drowning of algal mounds records from the upper carboniferous lower pseudoschwagerina limestone carnic alps austria abstract anthracoporella algal mounds up to 22 m thick occur within the cyclic sequences of the lower pseudoschwagerina limestone uppermost carboniferous carnic alps austria their depositional environment lay between the wave base and the base of the photic zone the algal mounds are overlain by dark well bedded cherty wackestones and packstones the cherty limestones contain cephalopods thick shelled brachiopods and sponge spicules and lack anthracoporella in growth position they are typical deeper water sediments deposited below the photic zone this sequence records drowning episodes the shallow water algal mounds were drowned by relative rise of sea level as sea bottom production shut down below the photic zone the sedimentological and paleontological evidence of drowning are supported by geochemical data of two measured sections the mean sulfur content of the well oxygenated algal limestones is 0 02 for both sections the toc values are 0 17 for the section ai and 0 10 for the section ar the s contents of the cherty limestones are approximately twice as high with values of 0 48 and 0 05 for the respective sections toc values of the cherty limestones are also significantly higher with 0 30 and 0 51 contents for the respective sections the cherty limestones document the termination of the mounds and the demise of reef building algae in each cycle this interval is therefore termed shroud facies the rapid sea level rise reported is a further proof for high magnitude sea level fluctuations in intervals of glacio eustasy the documented drowning mode is novel through the definable interval of drowning the repeated events during a short time interval the full record of pre syn and post drowning deposits and the unequivocal attribution to glacio eustatic sea level rise this mode seems to be characteristic of an icehouse period and clearly differs from the drowning mode in greenhouse periods which is often gradual lacks an unequivocal cause and is often preceded by subaerial exposure

regional variations in atmospheric deposition and sources of anthropogenic lead in lake sediments across the canadian arctic stable pb isotope profiles in dated lake sediment cores were used to gauge the relative amounts and possible sources of anthropogenic pb deposited from the atmosphere in different regions of the canadian arctic a distinct north south difference was found in four high arctic lakes i e north of 66 n in this study recent pb isotopic shifts or concentration increases attributable to anthropogenic pb were negligible the maximum possible contribution from anthropogenic pb was 0 to 19 of acid leachable pb in the 1980s or 1990s in contrast two lakes in the hudson bay region displayed significantly lower pb isotope ratios and threefold to fivefold increases of pb concentrations in modern sediments corresponding to anthropogenic pb inputs of at least 72 to 91 of leachable pb eurasian urban and industrial pb is known to dominate the high arctic atmosphere a possible explanation for its negligible influence on northern lake sediments is that atmospheric pb deposition at northern latitudes is reduced compared with southern regions and is small compared to local geological inputs 210pb deposition declines with increasing latitude apparently because of declining precipitation rates stable pb deposition may be similarly affected meteorological considerations and variations in the post 1900 pb isotopic trajectories indicated that the predominant anthropogenic pb source region in nw hudson bay was eurasia while in se hudson bay it was canada and the united states with a minor eurasian component

calcite and aragonite precipitation under controlled instantaneous supersaturation elucidating the role of caco3 saturation state and mg ca ratio on calcium carbonate polymorphism abstract for many decades researchers have attempted to clarify the factors controlling the precipitation of calcium carbonate polymorphs and the incorporation of mg into calcite precipitating in natural systems in this study a novel experimental approach delineates the role of instantaneous supersaturation and solution mg ca ratio in calcium carbonate mineralogy and composition the results of this study show that in solutions with different mg ca ratios the transition between the aragonite and the calcite aragonite precipitation fields is controlled by a combination of the saturation state of the solution with respect to caco3 and the mg ca ratio in solution the data show that for increasing solution mg ca ratios progressively higher supersaturation level is required for calcite precipitation the predominance of aragonite at high solution mg ca and low supersaturations is attributed to a relative decrease in calcite growth rates as a result of increasing incorporation of mg2 in the calcite lattice at higher solution mg ca ratios as suggested by abundant experimental work increasing solution mg ca decreases the growth rate of calcite while aragonite growth rates stay unaffected our experiments do demonstrate that despite decreased growth rate the percentage of mgco3 in calcite increases with increasing solution mg ca ratio as calcite growth rates decrease aragonite growth rates stay constant and it becomes the dominant mineral phase in solutions with high mg ca ratio and low supersaturations these findings are relevant to present day mineralogical distributions in carbonate systems and might be the key to elucidate the environmental conditions responsible for mineralogic changes through geologic time the observed dependence of calcium carbonate mineralogy on solution composition and supersaturation suggests that carbonate mineralogy is controlled by kinetics of growth

submarine cementation in a high energy platform reef one tree reef southern great barrier reef three major framework facies algal pavement coral heads and branching corals show varying degrees of cementation the widest distribution and greatest variety of submarine cements occur within those facies or subfacies that have extensive encrustation by coralline algae these are found beneath the windward margin and within the patch reef drilled both mg calcite and aragonite cements exhibit diverse fabrics and textures mg calcite in the dominant cement and is present as both an interskeletal and intraskeletal infill whereas aragonite cement is exclusively intraskeletal interskeletal cements are only developed within those facies capable of trapping significant quantities of fine grained internal sediment lithified crusts with either a laminated or columnar morphology are a prominent cavity infill within many of the reef framework facies organic influence during formation peloids which are the major component of the lithified crusts as well as many other cavity infillings are a particular form of mg calcite micrite and have nucleated within the interstitial waters of the reef microcrystalline rim cements around the peloids have often cemented them into a coherent mass that resembles detrital lime mudstones modified journal abstract

kinematic analysis of strong motion p and sv waves from the sterling event p and sv velocity waveforms from the sterling explosion of december 3 1966 are analyzed from a point of view often taken in earthquake source studies the detonation occurred in the cavity excavated by the salmon explosion within the tatum salt dome mississippii velocity recordings taken from nearby borehole strong motion instruments show the occurrence of significant sv energy perret 1968a b kinematic source models are constructed by considering constraints afforded by the preshot cavity condition of the surrounding material and aspects of the p and sv waveforms such as wave polarity and duration waveforms for these models are computed and compared directly with the data modeling results suggest that the sv waves were radiated primarily by induced normal faulting occurring beneath the cavity rather than by an asymmetric pressure distribution based on the preshot cavity geometry secodary arrivals within the p waveforms and sv amplitudes suggest that these normal faults also had a component of tensional displacement which was probably due to forceable injection of material from the blast a measurement for q sub beta of 35 is obtained for salt from the amplitude decay and pulse width changes observed for sv waves along a profile taken at shot level more this value for q sub beta is for the region away from the cracked area induced by the previous salmon explosion and qualitatively explains the differing frequency content observed at the closest sterling sensors between p and sv waves the anomalous sv radiation has little to do with tectonic stress release but is a result of the medium s geometry and anisotropy less

sea ice and oxygen isotopes in foxe basin hudson bay and hudson strait canada the summer distribution of sea ice meltwater and river runoff and the surface circulation in foxe basin hudson bay and hudson strait have been studied by oxygen isotope techniques on the basis of oxygen isotope and salinity relationships the reduction of surface salinity in summer in foxe basin is predominantly due to sea ice meltwater river runoff and sea ice meltwater contribute equally to the summer surface layer in northern hudson bay the isotopic data clearly show the flow of foxe basin water through roes welcome sound into northwestern hudson bay but no evidence for this outflow is found in the passages connecting hudson bay and hudson strait oxygen isotopes indicate that recent river runoff is concentrated in a narrow band along the south side of hudson strait the wide variety of relationships between oxygen isotope ratios and salinity is explained by the known ice dynamics and the seasonal variability predicted from ice melting and freezing models

source parameters of two rift associated intraplate earthquakes in peninsular india the bhadrachalam earthquake of april 13 1969 and the broach earthquake of march 23 1970 abstract the bhadrachalam earthquake of april 13 1969 and the broach earthquake of march 23 1970 are two major intraplate earthquakes associated with paleorift zones in the stable continental region of peninsular india these two events shook very large portions of the peninsula and casualties were reported for the broach earthquake ancient rifts have recently been identified as a major seismogenic tectonic feature for intraplate seismicity in stable continental regions p wave first motions and waveforms of long period teleseismic p and sh waves have been modeled to constrain the focal mechanisms and to determine the source parameters for the earthquakes previous investigators proposed multiple fault plane solutions for each of the events in this paper some of the early solutions are eliminated and the best source mechanism is derived for each earthquake for the bhadrachalam earthquake the focal mechanism determined is predominantly strike slip strike 245 dip 72 rake 358 the strike direction of the ne sw trending nodal plane is in good agreement with the trend of the observed isoseismals and is probably the fault plane the seismic moment is 4 59 1024 dyne cm and the moment magnitude mw is determined to be 5 7 the focal depth and the static stress drop are estimated to be 10 km and 17 bar respectively the strike slip motion represents a reactivated fault motion under the present day stress field for the broach earthquake the focal mechanism determined is reverse faulting with a strike slip component strike 273 dip 58 rake 130 the direction of the e w striking nodal plane is in good agreement with the mapped narmada fault dislocation direction of fissures and the trend of the isoseismals the seismic moment and moment magnitude are determined to be 1 39 1024 dyne cm and 5 4 respectivety the focal depth and the stress drop are estimated to be 11 km and 9 bar respectively the reverse motion of this event represents an inverted slip or tectonic inversion within a rift zone under the present day compressional stress field some rift associated earthquakes are characterized by large multiple shocks with significant strike slip motions the two indian earthquakes however occurred as regular main shock aftershock sequences and represent a different mode of strain release these two earthquakes also represent events with low stress drops and relatively long recurrence intervals the interpretation of this last observation is uncertain and needs more study in the future

high resolution seismo stratigraphy and sedimentological properties of late and postglacial sediments in lac guillaume delisle estuary and nastapoka sound eastern hudson bay lac guillaume delisle estuary and nastapoka sound are two sedimentary basins that recorded the late quaternary deglaciation on the eastern coast of hudson bay acoustic profiles reveal an average sediments thickness of 15 m in the estuary and 6 m in the sound these sediments reach 70 m thick in deep glacial troughs within the studied basins four seismo stratigraphic units overlying the acoustic basement were recognized unit 1 subaqueous ice contact and draped glaciomarine deposits associated with the quebec labrador ice sector qlis of the laurentide ice sheet lis and the tyrrell sea records the presence of a short ice marginal stillstand during glacial retreat unit 2 paraglacial and postglacial fluvial deltaic deposits and unit 3 postglacial silty deposits result from erosion of emerged sediments and redeposition in response to changes in relative sea level rsl finally unit 4 is composed of deformed deposits associated with a mass wasting event the stratigraphic sequence and the spatia

surface sediment dinoflagellate cysts from the hudson bay system and their relation to freshwater and nutrient cycling abstract surface sediment samples from the hudson bay system were analysed in order to examine the role of key regulators of arctic marine productivity light and nutrients as affected by freshwater stratification and sea ice cover on the spatial distribution and production of dinoflagellate cysts total cyst fluxes vary from 0 2 10 6 to 30 6 10 6 cysts m 2 a 1 with the highest values observed in eastern hudson bay a total of 24 cyst taxa representing 11 genera of five orders were identified and distribution maps of the most common taxa have been produced this is the first record of echinidinium aculeatum echinidinium karaense cf echinidinium delicatum islandinium brevispinosum selenopemphix quanta cysts of protoperidinium americanum cysts of cf biecheleria sp and polarella glacialis in the hudson bay system dinoflagellate cyst assemblages show distinct spatial patterns revealing three compositional domains eastern hudson bay western central hudson bay and hudson strait the eastern domain is characterised by a dominance of autotrophic cysts of pentapharsodinium dalei whereas the western central domain is characterised by autotrophic operculodinium centrocarpum with some contribution by heterotrophic polykrikos sp var arctic morphotype and polykrikos spp sites from hudson strait are distinguished by an overwhelming prevalence of heterotrophic protoperidiniaceae cysts mainly islandinium minutum and have the highest values of sedimentary biogenic silica used as a proxy for diatom productivity sediment geochemical tracers are used as proxies for freshwater inputs lignin and its biomarkers and nitrate availability nitrogen isotopes and sea ice concentrations derived from passive microwave data as a proxy for light availability sea ice regulated length of the dark season has a negligible influence on the proportion and production of heterotrophic dark adapted versus autotrophic light dependent dinoflagellate cysts perhaps due to the location of our study area on the southern fringe of the arctic instead cyst populations in hudson bay are primarily regulated by vertical stratification and nitrate availability while in hudson strait the pivotal mechanism constitutes food availability

