successive estimation of a tsunami wavefield without earthquake source data a data assimilation approach toward real time tsunami forecasting we propose a tsunami forecasting method based on a data assimilation technique designed for dense tsunameter networks rather than using seismic source parameters or initial sea surface height as the initial condition of for a tsunami forecasting it estimates the current tsunami wavefield tsunami height and tsunami velocity in real time by repeatedly assimilating dense tsunami data into a numerical simulation numerical experiments were performed using a simple 1 d station array and the 2 d layout of the new s net tsunameter network around the japan trench treating a synthetic tsunami calculated by the finite difference method as observed data the data assimilation reproduced the assumed tsunami wavefield before the tsunami struck the coastline because the method estimates the full tsunami wavefield including velocity these wavefields can be used as initial conditions for other tsunami simulations to calculate inundation or runup for real time forecasting

trapping and binding a review of the factors controlling the development of fossil agglutinated microbialites and their distribution in space and time trapping and binding of allochthonous grains by benthic microbial communities has been considered a fundamental process of microbialite accretion since its discovery in popular shallow marine modern examples bahamas and shark bay however agglutinated textures are rare in fossil microbialites and thus the role of trapping and binding has been debated in the last four decades recently renewed attention on this subject has produced new findings of fossil agglutinated microbialites those mainly formed by trapping and binding and analogous to modern examples but they are still few and geologically recent mainly post paleozoic when compared to the 3 5 gyr long record of microbialites in order to better understand this discrepancy between modern and fossil examples an extensive literature review is presented here providing the first thorough database of agglutinated microbialites which shows that all of them are formed in shallow marine environments and most under tidal influence in addition a lower cretaceous example is described including very diverse microbialites each of them formed in a particular paleoenvironment some of these microbialites developed in grainy settings but only those formed in marginal marine tide influenced environments accreted mainly by trapping and binding the surrounding grains being analogous of modern agglutinated microbialites and matching the environmental pattern observed in the literature database the combination of the literature review with the case study allows to discuss the factors that control and enhance trapping and binding a occurrence of grains in the microbialite environment b frequent currents that mobilize the grains and supply them onto the microbialite surface c high concentration and diversity of electrolytes in the water to increase the adhesiveness of the extracellular polymeric substances eps of the microbialite surface and d a caco3 saturation state not high enough to promote early and strong carbonate precipitation within eps which would eventually decrease its availability to adhere grains therefore this review shows that the keys to solve the trapping and binding debate may be environmental because the conjuction of these hydrodynamic and hydrochemical parameters is preferentially achieved in shallow marine settings and especially in those influenced by tides at least since mesozoic times this explains the limited environmental and stratigraphic distribution of microbialites mainly formed by trapping and binding and opens new ways to look geologically and microbiologically at this process so often cited and yet so rare

a revised tsunami source model for the 1707 hoei earthquake and simulation of tsunami inundation of ryujin lake kyushu japan 1 based on many recent findings such as those for geodetic data from japan s geonet nationwide gps network and geological investigations of a tsunami inundated ryujin lake in kyushu we present a revised source rupture model for the great 1707 hoei earthquake that occurred in the nankai trough off southwestern japan the source rupture area of the new hoei earthquake source model extends further to the hyuga nada more than 70 km beyond the currently accepted location at the westernmost end of shikoku numerical simulation of the tsunami using a new source rupture model for the hoei earthquake explains the distribution of the very high tsunami observed along the pacific coast from western shikoku to kyushu more consistently a simulation of the tsunami runup into ryujin lake using the onshore tsunami estimated by the new model demonstrates a tsunami inundation process inflow and outflow speeds affect transport and deposition of sand in the lake and around the channel connecting it to the sea tsunamis from the 684 tenmu 1361 shokei and 1707 hoei earthquakes deposited sand in ryujin lake and around the channel connecting it to the sea but lesser tsunamis from other earthquakes were unable to reach ryujin lake this irregular behavior suggests that in addition to the regular nankai trough earthquake cycle of 100 150 years there is a hyperearthquake cycle of 300 500 years these greater earthquakes produce the largest tsunamis from western shikoku to kyushu

fully coupled simulations of megathrust earthquakes and tsunamis in the japan trench nankai trough and cascadia subduction zone subduction zone earthquakes can produce significant seafloor deformation and devastating tsunamis real subduction zones display remarkable diversity in fault geometry and structure and accordingly exhibit a variety of styles of earthquake rupture and tsunamigenic behavior we perform fully coupled earthquake and tsunami simulations for three subduction zones the japan trench the nankai trough and the cascadia subduction zone we use data from seismic surveys drilling expeditions and laboratory experiments to construct detailed 2d models of the subduction zones with realistic geometry structure friction and prestress greater prestress and rate and state friction parameters that are more velocity weakening generally lead to enhanced slip seafloor deformation and tsunami amplitude the japan trench s small sedimentary prism enhances shallow slip but has only a small effect on tsunami height in nankai where there is a prominent splay fault frictional parameters and off fault material properties both influence the choice of rupture pathway in complex ways the splay generates tsunami waves more efficiently than the decollement rupture in cascadia is buried beneath the seafloor but causes a tsunami that is highly complex due to the rough seafloor bathymetry neglecting compliant sediment layers leads to substantially different rupture behavior and tsunami height we demonstrate that horizontal seafloor displacement is a major contributor to tsunami generation in all subduction zones studied we document how the nonhydrostatic response of the ocean at short wavelengths smooths the initial tsunami source relative to commonly used approach for setting tsunami initial conditions finally we determine self consistent tsunami initial conditions by isolating tsunami waves from seismic and acoustic waves at a final simulation time and backpropagating them to their initial state using an adjoint method we find no evidence to support claims that horizontal momentum transfer from the solid earth to the ocean is important in tsunami generation

the tsunami mode of a flat earth and its excitation by earthquake sources summary tsunami generation by earthquakes in a flat isotropic elastic vertically stratified earth underlying a uniform depth incompressible ocean can be studied in terms of the tsunami normal mode of the combined ocean solid earth system we derive in a way that demonstrates their natural extension from traditional approaches to tsunami theory the equations and boundary conditions governing the tsunami mode displacement and stress eigenfunctions then solve the excitation problem by a variational method this leads to a straightforward expression for the far field tsunami displace ments due to a point moment tensor source in the solid earth numerically computed spectra and waveforms reveal clearly the dependence of the far field tsunami on the source depth duration moment and mechanism

ams carbon 14 dating of microbial carbonates in holocene coral reefs western luzon philippines abstract microbial carbonates microbialites occurred in the holocene coral reefs at paraoir the philippines these microbialites appeal grayish to buff in color with a stromatolitic to thrombolitic structures and encrust on corals directly or on a thin layer of calcareous red algae or encrusting foraminifera that covered the corals first the microbialites only occur in the lower earlier parts of the holocene reef sequence where heliopora coerulea dominated no microbial carbonates were observed in the upper younger part of the holocene reefs that is interpreted to grow in water depth shallower than 6 m on the basis of coral community samples of microbial carbonate and associated coral were dated by ams 14 c the results show that the microbialites formed about 10 to 7 5 kyr bp nearly coeval to or a few hundred years younger than the corals on which the microbialites encrusted ams 14 c ages of samples recovered at reef margins are consistent to 230 th ages of corals associated with the microbialites but those recovered in the back reef are much older that the previously published 230 th ages of corals and interpreted to be reworked into the backreef it is proposed that the microbialites at paraoir formed in early holocene on reef slope when the deglacial sea level was rising rapidly after 7 5 kyr bp when the sea level rise slowed down and coral reefs caught up with sea level the condition became favorable to corals prospered in shallow water and no longer suitable for microbialite formation

microbial mats as bioreactors populations processes and products microbial mats are dynamic and complex ecosystems exhibiting spatial and temporal heterogeneity the physical chemical environment is typified by steep gradients and distinct microenvironments these microenvironments support a great diversity of species with a wide range of metabolic processes these processes often result in coupled reactions and biogeochemical cycles and produce important end products such as trace gases and mineral precipitates the latter can impact the composition and character of the sediment imparting a biosignature these biosignatures can be preserved in the rock record and are useful in the interpretation of fossil record on earth and possibly as an indication of life on other planetary bodies the modern marine stromatolites of the exuma cays bahamas provide an ideal system for studying the populations processes and products in a microbial ecosystem using a multidisciplinary approach in order to acquire redox energy microbial populations need to carry out metabolic reactions at rates faster than the equivalent chemical abiotic reactions as such microbes can be viewed as bioreactors that preferably oxidize carbon to co2 to maximize the energy yield the study of the microbial role in carbonate sedimentation and lithification in these stromatolites provides a picture of microbial mats as bioreactors producing a biosignature

