deposit from a giant wave on the island of lanai hawaii limestone bearing gravel the newly named hulopoe gravel blankets the coastal slopes on lanai the deposit which reaches a maximum altitude of 326 meters formerly was believed to have been deposited along several different ancient marine strandlines but dated submerged coral reefs and tide gauge measurements indicate that the southeastern hawaiian islands sink so fast that former worldwide high stands of the sea now lie beneath local sea level evidence indicates that the hulopoe gravel and similar deposits on nearby islands were deposited during the pleistocene by a giant wave generated by a submarine landslide on a sea scarp south of lanai

precambrian ophiolites cambrian island arc and variscan suture in the south carpathian balkan region a late proterozoic ophiolite in the south carpathian balkan region has a total surface outcrop area of 400 km 2 it is a complete ophiolitic section that includes mid ocean ridge basalts indicating that it was formed in a large ocean the oceanic crust is unconformably overlain by an ensimatic island arc of cambrian age the ophiolite island arc assemblage was obducted over the moesian platform during early ordovician time both sequences are now incorporated in a continental block as a result of intracontinental convergence which took place in variscan time the ophiolite is situated along the thracian suture which divides the moesian platform and the thracian continental fragment this suture is part of a larger one referred to as the south european suture that is situated between the thracian massif and the adriatic plate to the southwest and the moesian platform bohemian and central french massif to the northeast

review of geochemical variation in lower palaeozoic metabasites from the ne bohemian massif intracratonic rifting and plume ridge interaction

landward fining from multiple sources in a sand sheet deposited by the 1929 grand banks tsunami newfoundland abstract a sandy deposit from the 1929 grand banks tsunami in newfoundland contains sediment from two distinct sources one from an inferred gravel shoreline close to the deposit and one from a sandy dune some 200 m seaward of the deposit the deposit ranges from 0 to 15 cm thick and is composed of a bimodal mix of fine and coarse sand we took approximately 100 core samples of this deposit in an attempt to characterize lateral grain size trends within the sand although the coarse fraction does fine with distance inland the fine fraction does not change size over the study area and the aggregate grain size changes in no systematic way we interpret this deposit to represent the mixture of material picked up at the bar with material picked up at the gravel shoreline the bar material does not fine in part because it is already fairly well sorted but also because it is far from its source the shoreline material on the other hand is poorly sorted so that the tsunami took only those grains it was capable of moving and deposited them near their source we estimated the size of the tsunami by determining the flow depth flow velocity combinations required to advect sand from the bar to the back of the deposit and by estimating the shear velocity required for motion of the largest grain we found during our survey this modeling indicates an average flow depth of about 2 5 2 8 m over the area at a flow velocity of 1 9 2 2 m s this estimate compares well with eyewitness accounts of a maximum flow depth of 7 m at the shoreline if our estimate represents an average over the whole study area

first indication of storegga tsunami deposits from east greenland a 2 73 m long sediment sequence from loon lake located at 18m a s l on outer geographical society o east greenland was investigated for its chronology and changes in physical and biogeochemical properties macrofossils and grain size distribution the predominance of marine fossils throughout the sequence dated by 14c ams to between 8630 and 7535 cal yr bp shows that the loon lake at that time was a marine basin which according to existing sea level curves was about 15 35 m deep the sequence mainly consists of fine grained homogeneous sediments which are interrupted by a 0 72 m thick sandy horizon with erosive basis and distinct fluctuations in the grain size distribution and in the physical and biogeochemical properties according to the radiocarbon dates this sandy horizon was deposited after 8500 8300 cal yr bp and is interpreted as originating from the storegga tsunami the record from loon lake provides the first indication of storegga tsunami deposits from east greenland copyright 2006 john wiley sons ltd

chaotic deposition by a giant wave molokai hawaii a coral basalt breccia conglomerate is exposed 60 m above present sea level and nearly 2 km inland from the present shoreline on the southwest side of east molokai volcano molokai the conglomerate is preserved mantling interfluves between gullies and forms a blanket like deposit 0 5 to 3 m thick no evidence of a wavecut terrace either within the blanket or at its upper or lower limits of exposure can be found no coral was found in growth position unsorted basalt clasts as large as boulder size are subrounded to angular randomly oriented and vary from 2 3 to 50 volume of the deposit the size of the largest basalt and coral fragments shows almost no systematic variation with elevation distance inland or lateral position parallel to the shore two indistinct rock units are present in a few places a lower carbonate rich unit that we interpret as an onwash facies and an upper basalt rich unit an offwash facies the carbonate rich onwash facies is dominated by biogenic debris especially fragments of coral and beach rock and gastropod and bivalve shells the offwash facies contains 40 to 90 basalt cobbles and boulders in a matrix of finely broken biogenic fragments where the distinct facies are lacking the proportion of basalt clasts increases crudely from the lower to the upper part of the conglomerate at a single place and from lower to higher elevation out crops where the deposit overlies a cinder cone several carbonate bearing elastic dikes extend from the conglomerate as much as 10 m down into the basalt cinders this deposit was apparently laid down by a giant wave that broke over an outer reef similar to the present fringing reef and advanced as a turbulent bore over the back reef flat picking up a slurry of carbonate rich debris and depositing it on the slopes inland as the wave advanced the offwash picked up loose basalt debris on its return flow u series dating of coral fragments indicates that the age of this deposit is 240 200 ka indicating the wave is distinct from that which produced a similar deposit on lanai about 100 ka this giant wave was most likely caused by one of the many large submarine landslides that have been identified on the lower slopes of the major hawaiian islands

provenance of upper precambrian lower cambrian shales in the central iberian zone spain evidence from a chemical and isotopic study geochemical and isotopic sr nd o data are presented for upper precambrian and lower cambrian shale sequences from the central iberian zone spain in order to define geochemical discriminants between them and to assess the nature of the source regions supplying these basins elemental data especially th sc ratios coupled with endt values of 2 5 suggest that the upper precambrian rocks contain a greater proportion of a much younger more mafic component than the lower cambrian sequence which has high th sc and endt of 7 3 coherent trends between elemental and o isotope data imply a homogeneous recycled source as the dominant provenance for the upper precambrian shales whereas a lack of such coherence for the lower cambrian sediments suggests a more heterogeneous provenance the sedimentological geochemical and isotopic data are consistent with the upper precambrian succession being derived ultimately from a polycyclic mixture of young pre cadomian mafic sources and older 2 ga crust in contrast the lower cambrian sequence was mainly derived from old more felsic crust which would have contributed increasingly greater proportions of material as the younger sources were progressively removed by erosion

the storegga slide tsunami comparing field observations with numerical simulations abstract deposits from the storegga tsunami have been found in coastal areas around the norwegian sea and north sea from the northeast coast of england to beyond the arctic circle in northern norway the tsunami deposits reach onshore elevations of 10 12 m above sea level of their time in western norway 3 6 m in northeast scotland and above 20 m on the shetland islands these elevations are compared with surface wave elevations derived from a numerical simulation of the storegga slide a good agreement is obtained for a retrogressive slide that descends at 25 30 m s and that has short time lags of 15 20 s between each individual slide block

impact ejecta at the paleocene eocene boundary extraterrestrial impacts have left a substantial imprint on the climate and evolutionary history of earth a rapid carbon cycle perturbation and global warming event about 56 million years ago at the paleocene eocene p e boundary the paleocene eocene thermal maximum was accompanied by rapid expansions of mammals and terrestrial plants and extinctions of deep sea benthic organisms here we report the discovery of silicate glass spherules in a discrete stratigraphic layer from three marine p e boundary sections on the atlantic margin distinct characteristics identify the spherules as microtektites and microkrystites indicating that an extraterrestrial impact occurred during the carbon isotope excursion at the p e boundary

foraminifera in elevated bermudian caves provide further evidence for 21 m eustatic sea level during marine isotope stage 11 abstract two hypotheses have been proposed to explain the origin of marine isotope stage mis 11 deposits in small bermudian caves at 21 m above modern sea level 1 a 21 m mis 11 eustatic sea level highstand and 2 a mis 11 mega tsunami event importantly the foraminifera reported in these caves have yet to be critically evaluated within a framework of coastal cave environments after statistically comparing foraminifera in modern bermudian littoral caves and the mis 11 calonectris pocket a 21 m cave to the largest available database of bermudian coastal foraminifera the assemblages found in modern littoral caves and calonectris pocket a cannot be statistically differentiated from lagoons this observation is expected considering littoral caves are simply sheltered extensions of a lagoon environment in the littoral zone where typical coastal processes waves storms homogenize and rework lagoonal reefal and occasional planktic taxa fossil protoconchs of the bermudian cave stygobite caecum caverna were also associated with the foraminifera these results indicate that the mis 11 bermudian caves are fossil littoral caves breached flank margin caves where the total mis 11 microfossil assemblage is preserving a signature of coeval sea level at 21 m brackish foraminifera polysaccammina pseudothurammina and anchialine gastropods 95 300 individuals indicate a brackish anchialine habitat developed in the elevated caves after the prolonged littoral environmental phase the onset of sea level regression following the 21 m highstand would first lower the ancient brackish ghyben herzberg lens

tectonics and magmatism in turkey and the surrounding area this volume contains 23 papers from a range of international contributors describing recent research into the tectonics and magmatism of turkey and its surroundings this region is sited at the collision zone between eurasia and afro arabia and as such provides an extraordinarily complete and well exposed record of the staged tectonic evolution of this sector of the alpine himalayan orogen the geological history of this area involves separation of continental fragments from the margin of gondwana their migration across the tethyan oceans the subsequent closure of these oceans and finally the development of the neotectonic regime which continues to evolve to the present day such a comprehensive record is relevant to the understanding of collisional zones worldwide the volume is divided into five sections tethyan evolution neotethyan ophiolites post tethyan basin evolution neotectonics and igneous activity the first two sections deal with tethyan oceans whose growth and subsequent closure dominated the geodynamic framework in the mesozoic and cenozoic the subsequent sections deal with more recent geological developments from the balkan peninsula in the west to the transcaucasus in the east that followed consumption of the tethyan oceans there is a broad mix of papers throughout the volume wide ranging review papers on ocean development and extensional tectonics are followed by detailed descriptions of petrology and geochemistry and geographically focused studies on basin evolution specific aspects of extensional and strike slip tectonics and discussions of the relationship of magmatic activity to the tectonic development of the area tectonics and magmatism in turkey and the surrounding area presents up to date results and ideas from a large number of international contributors on a wide range of current research activity in this region it is essential reading for all geoscientists with an interest in both academic and applied aspects of eastern mediterranean geology