lithified and unlithified mg calcite precipitates in tropical reef environments abstract push cores from the branching coral framework of lagoonal reefs in belize and panama indicate that the micritic mg calcite in the unlithified mud matrix is similar in composition to the well documented submarine lithified micritic crusts and infillings found in open reef framework the sediment matrix of the lagoonal framework contains significant concentrations of 12 to 13 mole mgco3 calcite that shows almost no signs of skeletal origins as indicated by a fairly consistent mineralogy and independent distribution patterns in sand silt and clay size fractions its sedimentological and mineralogical similarity to cemented micritic crusts and infillings suggests that the precipitation of micritic mg calcite is widespread in tropical reef waters and becomes lithified when precipitated in open frameworks but remains unlithified when trapped in impermeable lagoonal muddy sediments

strike slip faulting on the northern margin of the south china sea evidence from two earthquakes offshore of hainan island china in december 1969 in december 1969 two earthquakes mb 4 7and4 8 occurred in a rift basin offshore of hainan island china in a passive continental margin environment by modeling short period p and long period sh waveforms recorded at wwssn stations we have determined the focal mechanisms and source parameters of these two events to be strike 45 7 dip 78 4 rake 6 7 focal depth 8 3 km seismic moment 1 73 0 4 1023 dyne cm and stress drop 56 6 bar for the 17 december event and strike 36 6 dip 60 4 rake 2 7 focal depth 8 3 km seismic moment 1 43 0 13 1023 dyne cm and stress drop 47 6 bar for the 20 december event results of relative location computed from differential arrival times indicate that the 20 december event is slightly deeper than the 17 december event but within the resolution limit of the waveform constraint analysis of the local tectonic setting geometry of isoseismals aftershock distribution and fault plane solutions indicate that the 17 december event probably ruptured along a ne sw striking fault on the northern margin of the songtao uplift in the qiongdongnan basin the 20 december event probably ruptured along another major ne sw striking fault on the northern margin of the qiongdongnan basin the fault motions of both earthquakes were almost pure left lateral strike slip p and t axes show that the epicentral area is subject to nearly horizontal n s directed compression and e w directed extension consistent with previously observed stress field in the area the two earthquakes represent reactivation of pre existing zones of weakness in the basin by the present day tectonic stress field a review of earthquakes in the region indicates that strike slip motion is characteristic of the seismotectonics of the northern margin of the south china sea

depth of faulting during the 1968 meckering australia earthquake sequence determined from waveform analysis of local seismograms waveforms for 11 foreshocks and 48 aftershocks of the ms 6 8 meckering earthquake recorded at the world wide standard seismograph network station mundaring are analyzed to determine the depth distribtion of faulting during this unusual intraplate earthquake sequence clear depth phases including sp and rg are seen in the local seismograms at distances of 60 95 km and are studied using synthetic seismograms computed using generalized ray theory and wave number integration techniques large rg s ratios seen on the vertical component short period data for many events imply source depths less than 2 km the short period p waveform contains the best depth estimator in the form of sp so that depth can be estimated to within an uncertainty of about 1 km for most events the foreshocks cluster at less than 2 km depth and most aftershocks occur within 1 km of the surface a few aftershocks occur as deep as 7 km these results are consistent with a previous teleseismic waveform study in which faulting was inferred to start near the surface at 1 5 km depth with rupture proceeding downward and not exceeding 6 km depth these results coupled with previous stress studies in the australian shield and models of crustal strength show that faulting in a cold shield area is a near surface phenomenon and implies that most of the crust is too strong to be fractured

major flux of terrigenous dissolved organic matter through the arctic ocean high latitude rivers supply the arctic ocean with a disproportionately large share of global riverine discharge and terrigenous dissolved organic matter dom we used the abundance of lignin a macromolecule unique to vascular plants and stable carbon isotope ratios 13c to trace the high molecular weight fraction of terrigenous dom in major water masses of the arctic ocean lignin oxidation products in ultrafiltered dom udom 1 000 da from arctic rivers were depleted in syringyl relative to vanillyl phenols s v 0 3 0 5 compared to udom in temperate and tropical rivers s v 0 5 1 2 indicating that gymnosperm vegetation is a major source of terrigenous udom to the arctic ocean high concentrations of lignin oxidation products 83 320 ng l 1 and a depletion of 13c 13c 23 0 to 21 9 in udom throughout the surface arctic ocean indicate that terrigenous udom accounts for a much greater fraction of the udom in the surface arctic 5 33 than in the pacific and atlantic oceans 0 7 2 4 in contrast udom in deep water from the arctic ocean as well as waters from throughout the greenland gyre had relatively low concentrations of lignin oxidation products 24 45 ng l 1 and was enriched in 13c 13c 21 0 to 20 8 terrigenous udom has a relatively short residence 1 6 yr in surface polar waters prior to export to the north atlantic ocean assuming that the bulk of arctic derived dom is compositionally similar to the udom fraction we estimate that 12 41 of terrigenous dom 2 9 10 3 tg c yr 1 discharged by rivers to the arctic ocean is exported to the north atlantic via surface waters of the east greenland current it appears very little terrigenous dom from the arctic is incorporated into north atlantic deep water and distributed globally via deep thermohaline circulation

holocene deltaic sedimentation along an emerging coast nastapoka river delta eastern hudson bay quebec eastern hudson bay is characterized by falling relative sea level as a result of post glacial isostatic rebound which makes the region a natural laboratory for rapid forced regression where the evolution of deltaic systems and offshore sedimentation patterns can be studied a multidisciplinary approach involving airphoto analysis offshore geophysical surveys sediment coring and facies and diatom analyses was used in this study of the nastapoka river delta the delta has formed as a result of the fluvial erosion of emerged quaternary sediments but is mainly subaqueous offshore in the prodelta zone the oldest deposits are glaciomarine laid down when the ice front of the receding laurentide ice sheet stood on the nastapoka hills some 7700 6800 years bp lateral equivalents of this glaciomarine unit are presently exposed on land the shallow water platform of the delta shows a thin surficial unit of wave worked sand that overlies fine grained deeper water deposits derived from erosion of clay soils

sub surface structures and site effects extracted from ambient noise in metropolitan guangzhou china abstract in this paper ambient noise is used to investigate near surface structures and site effects in metropolitan guangzhou we deployed 94 short period stations across guangzhou area and later a dense linear array across the shougouling fault sf using more than one month s continuous data we invert three dimensional shear wave velocity structures of guangzhou area via ambient noise tomography results show low velocity near the guangzhou conghua fault gcf shougouling fault sf and beneath the alluvial plain in the south region meanwhile high velocity anomalies are beneath the mountain area in northeastern region moreover we obtain the sediment thickness and sub surface shear wave velocity structures around the shougouling fault sf by horizontal to vertical spectral ratio hvsr method hvsr results show a significant shift in the thickness of the sedimentary layer across the sf shear wave velocity derived from hvsr curves has a consistent trend of variation with the sediment thickness our results provide a better understanding of sub surface structures of metropolitan guangzhou and can be served as a reference model for geological disaster migration prediction in the city

nearshore erosion by combined ice scouring and near bottom currents in eastern hudson bay canada abstract a study of nearshore sedimentary processes was carried out in manitounuk sound a sheltered environment protected by rocky islands along eastern hudson bay high resolution seismic profiles suggest that up to 10 m of holocene sediments were eroded in less than 15 m water depth although these shallow depths are affected by low energy waves and currents according to our measurements of near bottom currents at 3 7 and 5 6 m water depths the threshold velocity for sediment motion 20 cm s 1 is only seldom exceeded and consequently the significant erosion of the nearshore deposits can hardly be explained by hydraulic processes alone geophysical data seismic and echosounding profiles suggest that the observed erosion is mainly due to bottom scouring by dragging ice keels these data show that the zone of maximum ice scouring between 8 and 12 m water depths corresponds to the zone of maximum erosion of holocene sediments because ice scouring in this area occurs when the sea is largely ice free wind induced near bottom currents probably contribute to the dispersal of the sediments resuspended by ice

organic carbon isotope ratios δ 13 c of arctic amerasian continental shelf sediments organic matter origins are inferred from carbon isotope ratios 13c in recent continental shelf sediments and major rivers from 465 locations from the north bering chukchi east siberian beaufort sea arctic amerasia generally there is a cross shelf increase in 13c which is due to progressive increased contribution seaward of marine derived organic carbon to surface sediments this conclusion is supported by the correlations between sediment 13c oc n and 15n the sources of total organic carbon toc to the amerasian margin sediments are primarily from marine water column phytoplankton and terrigenous c3 plants constituted of tundra taiga and angiosperms in contrast to more temperate regions the source of toc from terrigenous c4 and cam plants to the study area is probably insignificant because these plants do not exist in the northern high latitudes the input of carbon to the northern alaskan shelf sediments from nearshore kelp community laminaria solidungula is generally insignificant as indicated by the absence of high sediment 13c values 16 5 to 13 6 which are typical of the macrophytes our study suggests that the isotopic composition of sediment toc has potential application in reconstructing temporal changes in delivery and accumulation of organic matter resulting from glacial interglacial changes in sea level and environments furthermore recycling and advection of the extensive deposits of terrestrially derived organic matter from land or the wide amerasian margin could be a mechanism for elevating total co2 and pco2 in the arctic basin halocline

sediment records of the influence of river damming on the dynamics of the nelson and churchill rivers western hudson bay canada during the last centuries two gravity cores 778 and 780 sampled at the nelson river mouth and one 776 at the churchill river mouth in western hudson bay canada were analyzed in order to identify the impact of dam construction on hydrology and sedimentary regime of both rivers another core 772 was sampled offshore and used as a reference core without a direct river influence core chronology was established using 14c and 210pb measurements cores 778 and 780 show greater variability than the others and the physical chemical magnetic and sedimentological properties measured on these cores reveal the presence of several hyperpycnites indicating the occurrence of hyperpycnal flows associated with floods of the nelson river these hyperpycnal flows were probably caused by ice jam formation which can increase both the flow and the sediment concentration following the breaching of such natural dams however these hyperpycnites are only observed in the lower parts of cores 778 and 780 it was not possible to establish a pr

modelling the sea ice ocean seasonal cycle in hudson bay foxe basin and hudson strait canada the seasonal cycle of water masses and sea ice in the hudson bay marine system is examined using a three dimensional coastal ice ocean model with 10 km horizontal resolution and realistic tidal atmospheric hydrologic and oceanic forcing the model includes a level 2 5 turbulent kinetic energy equation multi category elastic viscous plastic sea ice rheology and two layer sea ice with a single snow layer results from a two year long model simulation between august 1996 and july 1998 are analyzed and compared with various observations the results demonstrate a consistent seasonal cycle in atmosphere ocean exchanges and the formation and circulation of water masses and sea ice the model reproduces the summer and winter surface mixed layers the general cyclonic circulation including the strong coastal current in eastern hudson bay and the inflow of oceanic waters into hudson bay the maximum sea ice growth rates are found in western foxe basin and in a relatively large and persistent polynya in northwestern hudson bay sea ice advection and ridging are more important than local thermodynamic growth in the regions of maximum sea ice cover concentration and thickness that are found in eastern foxe basin and southern hudson bay the estimate of freshwater transport to the labrador sea confirms a broad maximum during wintertime that is associated with the previous summer s freshwater moving through hudson strait from southern hudson bay tidally driven mixing is shown to have a strong effect on the modeled ice ocean circulation