microbial carbonates the geological record of the calcified bacterial algal mats and biofilms summary deposits produced by microbial growth and metabolism have been important components of carbonate sediments since the archaean geologically best known in seas and lakes microbial carbonates are also important at the present day in fluviatile spring cave and soil environments the principal organisms involved are bacteria particularly cyanobacteria small algae and fungi that participate in the growth of microbial biofilms and mats grain trapping is locally important but the key process is precipitation producing reefal accumulations of calcified microbes and enhancing mat accretion and preservation various metabolic processes such as photosynthetic uptake of co2 and or hco3 by cyanobacteria and ammonification denitrification and sulphate reduction by other bacteria can increase alkalinity and stimulate carbonate precipitation extracellular polymeric substances widely produced by microbes for attachment and protection are important in providing nucleation sites and facilitating sediment trapping microbial carbonate microfabrics are heterogeneous they commonly incorporate trapped particles and in situ algae and invertebrates and crystals form around bacterial cells but the main component is dense clotted or peloidal micrite resulting from calcification of bacterial cells sheaths and biofilm and from phytoplankton stimulated whiting nucleation interpretation of these texturally convergent and often inscrutable fabrics is a challenge conspicuous accumulations are large domes and columns with laminated stromatolite clotted thrombolite and other macrofabrics which may be either agglutinated or mainly composed of calcified or spar encrusted microbes stromatolite lamination appears to be primary but clotted thrombolite fabrics can be primary or secondary microbial precipitation also contributes to hot spring travertine cold spring mound calcrete cave crust and coated grain deposits as well as influencing carbonate cementation recrystallization and replacement microbial carbonate is biologically stimulated but also requires favourable saturation state in ambient water and thus relies uniquely on a combination of biotic and abiotic factors this overriding environmental control is seen at the present day by the localization of microbial carbonates in calcareous streams and springs and in shallow tropical seas and in the past by temporal variation in abundance of marine microbial carbonates patterns of cyanobacterial calcification and microbial dome formation through time appear to reflect fluctuations in seawater chemistry stromatolites appeared at 3450 ma and were generally diverse and abundant from 2800 to 1000 ma inception of a proterozoic decline variously identified at 2000 1000 and 675 ma has been attributed to eukaryote competition and or reduced lithification thrombolites and dendrolites mainly formed by calcified cyanobacteria became important early in the palaeozoic and reappeared in the late devonian microbial carbonates retained importance through much of the mesozoic became scarcer in marine environments in the cenozoic but locally re emerged as large agglutinated domes possibly reflecting increased algal involvement and thick micritic reef crusts in the late neogene famous modern examples at shark bay and lee stocking island are composite coarse agglutinated domes and columns with complex bacterial algal mats occurring in environments that are both stressed and current swept products of mat evolution ecological refugia sites of enhanced early lithification or all three

genesis of diamond a mantle saga a model for the genesis of natural diamond is presented based on the physical chemical and mineralogical properties and features of diamond optical studies suggest that individual diamonds have had complex growth histories in which growth and dissolution may have occurred growth was not always continuous nor did diamonds grow in necessarily similar chemical environments evidence for this is provided by variation in the nitrogen and trace element contents in diamonds as well as information from studies of the minerals included in diamond isotopic data suggest that diamonds formed from carbon whose sources varied isotopically the possibility exists that some diamonds may be products of recycled subducted carbon whereas others have formed from primordial material either through magmatic or metasomatic processes it is also likely that most diamonds formed in the archaean or proterozoic the cognate host rocks for diamond in the mantle were several but can be broadly grouped into eclogitic and ultramafic peridotitic however in mineralogic and chemical detail these rocks are quite diverse although diamond is commonly found in kimberlite and in lamproite at the earth s surface these two rocks are not genetically related to diamond formation instead they are the transporting vehicles in which diamond ascended rapidly from mantle depths to the crust

modern microbial mats in siliciclastic tidal flats evolution structure and the role of hydrodynamics microbial mats in coastal environments play an important role in both stabilizing the sediment and preserving sedimentary structures they represent the first biological systems that appeared on earth even forming large fossils in carbonate settings known as stromatolites however microbial mats have also been recognized for siliciclastic environments as sandy mat structures in particular mats are the primary element of the so called microbially induced sedimentary structures miss and their various types represent very useful proxies for the interpretation of the environmental conditions in which they were formed the objectives of this paper are twofold the first is to provide a general background review of microbial mats in tidal flats including their evolution structure and morphology the second objective is to provide a modern case study in which we examine the role of storms relative to day to day tidal currents although tidal currents could be an important eroding factor we demonstrate that waves no matter their magnitude play a significant role in developing different types of miss such as wrinkle structures and eroding mats into flipped over fragments furthermore we also show the significance of wave induced pressure onto groundwater in forming other types of miss as kinneya structures and petee ridges knowing the environmental conditions to which present day microbial mats are subject and how they evolve upon drastic changes in those conditions i e storm events represent an important basis for the interpretation of fossil miss

linked 3 d modelling of megathrust earthquake tsunami events from subduction to tsunami run up e h m t u and a a g acknowledge additional support by the german research foundation dfg projects no ga 2465 2 1 ga 2465 3 1 by bacatec project no a4 and baylat by konwihr the bavarian competence network for technical and scientific high performance computing project newwave by kaust crg gast grant no ors 2016 crg5 3027 and fragen grant no ors 2017 crg6 3389 02 by the european union s horizon 2020 research and innovation program exahype grant no 671698 cheese grant no 823844 and tear grant no 852992

hydro acoustic and tsunami waves generated by the 2012 haida gwaii earthquake modeling and in situ measurements detection of low frequency hydro acoustic waves as precursor components of destructive tsunamis can enhance the promptness and the accuracy of tsunami early warning systems tews we reconstruct the hydro acoustic wave field generated by the 2012 haida gwaii tsunamigenic earthquake using a 2 d horizontal numerical model based on the integration over the depth of the compressible fluid wave equation and considering a mild sloped rigid seabed spectral analysis of the wave field obtained at different water depths and distances from the source revealed the frequency range of low frequency elastic oscillations of sea water the resulting 2 d numerical model gave us the opportunity to study the hydro acoustic wave propagation in a large scale domain with available computers and to support the idea of deep sea observatory and data interpretation the model provides satisfactory results compared with in situ measurements in the reproduction of the long gravitational waves differences between numerical results and field data are probably due to the lack of exact knowledge of sea bottom motion and to the rigid seabed approximation indicating the need for further study of poro elastic bottom effects

composition of primary kimberlite magma constraints from melting and diamond dissolution experiments experiments are applied to constrain the composition of primary kimberlitic magmas which were in equilibrium with lithospheric peridotite and could resorb the entrained diamond to form typical dissolution features the experiments are run on samples of a model carbonatite and a melt of the udachnaya kimberlite at 6 3 gpa and 1400 c and at unbuffered or re reo2 buffered oxygen fugacity 1 2 log units above ni nio near liquidus dry fe3 free carbonatitic melt derived from carbonated harzburgite is saturated with the ol grt opx mgs assemblage and is almost inert to diamond carbonatitic melts that bear 4 6 6 8 wt fe2o3 or 1 5 wt h2o are in equilibrium only with mgs ol near the liquidus dissolution of diamond by these melts produces surface textures uncommon corrosion sculptures or common negative oriented trigons shield shaped laminae and elongate hillocks to kimberlitic diamonds the near liquidus melt of the udachnaya kimberlite yakutia with 10 12 wt h2o is saturated with the ol grt cpx assemblage and may result from melting of carbonated garnet bearing wehrlite hydrous kimberlitic melt likewise resorbs diamonds forming typical negative oriented trigons shield shaped laminae and elongate hillocks on their surfaces therefore the melts that could originate in the thermal conditions of subcratonic lithosphere entrain diamond and dissolve it to produce dissolution features on crystal surfaces were compositionally close to kimberlite 16 19 wt sio2 and rich in h2o dry fe3 bearing carbonatites with fo2 controlled by the ferric ferrous equilibrium slightly above the ni nio buffer cannot be diamond carriers

sediment effect on tsunami generation of the 1896 sanriku tsunami earthquake the 1896 sanriku earthquake was one of the most devastating tsunami earthquakes which generated an anomalously larger tsunami than expected from its seismic waves previous studies indicate that the earthquake occurred beneath the accretionary wedge near the trench axis it was pointed out recently that sediments near a toe of an inner trench slope with a large horizontal movement due to the earthquake might have caused an additional uplift in this paper the effect of the additional uplift to tsunami generation of the 1896 sanriku tsunami earthquake is quantified we estimate the slip of the earthquake by numerically computing tsunamis and comparing their waveforms with those recorded at three tide gauges the estimated slip for the model without the additional uplift is 10 4 m and those with the additional uplift are 5 9 6 7 m this indicates that the additional uplift of the sediments near the trench has a large effect on the tsunami generation

the role of endolithic cyanobacteria in the formation of lithified laminae in bahamian stromatolites the microboring activity of endolithic cyanobacteria plays a major role in the formation of the dominant lithified laminae in modern marine stromatolites in the exuma cays bahamas these stromatolites are composed primarily of fine grained carbonate sand that is trapped and bound by the filamentous cyanobacteria schizothrix sp periodic introduction of coccoid endolithic cyanobacteria solentia sp during hiatuses in stromatolite growth associated with very low rates of sedimentation results in the formation of lithified horizons 200 1000 lm thick these layers consist of micritized grains that are welded together at point contacts the micritization is caused by extensive microboring and carbonate precipitation within boreholes concurrent with endolithic activity grain welding occurs when boreholes cross from one grain to another at point contacts thus microboring destroys original grain textures but at the same time plays a constructional role in stromatolite growth by forming lithified layers of welded grains these lateral bands of fused carbonate grains help to stabilize and preserve the stromatolite deposits

