrrhotite under nonhydrostatic pressure magnetic remanence in single domain pyrrhotite is largely insensitive to pressure until 2 gpa whereas the remanence of multidomain pyrrhotite increases 50 over that of initial conditions by 2 gpa and then decreases until only 33 of the original remanence remains by 4 5 gpa in contrast magnetic coercivity increases with increasing pressure to 4 5 gpa below 1 5 gpa multidomain pyrrhotite obeys neel theory with a positive correlation between coercivity and remanence above 1 5 gpa it behaves single domain like yet distinctly different from uncompressed single domain pyrrhotite the ratio of magnetic coercivity and remanence follows a logarithmic law with respect to pressure which can potentially be used as a geobarometer owing to the greater thermal expansion of pyrrhotite with respect to diamond pyrrhotite inclusions in diamonds experience a confining pressure at earth s surface applying our experimentally derived magnetic geobarometer to pyrrhotite bearing diamonds from botswana and the central african republic suggests the pressures of the pyrrhotite inclusions in the diamonds range from 1 3 to 2 1 gpa these overpressures constrain the mantle source pressures from 5 4 to 9 5 gpa depending on which bulk modulus and thermal expansion coefficients of the two phases are used

palaeotsunami deposits a new zealand perspective abstract over the past few years geological investigations of coastal sediments in new zealand have provided evidence of past tsunami the identification of palaeotsunami deposits is helping to increase our knowledge about the sources magnitude and frequency of these events this paper briefly outlines both the key diagnostic characteristics used in new zealand to identify palaeotsunami deposits and the emerging findings related to recent research

serpentinization of the martian crust during noachian abstract this paper proposes a model of serpentinization of the southern martian crust that may explain the topographic dichotomy the absence of an associated free air gravity anomaly and the presence of strong magnetic anomalies in the southern hemisphere the thermodynamical conditions for serpentinization were likely met in the lithosphere during the noachian period this process may have decreased the density in the southern crust and created the topographic dichotomy different reactions of serpentinization that can form magnetite have been considered assuming an intense magnetic field core dynamo we obtain chemical remanent magnetizations that are in the order of the estimates deduced from martian magnetic anomaly studies the pertinence and the implications of our model concerning the early thermal evolution of mars are discussed with emphasis on the intensity of the paleo magnetic field

carbon and oxygen isotope study of the active water carbonate system in a karstic mediterranean cave implications for paleoclimate research in semiarid regions abstract in a semiarid climatic zone such as the eastern mediterranean region annual rainfall variations and fractionation processes in the epikarst zone exert a profound influence on the isotopic compositions of waters seeping into a cave consequently the isotopic compositions of speleothems depositing from cave waters may show complex variations that need to be understood if they are to be exploited for paleoclimate studies this is confirmed by a four year study of the active carbonate water system in the soreq cave israel the 18o smow values of cave waters range from 6 3 to 3 5 the highest 18o values occur at the end of the dry season in waters dripping from stalactites and reflect evaporation processes in the epikarst zone whereas the lowest values occur in rapidly dripping fast drip waters at the peak of the rainy seasons however even fast drip waters are about 1 5 heavier than the rainfall above the cave which is taken to reflect the mixing of fresh with residual evaporated water in the epikarst zone 13c pdb values of dissolved inorganic carbon dic vary from 15 6 to 5 4 with fast drip waters having lower 13c values mostly 15 6 to 12 and higher dic concentrations relative to pool and stalactite drip water the low 13c values of fast drip waters and their supersaturation with respect to calcium carbonate indicates that the seepage waters have dissolved both soil co2 derived from overlying c3 type vegetation and marine dolomite host rock the 18o pdb values of various types of present day low magnesium calcite lmc speleothems range from 6 5 to 4 3 and 13c values from 13 to 5 5 and are not correlated with speleothem type an analysis of 18o values of present day calcite rafts and pool waters shows that they form in oxygen isotope equilibrium similarly the measured ranges of 13c and 18o values for all types of present day speleothems are consistent with equilibrium deposition at cave temperatures the 13c 18o range of contemporary lmc thus reflects the variations in temperatures and isotopic compositions of the presentday cave waters the 10 variation in the 13c values in waters can be modeled by a simple rayleigh calculation of the carbon isotope fractionation accompanying co2 degassing and carbonate precipitation these variations may obscure the differences in the carbon isotopic composition of speleothems that could arise when vegetation cover changes from c3 to c4 type plants this consideration emphasizes that it is necessary to characterize the full range of 13c values associated with contemporaneous speleothems in order to clarify the effects of degassing from those due to differing vegetation types isotopic studies of a number of different types of fossil lmc speleothems show many of them to exhibit isotopic trends that are similar to those of present day lmc but others show both higher and lower 18o ranges in particular the higher 18o range has been shown by independent age measurements to be associated with a period of drier conditions the results of the study thus indicate that it is necessary to work on a well calibrated cave system in semiarid climates and that the fossil speleothem record should be obtained from different types of contemporaneous deposit in order to fully characterize the 18o 13c range representative of any given climatic period

geophysical and magneto structural study of the maâdna structure talemzane algeria insights on its age and origin the ma dna structure is located approximately 400 km south of algiers 33 19 n 4 19 e and emplaced in upper cretaceous to eocene limestones although accepted as an impact crater on the basis of alleged observations of shock diagnostic features such as planar deformation features pdfs in quartz grains previous works were limited and further studies are desirable to ascertain the structure formation process and its age for this purpose the crater was investigated using a multidisciplinary approach including field observations detailed cartography of the different geological and structural units geophysical surveys anisotropy of magnetic susceptibility paleomagnetism and petrography of the collected samples we found that the magnetic and gravimetric profiles highlight a succession of positive and negative anomalies ones that might indicate the occurrence of a causative material which is at least in part identical geophysical analysis and modeling suggest the presence of this material within the crater at a depth of about 100 m below the surface using soil magnetic susceptibility measurements the shallowest magnetized zone in the central part of the crater is identified as a recently deposited material paleomagnetic and rock magnetic experiments combined with petrographic observations show that detrital hematite is the main magnetic carrier although often associated with magnetite a primary magnetization is inferred from a stable remanence with both normal and reverse directions carried by these two minerals although this is supposed to be a chemical remagnetization its normal polarity nature is considered to be a pliocene component subsequent to the crater formation the pole falls onto the miocene pliocene part of the african apparent polar wander path apwp consequently we estimate then formation of the ma adna crater to have occurred during the time period extending from the late miocene to the early pliocene unfortunately our field and laboratory investigations do not allow us to confirm an impact origin for the crater as neither shatter cones nor shocked minerals were found a dissolved diapir with inverted relief is suggested as an alternative to the impact hypothesis which can still be considered as plausible only a drilling may provide a definite answer

three dimensional magnetic imaging of the chicxulub crater although few magnetization measurements are available for the structural elements of the chicxulub impact crater the magnetization intensities of the melt sheet upper breccia unit and central uplift are 3 4 orders of magnitude greater than the 3 to 4 km thick carbonate and evaporite stratigraphy covering the yucatan block this allows three dimensional modeling of the crater s structure by inversion using a two layer model two layers are separately inverted by dividing the crater s magnetic field expression into 40 km wavelength components the upper layer average depth 2 km models the distribution of highly magnetized zones in the crater s melt sheet the lower layer average depth 5 km represents relief on the yucatan block s basement surface and effectively maps the crater s 50 km diameter central uplift and possibly the expression of the surrounding collapsed disruption cavity fill the shallower magnetized zones consist of two generally concentric distributions at radii of 20 and 45 km these highly magnetized zones are thought to result from hydrothermal systems localized at the edge of the central uplift and the collapsed disruption cavity having produced magnetic phases during alteration of the melt sheet

preservation and detectability of shock induced magnetization preservation and detectability of shock induced magnetization abstract an understanding of the effects of hypervelocity impacts on the magnetization of natural samples is required for interpreting paleomagnetic records of meteorites lunar rocks and cratered planetary surfaces rocks containing ferromagnetic minerals have been shown to acquire shock remanent magnetization srm due to the passage of a shock wave in the presence of an ambient magnetic field in this study we conducted pressure remanent magnetization prm acquisition experiments on a variety of natural samples as an analog for srm acquisition at pressures ranging up to 1 8 gpa comparison of the alternating field af and thermal demagnetization behavior of prm confirms that af demagnetization is a more efficient method for removing srm overprints than thermal demagnetization because srm may persist to unblocking temperatures approaching the curie temperatures of magnetic minerals the blocking of srm to high temperatures suggests that srm could persist without being eradicated by viscous relaxation over geologic timescales however srm has been rarely observed in natural samples likely because of two factors 1 other forms of impact related remanence e g thermal remanent magnetization from impact related heating or chemical remanent magnetization from post impact hydrothermal activity are often acquired by target rocks that overprint srm and 2 low srm acquisition efficiencies may prevent srm from being distinguished from the underlying primary remanence or other overprints due to its low magnetization intensity sonia m tikoo 1 2 jerome gattacceca 3 4 nicholas l swanson hysell 1 benjamin p weiss 1 4 clement suavet 4 and cecile cournede 3 department of earth and planetary science university of california berkeley ca 94720 usa berkeley geochronology center 2455 ridge road berkeley ca 94709 usa cnrs aix marseille university cerege um34 aix en provence france department of earth atmospheric and planetary sciences massachusetts institute of technology mit 77 massachusetts avenue cambridge ma 02139 usa final version for publication in journal of geophysical research planets accepted 07 24 2015 doi 10 1002 2015je004840