crustal stress field perturbations in the continental margin around the korean peninsula and japanese islands abstract seismic activity and focal mechanisms are governed by the effective stress field that is a combined result of regional tectonic processes and local stress perturbation this study investigates the regional variation in the stress field in the eastern continental margin of the eurasian plate around the korean peninsula and japanese islands using a damped stress inversion technique based on the focal mechanism solutions of regional earthquakes the dominant compressional stress is directed ene wsw around the korean peninsula and eastern china e w at the central east sea and northern and southern japan nw se at central japan and n s around the northern nankai trough the dominant compression direction changes rapidly in the east sea and japanese islands which may be due to the combined effects of tectonic loading in the subduction zones off the japanese islands and the india eurasia plate boundary the crustal stress fields around the subduction zones off the japanese islands present characteristic depth dependent orientations the orientations of the largest horizontal stress components h in the subduction zones are subparallel with the plate convergence directions at shallow depths the h orientations are observed to rotate clockwise with the depth owing to slab subduction and lithospheric deformation the regional stress field around the japanese islands was perturbed temporally by the 2011 m9 0 tohoku oki megathrust earthquake the regional stress field was recovered in a couple of years the stress field and tectonic structures are mutually affected causing stress field distortion and a localized mixture of earthquakes in different faulting types

the greenland earthquake of 11 july 1987 and postglacial fault reactivation along a passive margin abstract intraplate earthquakes in many cases occur near continental margins this observation applies very well to the case of greenland a stable continental region with low seismicity the seismicity of greenland is nearly totally concentrated along the coastlines of the island where it is relatively free of ice cover on 11 july 1987 the largest greenland earthquake of instrumental record m b 5 5 m w 5 4 occurred in continental crust off the northeastern coast in the wandel sea waveforms of long and short period teleseismic p and long period teleseismic sh waves have been modeled to estimate the source parameters for this earthquake the focal mechanism determined is a normal faulting with a strike slip component strike 148 dip 59 and rake 131 the strike direction of one of the nodal planes was found to be consistent with the direction of the dominant structural trend observed in the area a previous normal faulting mechanism with very different strike directions for this event was found to have inferior waveform fit and is not consistent with the fault strike directions from the local geological setting the seismic moment of the july 1987 earthquake is 1 75 10 24 dyne cm the focal depth and stress drop are 5 km and 389 bars respectively the high stress drop may relate to the relatively long earthquake repeat time in the region the observed normal faulting of this earthquake can be interpreted as a rupture due to an extensional stress field at the forebulge outside of the ice sheet because of deglaciation flexure in the region another major earthquake 26 november 1971 m b 5 1 311 km to the south of the 11 july 1987 event was likewise determined to be normal faulting and can be explained as another event triggered by deglaciation in addition we find that the sparse general seismicity of greenland can also be related to postglacial rebound

morphodynamic evolution self organisation and instability of coarse clastic barriers on paraglacial coasts abstract beaches and barriers on many mid to high latitude coasts comprise mixtures of fine and coarse clastic materials forming a distinctive morphodynamic environment in many cases the sediments are derived primarily from limited glacigenic deposits and the coasts are considered paraglacial over relatively long time scales decades to centuries coarse clastic barriers on such coasts show evidence of self organisation through large scale morphological evolution and facies differentiation this process involves gradual reworking partitioning and textural sorting of material toward transport minima long intervals of slow evolution are punctuated by episodes of rapid reorganisation involving breakdown of stable barrier structures and facies patterns remixing of sediment and accelerated migration of transgressive systems drift aligned systems develop longshore cell structure sometimes leading to breaching and segmentation and may evolve toward progressively greater swash alignment under appropriate circumstances swash aligned systems may experience catastrophic transformation when appropriate environmental triggers lead to threshold exceedance in the morphodynamics of the shore system adjacent barriers may show quite different behaviour depending on the antecedent states of individual coastal cells while appropriate parameterisations and sediment budget formulations allow us to model the long term evolution of some barrier structures the non linear dynamics that appear to dominate large scale behaviour may limit predictability the identification of stability threshold criteria remains an important research priority

observation of glacial isostatic adjustment in stable north america with gps 1 motions of three hundred and sixty global positioning system gps sites in canada and the united states yield a detailed image of the vertical and horizontal velocity fields within the nominally stable interior of the north american plate by far the strongest signal is the effect of glacial isostatic adjustment gia due to ice mass unloading during deglaciation vertical velocities show present day uplift 10 mm yr near hudson bay the site of thickest ice at the last glacial maximum the uplift rates generally decrease with distance from hudson bay and change to subsidence 1 2 mm yr south of the great lakes the hinge line separating uplift from subsidence is consistent with data from water level gauges along the great lakes showing uplift along the northern shores and subsidence along the southern ones horizontal motions show outward motion from hudson bay with complex local variations especially in the far field although the vertical motions are generally consistent with the predictions of gia models the horizontal data illustrate the need and opportunity to improve the models via more accurate descriptions of the ice load and laterally variable mantle viscosity

high resolution seismic stratigraphy of late quaternary deposits in manitounouk sound northern quebec effects of rapid postglacial emergence manitounouk sound contains a succession of postglacial deposits consisting of three acoustic units separated by disconformities from base to top these are 1 a stratified draped unit interpreted as of glaciolacustrine and glaciomarine origin 2 an onlapping basin fill unit of thick transparent beds interpreted as gravity flow deposits and 3 a divergent fill unit of stratified and transparent modern marine deposits the gravity flow deposits of unit 2 pass laterally into slide scars that truncate unit 1 pollen and dinoflagellate analysis of cores correlated with the acoustic sections indicate that unit 1 is of early holocene age and confirms a glaciomarine environment unit 3 contains modern assemblages of pollen and dinoflagellates the slide scar and gravity flow deposits of unit 2 correspond to the period of transition from glaciomarine to modern conditions and are interpreted to result from a period of relatively intense earthquake activity due to stress release along faults during or shortly

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

depth transect of an upper triassic rhaetian reef from gosau austria microfacies and community ecology abstract in the late triassic 235 201 3 ma scleractinian corals and hypercalcified sponges built large diverse reef ecosystems the most famous of which are the dachstein reefs this study presents a depth transect along an upper triassic lower rhaetian dachstein reef from the gosausee margin of the dachsteingebirge gosau austria the gosausee microbial sponge coral reef is a complete barrier reef with an almost continuous fore reef to lagoon transect preserved a very rare occurrence for the triassic and thus provides a window into depth zonation of dachstein type reef facies and biotic succession the gosausee reef facies exhibit strong depth control and five classic reef facies or zones are identified the fore reef reef front reef crest back reef and lagoon facies thin rare microbial fabrics and a high abundance of fine grained mud rich skeletal wackestones transported reef debris characterize the deepest fore reef as the reef shallows muddy sediments decrease in abundance and are replaced by microbial fabrics corals and cements abundant sponges microbial crusts and thick marine cements typify the reef crest whereas microbialite coated phaceloid corals are dominant in the back reef facies heavily cemented oncoids or microbial sponge bindstones are characteristic of the lagoon based on their compositional and biotic similarities the gosausee reef was likely part of the same barrier reef systems as the source reef for the gosaukamm reef breccia one of the classic norian rhaetian dachstein reefs the reef zones of the gosausee margin can be used to interpret the depth or reef zone of less well preserved reef fragments can inform models of community ecology and niche utilization in the late triassic and highlight the need for additional research into the environmental factors that controlled biotic distribution in upper triassic reefs

a sediment and organic carbon budget for the canadian beaufort shelf abstract the arctic ocean accounts for 20 of the world s continental shelves because the arctic is sensitive to global change budgets of organic carbon for its shelves are of immediate interest the mackenzie shelf of the canadian beaufort sea is the best north american proxy for the enormous eurasian shelves large area large river input and the only site for which a complete organic carbon budget can be attempted due to an extensive data base a mass balance for the mackenzie shelf has been constructed for sediments terrestrial organic carbon and primary produced carbon we have considered allochthonous inputs from the mackenzie river from coastal erosion from smaller rivers from groundwater from the atmosphere and import by ice the mackenzie river dominates the supply to the beaufort shelf of inorganic sediment 127 mt a 1 and paniculate and dissolved terrestrial carbon 2 1 mt a 1 poc 1 3 mt a 1 doc the combined input from all other sources contributes only about 5 of the mackenzie load using sediment accumulation data we estimate that about half of the sediment supply is trapped in the delta about 40 on the shelf and the remainder escapes the shelf edge by various processes autochthonous primary production in the delta and on the shelf adds a further 3 3 mt a 1 of particulate organic carbon a box model has been constructed to account for sediment terrestrial organic carbon and primary produced carbon whereas about 60 of the terrestrial poc is preserved in delta and shelf sediments it appears that most 97 of the primary produced carbon is recycled and not preserved in sediments confidence in the budget should be improved by focusing future research on the determination of modern sedimentation rates on the delta and shelf measurement of organic carbon content of deltaic sediments determination of primary production on the shelf and determination of the relative proportions of terrestrial and marine organic carbon preserved in sediments

a procedure for modelling shallow dislocation sources summary expressions for displacements on the surface of a layered half space due to an arbitrary oriented shear dislocation are given in terms of generalized ray expansions useful approximations of these expressions for shallow events as recorded at teleseismic distances for realistic earth models are presented the results of this procedure are used to generate synthetic p sv and sh waveforms for various assumptions of stress drop

characterization of siberian arctic coastal sediments implications for terrestrial organic carbon export surface sediments were collected during the 2000 transarctic expedition along the siberian arctic coastline including the ob yenisey khatanga lena and indigirka estuaries sediments were chara

the 1984 southern yellow sea earthquake of eastern china source properties and seismotectonic implications for a stable continental area on 21 may 1984 a strong shock ms 6 3 mb 5 7 occurred in the southern yellow sea which shook the densely populated coastal area of eastern china about 1 min before the main shock a foreshock of mb 5 4 occurred because of interference from the foreshock no reliable p wave first motions or focal mechanisms have been obtained for the main shock from local seismic data in this paper long period teleseismic data have been used to investigate the source mechanism fault plane solutions determined from first motions as well as p and sh waveforms show a predominant strike slip motion with a small dip slip component on a steeply dipping plane the tectonic environment of this event supports the observation that margins of former rifts tend to be sites of midplate seismic source regions the yellow sea developed in a cratonic environment due to early cenozoic rifting the major graben faults strike nne ssw to ne sw and are intersected by second order faults trending wnw ese aftershock distribution suggests that the fault which generated the main shock probably strikes wnw ese the mechanism determined in this paper strikes 120 dips 88 and slips 28 this solution suggests that the earthquake ruptured along a secondary fault near the intersection of a more major nne ssw trending fault the epicentral area is subject to to an ene wsw compression and a nnw sse extension the seismic moment and focal depth are determined to be 1 09 1025 dyne cm and 12 4 km respectively relative hypocentral locations indicate that the focal depth of the foreshock is similar to that of the main shock and the hypocenter of the foreshock is located very close to the wnw ese striking nodal plane of the main shock mechanism and is about 20 km away from the main shock hypocenter source properties of the southern yellow sea earthquake have been compared with those of three major earthquakes of north china the stress drop of the yellow sea earthquake is determined to be about 42 bars this value is much lower than the stress drops computed for the 1966 hsingtai and the 1975 haicheng earthquakes of north china the southern yellow sea is characterized by short recurrence intervals while the hsingtai and haicheng areas have very long recurrence intervals the short recurrence intervals and low stress drop may reflect a lower material strength at the source region in the yellow sea