on the resonant behavior of a weakly compressible water layer during tsunamigenic earthquakes tsunamigenic earthquakes trigger pressure waves in the ocean given the weak compressibility of the sea water for particular conditions a resonant behavior of the water layer can occur which influences the energy transfer from the sea bed motion to the ocean in this paper the resonance conditions are explained and analyzed focusing on the hydro acoustic waves in the proximity of the earthquake area a preliminary estimation of the generation parameters sea bed rising time velocity is given by means of parametric numerical simulations for simplified conditions the results confirm the importance of measuring modeling and interpreting such waves for tsunami early detection and warning

production and cycling of natural microbial exopolymers eps within a marine stromatolite extracellular polymeric secretions eps that are produced by cyanobacteria represent potential structuring agents in the formation of marine stromatolites the abundance production and degradation of eps in the upper layers of a microbial mat forming shallow subtidal stromatolites at highborne cay bahamas were determined using 14 c tracer experiments and were integrated with measurements of other microbial community parameters the upper regions of a type 2 reid r p visscher p t decho a w stolz j bebout b macintyre i g dupraz c pinckney j paerl h prufert bebout l steppe t des marais d 2000 the role of microbes in accretion lamination and early lithification of modern marine stromatolites nature london 406 989 992 stromatolite mat exhibited a distinct layering of alternating bgreenq cyanobacteria rich layers layers 1 and 3 and bwhiteq layers layers 2 and 4 and the natural abundance of eps varied significantly depending on the mat layer the highest eps abundance occurred in layer 2 the production of new eps as estimated by the incorporation of 14 c bicarbonate into eps occurred in all layers examined with the highest production in layer 1 and during periods of photosynthesis i e daylight hours a large pool i e up to 49 of the total 14 cbicarbonate uptake was released as low molecular weight mw dissolved organic carbon doc this doc was rapidly mineralized to co2 by heterotrophic bacteria eps degradation as determined by the conversion of 14 c eps to 14 co2 was slowest in layer 2 results of slurry experiments examining o2 uptake following additions of organic substrates including eps supported this degradation trend and further demonstrated selective utilization by heterotrophs of specific monomers such as acetate ethanol and uronic acids results indicated that natural eps may be rapidly transformed post secretion by heterotrophic degradation specifically by sulfate reducing bacteria to a more refractory remnant polymer that is relatively slow to accumulate a mass balance analysis suggested that a layer specific pattern in eps and low mw doc turnover may contribute to major carbonate precipitation events within stromatolites our findings represent the first estimate of eps

metasomatic diamond growth a multi isotope study 13c 15n 33s 34s of sulphide inclusions and their host diamonds from jwaneng botswana abstract the formation of diamond through metasomatic events from volatiles enriched fluids melts brought into pre existing mantle rocks has been suggested from a series of independent studies however the link between these hypothetical volatile rich fluids and deep seated mineral inclusions mostly silicate and sulphides entrapped in diamonds remains unclear yet the relationship between these two species may provide the key to our understanding of diamond crystallization in order to address the relationship between the origin and formation of diamonds and their mineral inclusions we carried out the first coupled stable isotopic study 13 c 15 n and multiple s isotopes as 34 s 33 s 33 s of diamonds containing sulphide inclusions using samples from the jwaneng kimberlite as our model system sulphides extracted from the present collection of 55 diamonds belong to either eclogitic e type 52 diamonds or peridotitic p type 3 diamonds paragenetic suites as attested by their cr and ni content cr 0 18 wt and ni 14 wt for p types sulphur isotopic compositions have been measured in situ by multicollector secondary ion mass spectrometry and reveal that peridotitic sulphide inclusions in diamonds n 4 lie on the terrestrial fractionation line whereas mass independent sulphur isotope fractionations mif are preserved inside eclogitic sulphides inclusions 0 5 33 s n 33 such large mif values extended here to the negative values recorded in archean sediments are thought to be produced through photochemical reactions in the archean atmosphere which implies that sulphides inclusions contain an archean sedimentary sulphur component that was transferred to the earth s mantle in contrast to this isotopic dichotomy between e type and p type sulphides the geochemical characteristics of their host diamonds 13 c 15 n n content n speciation are largely homogeneous throughout the population and differ from silicate bearing diamonds previously studied in the same locality sulphide bearing diamonds appear to define a distinct population which might reflect a different crystallization process characterized by carbon and nitrogen isotopic compositions falling within the range of unfractionated mantle values the lack of a distinct isotopic signature of recycled sedimentary nitrogen and carbon in sulphide bearing diamonds leads us to infer that sulphide bearing jwaneng diamonds were not derived from the same chemical reservoir as their inclusions one possible formation mechanism that is compatible with our observations is diamond crystallization from a mantle derived carbon bearing fluid associated with pre existing sedimentary sulphide minerals this model has important implications for the interpretation of diamond ages obtained from sulphide inclusions using re os systematics here we suggest that the incorporation of a significant amount of mantle related sulphur during a diamond growth event into the original sulphide could lead to a re equilibration of the re os isotope composition in any inclusion and accordingly account for some scatter on re os isochrons

scattering of teleseismic p waves by the japan trench a significant effect of reverberation in the seawater column abstract we detected a scattered wave train in data from the high sensitivity seismograph network in japan hi net following the arrival of the near vertically incident p wave generated by the 2009 earthquake mw 7 8 off the south island of new zealand the scattered wave train represented predominantly vertical ground motion at a period of 20 to 50 s and with an apparent velocity of 3 5 km s it propagated cylindrically westward through the kanto area of central japan array analysis showed that the scattered wave train developed beneath the pacific ocean near the boso triple junction southeast of the kanto area a 3d finite difference simulation of seismic wave propagation using a high resolution model incorporating subsurface structure topography and bathymetry revealed that the strong scattered waves that were generated along the japan trench and propagated normal to the trench axis represented multiple reverberations of seismic waves between the seafloor and the pacific plate boundary in addition strong reverberation of acoustic waves in the seawater column above the boso triple junction causes elongated scattered waves which reasonably explains our observations

magnetic susceptibility as a biosignature in stromatolites abstract microbialites have long been a focus of study in geobiology because they are macroscopic sedimentary records of the activities of microscopic organisms however abiotic processes can result in microbialite like morphologies developing robust tools for substantiating the biogenicity of putative microbialites remains an important challenge here we report a new potential biosignature based on the detrital magnetic mineral component present in nearly all sedimentary rocks detrital grains falling onto a hard abiogenic chemically precipitated structure would be expected to roll off surfaces at high incline angles thus the distribution of grains in an abiogenic microbialite should exhibit a dependence on the dip angle along laminae in contrast a microbialite formed by the active trapping and binding of detrital grains by microorganisms could exhibit a distribution of detrital grains significantly less dependent on the dip angle of the laminae however given that most ancient stromatolites are micritic composed of carbonate mud tracking detrital grains vs precipitated carbonate is not straightforward recent advances in our ability to measure miniscule magnetic fields open up the possibility to map magnetic susceptibility as a tracer of detrital grains in stromatolites in abiogenic carbonate precipitation experiments magnetic susceptibility fell to zero when the growth surface was inclined above 30 the angle at which grains rolled off in cyanobacterial mat experiments even vertically inclined mats held magnetic material the results indicate that cyanobacterial mats trap and bind small grains more readily than abiogenic carbonate precipitates alone a variety of stromatolites of known and unknown biogenicity were then analyzed tested stromatolites span many different ages eocene to holocene and depositional environments hot springs lakes and compositional forms micritic sparry crusts etc the results were consistent with the laboratory results the results of these experiments suggest that magnetic susceptibility shows promise as a new biosignature in the study of putative microbialites

on the unusual characteristics of the diamonds from letseng la terae kimberlites lesotho abstract the letseng la terae kimberlites are situated 3100 m above sea level in the maloti mountains of lesotho southern africa the principal economic bodies are two late cretaceous low grade 1 3 5 carats hundred ton cpht kimberlite pipes that host high value diamonds realising us 2000 2500 carat ct in 2008 terms locally the larger kimberlite body is referred to as the main pipe 17 2 ha and the smaller one is called the satellite pipe 5 2 ha these pipes and their associated eluvial and proximal alluvial deposits are renowned for yielding large d colour gem quality diamonds including 100 carat ct stones earlier artisanal effort 1959 1977 and formal mining 1977 1982 produced 335 000 carats cts including the 601 ct lesotho brown in 1968 in 2003 letseng diamonds limited re commenced mining operations and had produced 265 000 cts by the end of july 2008 including 24 100 ct diamonds the largest of which was the 603 ct lesotho promise we report here on the unusual characteristics of the letseng diamond population that include i 75 gem quality that is more commonly associated with alluvial diamond deposits ii large average stone size of ca 1 carat stone ct stn that is also more typical of certain alluvial diamond placers iii high yielding rounded to flattened irregular resorbed dodecahedral shapes main pipe 67 and satellite pipe 87 with subordinate dodecahedral macle main pipe 32 and satellite pipe 12 and broken ca 1 forms in both pipes the octahedral component is virtually absent iv economically favourable colour mix ca 33 white colour diamonds in both pipes v abundance of nitrogen free d colour type iia diamonds that dominate the internationally recognised special stone size fraction which covers all diamonds larger than 10 8 cts main pipe 32 and satellite pipe 51 during 2008 these larger special diamonds commanded prices in excess of us 15 000 ct contributing ca 75 of the revenue generated by the letseng mine furthermore of the 24 100 ct diamonds recovered between november 2003 and july 2008 18 75 were type iia d colour diamonds that also fetched prices mostly in excess of us 25 000 ct therefore the type iia diamonds boost significantly the revenue per unit measure in this case the us ton of the letseng la terae pipes making these low grade kimberlites economic to mine