rugose corals at the tournaisian visean transition in the central taurides s turkey palaeobiogeography and palaeoceanography of the asian gondwana margin abstract this paper gives the first taxonomic description of the upper tournaisian lower visean rugose coral fauna of the yaricak formation aladag unit central taurides south turkey fifteen species belonging to twelve genera were identified one species is newly described eokoninckocarinia gemmina the corals are stratigraphically distributed in four assemblages the two typical assemblages of the upper tournaisian are composed of widely distributed taxa uralinia caninia proheterelasma zaphrentites the assemblage crossing the tournaisian visean boundary is characterized by eurasian and cosmopolitan and widely distributed taxa calmiussiphyllum siphonophyllia bifossularia amygdalophyllum caninophyllum keyserlingophyllum and asian taxa kueichouphyllum the youngest assemblage dominated by eokoninckocarinia gemmina sp nov has yielded foraminifers moliniacian lower visean in age these assemblages form a low diversity level bottom community which is typical of the south palaeotethys kueichouphyllum zone extending along the asian margin of gondwana cimmerian terrane during lower carboniferous times as in the other cimmerian blocks all the corals are solitary and colonial taxa are virtually absent this absence is tentatively explained by the high palaeolatitude c 50 s position of the cimmerian terrane in the southern part of the palaeotethys ocean for this time slice a cold water palaeo current running eastward along the gondwana margin might also be considered as it possibly could explain the wide distribution of the kueichouphyllum fauna restricted east of africa in the southern coast of the palaeotethys palaeoceanography palaeoclimate and facies issues are discussed as possible causes of the diversity gradient observed between the eastern australia malaya and the western north africa margin of the gondwana

discovery of high pressure zrsio4 polymorph in naturally occurring shock metamorphosed zircons shock metamorphosed zircons were recovered from an upper eocene impact ejecta layer probably from the chesapeake bay impact structure found at three deep sea drilling project ocean drilling program sites 612 903 and 904 on the upper continental slope off new jersey the shocked zircons exhibit granular textures and some have planar features x ray diffraction patterns show that some of the shocked zircons contain a high pressure zrsio4 polymorph with a scheelite type structure that was first produced in laboratory experiments in 1969 the presence of the high pressure zrsio4 polymorph in some of the zircons indicates that they have been shock metamorphosed at pressures between 20 and 90 gpa the discovery of this phase in naturally occurring shocked zircons confirms previous predictions that this phase would be found in shock metamorphosed rocks from impact structures and it provides a new tool for calibrating peak shock pressures in impact structures and ejecta in addition because the high pressure zrsio4 polymorph has now been found in naturally occurring samples it can be given a mineral name

nd and sr isotopic compositions of tektite material from barbados and their relationship to north american tektites isotopic analyses of nd and sr on individual microtektites and a bulk microtektite sample from barbados show them to have a very well defined isotopic composition these data plot on an e sr e nd diagram precisely within the narrow field determined by north american tektites e sr 111 e nd 6 2 they yield an nd model age of 0 6 ae these results show that the microtektites from the oceanic beds of late eocene age are derived from the same target as the north american tektites and should be associated with the same event samples of the deep sea sediments in which the barbados microtektites occur are found to have isotopic signatures which appear to reflect ambient sea water and detrital sediments they cannot be the source of sr or nd in the tektites following the arguments of shaw and wasserburg 1982 we conclude that the target area which produced the north american tektite field was composed of sediments eocambrian or younger derived from very late precambrian crust glass beads from lake wanapitei crater are isotopically different from all other tektites e sr 960 e nd 31 4 and cannot be related to the north american tektites

origin of bermuda s clay rich quaternary paleosols and their paleoclimatic significance red clayey paleosols that are chiefly the product of aerosolic dust deposition are interbedded in the quaternary carbonate formations of the bermuda oceanic island system these paleosols provide a basis for reconstructing quaternary atmospheric circulation patterns in the northwestern atlantic geochemical analyses were performed on representative paleosol samples to identify their parent dust source fine grained fractions were analyzed by energy dispersive x ray fluorescence to determine trace element zr y la ti and nb concentrations and to derive geochemical signatures based on immobile element ratios these ratios were compared with geochemical signatures determined for three possible sources of airborne dust 1 great plains loess 2 mississippi river valley loess and 3 saharan dust the zr y and zr la ratios provided the clearest distinction between the hypothesized dust sources the low ratios in the paleosol b horizons most closely resemble saharan dust in the 2 m size class fraction contributions from the two north american loessial source areas could not be clearly detected thus bermuda paleosols have a predominantly saharan aerosolic dust signature saharan dust deposition on bermuda during successive quaternary glacial periods is consistent with patterns of general circulation models which indicate that during glacial maxima the northeast summer trade winds were stronger than at present and reached latitudes higher than 30on despite lower than present sea surface temperatures in the north atlantic

marine isotope stage 11 palaeoclimates palaeoenvironments and its role as an analogue for the current interglacial abstract interglacials of the quaternary period are currently the focus of a great deal of attention within the scientific community this is primarily because they play a vital role in distinguishing between natural and human climate change in the current interglacial and in understanding how the holocene would evolve in the absence of anthropogenic greenhouse warming in this respect marine isotope stage 11 mis 11 ca 410 000 yr bp is one of the key interglacial stages of the past 450 000 yr the pattern of insolation variability that occurs during mis 11 matches that which occurs in the holocene more closely than in any other warm stage of the past half a million years in addition there is now an extensive range of evidence for mis 11 palaeoclimates and palaeoenvironments from marine ice core lacustrine and terrestrial sequences the aim of this paper is to provide a comprehensive review of the current state of our understanding of mis 11 this is the first paper to provide a detailed review of mis 11 that incorporates the wide range of marine ice core long lacustrine and terrestrial records that have been generated over the last ten years since the last major overview crucially it is the first review of mis 11 that incorporates a detailed synthesis of the high resolution terrestrial sequences of western and central europe this paper therefore provides a holistic integration of a diverse range of proxies and archives to provide a detailed understanding of the expression of mis 11 in the earth system in particular the review focuses on 1 the climatic background of mis 11 2 the robustness of the identification of mis 11 in a diverse range of sequences 3 the climatic structure of mis 11 4 the magnitude of warmth that occurred in this warm stage 5 mis 11 sea level magnitude and variability 6 the duration of mis 11 7 evidence for abrupt climatic events within the interglacial of mis 11 and 8 precipitation patterns and trends during this interglacial the paper concludes by considering how useful mis 11 is as an analogue for holocene climates and compares it with other proposed analogues such as mis 19 with particular reference to the early anthropogenic hypothesis

how many impact generated microspherule layers in the upper eocene abstract upper eocene microspherules microtektites and microkrystites have been found in deep sea sediments from the western north atlantic caribbean gulf of mexico equatorial pacific and eastern equatorial indian ocean recent studies proposed that there are three or four microspherule layers the north american microtektite and microkrystite couplet in chron c15 and one or two significantly older layer s in chron c16 in dsdp sites 216 292 and 612 based on calcareous nannofossil biochronologic and morphometric data i suggest that the microspherules in the latter sites correlate with the north american microtektite microkrystite couplet my results as well as previously published data are all compatible with the model of one couplet of microtektites microkrystites the inference of three or four microspherule layers in the upper eocene is shown to be an artifact of interpretation

ocean drilling project hole 689b spherules and upper eocene microtektite and clinopyroxene bearing spherule strewn fields montanari et al 1993 reported a positive ir anomaly in the upper eocene sediments from ocean drilling program hole 689b on the maud rise southern ocean vonhof 1998 described microtektites and clinopyroxene bearing cpx spherules associated with the ir anomaly in hole 689b and suggested that they belong to the north american and equatorial pacific cpx strewn fields respectively we searched a suite of 27 samples taken through the spherule layer from hole 689b and we recovered 386 microtektites and 667 cpx spherules we studied the petrography of the microtektites and cpx spherules and determined the major element compositions of 31 microtektites and 14 cpx spherules using energy dispersive x ray analysis we also determined the minor element compositions of eight microtektites using instrumental neutron activation analysis we found that the peak abundance of cpx spherules is 2 cm below the peak abundance of the microtektites 128 7 m below sea floor which suggests that the cpx spherule layer may be slightly older 3 5 ka the microtektites are mostly spherical and are generally transparent and colorless they are similar to the north american microtektites in composition the biggest differences being their generally lower na2o and generally higher zr ba and ir up to 0 3 ppb contents we agree with vonhof 1998 that the hole 689b microtektites probably belong to the north american tektite strewn field we calculate that the number of microtektites 125 m cm2 at hole 689b is 52 this number is close to the concentration predicted by extrapolation of the trend of concentration vs distance from the chesapeake bay structure based on data from other north american microtektite bearing sites thus the north american strewn field may be at least four times larger than previously mapped the hole 689b cpx spherules range from translucent yellow to opaque black but most are opaque tan to dark brown they are generally spherical in shape and all are 125 m in diameter some contain ni rich spinels in addition to clinopyroxene microlites the cpx spherules are petrographically and compositionally similar to cpx spherules previously found in the northwestern atlantic ocean caribbean sea gulf of mexico equatorial pacific and eastern indian ocean the abundance and widespread geographic occurrence of these spherules suggest that the strewn field may be global in geographic extent assuming a global extent we estimate that there may be at least 25 billion metric tons of cpx spherules in the strewn field based on age size and geographic location we speculate that the 100 km diameter popigai crater in northern siberia may be the source of the cpx spherule layer

impact ejecta in upper eocene deposits at massignano italy previous workers have shown that an impact ejecta layer at massignano italy contains a positive ir anomaly flattened spheroids pancake spherules ni rich spinel crystals and shocked quartz with multiple sets of planar deformation features because of sample sizes and work by different investigators it was not clear if the shocked quartz is associated with the ir anomaly and pancake spherules or if it belongs to a separate impact event to address this problem we carried out a high resolution stratigraphic study of this ejecta layer the ejecta layer was sampled continuously at 1 cm intervals in two adjacent columns the carbonate was removed with dilute hcl and the noncarbonate fraction was gently sieved pancake spherules were recovered from the 250 500 m size fraction and counted at the peak abundance the number of pancake spherules in the 250 500 m size fraction is about 67 g of sample the pancake spherules removed from the 250 500 m size fraction are mostly translucent to opaque pale green but some have a grey color or dark opaque patches due to a coating of ni and cr rich spinel crystals energy dispersive x ray analysis and xray diffraction data indicate that the green spherules are composed of iron rich smectite probably nontronite black opaque spinel stringers dark spinel rich pancake spherules usually 200 m across can be seen in a polished section of a block that includes the ejecta layer none of the dark spinel rich pancake spherules were recovered from the sieved non carbonate fraction due to their fragile nature but we believe that they are from the same impact event as the green pancake spherules the 250 m size fractions from both columns were disaggregated using ultrasonics and re sieved the 63 125 m size fractions were then searched for shocked quartz using a petrographic microscope at the peak abundance level the number of shocked quartz grains in the 63 125 m size fraction is about 7 g of sample some of the shocked quartz grains have a toasted appearance these grains have a brownish color and contain a patchy distribution of faint densely spaced planar deformation features pdfs polymineralic fragments containing one or two shocked quartz grains with one or two sets of pdfs were observed they appear to have an organic matrix and are probably fragments of agglutinated foraminiferal tests we searched for but did not find coesite or shocked zircons we found that the peak abundance of the shocked quartz is within a centimeter of the peak abundance of the green pancake spherules we conclude that the pancake spherules are diagenetically altered clinopyroxene bearing spherules and that the shocked quartz green and presumably the dark spinel rich pancake spherules and ir anomaly all belong to the same impact event this conclusion is consistent with previous suggestions that the cpx spherule layer may be from the 100 km diameter popigai impact crater in northern siberia