climate change and recent sedimentation in nastapoka sound eastern coast of hudson bay in an attempt to determine to what extent the impact of recent climate changes that occurred east of hudson bay including important reduction of areas in permafrost had on the coastal marine environment a series of shallow cores were extracted from the seabed off the mouth of the sheldrake river in nastapoka sound a total of 25 cores were taken in april 2009 from the ice cover a preliminary seafloor map was first done to help in the selection of the coring sites nastapoka sound has a complex subaqueous relief formed of asymmetric ridges and deep basins after preliminary sedimentological analyses six of the cores were selected for physical and chronological analyses 14c 210pb and 137cs dating among them three were selected for elemental c n oc tn and isotopic 13c 15n analyses to identify sedimentary organic matter sources sedimentation processes are complex and are primarily driven by bottom currents this is confirmed by the absence of a clay fraction in several cores some erosi

recent change in organic carbon flux to arctic ocean deep basins evidence from acid volatile sulfide manganese and rhenium discord in sediments evidence of recent large scale change in redox conditions in arctic ocean basin sediments is found in profiles of solid phase acid volatile sulfide avs mn and re avs occurs at 2 5 5 5 cm in sediment cores collected from all major arctic basins implying that presently there is a sufficient supply of organic carbon oc to deplete o 2 and form sulfide re which is mobile under oxic conditions but precipitates under suboxic or anoxic conditions is not found enriched in the sediments suggesting that avs is a recent product of enhanced oc fluxes estimated diffusion rates suggest that avs production is recent and that a change from oxic to anoxic diagenesis has taken place within the past 50 y the most likely origin for such widespread change is the ice climate and we infer that reduction in ice cover over the past several decades has led to enhanced oc fluxes to the sea floor

regional waveform constraints on the source parameters of the xunwu china earthquake of 2 august 1987 with implications for mid plate seismotectonics abstract the xunwu china earthquake of 2 august 1987 m s 5 3 was a damaging intraplate event in a stable continental region in this paper long period p and sh waves recorded by the world wide standardized seismograph network and the chinese standard seismic network stations within 30 epicentral distance have been modeled to determine the focal mechanism and source parameters of the mainshock using body wave waveform synthesis and p wave first motions the focal parameters are determined as follows strike 338 6 dip 53 4 rake 39 7 focal depth 7 4 k moment 3 63 1 57 10 23 dyn cm and stress drop 2 6 1 2 bars analysis of the local tectonic setting geometry of isoseismals and aftershock distribution indicates that the earthquake probably ruptured along a nw se striking secondary fault near its intersection with a nne ssw trending major fault the fault motion was normal oblique slip with a left lateral strike slip component based on the p and t axes the epicentral area is subject to nw se compression with a relatively large plunge and a nearly horizontal ne sw extension the observed large plunge of the p axis is probably due to an anomalous local stress field in comparison with other intraplate events the stress drop of the xunwu earthquake is very low suggesting a weak and fractured crustal medium in the epicentral region

dating quaternary raised coral terraces along the saudi arabian red sea coast abstract late pleistocene raised coral reef terraces form extensive outcrops up to 5 km wide along the saudi coast porites coral were dated using u th while clastic sediment from jeddah was dated using thermoluminescence the pooled mean age for the coral samples is 121 5 0 2 ka suggesting mis 5e even for the uplifted 16 20 m high terrace in the north at haql in jeddah the mis 5e back reef succession is overlain by fluvial sediment that gave a tl age of 66 13 ka the structure and faunal composition of the coral terraces suggests that they accumulated in broad shallow embayments following the last interglacial transgression the consistent elevation of these terraces suggests that the central and southern saudi coast has been tectonically stable for at least the past 125 000 years and the coral reef terraces at 3 5 5 5 m elevation are consistent with the mis 5e sea level high stand that peaked at 6 9 m above present sea level the saudi coastal coral terrace north of duba shows progressive uplift to 16 20 m near haql since 108 120 ka as a result of ongoing transform faulting in the gulf of aqaba

late permian paleomagnetic pole from dikes of the tarim craton china we have obtained a late permian paleomagnetic pole from dikes in the tarim craton of china directions of magnetization from 21 mafic and ultramafic dikes at three localities pass a fold test at the 95 confidence level the new paleomagnetic pole lies at lat 66 n long 181 e n 21 k 61 and 95 3 9 on the basis of a comparison with paleomagnetic data from adjacent tectonic units we conclude that 1 the late permian paleolatitude of the tarim craton differs from that of the sino korean craton suggesting that the two cratons were distinct tectonic units in late permian time 2 there was relative motion between the tarim craton and the siberian craton after late permian time and 3 negligible relative motions have occured between different thrust sheets in the keping bachu area of the north western tarim craton

organic matter compositions of rivers draining into hudson bay present day trends and potential as recorders of future climate change concentrations and compositions of particulate and dissolved organic carbon poc and doc respectively and aromatic compounds including lignin were analyzed in water samples from 17 rivers flowing into hudson bay northern canada these rivers incorporate basins to the south with no permafrost to basins in the north with continuous permafrost and dominant vegetation systems that include boreal forest the hudson plains taiga shield and tundra major latitudinal trends in organic carbon and lignin concentrations and compositions were evident with both doc and dissolved lignin concentrations dominating over their particulate counterparts and exhibiting significant correlations with total dissolved and suspended solids respectively the composition of lignin reaction products in terms of the syringyl cinnamyl and vanillyl compositions indicate mixed sources of vascular land plant derived organic carbon with woody gymnosperms contributions dominating in the southern river basins whereas nonwoody angiosperm sources were more important in the most northerly rivers the composition of nonlignin aromatic compounds which provides a tracer for nonvascular plant contributions suggests stronger contributions from sphagnum mosses to dissolved organic matter in rivers below the tree line including those with large peat bogs in their basins acid aldehyde ratios of the lignin products together with 14c data for doc in selected rivers indicate that doc has generally undergone greater alteration than poc interestingly several northern rivers exhibited relatively old doc according to the 14c data suggesting that either old doc is being released from permafrost or old doc survives river transport in these rivers

characterization of sedimentary organic matter in recent marine sediments from hudson bay canada by rock eval pyrolysis abstract a combination of rock eval pyrolysis and isotopic analyses is used to characterize the sources and distribution of organic matter in modern marine sediments from the subarctic hudson bay including hudson strait and foxe basin canada this approach reveals organic matter contributions from both marine and terrigenous sources with spatial patterns and varying degrees of degradation that are consistent with inferences from traditional geochemical tracers for modern organic matter rock eval parameters characterize hudson bay organic matter with low hydrogen index high oxygen index and a high degree of residual carbon that suggests heavily reworked materials locations of higher primary productivity in hudson strait foxe basin the northeast and far west of hudson bay and the concentration of watershed runoff in the southern part of hudson bay can be delineated using the ratios between hydrogen and oxygen indices and from the distribution of labile organic carbon relatively high temperatures of peak hydrocarbon yield identify an advanced state of om degradation or humic substances as important classes of organic carbon compounds in the majority of the sediment such highly degraded and oxygenated organic matter is unusual compared to that typically observed in other arctic shelf seas and is consistent with a strong role for sediment and organic matter recycling in hudson bay in the offshore region the source of highly oxidized and labile organic matter identified by rock eval parameters is resolved with 13 c and biomarker information that also permit examination of the sediment biogeochemical regime this approach suggests that a distinct association with mn enriched sediment contributes to the oxidization signal by abiotic or biological mn related processes these interpretations extend the limited information available on using rock eval analyses to characterize organic matter in recently deposited marine sediments and describe an important consideration to using this method in mn enriched environments

regional stress field of the indian plate we have calculated the regional stress field in the indian plate implementing dependence of slab pull and ridge push on the age of the oceanic lithosphere in the finite element procedure the high level of the calculated stress field order of a few kbar and the dominance of compression in the plate are consequences of the unique dynamic situation of the present day indian plate the calculated stress field explains the concentration of intraplate deformation in the region of the ninetyeast ridge and yields insight into the variations in stress directions in the australian continent

earthquake multiplets in the southeastern solomon islands the 350 km stretch of the solomon islands trench that lies adjacent to the islands of guadalcanal and san cristobal has been the site of 10 large shallow earthquakes since 1966 june 15 1966 doublet m s 7 7 7 3 may 20 21 1977 quadruplet m s 6 7 7 5 7 5 7 5 november 4 5 1978 doublet m s 6 9 7 1 and two single events on october 23 1979 m s 7 1 and february 7 1984 m s 7 7 analyses of p wave first motions aftershock distributions p wave forms recorded at epicentral distances of 30 to 90 on the wwssn and 256 s period rayleigh wave spectra obtained from the ida and gdsn networks are used to examine the source characteristics of the events the close temporal association and large size of earthquakes precluded collection of useful seismograms for the latter of the two 1966 events and the second and third events of the 1977 sequence p waveforms analyzed show smooth traces that can be modeled with simple trapezoidal source time functions located at shallow 15 45 km depths focal mechanisms are consistent with oblique subduction of the indian plate beneath the pacific plate at about n73 e estimates of seismic moment for individual events range from 0 2 to 2 3 10 27 dyne cm average stress drops of the sequences are estimated to range between 10 and 40 bars this section of island arc may have ruptured in a similar sequence of earthquakes during the 1930 s conversion of the cumulative seismic moment to displacement and averaging over 40 years suggests a convergence rate of about 4 5 cm year 1 about one half of the rates that have been assessed on the basis of seafloor magnetic lineations

microbial deposits in the aftermath of the end permian mass extinction a diverging case from the mineral mountains utah usa the lower triassic mineral mountains area utah usa preserves diversified smithian and spathian reefs and bioaccumulations that contain fenestral microbialites and various benthic and pelagic organisms ecological and environmental changes during the early triassic are commonly assumed to be associated with numerous perturbations productivity changes acidifica tion redox changes hypercapnia eustatism and temperature changes post dating the permian triassic mass extinction new data acquired in the mineral mountains sediments provide evidence to decipher the relationships between depositional environments and the growth and distribution of microbial structures these data also help to understand better the controlling factors acting upon sedimentation and community turnovers through the smithian early spathian the studied section records a large scale depositional sequence during the dienerian spathian interval during the transgression depositional environments evolved from a coastal bay with continental deposits to intertidal fenestral microbial limestones shallow subtidal marine sponge microbial reefs to deep subtidal mud dominated limestones storm induced deposits microbialite sponge reefs and shallow subtidal deposits indicate the regression three microbialite associations occur in ascending order i a red beds microbialite association deposited in low energy hypersaline supratidal conditions where microbialites consist of microbial mats and poorly preserved microbially induced sedimentary structure ii a smithian microbialite association formed in moderate to high energy tidal conditions where microbialites include stromatolites and associated carbonate grains oncoids ooids and peloids and iii a spathian microbialite association developed in low energy offshore conditions that is preserved as multiple decimetre thick isolated domes and coalescent domes data indicate that the morphologies of the three microbialite associations are controlled primarily by accommodation hydrodynamics bathymetry and grain supply this study suggests that microbial constructions are controlled by changes between trapping and binding versus precipitation processes in variable hydrodynamic conditions due to the presence of numerous metazoans associated with microbialites throughout the smithian increase in accommodation and spathian decrease in accommodation the commonly assumed anachronistic character of the early triassic microbialites and the traditional view of prolonged deleterious conditions during the early triassic time interval is questioned

sources and accumulation of sediment and particulate organic carbon in a subarctic fjard estuary 210pb 137cs and δ13c records from lake melville labrador the sources and distribution of sediment and particulate organic carbon oc to lake melville labrador were characterized to better understand impacts from climate and hydrological changes to the system mass accumulation rates mars across the lake melville system lms were established from 15 sediment cores collected in 2013 and 2014 by fitting excess 210pb 210pbex profiles to a two layer advection diffusion model mars validated using 137cs varied between 0 04 and 0 41 g cm 2 a 1 and overall decreased with increasing distance from the churchill river which drains into goose bay a western extension of lake melville the churchill river is the greatest source of sediment to the system but surprisingly mars were greatest in western lake melville rather than goose bay reflecting the contribution of fine material carried eastward in the churchill river plume and inputs from nearby tributaries a comparison of 137cs and 210pbex inventories to expected atmospheric fallout 1 5 and 23 6 disintegr