sedimentology and petrography of dredged carbonate sands from stocking island bahamas implications for meteoric diagenesis and aeolianite formation abstract piles of carbonate sand dredged onto stocking island exuma chain bahamas during world war ii are now relatively well lithified down to a depth of about 80 cm and may contain up to 8 of interstitial calcite cement a volume comparable to that measured from 1000 yr old beach ridges elsewhere in the bahamas rates of meteoric diagenetic changes are thus more rapid than previously assessed in this area 600 cm3 of calcite cement produced by m3 of rock per year preservation of hydrodynamic sedimentary structures footprints and the lack of aeolian bedforms e g dunes ripples on the surface of these sediments further show they have not been reworked by the wind at all therefore the carbonate aeolianites of holocene and pleistocene ages forming the bulk of the islands of bermuda and the bahamas were likely deposited during relatively dry periods when the effects of meteoric diagenesis were limited reduced moisture along with sediment availability and wind energy appears as a key player in carbonate aeolianite genesis

three dimensional cathodoluminescence imaging and electron backscatter diffraction tools for studying the genetic nature of diamond inclusions as a step towards resolving the genesis of inclusions in diamonds a new technique is presented this technique combines cathodoluminescence cl and electron backscatter diffraction ebsd using a focused ion beam scanning electron microscope fib sem instrument with the aim of determining in detail the three dimensional diamond zonation adjacent to a diamond inclusion ebsd reveals that mineral inclusions in a single diamond have similar crystallographic orientations to the host within 0 4 the chromite inclusions record a systematic change in mg and cr from core to the rim of the diamond that corresponds with a 80 c decrease of their formation temperature as established by zinc thermometry a chromite inclusion positioned adjacent to a boundary between two major diamond growth zones is multi faceted with preferred octahedral and cubic faces the chromite is surrounded by a volume of non luminescent diamond cl halo that partially obscures any diamond growth structures the cl halo has apparent crystallographic morphology with symmetrically oriented pointed features the cl halo is enriched in 200 ppm cr and 80 ppm fe and is interpreted to have a secondary origin as it overprints a major primary diamond growth structure the diamond zonation adjacent to the chromite is complex and records both syngenetic and protogenetic features based on current inclusion entrapment models in this specific case a syngenetic origin is favoured with the complex form of the inclusion and growth layers indicating changes of growth rates at the diamond chromite interface combined ebsd and 3d cl imaging appears an extremely useful tool in resolving the ongoing discussion about the timing of inclusion growth and the significance of diamond inclusion studies

synthesizing ocean bottom pressure records including seismic wave and tsunami contributions toward realistic tests of monitoring systems the present study proposes a method for synthesizing the ocean bottom pressure records during a tsunamigenic earthquake firstly a linear seismic wave simulation is conducted with a kinematic earthquake fault model as a source then a nonlinear tsunami simulation is conducted using the sea bottom movement calculated in the seismic wave simulation by using these simulation results this method can provide realistic ocean bottom pressure change data including both seismic and tsunami contributions a simple theoretical consideration indicates that the dynamic pressure change caused by the sea bottom acceleration can contribute significantly until the duration of 90 s for a depth of 4000 m in the ocean the performance of a tsunami monitoring system was investigated using the synthesized ocean bottom pressure records it indicates that the system based on the hydrostatic approximation could not measure the actual tsunami height when the time does not elapse enough the dynamic pressure change and the permanent sea bottom deformation inside the source region break the condition of a simple hydrostatic approximation a tsunami source estimation method of tfish is also examined even though the synthesized records contain a large dynamic pressure change which is not considered in the algorithm tfish showed a satisfactory performance when 5 min after the earthquake occurrence the pressure records synthesized in this study including both seismic wave and tsunami contributions are more practical for evaluating the performance of our monitoring ability whereas most tsunami monitoring tests neglect the seismic wave contribution

occurrence and significance of microbialites in the uplifted tasmaloum reef sw espiritu santo sw pacific abstract in the sw pacific ocean subduction of the d entrecasteaux ridge system has caused rapid uplift of the central new hebrides island arc the maximum uplift rate of 6 mm yr 1 occurs along the southwest coast of espiritu santo island near tasmaloum the tasmaloum uplifted reef sequence internal structure which is strongly linked to its tectonic context was investigated through a series of drill holes to depths up to 42 m although a stable tropical coast would undergo approximately 120 m of post glacial sea level rise the net relative sea level rise on such a rapidly uplifting coast is only about 20 m colonization of the tasmaloum fringing reef occurred by 24 ka upon a pre reef substrate composed of a thick bioclastic sand formation accumulated during the last glacial period during the post glacial sea level rise the vertical succession of reef assemblages reflects environmental and bathymetric variations controlled by the interplay of rapid but variable rates of sea level rise and more or less constant uplift of 5 6 mm yr 1 microbialite crusts composed of high magnesian calcite laminae occur in the tasmaloum reef from 20 to 6 ka and are particularly abundant from 16 to 10 ka the development of microbialite crusts is related to nutrient enrichment of interstitial waters through mixing with meteoric groundwater after 6 ka when sea level ceased rising in the region and continuing uplift caused rapid emergence of the reef microbialites disappear within the subtidal assemblages several explanations can be put forward for their disappearance in particular nutrient input changes are a likely cause a new hydrologic and oceanographic regime was established when sea level ceased rising this change was accompanied by warming of tropical waters

conditions of diamond growth a proton microprobe study of inclusions in west australian diamonds crystalline primary inclusions in diamonds from the argyle and ellendale lamproites have been analyzed for mn ni cu zn ga pb rb sr y zr nb ta ba and mo by proton microprobe eclogite suite inclusions dominate at argyle and occur in equal proportions with peridotite suite inclusions at ellendale eclogitic phases present include garnet omphacitic clinopyroxene coesite rutile kyanite and sulfide eclogitic clinopyroxenes are commonly rich in k and contain 300 1060 ppm sr and 3 70 ppm zr k rb increases with k content up to 1400 at 0 7 1 1 k rutiles have high zr and nb contents with zr nb 1 5 4 and nb ta 16 of the peridotite suite inclusions olivine commonly contains 10 ppm sr and mo cr pyropes are depleted in sr y and zr and enriched in ni relative to eclogitic garnets

seismogenic deformation structures in microbialites and mudstones silurian lockport dolomite northwestern ohio u s a syndepositional deformation structures are present at two different stratigraphic levels in the silurian lockport dolomite at a quarry in maumee ohio such structures are absent in this unit at twelve other quarries in northwestern ohio the structures at maumee present within stromatolites thrombolites and variably bedded mudstones include convolute layers homogenization of bedding and breccia clasts clasts of stromatolites boudinage structures normal reverse and thrust faults and discordant and concordant breccias the distribution of deformation structures within beds suggests substantial control from substrate rheology possibly resulting from differences in degrees of lithification and from variations in water content the extensive variety of syndepositional deformation structures juxtaposed evidence for nearly synchronous compression and dilation proximity 4 5 km of the structures to the largest fault in northwestern ohio the bowling green fault and the restricted geographic distribution of the deformation structures suggest seismic shaking as a probable mode of genesis similarities between features produced by seismogenic deformation of siliciclastic sediments and deformation features in the lockport dolomite provide additional evidence that the latter features are seismogenic it is postulated that two earthquakes one with a magnitude 5 caused the formation of the syndepositional deformation structures present in the youngest facies in the lockport dolomite at maumee quarry the bowling green fault 4 5 km west of maumee was a growth fault during formation of the lockport dolomite and is considered to have been the source of earthquakes that created the syndepositonal deformation structures in this unit at maumee quarry evidence from the lockport dolomite in northwestern ohio suggests that seismogenic deformation structures created by two earthquakes along the bowling green fault with magnitudes of 5 did not form in this unit over large areas i e all of northwestern ohio this evidence challenges the suggestion that syndepositional seismogenic deformation structures are always formed over a large area

