ground roll a potential tool for constraining shallow shear wave structure the objective of this study is to demonstrate that a laterally varying shallow s wave structure derived from the dispersion of the ground roll can explain observed lateral variations in the direct s wave arrival the data set consists of multichannel seismic refraction data from a usgs gsc survey in the state of maine and the province of quebec these data exhibit significant lateral changes in the moveout of the ground roll as well as the s wave first arrivals a sequence of surface wave processing steps are used to obtain a final laterally varying s wave velocity model these steps include visual examination of the data stacking waveform inversion of selected traces phase velocity adjustment by crosscorrelation and phase velocity inversion these models are used to predict the s wave first arrivals by using two dimensional 2d ray tracing techniques observed and calculated s wave arrivals match well over 30 km long data paths where lateral variations in the s wave velocity in the upper 1 2 km a

a 5 my chronology of carbonate platform margin aggradation southwestern little bahama bank bahamas abstract results of integrated age dating are reported from two core borings 60 m and 61 m on the southwestern margin of little bahama bank lbb on the outer margin core gb 1 seven chronostratigraphic units some unconformity bounded are correlated with of the inner margin core gb 2 about 11 km away to the north the southern margin of lbb shows a general shallowing upward succession that records three distinct intervals of differing sediment accumulation this outer margin core progresses from a relatively deep water 30 m margin at 5 6 ma to shallower reef associated sands about 5 ma and reefal conditions 5 3 ma followed by peloidal sands 3 2 ma and subaerial exposure around 2 1 ma and finally intermittent quaternary nonskeletal sedimentation 1 ma to holocene the facies indicate a change from a windward open type margin 30 m water depth to a windward protected type margin reef island this change in the platform margin may have been in response to reef accretion along the margin the long lived reefal or near reef facies in the outer margin core suggests that this margin has been predominantly aggradational since at least the earliest pliocene in contrast to the rapidly prograding margins on other bahamian platforms during the same time period however the general facies succession from transgressive highstand early pliocene to lowstand mid pliocene early pleistocene to intermittent highstand mid late pleistocene is consistent with dated successions from other platforms the three sediment accumulation intervals and their respective facies likely representing third order scale sea level fluctuations are also consistent with changes in both the proposed eustatic curve and the oxygen isotope curve

enhanced carbon dioxide outgassing from the eastern equatorial atlantic during the last glacial biological productivity and carbon export in the equatorial atlantic are thought to have been dramatically higher during the last glacial period than during the holocene here we reconstruct the ph and co2 content of surface waters from the eastern equatorial atlantic ocean over the past 30 k y using the boron isotope composition of globigerinoides ruber a mixed layer dwelling planktic foraminifera our new record combined with previously published data indicates that during the last glacial in contrast to today a strong west to east gradient existed in the extent of air sea equilibrium with respect to pco2 pco2 with the eastern equatorial atlantic acting as a significant source of co2 100 atm while the western atlantic remained close to equilibrium 25 atm this pattern suggests that a fivefold increase in the upwelling rate of deeper waters drove increased atlantic productivity and large scale regional cooling during the last glacial but the higher than modern pco2 in the east indicates that export production did not keep up with enhanced upwelling of nutrients however the downstream decline of pco2 provides evidence that the unused nutrients from the east were eventually used for biologic carbon export thereby effectively negating the impact of changes in upwelling on atmospheric co2 levels our findings indicate that the equatorial atlantic exerted a minimal role in contributing to lower glacial age atmospheric co2

neritic carbonate for six submerged coral reefs from northern australia implications for holocene global carbon dioxide abstract total contribution of six recently discovered submerged coral reefs in northern australia to holocene neritic caco3 and co2 is assessed to address a gap in global budgets caco3 production for the reef framework and inter reefal deposits is 0 26 0 28 mt holocene co2 production is 0 14 0 16 mt coral and coralline algae are the dominant sources of holocene caco3 although foraminifers and molluscs are the dominant constituents of inter reefal deposits the total amount of holocene neritic caco3 produced by the six submerged coral reefs is several orders of magnitude smaller than that calculated using accepted caco3 production values because of very low production a give up growth history and presumed significant dissolution and exports the contribution of submerged coral reefs to global holocene neritic caco3 is estimated to be 0 26 0 62 gt which yields 0 15 0 37 gt of co2 this amount of co2 is 0 02 0 05 of the 780 gt added to the atmosphere since 18 kyr bp contributions from australian submerged coral reefs are estimated to be 0 05 gt caco3 and 0 03 gt co2 for an emergent reef area of 47 9 103 km2 based on the growth history of the submerged coral reefs in the gulf of carpentaria maximum global holocene caco3 fluxes could have attained 0 3 gt yr 1 between 11 and 7 ka bp this additional caco3 would have culminated in a maximum caco3 production from all emergent and submerged coral reefs of 1 2 gt yr 1 and neritic caco3 production of 2 75 gt yr 1 the dilemma remains that the global area and caco3 mass of submerged coral reefs are currently unknown it is inevitable that many more submerged coral reefs will be found our findings imply that submerged coral reefs are a small but fundamental source of holocene neritic caco3 and co2

large scale carbonate platform development of cay sal bank bahamas and implications for associated reef geomorphology abstract the bahama archipelago consists of an arcuate chain of carbonate platforms average water depths on the platform tops such as the great bahama bank gbb are typically 10 m or less with coral reef rimmed margins thick sediment accumulations and the frequent occurrence of islands there are however exceptions for example cay sal bank csb a little studied detached bahamian carbonate platform with depths ranging from 30 to 7 m is only slightly deeper than the gbb but devoid of islands lacks platform margin coral reefs and holds little sediment on the platform top the platform is incipiently drowned csb is interesting as it is conspicuously larger 6000 sq km than other incipiently drowned platforms in the region such as serranilla bank 1100 sq km and the cat island platform 1500 sq km field and remote sensing data are assembled to provide insight into the sedimentology and geomorphology of the csb the influence of ocean climate regional hydrodynamics and holocene flooding history are investigated to understand why platform margin coral reef growth on csb has been unable to keep pace with holocene sea level rise a decade of regional sea surface temperature data for the bahamas report csb to be situated in the same ocean climate regime as gbb temperature cannot explain the platform s different morphologies the florida current has been evoked as a possible reason for the immature development of platform top processes on the csb but numeric modeling suggests its influence to be restricted to the deep flanks of the bank further sediment distribution on csb including infill patterns of karst depressions suggest trade winds easterlies to drive platform top hydrodynamics by assembling a satellite derived bathymetry map it can be shown that csb flooded earlier and at relatively higher rates of holocene sea level rise than its neighboring platforms flooding history is identified as the most feasible explanation for the atypical morphology of the csb by contrasting the present day morphology of the csb and the gbb the work emphasizes how subtle differences in relative sea level history can influence the growth of platform margin coral reefs features that in turn can conspire to set even closely neighboring carbonate platforms on divergent paths with regard to the development of marine landforms this insight is relevant to interpreting the morphological diversity of carbonate platforms in the modern ocean and in the rock record