late winter early spring sedimentation off the great whale river southeastern hudson bay sediment traps were used to measure particle settling fluxes in serial moorings offshore of great whale river hudson bay both under the late winter sea ice cover and during and after breakup before breakup the settling fluxes ranged between 0 25 and 2 g cm 2 100 a 1 increasing from april to may in response to the progressively larger under ice algal biomass fluxes also increased with depth during and after breakup including the early summer period of peak runoff sedimentation rates increased to values of up to 33 g cm 2 100 a 1 these fluxes agree with the mean sedimentation rate determined from 210 pb activities in the underlying sediments

dynamics of the laurentide ice sheet in hudson bay canada abstract interpretation of sidescan sonar and high resolution sub bottom seismic data from hudson bay has led to the development of a model for final disintegration of the laurentide ice sheet the well preserved geomorphic features observed from the bay floor are similar to subaerially exposed glaciogenic features observed around the perimeter of hudson bay and can be related to the following three paleoenvironments subglacial erosion deposition ice margin deposition and reworking and post glacial reworking and burial subglacial features observed include fluted terrains with superimposed rogen moraines relief attributed to ice surging eskers subglacial channels and dead ice topography de geer moraines and recessional moraine complexes indicate the mechanism and orientation of ice breakup retreat the orientations of these features are locally consistent with regional trends indicating the overall direction of ice sheet flow and retreat during the last phase of the laurentide ice sheet subglacial channel complexes incised into the till and bedrock and high energy bedforms deposited on the till surface occur in present day water depths down to 160 m due to isostatic depression these could have been as much as 315 m deeper at the time of formation they indicate a wet based glacier with high energy subglacial drainage during the late phases of ice retreat the sidescan sonar data also reveal numerous zones of distinctive morphology attributed to ice breakup and post glacial processes cross cutting relationships allow the determination of the relative ages of these zones from oldest to youngest these zones are interpreted to represent scouring of the bedrock and overburden by the remnants of the ice sheet seafloor scouring by tabular icebergs which moved in a tidally induced arcuate pattern or under the influence of massive glacial lake outflows development of dead ice topography under residual ice masses and random iceberg scouring by smaller icebergs restricted to present day water depths of less than 180 m recently published reconstructions of the collapse of the laurentide ice sheet based on dated quaternary sections on land suggest that the bay was rapidly deglaciated in approximately 400 years the well preserved and distinctive glaciogenic and stratigraphic indicators observed from the bay floor suggest that they were formed by a succession of mechanisms which were too short lived to obliterate the underlying evidence of deglaciation this supports the interpretation of extremely rapid deglaciation of hudson bay and points out that subsequent marine processes have not been sufficient to obliterate the glacial features

sediment and particulate organic carbon budgets of a subarctic estuarine fjard lake melville labrador abstract sediment and particulate organic carbon poc budgets constructed for oceanic regions provide a means to quantify the burial of poc providing a baseline against which future change can be measured here we developed the first mass balance budgets of sediment and poc terrestrial and marine for the lake melville system lms goose bay and lake melville in central labrador using previously published data 210pb based mass accumulation rates river discharge and total suspended solids together with measurements of oc and 13c signatures within dated sediment cores collected from the lms basins and water from main tributaries and groswater bay a two end member mixing model was used to establish fractions of terrigenous and marine poc overall our mass balance budgets show that the churchill river is the major supply of sediment 16 7 7 8 108 kg y 1 and pocterr 18 4 6 6 106 kg y 1 to the lms accounting for 47 and 56 of the total input to the system respectively although the churchill river drains directly into goose bay along with the smaller goose river the majority of sediment 12 9 7 8 108 kg y 1 and pocterr 11 8 7 0 106 kg y 1 is transported eastward through the surface water plume into lake melville inputs of pocmar from autochthonous primary production estimated by applying an empirical relationship between sediment surface flux of pocmar and water depth to goose bay 1 8 106 kg y 1 and lake melville 98 3 4 7 106 kg y 1 increase with increasing distance from the churchill river to investigate the potential changes to the sediment load of the churchill river to the lms following impoundment at muskrat falls we calculated the sediment increase using the median reservoir shoreline erosion potential this approach showed that the delivery of sediment and pocterr to the lms by the churchill river may double during the two years following impoundment of the lower churchill river

faulting mechanisms of the liyang china earthquakes of 1974 and 1979 from regional and teleseismic waveforms evidence of tectonic inversion under a fault bounded basin abstract the liyang earthquakes of 1974 and 1979 were two moderately sized but destructive events in eastern china the first shock m s 5 5 occurred on 22 april 1974 in a densely populated area and the second one m s 5 7 took place on 9 july 1979 near the same location the epicenters were located near the intersection of two faults and inside a late mesozoic to late tertiary sedimentary extensional basin in this article long period p and sh waveforms between 2 and 90 and short period teleseismic p waveforms were used to determine strike slip source mechanisms with large reverse faulting components that occurred for both events these mechanisms are significantly different from earlier determined solutions reached through p wave first motions which found strike slip and normal slip components for the two events the solution of the 1974 event obtained from this study strikes 126 dips 71 and slips 33 the focal depth seismic moment and stress drop are determined to be 12 km 8 4 10 23 dyne cm and 41 bars respectively the mechanism of the 1979 event strikes 41 dips 64 and slips 147 the focal depth seismic moment and stress drop are found to be 7 5 km 1 6 10 24 dyne cm and 152 bars respectively seismic data and local observations suggest that the 1974 event ruptured a wnw striking fault for the 1979 event the fault plane is difficult to resolve the observed oblique reverse faulting is relatively rare for major earthquakes in eastern china and probably represents a reactivated and inverted fault motion beneath a structural basin under the present day e w to ene wsw compressional stress field

the impact of climate change on an emerging coastline affected by discontinuous permafrost manitounuk strait northern quebec a comparative analysis of air photos and a field survey show that permafrost affected sectors of the coastline along manitounuk strait receded at an increasing rate between 1950 and 1995 these sectors are in bays where post glacial tyrrell sea clays outcrop during the same period sand beaches at the mouths of streams and rock and till shorelines on headlands prograded at the pace of isostatic uplift permafrost that had aggraded and formed lithalsas and plateaus during the 19th century i e during the little ice age had expanded over the tidal marsh and had locally provoked accelerated coastal emergence as frost heaving added to post glacial isostatic uplift climate warming during the 20th century particularly during the summer months generated a chain of impacts involving forest growth snow cover ground warming and permafrost degradation waves and tidal currents are mainly responsible for the evacuation and transport of thermokarst produced silts and clays from the shore into the marine basin

palaeoecological significance of lithophaga borings in albian stromatolites se nigeria abstract irregular stromatolitic structures within the mfamosing limestone in the calabar flank se nigeria contain up to five generations of middle to late albian bivalve lithophaga borings at close spacings the stromatolitic bodies occurring at more than one horizon are observable at the quarry type locality and other exposures fringing the precambrian oban massif shells of the boring bivalve often were preserved in their living position evidence of intervening erosion between the bored stromatolitic beds at any horizon is lacking integration of data from the lithophaga borings with that of the stromatolites suggests that the latter formed subtidally and underwent synsedimentary lithification in a shallow

large intraplate earthquakes and static stress changes in the south china coastal region abstract a number of moderate earthquakes occurred in the south china continental edge or coastal area several large earthquakes are sparsely distributed along the seismic belt with the northeast direction between the south china and the continental shelf of the south china sea coulomb stress changes of the 1969 yangjiang main shock ms 6 4 with the following events of the 1986 ml 5 4 the 1987 ml 5 4 and the 2004 ml 5 2 in the yangbian bay area are studied the complex stress patterns of the main shock caused by the dextral pinggang strike slip fault imported on the planes of the normal fault strike slip fault and thrust fault of three events indicate that the distribution of aftershocks mainly located in the areas of positive stress changes and part of aftershocks fall into the stress shadow area due to the reactivity of the local faults the 1969 yangjiang event occurred between the intraplate and the broad plate boundary zone setting when we apply on the empirical relationship between the aftershock durations and the fault loading rate the intersection fault model is proposed and could explain the stress changes of the yangjiang earthquake sequences in south china coastal area the future hazard assessment requires to take account of the stress increase area along the tip of the main shock source fault and off fault stress increase area

atlantic water flow pathways revealed by lead contamination in arctic basin sediments contaminant lead in sediments underlying boundary currents in the arctic ocean provides an image of current organization and stability during the past 50 years the sediment distributions of lead stable lead isotope ratios and lead 210 in the major arctic ocean basins reveal close coupling of the eurasian basin with the north atlantic during the 20th century they indicate that the atlantic water boundary current in the eurasian basin has been a prominent pathway that contaminant lead from the laptev sea supplies surface water in the transpolar drift and that the canadian and eurasian basins have been historically decoupled

distribution and sources of organic matter in surface marine sediments across the north american arctic margin 1 as part of the international polar year research program we conducted a survey of surface marine sediments from box cores along a section extending from the bering sea to davis strait via the canadian archipelago we used bulk elemental and isotopic compositions together with biomarkers and principal components analysis to elucidate the distribution of marine and terrestrial organic matter in different regions of the north american arctic margin marked regional contrasts were observed in organic carbon loadings with the highest values 1m g cm 2 sediment found in sites along barrow canyon and the chukchi and bering shelves all of which were characterized by sediments with low oxygen exposure as inferred from thin layers 2 cm of mn oxihydroxides we found strong regional differences in inorganic carbon concentrations with sites from the canadian archipelago and lancaster sound displaying elevated values 2 7 wt and highly depleted 14 c compositions consistent with inputs from bedrock carbonates organic carbon nitrogen ratios stable carbon isotopes and terrigenous organic biomarkers lignin phenols and cutin acids all indicate marked regional differences in the proportions of marine and terrigenous organic matter present in surface sediments regions such as barrow canyon and the mackenzie river shelf were characterized by the highest contributions of landderived organic matter with compositional characteristics that suggested distinct sources and provenance in contrast sediments from the canadian archipelago and davis strait had the smallest contributions of terrigenous organic matter and the lowest organic carbon loadings indicative of a high degree of post depositional oxidation

hudson bay river sediments and regional glaciation iii implications of mineralogical studies for wisconsinan and earlier ice flow patterns mineralogical studies of river sediments from the hudson bay and james bay lowlands suggest that the glacial erosion of pre devonian paleozoic carbonate rocks played an important role in the production of calcite enriched debris in the cape henrietta maria watershed ice flowing southwesterly across devonian basins in western hudson bay and the james bay lowlands would largely bypass the intervening cape area enrichment of iron in river sands of the cape watershed is attributed to proterozoic ferruginous sources now largely submerged under the waters of eastern hudson bay distributional patterns of carbonates and iron indicate that the dominant flow of ice from eastern hudson bay was southwesterly toward cape henrietta maria without major flow from the area of proterozoic bedrock into the nelson river watershed in the cape area iron enrichment due to proterozoic sources significantly overshadows possible contributions from siderite bearing devonian bedrock the fluvial sediment data are consistent with