links between climate and sea levels for the past three million years the oscillations between glacial and interglacial climate conditions over the past three million years have been characterized by a transfer of immense amounts of water between two of its largest reservoirs on earth the ice sheets and the oceans since the latest of these oscillations the last glacial maximum between about 30 000 and 19 000 years ago approximately 50 million cubic kilometres of ice has melted from the land based ice sheets raising global sea level by approximately 130 metres such rapid changes in sea level are part of a complex pattern of interactions between the atmosphere oceans ice sheets and solid earth all of which have different response timescales the trigger for the sea level fluctuations most probably lies with changes in insolation caused by astronomical forcing but internal feedback cycles complicate the simple model of causes and effects

tectonics and plate tectonics model for the variscan belt of europe abstract a plate tectonics model is presented to explain the tectonometamorphic characteristics of the european variscides after the closing of two oceanic domains by two sided subduction 500 420 ma and obduction 420 380 ma collision of the european and african continental plates occurred we propose that the subsequent complex intracontinental deformation 380 290 ma is the result of a double subduction of the continental lithosphere accompanied by crust mantle decollement this mechanism explains the progressive crustal thickening and migration of the deformation through time from the sutures toward the external parts of the variscan belt accounting for this model and for the relationships between the european variscides and the other paleozoic peri atlantic belts caledonides appalachian mauritanides and morocco we infer the relative positions of africa america and europe between the silurian and the permian

slope failures on the flanks of the western canary islands abstract landslides have been a key process in the evolution of the western canary islands the younger and more volcanically active canary islands el hierro la palma and tenerife show the clearest evidence of recent landslide activity the evidence includes landslide scars on the island flanks debris deposits on the lower island slopes and volcaniclastic turbidites on the floor of the adjacent ocean basins at least 14 large landslides have occurred on the flanks of the el hierro la palma and tenerife the majority of these in the last 1 million years with the youngest on the northwest flank of el hierro as recent as 15 thousand years in age older landslides undoubtedly occurred but are difficult to quantify because the evidence is buried beneath younger volcanic rocks and sediments landslides on the canary island flanks can be categorised as debris avalanches slumps or debris flows debris avalanches are long runout catastrophic failures which typically affect only the superficial part of the island volcanic sequence up to a maximum thickness of 1 to 2 km they are the commonest type of landslide mapped in contrast slumps move short distances and are deep rooted landslides which may affect the entire thickness of the volcanic edifice debris flows are defined as landslides which primarily affect the sedimentary cover of the submarine island flanks some landslides are complex events involving more than one of the above end member processes individual debris avalanches have volumes in the range of 50 500 km3 cover several thousand km2 of seafloor and have runout distances of up to 130 km from source overall debris avalanche deposits account for about 10 of the total volcanic edifices of the small relatively young islands of el hierro and la palma some parameters such as deposit volumes and landslide ages are difficult to quantify the key characteristics of debris avalanches include a relatively narrow headwall and chute above 3000 m water depth on the island flanks broadening into a depositional lobe below 3000 m debris avalanche deposits have a typically blocky morphology with individual blocks up to a kilometre or more in diameter however considerable variation exists between different avalanche deposits at one extreme the el golfo debris avalanche on el hierro has few large blocks scattered randomly across the avalanche surface at the other icod on the north flank of tenerife has much more numerous but smaller blocks over most of its surface with a few very large blocks confined to the margins of the deposit icod also exhibits flow structures longitudinal shears and pressure ridges that are absent in el golfo the primary controls on the block structure and distribution are inferred to be related to the nature of the landslide material and to flow processes observations in experimental debris flows show that the differences between the el golfo and icod landslide deposits are probably controlled by the greater proportion of fine grained material in the icod landslide this in turn relates to the nature of the failed volcanic rocks which are almost entirely basalt on el hierro but include a much greater proportion of pyroclastic deposits on tenerife landslide occurrence appears to be primarily controlled by the locations of volcanic rift zones on the islands with landslides propagating perpendicular to the rift orientation however this does not explain the uneven distribution of landslides on some islands which seems to indicate that unstable flanks are a weakness that can be carried forward during island development this may occur because certain island flanks are steeper extend to greater water depths or are less buttressed by the surrounding topography and because volcanic production following a landslide my be concentrated in the landslide scar thus focussing subsequent landslide potential in this area landslides are primarily a result of volcanic construction to a point where the mass of volcanic products fails under its own weight although the actual triggering factors are poorly understood they may include or be influenced by dyke intrusion pore pressure changes related to intrusion seismicity or sealevel climate changes a possible relationship between caldera collapse and landsliding on tenerife is not in our interpretation supported by the available evidence

a 20 m middle pleistocene sea level highstand bermuda and the bahamas due to partial collapse of antarctic ice marine deposits at 20 3 m on the tectonically stable coastlines of bermuda and the bahamas support the hypothesis of a partial collapse of the antarctic ice sheet during the middle pleistocene beach sediments fill a sea cave at 22 m in bermuda and horizontal fenestrae filled beds crop out on platforms at two sites as high as 21 m in eleuthera bahamas carbonate beach sands are bound by an early generation of isopachous fibrous cement that is characteristic of a phreatic marine environment amino acid racemization and tims thermal ionization mass spectrometry dates constrain the age of the deposits to between 390 and 550 ka while proxy evidence supports a correlation with oxygen isotope stage 11 this direct geologic evidence of a 20 decrease in polar ice during the middle pleistocene has important implications for the stability of ice sheets during warm interglaciations

coesite and shocked quartz discovered in the australasian and north american microtektite layers samples from the north american australasian and ivory coast microtektite layers were examined for unmelted impact ejecta 125 m size coesite and shocked quartz identified by x ray diffraction were found at all the sites where a well defined north american microtektite layer had previously been documented coesite and shocked quartz were also foundin seven out of 33 cores from the australasian strewn field however no coesite or shocked quartz was found associated with the ivory coast microtektite layer stishovite was also found at three of the australasian sites all of the australasian cores containing coesite and shocked quartz were taken from within 2000 km of indochina which is believed by most to be the source area for the australasian tektites and microtektites six of the seven cores have the highest concentrations of microtektites ever determined for australasian microtektite bearing cores the seventh core did not contain any microtektites which may be consistent with the hypothesis that the microtektites were deposited in a raylike pattern the discovery of coesite and impact ejecta associated with both the north american and australasian microtektite layers provides further support for the hypothesis of terrestrial impact origin of tektites

aminostratigraphic correlations and paleotemperature implications pliocene pleistocene high sea level deposits northwestern alaska abstract multiple periods of late pliocene and pleistocene high sea level are recorded by surficial deposits along the coastal plains of northwestern alaska analyses of the extent of amino acid epimerization in fossil molluscan shells from the nome coastal plain of the northern bering sea coast and from the alaskan arctic coastal plain of the chukchi and beaufort sea coasts allow recognition of at least five intervals of higher than present relative sea level three late pliocene transgressions are represented at nome by the complex and protracted beringian transgression and on the arctic coastal plain by the colvillian bigbendian and fishcreekian transgressions these were followed by a lengthy period of non marine deposition during the early pleistocene when sea level did not reach above its present position a middle pleistocene high sea level event is represented at nome by the anvilian transgression and on the arctic coastal plain by the wainwrightian transgression anvilian deposits at the type locality are considerably younger than previously thought perhaps as young as oxygen isotope stage 11 410 000 bp finally the last interglacial pelukian transgression is represented discontinuously along the shores of northwestern alaska amino acid epimerization data together with previous paleomagnetic measurements radiometric age determinations and paleontologic evidence provide geochronological constraints on the sequence of marine deposits they form the basis of regional correlations and offer a means of evaluating the post depositional thermal history of the high sea level deposits provisional correlations between marine units at nome and the artic coastal plain indicate that the temperature difference that separates the two sites today had existed by about 3 0 ma since that time the effective diagenetic temperature was lowered by about 3 4 c at both sites and the mean annual temperature was lowered considerably more this temperature decrease was largely accomplished by the close of the fishcreekian beringian iii transgression ca 2 5 2 1 ma since then intervals of warm temperature must have been extremely brief these data suggest that the steep latitudinal temperature gradient and the frigid temperatures that characterize the high latitudes of alaska today are ancient features of arctic climate

palaeozoic terranes and their lithospheric boundaries within the trans european suture zone tesz a review the trans european suture zone tesz is a broad and complex zone of terrane accretion separating ancient lithosphere of the baltic shield and east european craton eec from the younger lithosphere of western and southern europe there is debate about the number of terranes involved and their origins the most significant terrane boundaries originally oceanic sutures are poorly exposed and are defined using faunal provinciality prominent geophysical lineaments may represent sub terrane boundaries within composite terranes the avalonia composite terrane was amalgamated to baltica in latest ician time the provenance of the malopolska and moravo silesian terranes whose neoproterozoic basement is suspect with respect to baltica but with which they nonetheless share faunal affinities is still debated the extent of the variscide rhenohercynian zone defines the southern limit of the early palaeozoic accreted terranes terranes within the bohemian massif exhibit hp metamorphism recording subduction driven collision prior to incorporation in the tesz collage itself associated with a hp event in romania the saxothuringian zone and rheic suture are directly juxtaposed with the eec and the crustal structure of the tesz has been much modified by post palaeozoic tectonism deep seismic reflection data where available show that the oceanic sutures are frequently associated with inclined reflectivity zones irz in the lithospheric mantle here inferred to mark relict subduction zones interpreting the age of subduction is complicated by offset of originally coplanar mantle and crustal segments of the irz resulting from early orogenic lithospheric delamination at the moho interface and or post orogenic reordering processes the mantle irz appear to indicate a n directed polarity for early palaeozoic subduction apparently incompatible with the geological evidence which indicates subduction of the tornquist sea beneath avalonia and a large amount of underthrusting of avalonia by baltica possible explanations for these apparently incompatible observations are evaluated