sedimentary dynamics and high frequency sequence stratigraphy of the southwestern slope of great bahama bank abstract new geophysical data from the leeward slope of great bahama bank show how contour currents shape the slope and induce re sedimentation processes along slope segments with high current control drift migration and current winnowing at the toe of slope form a deep moat here the slope progradation is inhibited by large channel incisions and the accumulation of large mass transport complexes triggered by current winnowing in areas where the slope is bathed by weaker currents the accumulation of mass transport complexes and channel incision is rather controlled by the position of the sea level large slope failures were triggered during the mid pleistocene transition and mid brunhes event both periods characterized by changes in the cyclicity or the amplitude of sea level fluctuations within the seismic stratigraphic framework of third order sequences four sequences of higher order were identified in the succession of the upper pleistocene these higher order sequences also show clear differences in function of the slope exposure to contour currents two stochastic models emphasize the role of the contour currents and slope morphology in the facies distribution in the upper pleistocene sequences in areas of high current influence the interplay of erosional and depositional processes form a complex facies pattern with downslope and along strike facies alterations in zones with lower current influence major facies alternations occur predominately in downslope direction and a layer cake pattern characterizes the along strike direction therefore this study highlights that contour currents are an underestimated driver for the sediment distribution and architecture of carbonate slopes

tectonic and diagenetically induced seal failure within the south western great bahamas bank abstract a deep 6 km well the doubloon saxon 1 well drilled in early 1986 on the great bahamas bank shows evidence of massive seal failure through tectonic and post tectonic diagenetic alteration seal failure occurred through a hydrodynamically induced chemical alteration of a carbonate limestone dolomite evaporite anhydrite halite sequence into a carbonate dolomite and dedolomite sequence evidence for this alteration includes a thick 3 5 km fractured dolomite sequence interbedded with dedolomites fracture origins include solution collapse of original evaporites as shown by anhydrite cement on fracture surfaces and cavernous porosity and by tectonic fracturing a major reverse fault penetrated with 1 km repeat additional evidence includes a temperature regression and geochemical anomalies above and below the proposed altered sequence it is concluded that massive seal failure is a contributing factor in limiting the petroleum potential of portions of the south western bahamas platform

cat island platform bahamas an incipiently drowned holocene carbonate shelf analyses of high resolution seismic reflection profiles and surface sediment samples indicate that the cat island shelf is presently in an incipiently drowned state this small carbonate bank is characterized by a thin 4 m coarse grained relict sediment cover along with limited reef development and a relatively deep 20 30 m margin indicating that it has been unable to keep up with holocene sea level rise early flooding at relatively high rates of sea level rise 4 m kyr 1 5 8 103 yr bp in conjunction with small bank size and relatively low elevation led to a reduced rate of carbonate accumulation and incipient drowning the shelf edge currently lies beneath the zone of maximum carbonate production and exposes the interior shelf to open marine conditions which may result in permanent drowning if it is unable to catch up with continued sea level rise sediment facies patterns are largely oriented perpendicular or oblique to the shelf edge and appear to be controlled by shelf circulation patterns focused by bank margin reentrants in comparison with most of the northern bahamas the cat island shelf was flooded earlier and at relatively higher rates of holocene sea level rise which led to selective drowning implying that carbonate platforms need not drown synchronously over widespread areas as commonly thought the potential rock record of this incipient drowning event would be a thin open marine sand sheet of highly degraded cryptocrystalline and aggregate grains associated with poorly developed reefs

the paradox of drowned reefs and carbonate platforms shallow water carbonate platforms and reefs are drowned when tectonic subsidence or rising sea level outpaces carbonate accumulation and benthonic carbonate production ceases drowned platforms are common in the geologic record but they present a paradox if one considers rates of processes involved during the early holocene when sea level rose at rates of 6 000 to 10 000 m yr mm 1 000 yr most reefs and platforms were outpaced by the rising sea during the late holocene with sea level rising 500 to 3 000 m yr in the atlantic caribbean area reefs and platforms started to recover built to sea level and prograded seaward 1 000 m yr is thus a conservative estimate of the average growth potential of modern reefs and platforms independently accumulation rates of prograding platforms in the geologic record suggest growth potential in excess of several hundred microns per year the growth potential of 1 000 m yr exceeds any relative rise of sea level caused by long term processes in the geologic record newly formed ocean crust subsides at a maximum of 250 m yr basin subsidence averages 10 to 100 m yr and sea level rises due to increased sea floor spreading amount to less than 10 m yr rapid pulses of relative rise of sea level or reduction of benthic growth by deterioration of the environment remain the only plausible explanations of drowning the geologic record shows examples of both of these processes global mass extinctions of reefs and platforms occurred in the middle cretaceous eustatic rise due to submarine volcanism or desiccation of a small ocean basin and the late devonian global crisis of ocean environment extraterrestrial cause drowning controlled by regional tectonics prevailed in the jurassic and early cretaceous of the tethyan realm and the drowning of mesozoic platforms in the western north atlantic seems to have been dictated by plate tectonic drift to higher latitudes

new evidence for drowned shelf edge reefs in the great barrier reef australia we present four new high resolution multibeam bathymetry datasets from the shelf edge of the northern great barrier reef gbr analysis of these data combined with chirp sub bottom profiles and existing submersible observation data provides a fresh insight into the detailed morphology and spatial distribution of submerged reefs and terraces at the shelf edge an extensive and persistent line of drowned shelf edge reefs exist on the gbr margin in about 40 to 70 m they appear as barrier reefs up to 200 m wide and comprising twin parallel ridges of rounded pinnacles subtle yet consistent terrace and step features lie between 78 and 114 m seaward of the shelf edge reefs in the southern study area submersible observations confirm that the drowned reefs now provide a favorable hard substrate for live soft corals and algae they form a consistent and extensive seabed habitat that extends for possibly 900 km along the gbr shelf edge the submerged reef and terraces features may reflect a complex history of growth and erosion during lower sea levels and are now capped by last deglaciation reef material

discriminating between different genetic types of marine ferro manganese crusts and nodules based on rare earth elements and yttrium marine ferro manganese fe mn crusts and nodules are metal rich chemical sediments that are archives of paleoceanographic proxies and potential metal resources and targets of deep sea mining traditionally crusts and nodules are subdivided into hydrogenetic diagenetic and hydrothermal types because these are characterized by different compositions and hence economic resource potential a useable genetic classification is not only a tool for geochemical studies but may also help to characterize potential exploration targets we propose two easy to use yet robust discrimination diagrams based on geochemical relationships controlling the rare earths and yttrium rey inventory of marine fe mn oxyhydr oxide deposits the rey are a set of trace elements that show coherent behavior are routinely determined in geochemical studies and for which the analytical quality can easily be evaluated graphs of ce anomaly vs nd concentration and ce anomaly vs y anomaly effectively discriminate between the different types of precipitates regardless of their diverse mineralogical composition both hydrogenetic crusts and nodules show positive ce anomalies negative y anomalies and high nd concentrations of 100 mg kg 1 although nodules tend to have slightly lower nd concentrations than crusts in marked contrast hydrothermal deposits generally yield negative ce anomalies positive y anomalies and low nd concentrations of 10 mg kg 1 in spite of their large geochemical mineralogical and sedimentological diversity diagenetic nodules show negative ce anomalies negative y anomalies and intermediate nd concentrations between 10 and 100 mg kg 1 we discuss the geochemical background of these diagrams the respective sources of rey in the different precipitates and address the processes that control their rey inventory besides the three end members we also use rey systematics to define mixed type diagenetic hydrogenetic nodules and classify well studied international reference standards