high energy coralgal stromatolite frameworks from holocene reefs tahiti french polynesia drill cores from holocene reefs on tahiti french polynesia reveal a framework composed of massive branching acroporids encrusted by coralline algae associated with sessile vermetid gastropods and arborescent foraminifers laminated micritic crusts form coatings over coral branches or more commonly over related encrusting organisms throughout the cored reef sections these crusts appear as a major structural and volumetric component of the reef framework the microbial nature of these micritic crusts is inferred from their typical organic growth forms and geometry the occurrence of microbial remains and stable isotope measurements the reef communities accumulated at depths less than 5 m below mean sea level in a high energy environment throughout vertical growth from 7140 170 yr bp to the present the nature of the involved benthic communities stable isotope data and high calcification rates of microbially encrusted corals strongly suggest that local environmental conditions have been optimal for reef development for the last 7000 years the causes of the predominance of microbial communities over actual encrusters red algae foraminifers remain problematic and could be related to short term fluctuations in ecological parameters microbial micritic crusts seemingly played a prominent role in protecting the coralgal colonies from bioeroders and grazers and possibly in strengthening the framework due to rapid lithification the record of similar microbial crusts in other quaternary reef tracts suggests that microbial communities may have played a more prominent role in quaternary reefs than presently recognized

phosphorus distribution c n p ratios and δ13coc in arctic temperate and tropical coastal sediments tools for characterizing bulk sedimentary organic matter abstract onshore offshore trends in phosphorus p organic carbon oc and total nitrogen tn concentration p distribution elemental organic c n p ratios and stable carbon isotopic composition of oc 13 c oc of surficial sediments are presented from three river dominated coastal regimes the mackenzie river beaufort shelf in the canadian arctic the mississippi delta and louisiana shelf in the temperate gulf of mexico and the tropical amazon shelf these parameters measured in surficial sediments from the three sites are used to assess changes in the importance of terrestrial and marine organic matter sources to sediments as a function of distance from the locus of riverine discharge trends in elemental ratio data from the arctic transect and a portion of the gulf of mexico transects can be explained in terms of a two end member mixture of terrestrial and marine phytodetritus in the arctic transect covariation of organic c p ratios with 13 c oc is consistent with a two end member mixture of terrestrial and marine organic matter a similar relationship between c p ratios and 13 c oc is not evident in gulf of mexico or amazon shelf sediments at these sites the two end member model fails to explain the data adequately the most striking feature of the onshore offshore trends in elemental oc op and oc tn ratios is the occurrence of low ratios in sediments from deep water stations in the gulf of mexico and all stations on the amazon shelf resulting from p and n enrichments exceeding the redfield ratio for marine plankton three explanations are discussed to account for these low ratios 1 the dominance of refractory op and on compounds in the residuum of degraded organic matter 2 differential sorption of op and n compounds regardless of lability on the surfaces of the fine grained sediments characteristic of these sites and 3 a dominance of bacterial biomass or components derived from bacterial biomass elemental ratios and 13 c oc signatures indicate that differential sorption may be most important in the deep water gulf of mexico sites in contrast elemental ratios and 13 c oc on the amazon shelf are most consistent with a sedimentary organic matter pool dominated by bacterial biomass or derivative substances

a new type of shelf margin deposit rigid microbial sheets and unconsolidated grainstones riddled with meter scale cavities middle cambrian microbial limestone contains a network of unusual predominantly horizontal cavities up to 2 m in length and 0 5 m in height the microbialite experienced rapid syndepositional lithification but adjacent grainstone sediments remained unlithified during deposition this juxtaposition contributed to sediment instability resulting in fracturing and brecciation of the lithified microbialite while unconsolidated grainstones underwent slumping and injection into some cavities remaining space within the cavities was colonized by a series of encrustations thin crusts 2 8 mm of laminated algal mats followed by several generations of calcified renalcis like cyanobacteria up to 45 mm thick remaining void space was partially filled by internal sediment and then sequentially occluded by banded radiaxial fibrous calcite herringbone calcite and finally saddle dolomite cements the radiaxial and herringbone calcite cements precipitated from porewaters derived from seawater that became anoxic through the breakdown of organic matter in the microbialite noteworthy is the presence of herringbone calcite cement not as a seafloor precipitate but as an early cavity fill we propose that the unusual bedding parallel fractures were caused by gravity collapse along a shallow platform margin coeval foreslope sediments show syndepositional slumping faulting and mass flow deposits these redeposited sediments contain boulders of microbialite and grainstone of platform margin provenance 1999 elsevier science b v all rights reserved

towards a sediment and organic carbon budget for hudson bay abstract a preliminary sediment and organic carbon budget is constructed for the hudson bay marine system based on published literature and new data collected from nine rivers and 13 sediment boxcores the budget considers the main inputs of terrestrial and marine components of sediment and organic carbon and the main sinks sediment burial and losses oxidation export to hudson strait sedimentation rates 0 032 0 23 g cm 2 yr 1 were estimated from 210 pb profiles and a sediment advection diffusion model in our cores and in two cores collected previously by lockhart et al lockhart w l et al 1998 fluxes of mercury to lake sediments in central and northern canada inferred from dated sediment cores biogeochemistry 40 163 173 sedimentation rates implied by the 210 pb profiles were verified against profiles of 137 cs and for some of the cores contaminant pb the sediment sink in hudson bay was estimated at 138 64 10 6 t a 1 by applying the average sedimentation rate to the area of active sedimentation in the bay 15 of the seafloor calculated according to a regional sedimentation map developed from seismic data josenhans h w et al 1988 preliminary seismostratigraphic and geomorphic interpretations of the quaternary sediments of hudson bay natural resources canada the known sediment sources to hudson bay include river input 11 6 6 10 6 t a 1 subaerial coastal erosion 8 4 10 6 t a 1 marine primary production 24 2 17 10 6 t a 1 and atmospheric deposition 0 5 10 6 t a 1 based on the available data the modern sediment input 44 3 18 10 6 t a 1 represents only about one third of the apparent sediment sink in hudson bay resuspension and lateral transport of shallow water deposits primarily glacigenic and winnowing from topographic highs likely consequences of the exceptional continuous relative sea level rsl fall in hudson bay provides a plausible source for the 116 10 6 t a 1 imbalance using organic carbon and 13 c values in the cores we estimate the burial of particulate organic carbon poc in sediments at 1 3 0 6 10 6 t c a 1 of which 80 is marine the importance of reworked glaciomarine carbon to the burial flux is difficult to estimate because modern autochthonous primary production provides a large source of poc to the system 16 1 7 10 6 t c a 1 and its degradation is not well constrained the 0 58 10 6 t c a 1 terrestrial carbon estimated to be transported as part of the redistributed sediment load accounts for almost one half the total terrigenous poc inputs to the bay if sediment and oc supply and burial in the hudson bay system are presently responding to the history of isostatic rebound as proposed here the task of predicting and measuring the additional consequences of river diversions and climate change e g sea ice permafrost runoff is rendered considerably more difficult

seismological constraints on the collision belt between the north and south china blocks in the yellow sea abstract the korean peninsula eastern china and the yellow sea comprise the eastern eurasian plate and are believed to share considerable tectonic evolution history the tectonic structures in the yellow sea are poorly understood raising difficulty in reconstruction of tectonic evolution history in the eastern eurasian plate the tectonic structures in the yellow sea are constrained by seismicity and fault plane solutions of earthquakes the fault plane solutions are determined by waveform inversions and seismic phase polarity analyses the ambient stress fields are deduced from the fault plane solutions the primary stress field around the yellow sea is composed of ene wsw directional compression and nnw sse directional tension normal faulting earthquakes with ene wsw directional strikes are observed in the central yellow sea between the shandong peninsula and the central korean peninsula the normal faulting region is interpreted to be a northern margin of collision belt between the north and south china blocks the normal faulting system suggests post collisional lithospheric delamination causing reverse activation of paleo thrustal faults that were developed by the collision between the north and south china blocks in the early jurassic period

peloidal fabrics in upper jurassic reefal limestones weald basin southern england abstract coraliferous limestones from the corallian group upper jurassic of subsurface of the weald basin southern england record the localized development of superimposed patch reefs and banks the reefal limestones exhibit a variety of peloidal fabrics in particular well sorted peloids 10 60 m in diameter with a well developed euhedral rim of fibrous sparry calcite around a micritic anhedral nucleus they occur in confined intraskeletal pores corals molluscs and borings growth cavities between framebuilders and as stromatolitic crusts the peloids in interskeletal cavities and as crusts resemble microbial precipitates and merge into spongiostromate fabrics the distribution of these peloidal fabrics seems to be facies related and is best developed in zones which had relatively low framework growth rates low sedimentation rates and moderate energy levels the peloids are identical in form and occurrence to those in some ancient and quaternary reefs the association of the peloids with stromatolitic coatings and spongiostromate fabrics leads us to interpret the peloids as microbial precipitates either by direct precipitation or by induction the abundance of microbial carbonate in these reefal limestones places them in an intermediate category between frame built reefs and microbial mud mounds

nature and environmental significance of microbialites in quaternary reefs the tahiti paradox drill cores from the bamer reef edge of tahiti exhibit 85 93 m thick coralgal sequences recording at least 13 500 years of continuous reef growth in optimal environmental conditions the cored reef sequences form an overall shallowingupward succession with assemblages of branching or massive colonies of porires at the base overlain by a robust branching community acropom gr dmmi robirstn heavily encrusted by coralline algae sessile vermetid gastropods and arborescent foraminifers which grew at depths less than 6 m microbialites generally form the last stage of encrustation of coral colonies or more commonly of related encrusting organisms thus appearing as a major structural component of the reef sequence where they may locally form 809 of the rock by volume they developed in an open cavity system of the reef framework with freely circulating normal marine water microbialites include laminated crusts and clotted micritic masses commonly associated in compound crusts probably feflecting differences in the composition of the involved biological communities and in biomineralization processes that controlled the accretion of the crusts the isotopic composition of the microbialites 2 05 to 3 92 i they underwent also indivitlual processes of biominrlali2ation besicles the overall decrease in lizht and enqy conditions rttlecting progressive burial by conil growth the widespread development of microbialites within the reef framework may be related to increased alkalinity and niitrient availability in interstitial waters due to temstrial groundwwr seepage and puiodic runoffs the tlevelopment of micrubialites in the cryptic niches of the reef framework ceased about 6000 years

source parameters of the anjar earthquake of july 21 1956 india and its seismotectonic implications for the kutch rift basin abstract the kutch rift basin is a major seismic region in india characterized by a low earthquake occurrence rate but a very high maximum intensity the largest event in the region is the great kutch earthquake of 1819 estimated m w 7 8 however lacking instrumental data its exact source parameters are not well known the anjar or rann of kutch earthquake of july 21 1956 m w 6 0 took place very close to the 1819 kutch event and caused considerable damage and casualties our modeled waveforms of teleseismic p and sh waves and p wave first motions determine a reverse faulting mechanism strike 235 dip 46 5 and rake 85 as well as source parameters for the anjar earthquake a previous strike slip mechanism for this event has been eliminated on the basis of waveform constraints the two nodal planes of our solution both strike northeast sub parallel to the trend of the kutch rift very close to the trend of the isoseismals the seismic moment is 1 19 10 25 dyne cm the focal depth and the stress drop are 15 km and 162 bar respectively the anjar reverse fault may represent a reactivated normal fault undergoing tectonic inversion in the kutch rift zone under present day compressional stress two larger earthquakes adjacent to anjar but outside of the kutch rift are also found to be mainly reverse faulting with a minor strike slip component judging from available information the great kutch event of 1819 is most likely a reverse faulting event

effect of oxygen on degradation rate of refractory and labile organic matter in continental margin sediments in order to study the effect of oxygen on degradation rate of bulk sedimentary organic matter we developed a new incubation method in contrast to most previous experiments 1 all of the sediment undergoing decomposition was maintained under oxygenated or oxygen free conditions and 2 organic matter of varying lability was studied the production of co2 during incubations of sediment in glass test tubes corrected for dissolution precipitation of calcium carbonates was used as a measure of degradation rates the laboratory experiments using surficial and buried continental shelf and slope sediment from the open skagerrak northeastern north sea demonstrated that the effect of oxygen on the degradation rate of sedimentary organic matter is a function of the lability of the decomposing material fresh material was degraded with little difference in rates in the presence or absence of oxygen whereas old material was decomposed significantly up to 3 6 times faster with oxygen than without oxygen an implication of these findings is that bioturbation by exposing old buried material to oxygen may enhance integrated organic carbon oxidation in marine sediments this constitutes a previously unexplored mechanism by which faunal reworking may stimulate carbon degradation the anoxic decomposition rates of organic material buried at 20 cm depth in sediment were the lowest measured we found however that the extent of oxidation of this buried old sediment was considerably larger than that of surficial sediment under oxygenated conditions which indicated that the oxic anoxic oxic redox transitions deposition under oxic conditions burial under anoxia and reexposure to oxygen promoted degradation our results therefore also suggest that the extent of long term decomposition of sedimentary organic material is smaller under oxygenated or anoxic conditions alone than when the material is exposed to the repeated activities of both oxic and anoxic microorganisms