tsunami deposits from the 1993 southwest hokkaido earthquake and the 1640 hokkaido komagatake eruption northern japan the southwest hokkaido tsunami of july 12th 1993 left continuous onshore sand deposits along the west coast of oshima peninsuka hokkaido northern japan we investigated spatial distribution and lithofacies of the new tsunami deposits for its identification of ancient tsunami deposits an eyewitness acount and bent plants helped our interpretation of the onshore tsunami behavior we regard the following properties as typical of the coastal tsunami sand deposits 1 the deposits cover the surface almost continuously on gentle topography 2 deposit thicknesses and mean grain sizes descrease with distance from the sea 3 deposit thicknesses and lithofacies vary greatly across local surface undulation 4 graded bedding reflecting tsunami runup and backwash is present in thick deposits 5 the deposits are widely distributed along the coast and extend inland several tens of meters to 100 m we examined a candidate for the paleo tsunami deposits associated with the 1640 komagatake eruption and confirmed that the similar patterns are typical of ancient tsunami deposits

tsunami sedimentation associated with the lisbon earthquake of 1 november ad 1755 boca do rio algarve portugal a description is given of a distinctive marine deposit at boca do rio on the algarve coast of portugal it is proposed here that the sediment accumulation was deposited by the tsunami generated by the lisbon earthquake of 1 november ad 1755 the deposit exhibits sedimentary characteristics quite unlike other coastal sediment accumulations that are deposited by more moderate wave regimes these include laterally continuous sand layers chaotic pebble horizons large amounts of gravel sized shell debris and distinctive assemblages of marine microfossils a preliminary attempt is made here to use the empirical field and laboratory data to define more clearly the processes of coastal sedimentation that characterize tsunami runup the use of tsunami sediments as time synchronous marker horizons is also discussed

horizontal and vertical variation of 2004 indian tsunami deposits an example of two transects along the western coast of thailand abstract we investigated horizontal and vertical variations in modern tsunami deposits along two transects at nam khem and khao lak western coast of thailand deposited by the large tsunami associated with the earthquake magnitude 9 0 of 26 december 2004 off sumatra indonesia tsunami waves 6 10 m high struck the area approximately 2 h after the earthquake tsunami deposits cover the low lying coastal plains and extend more than 1 km inland from the shoreline no landward decrease in sediment thicknesses was found clearly at either transect terrace scarps and a steep slope behind the coastal plain probably stopped tsunami deposition further inland causing substantial sediments to be deposited in front of these features very clear vertical variations in grain size and multiple layers are found in the deposits to about 600 m inland at nam khem fine grained sediments overlie the coarse grained sediments of the basal layer of the tsunami deposits at some sites the fine grained sediments are overlain by another layer of coarse grained sediments suggesting deposits laid down in succession by multiple waves the basal coarse grained sediments at nam khem fine landward the up flow waned inland based on the assumption that the grain size of the basal deposits relates to the strength of the up flow these results are potentially useful in disaster prevention and coastal environmental change management as well as for interpreting paleotsunami deposits in geological records

spatial and temporal variability in the stable isotope systematics of modern precipitation in china implications for paleoclimate reconstructions the stable isotopic composition of materials such as glacial ice tree rings lake sediments and speleothems from low to mid latitudes contains information about past changes in temperature t and precipitation amount p however the transfer functions which link 18op to changes in t or p d 18op dt and d 18op dp can exhibit significant temporal and spatial variability in these regions in areas affected by the southeast asian monsoon past variations in 18o and d of precipitation have been attributed to variations in monsoon intensity storm tracks and or variations in temperature proper interpretation of past 18op variations here requires an understanding of these complicated stable isotope systematics since temperature and precipitation are positively correlated in china and have opposite effects on 18op it is necessary to determine which of these effects is dominant for a specific region in order to perform even qualitative paleoclimate reconstructions here we evaluate the value of the transfer functions in modern precipitation to more accurately interpret the paleorecord the strength of these transfer functions in china is investigated using multiple regression analysis of data from 10 sites within the global network for isotopes in precipitation gnip 18op is modeled as a function of both temperature and precipitation the magnitude and signs of the transfer functions at any given site are closely related to the degree of summer monsoon influence 18op values at sites with intense summer monsoon precipitation are more dependent on the amount of precipitation than on temperature and therefore exhibit more negative values in the summer in contrast 18op values at sites that are unaffected by summer monsoon precipitation exhibit strong relationships between 18op and temperature the sites that are near the northern limit of the summer monsoon exhibit dependence on both temperature and amount of precipitation comparison with simple linear models 18op as a function of t or p and a geographic model 18op as a function of latitude and altitude shows that the multiple regression model is more successful at reproducing 18op values at sites that are strongly influenced by the summer monsoon the fact that the transfer function values are highly spatially variable and closely related to the degree of summer monsoon influence suggests that these values may also vary temporally since the southeast asian monsoon intensity is known to exhibit large variations on a number of timescales annual to glacial interglacial and the magnitude and sign of the transfer functions is related to monsoon intensity we suggest that as monsoon intensity changes the magnitude and possibly even the sign of the transfer functions may vary therefore quantitative paleoclimate reconstructions based on 18op variations may not be valid

impact generated hydrothermal systems on earth and mars it has long been suggested that hydrothermal systems might have provided habitats for the origin and evolution of early life on earth and possibly other planets such as mars in this contribution we show that most impact events that result in the formation of complex impact craters i e 2 4 and 5 10 km diameter on earth and mars respectively are potentially capable of generating a hydrothermal system consideration of the impact cratering record on earth suggests that the presence of an impact crater lake is critical for determining the longevity and size of the hydrothermal system we show that there are six main locations within and around impact craters on earth where impact generated hydrothermal deposits can form 1 crater fill impact melt rocks and melt bearing breccias 2 interior of central uplifts 3 outer margin of central uplifts 4 impact ejecta deposits 5 crater rim region and 6 post impact crater lake sediments we suggest that these six locations are applicable to mars as well evidence for impact generated hydrothermal alteration ranges from discrete vugs and veins to pervasive alteration depending on the setting and nature of the system a variety of hydrothermal minerals have been documented in terrestrial impact structures and these can be grouped into three broad categories 1 hydrothermally altered target rock assemblages 2 primary hydrothermal minerals precipitated from solutions and 3 secondary assemblages formed by the alteration of primary hydrothermal minerals target lithology and the origin of the hydrothermal fluids strongly influences the hydrothermal mineral assemblages formed in these post impact hydrothermal systems there is a growing body of evidence for impact generated hydrothermal activity on mars although further detailed studies using high resolution imagery and multispectral information are required such studies have only been done in detail for a handful of martian craters the best example so far is from toro crater marzo g a davila a f tornabene l l dohm j m fairen a g gross c kneissl t bishop j l roush t l mckay c p 2010 icarus 208 667 683 we also present new evidence for impact generated hydrothermal deposits within an unnamed 32 km diameter crater 350 km away from toro and within the larger holden crater synthesizing observations of impact craters on earth and mars we suggest that if there was life on mars early in its history then hydrothermal deposits associated with impact craters may provide the best and most numerous opportunities for finding preserved evidence for life on mars moreover hydrothermally altered and precipitated rocks can provide nutrients and habitats for life long after hydrothermal activity has ceased

shock induced changes in density and porosity in shock metamorphosed crystalline rocks haughton impact structure canada abstract shock metamorphism can occur at transient pressures that reach tens of gpa and well over 1000 c altering the target material on both megascopic and microscopic scales this study explores the effects of shock metamorphism on crystalline quartzofeldspathic basement material from the haughton impact structure on devon island arctic canada shock levels were assigned to samples based on petrographic examination of main mineral phases conventional shock classification schemes proved to incompletely describe the haughton samples so a modified shock classification system is presented fifty two crystalline bedrock samples from the clast rich impact melt rocks in the crater and one reference site outside of the crater were classified using this system the shock levels range from 0 to 7 according to the new shock stage classification proposed here i e stages 0 iv after the stoffler classification indicating shock pressures ranging from 0 to approximately 80 gpa the second aspect of this study involved measuring bulk physical characteristics of the shocked samples the bulk density grain density and porosity were determined using a water displacement method a bead displacement method and a hepycnometer results suggest a nonlinear negative correlation between density and shock level such that densities of crystalline rocks with original densities of approximately 3 g cm 3 are reduced to 1 0 g cm 3 at high shock levels the results also show a positive nonlinear correlation between porosity and shock level these data illustrate the effect of shock on the bulk physical characteristics of crystalline rocks and has implications for assessing the habitability of shocked rocks

geological overview and cratering model for the haughton impact structure devon island canadian high arctic the haughton impact structure has been the focus of systematic multi disciplinary field and laboratory research activities over the past several years regional geological mapping has refined the sedimentary target stratigraphy and constrained the thickness of the sedimentary sequence at the time of impact to 1880 m new 40ar 39ar dates place the impact event at 39 ma in the late eocene haughton has an apparent crater diameter of 23 km with an estimated rim final crater diameter of 16 km the structure lacks a central topographic peak or peak ring which is unusual for craters of this size geological mapping and sampling reveals that a series of different impactites are present at haughton the volumetrically dominant crater fill impact melt breccias contain a calcite anhydrite silicate glass groundmass all of which have been shown to represent impact generated melt phases these impactites are therefore stratigraphically and genetically equivalent to coherent impact melt rocks present in craters developed in crystalline targets the crater fill impactites provided a heat source that drove a post impact hydrothermal system during this time haughton would have represented a transient warm wet microbial oasis a subsequent episode of erosion during which time substantial amounts of impactites were removed was followed by the deposition of intracrater lacustrine sediments of the haughton formation during the miocene present day intracrater lakes and ponds preserve a detailed paleoenvironmental record dating back to the last glaciation in the high arctic modern modification of the landscape is dominated by seasonal regional glacial and niveal melting and local periglacial processes the impact processing of target materials improved the opportunities for colonization and has provided several present day habitats suitable for microbial life that otherwise do not exist in the surrounding terrain