global trends and environmental issues in nickel mining sulfides versus laterites abstract nickel ni is an important metal in modern infrastructure and technology with major uses in stainless steel alloys electroplating and rechargeable batteries economic ni resources are found in either sulfide or laterite type ores although the majority of economic resources are contained in laterite ores the bulk of historic ni production has been derived from sulfide ores since laterites require more complex processing to meet future demand for ni there is an increasing amount of ni being mined from laterite ores leading to increasing energy and greenhouse gas emission costs for ni production in many of the major ni fields of the world environmental impacts have also been significant especially in sudbury in canada and the taimyr and kola peninsulas in russia a major gap in the literature remains on historical trends in global ni mining especially with respect to primary aspects such as production known economic resources and ore grades and type this paper compiles and analyses a wide array of data on global ni mining presenting a coherent picture of major historical trends and the current industry configuration the paper includes unique historical data sets for major ni fields especially the sudbury basin and thompson fields in canada and the kambalda field in australia by understanding these critical mega trends in the ni industry it is possible to better understand unfolding global issues such as environmental impacts greenhouse gas emissions climate change and potential industry responses and whether peak nickel is a viable concept and the implications these issues have for ni production and demand the data trends and issues synthesized in this paper therefore provide a compelling picture of the ni industry and should help to inform current research and policy directions

the extension of grenville basement beneath the northern appalachians results from the quebec maine seismic reflection and refraction surveys from 1983 to 1984 the united states geological survey and the geological survey of canada undertook a series of seismic experiments to determine the crustal structure of the appalachian mountain belt in maine and southeast quebec these experiments included four deep crustal seismic reflection profiles perpendicular to the strike of regional geological trends and several high resolution refraction wide angle reflection profiles both parallel and perpendicular to strike here the data recorded in quebec and the northwest part of maine are interpreted in conjunction with existing reflection profiles from quebec synthetic seismogram calculations in laterally varying media are used to model the refraction wide angle reflection data while reprocessing migration and attribute plotting are used in the interpretation of the reflection data a major zone of reflections extending over a distance exceeding 200 km can be traced from shallow depths beneath the st lawrence lowlands southeast to about 25 km depth beneath the southeast edge of the chain lakes massif this zone of reflections is interpreted as a master decollement separating autochthonous grenville basement from overlying allochthonous rocks of the appalachian orogen including foreshortened miogeoclinal rocks the remnants of one or more magmatic arcs the connecticut valley gaspe synclinorium and the chain lakes massif in the vicinity of the chain lakes massif extension has caused grenville basement to be thinned by as much as 40 reflections from the decollement show strong layering and evidence for basement faulting associated with the guadeloupe and other faults normal incidence and wide angle reflections are observed to be almost continuous beneath the baie verte brompton line and connecticut valley gaspe synclinorium indicating that the baie verte brompton line is confined to the upper crust the connecticut valley gaspe synclinorium is characterized by p wave velocities of about 5 3 km s 1 and is shown to be a shallow structure with a maximum depth of about 3 km rock velocities immediately below the connecticut valley gaspe synclinorium are typical of chain lakes material 6 1 km s 1 a new model for the tectonic development of the region is proposed in which all pre silurian units between the baie verte brompton line and the southeastern edge of the chain lakes massif are allochthonous and confined to the upper crust we infer that the chain lakes massif volcanics of the ascot weedon formation and associated deeper crustal rocks were thrust over grenvillian basement as a composite unit and may now underlie parts of the connecticut valley gaspe synclinorium

shear wave velocity structure of sediments from the inversion of explosion induced rayleigh waves comparison with cross hole measurements rayleigh waves generated by a 10 kg dynamite explosion were recorded along a dense linear array of 47 seismic stations the array had a total length of 1 4 km and it was deployed on the sediments of the po river floodplain near the city of ferrara northern italy the recorded signals were dominated by fundamental mode rayleigh waves several techniques including multiple filter analysis phase velocity stacking and single station cross correlation were used to obtain group and phase velocity dispersion from subsets for the data set synthetic seismograms were computed for one velocity structure showing a good match to the recorded waveforms late rayleigh wave codas were characterized by persistent monochromatic ringing interpreted as due to surface waves scattered by weak lateral heterogeneities scattering within the alluvium of the great po river valley likely occurred across a reticular system of ancient secondary river beds compared to the rest of the floodplain these preferential directions of local drainage are characterized by different sedimentary environments the availability of in situ cross hole measurements of shear wave velocities allowed the comparison with our results from surface observations demonstrating that the analysis of explosion induced rayleigh waves can be used for the geophysical characterization of flat layered structures at a local scale for seismic engineering purposes

a giant underwater encrusted stalactite from the blue hole lighthouse reef belize revisited a complex history of biologically induced carbonate accretion under changing meteoric and marine conditions a late pleistocene to holocene submerged and encrusted speleothem exhibits a complex history including a meteoric phase and two marine phases a combined study using petrography mineralogy and inorganic and organic geochemistry as well as geochronology has shown that phototrophic and heterotrophic biological activity impacted carbonate precipitation during all phases of carbonate accretion the stalactite formed ca 30 m below modern sea level at a marginal overhang in the blue hole of lighthouse reef atoll unlike purely meteoric speleothems the belize example consists of a meteoric core a marine aragonite crust and a serpulid micrite rich outer crust as a result of postglacial flooding of the karst cave the core of the stalactite has a tufaceous texture containing algal or microbial remains and consists entirely of low magnesium calcite formed 19 55 10 68 kyr bp the texture suggests that the stalactite formed at the cave entrance and hence the former cave ceiling had apparently collapsed earlier during the pleistocene oxygen 18o and carbon 13c isotopes across the core suggest a trend towards drier conditions and reduced soil and plant cover after the last glacial maximum the marine aragonite crust consists of stacked botryoids in which individual crystals up to 700 lm have dark terminations enriched in high magnesium calcite this crust accreted from 10 82 to 9 95 kyr bp in warm shallow water during the early holocene thermal optimum carbonate accretion rates were considerable and averaged 125 m yr the crust has a dense laminated texture on one side and a porous shrubby texture on the other the presence of n c16 1 5 n c17 1 6 and 10me c16 fatty acids in the laminated crust suggests that sulfate reducing bacteria contributed to aragonite formation in an environment that was less open than the formation environment of the porous crust where these biomarkers are lacking n c16 1 5 n c17 1 6 or are less abundant 10me c16 enrichment of 34s and 18o in carbonate associated sulfate cas relative to seawater sulfate also suggests sulfate reduction during carbonate formation the greater contribution of heterotrophic processes to aragonite precipitation in the laminated crust is also reflected in 13c values as low as 1 3 whereas no such depletion is observed in the aragonite of the porous crust 13c values as low as 0 0 a pronounced isotopic variability and excursions to positive 13c values as high as 3 5 0 in the inner half of the laminated crust indicate an episodic local impact of photosynthesis on aragonite precipitation whereas the lack of such excursions in the porous crust 13c values as high as 1 5 0 is again best explained by a more open environment of formation after a ca 5 kyr hiatus from 4 39 kyr bp a biogenic crust of abundant serpulids and finely crystalline microbial and detrital carbonate consisting of high magnesium calcite and aragonite accreted on the outer surface of the stalactite outermost crust accretion was probably influenced by the inundation of the lighthouse reef lagoon that started to shed abundant fine grained carbonate sediment into the blue hole the stalactite broke off the cave ceiling either before or after the formation of the outermost crust likely due to seismic movements along the nearby plate boundary the study demonstrates that like speleothems from the terrestrial realm submerged stalactites may have had complex histories with great potential as paleoenvironmental archives