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

crystal forms and surface textures of alluvial diamonds from the western region of the central african republic the most common crystal forms of the diamonds from the alluvial deposits in the western region of the central african republic were examined by scanning electron microscope sem in an attempt to determine their geological history the marks observed are related to two distinct periods in the geological history of the diamonds the magmatic episode and their hydraulic transport the effects of significant magmatic corrosion undergone by the diamonds during their ascent from the upper mantle are shown by the predominance of rhombododecahedral forms over octahedral forms and the frequent occurrence on the crystal faces of pyramidal depressions with triangular 111 or square 100 bases as well as of v shaped figures 111 or stepped figures on the faces around the ternary axes some impact marks probably occurred during the explosive episode of kimberlite extrusion other impact marks the marks of general wear and the high proportion of gemstone quality diamonds indicate the lengthy transport they thus also indicate that the diamonds have undergone a prolonged geological history after the erosion of the kimberlite this suggests that the kimberlite are separated from the carnot sandstone formation by a considerable distance the diamonds were stored in albian maastrichtian rocks before they become concentrated in the recent alluvium

submerged upper holocene beachrock on san salvador island bahamas implications for recent sea level history sedimentological petrographic and radiometric data from a submerged beachrock on san salvador island bahamas provide new information about the late holocene sea level history in this area

synthesizing sea surface height change including seismic waves and tsunami using a dynamic rupture scenario of anticipated nankai trough earthquakes abstract the development of offshore observation technology will provide researchers with tsunami records from within an earthquake focal area but this will create new problems because seismic waves coexist with tsunami inside a focal area the seismic waves could act as noise for the tsunami signal this study shows an efficient method to calculate sea surface height change caused by an earthquake including both seismic waves and tsunami simulation results indicate that seismic waves overlap with tsunami both affect the change in sea surface height although most previous tsunami studies have neglected the contribution of seismic waves we also numerically simulated the sea surface displacement wavefield and hypothesized results for an anticipated rupture scenario of a huge earthquake that may possibly occur in the nankai trough japan the synthesized record could be used to evaluate the performance of a real time tsunami prediction method additionally we discussed the similarity and difference between two kinds of tsunami waveforms the displacement of the sea surface and the pressure change at the sea bottom although seismic waves appeared in both waveforms the contribution of seismic waves was lower in the displacement at the sea surface than in the pressure change at the sea bottom

theoretical basis of the amplitude source location method for volcano seismic signals the source location method using high frequency seismic amplitudes based on the assumption of isotropic radiation of s waves has been used successfully to locate seismic events and tremor at volcanoes this amplitude source location asl method overcomes the limitations of traditional hypocenter determination methods that use onset arrival times and has great potential to improve volcano seismic monitoring and the investigation of source processes of volcano seismic signals however theoretical justification of the basic assumption used in the asl method has not been provided in previous studies in this study we tested the asl method by using seismic waveforms simulated with a finite difference method in realistic heterogeneous volcanic structures with intrinsic attenuation and topography our results showed that asl determinations were successful when using waveforms characterized by multiple scattering that can be approximated by the diffusion model we found that the energy solution of the diffusion model provided an amplitude distance relation that is similar to that used in the asl method our results suggest that the asl method is applicable to high frequency seismograms in highly heterogeneous media with transport mean free paths of 103 m or smaller and strong intrinsic attenuation these medium parameters are consistent with those estimated at various volcanoes our study validates the basic assumption of the asl method and justifies its use to locate the sources of high frequency seismic signals observed at volcanoes

origin and significance of lamination in lower cretaceous stromatolites and proposal for a quantitative approach stromatolite lamination is typically defined as alternation of dark and light laminae study of lower cretaceous stromatolites fromthe leza fm n spain supports this statement but recognises additional complexities in lamination that have implications for interpreting accretion processes these stromatolites are partial analogues of present day coarse grained carbonate stromatolites in the bahamas and shark bay australia that mainly form by trapping and binding carbonate sand the leza examples contain both grain rich and micrite rich laminae with scarce particles suggesting that they accreted both by trapping and not trapping grains lamination in modern and ancient coarse grained stromatolites is commonly defined by thinmicritic crusts that formed during interruptions in accretion and separate contiguous grainy laminae repetitive lamination leza examples also contain these thin hiatal crusts and locally showrepetitive lamination but their conspicuous macroscopic lamination is defined by thicker alternating grain rich and micrite rich laminae alternating lamination this indicates that although hiatuses in accretion occurred change in accretion process was the main cause of macroscopic lamination these differences in accretion processes and lamination styles between leza examples and modern coarse grained stromatolites may reflect differences in their environmental settings modern examples occur in shallow marine tidal environments whereas leza fm coarse grained stromatolites developed in ideinfluencedwater bodies in coastal wetlands that experienced fluctuations inwater salinity and hydrochemistry analysis of lamina thickness in these cretaceous stromatolites and similar published examples provides a quantitative approach to the processes that underlie stromatolite lamination

near field tsunami forecasting from cabled ocean bottom pressure data 1 we propose a method for near field tsunami forecasting from data acquired by cabled offshore ocean bottom tsunami meters obtms in real time we first invert tsunami waveforms recorded at obtms to estimate the spatial distribution of initial sea surface displacements in the tsunami source region without making any assumptions about fault geometry and earthquake magnitude then we synthesize the coastal tsunami waveforms from the estimated sea surface displacement distribution to improve the reliability of the tsunami forecasting we use updated obtm data to repeat the forecast calculation at 1 min intervals we tested our method by simulating the 1896 sanriku tsunami earthquake which caused a devastating tsunami with maximum runup height of 38 m along the pacific coast of northeastern japan instead of real obtm records proxies were used the simulation demonstrated that our method provided accurate estimations of coastal arrival times and amplitudes of the first peak of the tsunami more than 20 min before the maximum amplitude wave reached the coastal site nearest to the source we also applied the method to real data of a small tsunami that was caused by a local earthquake and successfully forecasted the tsunami at coastal tide stations we found that accuracy of our estimated coastal tsunami amplitudes can be affected by the spatial relationship between the tsunami source and the offshore observation stations our numerical simulation showed that even more accurate tsunami amplitude forecasts would be achieved by deployment of additional offshore stations separated by a distance comparable to the trench parallel length of the tsunami source

ground motion in kuwait from regional and local earthquakes potential effects on tall buildings in recent years the construction of tall buildings has been increasing in many countries including kuwait and other gulf states these tall buildings are especially sensitive to ground shaking due to long period seismic surface waves although kuwait is relatively aseismic it has been affected by large mw 6 regional earthquakes in the zagros fold thrust belt zftb accurate ground motion prediction for large earthquakes is important to assess the seismic hazard to tall buildings in this study we first analyze the observed ground motions due to two earthquakes widely felt in kuwait the 08 18 2014 mw 6 2 earthquake 360 km nne of kuwait city and the 11 12 2017 mw 7 3 earthquake 642 km nne of kuwait city the peak spectral displacement periods of the ground motion from the 08 18 2014 mw 6 2 earthquake matched well with the ambient vibration spectra of the tallest building the al hamra tower we calculate the ground motions from potential regional and local earthquakes we use a velocity model obtained by matching the observed seismograms of the 2014 and 2017 earthquakes we calculate ground motions in kuwait due to a regional mw 7 5 earthquake and a local mw 5 0 earthquakes our study shows that a significant source of seismic hazard to tall buildings in kuwait comes from the regional tectonic earthquakes however local earthquakes have the potential to generate high peak ground accelerations 98 cm s2 close to their epicenters

recycling of crustal materials through study of ultrahigh pressure minerals in collisional orogens ophiolites and mantle xenoliths a review abstract newly recognized occurrences of ultrahigh pressure uh p minerals including diamonds in ultrahigh temperature uh t felsic granulites of orogenic belts in chromitites associated with ophiolitic complexes and in mantle xenoliths suggest the recycling of crustal materials through deep subduction mantle upwelling and return to the earth s surface this circulation process is supported by crust derived mineral inclusions in deep seated zircons chromites and diamonds from collision type orogens from eclogitic xenoliths in kimberlites and from chromitities of several alpine himalayan and polar ural ophiolites some of these minerals contain low atomic number elements typified by crustal isotopic signatures ophiolite type diamonds in placer deposits and as inclusions in chromitites together with numerous highly reduced minerals and alloys appear to have formed near the mantle transition zone in addition to ringwoodite and inferred stishovite a number of nanometric minerals have been identified as inclusions employing state of the art analytical tools reconstitution of now exsolved precursor uh p phases and recognition of subtle decompression microstructures produced during exhumation reflect earlier uh p conditions for example tibetan chromites containing exsolution lamellae of coesite diopside suggest that the original chromitites formed at p 9 10 gpa at depths of 250 300 km the precursor phase most likely had a ca ferrite or a ca titanite structure both are polymorphs of chromite and at 2000 c would have formed at minimum pressures of p 12 5 or 20 gpa respectively some podiform chromitites and host peridotites contain rare minerals of undoubted crustal origin including zircon feldspars garnet kyanite andalusite quartz and rutile the zircons possess much older u pb ages than the time of ophiolite formation these uh p mineral bearing chromitite hosts evidently had a deep seated evolution prior to extensional mantle upwelling and partial melting at shallow depths to form the overlying ophiolite complexes these new findings together with stable isotopic and inclusion characteristics of diamonds provide compelling evidence for profound underflow of both oceanic and continental lithosphere recycling of surface organic carbon into the lower mantle and ascent to the earth s surface through mantle upwelling intensified study of uh p granulite facies lower crustal basement and ophiolitic chromitites should allow a better understanding of the geodynamics of subduction and crustal cycling

stromatolite lamination frequency walker lake nevada implications for stromatolites as biosignatures lamination in stromatolites considered some of the oldest fossils on earth is commonly interpreted to record the periodic response of a microbial community to daily seasonal or perhaps yearly environmental forcing but the inability to date ancient stromatolites precludes an understanding of the lamination formation processes we use high resolution 14c dating of holocene stromatolites from walker lake nevada united states to construct a record of lamination rate over the course of accretion laminae formed with a period of 5 6 1 6 yr lamination at the base of the structure 1 6 2 8 1 9 yr lamination in the middle and 4 5 0 8 yr lamination at the top of the laminated portion the predominant 4 6 yr periodicity indicates that lamination formation is likely more closely related to regional climate forcing e g el nino southern oscillation versus the typical diurnal or seasonal changes in microbial mats traditionally assumed for most ancient stromatolites thus generalizations regarding the influence of microbial mats on stromatolite lamination and the use of stromatolites as biosignatures need careful consideration