alkane terpene and polycyclic aromatic hydrocarbon geochemistry of the mackenzie river and mackenzie shelf riverine contributions to beaufort sea coastal sediment abstract to study the largest source of river sediment to the arctic ocean we have collected suspended particulates from the mackenzie river in all seasons and sediments from the mackenzie shelf between the river mouth and the shelf edge these samples have been analyzed for alkanes triterpenes and polycyclic aromatic hydrocarbons pahs we found that naturally occurring hydrocarbons predominate in the river and on the shelf these hydrocarbons include biogenic alkanes and triterpenes with a higher plant peat origin diagenetic pahs from peat and plant detritus petrogenic alkanes triterpenes and pahs from oil seeps and or bitumens and combustion pahs that are likely relict in peat deposits because these components vary independently the season is found to strongly influence the concentration and composition of hydrocarbons in the mackenzie river while essentially the same pattern of alkanes diagenetic hopanes and alkyl pahs is observed in all river and most shelf sediment samples alkane and triterpene concentration variations are strongly linked to the relative amount of higher plant peat material polycyclic aromatic hydrocarbon molecular mass profiles also appear to be tied primarily to varying proportions of peat with an additional petrogenic component which is most likely associated with lithic material mobilized by the mackenzie river at freshet consistent with the general lack of alkyl pahs in peat the higher pahs found in the river are probably derived from forest and tundra fires a few anthropogenic pyrogenic compounds are manifest only at the shelf edge probably due to a weakening of the river influence we take this observation of pyrogenic pahs and the pronounced source differences between two sediment samples collected at the shelf edge as evidence of a transition from dominance by the mackenzie river to the geochemistry prevalent in arctic regions far removed from major rivers

broadband time domain modeling of earthquakes from friuli italy short period sp and long period lp seismograms written by the main shock and two principal aftershocks of the 1976 friuli italy earthquake sequence are modeled in the time domain using synthetic seismograms the main shock occurred on 6 may 1976 20h 00m m s 6 5 and both aftershocks on 15 september 1976 03h 15m m s 6 0 and 09h 21m m s 5 9 source models were determined initially by trial and error and then refined using a waveform inversion program two point sources of radiation are required to adequately model the aftershock short period records for the 09h 21m aftershock the model derived from short period records also produces good fits to the long period data the seismic moment of this earthquake is found to be 0 8 to 1 0 10 25 dyne cm the sp model for the 03h 15m aftershock on the other hand predicts long period synthetics which do not agree with the observations in particular the sp moment 0 37 10 25 dyne cm is about formula times smaller than the lp moment 1 10 25 dyne cm adding a long period component to the sp model considerably improves lp waveform and moment agreement in the case of the main shock a reasonable fit to the observed sp data is obtained using three point sources of radiation however lp synthetics computed using this model do not agree with the observations and the sp moment 0 65 10 25 dyne cm is a small fraction of the lp moment 3 to 5 10 25 dyne cm time function durations indicate that the individual events inferred from the sp records are radiated from patches of the fault having radii of 2 to 4 km and stress drops in the range 35 to 276 bars in comparison stress drops estimated from lp data are found to be 12 bars main shock and 24 bars 09h 21m aftershock these observations suggest that the short period instruments are sensitive to the high frequency radiation emitted from small high stress drop areas on the fault plane whereas the long period instruments record the overall motion during the earthquake

recent sedimentation and organic carbon burial in a shelf sea the north sea to obtain a carbon budget of the north sea recent sedimentation rates and organic carbon and nitrogen concentrations were determined on 27 box cores from the shallow north sea with a water depth 200 m and a surface area of 500 103 km2 the sedimentation rates in these box cores range from 5 to 35 cm 100 year 1 corg concentrations are 0 05 1 based on these numbers and published data the total amount of corg buried in the shallow north sea is calculated as 1 105 tons year 1 in large parts of the shallow north sea recent sedimentation is nearly absent reworking of relict deposits and partial mixing of these deposits with small amounts of recent fine grained sediments by biological and physical processes and human activities beam trawl fishery result in apparent sedimentation rates which are likely to exceed the real net sedimentation rates considerably the results of this study suggest that the majority of the organic matter is exported from the shelf over the shelf edge into the norwegian sea and into inner shelf deeps skagerrak and norwegian channel coarse grained shelf sediments are only of minor significance for the preservation of organic matter

a contemporary sediment and organic carbon budget for the kara sea shelf siberia it has recently been realized that the arctic undergoes drastic changes probably resulting from global change induced processes this acts on the cycling of matter and on biogenic elements in the arctic ocean having feedback mechanisms with the global climate for example by interacting with atmospheric trace gas concentration a contemporary budget for biogenic elements as well as suspended matter for the arctic ocean as a baseline for comparison with effects of further global change is thus needed available budgets are based on the late holocene sedimentary record and are therefore quiet different from the present which has already been affected by the intense anthropogenic activity of the last centuries we calculated a contemporary suspended matter and organic carbon budget for the kara sea utilizing the numerous available data from the recent literature as well as our own data from russian german sirro siberian river run off expeditions for calculation of the budgets we used a multi box model to simplify the kara sea shelf and estuary system input was assumed to comprise riverine and eolian input as well as coastal erosion output was assumed to consist of sedimentation and export to the arctic ocean exchange with the adjacent seas was considered in our budget and primary production as well as recycling of organic material was taken into account according to our calculations about 18 510 6 ty r 1 of sediments and 0 3710 6 t yr 1 of organic carbon are buried in the estuaries whereas 20 910 6 ty r 1 sediment and 0 3110 6 ty r 1 organic carbon are buried on the shelf most sources and sinks of our organic carbon budget of the kara sea are in the same order of magnitude making it a region very sensitive to further changes d 2005 elsevier b v all rights reserved

calcium carbonate cementation of sand a method for producing artificially cemented samples for geotechnical testing and a comparison with natural cementation processes abstract the experience of dutch dredging companies is that cemented layers in holocene calcareous sands are much more frequent than expected in an effort to alleviate this problem a method for producing slightly calcium carbonate cemented sand is presented these samples being used to better constrain the geotechnical parameters of slightly cemented carbonate sands when assessing dredging conditions the most important environments where early marine cementation mainly by high magnesian calcite and aragonite occur are intertidal beaches and tidal flats subtidal sandflats and reefs each environment has its typical occurrence and dimension of cemented layers and a characteristic form and distribution of cementing materials within the sandstone it is therefore expected that sandstones from each environment will have a distinct set of geotechnical properties important factors controlling calcium carbonate cementation are the chemistry of the seawater the source of the cementing material the physical conditions in terms of hydraulic energy sedimentary parameters such as permeability texture and composition of the sand and an initially stabilizer of the loose sediment all these factors and the way in which they relate to each other explain large variability in marine cement forms and the variability of the geotechnical properties of the cemented calcareous sediments the factors controlling early cementation in the shallow marine environment are discussed in order to evaluate the boundary conditions for a laboratory model used to produce artificially cemented and by simulating natural subtidal cementation processes the resulting cemented sands are shown to be comparable with natural sandstones and to exhibit similar behaviour during strain tests for the purposes of assessing dredging conditions these artificial samples have advantages over natural samples

source modeling of the hsingtai china earthquakes of march 1966 abstract the hsingtai china earthquakes of march 1966 were a series of destructive earthquakes associated with the shu lu graben five strong shocks of ms 6 occurred within a period of less than a month the largest of which was ms 7 2 body and surface waves over the period range from several to 100 s have been modeled for the four largest events using synthetic seismograms in the time domain and spectral analysis in the frequency domain data from ground deformation local geology regional seismic network and teleseismic joint epicenter determination have also been used to constrain the source model and the rupture process the fault mechanism of the hsingtai sequence was mainly strike slip with a small component of normal dip slip the strikes of the four largest shocks range from n26 to 30 e approximately along strike of the major faults of the shu lu graben and the aftershock distribution the source mechanisms can be explained with a nnw sse extensional stress and a nee sww compressional stress acting in the area the major shocks all had focal depths 10 km the four largest shocks in the sequence were characterized by a relatively simple and smooth dislocation time history the durations of the far field source time functions ranged from 3 5 to 5 s while the rise times were all 1 s the seismic moments of the four largest earthquakes ranged from 1 43 1025 to 1 51 1026 dyne cm 1 the fault sizes of the four events were very close assuming circular faults the diameters of the four events were determined to be between 10 and 14 km stress drops varied from 52 to 194 bars a trend of increasing stress drop with earthquake size was observed a survey of stress drop determinations for 15 major intraplate earthquakes shows that on the average the magnitude of stress drop of oceanic intraplate earthquakes and passive continental margin events is higher 200 to several hundred bars than that of continental intraplate earthquakes 100 bars or less

la limite holocene pleistocene dans le recif frangeant ricaudy nouvelle caledonie geochronologie facies et diagenese implications eustatiques et neotectoniques abstract the holocene pleistocene unconformity is identified from radiocarbon dating of coral samples taken from drill holes through the ricaudy fringing reef at noumea new caledonia analysis of facies and diagenetic features permit the reconstruction of the recent reef history and allow the recognition of an unconformity between holocene and pleistocene coral limestones the holocene pleistocene boundary appears at different depths in the fringing reef about 3 m near the shoreline and 5 to 6 m near the seaward reef edge this unconformity is related to emergence and subaerial exposure of a pleistocene reef which has retained freshwater diagenetic features and an overlying paleosol the overlying holocene coral reef complex formed during the following transgression radiocarbon dating of the holocene reef samples indicates that reef growth reached rates of 5 mm yr two ages of 5690 90 yrs b p and 4910 420 yrs b p are found at low tide level this indicates the age at which the reef reached sea level two hypotheses can be proposed to explain the cessation of reef growth in the ricaudy fringing reef at 5500 yrs b p 1 active uplift coeval with holocene transgression and 2 high sea level in the holocene the occurrence of a high stand in the sea level at 5400 yrs b p is the most probable ample evidence is found in some places on new caledonia

fringing reef growth over a shallow last interglacial reef foundation at a mid shelf high island holbourne island central great barrier reef fringing reefs are rare on the mid shelf of the central great barrier reef with holocene development histories established for a few examples the paucity of reef growth records from mid shelf fringing reefs has limited opportunities for comparisons with inshore fringing reef growth records to better understand the influence of changes in environmental conditions on reef growth with distance offshore the long term development of the mid shelf fringing reef at holbourne island was reconstructed using nine percussion and drill cores that captured the entire holocene period of reef growth the cores were chronologically constrained by 16 high precision th 230 ages a weathered pleistocene reef substrate was u th dated as last interglacial open system age of 131 100 1000 cal ybp and this provides the underlying foundation upon which the holocene reef initiated prior to similar to 7520 20 cal ybp the last interglacial reef was encountered 5 9 m below the present reef surface and is the shallowest confirmed last interglacial reef in the central gbr region to date most of the holocene reef structure was emplaced within 1000 years of initiation the chronostratigraphy and contemporary geomorphology of the fringing reef at holboume island preserve evidence of re working and stripping of the reef structure by cyclones this evidence includes 1 an age hiatus in core data of similar to 3500 years 6238 18 to 2683 10 cal ybp 2 the abundance of detrital branching coral rubble material within the core facies 3 the surface elevations and ages of fossil microatolls which reveal that storm induced ponding of water during low tidal stages up to 55 cm deep has been active but intermittent across the reef flat for at least 600 years and is still active today and 4 long standing shingle ridges onshore and modern shingle ridges on the reef flat