partitioned waveform inversion and two dimensional structure under the network of autonomously recording seismographs nonlinear optimization methods are very effective in finding models that predict optimal waveform fits to observed seismograms provided the number of model parameters is small to reduce the size of the large scale two or three dimensional seismic modelling problem path integrals over seismic velocities may be defined as model parameters instead of the seismic velocities themselves this partitions the large scale optimization problem into a number of independent small scale problems and reduces the computational effort by several orders of magnitude the path integral parameters are transformed such that their correlation matrix becomes diagonal a linear inversion performs the mapping from the space of path integral parameters into the model space of seismic velocities and makes backus gilbert resolution analysis possible the method has been applied to body wave and surface wave data from the broadband portable network of autonomously recording seismographs nars in western europe using a surface wave ray approximation to generate synthetics by mode summation waveforms were fitted for frequencies as high as 50 mhz variations in s velocity as large as 6 1 have been established with a vertical resolution of 100 150 km and a horizontal resolution as small as 400 km in parts of the model although a low velocity layer is present under the southern part of the nars array such layer is very weak or absent north of the paris basin horizontal velocity gradients are well resolved down to 400 km depth

the gomantong limestone of eastern borneo a sedimentological comparison with the near contemporaneous luconia province abstract the luconia province lying to the north of borneo is an important hydrocarbon bearing province faulting in the oligo miocene led to the uplift of a series of blocks upon which at least 240 carbonate build ups were developed in the late lower to middle miocene as part of the search for appropriate analogues an extensive field study was undertaken on the slightly older to contemporaneous gomantong limestone which outcrops in eastern sabah some 800 km to the east of the luconia province in eastern sabah southeast of the crocker range eocene to miocene clastic and subordinate carbonate sedimentary rocks were deposited in a large east west trending foreland basin the gomantong limestone outcrops in the eastern third of this basin the central sabah basin and is interpreted as having been deposited in shallower shoaling portions of the basin exposure is limited to isolated outcrops of deformed often overturned or steeply dipping carbonates the studied localities form a linear trend extending some 50 km in a ssw nne orientation the bulk of the limestone consists of coral dominated framestones and boundstones and associated fore reef and open marine facies coral morphology foraminiferal coralline red algal content and detailed sedimentological observations enabled an interpretation of the depositional settings of these carbonates to be made the varied carbonate deposits were then interpreted in terms of palaeobathymetry a very rich fauna is present throughout the formation with some intervals dominated by large benthic foraminifera particularly lepidocyclina these indicate a chattian to burdigalian age interpreted depositional environments range from open marine shelfal marls to a variety of reef associated deposits these have been subdivided on the basis of the dominant component corals coralline algae foraminifera or siliciclastic components limited burial of these carbonates has resulted in excellent preservation of these sediments with very little diagenetic alteration the gomantong limestone is interpreted to have been deposited in an open shelf setting adjacent to an east west trending shoreline this shoreline bordered a palaeohigh within the foreland basin and the basin is interpreted to have deepened to the north this is in extreme contrast to the isolated carbonate build ups in the luconia province to the west similarities in primary facies can be observed and both the gomantong limestone and luconia province exhibit evidence of drowning events but the facies are affected by very different diagenetic histories which have left the two provinces with completely different reservoir characteristics the disparity in secondary alteration shows the tremendous importance of diagenesis on the development of porosity in carbonates

retrieving lateral variations from surface wave dispersion curves surface wave analysis is usually applied as a 1d tool to estimate v s profiles here we evaluate the potential of surface wave analysis for the case of lateral variations lateral variations can be characterized by exploiting the data redundancy of the ground roll contained in multifold seismic data first an automatic processing procedure is applied that allows stacking dispersion curves obtained from different records and which retrieves experimental uncertainties this is carried out by sliding a window along a seismic line to obtain an ensemble of dispersion curves associated to a series of spatial coordinates then a laterally constrained inversion algorithm is adopted to handle 2d effects although a 1d model has been assumed for the forward problem solution we have conducted different tests on three synthetic data sets to evaluate the effects of the processing parameters and of the constraints on the inversion results the same procedure applied to the synthetic data was then tested on a field case both the synthetic and field data show that the proposed approach allows smooth lateral variations to be properly retrieved and that the introduction of lateral constraints improves the final result compared to individual inversions

evolution of the northern nicaragua rise during the oligocene miocene drowning by environmental factors abstract possible causes to explain platform drowning have been hotly debated by carbonate sedimentologists for more than a decade now in this paper we present multiple evidence to explain the drowning of a carbonate megabank that covered most of the modern northern nicaragua rise nnr during an interval spanning from late oligocene to early miocene by the interaction of several environmental factors the recovery during odp leg 165 of late oligocene to middle miocene sedimentary sequences in the sub seafloor of the modern channels and basin pedro channel and walton basin respectively that dissect the nnr site 1000 and south of the rise in the colombian basin site 999 combined with information from dredged rock samples allows us to explore in more detail the timing and possible mechanisms responsible for the drowning of the megabank and its relationship to miocene climate change the modern system of isolated banks and shelves dissected by a series of intervening seaways and basins on the nnr has evolved from a continuous shallow water carbonate megabank that extended from the honduras nicaraguan mainland to the modern island of jamaica available information suggests that this megabank broke apart and partially drowned in the late part of the late oligocene at around 27 ma and finally foundered during the late early miocene around 20 ma resulting in limited neritic coral growth in the areas where the modern isolated carbonate banks and shelves are occurring today available information also suggests that the southern and central parts of pedro channel were already a deep water area before the major episode of platform drowning and its formation predates the initiation of the caribbean current however after the partial drowning of the megabank the channel has become a major pathway for the caribbean current stratigraphic units identified in deep water carbonates sampled at odp sites 999 and 1000 help to constrain the environmental setting leading to the drowning of the banks changes in lithology and mass accumulation rates of both the carbonate and non carbonate fraction parallel stable isotope shifts and likely indicate regional changes in climate and circulation during the late oligocene middle miocene interval carbonate mass accumulation rates mars at site 999 suggest increased regional productivity during the early miocene terrigenous mars at both sites 999 and 1000 show a general increase from the burdigalian through the serravallian the temporal association among episodes of neritic platform deposition followed by increased productivity as identified by higher carbonate mars and positive excursion in carbon isotopes suggests that oceanographic changes such as local upwelling and nutrification have led to the partial drowning of the nnr megabank