on the efficiency of shock magnetization processes abstract the acquisition of remanent magnetization caused by hypervelocity impacts may be a major contribution to the remanent magnetization of planetary surfaces and meteorites in this paper we investigate the properties of shock remanent magnetization srm and in particular the relative efficiency of this phenomenon with respect to thermoremanent magnetization trm a parameter of interest for the understanding of the magnetic signatures of impact basins on extraterrestrial bodies we imparted shock remanent magnetization on basalt and microdiorite samples using laser shock in controlled magnetic field shock modeling indicates a pressure range of 0 6 1 5 gpa for our experiments the results confirm that the srm is parallel to the ambient magnetic field srm increases linearly with the ambient field in the 1 2500 t range the intensity of srm is independent of the angle between the shock direction and the direction of the ambient field the coercivity spectrum of srm is shifted towards lower values compared to the coercivity spectra of trm and isothermal remanent magnetization for the two studied lithologies the efficiency of srm versus trm acquisition is 17 for the basalt and is 36 for the microdiorite this efficiency depends on the magnetic mineralogy and increases with decreasing coercivity the rather high efficiency values that we obtained show that a significant remanent magnetization can be acquired by the crust during an hypervelocity impact on a planetary surface in the presence of an ambient field

effect of shock on the magnetic properties of pyrrhotite the martian crust and meteorites 1 we performed planar shock recovery experiments on natural pyrrhotite at pressures up to 6 9 gpa we find that high field isothermal remanent magnetization in pyrrhotite is demagnetized up to 90 by shock due to preferential removal of low coercivity components of magnetization contrary to static experiments we do not observe complete demagnetization post shock permanent changes in magnetic properties include increasing saturation isothermal remanent magnetization bulk coercivity and low temperature memory and changes in squareness of hysteresis these changes are consistent with an increase in the volume fraction of single domain grains the lack of magnetic anomalies over large martian impact basins is not expected to be solely due to shock demagnetization of the crust we find that pyrrhotite bearing rocks and meteorites can retain records of martian magnetic fields even if shocked to pressures approaching 7 gpa however some paleointensity techniques may underestimate this field

comparison of speleothem δ18o records from eastern china with solar insolation ice core and marine records similarities and discrepancies on different time scales abstract four 230 th dated 18 o records in three stalagmites one from dragon spring stalagmite l12 and two from golden lion caves stalagmites jsd 01 and jsd 02 located in libo county southeast guizhou china are presented these records cover age ranges of 0 75 2 ka late holocene 9 9 6 ka early holocene 87 9 88 2 ka and 93 8 95 2 ka late pleistocene they fit well with the published dongge cave record from the same area where the climate has been much influenced by the east asian monsoon the agreement reinforces the role of stalagmite 18 o as a proxy for regional precipitation or monsoon strength on millennial or longer time scales the 18 o record of dongge cave resembles those of sanbao cave in hubei and hulu cave in jiangsu of china the matching of these records with the northern hemisphere solar insolation variations points to the importance of insolation in affecting the east asian summer monsoon strength on 10 3 10 4 yr scales while the monsoon variations as depicted by these chinese speleothem 18 o records show a strong coupling to insolation s precession component 23 kyr period other climate records of global significance extracted from oceanic and terrestrial deposits e g deep sea sediments polar ice cores cave deposits from non monsoonal regions do not although the latter records were thought to be also influenced by the large changes in global ice volume they show variations modulated chiefly by insolation due to earth s eccentricity change 100 kyr period it is hypothesized that precession variations control the distribution of solar insolation between the northern and southern hemispheres the itcz position and the modulation of low latitude summer monsoon variability increasing rainfall and or summer winter precipitation ratio brought about by strong summer monsoons leads to 18 o depletion in stalagmites grown in monsoonal regions one should use caution to compare speleothem 18 o records with other paleoclimate records reflecting pleistocene ice ages on 10 4 10 5 yr timescales

tsunami deposits and recurrence on a typhoon prone coast of northern taiwan from the last millennium abstract widely known for its hazardous history taiwan holds valuable records of nw pacific tsunamis and typhoons despite the similarity between tsunami and typhoon deposits historical accounts enabled the identification of the 1867 tsunami deposit on the northern coast through matching with the record setting inundation however the identification of prehistoric tsunami deposits has been hindered by severe sediment reworking and post depositional changes produced by the typhoon prone tropical and humid climate in this study we investigated the upper holocene facies and their sediment sources and radiocarbon ages on distal floodplains and rocky backshores of the northern coast where sediment reworking is less intense four decimetre thick gravelly layers were identified intercalated with fluvial mud and colluvium the gravelly layers are composed of beach derived quartz rich sand and rounded gravels of the sedimentary basement rocks longshore drift andesite and stranded pumice the remarkable layer thickness gravel size and quartz richness were determined to have endured post depositional changes the event layers are sharp based matrix supported and poorly sorted and have recorded scouring sediment entrainment and rapid fallout of suspension rich turbulent flows that probably originated with tsunamis the event layers occur 0 5 0 8 km inland and 3 11 5 m above sea level matching the 1867 tsunami inundation and wave height respectively radiocarbon dating tied the event layers to the 1867 tsunami and three prehistoric events that occurred in the periods 1545 to 1810 1293 to 1414 and 1090 to 1235 representing a recurrence interval of 83 436 years over the last millennium

tectonics of complex crater formation as revealed by the haughton impact structure devon island canadian high arctic the results of a systematic field mapping campaign at the haughton impact structure have revealed new information about the tectonic evolution of mid size complex impact structures these studies reveal that several structures are generated during the initial compressive outward directed growth of the transient cavity during the excavation stage of crater formation 1 sub vertical radial faults and fractures 2 sub horizontal bedding parallel detachment faults and 3 minor concentric faults and fractures uplift of the transient cavity floor toward the end of the excavation stage produces a central uplift compressional inward directed deformation results in the duplication of strata along thrust faults and folds it is notable that haughton lacks a central topographic peak or peak ring the gravitational collapse of transient cavity walls involves the complex interaction of a series of interconnected radial and concentric faults while the outermost concentric faults dip in toward the crater center the majority of the innermost faults at haughton dip away from the center complex interactions between an outward directed collapsing central uplift and inward collapsing crater walls during the final stages of crater modification resulted in a structural ring of uplifted intensely faulted sub vertical and or overturned strata at a radial distance from the crater center of 5 0 6 5 km converging flow during the collapse of transient cavity walls was accommodated by the formation of several structures 1 sub vertical radial faults and folds 2 positive flower structures and chaotically brecciated ridges 3 rollover anticlines in the hanging walls of major listric faults and 4 antithetic faults and crestal collapse grabens oblique strike slip i e centripetal movement along concentric faults also accommodated strain during the final stages of readjustment during the crater modification stage it is clear that deformation during collapse of the transient cavity walls at haughton was brittle and localized along discrete fault planes separating kilometer size blocks

a case study of impact induced hydrothermal activity the haughton impact structure devon island canadian high arctic the well preserved state and excellent exposure at the 39 ma haughton impact structure 23 km in diameter allows a clearer picture to be made of the nature and distribution of hydrothermal deposits within mid size complex impact craters a moderate to low temperature hydrothermal system was generated at haughton by the interaction of groundwaters with the hot impact melt breccias that filled the interior of the crater four distinct settings and styles of hydrothermal mineralization are recognized at haughton a vugs and veins within the impact melt breccias with an increase in intensity of alteration towards the base b cementation of brecciated lithologies in the interior of the central uplift c intense veining around the heavily faulted and fractured outer margin of the central uplift and d hydrothermal pipe structures or gossans and mineralization along fault surfaces around the faulted crater rim each setting is associated with a different suite of hydrothermal minerals that were deposited at different stages in the development of the hydrothermal system minor early quartz precipitation in the impact melt breccias was followed by the deposition of calcite and marcasite within cavities and fractures plus minor celestite barite and fluorite this occurred at temperatures of at least 200 c and down to 100 120 c hydrothermal circulation through the faulted crater rim with the deposition of calcite quartz marcasite and pyrite occurred at similar temperatures quartz mineralization within breccias of the interior of the central uplift occurred in two distinct episodes 250 down to 90 c and 80 c appreciation of the structural features of impact craters has proven to be key to understanding the distribution of hydrothermal deposits at haughton

strong remanent magnetization in pyrrhotite a structurally controlled example from the paleoproterozoic tanami orogenic gold province northern australia abstract rocks associated with an orogenic gold system in the paleoproterozoic granites tanami inlier of northern australia exhibit strong natural remanent magnetism identifiable in regional aeromagnetic data petrographical analysis indicates the two dominant magnetic minerals in the rocks of this region are multidomain magnetite and monoclinic pyrrhotite chemical analysis using an electron microprobe has determined that the magnetite and pyrrhotite are stoichiometrically pure without significant elemental substitution alternating field demagnetization curie temperature and hysteresis analysis indicates that the remanently magnetized phase is monoclinic pyrrhotite with low magnetic susceptibility in contrast multidomain magnetites lack remanence and have high magnetic susceptibilities pyrrhotite is preserved in the rock mass along with other sulfide minerals as millimeter scale veins parallel to regionally developed penetrative mylonitic shear bands c planes formed during sulfide remobilization in the waning cooling stages of hydrothermal au deposition in contrast magnetite grains exhibit porphyroblastic textures consistent with formation during prograde to peak metamorphism indicating formation prior to pyrrhotite earlier in the orogenic cycle because of the low curie temperature ca 325 c of pyrrhotite it is therefore likely that remanent magnetization effects observed in aeromagnetic images of the tanami inlier are associated with structures intimately related to the late stages of au mineralization during retrograde greenschist metamorphism after the peak thermal point of the orogenic cycle