age and provenance of the target materials for tektites and possible impactites as inferred from sm nd and rb sr systematics sm nd and rb sr analyses of tektites and other impactites can be used to place constraints on the age and provenance of target materials which were impact melted to form these objects tektites have large negative e nd 0 values and are uniform within each tektite group while the e sr 0 are large positive values and show considerable variation within each group chemical trace element and isotopic compositions of tektites are consistent with production by melting of sediments derived from old terrestrial continental crust each tektite group is characterized by a uniform nd model age t chur nd interpreted as the time of formation of the crustal segment which weathered to form the parent sediment for the tektites 1 1 15 ae for australasian tektites 2 1 91 ae for ivory coast tektites 3 0 9 ae for moldavites 4 0 65 ae for north american tektites and 5 0 9 ae for high si irghizites sr model ages t ur sr are variable within each group reflecting rb sr fractionation and in the favorable limit of very high rb sr ratios approach the time of sedimentation of the parent material which melted to form the tektites australasian tektites are derived from 0 25 ae sediments moldavites from 0 0 ae sediments ivory coast tektites from 0 95 ae sediments possible parent sediments of other tektite groups have poorly constrained ages our data on moldavites and ivory coast tektites are consistent with derivation from the ries and bosumtwi craters respectively irghizites are isotopically distinct from australasian tektites and are probably not related sanidine spherules from a cretaceous tertiary boundary clay have initial e nd 2 e sr 5 and are not derived from old continental crust or meteoritic feldspar they may represent a mixture of basaltic oceanic crust and sediments implying an oceanic impact these isotopic results are also consistent with a volcanic origin for the spherules

refining estimates of polar ice volumes during the mis11 interglacial using sea level records from south africa abstractpeak eustatic sea level esl or minimum ice volume during the protracted marine isotope stage 11 mis11 interglacial at 420 ka remains a matter of contention a recent study of high stand markers of mis11 age from the tectonically stable southern coast of south africa estimated a peak esl of 13 m the present study refines this estimate by taking into account both the uncertainty in the correction for glacial isostatic adjustment gia and the geographic variability of sea level change following polar ice sheet collapse in regard to the latter the authors demonstrate using gravitationally self consistent numerical predictions of postglacial sea level change that rapid melting from any of the three major polar ice sheets west antarctic greenland or east antarctic will lead to a local sea level rise in southern south africa that is 15 20 higher than the eustatic sea level rise associated with the ice sheet collapse taking this amplification and a range of possible gia corrections int

elevated marine deposits in bermuda record a late quaternary megatsunami deposits of coral bearing marine shell conglomerate exposed at elevations higher than 20 m above present day mean sea level msl in bermuda and the bahamas have previously been interpreted as relict intertidal deposits formed during marine isotope stage mis 11 ca 360 420 ka before present on the strength of this evidence a sea level highstand more than 20 m higher than present day msl was inferred for the mis 11 interglacial despite a lack of clear supporting evidence in the oxygen isotope records of deep sea sediment cores we have critically re examined the elevated marine deposits in bermuda and find their geological setting sedimentary relations and microfaunal assemblages to be inconsistent with intertidal deposition over an extended period rather these deposits which comprise a poorly sorted mixture of reef lagoon and shoreline sediments appear to have been carried tens of meters inside karst caves presumably by large waves at some time earlier than ca 310 360 ka before present mis 9 11 we hypothesize that these deposits are the result of a large tsunami during the mid pleistocene in which bermuda was impacted by a wave set that carried sediments from the surrounding reef platform and nearshore waters over the eolianite atoll likely causes for such a megatsunami are the flank collapse of an atlantic island volcano such as the roughly synchronous julan or orotava submarine landslides in the canary islands or a giant submarine landslide on the atlantic continental margin

establishing the link between the chesapeake bay impact structure and the north american tektite strewn field the sr nd isotopic evidence the chesapeake bay impact structure which is about 35 ma old has previously been proposed as the possible source crater of the north american tektites nat here we report major and trace element data as well as the first sr nd isotope data for drill core and outcrop samples of target lithologies crater fill breccias and post impact sediments of the chesapeake bay impact structure the unconsolidated sediments cretaceous to middle eocene in age have srt 35 7 ma of 54 to 272 and ndt 35 7 ma ranging from 6 5 to 10 8 one sample from the granitic basement with a tndchur model age of 1 36 ga yielded an srt 35 7 ma of 188 and an ndt 35 7 ma of 5 7 the exmore breccia crater fill can be explained as a mix of the measured target sediments and the granite plus an as yet undetermined component the post impact sediments of the chickahominy formation have slightly higher tndchur model ages of about 1 55 ga indicating a contribution of some older materials newly analyzed bediasites have the following isotope parameters 104 to 119 srt 35 7 ma 5 7 ndt 35 7 ma 0 47 ga tsrur and 1 15 ga tndchur which is in excellent agreement with previously published data for samples of the nat strewn field target rocks with highly radiogenic sr isotopic composition as required for explaining the isotopic characteristics of deep sea drilling project dsdp site 612 tektites were not among the analyzed sample suite based on the new isotope data we exclude any relation between the na tektites and the popigai impact crater although they have identical ages within 2 errors the chesapeake bay structure however is now clearly constrained as the source crater for the north american tektites although the present data set obviously does not include all target lithologies that have contributed to the composition of the tektites

early ordovician orogenic event in galicia nw spain evidence from u pb ages in the uppermost unit of the ordenes complex new u pb data zircon monazite and rutile obtained from rocks of the uppermost allochthon in the variscan belt of nw spain indicate that the hangingwall to the suture includes an allochthonous unit with a pre variscan tectonothermal evolution this evolution is characterised by an early ordovician 498 500 ma bimodal magmatism followed almost immediately 493 498 ma by a barrovian style metamorphism up to the granulite facies the metamorphism subsequent to the igneous intrusions requires convergence and crustal thickening in order to generate the barrovian facies pattern shown by the lithologies of the uppermost allochthon the almost coeval magmatism and metamorphism and the chemistry of the metabasites suggest an accretionary complex probably related to a volcanic arc as the most probable setting for the origin of the uppermost unit the implications of the existence of early ordovician convergent plate boundaries are discussed in the context of gondwana laurentia avalon interactions

deducing the ancestry of terranes shrimp evidence for south america derived gondwana fragments in central europe we present here an example of how the sensitive high resolution ion microprobe shrimp zircon dating method can provide a terrane specific geochronological fingerprint for a rock and thus help to reveal major tectonic boundaries within orogens this method applied to inherited zircons in a ca 580 ma metagranitoid rock from the eastern bohemian massif has provided for the first time in the central european variscan basement unequivocal evidence for mesoproterozoic and late paleoproterozoic geologic events ca 1 2 ga 1 5 ga and 1 65 1 8 ga the recognition of such zircon ages has important consequences because it implies that parts of the precambrian section of variscan central europe were originally derived from a grenvillian cratonic province as opposed to the common assumption of an african connection a comparison with previously published shrimp data suggests however that these mesoproterozoic and late paleoproterozoic zircon ages may be restricted to the moravo silesian unit in the eastern variscides whereas the saxothuringian and moldanubian zones appear to contain a typical north african i e neoproterozoic plus eburnian inherited zircon age spectrum this finding supports new tectonic concepts according to which variscan europe is composed of a number of completely unrelated terranes with extremely different paleogeographic origins the moravo silesian unit can be best interpreted as a peri gondwana terrane which was situated in the realm of the amazonian cratonic province by the late precambrian comparable to the avalonian terranes of north america and the united kingdom

extraterrestrial ni rich spinel in upper eocene sediments from massignano italy evidence of a major cosmic event at the end of the eocene is given by the finding of at least one possibly two or more impact horizons containing microtektites microkrystites shocked quartz and unusually high iridium concentrations we report here the discovery in the global stratotype of the eocene oligocene boundary at massignano in italy of ni rich spinel a mineral that forms by the interaction of meteoritic bodies with the earth s atmosphere a maximum concentration of 800 crystals mg 1 corresponding to a flux of 2 107 crystals cm 2 is observed in a well dated layer 35 7 0 4 ma that also contains shocked quartz and iridium the crystals are found clustered in flattened spheroids the probable relic of their host bodies the chemical and physical characteristics of the spinel crystals indicate that the spheroids formed by interaction of dust particles in the upper part of the atmosphere rather than by ablation of large objects as proposed for the spinel bearing spheroids found at the cretaceous tertiary boundary the most likely explanation is that the dust particles were generated by a large cometary impact whether this impact is the one that produced microtektites and or microkrystites or another one that may have occurred shortly after or before is still questionable additional searching for ni rich spinel at other upper eocene sections may help to answer this question

a giant landslide on the north flank of tenerife canary islands the extent of mass wasting along the north flank of tenerife has been mapped using swath bathymetry gloria side scan sonar and 3 5 khz echo sounder data the marine surveys show that north of tenerife a giant landslide is exposed over an area of 5500 km2 of the seafloor more than twice the surface area of the island the landslide truncates an older ridge and valley topography that is associated with the shield building basalts on tenerife we interpret the ridge and valley topography as the result of subaerial erosion the landslide is estimated to have a length of 100 km a width of up to 80 km and a volume of about 1000 km3 it extends onshore into the orotava and icod valleys which have been interpreted as of landslide origin k ar dating of basaltic flows in the steep headwall of orotava suggests an age of formation for the valley is younger than 0 78 ma and may even be younger than 0 27 ma the icod valley is located immediately to the north of the most recent volcano on tenerife las canadas and has been associated with the collapse of its caldera between 1 2 and 0 2 ma a young age for the landslide is supported by the 3 5 khz echo sounder data which show that the landslide is draped by a thin 10 m layer of younger sediment the landslide did not form however during a single catastrophic event but represents the amalgamation of a number of separate landslides the occurrence of the ridge and valley topography in water depths of up to 2 5 km suggests that the shield building basalts have subsided by at least this amount since they formed 3 3 8 0 ma we speculate that this subsidence is caused by some form of stress relaxation that occurs in the underlying lithosphere the giant landslide imaged in our sonar data is associated with the late stages in the development of the most recent volcano on tenerife las canadas which only began at about 1 8 ma thus landsliding may be a particular feature of the time soon after emplacement when because of incomplete isostatic adjustment oceanic volcanoes have their greatest elevations above sea level and therefore are most susceptible to slope failure