submerged coral reefs in the gulf of carpentaria australia abstract we report the discovery of three submerged living patch coral reefs covering 80 km 2 in the southern gulf of carpentaria australia an area previously thought not to contain coral bioherms the patch reefs have their upper surfaces at a mean water depth of 28 6 0 5 m and were consequently not detected by satellites or aerial photographs the reefs were only recognised in our survey using multibeam swath sonar supplemented with seabed sampling and under water video their existence points to an earlier late quaternary phase of framework reef growth probably under cooler climate and lower sea level conditions than today submerged reefs with surfaces between 20 and 30 m water depth occur in other regions of the earth and existing bathymetry indicates they could be widespread in the gulf many tropical regions that today do not support patch or barrier reefs for reasons similar to the modern gulf may have done so in the past when environmental conditions were more suitable submerged reefs may provide an important refuge for corals during the next few decades when near surface reefs are threatened by widespread coral bleaching due to warmer global sea surface temperatures

seismic velocity and q model for the shallow structure of the arabian shield from short period rayleigh waves the shear velocity and q sub beta structure for the upper 1 km in different tectonic regions of the arabian shield have been investigated using high frequency vertical component records of rayleigh waves 1 20 hz which were recorded at source to receiver separations 55 80 km during a deep seismic refraction survey group and phase velocities of the fundamental and first higher modes were inverted for the shear wave velocity structure rayleigh wave attenuation coefficients were determined from the decay of the amplitude spectrum of the fundamental mode and used to invert for the q sub beta structure models derived from the data were tested by calculating synthetic seismograms for the fundamental and the first higher modes from surface wave theory with a center of compression used to represent the source both band pass filtered step and dirac delta source time functions were tested modeling indicates that the shear wave velocity of the shield increases from 2 6 km s to 3 4 km s in the upper 400 m of the crust q sub beta increases from 30 in the upper 50 m to 150 at 500 m depth the underlying material has a q sub beta of 400 500 for the outcropping igneous rocks such as granite and may reach values higher than 700 for the metamorphic green schist rock a band pass filtered dirac delta source time function produces the synthetic that is the best fit with observations

the latemar a middle triassic polygonal fault block platform controlled by synsedimentary tectonics abstract detailed field mapping of a middle triassic carbonate buildup the latemar in the western dolomites northern italy has been carried out the latemar is an isolated carbonate buildup that nucleates on a fault bounded structural high horst cut into the underlying late anisian carbonate bank of the contrin fm this study demonstrates that extensional synsedimentary tectonics is the main factor controlling its geometry and provides an age for this tectonic phase in an early phase slopes were mostly composed of well bedded clinostratified grainstones and rudstones in a later stage the deposition of grainstones was accompanied by the emplacement of clinostratified megabreccias the upper portion of slopes is a microbial boundstone with abundant tubiphytes and patches or lenses of grainstone boundstones may occasionally expand into the platform interior and downward to the base of the slope the depositional profile was that of a mounded platform the buildup is dissected by a dense framework of high angle fractures and faults and by magmatic and sedimentary dikes exhibiting two principal directions trending nnw sse and ene wsw faults trending wnw ese were also observed magmatic dikes are related to the emplacement of the nearby predazzo intrusion and are thus upper ladinian kinematic indicators of strike slip activity were observed on fault planes trending nne ssw and nnw sse that can be attributed to cenozoic alpine tectonics faults magmatic dikes and sedimentary dikes show systematic cross cutting relationships with strike slip faults cutting magmatic dikes and magmatic dikes cutting sedimentary neptunian dikes ene wsw and wnw ese faults are cut by all other structures and record the oldest tectonic activity in the region structural analysis attributes this tectonic phase to an extensional stress field with a direction of maximum extension oriented ca n s several lines of evidence including sealed faults and growth wedge geometries allow us to recognize this old tectonic phase as syndepositional and to date it to the latest anisian avisianum and crassus ammonoid biochronozones the horse shoe shape of the platform and its margins rectilinear for long tracts are explained by the existence of a network of extensional faults whose activity lasted for part of the growth of the platform the latemar is thus a polygonal fault block platform controlled by synsedimentary tectonics the resulting sedimentary architecture is that of a growth wedge deposited probably on the uplifted side of a submerged half graben continuous reactivation of faults at platform margins locally determined anomalous facies transitions with well layered platform interior directly in contact with the clinostratified slopes

controls and development of late quaternary periplatform carbonate stratigraphy in walton basin northeastern nicaragua rise caribbean sea the late quaternary sedimentary record in periplatform oozes and muds deposited on the northern nicaragua rise results from the interplay of four main controls 1 input of pelagic carbonates and bank derived fine aragonite and magnesian calcite 2 input of siliciclastic sediments 3 dispersal and removal of sediments by the caribbean current and 4 partial seafloor dissolution of metastable carbonates high accumulation rates of the calcite coarse sediment fraction throughout the study area demonstrate that planktonic foraminiferal productivity peaked during interglacial stages neritic carbonate productivity also peaked during interglacial stages when bank and shelf tops along the nicaragua rise were submerged within the photic zone because the bank and shelf tops remained mostly exposed during glacial stages the surface area available for the neritic carbonate productivity was drastically reduced to a narrow band along the margins of pedro bank and the southern shelf of jamaica a large volume of siliciclastic sediments transported from the coastal area of south america and the eastern and western regions of jamaica were deposited during glacial stages within the eastern and western deep extensions of walton basin this finding contrasts with the input pattern of siliciclastic sediments in walton basin itself where the largest input of siliciclastic sediments occurred at each of the interglacial climatic optima corresponding to intervals of maximum sea level transgression finally cores in water depths exceeding 1100 m display during interglacial stages aragonite accumulation rates systematically lower than rates in cores from water depths shallower than 1100 m this indicates that some bank derived aragonite and magnesian calcite has been partially removed by seafloor dissolution in areas from water depths exceeding 1100 m results from this study on the northeastern nicaragua rise indicate that not only do offbank transport and water column saturation state influence the late quaternary record but also that the variable strength of the caribbean current and the proximity of sources for siliciclastic sediments have played a major role in the development of the late quaternary periplatform high resolution stratigraphy

a comparison of reflection and refraction processing and interpretation methods applied to conventional refraction data from coastal maine abstract in 1984 the u s geological society collected 850 km of refraction data in lines parallel and perpendicular to regional strike of the appalachian orogen in maine and southeastern quebec a 100 km long strike line in coastal maine west of penobscot bay is here interpreted on the basis of both refracted and reflected phases techniques used in seismic reflection processing including normal movement velocity corrections and common mid point stacking were applied to the refraction data in order to enhance the visibility of reflected phases the geometries of the most laterally continuous reflections as defined by these techniques can be correlated with reflections seen on a crossing near vertical reflection profile conventional ray tracing analysis of refracted and wide angle reflected phases in the refraction data constrains the velocity structure to about 14 km depth and provides evidence for high veiocity material 6 5 km sec between 4 and 7 km depth and for lower velocities