iron deficiency in pyrrhotite of suevites from the chesapeake bay impact crater usa a consequence of shock metamorphism abstract pyrrhotite from suevite of the 35 ma chesapeake bay impact structure cbis shows a shock metamorphism and we report on several mineralogical and magnetic features pyrrhotite shows strong brittle deformation with a high density of stacking faults twinning parallel to the hexagonal 001 planes and average fault distances in the order of 10 nm although the determination of a superstructure was not possible due to the lattice defects the reflections of the nias subcell which is typical of all pyrrhotite modifications were clearly detected this phase is ferrimagnetic with a curie temperature tc between 350 and 365 c and suevite with this phase does not show the 34 k transition the most peculiar feature is the low metal sulfur ratio of 0 81 which indicates a distinctly higher vacancy concentration than for 4c pyrrhotite and a composition close to smythite fe9s11 this phase carries a stable natural remanent magnetization and is relatively hard magnetic steep inclinations of the natural remanent magnetization vector however suggest that this phase has been remagnetized by the drilling process a possible explanation is the magnetic domain size of faultless areas of about 10 nm in diameter which is at the lower limit of the single domain size near the threshold below which superparamagnetic behavior occurs the low thermal stability of this phase excludes postshock heating above 300 c for the suevite of the cbis our results imply that the iron deficient pyrrhotite is produced by shock metamorphism although an iron loss due to shock has never been reported before for pyrrhotite

tsunami sedimentary facies deposited by the storegga tsunami in shallow marine basins and coastal lakes western norway sedimentary successions in small coastal lakes situated from 0 to 11 m above the 7000 year bp shoreline along the western coast of norway contain a distinctive deposit very different from the sediments above and below the deposit is interpreted to be the result of a tsunami inundating the coastal lakes an erosional unconformity underlies the tsunami facies and is traced throughout the basins with most erosion found at the seaward portion of the lakes the lowermost tsunami facies is a graded or massive sand that locally contains marine fossils the sand thins and decreases in grain size in a landward direction above follows coarse organic detritus with rip up clasts here termed organic conglomerate and finer organic detritus the tsunami unit generally fines and thins upwards the higher basins 6 11 m above the 7000 year shoreline show one sand bed whereas basins closer to the sea level 7000 years ago may show several sand beds separated by organic detritus these alternations in the lower basins may reflect repeated waves of sea water entering the lakes in basins that were some few metres below sea level at 7000 years bp the tsunami deposit is more minerogenic and commonly present as graded sand beds but also in some of these shallow marine basins organic rich facies occur between the sand beds the total thickness of the tsunami deposit is 20 100 cm in most studied sites an erosional and depositional model of the tsunami facies is developed

sequence of sedimentation processes caused by the 1992 flores tsunami evidence from babi island sedimentation processes caused by a modern tsunami have been discussed from the point of view of geologic and numerical investigations of the 1992 flores tsunami in indonesia geologic evidence on babi island shows an invasion of two waves of different direction and magnitude which resulted in widespread deposition of marine sand on the north and south southwest shores on the latter coarse and well sorted carbonate sand containing molluscan shells suggests that much more destructive waves swept across the southern coast as compared with the northern coast where the deposit included medium carbonate sand with a silty component a physical explanation for such destructive waves on the southern coast of babi is provided by a numerical simulation of the tsunami generation and propagation the geologic and numerical results indicate that an isolated island surrounded by a circular shoreline or reef edge will be subject to the most destructive waves on the coast on the back side of the island relative to the tsunami source

inflow and outflow facies from the 1993 tsunami in southwest hokkaido abstract we describe in detail the sedimentary facies provenance and grain size distributions of the 1993 tsunami deposits in the lower reaches of usubetsu river only two lithofacies were recognized a gravel lobe facies glf and a sand sheet facies ssf the gravel lobe facies was deposited rapidly by a hydraulic jump in contrast the sand sheet facies which contains both current ripples and dunes was deposited by a traction current under subcritical flow conditions we identified four stratigraphic units unit 1 unit 2 unit 3 and unit 4 in ascending order we interpreted units 1 and 2 as having been deposited by the inflow and outflow events of the first run up and units 3 and 4 by the inflow and outflow events of the second run up respectively units 3 and 4 were more widely distributed and coarser grained than units 1 and 2 because the second run up was larger than the first run up furthermore unit 4 was more widely distributed than unit 3 because the outflow eroded the inflow deposits grain size distributions of the inflow and outflow deposits were clearly different unit 4 deposits had a peak at 2 5 phi p 1 population in contrast unit 3 deposits had a bimodal distribution with peaks at 0 5 1 5 phi p 2 population and at 2 5 phi p 1 population a comparison of the tsunami deposits with other sedimentary deposits near the study area showed that the tsunami deposits were mainly derived from the seabed at depths below 5 5 m in the offshore area where the marine sands are about 2 2 5 phi in size and thus are the source of the p 1 population the p 2 population is derived from coarse 0 5 2 phi fluvial materials eroded during the tsunami run up according to our calculations benthic foraminiferal tests were entrained from the comparatively deep seabed at depths up to 100 m during the tsunami run up and included in the tsunami deposits

tsunami induced sediment transport in the abyssal mediterranean sea an unusual stratigraphic unit nicknamed homogenite fills topographic lows in the complex ridge and trough bathymetry at two survey sites on the western mediterranean ridge and the calabrian ridge on near bottom 4 khz seismic reflection profiles this unit us an acoustically transparent near surface flat lying layer whereas in cores it is a homogeneous gray marl as much as 7 m thick grain size decreases upcore within the unit implying that it was deposited in a single event controlled by gravitational settling the stratigraphic position of the homogenite relative to a firmly dated sapropel bed suggests emplacement between 4400 and 3100 yr b p the source of the homogenite is inferred to be the nearby basin walls farther east two other sites with similar rugged topography lack homogenite entirely a triggering mechanism is required which is capable of initiating massive sediment transport simultaneously in many separate basins at the western two survey sites but which is not effective at the eastern sites a large archeologically recorded earthquake of the correct age is considered and rejected because its epicenter is closer to the nonhomogenite bearing sites than to the sites where this sediment type was observed and because several other earthquakes of comparable magnitude have since been recorded in the area whereas the homogenite is unique the 3 500 yr b p collapse of the caldera of the volcano of santorini caused a huge tsunami which is recorded archeologically and geologically around the eastern mediterranean because of refraction of the tsunami by the bathymetry and because the caldera collapsed in its southwest corner a disproportionate amount of tsunami energy was directed toward the western area where homogenite is observed in contrast the homogenite free sites were relatively sheltered an order of magnitude calculation shows that the near bottom oscillating currents accompanying the santorini tsunami were at or above the threshold erosion velocity at the homogenite bearing sites in addition the near bottom pressure pulse under the tsunami at the homogenite bearing sites was sufficient to cause liquefaction of sediments neither mechanism was adequate to cause sediment transport or slope failure at the homogenite free sites

ancient impact and aqueous processes at endeavour crater mars the rover opportunity has investigated the rim of endeavour crater a large ancient impact crater on mars basaltic breccias produced by the impact form the rim deposits with stratigraphy similar to that observed at similar sized craters on earth highly localized zinc enrichments in some breccia materials suggest hydrothermal alteration of rim deposits gypsum rich veins cut sedimentary rocks adjacent to the crater rim the gypsum was precipitated from low temperature aqueous fluids flowing upward from the ancient materials of the rim leading temporarily to potentially habitable conditions and providing some of the waters involved in formation of the ubiquitous sulfate rich sandstones of the meridiani region

stratigraphic evidence for pre 2004 tsunamis in southwestern thailand abstract the 2004 sumatra andaman earthquake and the associated indian ocean tsunami vastly exceeded the size of their predecessors from the previous two centuries or more we sought clues on how often large tsunamis occur by taking 9 shallow cores 0 5 2 0 km inland from the modern shore on a holocene beach ridge plain of phra thong island 125 km north of phuket we tentatively correlated one sand sheet among these cores and found a second sand bed beneath in one of the cores we infer that these deposits represent two pre 2004 tsunamis the island s setting precludes river floods and tends to rule out storms as causes of the sand deposition establishment of the beach ridge plain requires that both the inferred tsunamis occurred after holocene sea levels approached their present position radiocarbon ages of bulk soil samples are consistent with this conclusion though root penetration into soil samples probably makes the ages appear younger one inferred tsunami occurred before ad 1300 and the other occurred before ad 1900 based on the age estimates the tsunamis probably originated along the sunda megathrust from where tsunamis can travel directly to the thailand coast