reply to mega highstand or megatsunami discussion of mcmurtry et al elevated marine deposits in bermuda record a late quaternary megatsunami sed geol 200 2007 155 165 by paul j hearty and storrs l olson our recent paper mcmurtry g m tappin d r sedwick p n wilkinson i fietzke j and sellwood b 2007a elevated marine deposits in bermuda record a late quaternary megatsunami sedimentary geol 200 155 165 critically re examined elevated marine deposits in bermuda and concluded that their geological setting sedimentary relations micropetrography and microfaunal assemblages were inconsistent with sustained intertidal deposition instead we hypothesized that these deposits were the result of a large tsunami that impacted the bermuda island platform during the mid pleistocene hearty and olson hearty p j and olson s l in press mega highstand or megatsunami discussion of mcmurtry et al elevated marine deposits in bermuda record a late quaternary megatsunami sedimentary geology 200 155 165 2007 aug 07 sedimentary geol 200 155 165 in their response attempt to refute our conclusions and claim the deposits to be the result of a 21 m eustatic sea level highstand during marine isotope stage mis 11 in our reply we answer the issues raised by hearty and olson hearty p j and olson s l in press mega highstand or megatsunami discussion of mcmurtry et al elevated marine deposits in bermuda record a late quaternary megatsunami sedimentary geology 200 155 165 2007 aug 07 sedimentary geol 200 155 165 and conclude that the bermuda deposits do not provide unequivocal evidence of a prolonged 21 m eustatic sea level highstand rather the sediments are more likely the result of a past megatsunami in the north atlantic basin

gondwana derived microcontinents the constituents of the variscan and alpine collisional orogens abstract the european variscan and alpine mountain chains are collisional orogens and are built up of pre variscan building blocks which in most cases originated at the gondwana margin such pre variscan elements were part of a pre ordovician archipelago like continental ribbon in the former eastern prolongation of avalonia and their present day distribution resulted from juxtaposition through variscan and or alpine tectonic evolution the well known nomenclatures applied to these mountain chains are the mirror of variscan resp alpine organization it is the aim of this paper to present a terminology taking into account their pre variscan evolution at the gondwana margin they may contain relics of volcanic islands with pieces of cadomian crust relics of volcanic arc settings and accretionary wedges which were separated from gondwana by initial stages of rheic ocean opening after a short lived ordovician orogenic event and amalgamation of these elements at the gondwanan margin the still continuing gondwana directed subduction triggered the formation of ordovician al rich granitoids and the latest ordovician opening of palaeo tethys an example from the alps external massifs illustrates the gradual reworking of gondwana derived pre variscan elements during the variscan and alpine tertiary orogenic cycles

zircon ages and nd isotopic and chemical compositions of orthogneisses from the black forest germany evidence for a cambrian magmatic arc single zircon u pb dating combined with 207pb 206pb ages obtained by the evaporation method constrains the emplacement of tonalitic trondhjemitic and granodioritic orthogneisses of the moldanubian zone in the black forest between 500 and 510 ma two detrital zircon populations of 1 9 and 1 6 ga indicate early middle proterozoic material in the former setting of the basement the initial end values range from 0 1 to 3 4 and mean crustal residence ages of 1 0 1 4 ga are consistent with involvement of early middle proterozoic crust and a subordinate juvenile component probably originating from subduction related melting of the mantle the orthogneisses have fractionated ree patterns and slightly higher k2o na2o ratios than typical low k tonalite trondhjemite granite suites the chemical data are interpreted as evidence for melting of amphibolite and contributions from evolved crust the emplacement of the orthogneisses was superceded by a high temperature metamorphic event at 480 ma which we interpret as a result of lithospheric thinning in a marginal basin behind a cambrian magmatic arc

the extraterrestrial impact evidence at the palaeocene eocene boundary and sequence of environmental change on the continental shelf we have identified clear evidence of an extraterrestrial impact within the onset of the carbon isotope excursion cie that defines the palaeocene eocene p e boundary hyperthermal event approx 56 ma from several sites on the eastern atlantic coastal plain and offshore we review and update the state of the evidence for an impact at the p e boundary including a k ar cooling age of the ejecta that is indistinguishable from the depositional age at the p e which establishes the ejecta horizon as an isochronous stratigraphic indicator at the p e immediately above the ejecta peak at the base of the coastal plain marlboro clay unit we identify a sharp increase in charcoal abundance coincident with the previously observed dramatic increase in magnetic nanoparticles of soil pyrogenic origin we therefore revisit the observed sequence of events through the p e boundary on the western atlantic coastal plain showing that an extraterrestrial impact led to wildfires landscape denudation and deposition of the thick marlboro clay whose base coincides with the spherule horizon and cie onset the sr ca ratio of the spherules indicates that the carbon responsible for the onset may be vaporized caco 3 target rock mixed with isotopically light carbon from the impactor or elsewhere crucially we do not argue that the impact was responsible for the full manifestation of the cie observed globally onset to recovery approx 170 kyr rather that a rapid onset was triggered by the impact and followed by additional carbon from other processes such as the eruption of the north atlantic igneous province such a scenario agrees well with recent modelling work though it should be revisited more explicitly this article is part of a discussion meeting issue hyperthermals rapid and extreme global warming in our geological past

sr and nd analyses of upper eocene spherules and their implications for target rocks upper eocene impact ejecta has been discovered all over the world the number of upper eocene impact layers and the geographic distribution of each layer based on major chemical composition and biostratigraphic data are not agreed upon we have performed four sr nd isotopic analyses of clinopyroxene bearing spherules cpx spherules and three sr nd analyses of microtektites from five deep sea drilling project ocean drilling program dsdp odp sites in the south atlantic and indian oceans our data support the hypothesis that there is only one cpx spherule layer in upper eocene sediments we also find that the microtektites associated with the cpx spherule layer in the south atlantic and indian oceans are not part of the north american tektite strewn field but belong to the same event that produced the cpx spherules the microtektites together with cpx spherules are more heterogeneous than microtektites tektites from other strewn fields no direct link has been established between the microtektites from this study and possible target rock at the popigai crater

megatsunami deposits on kohala volcano hawaii from flank collapse of mauna loa the origin of coastal and high elevation marine gravels on the hawaiian islands of lanai and molokai is controversial because the vertical tectonics of these islands is poorly constrained the gravels are either from eustatic highstands or were left by massive tsunamis from offshore giant landslides in contrast at kohala on the island of hawaii where continuous subsidence is well established lithofacies analysis and dating of a fossiliferous marine conglomerate 1 5 61 m above present sea level support a tsunami origin and indicate a runup of 400 m 6 km inland the conglomerate age 110 10 ka suggests a tsunami caused by the ca 120 ka giant alika 2 landslide from nearby mauna loa volcano

upper eocene tektite and impact ejecta layer on the continental slope off new jersey during leg 150 of the ocean drilling project odp two sites 903c and 904a were cored that have sediments of the same biostratigraphic age as the upper eocene tektite bearing ejecta layer at deep sea drilling project dsdp site 612 core 45x from odp site 904a 4 km north of site 612 contains a 5 cm thick tektite bearing ejecta layer and core 56 from site 903c 8 km north northwest of site 904 contains a 2 cm thick layer of impact ejecta without any tektite or impact glass shocked quartz and feldspar grains with multiple sets of planar deformation features pdfs and abundant coesite bearing grains are present at both sites the major oxide contents trace element compositions and rare earth element ree patterns of the site 904 tektites are similar to those of the site 612 tektites and to north american tektites especially bediasites the sr and nd values for one composite tektite sample from site 904 fall within the range previously obtained for the site 612 tektites which defines a linear trend that if extrapolated would intersect the values obtained for north american tektites the water contents of eight tektite fragments from site 904 range from 0 017 to 0 098 wt and thus are somewhat higher than is typical for tektites the heavy mineral assemblages of the 63 125 m size fractions from the ejecta layers at sites 612 903 and 904 are all similar therefore we conclude that the ejecta layer at all three sites is from the same impact event and that the tektites at sites 904 and 612 belong to the north american tektite strewn field clinopyroxene bearing cpx spherules occur below or in the lower part of the main ejecta layer at all three sites at all three sites the cpx spherules have been partly or completely replaced with pyrite that preserved the original crystalline textures site 612 903 and 904 cpx spherules are similar to those found in the caribbean sea gulf of mexico central equatorial pacific western equatorial pacific and eastern indian ocean the cpx event appears to have preceded the north american tektite event by 10 15 ka or less the fining upward sequence at all three sites and concentration of the denser unmelted impact ejecta at the top of the tektite layer at sites 612 and 904 suggest that the tektite bearing ejecta layers are not the result of downslope redeposition and that the unmelted ejecta landed after the glass geographic variations in thickness of the tektite bearing ejecta layer the lack of carbonate clasts in the ejecta layer and the low cao content of the tektite glass suggest that the ejecta including the tektite glass were derived from the chesapeake bay structure rather than from the toms canyon structure a sharp decline in microfossil abundances suggests that local environmental changes caused by the impact may have had adverse effects on benthic foraminifera radiolaria sponges and fish as well as the planktic foraminifera

early ordovician continental break up in variscan europe ndsr isotope and trace element evidence from bimodal igneous associations of the southern massif central france abstract the high grade marvejols group and the low grade albigeois cevennes sedimentary sequence contain bimodal igneous rocks of early ordovician age which are representative of a widespread thermal event in the european variscides comparison of their nd sr isotope and trace element characteristics provides additional evidence for their origin in an ensialic extensional setting as an alternative to the back arc model proposed by previous authors we propose that these associations record a continental break up episode unrelated to contemporaneous subduction in this model the widespread early paleozoic bimodal magmatism marks the birth of a mid european oceanic arm we propose that the break up was controlled by both transtensional processes and mantle plume activity high grade associations such as the marvejols group and low grade bimodal associations such as the albigeois cevennes might be regarded as representing opposite rifted passive margins the northern marvejols type margin was involved in a late ordovician silurian subduction like process with hp ht metamorphism in contrast the southern albigeois cevennes margin remained largely unaffected possibly as part of the overriding plate of the subduction zone pseudo calc alkaline signatures unrelated to subduction processes may occur in magmatic rocks associated with continental break up episodes in this case negative nb anomalies are produced by the addition of crustal components enriched in th and lree relative to nb this inferred alternative origin of nb anomalies has important bearing on the paleogeodynamic settings based on geochemical data

late eocene microkrystites and microtektites at maud rise ocean drilling project hole 689b southern ocean suggest a global extension of the approximately 35 5 ma pacific impact ejecta strewn field late eocene microtektites and microkrystites recovered from ocean drilling project hole 689b at maud rise southern ocean are stratigraphically and geochemically compared to spherules from the north american and pacific strewn fields and to devitrified spherules fiom the eocene oligocene global stratotype section and point section in massignano italy the odp 689b microkrystites compare well to the pacific strewn field microkrystites which suggests that the geographic extent of the pacific strewn field was much larger than previously documented the elemental composition of microtektites of odp hole 689b is comparable to tektites of the north american strewn field their 87sr 86sr ratio however is different we tentatively interpret this to reflect geochemical heterogeneity within the north american strewn field but can not exclude the option that the chemical discrepancies result from the existence of a third late eocene impact site