electrical resistivity tomography imaging of the near surface structure of the solfatara crater campi flegrei naples italy we describe the results from an electrical resistivity tomography ert survey performed inside the solfatara crater located in the central part of the campi flegrei cf composite caldera the solfatara volcano represents the most active zone within the cf area in terms of hydrothermal manifestations and local seismicity eight dipole dipole ert lines have been measured with the aim of deducing a 3d resistivity model for the upper 80 m beneath the solfatara the results have allowed classification of the shallow structure below the crater into a low resistivity lr class up to about 4 m an intermediate resistivity ir class from 5 m up to 50 m and a high resistivity hr class from 60 m onward in order to solve the ambiguities arising in the interpretation of the nature of these bodies a comparison has been done between the 3d ert model and the co2 flux soil temperature and gravity maps over the same area by combining all of these parameters the whole lr body has been ascribed to a water dominated geothermal basin and the hr body to a steam gas dominated reservoir finally the ir class has been interpreted as a widespread background situation with intermediate character where volatiles and condensates can coexist in the same volumes at variable percentages coherently with the resistivity variation within this class since fluid dynamics in the solfatara crater change rapidly ert surveys repeated in the future are expected to be of great help in monitoring possible pre eruptive changes as well as in better following evolution of the local geothermal system

miocene stable isotope record a detailed deep pacific ocean study and its paleoclimatic implications deep sea drilling project site 289 in the western equatorial pacific has yielded an extremely detailed record of the carbon and oxygen isotopic changes in the miocene deep ocean the isotopic record reflects major changes in paleoclimate and paleoceanography probably dominated by a major phase of antarctic ice cap growth the transition from a relatively unglaciated world to one similar to today occurred between 16 5 x 10 6 and 13 x 10 6 years before the present with the greatest change occurring between approximately 14 8 x 10 6 and 14 0 x 10 6 years before the present

carbonate sand bodies along contrasting shallow bank margins facing open seaways in northern bahamas high resolution seismic profiling bottom sampling and aerial and space imagery show that widely contrasting carbonate sand bodies are present along the shallow windward leeward and tide dominated margins of little and great bahama banks which face open seaways the northwest providence channel and the northern straits of florida this high diversity in sand bodies and their associated bank margins is due to variations in the level duration and magnitude of the physical energy flux across the edges of the platforms in the bahamas the dominant winds waves and currents are from the east hence easterly facing margins are windward westerly facing margins are leeward where strong tidal currents are present because of adjacent basin shape the windward and leeward effects are diminished thus bank margin orientation relative to the climatic energy patterns appears to assert the major controls upon sedimentation antecedent topography in the form of islands or subtidal rock ridges creates energy barriers which can control the direction and volume of sediment flux on or off the banks along windward margins energy barriers such as large islands not only block the bankward transport of sands but appear to augment offbank transport by setting up seaward flows in contrast along leeward margins energy barriers prevent the vigorous offbank sand transport that normally occurs when these margins are open and water flow is unrestricted in addition sand body geometry and grain type are controlled by bank margin orientation along windward open margins skeletal sands accumulate in the lee of low relief mostly relict reefs these margins are generally sediment barren having only a sporadic thin veneer of sand along leeward open margins a broad 10 10 km thick 12 m bankward thinning blanket of sand rich in nonskeletal components peloids composite grains lies on top of rock ridges and reefs large asymmetric sand waves superimposed on this sand body indicate net offbank sand transport along the tide dominated margin large broad oolitic sand lobes have migrated onto adjacent lagoonal muddy sands and indicate net bankward transport we suggest the following classification of modern shallow carbonate bank margins 1 windward open 2 windward protected 3 leeward open 4 leeward protected 5 tide dominated this classification seems to fit many ancient analogs and may be useful in paleoenvironmental reconstructions

improved parameterization to invert rayleigh wave data for shallow profiles containing stiff inclusions inversion of shear wave velocity profiles from phase velocity measurements of rayleigh wave energy for sites containing stiff layers can be erroneous if such layers are not characterized in the starting or reference model incorporation of a priori knowledge then is key for converging upon a realistic or meaningful solution resolving soil profiles in desert regions where stiff layers cemented with calcium carbonate are intermixed with softer uncemented media is an application for which locating shallow stiff inclusions has important implications identification of the stiff layers is critical for foundation design and cost estimating of excavations a parameterization that seems adequate for this problem is to solve for anticipated high stiffness layers embedded in a coarser background profile that captures the general shear wave velocity trend of the study area the optimization is accomplished by using simulated annealing uncertainty measures resulting from the inversion are helpful for describing the influence of the parameterization on final model estimates

offbank transport of carbonate sands along open leeward bank margins northern bahamas abstract vigorous offbank transport of carbonate sands occurs along the west facing leeward open margins of little and great bahama bank large offbank oriented sand waves thick sand bodies covering reefs and shallow water sands mostly non skeletal obtained from adjacent deep flanks all demonstrate the existence of this shallow to deep pathway of sediment transport a variety of data suggests that transport occurs during storms and not during normal tidal current fluctuations an abundance of composite grains as well as vertical sequences of submarine cemented horizons seen via seismic profiling within the marginal sand bodies indicate cyclic periods of relative quiescence followed by moments of intense sediment movement current meter data obtained during six weeks of low wind activity show that critical threshold velocities for sand transport are only barely exceeded during portions of the tidal cycle these flows coupled with higher frequency bottom currents generated by surface gravity waves winnow the sands but do not provide significant net offbank transport offbank sand transport provides material to the shallow and deep bank margins enabling them to expand during sea level highstands each sea level fluctuation is likely to produce within the shallow margins a vertical sequence of basal reefs covered by a thick non skeletal calcarenite capped by a subaerially exposed diagenetically altered surface shallow water sands carried off the marginal escarpment help to construct deep flanks and large sediment drifts

modeled estimates of global reef habitat and carbonate production since the last glacial maximum estimated changes in reef area and caco3 production since the last glacial maximum lgm are presented for the first time based on a model reefhab which uses measured environmental data to predict global distribution of reef habitat suitable reef habitat is defined by temperature salinity nutrients and the depth attenuated level of photosynthetically available radiation par caco3 production is calculated as a function of par when minimum par levels were chosen to restrict reef growth to 30 m depth and less modern reef area totaled 584 746 10 km global carbonate production which takes into account topographic relief as a control on carbonate accumulation was 1 00 gt yr 1 these values are close to the most widely accepted estimates of reef area and carbonate production and demonstrate that basic environmental data can be used to define reef habitat and calcification to simulate reef habitat changes since the lgm the model was run at 1 kyr intervals using appropriate sea level and temperature values these runs show that at the lgm reef area was restricted to 20 of that today and carbonate production to 27 due primarily to a reduction in available space at the lower sea level and secondarily to lower sea surface temperatures nonetheless these values suggest that reef growth prior to shelf flooding was more extensive than previously thought a crude estimate of reef released co2 to the atmosphere since the lgm is of the same order of magnitude as the atmospheric co2 change recorded in the vostok ice core which emphasizes the role of neritic carbonates within the global carbon cycle this model currently addresses only the major physical and chemical controls on reef carbonate production but it provides a template for estimating shallow tropical carbonate production both in the present and in the past as such the model highlights several long standing issues regarding reef carbonates particularly in terms of better defining the roles of light temperature aragonite saturation state and topography on reef calcification