impact induced microbial endolithic habitats asteroid and comet impacts on earth are commonly viewed as agents of ecosystem destruction be it on local or global scales however for some microbial communities impacts may represent an opportunity for habitat formation as some substrates are rendered more suitable for colonization when processed by impacts we describe how heavily shocked gneissic crystalline basement rocks exposed at the haughton impact structure devon island nunavut arctic canada are hosts to endolithic photosynthetic microorganisms in significantly greater abundance than lesser shocked or unshocked gneisses two factors contribute to this enhancement a increased porosity due to impact fracturing and differential mineral vaporization and b increased translucence due to the selective vaporization of opaque mineral phases using biological ultraviolet radiation dosimetry and by measuring the concentrations of photoprotective compounds we demonstrate that a covering of 0 8 mm of shocked gneiss can provide substantial protection from ultraviolet radiation reducing the inactivation of bacillus subtilis spores by 2 orders of magnitude the colonisation of the shocked habitat represents a potential mechanism for pioneer microorganisms to invade an impact structure in the earliest stages of post impact primary succession the communities are analogous to the endolithic communities associated with sedimentary rocks in antarctica but because they occur in shocked crystalline rocks they illustrate a mechanism for the creation of microbial habitats on planetary surfaces that do not have exposed sedimentary units this might have been the case on early earth the data have implications for the microhabitats in which biological signatures might be sought on mars

a paleozoic age for the tunnunik impact structure we report paleomagnetic directions from the target rocks of the tunnunik impact structure as well as from lithic impact breccia dikes that formed during the impact event the target sedimentary rocks have been remagnetized after impact related tilting during a reverse polarity interval their magnetization is unblocked up to 350 degrees c the diabase dikes intruding into these sediments retained their original magnetization which unblocks above 400 degrees c the impact breccia records a paleomagnetic direction similar to that of the overprints in the target sedimentary rocks the comparison of the resulting virtual geomagnetic pole for the tunnunik impact structure with the apparent polar wander path for laurentia combined with biostratigraphic constraints from the target sedimentary rocks is most consistent with an impact age in the late ordovician or silurian around 430 450 ma soon after the deposition of the youngest impacted sedimentary rocks our results from the overprinted sedimentary rocks and diabase dikes imply that the postimpact temperature of the studied rocks was about 350 degrees c

a tsunami about 1000 years ago in puget sound washington water surged from puget sound sometime between 1000 and 1100 years ago overrunning tidal marshes and mantling them with centimeters of sand one overrun site is 10 kilometers northwest of downtown seattle another is on whidbey island some 30 kilometers farther north neither site has been widely mantled with sand at any other time in the past 2000 years deposition of the sand coincided to the year or less with abrupt probably tectonic subsidence at the seattle site and with landsliding into nearby lake washington these findings show that a tsunami was generated in puget sound and they tend to confirm that a large shallow earthquake occurred in the seattle area about 1000 years ago

analysis of environmental controls on tsunami deposit texture abstract tsunamis transport large amounts of sediment and can leave recognisable signatures in the landscape the form and composition of onshore tsunami deposits are a function of wave dynamics sediment availability and characteristics of the local environment the latter of which also partially controls preservation of the deposit this research reviews these relationships in a global context and assesses the connection between tsunami deposit particle size and four controlling parameters climate temperature and rainfall density of tsunami sediments degree of coastal protection and distance between tsunami source and sediment deposition an international dataset of tsunami deposit locations and texture was compiled from published literature and existing databases values for environmental variables were calculated for each location from global datasets of temperature rainfall coastline shape and tsunami source locations spearman s rank order correlation principal component analysis pca and hierarchical cluster analysis ca were used to analyse relationships between these variables pca results show an inverse relationship between particle size and sediment density climate variables and distance from source ca results support this suggesting a cluster structure controlled primarily by particle size and secondly by climate and sediment density these relationships can be explained by the influence of the environment on antecedent morphology and the composition of sediments available for tsunami transport

petrography and shock related remagnetization of pyrrhotite in drill cores from the bosumtwi impact crater drilling project ghana rock magnetic and magnetic mineralogy data are presented from the international continental scientific drilling program icdp drill cores lb 07a and lb 08a of the bosumtwi impact structure in order to understand the magnetic behavior of impact and target lithologies and their impact related remagnetization mechanism basic data for the interpretation of the magnetic anomaly patterns and the magnetic borehole measurements as well as for new magnetic modeling are provided magnetic susceptibility 150 500 10 6 si and natural remanent magnetization 10 3 10 1 a m are generally weak but locally higher values up to 10 6 10 3 si and 43 a m occur sixty three percent of the investigated rock specimens show q values above 1 indicating that remanence clearly dominates over induced magnetization which is a typical feature of impact structures ferrimagnetic pyrrhotite is the main magnetite phase which occurs besides minor magnetite and a magnetic phase with a curie temperature between 330 and 350 c interpreted as anomalous pyrrhotite coercive forces are between 20 and 40 mt brecciation and fracturing of pyrrhotite is a common feature confirming its pre impact origin grain sizes of pyrrhotite show a large variation but the numerous stress induced nanostructures observable by transmission electron microscopy tem are assumed to behave as single domain grains we suggest that the drilled rocks lost their pre shock remanence memory during the shock event and acquired a new stable remanence during shock induced grain size reduction the observed brittle microstructures indicate temperatures not higher than 250 c which is below the curie temperature of ferrimagnetic pyrrhotite 310 c

d h ratios of fluid inclusions of soreq cave israel speleothems as a guide to the eastern mediterranean meteoric line relationships in the last 120 ky abstract d h studies of fluid inclusions of speleothems of the soreq cave israel are made using the method of vacuum thermal extraction d h measurements of present day carbonate pool margins and waters show that the value of the vacuum thermal extraction fractionation ex d extracted water d cave water is 30 0 1 4 for the soreq cave deposits d h analyses of fluid inclusions of two fossil speleothems formed during periods equivalent to glacial times suggest that their isotopic compositions follow the global meteoric water line mwl d 18 o relationship compared to present day waters which follow the mediterranean meteoric water line mmwl trend two samples from interglacial periods show isotopic trends between these lines these differences are presumed to reflect cooler less evaporative conditions in the eastern mediterranean sea during glacial times

buried impact craters a topographic analysis of quasi circular depressions utopia basin mars 1 many quasi circular depressions qcds revealed in the mars orbiter laser altimeter data set have no obvious structural representation in visible images of mars it has been suggested that these qcds are surface representations of buried impact craters and on the basis of this assumption cumulative count versus diameter plots of qcds in the northern lowlands have been constructed to date the buried lowland floor if the qcds are in fact buried impact craters their surface relief should scale directly with their diameter this relationship holds true for 115 qcds with diameters ranging from 7 to 100 km within roughly 1500 km of the center of the utopia basin the coefficient of determination r2 of the relationship more closely approaches 1 when qcds in zones of comparable cover thickness are evaluated the surface relief versus diameter relationship of 55 randomly selected pseudo qcds was also determined their poor correlation indicates that the direct relationship of surface relief to diameter of actual qcds is due to differential compaction of a cover material over buried impact craters and is not just a random effect of qcd diameter the slope of the trend of the qcds surface relief versus diameter when divided into zones of comparable cover thickness can be used to determine which zones have thicker or thinner cover

the lake bosumtwi meteorite impact structure ghana where is the magnetic source the bosumtwi impact structure ghana is a young and well preserved structure where a vast amount of information is available to constrain any geophysical model previous analysis of the airborne magnetic data and results of numerical simulation of impact predicted a strongly magnetic impact melt body underneath the lake recent drilling through the structure did not penetrate such an expected impact melt rock magnetic source a new 3 d magnetic model for the structure was constructed based on a newly acquired higher resolution marine magnetic data set with consideration of the observed gravity data on the lake previous seismic models and the magnetic properties and lithology identified in the two international continental scientific drilling program icdp deep boreholes the new model contains highly magnetic bodies located in the northeast sector of the structure not centered onto the drilling sites as in previous models higher magnetization than that measured in outcropping impactites had to be assigned to the unexposed source bodies integration of the new model with the borehole petrophysics and published geology indicates that these bodies likely correspond to an extension to the south of the kumasi batholith which outcrops to the northeast of the structure the possibility that these source bodies are related to the seismically identified central uplift or to an unmapped impact melt sheet predicted by previous models of the structure is not supported detailed magnetic scanning of the kumasi batholith to the north and the bansu intrusion to the south would provide a test for this interpretation

impactites of the haughton impact structure devon island canadian high arctic contrary to the previous interpretation of a single allochthonous impactite lithology combined field optical and analytical scanning electron microscopy sem studies have revealed the presence of a series of impactites at the haughton impact structure in the crater interior there is a consistent upward sequence from parautochthonous target rocks overlain by parautochthonous lithic monomict breccias through allochthonous lithic polymict breccia into pale grey allochthonous impact melt breccias the groundmass of the pale grey impact melt breccias consists of microcrystalline calcite silicate impact melt glass and anhydrite analytical data and microtextures indicate that these phases represent a series of impact generated melts that were molten at the time of and following deposition impact melt glass clasts are present in approximately half of the samples studied consideration of the groundmass phases and impact glass clasts reveal that impactites of the crater interior contain shock melted sedimentary material from depths of 920 to 200 to 760 m and are interpreted as remnants of the continuous ejecta blanket the pale grey impact melt breccias although similar to the impact melt breccias of the crater interior are more carbonate rich and do not appear to have incorporated clasts from the crystalline basement thus the spatial distribution of the crater fill impactites at haughton the stratigraphic succession from target rocks to allochthonous impactites the recognition of large volumes of impact melt breccias and their probable original volume are all analogous to characteristics of coherent impact melt layers in comparatively sized structures formed in crystalline targets