shocked quartz from the late eocene impact evidence from massignano italy this paper reports the discovery of shocked quartz grains within a well dated upper eocene marlstone at the massignano outcrop ancona italy the shocked quartz reaches a maximum concentration of 1 6 0 4 grains per cubic centimetre of bulk rock a modest ir anomaly is also coincident with the shocked quartz and together they strongly support an impact origin moreover this impact layer has a precise interpolated radiometric age of 35 7 0 4 ma although impact evidence found throughout the world indicates that at least two large impacts did occur during this time the actual number timing and environmental effects of these impact events remain unclear the late eocene was a critical time in earth history because of significant climatic biotic and environmental crises

the hulopoe gravel lanai hawaii new sedimentological data and their bearing on the giant wave mega tsunami emplacement hypothesis recognition that many oceanic islands are shaped by giant landslides has highlighted claims that the hulopoe gravel on south lanai hawaii was deposited by giant waves mega tsunami generated by such a landslide this interpretation is controversial resolution of the controversy has global implications because mass wasting of oceanic islands has been a common process for as long as hot spot volcanism has affected the ocean basins thus if mega tsunami are attendant upon the mass wasting process their effect on earth surface processes should be discernible for much of geological time and may be comparable to that resulting from bolide impacts that form astroblemes detailed facies analysis of the pebble cobble and boulder gravels that form the hulopoe gravel type section shows that the gravels are composed predominantly of basalt clasts with appreciable amounts of limestone clasts in 8 of the 14 beds present deposition was not continuous eight disconformities are recognized in the 9 2 m type section three of which are associated with truncated paleosols the hulopoe gravel was not deposited by a single tsunami at 105 ka as has been proposed one bed is clearly an alluvial deposit the origins of others are unclear but the facies data do not exclude tsunami as one of the processes that deposited individual beds within the hulopoe gravel either above or below sea level

a synthesis and review of the geological evidence for palaeotsunamis along the coast of southeast australia the evidence issues and potential ways forward abstract in recent years the role of extreme events such as tsunamis and storms in shaping coastal evolution and change has been increasingly appreciated around the world tsunami geologists are increasingly recognising the signatures of palaeotsunamis almost everywhere they look and in many cases base their interpretations on similar evidence for quaternary tsunamis first identified in australia geological research suggests that the coast of south east australia and others worldwide may have been impacted by palaeotsunamis many times larger than the catastrophic 2004 indian ocean and 2011 t hoku events in australia the debate centres on the hypothesis that the coast of south east australia preserves evidence for repeated large magnitude quaternary tsunamis if independently validated this hypothesis has profound implications for risk despite the potential importance of this hypothesis no synthesis or comprehensive review of the proposed geological evidence and chronology exists as a result it is difficult to assess the evidence and to draw conclusions about the nature of the hazard and risk along the coast this synthesis details the spatial distribution of reported palaeotsunami deposits along the coast of new south wales south east australia and summarises the distribution of different types of sedimentary and erosional evidence the age range of reported palaeotsunami deposits is identified and mapped before discussing same age chronologically correlated deposits these data are then used to draw broad conclusions about the evidence and identify future research questions to aid in the testing of the hypothesis for repeated tsunami inundation we show that 60 sites are purported to contain evidence of tsunami inundation over 650 km of the south east australian coast with a spatial concentration south of sydney geomorphic evidence distinctly different to that used elsewhere in global palaeotsunami studies is reported at 54 sites with erosional features described as the most frequent indication of inundation proposed tsunami deposits are evident at 44 sites with the dominant deposit type being imbricated boulder stacks radiocarbon dating at 39 of the sites led to a proposition of nine events during the quaternary eight of which occurred during the holocene interestingly 18 sites have no chronological data associated with them alternative interpretations are offered at six type field sites purported to contain palaeotsunami evidence attention is drawn to the disjunct between historical and geological scales of tsunami inundation in the region in addition to the contrast between the scale of reported palaeotsunamis and the robust evidence of smaller events a synthesis of research into the nature of the evidence is offered including critiques of evidence type and mechanisms a critical review of the chronological data is also presented in addition to the recalibration and analysis of published radiocarbon data the paper concludes with an outline of research questions for further work on proposed palaeotsunami sites in australia as well as a statement about likely risk in south east australia it also advocates the need for caution when interpreting evidence for palaeotsunamis elsewhere around the world when those interpretations are based on signatures originally reported in south east australia

late eocene north american microtektites and clinopyroxene bearing spherules approximately 35 m y ago two events separated by only 10 000 20 000 years each spread roughly 1 billion metric tons of silicate spherules over large areas of the earth s surface the older event produced mostly clinopyroxene bearing spherules cpx spherules the cpx spherules have been found in the caribbean sea gulf of mexico equatorial pacific and eastern equatorial indian ocean the cpx spherule layer is associated with an iridium anomaly and appears to coincide with the extinction of several species of radiolaria the composition and widespread distribution of the cpx spherules indicate that they were formed by an impact event the younger layer of spherules consists of microtektites belonging to the north american tektite strewn field based on age and elemental and isotopic composition the north american microtektites have been found in the western equatorial atlantic on barbados in the caribbean sea and in the gulf of mexico the north american microtektite layer is not synchronous with an iridium anomaly nor does it appear to be associated with any major changes in the microfossils neither the cpx spherule event nor the north american tektite event appears to be associated with a climatic change but no detailed studies have been made across either layer excluding the cpx layer which contains mostly crystal bearing spherules the evidence at the present time indicates that there is only one late eocene microtektite layer and it is part of the north american strewn field

a non cylindrical model for the northwest iberian allochthonous terranes and their equivalents in the hercynian belt of western europe abstract a case is made for a non cylindrical development of the european hercynian belt far travelled allochthonous terranes in the belt consist of a mixture of units including catazonal units ophiolites and units derived from the continental margin of gondwana they often depict a metamorphic history of intermediate to high pressure type and caledonian to eo hercynian age and are thought to have been put together in the early stages of the orogeny through a process partly obductive directed onto the continental margin of gondwana considerations upon the disposition of the terranes their relationships with the paleogeography of the gondwana realm and the structures in them suggest that their emplacement took place in an oblique fashion at a small angle to the margin of the continent the proposed allochthon could be related to the development of an island arc or a wedge like subplate in the southern part of the baltica plate later convergence between gondwana and laurussia involving transcurrent mostly dextral movements combined with tectonic escape phenomena would account for the present complexity of the belt and for the narrow strip the allochthonous terranes delineate in westernmost europe

transformation of a magmatic arc and an orogenic root during oblique collision and it s consequences for the evolution of the european variscides mid german crystalline rise the architecture of the european variscides has been subdivided by kossmat 1927 into paleogeographically coherent units which are presently interpreted as former plate fragments the mid german crystalline rise mgcr separates two fragments rhenohercynian and saxothuringian belts at the site of an inferred plate boundary and reequilibrated orogenic root the commonly favoured model interprets the mgcr as the magmatic arc on saxothuringian crust above a south dipping subduction zone in upper devonian and carboniferous times data from the mgcr the kinematic evolution of the mid european variscides and first order volume balancing suggest a reinterpretation of this unit which challenges classical views on the mgcr as well as on the subdivision of variscan architecture the mgcr is composed of two rock groups with different tectonic identity a lower carboniferous low pressure high temperature magmatic arc association on lower paleozoic basement rests tectonically on a stack of medium pressuremedium temperature rocks of inferred rhenohercynian origin the latter were tectonically accreted to the base of the overriding plate by tectonic underplating the entire process was controlled by oblique convergence this led to regional partitioning of the plate kinematic vector into contractional domains lower rhenohercynian plate and back arc area of the upper saxothuringian plate bulk heterogeneous plate margin parallel extensional domains mgcr and plate margin parallel wrench domains mgcr boundaries during this process material was continually transferred from the lower plate to the upper plate uplifted and exhumed by net crustal extension the concomitant removal of parts of the former arc and the entire orogenic root necessitates a reappraisal of variscan architecture and evolution

a sustained 21 m sea level highstand during mis 11 400 ka direct fossil and sedimentary evidence from bermuda abstract a small protected karstic feature exposed in a limestone quarry in bermuda preserved abundant sedimentary and biogenic materials documenting a transgressive phase still stand and regressive phase of a sea level in excess of 21 3 m above present during marine isotope stage mis 11 400 ka as determined by u th dating and amino acid racemization cobbles and marine sediments deposited during the high energy transgressive phase exhibit rim cements indicating a subsequent phreatic environment this was succeeded stratigraphically by a still stand deposition of fine calcareous lagoonal sediments containing bioclasts of red algae and benthic and planktonic foraminifera that was intensely burrowed by marine invertebrates probably upogebiid shrimp that could not be produced under any condition other than sustained marine submergence overlying this were pure carbonate beach sands of a low energy regressive phase containing abundant remains of terrestrial and marine vertebrates and invertebrates the considerable diversity of this fauna along with taphonomic evidence from seabird remains indicates deposition by high run up waves over a minimum duration of months if not years the maximum duration has yet to be determined but probably did not exceed one or two thousand years the most abundant snails in this fauna are two species indicative of brackish water and high tide line showing that a ghyben herzberg lens must have existed at 20 m the nature of these sediments and fossil accumulation is incompatible with tsunami deposition and given the absence of evidence for tectonic uplift of the bermuda pedestal or platform provide proof that sea level during mis 11 exceeded 20 m a fact that has widespread ramifications for geologists biogeographers and human demographics along the world s coastlines

late eocene impact ejecta geochemical and isotopic connections with the popigai impact structure late eocene microtektites and crystal bearing microkrystites extracted from dsdp and odp cores from the atlantic pacific and indian oceans have been analyzed to address their provenance a new analysis of nd and sr isotopic compositions confirms previous work and the assignment of the uppermost microtektite layer to the north american tektites which are associated with the 35 5 ma 85 km diameter chesapeake impact structure of virginia usa extensive major element and nd and sr isotopic analyses of the microkrystites from the lowermost layer were obtained the melanocratic microkrystites from sites 216 and 462 in the indian and pacific oceans possess major element chemistries sr and nd isotopic signatures and sm nd t chur model ages similar to those of tagamite melt rocks in the popigai impact structure they also possess rb sr t ur model ages that are younger than the tagamite t chur ages by up to 1 ga which require a process as yet undefined of rb sr enrichment these melanocratic microkrystites are consistent with a provenance from the 35 7 ma 100 km diameter popigai impact structure of siberia russia while ruling out other contemporaneous structures as a source melanocratic microkrystites from other sites and leucocratic microkrystites from all sites possess a wide range of isotopic compositions 143 nd values of 16 to 27 7 and 87 sr values of 4 1 354 0 making the association with popigai tagamites less clear these microkrystites may have been derived by the melting of target rocks of mixed composition which were ejected without homogenization dark glass and felsic inclusions extracted from popigai tagamites possess 143 nd and 87 sr values of 26 7 to 27 8 and 374 7 and 432 4 respectively and t chur and t ur model ages of 1640 1870 ma and 240 1830 ma respectively which require the preservation of initially present heterogeneity in the source materials the leucocratic microkrystites possess diverse isotopic compositions that may reflect the melting of supra basement sedimentary rocks from popigai or early basement melts that were ejected prior to homogenization of the popigai tagamites the ejection of melt rocks with chemistries consistent with a basement provenance rather than the surface 1 km of sedimentary cover rocks atypically indicates a non surficial source to some of the ejecta microkrystites from two adjacent biozones possess statistically indistinguishable major element compositions suggesting they have a single source the occurrence of microkrystites derived from a single impact event but in different biozones can be explained by 1 diachronous biozone boundaries 2 post accumulation sedimentary reworking or 3 erroneous biozonation