holocene sedimentation in a blue hole surrounded by carbonate tidal flats in the bahamas autogenic versus allogenic processes abstract the sediment in north atlantic blue holes preserves paleoclimate records however accurate paleoclimate reconstructions require an improved understanding of allogenic versus autogenic processes controlling blue hole sedimentation here we provide a detailed case study of the holocene stratigraphy within freshwater river blue hole which is currently surrounded by carbonate tidal flats in the northern bahamas abaco island during the holocene concomitant coastal aquifer elevation and relative sea level rise controlled internal blue hole depositional environments the general holocene facies succession observed is i basal detrital and freshwater peat ii palustrine to lacustrine marl iii algal sapropel and finally iv bedded carbonate mud during the middle holocene when groundwater levels were lower small changes in accommodation space that were inherited from the bedrock surface below

tectonic subsidence flexure and global changes of sea level tectonic models for the evolution of passive continental margins predict that following rifting sediments should progressively onlap basement at the edge of a margin as the lithosphere cools and increases its flexural rigidity with age the pattern of modelled onlap is strikingly similar to that used by vail and colleagues to estimate sea level rise through geological time this similarity suggests that major portions of stratigraphical sequences at margins may have a tectonic rather than eustatic control the patterns of onlap used by vail and colleagues may be widespread however because several widely separated passive margins rifted at similar times but they are unlikely to be worldwide

seismic stratigraphy of the blue hole lighthouse reef belize a late holocene climate and storm archive abstract five seismic units may be identified in the 8 m thick holocene sediment package at the bottom of the blue hole a 120 m deep sinkhole located in the atoll lagoon of lighthouse reef belize these units may be correlated with the succession of an existing 5 85 m long sediment core that reaches back to 1 385 kyrs bp the identification of seismic units is based on the fact that uniform fine grained background sediments show weak reflections while alternating background and coarser grained event storm beds exhibit strong reflections in the seismic profiles the main source of sediments is the marginal atoll reef and adjacent lagoon area to the east and north northeasterly winds and storms transport sediment into the blue hole as seen in the eastward increase in sediment thickness i e the eastward shallowing of the blue hole previous assumptions of much thicker holocene sediment packages in the blue hole could not be confirmed so far close to 6 m long cores were retrieved from the blue hole but the base of the sedimentary succession remains to be recovered the nature of the basal sediments is unknown but mid holocene and possibly older pleistocene sinkhole deposits can be expected the number of event beds identified in the blue hole n 37 during a 1 385 kyr long period and the number of cyclones listed in historical databases suggest that only strong hurricanes categories 4 and 5 left event beds in the blue hole sedimentary succession storm beds are numerous during 1 3 0 9 kyrs bp and 0 8 0 5 kyrs bp

depositional bias and environmental change important factors in sequence stratigraphy abstract differences among depositional systems here called depositional bias strongly influence sequence patterns siliciclastics and shallow water carbonates for instance shed most of their sediment during opposite phases of a sea level cycle lowstand shedding and highstand shedding respectively furthermore the two systems generate their own system specific relief on the sea floor disperse their sediment load along different avenues and differ in the way they are deactivated reefs and carbonate platforms can be drowned whereas siliciclastic deposition can be shut off and renewed at any depth as a consequence of these differences pronounced unconformities drowning unconformities develop where carbonate platforms are terminated and buried by siliciclastics the siliciclastic to carbonate transition tends to be more gradual drowned platforms and drowning unconformities appeared world wide in great abundance in the miocene cretaceous valanginian turonian jurassic toarcian and devonian frasnian famennian examples of drowning unconformities interpreted as sequence boundaries include those of the early cretaceous platforms off new jersey and off morocco the mid cretaceous unconformity in the gulf of mexico and miocene unconformities on top of reefs in the far east the eustatic cycles postulated from sequence stratigraphy are a very unlikely cause for the mass drownings of reefs and platforms either the rates of rise are an order of magnitude lower than the growth potential of platforms or cycle amplitudes are too small or the cycles are too short and subsidence too slow to remove platforms permanently from the photic zone the critical element in the mass drowning seems to be environmental stress that reduces the growth potential of carbonate systems thus drowning unconformities demonstrate the importance of environmental change as a control on sequence development other examples of dominantly environment controlled sequences include slope deposits shaped by shifting currents e g florida and blake plateau and basin fills that were controlled by changes in sediment input related to tectonic alteration of the drainage in the hinterland e g gulf of mexico environmental change must be considered as a third independent factor that competes with eustatic and tectonically driven regional changes of sea level for control of sequences the definition of sequences and sequence boundaries should be broad enough to include the possibility of non sea level controls

sedimentary dynamics along carbonate slopes bahamas archipelago hydroacoustic and sedimentological data in the santaren channel covering both the leeward slope of great bahama bank and the windward slope of cay sal bank allow new insights into carbonate platform slope sedimentation the data document the interplay between depositional and erosive processes on both slopes through time and provide information on the current regime and its influence on the slope sedimentary processes this study emphasizes the diversity and complexity of the slope morphology and the sediment distribution of the youngest high frequency sequence which has developed since the last glacial maximum the processes triggering slope failures and the formation of channels and gullies differ on both slopes at the leeward slope of the great bahama bank extensive slope failures occurred primarily during sea level lowering following an interglacial these slope failures created a slope morphology that channelizes the exported platform sediments during the subsequent highstand at the windward slope of cay sal bank contour currents and the local tectonic regime are responsible for slope failures during sea level lowstands downwelling induces turbidity currents the interaction of turbidity and contour currents leads to the formation of a system of furrows and slope parallel sediment ridges the discovered heterogeneities in slope sedimentation improve the understanding of carbonate slope sedimentation and provide implications for sequence stratigraphic interpretation of carbonate platform slopes

carbonates and relative changes in sea level abstract in the geologic record some of the most accurate gauges of changes in sea level are the sediment type geometry and diagenesis of carbonate shelves and platforms this is because carbonates frequently occur at or very near sea level and are usually less compacted than siliciclastics world wide changes in relative sea level the sum of eustatic sea level changes sedimentation and crustal movements have occurred repeatedly and cyclicly through geologic time producing characteristic responses in carbonates 1 1 relative rises in sea level usually caused by the cumulative effect of tectonic subsidence and eustatic rise may result in the following 1 1 a drowned carbonate reefs or platforms here carbonate growth potential is exceeded by relative sea level rise and is characterized by shallow water sediments overlain by hardgrounds and or deep water sediments some of which may be condensed sequences 1 2 b platforms where only the fast growing rim and patches of the interior are able to match sea level rise while the remainder of the platform is drowned temporarily 1 3 c platforms which keep up and maintain a flat top at sea level and contain shallow water sediments whose thickness at the least matches the height of the sea level rise if terrigenous supply is limited prograding sheets of shelf carbonate occur frequently capped by supratidal evaporites with prograding shelf margin carbonate clinoforms and turbidites if terrigenous supply is high the shelf carbonates encroach on deltaics 2 2 relative drops in sea level caused by crustal uplift or by subsidence being outpaced by a eustatic drop in sea level cause karst and soil development over shelves and platforms deposition of deep water evaporites in adjacent semi enclosed basins and in open marine basins the deposition of deltaic and aeolian clastics that bypassed the shelf falls are accompanied by platform wide fresh water diagenesis during relative sea level rises marine diagenesis is common in the subtidal portions of the shoaling upward carbonates and fresh water diagenesis and dolomitization and sulphate deposition is common in their intertidal and supratidal portions the stratigraphic significance of these reponses to relative sea level change is that many are tied to eustatic events and so are predictable within a basin of deposition