microbialites in a modern lagoonal environment nature and distribution tikehau atoll french polynesia abstract microbialites including stromatolitic structures gelatinous masses and mats develop in tikehau lagoon tuamotu french polynesia on the flanks and slopes of numerous pinnacles and motu islets between 0 and 25 m deep on coral colonies algal tufts or on lagoonal sediments individual stromatolitic structures consist of hemispherical domes and are produced by monospecific populations of filamentous cyanobacteria belonging to three distinctive phormidium species symploca and possibly to one new species of schizothrix gelatinous masses hanging from the ceiling of caverns are produced by phormidium laysanense microbial mats are well developed at all depths on pinnacle slopes and are produced by either monospecific or mixed cyanobacterial populations the study of micro and ultrastructure of stromatolites reveals that they result both from trapping and binding of sediments and from carbonate precipitation in addition to phototrophic biomineralization pervasive carbonate precipitation occurred in association with decaying organic matter the basic constructional elements of the precipitated carbonate consist of 0 1 0 2 m rounded bodies that form very fine anhedral to subhedral micrite their surfaces comprise extremely small carbonate granules 20 50 nm gradual changes ageing in the ultrastructure of carbonate precipitates include the precipitation of successive euhedral calcite layers around these grains widespread development of microbialites in this pristine lagoonal environment results from rapid blooms of microbial benthic communities possibly induced by temporary and local nutrient pulses nutrients seem to undergo a restricted circulation between the sediment and pinnacle reef frameworks pinnacles and reef islets are repeatedly affected by catastrophic storm events which cause redistribution of sediments and nutrients

microbial biofacies and the influence of metazoans in holocene deposits of the lagoa salgada rio de janeiro state brazil

stromatolite provinces of hamelin pool physiographic controls on stromatolites and associated lithofacies recent studies recognized distinct stromatolite provinces in hamelin pool western australia each with morphologically distinct stromatolite structures paired with characteristic shelf physiography in the present paper we couple detailed lithofacies mapping with hamelin pool bathymetry and consider physiography as a control of sedimentation processes including stromatolite development bathymetric transects derived from a high resolution bathymetry map with depths from 0 to 11 meters allow calculation of slope gradients in the provinces as in other settings bathymetry is linked to energy regimes which in turn appear to be coupled with variations in stromatolite morphologies and associated lithofacies as follows 1 low gradient ramps with low energy settings are associated with sheet mats and elongate clustered stromatolites that exhibit regular spatial patterns possibly indicative of self organization 2 low gradients coupled with high energy settings resulting from strong winds result in seif stromatolites with pronounced directional bands 3 medium to steep gradients coupled with medium to high energy are associated with individual and merged stromatolites often with thin basal necks 4 headlands and promontories where the topography deflects currents are associated with elongate nested stromatolites and 5 medium to high energy slopes typically found at promontory edges and shelf margins are dominated by blocky pavement observations linking stromatolite morphology to physiography in a modern microbial system provide insight into the long lived debate about biology versus environment in controlling stromatolite morphology when physiography leads to a high energy regime environmental controls are the main factor determining stromatolite morphology in contrast when physiography promotes a low energy environment the response of biological communities becomes the main driver of macroscale stromatolite morphology

microbial foraminiferal episodes in the early aptian of the southern tethyan margin ecological significance and possible relation to oceanic anoxic event 1a two regionally significant microbial foraminiferal episodes 150 kyr each occur within the early aptian shallow marine platform in oman and throughout eastern arabia the stratigraphically lower of these two intervals is characterized by isolated or coalescent domes that share similarities with modern open marine stromatolites from the exuma cays bahamas the upper interval is predominantly built by a problematic lithocodium bacinella consortium in buildup and massive boundstone facies based on highresolution chemostratigraphy these shoalwater intervals are coeval with oceanic anoxic event 1a oae1a livello selli field evidence demonstrates that the buildup episodes alternate with stratigraphic intervals dominated by rudist bivalves this biotic pattern is also recognized in other coeval tethyan sections and is perhaps a characteristic shoalwater expression of the oae1a the short lived regional expansions of this microbial foraminiferal out ofbalance facies cannot be explained by local environmental factors salinity and oxygen level alone and the buildup consortia do not occupy stressed refugia in the absence of grazing metazoans judging from recent analogues the main fossil groups i e microbial assemblages macroalgae larger sessile foraminifera and rudist bivalves all favoured elevated trophic levels but with different tolerance limits the implication of this is that the influence of palaeofertility events possibly related to oae1a on carbonate platform community structures must be investigated the observations made in these coastal sections are a significant first step for the improved understanding of the early aptian period of biotic oceanic and climatic change

automicrites in modern cyanobacterial stromatolitic deposits of rangiroa tuamotu archipelago french polynesia biochemical parameters underlaying their formation this paper provides evidence of the role of the proteinaceous constituents of the sedimentary organic matter in the control of ca mg carbonate precipitation within recent stromatolitic sediments belonging to the kopara type rangiroa tuamotu archipelago french polynesia millimeter to cm thick alternating carbonate rich and carbonate poor layers allow the separation by hand of these two contrasted types of layers with respect to carbonate content the study aims 1 to decipher the potential compartments cyanobacterially derived and dissolved organic matter for proteins that interact with divalent cations to compare their biochemical composition with those of the intramineral organic matrices that incorporate fine authigenic micrites when they form 2 to discriminate the ageing processes of organic matter including om mineralized by caco3 3 to correlate the biochemical features of protein rich molecules dissolved in natural pore waters extracted from different sediment layers either carbonate rich or carbonate poor with experimental tests of the efficiency of these same protein rich molecules in the role of calcium carbonate inhibitors the extracted natural macromolecules definitely control the rate of in vitro calcium carbonate precipitation they exert an inhibiting effect which strength depends on the type of layer carbonate rich or carbonate poor out of which they have been extracted the quality with respect to their aspartic and or glutamic acid contents as well as the amount of soluble protein rich macromolecules present in the pore waters in each layer plays a key role in active calcification processes as a matter of fact pore waters of carbonate poor layers deliver high concentrations of dissolved aspartic rich macromolecules that are shown to inhibit strongly calcium carbonate precipitation in experimental conditions the consequence of such experimentally based results as well as the correlation with the actual intensity of calcification in natural sediment layers is crucial for discussing calcium carbonate balance or the formation of laminations in paleoenvironments

tsunami waveform inversion including dispersive waves the 2004 earthquake off kii peninsula japan 1 long waves are often assumed to model tsunamis but the wavelength of the initial water height distribution produced by a large submarine earthquake particularly in the direction perpendicular to the fault strike is sometimes not much greater than the water depth the resulting tsunami may have a dispersive character that cannot be simulated based on a conventional long wave approximation the 2004 earthquake off kii peninsula m 7 4 on the southern coast of japan indeed produced a dispersive tsunami that was recorded at two stations located off shikoku for the foreshock m 7 1 on the contrary a dominant dispersive tsunami was not recognized at these stations because dispersive waves show strong directional dependence with respect to the fault strike the above difference indicates that the strikes of the main shock and the foreshock were different we conducted a tsunami waveform inversion analysis based on the dispersive tsunami equations to estimate the initial water height distribution of the main shock the estimated initial water height distribution overlapped with the aftershock region suggesting that the fault strike was perpendicular to the trough axis and the total displaced water volume was 1 7 2 0 109 m3 when we used the conventional long wave approximation the estimated initial water height distribution extended considerably from the aftershock area because artificial sources were needed outside the aftershock area to reproduce the observed dispersive waves

fdm simulation of seismic waves ocean acoustic waves and tsunamis based on tsunami coupled equations of motion we have developed a new unified modeling technique for the total simulation of seismic waves ocean acoustic waves and tsunamis resulting from earthquakes based on a finite difference method simulation of the 3d equations of motion using the equilibrium between the pressure gradient and gravity in these equations tsunami propagation is naturally incorporated in the simulation based on the equations of motion the performance of the parallel computation for the newly developed tsunami coupled equations using a domain partitioning procedure shows a high efficiency coefficient with a large number of cpu cores the simulation results show how the near field term associated with seismic waves produced by shallow earthquakes leads to a permanent coseismic deformation of the ground surface which gives rise to the initial tsunami on the sea surface propagation of the tsunami along the sea surface as a gravity wave and ocean acoustic waves in seawater with high frequency multiple p wave reflections between the free surface and sea bottom are also clearly demonstrated by the present simulations we find a good agreement in the tsunami waveform between our results and those obtained by other simulations based on an analytical model and the navier stokes equations demonstrating the effectiveness of the tsunami coupling simulation model based on this simulation we show that the ratio of the amplitude of ocean acoustic waves to the height of the tsunami both of which are produced by the earthquake strongly depends on the rise time of the earthquake rupture this ratio can be used to obtain a more detailed understanding of the source rupture processes of subduction zone earthquakes and for implementing an improved tsunami alert system for slow tsunami earthquakes