the effect of bioturbation and adsorption gradients on solid and dissolved radium profiles in sediments from the eastern equatorial pacific abstract remobilization of mn resulting from the diagenetic oxidation of organic carbon causes steep adsorption gradients within hemipelagic sediments of the eastern equatorial pacific transport of ra along these gradients is capable of maintaining marked 226ra 230th disequilibrium in the surface sediments pore water and solid phase 226ra profiles measured in cores from two sites in this area are modeled by adjusting the ra adsorption coefficient as a function of the depth varying mn content at manop site m the high organic carbon accumulation rate causes a sharp redox gradient within the upper 10 cm of sediment biological mixing is constant and rapid 500 cm2 kyr in this upper layer below which the mn content the ra adsorption coefficient and the 226 ra 230 th ratio are all sharply reduced at manop site h the organic carbon accumulation rate is less and therefore the redox gradient is expanded over a greater depth scale in the surface sediment biological mixing is slower decreases with depth and gradients in the adsorption coefficients and 226 ra 230 th ratio are less marked than at site m

hauterivian shallow marine calcareous biogenic mounds s e spain abstract hauterivian biogenic deposits from the prebetic northern margin near caudete albacete province southeastern spain are represented by low domed bodies less than 10 m thick surrounded by bioclastic sediments and capped by siliciclastics they consist of a coral stromatoporoid and microbial framework with cavities filled by mud rapidly lithified intermound bioclastics derived from the mound organic community reflect high energy conditions and shallow water settings mound growth and architecture were controlled by nutrient fluxes and internal light gradients comparisons with closely related structures from the palaeozoic and the recent show some similarities but also significant differences the example documented here also departs from other cretaceous occurrences

origin of meter scale submarine cavities and herringbone calcite cement in a cambrian microbial reef ledger formation u s a abstract meter scale submarine cavities in middle cambrian shelf margin microbial reef strata indicate large scale dewatering processes in conjunction with substrate instability related to interreef channeling and shelf edge downslope creep and slip syndepositional cement precipitation within the cavities preserved delicate microbial fabrics and stabilized the reef system radiaxial fibrous calcite and herringbone calcite cements line the cavity interiors isopachously the two phases cannot be discriminated on the basis of fe mn or sr contents but do have different isotopic signatures slightly more negative 13c values in herringbone calcite suggest that abrupt transitions between radiaxial fibrous and herringbone calcite cement are the result of rapid and repeated changes in pore fluid oxygen levels storm driven pore water circulation renewed oxygenated seawater flow into the cavities resulting in precipitation of radiaxial fibrous calcite a threshold level of oxygen reduction resulted in the change to herringbone calcite precipitation the pore fluids associated with herringbone calcite did not have elevated mn or fe concentrations as suggested in previous studies herringbone calcite appears to be more susceptible to diagenetic alteration than radiaxial fibrous cement however as indicated by greater resetting of oxygen isotope values

a general model of paraglacial landscape response a unifying attribute of all forms of paraglacial response is that deglaciation results in the exposure of unstable or metastable sediment sources that are subsequently tapped by a wide variety of processes over a wide range of timescales the paraglacial period in different geomorphological contexts is therefore con ditioned by two variables glacially conditioned sediment release and rate of sediment reworking under steady state conditions the latter may be approximated by an exhaustion model in which sediment yield is related to the amount of remaining available sediment by a negative exponential function this model offers an approximation for the behaviour of primary paraglacial systems in which glacigenic sediment sources are not replenished the long term behaviour of secondary primarily uvial paraglacial systems in which sediment inputs include both in situ and reworked glacigenic sediment appears intrinsically more complex but consistent with an exhaustion model if initial sediment avai

body wave waveform constraints on the source parameters of the yangjiang china earthquake of july 25 1969 a devastating earthquake in a stable continental region on july 25 1969 anm s 5 9 earthquake shook the kwangtung province near yangjiang china casualties and extensive damage were reported in the epicentral area the yangjiang earthquake occurred within the passive margin located along china s southeast coast this stable continental setting is seismically one of the most quiet regions of china historic records indicate this earthquake to have been the first devastating one in the area a remarkable feature of this earthquake sequence is that its foreshocks and aftershocks are relatively small in terms of number and magnitude despite the relatively large main shock waveforms of long and short period teleseismicp and long period teleseismicsh waves have been modeled to estimate the source parameters for this earthquake the focal mechanism determined is predominately strike slip with a small normal component strike 263 dip 79 rake 194 and is in good agreement with observations in the epicentral area regarding dislocation direction of fissures distribution of aftershocks and isoseismals the average seismic moment is 5 15 1024 dyne cm and the focal depth is estimated to be 9 km the earthquake is characterized by a rather short source time function and a high stress drop of approximately 380 bars the observed pattern of the foreshock main shock aftershock sequence is interpreted in terms of the large stress drop associated with the main shock and the material properties at and near the source thep axis orientation lies roughly nw se and is consistent with the maximum compressive stress observed along the coast of southeast china this stress orientation is consistent with the nw subducting philippine sea plate and the se ward push from central china due to the convergence between indian and eurasian subcontinents

modeling of the koyna india aftershock of 12 december 1967 short period teleseismic and near regional long period waveforms from a large aftershock mb 5 3 origin time 06 18 36 8 utc of the 10 december 1967 koyna main event were modeled to determine source depth and focal mechanism identification of pp and sp on the short period waveforms yielded a well constrained source depth of 3 5 to 4 0 km the focal mechanism was determined using a systematic trial and error grid testing technique in which seven p first motions two sh first motions two teleseismic pp p ratios one teleseismic sp p ratio and one regional sh p ratio were included this heterogeneous but sparse data set yielded a constrained normal fault mechanism at 100 20 strike 40 10 dip and 240 20 rake rupture directivity is inferred from consistently high surface reflection direct wave amplitude ratios a circular fault of 1 km radius with a rupture initiation point at the lower edge and an assumed rupture velocity of 0 9 vs explains the anomalously high amplitude ratios and yields a seismic moment of 3 8 1023 dyne cm the shallow source depth is similar to that found for the main event 4 5 km and the 13 september foreshocks 5 km in previous modeling studies and is consistent with the premise that the koyna earthquakes were triggered by the impoundment of the koyna reservoir however the normal fault mechanism differs substantially from the previous events which were left lateral strike slip faults trending nne the differing aftershock mechanism is probably due to the reactivation of old faults in the koyna area caused by stress readjustment after the koyna main event

internal precipitation of microcrystalline carbonate a fundamental problem for sedimentologists abstract recent studies of submarine lithification have shown that microcrystalline carbonate or carbonate mud traditionally thought to represent ooze deposited in quiet water commonly forms as an internal precipitate below the sediment water interface this internally precipitated micrite alters the mud grain ratio of pre existing sedimentary deposits and invalidates classifications that relate the amount of micrite matrix in limestones to the degree of water energy associated with the environment of deposition

the great barrier reef a 700 000 year diagenetic history a deep borehole through ribbon reef 5 in the great barrier reef off north eastern australia has identified a variety of cements including epitaxial radial prismatic and spherular aragonite together with blocky prismatic and fibrous calcite these cements are discontinuously arranged within the sequence that consists predominantly of grainstones but locally includes clotted muddy and filamentous textures that may be of microbial origin calcite cements vary in morphology with groups of crystals that include acute scalenohedral rhombohedral and flattened concordant terminations these show varying densities of inclusions that locally define growth zones and in some terminations divide in the manner of split crystals to form fibrous fringes morphological changes in calcite are inferred to reflect changes in water chemistry and crystal growth rates at the time of growth allied to their relationship to the palaeo water table and linked in turn to changes in sea level neomorphism and dissolution are widespread and variations in the severity of both imply response to the degree of undersaturation of pore waters that at times were probably balanced within very narrow limits a total of 10 depositional units are identified those units at the base of the borehole reflect deposition and diagenesis within a marine environment the influence of meteoric waters indicated by stable isotopes is first apparent at the top of unit 1 and in unit 2 184 to 155 m below sea floor petrographic evidence of vadose conditions appears at the tops of unit 3 131 to 99 m below sea floor units 4 to 8 all deposited under marine conditions provide isotopic evidence of meteoric or mixing zone waters and petrographic indicators of vadose conditions typically at the top of the units evidence indicates that in unit 5 the water table was mobile and units 6a 6b 7 and 8 all characterized by ultraviolet fluorescent cements are capped by sub aerial erosion surfaces unit 9 the holocene reflects the recent re establishment of marine conditions the extent of alteration of the entire sequence reflects the substantial and pervasive influence of meteoric waters this effect is interpreted as a result of a greater rainfall and river flow from the mainland during early and late stages of interstadial periods the study reflects progress in the ability to recognize the diagenetic signal generated by sea level change however whereas the isotopic results reflect the changing relationships between vadose and phreatic zones in groundwater systems beneath successive emergent surfaces their correspondence with petrographic features is expressed only weakly and commonly lacks the systematic sequential overprinting implied by the distribution of cathodoluminescent zones of cements in many ancient limestones

paleoenvironmental reconstruction of a downslope accretion history from coralgal coralline sponge rubble to mud mound deposits eocene ainsa basin spain abstract in the lutetian intraslope ainsa sub basin small sub spherical carbonate mud mounds occur associated with hemipelagic marls and mixed gravity flow deposits the studied mud mounds consist of a mixture of allochthonous parautochthonous and autochthonous components that show evidences of reworking bioerosion and accretion by different fossil assemblages at different growth stages the crusts of microbial lithistid sponges played an important role stabilizing the rubble of coralgal coralline sponges and formed low relief small benthic patches in a dominant marly soft slope environment these accidental hard substrates turned into suitable initiation nucleation sites for automicrite production dense and peloidal automicrites on which the small mud mounds dominated by opportunistic epi and infaunal heterozoan assemblages grew a detailed microfacies mapping and paleoenvironmental analysis reveals a multi episodic downslope accretion history starred by demosponges coralline and lithistid sponges agariciid corals calcareous red algae putative microbial benthic communities and diverse sclerobionts from the upper slope to the middle slope the analyzed mud mound microfacies are compared with similar fossil assemblages and growth fabrics described in many fossil mud mounds and with recent deep water fore reefs and cave environments

reef talus a popular misconception reef fronts have traditionally been regarded as comprising debris derived by contemporaneous erosion of the reef however evidence from wave transport indicates that on present day reefs the bulk of the debris generated in this way accumulates in the back reef area with only finer grained sediment carried off reef by retreating flows or by overwash nevertheless in contrast to this observation fore reef debris slopes are commonly considered characteristic of phanerozoic reefs this apparent error reflects the conflation of processes defining contemporary growth and accretion of the reef and the corresponding long term accretion of the carbonate platform on which it rests present day reefs are commonly although not exclusively additions to long lived carbonate platforms growth of the latter is intermittent and has been moderated by changes in sea level that for recent reefs have been on time scales of less than 100 ka during low sea level stands growth ceases or is translated downslope and earlier deposits are subject to lithification and subaerial erosion similar changes are applied on a larger scale to the aggrading growth of carbonate platforms but the bulk accretion of these includes quite different processes and reflects far longer timescales during low sea level stands the margins of platforms commonly become unstable with instability reflected in slope failure and in the shedding of blocks ranging from metres to kilometres in diameter associated with the generation of debris flows and turbidites it is argued that these are the materials that are commonly described as reef talus in ancient structures although their formation is largely independent of any contemporary reef growth difficulties arise where the reef and the platform are treated as a single functional entity it is important to recognize the conceptual distinction between them reef talus is a misleading description of the debris predominantly generated by platform erosion and slope failure