record of a mid pleistocene depositional anomaly in west antarctic continental margin sediments an indicator for ice sheet collapse abstract modern global warming is likely to cause future melting of earth s polar ice sheets that may result in dramatic sea level rise a possible collapse of the west antarctic ice sheet wais alone which is considered highly vulnerable as it is mainly based below sea level may raise global sea level by up to 5 6 m despite the importance of the wais for changes in global sea level its response to the glacial interglacial cycles of the quaternary is poorly constrained moreover the geological evidence for the disintegration of the wais at some time within the last ca 750 kyr possibly during marine isotope stage mis 11 424 374 ka is ambiguous here we present physical properties palaeomagnetic geochemical and clay mineralogical data from a glaciomarine sedimentary sequence that was recovered from the west antarctic continental margin in the amundsen sea and spans more than the last 1 myr within the sedimentary sequence proxies for biological productivity such as biogenic opal and the barium aluminum ratio and the supply of lithogenic detritus from the west antarctic hinterland such as ice rafted debris and clay minerals exhibit cyclic fluctuations in accordance with the glacial interglacial cycles of the quaternary a prominent depositional anomaly spans mis 15 mis 13 621 478 ka the proxies for biological productivity and lithogenic sediment supply indicate that this interval has the characteristics of a single prolonged interglacial period even though no proxy suggests environmental conditions much different from today we conclude that if the wais collapsed during the last 800 kyr then mis 15 mis 13 was the most likely time period apparently the duration rather than the strength of interglacial conditions was the crucial factor for the wais drawdown a comparison with various marine and terrestrial climate archives from around the world corroborates that unusual environmental conditions prevailed throughout mis 15 mis 13 some of these anomalies are observed in the pelagic southern ocean and the south atlantic and might originate in major ice sheet drawdown in antarctica but further research is required to test this hypothesis

landward fining in onshore gravel as evidence for a late pleistocene tsunami on molokai hawaii a conglomerate on the south coast of molokai hawaii has simple trends in carbonate clast abundance and size that are explained better by tsunami deposition than by shoreline uplift the conglomerate extends as much as 2 km inland and to 72 m above present sea level it consists mainly of basalt boulders derived from underlying bedrock but also contains carbonate pebbles and cobbles derived from coral reefs whereas basalt clasts display no vertical or lateral trend in size carbonate clasts decrease in abundance and get smaller with elevation and distance from shore the origin of the conglomerate is controversial it may have been produced by either a single tsunami or by wave action at multiple higher sea levels on molokai the deposit is best explained as the result of a single tsunami because only such a tsunami could move large grains so far inland and produce a simple trend in carbonate clasts while imparting no trend to the basalt clasts

a simple model for calculating tsunami flow speed from tsunami deposits abstract this paper presents a simple model for tsunami sedimentation that can be applied to calculate tsunami flow speed from the thickness and grain size of a tsunami deposit the inverse problem for sandy tsunami deposits where grain size and thickness vary gradually in the direction of transport tsunami sediment transport is modeled as a steady spatially uniform process the amount of sediment in suspension is assumed to be in equilibrium with the steady portion of the long period slowing varying uprush portion of the tsunami spatial flow deceleration is assumed to be small and not to contribute significantly to the tsunami deposit tsunami deposits are formed from sediment settling from the water column when flow speeds on land go to zero everywhere at the time of maximum tsunami inundation there is little erosion of the deposit by return flow because it is a slow flow and is concentrated in topographic lows variations in grain size of the deposit are found to have more effect on calculated tsunami flow speed than deposit thickness the model is tested using field data collected at arop papua new guinea soon after the 1998 tsunami speed estimates of 14 m s at 200 m inland from the shoreline compare favorably with those from a 1 d inundation model and from application of bernoulli s principle to water levels on buildings left standing after the tsunami as evidence that the model is applicable to some sandy tsunami deposits the model reproduces the observed normal grading and vertical variation in sorting and skewness of a deposit formed by the 1998 tsunami

late eocene microtektites and radiolarian extinctions on barbados a late eocene microtektite layer has been found in three exposed sections on barbados west indies these microtektites and associated tektite fragments are compositionally similar to the north american tektites and thus like the caribbean and gulf of mexico microtektites may belong to the strewn field of north american microtektites which have been found in deep sea deposits from the caribbean sea across the pacific and into the northeastern indian ocean1 2 the north american layer has been reported to be approximately synchronous with several radiolarian extinctions3 4 and with an anomaly in iridium concentrations5 7 and it has been hypothesized that the microtektites the extinctions and the iridium anomaly are all related to an asteroid impact we report here that the radiolarian extinctions predate the microtektite layer and that the highest ir concentrations apparently coincide with the extinctions thus although the extinctions may be causally related to the ir anomaly the microtektites appear not to be

chromium isotopes in late eocene impact spherules indicate a likely asteroid belt provenance abstract spherules and magnetic fractions extracted from two late eocene impact deposits massignano italy and ocean drilling program hole 709c western indian ocean have anomalous concentrations of ir and high concentrations of cr ni co and fe an excess of 53 cr relative to 53 cr 52 cr ratios in terrestrial samples shows that much of the cr in these samples is extraterrestrial the absence of relatively large 54 cr excesses as found in carbonaceous chondrites precludes a carbonaceous chondrite source and the data best fit ordinary chondrites the two localities produced samples with somewhat different elemental and isotopic compositions but these are likely different components of the same impact rather than from two distinct impacts the multiple impacts and dust deposition in the late eocene were more likely caused by disruption of a large asteroid in the inner asteroid belt than by a comet shower the brangane asteroid family may be the result of this disruption the source of the dust and impactors in the late eocene and its members may be composed of h chondrite lithologies based upon the coeval 35 ma peak in h chondrite cosmic ray exposure ages

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

review of nd isotopic data and xenocrystic and detrital zircon ages from the pre variscan basement in the eastern bohemian massif speculations on palinspastic reconstructions

early cambrian oceanic plagiogranite in the silvretta nappe eastern alps geochemical zircon u pb and rb sr data from garnet hornblende plagioclase gneisses garnet hornblende plagioclase gneisses rich in incompatible elements occur in the crystalline basement of the austro alpine silvretta nappe and are associated with clinopyroxene norites and harzburgite cumulates it is proposed here that the gneisses were formerly oceanic plagiogranites an end 530 value of 5 6 for the gneisses as well as initial87sr 86sr values of 0 7036 0 7037 for the gabbroic rocks and 0 7026 0 7027 for the ultramafic rocks suggest a mantle source for this rock association the geochemical characteristics of the garnet hornblende plagioclase gneisses indicate that their precursors were derived by fractional crystallization from a basaltic parent magma by the same process which produced the adjacent clinopyroxene norites and ultramafic cumulates as well the combined u pb upper intercept ages of zircons from two gneiss samples yield an igneous crystallization age of 532 30 ma similar to previously dated mostly calcalkaline orthogneisses in the same area high quality transparent zircons showed the least degree of discordance but contain extremely low u and pb levels the rock suite including this plagiogranite was emplaced within oceanic crust which formed in the latest precambrian early palaeozoic off the northern continental margin of gondwana

catastrophic collapse of the volcanic island of hierro 15 ka ago and the history of landslides in the canary islands landslides play an important role in the evolution of many volcanic islands producing huge fields of blocky volcanic debris on their submarine slopes sidescan sonar images presented in this paper provide evidence for a large debris avalanche el golfo on the northern flank of hierro island in the canary islands angular blocks as much as 1 2 km across and 200 m high cover the debris avalanche surface el golfo avalanche is related to both the canary debris flow and a volcaniclastic turbidite found in the madeira abyssal plain 600 km west of the canaries dating of the turbidite and the failure scarp onshore indicates that the failure probably occurred between 13 and 17 ka there appears to be a general correlation between volcaniclastic turbidites in the abyssal plain sequence and landslides in the canaries during the past 750 ka tentatively this correlation suggests that seven major landslides have affected the canaries in that time

mega highstand or megatsunami discussion of mcmurtry et al elevated marine deposits in bermuda record a late quaternary megatsunami sed geol 200 2007 155 165 abstract graded sorted rounded and ponded marine sand and conglomerate deposited in caves and on an erosional terrace at 20 m on bermuda previously interpreted as originating in a eustatic highstand of sea level during the middle pleistocene were reinterpreted by mcmurtry et al 2007 as the result of a great 20 m megatsunami at sea propagating out across the north atlantic from the canary islands cresting and rolling up and over the bermuda platform however no middle pleistocene tsunami deposits have been reported elsewhere on bermuda or anywhere else around the north atlantic rim the tsunami origin is unsupportable whereas the available evidence unequivocally establishes a 21 m eustatic sea level during the middle pleistocene mis 11 interglacial

characteristics of shocked quartz in late eocene impact ejecta from massignano ancona italy clues to shock conditions and source crater the microstructure and optical properties of shocked quartz discovered in a distal ejecta horizon of the stratigraphically continuous upper eocene section at massignano italy have been investigated in detail the microstructural observations confirm the impact origin of the shocked quartz grains and reveal that the optically visible planar lamellae are well preserved amorphous to partially recrystallized planar deformation features refractive index measurements of shocked quartz and analysis of the orientation and thickness of planar deformation features indicate shock pressures of 10 to 26 gpa at ambient preshock temperature altogether the characteristics of shocked quartz from massignano imply a nonporous quartz rich near surface rock as its source popigai russia is favored as the source crater because of the presence of compact quartzites in its preimpact cover