environmental controls on microbial community cycling in modern marine stromatolites living stromatolites on the margins of exuma sound bahamas are the only examples of modern stromatolites forming in open marine conditions similar to those that may have existed on precambrian platforms six microbial mat types have previously been documented on the surfaces of stromatolites along the eastern side of highborne cay schizothrix solentia heterotrophic biofilm stalked diatom tube diatom and phormidium mats cycling of these communities create laminae with distinct microstructures subsurface laminae thus represent a chronology of former surface mats the present study documents the effects of environmental factors on surface microbial communities of modern marine stromatolites and identifies potential causes of microbial mat cycling mat type and burial state at 43 markers along a stromatolitic reef on the margin of highborne cay were monitored over a two year period 2005 2006 key environmental parameters i e temperature light wind water chemistry were also monitored results indicated that the composition of stromatolite surface mats and transitions from one mat type to another are controlled by both seasonal and stochastic events all six stromatolite mat communities at highborne cay showed significant correlations with water temperature heterotrophic biofilms solentia stalked diatom and phormidium mats showed positive correlations with temperature whereas schizothrix and tube diatom communities showed negative correlations a significant correlation with light photosynthetically active radiation par was detected only for the heterotrophic biofilm community no significant correlations were found between mat type and the monitored wind intensity data but field observations indicated that wind related events such as storms and sand abrasion play important roles in the transitions from one mat type to another an integrated model of stromatolite mat community cycling is developed that includes both predictable seasonal environmental variation and stochastic events the long term monitoring of mat communities on highborne cay stromatolites and the resulting model are an important step in understanding morphogenesis of modern marine stromatolites with implications for interpreting patterns of stromatolite lamination in the geologic record

tem analysis of microbial mediated sedimentation and lithification in modern marine stromatolites three sedimentary processes are involved in the growth of living stromatolites at highborne cay bahamas 1 trapping of oolitic sands 2 formation of surface micritic crusts and 3 formation of fused grain laminae the microbial role in each process was investigated by examining the stromatolites using transmission electron microscopy species composition and physiological state of the bacteria were discerned by ultrastructure a well dispersed population of schizothrix gebeleinii was observed in rapidly accreting surface layers their filaments produce copious quantities of amorphous exopolymer and condensed sheath that surround individual and pairs of cells both fresh and degraded sheaths are however devoid of carbonate precipitates this suggests that the primary roles of s gebeleinii are the trapping and binding of unconsolidated sediment and the production of extra cellular polymeric secretions surface micritic layers are composed primarily of needle shaped crystals of aragonite the uppermost surface of the micritic crust is coated with a biofilm comprised primarily of small gram negative bacteria i e sulfate reducing bacteria that range in size from 250 to 500 nm in diameter and up to 1 m in length empty cyanobacterial sheaths and occasional gram positive spores were also observed thin sections through resin casts of ooid microborings in the fused grain laminae show cells of the endolithic cyanbacterium solentia sp and evidence of an organic matrix the micritic crusts and fused grain layers became lithified laminae that were preserved at depth although the organisms that formed them were not this suggests that morphological remains of these organisms i e microfossils in ancient stromatolites should not be expected

analytical model for gravity and rayleigh wave investigation in the layered ocean earth structure in terms of the linear theory of elasticity we analyze the gravity and rayleigh wave excitation and propagation process in a three layered ocean earth model which includes a superficial liquid layer and two layers of sediments soft and hard to compute the oceanic surface wave dispersion function the thomson haskell matrix method is used the solution is obtained by applying the normal mode formalism to the flat homogeneous layered ocean earth structure based on this theory the spectra of the excitation functions are investigated in detail for 45 thrust dip slip and strike slip point sources in the half space a numerical experiment reveals that the rigidity of the rock exerts a strong influence on both gravity and rayleigh waves in the case of rayleigh waves a layered structure of the bottom strongly affects the propagation process the main focus of the present study is to model tsunami and tsunamigenic events it is well known from observations that earthquakes that generate abnormally large tsunamis are mostly thrust events characterized by long source duration 2 4 times longer than typical earthquakes of similar moment and shallow source depth and are located near the trench axis meanwhile typical tsunamigenic earthquakes are generally dip slip and thrust events with depths between 15 and 50 km on this basis and using the distributed model of seismic source the influence of source mechanism location and source duration on the tsunami wave amplitude are investigated here the results of our model computations of the seismic sea waves from tsunami and tsunamigenic earthquake are in good agreement with real observation data

scattering of trapped p and s waves in the hydrated subducting crust of the philippine sea plate at shallow depths beneath the kanto region japan

micro tsunami from a local interplate earthquake detected by cabled offshore tsunami observation in northeastern japan a micro tsunami from an interplate earthquake mw 6 1 was observed in 1998 on ocean bottom tsunami meters obtms deployed east off the northeastern japan the offshore tsunami data without complex distortions due to the coastal topography enable us to estimate reliable tsunami source parameters the observed amplitude was about 1 5 cm at epicentral distance less than 100 km we numerically computed the tsunami waveform by solving the linear boussinesq equations the observed tsunami waveforms are well explained by synthetic waveforms assuming the fault width of 10 15 km the depth of the fault is estimated as 5 10 km below the seafloor which is in good agreement with the location of the plate boundary defined by previous seismic studies

delineating and quantifying depositional facies patterns in carbonate reservoirs insight from modern analogs modern carbonate settings have long been used as analogs for interpreting various environments of deposition in subsurface data sets based on well log and core data and have provided examples of how these environments can be interrelated within a larger context this study focuses on carbonate sands in the exuma islands part of the great bahama bank to show how modern settings can be better used for reservoir analogs by emphasizing visualization and quantification techniques that conceptually delineate aspects of potential grainstone reservoir distribution and heterogeneity along the windward margin of the exumas the association of tidal deltas channels and islands forms an exploration scale linear belt of mostly ooid sand approximately 5 10 km 3 1 6 mi wide and 170 km 106 mi long paralleling the platform margin but set back from the platform edge the distribution of carbonate sands in the exumas was assessed with a digital elevation model and satellite imagery by selecting different water depth intervals parts of the sand belt were highlighted for visual analysis and extracted for measurements of size and shape for example 37 of the sand belt comprises shallowest sands in which the largest areas greater than 100 000 m2 1 07 million ft2 are highly sinuous and maintain connectivity the sand belt was also subdivided into various depositional settings flood tidal delta lobes comprise 85 of the sand belt tidal channels and islands add further heterogeneity to the sand belt channels average about 3 km 1 8 mi in length and have regular but locally variable spacing a representative island shows how the syndepositional topography of holocene ridges develops complexly around antecedent pleistocene topography

boron partitioning in the upper mantle an experimental and ion probe study piston cylinder experiments were performed on two natural spinel lherzolites from lherz french pyrenees and kilbourne hole usa in order to determine the distribution coefficients of boron between minerals and melt for upper mantle conditions additionally a morb glass and its phenocrysts were taken as a low pressure analogue boron concentration measurements were made by ion probe the only technique suitable for in situ 10 m boron concentration measurements in the range 0 1 1 ppm the two starting peridotites samples have low bulk boron concentrations of 0 96 and 0 81 ppm boron distribution coefficients were determined from 1 direct measurement of melt and crystals in contact and 2 calculations from profiles of several tens of measurements made using 10 m diameter spots containing variable proportions of crystals and melt distribution coefficients between minerals and melt decrease in the following order dcpx melt 0 117 dsp melt 0 08 dol melt 0 034 dopx melt 0 027 the limited ranges of composition pressure and temperature investigated mimic natural conditions for basalt genesis but sharply limit the present data for determining variations of partition coefficients with p t and x however boron behavior seems to follow roughly that of aluminum since the al richest minerals are the ones with the highest boron distribution coefficients the dol melt values increase with pressure which is similar to what has been observed for the distribution coefficient of aluminum between olivine and melt boron is therefore strongly incompatible during partial melting in the mantle using these distribution coefficients and assuming that morb have been produced by 5 20 partial melting the depleted mantle source of morb is estimated to contain 0 05 0 3 ppm b these values correspond to the lower limit for the mean boron content of chondrites 0 55 0 3 ppm but are in accordance with a simple budget of boron between mantle crust and seawater in fact a simple mass balance calculation where all the boron hosted in the crust and in seawater is presumed to have been extracted from an upper mantle of chondritic original boron content yields a boron content for the depleted upper mantle of 0 3 ppm at present because in situ boron concentration measurements under the ppm level at the m scale are now possible with the ion probe and because of its strong partitioning in melts and possible partitioning in fluids boron is a potentially very powerful geochemical tracer for the study of mantle processes such as basalt genesis or metasomatism

microbial deposits in upper miocene carbonates mallorca spain the santanyi limestone a 30 35 m thick upper miocene limestone succession cropping out in mallorca contains abundant microbialite deposits the shape microstructure and texture of which was controlled by environmental factors depth energy and salinity three main types of microbialites are distinguished 1 domed dnos and stratiform mostly undulate unos non oolitic stromatolites 2 undulate oolitic laminites uol and 3 domed oolitic thrombolites dots based on lithofacies associations and occurrence of microbialite types the santanyi limestone succession is subdivided into five stratigraphic units i to v separated by sharp surfaces within units ii iii and v the vertical evolution of microbialites was induced by changes in accommodation space depth 1 intertidal very shallow subtidal conditions at the base were induced by flooding over a wide area 2 continued sea level rise caused submergence to subtidal conditions and 3 a significant bathymetric decrease created the sharp surface bounding these units in units ii and iii nos accumulated in variable energy and depth conditions as buildups with thick somewhat discontinuous and mostly non isopachous lamination surrounded by oolitic grainstones with wave and current structures and oolitic intraclasts in contrast thin and generally regular and smooth lamination of nos in unit v suggests along with the absence of oolite grainstones and macrobiota calm and restricted maybe more saline conditions uol consisting of oolitic layers separated by thin micritic laminae developed adjacent to nos in units ii and iii and to dot at the lower part of unit iii in shallow water and low energy conditions both ooids and micrite laminae have evidence for biogenesis micritized ooids containing microbial remains are common micritic laminae in uol and the dark micritic laminae in nos are thought to represent bacterially enhanced calcite precipitation and lithification during periods of low sedimentation oolitic thrombolites containing macrobiota are only present in unit iii they represent deeper and open marine conditions affected by high energy events in which microbially mediated precipitation favoured microbialite accretion and lithification