traces of tsunami preserved in inter tidal lacustrine and marsh deposits some examples from northeast japan the japan sea earthquake of may 26 1983 triggered a large scale tsunami that surged over the coast of ne japan and caused considerable damage the tsunami resulted in peculiar sedimentary processes on the coast depending on the hydraulic scale of the tsunami three kinds of sedimentary processes were recognized each of which left unique deposits such deposits are expected to remain in sedimentary sequences preserving remarkable sedimentary facies borehole samples drilled at different localities in coastal regions have been examined to detect traces of ancient tsunamis sedimentological and geochemical studies of the samples reveal that layered deposits similar to those developed by the tsunami of the japan sea earthquake are common in the drilled cores estimated ages of these deposits are exactly equivalent to the dates of ancient tsunamis documented in historical records these results show that the invasion of tsunamis is recorded in coastal depositional sequences from analyses of long borehol

truncated flame structures within a deposit of the indian ocean tsunami evidence of syn sedimentary deformation this study reveals the three dimensional morphology and syn sedimentary formation processes of a deformation structure termed truncated flame structures which is found in a terrestrial tsunami deposit in southern thailand that formed during the 2004 indian ocean tsunami the structure was found at the boundary between a lower fine grained layer and an upper coarse grained layer that are related to two runup events in order to confirm the morphology of the structure the authors excavated two trenches and an opencast pit when viewed in a cross section oriented parallel to the direction of the runup current the deformed boundary has an irregularly bulging profile similar to that observed in flame structures the protruding structures are inclined towards the downstream direction of the runup current and are truncated horizontally along their upper surface by parallel laminations in the overlying layer when viewed in a cross section oriented perpendicular to the current direction it appears that parts of the upper layer descend into the lower layer as lobate masses in places these masses are completely detached from the main part of the upper layer forming circular or elliptical shapes the contact between the lower layer and the main part of the upper layer is a planar truncation surface opencast excavation of the contact surface revealed that the deformed structures have flat sinuous horseshoe crests that open in a downstream direction it is possible for the runup current to generate shear stress such that it deforms the boundary into a truncated flame structure moreover the observations made in this study indicate the syn sedimentary development of the structure deformation and truncation occurred simultaneously in association with the runup current that formed the upper layer truncated flame structures can be used as a criterion in identifying the syn sedimentary deformation of substrate the structures are indicative of unidirectional flow with sufficiently high shear velocity to deform unconsolidated substrate as in the present case the truncated flame structures may be characteristic of tsunami events that involve strong unidirectional currents on land due to the extraordinarily long wave period of tsunamis rather than other events such as storm surges or flooding

geophysical signature of the tunnunik impact structure northwest territories canada in 2011 the discovery of shatter cones confirmed the 28 km diameter tunnunik complex impact structure northwest territories canada this study presents the first results of ground based electromagnetic gravimetric and magnetic surveys over this impact structure its central area is characterized by a 10 km wide negative gravity anomaly of about 3 mgal amplitude roughly corresponding to the area of shatter cones and associated with a positive magnetic field anomaly of 120 nt amplitude and 3 km wavelength the latter correlates well with the location of the deepest uplifted strata an impact tilted proterozoic dolomite layer of the shaler supergroup exposed near the center of the structure and intruded by dolerite dykes locally electromagnetic field data unveil a conductive superficial formation which corresponds to an 80 100 m thick sand layer covering the impact structure based on measurements of magnetic properties of rock samples we model the source of the magnetic anomaly as the magnetic sediments of the shaler supergroup combined with a core of uplifted crystalline basement with enhanced magnetization more classically the low gravity signature is attributed to a reduction in density measured on the brecciated target rocks and to the isolated sand formations however the present day fractured zone does not extend deeper than 1 km in our model indicating a possible 1 5 km of erosion since the time of impact about 430 ma ago

spatial variations of monsoonal rain in eastern china instrumental historic and speleothem records abstract we select four caves and their nearby cities in the monsoonal region of china for studying the relationships among precipitation temperature summer monsoon intensity and stalagmite 18o the instrumental historic and stalagmite 18o records from these areas show strong spatial disparities on annual to decadal scales so that climatic conditions in a single location cannot represent these of the entire eastern china on time scales

high resolution δ18o and δ13c records during the past 65 ka from fengyu cave in guilin variation of monsoonal climates in south china abstract the 18 o and 13 c records of a 230 th u dated 2 2 m long stalagmite from fengyu cave in south china provide a continuous decadal resolution with 3698 measurements proxy for regional climatic and environmental conditions during 4 65 ka this single stalagmite reveals all heinrich cold events most dansgaard oeschger warm events deglaciation and holocene optimum generally supporting the hulu and dongge records on 5000 10000 year time scales the 18 o and 13 c variations show strongly positive correlations r 0 7 reflecting that a common climatic factor controls both 18 o and 13 c of f 1 the comparison of the speleothem ice core insolation and marine records reveals strong linkages between n atlantic temperature and the asian summer monsoon over most of the study period however there are some regional discrepancies between the stalagmite 18 o records following the deglaciation although the nh summer insolation provides the major forcing on asian monsoon variability over orbital time scales the weakest summer monsoon intensity during the last glacial occurred ca 16 ka corresponding to the heinrich event 1 a 5 6 ky lag from the minimum insolation during the last glacial maximum variations in the monsoonal climate of the study area over the past 700 years have been reconstructed from the 18 o and 13 c records of a 14 6 cm long stalagmite f4 in fengyu cave showing wet conditions between ad 1550 and ad 1850 the little ice age and relatively dry conditions before and after this interval human impacts on local vegetation since ad 1700 were recorded by the 13 c record of stalagmite f4

origin of the central magnetic anomaly at the haughton impact structure canada the 23 km diameter well preserved haughton impact structure shows a rather unique combination of a positive magnetic anomaly with a negative gravity anomaly over the center of its central uplift using a new ground magnetic dataset and several modeling approaches we investigate the properties and geometry of its central magnetized source our results confirm that a km sized magnetic body with a narrow near surface extension is necessary to account for the anomaly additional measurements of rock magnetic properties of samples of all lithologies encountered in and outside the crater show that the target sedimentary rocks and the vast majority of the precambrian basement rocks cannot be the source of the magnetic anomaly while in larger impact structures such magnetic anomalies are often explained by magmatic mafic intrusions or highly magnetic glass lenses in the impact melt rocks we propose that impact generated hydrothermal activity enhanced the magnetization of the highly porous unmelted uplifted basement rocks such a process may be considered for the interpretation of the geophysical signature of planetary impact craters

onshore tsunami deposits caused by the 1993 southwest hokkaido and 1983 japan sea earthquakes onshore tsunami deposits resulting from the 1993 southwest hokkaido and 1983 japan sea earthquakes were described to evaluate the feasibility of tsunami deposits for inferring paleoseismic events along submarine faults tsunami deposits were divided into three types based on their composition and aerial distribution a deposits consisting only of floating materials b locally distributed siliclastic deposits and c widespread siliclastic deposits the most widely distributed tsunami deposits consist of the first two types type c deposits are mostly limited to areas where the higher tsunami runup was observed the scale of tsunami represented by vertical tsunami runup is an important factor controlling the volume of tsunami deposits the thickest deposits about 10 cm occur behind coastal dunes to produce thick siliclastic tsunami deposits a suitable source area such as sand bar or dune must be available in addition to sufficient vertical tsunami runup estimation of the amounts of erosion and deposition indicates that tsunami deposits were derived from both onshore and shoreface regions the composition and grain size of the tsunami deposits strongly reflect the nature of the sedimentary materials of their source area sedimentary structures of the tsunami deposits suggest both low and high flow regimes consequently it seems very difficult to identify tsunami deposits based only on grain size distribution or sedimentary structure of a single site in ancient successions

coastal sedimentation associated with the december 26 2004 tsunami in lhok nga west banda aceh sumatra indonesia abstract with wave heights of 30 m and runups reaching 50 m a s l and 6 km inland the december 26 2004 tsunami in sumatra was one of the largest tsunamis in recorded human history in this paper we present a description of the event in the lhok nga bay west coast of banda aceh and an interpretation of the tsunami sand deposits mostly based upon grain size analysis the 3 5 km long transect of lampuuk displays two landward fining thinning and sorting sequences the thickest cross sections of the first sequence of deposits 0 1 5 km inland suggest a deposition by three consecutive runups inflows and a final backwash return flow or outflow from 1 5 to 3 5 km inland the record is dominated by the second and highest wave 15 30 m normally graded couplets or triplets of layers were used to identify the runup of each wave the topmost layers interpreted as the backwash deposition describe a seaward sequence of increasing mean grain size and decreasing degree of sorting the local effects of the topography could be identified thickest deposits in the topographic lows 50 80 cm great spatial variations in thickness and upper laminated texture when the sedimentation was limited by steep slopes landward coarsening and very poor sorting at the wave breaking point bimodal grain size distributions reflecting different sources of sediments finally by coupling the longitudinal and vertical trends of the 26 cross sections we propose a model of sediment transport and deposition in a large tsunami wave

timing and structure of the younger dryas event in northern china a high resolution and absolute dated stalagmite record from kulishu cave beijing characterizes asian monsoon am history in northern china between ca 14 and 10 5 ka bp thousand yrs before present present 1950 including the entire younger dryas yd event using 230 th dates and counting of annual layers the shift into the yd began at 12 850 40 yr bp and took w340 yrs and the shift out of the yd began at 11 560 40 yr bp and took 38 yrs best estimate w20 yrs broadly similar to previously reported am records from central and southeastern china the more gradual nature of the start of the yd event as observed in the am records appears to contrast with the more abrupt beginning observed in the greenland ice records the total amplitude of the am yd event is also smaller than the amplitude of the am heinrich stadial 1 event in addition the general rising trend of the am during the bolling allerod period contrasts with the general cooling trend in greenland temperature during that time the influence of rising insolation on the am may explain this observation