evidence for a low o2 archean atmosphere from nickel rich chrome spinels in 3 24 ga impact spherules barberton greenstone belt south africa abstract the composition of spinels in 3 24 billion year old archean impact spherules in the s3 spherule bed in the barberton greenstone belt south africa provides important clues about the environments within which they formed including the redox conditions of the impact plume and the oxygen levels in the early atmosphere despite pervasive diagenetic alteration of the impact spherules and nearly complete alteration of primary mineralogy primary ni rich chrome spinel is preserved the impact spinels are significantly more oxidized than detrital spinels of komatiitic origin that are also present in the spherule bed the average fe 3 fe t atoms value in the ni rich impact spinels is 0 43 whereas the average fe 3 fe t of detrital spinels is 0 17 fe 3 fe t ratios of the impact spinels range from 0 26 to 0 69 atoms and suggest formation at oxygen fugacities below 10 4 bar based on comparisons with experimental results comparison of the s3 impact spinels with similar spinels from the k t boundary layer eocene impact layer and late pliocene impact layer also suggests much lower o 2 levels in the 3 24 ga atmosphere oxidation of spinels present in condensed melt droplets was affected by the oxygen fugacity of the atmospheric component mixed with the ejected plume and the broad range in values may reflect f o 2 heterogeneity both temporally and spatially within the impact produced rock vapor plume compositional and morphological variability of spinels in the spherules suggests temperature and cooling rate were heterogeneous through the plume

multiple microtektite horizons in upper eocene marine sediments no evidence for mass extinctions microtektites have been recovered from three horizons in eight middle eocene to middle oligocene marine sediment sequences five of these occurrences are coeval and of latest eocene age 37 5 to 38 0 million years ago three are coeval and of early late eocene age 38 5 to 39 5 million years ago and three are of middle oligocene age 31 to 32 million years ago in addition rare probable microtektites have been found in sediments with ages of about 36 0 to 36 5 million years the microtektite horizon at 37 5 to 38 0 million years can be correlated with the north american tektite strewn field which has a fission track age minimum of 34 to 35 million years and a paleomagnetic age of 37 5 to 38 0 million years there is no evidence for mass faunal extinctions at any of the microtektite horizons many of the distinct faunal changes that occurred in the middle eocene to middle oligocene can be related to the formation of the antarctic ice sheet and the associated cooling phenomena and intensification of bottom currents that led to large scale dissolution of calcium carbonate and erosion which created areally extensive hiatuses in the deep sea sediment records the occurrence of microtektite horizons of several ages and the lack of evidence for faunal extinctions suggest that the effects of extraterrestrial bolide impacts may be unimportant in the biologic realm during middle eocene to middle oligocene time

upper devonian and mississippian foraminiferal and rugose coral zonations of belgium and northern france a tool for eurasian correlations the radiation of early carboniferous foraminifers and rugose corals following the devonian carboniferous crisis offers the best tool for high resolution correlations in the mississippian together with the conodonts in the tournaisian notably in the namur dinant basin however some of the guides are facies controlled and an integrated approach combining biostratigraphy sedimentology and sequence stratigraphy is critical to identify delayed entries potential stratigraphic gaps and to avoid diachronous correlations the main difficulty is in correlating shallow and deeper water facies at any given time in existing zonations the visean part of the scheme is always more detailed reflecting the widespread development of shallow water platforms in the early visean which created conditions more suitable for foraminifers and rugose corals over large areas in contrast the tournaisian zones less well documented reflect unfavourable environmental conditions in the lower ramp dinant sedimentation area and pervasive dolomitization of the inner ramp condroz and namur sedimentation areas recent progress in understanding the belgian early carboniferous sequence stratigraphy and lithostratigraphy and revision of the biostratigraphy of the key sections strongly modify former biostratigraphic interpretations improvements mainly concern the latest devonian the late tournaisian and the early visean the late devonian and the tournaisian are equated with foraminifer zones dfz1 to dfz8 and mfz1 to mfz8 respectively the visean correlates with zones mfz9 to mfz14 zone mfz15 straddles the visean namurian boundary and zone mfz16 is the youngest mississippian zone the rugose corals allow the recognition of ten zones rc0 to rc9 covering the strunian late famennian to serpukhovian interval discrepancies with former zonations are discussed the moliniacian stage is emended to restore the coincidence between its base and that of the visean

stratigraphic constraints on the timing and emplacement of the alika 2 giant hawaiian submarine landslide abstract previous work has found evidence for giant tsunami waves that impacted the coasts of lanai molokai and other southern hawaiian islands tentatively dated at 100 and 200 ka by u series methods on uplifted coral clasts seafloor imaging and related work off hawaii island has suggested the alika phase 2 debris avalanche as the source of the 100 ka giant wave deposits although its precise age has been elusive more recently a basaltic sand bed in odp site 842 300 km west of hawaii estimated at 100 20 ka has been suggested to correlate with this or another large hawaiian landslide our approach to the timing and linkage of giant submarine landslides and paleo tsunami deposits is a detailed stratigraphic survey of pelagic deposits proximal to the landslide feature beginning with a suite of seven piston gravity and box cores collected in the vicinity of the alika 2 slide we used u series dating techniques including excess 230 th and 210 pb profiling high resolution paleomagnetic stratigraphy including continuous u channel analysis 18 o stratigraphy visual and x ray sediment lithology and the petrology and geochemistry of the included turbidites and ash layers minimum ages for the alika phase 2a slide from detailed investigation of two of the cores are 112 15 ka and 125 24 ka 2 based on excess 230 th dating a less precise age for the alika phase 1 and or south kona slide is 242 80 ka 2 consistent with previous geological estimates oxygen isotope analyses of entrained planktonic foraminifera better constrain the alika phase 2a maximum age at 127 5 ka which corresponds to the beginning of the stage 5e interglacial period it is proposed that triggering of these giant landslides may be related to climate change when wetter periods increase the possibility of groundwater intrusion and consequent phreatomagmatic eruptions of shallow magma chambers our study indicates the contemporaneity of the alika giant submarine landslides and distal deposits from enormous turbidity currents as well as coral clasts reported to be tsunami deposits on lanai and molokai through direct dating and compositional analysis of the landslide deposits

lower carboniferous rugose corals from the arabian plate an insight from the hakkari area se turkey abstract the koprulu formation of the hakkari area se turkey is composed of a mixed carbonate siliciclastic succession of early carboniferous age the lower part of the formation yielded an abundant but poorly diversified coral fauna composed of small non dissepimented solitary rugose corals namely rotiphyllum cf simulatum fedorowski 2009 zaphrentites parallela carruthers 1910 cf gorizdronia gen et sp indet amplexizaphrentis sp and amplexizaphrentis zapense sp nov and specimens of caninia cf cornucopiae michelin in gervais 1840 a dissepimented solitary coral showing a counter septum related columella the lower part of the koprulu formation is of supposed late tournaisian age based on micropaleontological data however the coral assemblage indicates rather an early visean age the hakkari corals form a strongly facies related association cyathaxonia fauna and are compared to other areas with some difficulties the most similar time equivalent faunal associations is that of the sinai peninsula ne egypt both localities belonged during early carboniferous times to the arabian platform situated along the northern margin of gondwana the gondwana related taurides units aladag north iran block and afghanistan characterized by a dominant carbonate facies and more diversified coral faunas formed during these times the distal parts of the arabian platform

a transmission electron microscope study of chassigny evidence for strong shock metamorphism chassigny is a shock metamorphosed dunite of probable martian origin in order to determine its degree of shock metamorphism and to define the starting conditions prior to its ejection from mars the shock signature of chassigny has been carefully examined by optical and electronoptical techniques dominant shock effects are the conversion of feldspars to diaplectic glass maskelynite the clino orthoenstatite inversion strong mosaicism of olivine and the activation of numerous planar fractures and c dislocations in olivine high resolution transmission electron microscopy tem reveals additionally the coexistance of planar fractures with so far unknown discontinuous fractures in olivine these findings point to a shock pressure of 35 gpa chassigny has thus experienced a high and similar degree of shock metamorphism as the shergottites the results of this study suggest that chassigny was at a shallow target position close to the point of impact when it was ejected

homogeneous impact melts produced by a heterogeneous target sr nd isotopic evidence from the popigai crater russia the 35 7 0 2 ma old popigai crater siberia with a diameter of about 100 km is one of the best preserved large terrestrial impact structures the heterogeneous target at the impact site consists of archean to lower proterozoic metamorphic rocks of the crystalline basement upper proterozoic quartzites and other clastic deposits as well as cambrian to cretaceous clastic sediments and sedimentary rocks including carbonate rocks moreover proterozoic and permo triassic dolerite dykes are found in the target area we report major element sr and nd isotope data for 13 of these target rocks and for various types of impactites the 15 analysed impactite samples include tagamites impact melt rocks suevites and impact glass from small veins furthermore two impact breccias and two impact glass coated gneiss bombs were analysed we discuss the relation of these impactites to the target lithologies and evaluate on the basis of literature data the relation of microkrystites and associated microtektites in upper eocene sediments to the popigai event the impactites have sio2 abundances ranging from 59 to 66 wt and show significant variations in the content of fe ca and ti they have present day 87sr 86sr ratios between 0 7191 and 0 7369 their sr model ages tsrur range from 1 9 to 2 3 ga the 143nd 144nd ratios for the impactite samples cluster between 0 5113 and 0 5115 the nd model ages tndchur range from 1 9 to 2 1 ga in an echur nd eur sr diagram the impactites and upper eocene microkrystites and associated microtektites plot in a field delimited by popigai target lithologies the impactites are restricted to the field of crystalline basement rocks and upper proterozoic quartzites but they show different isotopic signatures in different crater sectors impactites and upper eocene microkrystites plot in different only partly overlapping clusters the leucocratic microkrystites and microtektites have a higher affinity to the post proterozoic rocks in the target area than the impactites seemingly the melanocratic microkrystites originated mostly from crystalline basement this data alignment supports the assumption that popigai is the source crater for all three types of ejecta for the first time clear relations are established of the geochemically variable upper eocene microkrystites and associated microtektites to specific target lithologies at popigai crater finally the observed range in sr and nd isotope parameters determined for impact melt lithologies that originated during the popigai event show a much higher variability than known from other craters this result indicates that mixing of impact melt which later formed tagamite sheets and glass particles in different impact breccias was incomplete at the time of ejecta dispersal

u th he zircon dating of chesapeake bay distal impact ejecta from odp site 1073 single crystal u th he dating has been undertaken on 21 detrital zircon grains extracted from a core sample from ocean drilling project odp site 1073 which is located 390 km northeast of the center of the chesapeake bay impact structure optical and electron imaging in combination with energy dispersive x ray microanalysis eds of zircon grains from this late eocene sediment shows clear evidence of shock metamorphism in some zircon grains which suggests that these shocked zircon crystals are distal ejecta from the formation of the 40 km diameter chesapeake bay impact structure u th he dates for zircon crystals from this sediment range from 33 49 0 94 to 305 1 8 6 ma 2 implying crystal to crystal variability in the degree of impact related resetting of u th he systematics and a range of different possible sources the two youngest zircon grains yield an inverse variance weighted mean u th he age of 33 99 0 71 ma 2 uncertainties n 2 mean square weighted deviation 2 6 probability p 11 which is interpreted to be the u th he age of formation of the chesapeake bay impact structure this age is in agreement with k ar 40ar 39ar and fission track dates for tektites from the north american strewn field which have been interpreted as associated with the chesapeake bay impact event