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

intertidal stromatolites in a fringing holocene reef complex bahamas intertidal stromatolites are major components of a fringing holocene reef complex at stocking island exuma cays bahamas trapping and binding of fine grained carbonate sand by microorganisms primarily filamentous cyanobacteria and diatoms and differential lithification of sediment have produced layered structures with up to 0 5 m of relief formation of these stromatolites in an environment of normal marine salinity is attributed to reduced competition from crustose red algae availability of a stable substrate and rapid cementation destruction of lamination in stocking island stromatolites by molluscs sponges and worms suggests that boring invertebrates play a key role in stromatolite preservation

seismic and tsunami wave propagation of the 2011 off the pacific coast of tohoku earthquake as inferred from the tsunami coupled finite difference simulation abstract the 2011 tohoku earthquake m 9 0 caused significant hazards including strong ground motion coseismic ground deformation and tsunamis for a deeper understanding of these phenomena we conducted a large scale parallel computer simulation by means of the finite difference method fdm with newly developed tsunami coupled equations of motion this method is based on the equations of motion for an elastic medium treating seawater as elastic material having zero s wave velocity tsunami waves are included by taking into account gravity and their equilibrium with the pressure gradient an effective method of fdm simulation using the state of the art massively parallelized k computer is also studied with the use of a 3d layered velocity structure that includes topography and bathymetry basement structure moho depth and plate boundaries and use of the appropriate source rupture model based on joint inversion of seismic waves and geodetic observations the simulated seismic waves demonstrate anomalous seismic wave propagation by the thick 3d basin structure inland we also found that the sea column acts as a strong absorber of seismic waves for shallow up dip slip on the ocean side coseismic deformation and tsunamis are dynamically generated in this simulation tsunami attacks on the subsided pacific coast are simulated without any additional assumptions we also modeled the tsunami and seismic records of ocean bottom pressure gauges above the fault because sea bottom tsunami and seismic observation is powerful but very complex recording both seismic and tsunami waves the use of these coupled numerical simulations has great potential for resolving complex source fault rupture processes in a 3d heterogeneous structure online material mpeg movies of fault slip seismic wave propagation seafloor and ground displacement and tsunamic propagation

simulation of tsunami induced by dynamic displacement of seabed due to seismic faulting in conventional tsunami simulation techniques simplifications have been employed by neglecting the dynamic seabed displacement resulting from fracturing of a seismic fault and considering only the static contribution the water layer is also assumed to be incompressible regardless of its acoustic effects they should be reconsidered in light of the state of the art technology because considerable discrepancies between numerical simulations and actual observation have been pointed out regarding for example arrival time and wave height in the present study tsunami simulation is conducted without using these kinds of simplification taking into account both the dynamic displacement and acoustic effects as a result thus simulated tsunamis are found to be remarkably larger in the wave height especially in the near fault area where these two effects are superposed in far field however tsunamis thus simulated are likely to show little difference in the wave height but show considerable difference in the arrival time in addition the present dynamic analysis is capable of simulating the water wave induced by the rayleigh wave propagated along the seabed

three dimensional simulation of tsunami generation and propagation application to intraplate events 1 a parallel finite difference numerical simulation program based on the navier stokes ns equations is developed for simulating 3 d tsunami generation and propagation we can simulate tsunami propagation over more than 1000 km using this program although such tsunami propagation over long distances has usually been conducted on the basis of on 2 d simulations some 2 d simulations have assumed that the initial tsunami distribution is identical to the sea bottom deformation caused by the earthquake the 3 d simulations however indicate that this assumption is inappropriate when the source width 2ax is less than 10 times the sea depth h 2ax 10h for a source process time of 20 s dispersion of tsunami appears when the source is of small size and the dispersion is more apparent in a direction perpendicular to the fault strike we also conduct tsunami simulations for two intraplate events the 2004 off kii peninsula m 7 4 and the 2007 off kuril islands m 8 1 events the 3 d tsunami simulation has successfully simulated the offshore tsunami and we obtained good agreement between the observations and the calculations for both events in particular for the 2004 off kii peninsula event although the 2 d linear long wave theory cannot simulate important characteristics in the record such as the arrival time of the peak amplitude and the dispersive tsunami the 3 d ns simulation is well able to model those characteristics

kimberlites in western liberia an overview of the geological setting in a plate tectonic framework the liberian kimberlite field lies in the southern part of the west african craton closely associated kimberlites are present in sierra leone ivory coast guinea and mali and as a group are structurally controlled within the archean basement complex of the leo uplift three major kimberlite dike lineaments are recognized in the northwest sector of liberia all with prominently developed n ne trends these lineaments are termed the kumgbo wuese trend the border trend and the lofa trend the areas of dike intrusion are covered by the bopolu geological quadrangle map of liberia the border trend is close to sierra leone the kumgbo wuese trend is to the east and the lofa trend is coincident with the lofa river only one kimberlite pipe has been recognized in liberia mano godua but a second may be present and both lie along the kumgbo wuese trend the kimberlite bodies intrude the 2700 m y old liberian age province which is comprised of granitic and granodioritic gneiss complexes two prominently developed features dominate the province a general ne sw basement fabric and an en echelon dolerite dike system that parallels the coast dated at 180 m y and considered to represent intrusion at the onset of continental fragmentation transecting dikes and related faults suggest a relative age for the kimberlites of 180 m y an estimate that corresponds to the 92 to 140 m y age for the sierra leone field there is indirect evidence that kimberlites in guinea and mali are of a similar age based on the fact these are on strike with kimberlites in liberia and sierra leone respectively trans atlantic correlations between west africa and northeast south america reveal a cyclic eruption of magma types that were generated in response to plate and continental movements it is postulated that liberian kimberlite emplacement was related to postplate motion crustal flexuring that reactivated precambrian basement sutures these sutures are parallel to and correlate with recognizable paleorift and paleocompressional zones within and adjacent to the west african craton long sustained periods of tectonic activity can be demonstrated and it is proposed that if brittle fractures are continuously reactivated these will serve as conduits to the upper mantle tapping kimberlite source regions at depths in excess of 100 km

graphite diamond relations in mantle rocks evidence from an eclogitic xenolith from the udachnaya kimberlite siberian craton relations of graphite and diamond have been studied in a garnet kyanite clinopyroxene sulfide coesite quartz diamond graphite eclogite xenolith from the udachnaya east kimberlite pipe in the yakutian diamond province euhedral crystals of diamond and graphite occur in the intra and intergranular space the equilibrium conditions of diamond formation reconstructed by geothermobarometry for the grt cpx ky coe mineral assemblage are 1020 40 c and 4 7 gpa raman imaging of graphite enclosed in diamond shows high ordering and a 9 cm 1 shift of the 1580 cm 1 band this raman shift of graphite as well as a 5 cm 1 shift of the 1332 cm 1 band of diamond indicate large residual stress in graphite and in diamond around the inclusion respectively according to ftir spectroscopy nitrogen in diamond is highly aggregated and exists mainly as the a centers while no other phases occur near graphite inclusions therefore diamond in the analyzed eclogite sample must be quite old it likely had crystallized long 1 byr before it became entrained with kimberlite melt new data show that graphite can stay in the upper mantle for billions of years without converting to diamond crystallization of various carbon polymorphs both in laboratory and natural systems remains poorly constrained graphite present in mantle and uhp rocks may be a metastable phase crystallized in the diamond stability field this fact should be taken into consideration when deducing petrological constrains and distinguishing diamond and graphite subfacies in upper mantle

crystallographic orientations of magnesiochromite inclusions in diamonds what do they tell us we have studied by x ray diffractometry the crystallographic orientation relationships cors between magnesiochromite mchr inclusions and their diamond hosts in gem quality stones from the mines udachnaya siberian russia damtshaa botswana and panda canada in total 36 inclusions in 23 diamonds in nearly half of the cases n 17 111 mchr is parallel within error to 111 diamond but the angular misorientation for other crystallographic directions is generally significant this relationship can be described as a case of rotational statistical cor in which inclusion and host share a single axis 1 df the remaining mchr diamond pairs n 19 have a random cor 2 df the presence of a rotational statistical cor indicates that the inclusions have physically interacted with the diamond before their final incorporation of all possible physical processes that may have influenced mchr orientation those driven by surface interactions are not considered likely because of the presence of fluid films around the inclusions mechanical interaction between euhedral crystals in a fluid rich environment is therefore proposed as the most likely mechanism to produce the observed rotational cor in this scenario neither a rotational nor a random cor can provide information on the relative timing of growth of mchr and diamond some multiple iso oriented inclusions within single diamonds however indicate that mchr was partially dissolved during diamond growth suggesting a protogenetic origin of these inclusions