terrestrial impact structures impact structures are the dominant landform on planets that have retained portions of their earliest crust the present surface of the earth however has comparatively few recognized impact structures this is due to its relative youthfulness and the dynamic nature of the terrestrial geosphere both of which serve to obscure and remove the impact record although not generally viewed as an important terrestrial as opposed to planetary geologic process the role of impact in earth evolution is now receiving mounting consideration for example large scale impact events may have been responsible for such phenomena as the formation of the earth s moon and certain mass extinctions in the biologic record the importance of the terrestrial impact record is greater than the relatively small number of known structures would indicate impact is a highly transient high energy event it is inherently difficult to study through experimentation because of the problem of scale in addition sophisticated finite element code calculations of impact cratering are gen erally limited to relatively early time phenomena as a result of high com putational costs terrestrial impact structures provide the only ground truth against which computational and experimental results can be com pared these structures provide information on aspects of the third dimen sion the preand postimpact distribution of target lithologies and the nature of the lithologic and mineralogic changes produced by the passage of a shock wave they also provide data for cratering rate estimates and in some cases on the nature of the impacting body in this review emphasis is placed on the nature of terrestrial impact structures the criteria for their identification and their contribution to

hydrothermal alteration in basalts from vargeao impact structure south brazil and implications for recognition of impact induced hydrothermalism on mars abstract the 12 km wide vargeao impact structure was formed 123 myr ago in the parana basaltic province southern brazil at this time the province region had a dry climate although a large brackish aquifer had been formed in the underlying sandstones it is therefore one of the best terrestrial analogs for studying impact related products on a dry martian surface environment with preserved ice rich ground the basalts within the impact structure display cm sized breccia veins filled with lithic clasts glassy remnants newly formed fe oxyhydroxides and secondary phases such as calcite phyllosilicates and subordinately quartz and zeolite the textural and mineralogical study of these phases demonstrate their hydrothermal origin although the very center of the structure has experienced the highest pressures and temperatures the most developed hydrothermal changes are recognized in an inner collar surrounding the central depression this inner collar is also the location of major modifications of the rock magnetic properties these magnetic signatures are related to the distribution of impact related faults and to the formation of new iron oxides geochemical modeling indicate that hydrothermal phases formation required low water rock ratios our observations therefore suggest that hydrothermal alteration took place following the perturbation of the aquifer by the impact but evidence for hydrothermal circulation is limited in comparison with other impact related hydrothermal systems this situation may be explained by the presence of the aquifer below the heat source such a setting being exceptional for the earth but common on mars however the spectroscopic signatures in visible near infrared images suggest that this kind of impact related hydrothermal alteration may be still indentified in large impact craters on mars by orbital instruments these results does not exclude the possibility that more developed alteration took place in breccias that are today eroded

palaeo climate reconstruction from stable isotope variations in speleothems a review abstract speleothems are now regarded as valuable archives of climatic conditions on the continents offering a number of advantages relative to other continental climate proxy recorders such as lake sediments and peat cores they are ideal materials for precise u series dating yielding ages in calendar years thereby circumventing the radiocarbon calibration problems associated with most other continental records stable isotope studies in speleothems have shifted away from attempting to provide palaeo temperature reconstructions to the attainable goal of providing precise estimates for the timing and duration of major o isotope defined climatic events characterised by high signal to noise ratios e g glacial interglacial transitions dansgaard oeschger oscillations the 8200 year event unlike the marine records speleothem data sets are not tuned and their independent chronology offers opportunities to critically assess leads and lags in the climate system that in turn can provide important insights into forcing and feedback mechanisms improved procedures for the extraction and measurement of stable isotope ratios in fluid inclusions trapped in speleothems are likely to provide in the near future a much enhanced basis for the quantitative interpretation of o isotope ratios in speleothem calcite the latter developments open up once again the tantalising prospect of palaeo temperature estimates but more importantly perhaps provide a direct test for a new generation of general circulation models whose hydrological cycles will incorporate the water isotopes the literature is reviewed briefly to provide for the reader a sense of the current state of the art and to provide some pointers for future research directions

paleomagnetism and rock magnetism of east and west clearwater lake impact structures the east and west cleawater lake impact structures wiy sh kimi lake quebec 26 and 32 km in diameter respectively have been proposed to represent an impact doublet we investigated their pale

87sr 86sr and sr ca in speleothems for paleoclimate reconstruction in central china between 70 and 280 kyr ago limestone cave deposits speleothems provide archives for past changes in regional climates over a range of timescales while 18o and 13c in speleothem calcite have been commonly used for reconstruction of paleoclimates we report here further efforts in the use of 87sr 86sr and sr ca signals in speleothem calcite to deduce paleomonsoon variability near the loess plateau of central china a two end member mass balance model of concentration and isotopic composition of strontium in a cave system is used to estimate variation of the 87sr 86sr ratio in sediments overlying a limestone cave we show that this ratio reflects climate driven variations in the provenance and the extent of chemical weathering of the epikarstic sediments the measurements of 87sr 86sr made on a well dated stalagmite sfl from buddha cave 33o40n 109o05 e show ratios of 0 71092 to 0 71133 0 00001 as 2 during relatively cold periods e g marine isotope stage mis 5b 5d and 8 lower than ratios of 0 71133 to 0 71194 during relatively warm periods e g mis 5a 5c 5e and 7 as changes in the sr ca ratio may affect speleothem 87sr 86sr we show that the direct use of speleothem 87sr 86sr is less ideal than our modeled 87sr 86sr for the exogenic sr source above the cave as a paleomonsoon proxy using the 18o 13c sr ca and 87sr 86sr records of the stalagmite we reconstruct the variability of the east asian monsoon for the time period between 70 and 280 kyr ago the results show that summer monsoons were more intense during interglacial periods than during glacial periods

new surveys of the chesapeake bay impact structure suggest melt pockets and target structure effect we present high resolution gravity and magnetic field survey results over the 85 km diameter chesapeake bay impact structure whereas a continuous melt sheet is antici pated at a crater this size shallow source magnetic field anomalies of 100 nt instead suggest that impact melt pooled in kilometer scaled pockets surrounding the base of a central peak a central anomaly of 300 nt may represent additional melt or rock that underwent shock induced remagnetization models predict that the total volume of the melt ranges from 0 4 to 10 km 3 a quantity that is several orders of magnitude smaller than expected for an impact structure this size however this volume is within predictions given a transient crater of diameter of 20 40 km for a target covered with water and sedimentary deposits such that melt fragments were widely dispersed at the time of impact gravity data delineate a gently sloping inner basin and a central peak via a contrast between crystalline and sedimentary rock both features are ovoid oriented parallel to larger preimpact basement structures conceptual models suggest how lateral differences in rock strength due to these preimpact structures helped to shape the crater s morphology during transient crater modification

the storegga slides evidence from eastern scotland for a possible tsunami abstract the second storegga slide on the continental slope off western norway has been dated at between 8000 and 5000 yrs b p a prominent sand layer in flandrian holocene deposits along the coast of eastern scotland and dated at approximately 7000 yrs b p may have been deposited by a tsunami generated by the slide the altitude and stratigraphy of the layer allow estimates to be made of the magnitude of the earthquake which initiated the slide

stable isotopic compositions of waters in the karst environments of china climatic implications abstract a total of 117 water samples including cave water ground water spring water and river water collected from the monsoonal area of china have been analyzed for their h and o isotope composition overall a 18o d correlation is observed of d 4 45 6 6 18o r2 0 90 and a significant evaporation effect observed for the southern sites average 18o and d site values generally correspond to those of precipitation in nearby cities with correlations of d 2 18 7 23 18o r2 0 95 for the sample sites and d 11 05 7 95 18o r2 0 95 for the cities the effects of rainfall amount and temperature on precipitation 18o were calculated using a simplified theoretical model derived from the rayleigh distillation equation which demonstrated that the sign of 18op vs t correlation is dependent on precipitation intensity the mean 18o value of cave waters exhibit decreasing trends with increasing latitude and reveal a spatial pattern of positive correlation with annual mean temperature and precipitation mainly reflecting isotopic fractionations in the moisture source traveling from the ocean side to the inland continent this spatial pattern implies that the 18o values recorded in the proxy climate records derived from speleothems might be influenced by shifts in monsoon boundary during the past especially between glacial and interglacial intervals

a high resolution absolute dated late pleistocene monsoon record from hulu cave china oxygen isotope records of five stalagmites from hulu cave near nanjing bear a remarkable resemblance to oxygen isotope records from greenland ice cores suggesting that east asian monsoon intensity changed in concert with greenland temperature between 11 000 and 75 000 years before the present yr b p between 11 000 and 30 000 yr b p the timing of changes in the monsoon as established with 230th dates generally agrees with the timing of temperature changes from the greenland ice sheet project two gisp2 core which supports gisp2 s chronology in this interval our record links north atlantic climate with the meridional transport of heat and moisture from the warmest part of the ocean where the summer east asian monsoon originates

geomagnetic field intensity recorded after impact in the ries meteorite crater germany summary we carried out palaeointensity experiments on 45 samples collected throughout the ca 15 ma ries crater germany to test whether meteorite impacts can influence the geodynamo a thellier thellier procedure with alteration tail and additivity checks yields a weighted average palaeointensity of 19 1 1 1 t from 15 samples that pass stringent data selection criteria the corresponding virtual dipole moment of 3 2 0 2 1022 am2 is relatively low but indistinguishable from the global palaeointensity database between 20 and 10 ma our results suggest that either the energy released during the ries meteorite impact event was too low to affect the geodynamo the ries impact lithologies cooled too fast to record any effect or the time averaged by the impact lithologies was long enough to record secular variation but that the geodynamo was remarkably stable over that time

timing and duration of the last interglacial inferred from high resolution u series chronology of stalagmite growth in southern hemisphere high precision th 230 u 238 ages for a stalagmite from newdegate cave in southern tasmania australia define a rare record of precipitation between 100 and 155 ka before the present the fastest stalagmite growth occurred between 129 2 1 6 and 122 1 2 0 ka similar to 61 5 mm ka coinciding with a time of prolific coral growth from western australia 128 122 ka this is the first high resolution continental record in the southern hemisphere that can be compared and correlated with the marine record such correlation shows that in southern australia the onset of full interglacial sea level and the initiation of highest precipitation on land were synchronous the stalagmite growth rate between 129 2 and 142 2 ka similar to 5 9 mm ka was lower than that between 142 2 and 154 5 ka similar to 18 7 mm ka implying drier conditions during the penultimate deglaciation despite rising temperature and sea level this asymmetrical precipitation pattern is caused by latitudinal movement of subtropical highs and an associated westerly circulation in response to a changing equator to pole temperature gradient both marine and continental records in australia strongly suggest that the insolation maximum between 126 and 128 ka at 65 degreesn was directly responsible for the maintenance of full last interglacial conditions although the triggers that initiated penultimate deglaciation at similar to 142 ka remain unsolved c 2001 elsevier science b v all rights reserved

tsunami deposits beneath tidal marshes on vancouver island british columbia thin sheets of sand occur within holocene mud and peat deposits beneath tidal marshes at tofino ucluelet and port alberni on vancouver island british columbia the sand sheets are extensive and have sharp upper and lower contacts in most cases they consist of moderately sorted massive sand and silty sand with abundant wood and other plant detritus at port alberni the thickest sheet has gravel and is graded the upper two sand sheets in the tofino ucluelet area and possibly the third are also present at port alberni eyewitness accounts and 137 cs analysis suggest that the uppermost thinnest sand was deposited by the tsunami triggered by the great alaska earthquake in 1964 the next oldest sand sheet has been radiocarbon dated at our data suggest that large tsunamis have struck the southern british columbia coast several times during the late holocene and that some were much larger than the 1964 tsunami which caused about 10 million damage 1964 canadian dollars to communities on vancouver island because such tsunamis can be expected in the future they pose a hazard to people and property in some coastal areas

a high resolution absolute dated holocene and deglacial asian monsoon record from dongge cave china abstract we present a continuous record of the asian monsoon over the last 16 ka from 18o measurements of stalagmite calcite over 900 oxygen isotopic measurements providing information on shifts in monsoon precipitation are combined with a chronology from 45 precise 230th dates 18o and therefore asian monsoon intensity generally follows changes in insolation although changes in 18o are generally accommodated in abrupt shifts in contrast to smoothly varying insolation indicating that threshold effects may be important 18o decreased dramatically 3 at the start of the holocene 11 5 ka and remained low for 6 ka four positive 18o events centered at 11225 97 yr bp 1 05 10880 117 yr bp 1 15 9165 75 yr bp 1 4 and a double event centered at 8260 64 yr bp 1 1 and 8080 74 yr bp 1 0 punctuated this period of high monsoon intensity all four events correlate within error with climate changes in greenland ice cores thus the relationship between the asian monsoon and the north atlantic observed during the glacial period appears to continue into the early holocene in addition three of the four events correlate within error with outburst events from lake agassiz the decline of monsoon intensity in the mid late holocene is characterized by an abrupt positive shift in 18o which occurs at 3550 59 yr bp 1 1 in 100 yr in addition the holocene is punctuated by numerous centennial and multi decadal scale events amplitudes 0 5 to 1 up to half the amplitude of the glacial interstadial events seen in the last glacial period thus holocene centennial and multi decadal scale monsoon variability is significant although not as large as glacial millennial scale variability the monsoon shows a strong connection with northern south american hydrological changes related by changes in itcz position spectral analysis of the 18o record shows significant peaks at solar periodicities of 208 yr and 86 yr suggesting variation is influenced by solar forcing however there are numerous other significant peaks including peaks at el nino frequencies observed for high resolution portions of the record between 8110 and 8250 yr which suggest that changes in oceanic and atmospheric circulation patterns in addition to those forced by solar changes are important in controlling holocene monsoon climate in addition for this high resolution portion we observe a distinctive biennial oscillation of the asian monsoon which has been associated with the tropospheric biennial oscillation tbo

the recovery and isotopic measurement of water from fluid inclusions in speleothems the isotopic composition of speleothems is a useful palaeoclimatic indicator but its value would be enhanced if information on the composition of the parent dripwaters could be recovered from fluid inclusions in the speleothem calcite to develop a robust method for extracting and measuring oxygen and hydrogen isotopic composition of fluid inclusions we have used anhydrous iceland spar and microlitre glass capillaries of water as an analogue system crushing the capillary and calcite together in a high vacuum cell we have investigated the adsorbtive and isotopic behaviour of water when exposed to clean fracture surfaces significant water adsorption occurs at room temperature accompanied by large negative isotopic shifts of both oxygen and hydrogen in the recovered foe water at h2o caco3 mass ratios c for 60 min totally desorbs the water and allows retrieval of the correct isotopic composition application of these methods to a british late holocene speleothem yields delta o 18 and delta h 2 compositions for the inclusion water which are closely comparable with the modern cave dripwaters and local precipitation the results show that isotopic compositions can be recovered from inclusion samples of l equivalent to approximately ig of calcite with precisions that are useful for palaeoclimatic research 0 4 for delta o 18 and 3 for delta h 2 greater precision than this will require replicate analysis for each speleothem growth increment copyright c 2001 elsevier science ltd

hydrothermally enhanced magnetization at the center of the haughton impact structure haughton is a 24 myr old mid size apparent diameter 23 km complex impact structure located on devon island in nunavut canada the center of the structure shows a negative gravity anomaly of 12 mgal coupled to a localized positive magnetic field anomaly of 900 nt a field expedition in 2013 led to the acquisition of new ground magnetic field mapping and electrical resistivity datasets as well as the first subsurface drill cores down to 13 m depth at the top of the magnetic field anomaly petrography rock magnetic and petrophysical measurements were performed on the cores and revealed two different types of clast rich polymict impactites 1 a white hydrothermally altered impact breccia not previously observed at haughton and 2 a grey impact breccia with no macroscopic sign of alteration in the altered core gypsum is present in macroscopic veins and in the form of intergranular selenite associated with colored and zoned carbonate clasts this altered core has a natural remanent magnetization nrm four to five times higher than materials from the other core but the same magnetic susceptibility their magnetization is still higher than the surrounding crater fill impact melt rocks x ray fluorescence data indicate a similar proportion of iron rich phases in both cores and an enrichment in silicates within the altered core in addition alternating field demagnetization results show that one main process remagnetized the rocks these results support the hypothesis that intense and possibly localized post impact hydrothermal alteration enhanced the magnetization of the clast rich impact melt rocks by crystallization of magnetite within the center of the haughton impact structure subsequent erosion was followed by in situ concentration in the subsurface leading to large magnetic gradient on surface

timing duration and transitions of the last interglacial asian monsoon thorium 230 ages and oxygen isotope ratios of stalagmites from dongge cave china characterize the asian monsoon and low latitude precipitation over the past 160 000 years numerous abrupt changes in 18o 16o values result from changes in tropical and subtropical precipitation driven by insolation and millennial scale circulation shifts the last interglacial monsoon lasted 9 7 1 1 thousand years beginning with an abrupt less than 200 years drop in 18o 16o values 129 3 0 9 thousand years ago and ending with an abrupt less than 300 years rise in 18o 16o values 119 6 0 6 thousand years ago the start coincides with insolation rise and measures of full interglacial conditions indicating that insolation triggered the final rise to full interglacial conditions

climate variability in central china over the last 1270 years revealed by high resolution stalagmite records oxygen and carbon isotopic variations in the upper section of a stalagmite sf 1 from buddha cave 33 40 n 109 05 e dated by 230th 234u 210pb and lamination counting to a time resolution as fine as 1 3 years have recorded climate changes in central china for the last 1270 years the changes include those corresponding to the medieval warm period little ice age and 20th century warming lending support to the global extent of these events the isotopic records also show cycles of 33 22 11 9 6 and 7 2 years the 33 year cycle could well represent the 35 year periodicity of climate fluctuations previously recognized in china and europe cycles of 22 11 and 9 6 years have often been associated with the sunspot or lunar orbit variations the 7 2 year cycle was recently identified also in tree ring records from an area close to buddha cave these cycles suggest that external forcing e g solar irradiance may affect the summer monsoon over eastern china the general consistency between the climate characteristics inferred from the stable isotope records of sf 1 and those from other proxy records underscores the value of stalagmites as recorders of paleoclimate

international geomagnetic reference field the eleventh generation the eleventh generation of the international geomagnetic reference field igrf was adopted in december 2009 by the international association of geomagnetism and aeronomy working group v mod it updates the previous igrf generation with a definitive main field model for epoch 2005 0 a main field model for epoch 2010 0 and a linear predictive secular variation model for 2010 0 2015 0 in this note the equations defining the igrf model are provided along with the spherical harmonic coefficients for the eleventh generation maps of the magnetic declination inclination and total intensity for epoch 2010 0 and their predicted rates of change for 2010 0 2015 0 are presented the recent evolution of the south atlantic anomaly and magnetic pole positions are also examined