quantifying the recoverable resources of by product metals the case of cobalt abstract the long term availability of mineral resources is crucial in underpinning human society technology and economic activity and managing anthropogenic environmental impacts this availability is increasingly true for metals that do not generally form the primary product of mines such as copper or iron but instead are recovered as by products or sometimes co products during the processing of primary ores also known as companion metals e g indium cobalt molybdenum rhenium selenium these metals however can be of significant economic and technological importance both to a mine s economics and in downstream applications it is therefore useful to develop methodologies to estimate the recoverable resource for such companion metals i e the amount that could if desired be extracted and put into use over the next several decades monitoring the supply and demand of these resources is important to enable the identification of any changes that may have significant repercussions for the global economy technology needs and the environment here we derive an estimate of the recoverable resource for cobalt co a metal used with increasing frequency and in larger amounts in modern technology that is mainly recovered as a by product of copper and nickel ore processing and production co only mines are few in number and typically small in size our methodology combines the reported size of ore bodies that host co with measured or estimated co concentrations in the ores within these bodies the dominantly by product nature of co means that uncertainties exist for some of the co grades as well as recovery rates given this we also split our total recoverable co resource using a resource estimate data quality classification into high medium and low quality data depending on factors such as whether statutory resource reporting codes were used during resource reporting this methodology indicates that a minimum of 26 8 mt co is present in current global co resources with 15 2 5 6 and 6 0 mt co in high medium and low quality resources respectively applying typical recovery rates for different ore types indicates that 15 9 mt of this co is recoverable with 10 7 2 6 and 2 6 mt co recoverable in high medium and low quality resources respectively this approach provides a basis for determining similar recoverable resource estimates of other companion metals such as indium rhenium selenium etc all of which are of increasing importance in modern day life

shallow crustal structure of chicxulub impact crater imaged with seismic gravity and magnetotelluric data inferences about the central uplift summary the structure of the onshore portion of the chicxulub impact crater yucatan mexico has been studied with seismic gravity and magnetotelluric mt exploration methods a dispersion analysis of rayleigh waves along a 150 km long east west profile permitted the shallow tertiary cover to be imaged to a depth of 400 m three layers were mapped the thickness of the first two layers increase as we approach the sinkhole ring from the exterior of the crater consistent with the existence of a central basin those thicknesses change from 100 150 m outside the crater rim to more than 200 m in the terrace zone at the crater centre the first layer is again approximately 100 m thick and has a low shear wave velocity approximately 1 km s 1 its velocity is slightly larger in the rest of the profile outside the central basin we observed a third layer with a shear wave velocity larger than 1 8 km s 1 but its thickness could not be determined the velocity distribution along our profile increases monotonously with depth without low velocity layers the inferred inward slope of the two shallow layers immediately outside the central basin correlates well with a smooth gravity gradient in addition we present results of detailed gravity measurements along a profile that coincides in part with the line covered by the seismic experiment these gravity measurements were inverted to obtain a density model in this model which is of course non unique the steep gravity gradients are explained by the faults along which the slumping of the terrace blocks took place two of these may correspond to the faults observed at radial distances of 85 and 96 km in offshore seismic data finally we show results obtained using mt soundings they provide additional independent constraints on the structure of the chicxulub crater mt soundings at the centre of the crater show a sharper increase in resistivity than elsewhere in the impact structure this sharper increase in resistivity may be related to the uplifted basement of the structural high at a depth of 4 km only the mt soundings located over the central gravity high display this feature our three different data sets are independently consistent with the existence of a central structural high in the crater and support a twin peak shape for this high

a detailed assessment of global rare earth element resources opportunities and challenges rare earth elements ree are indispensable to infrastructure technology and modern lifestyles which has led to an increasing demand for these elements the current global rare earth oxides reo market is dominated by chinese production which peaked in 2006 at 133 000 tonnes reo per year accounting for some 97 1 of global production causing concern about the long term supply of ree resources although the ree consist of 17 individual elements 15 lanthanides plus scandium and yttrium that are hosted by numerous types of mineralization the relatively modest scale of the global ree mining sector has limited our knowledge of ree mineral resources and mineralizing systems compared to metals such as copper and iron which are produced in much larger quantities in order to quantitatively analyze the mineralogy concentrations and geologic types of ree deposits we compiled a global dataset of ree mineral resources based on the most recently available data 2013 2014 this compilation yields minimum global contained total rare earth oxides plus yttrium oxide treo y resources of 619 5 mt split between 267 deposits deposits with available grade and tonnage data 260 of the 267 deposits in our database contain some 88 483 mt of mineral resources at an average concentration of 0 63 treo y hosting 553 7 mt treo y of the 267 total deposits in our database some 160 have mineral resources reported using statutory mining codes e g jorc ni43 101 samrec with the remaining 107 projects having crirsco noncompliant mineral resources that are based on information available in the industry literature and peer reviewed scientific articles approximately 51 4 of global reo resources are hosted by carbonatite deposits and bastnasite monazite and xenotime are the three most significant ree minerals accounting for 90 of the total resources within our database in terms of ree resources by individual country china dominates currently known treo y resources 268 1 mt accounting for 43 of the global reo resources within our database with australia russia canada and brazil having 64 5 62 3 48 3 and 47 1 mt of contained treo y resources respectively some 84 3 mt treo y is hosted within tailings dominated by tailings from bayan obo but with smaller resources at palabora steenkampskraal and mary kathleen and 12 4 mt treo y is hosted by monazite within heavy mineral sands projects illustrating the potential for reo production from resources other than traditional hard rock mining global ree resources are dominated by the light ree having an average light reo lreo la gd to heavy reo tb lu and y ratio of 13 1 these ree deposits contain an average of 81 ppm th and 127 ppm u indicating that radioactive waste associated with ree extraction and refining could be a concern modeling the 2012 global production figures of 110 kt treo y combined with an assumed 5 annual growth in ree demand indicates that known ree resources could sustain production until 2100 and that geologic scarcity is not an immediate problem this suggests that other issues such as environmental economic and social factors will strongly influence the development of ree resources

impact of cretaceous sea level rise and anoxic events on the mesozoic carbonate platform of yugoslavia the adriatic dinaric carbonate platform of yugoslavia was influenced by rapid sea level rise and an oceanic anoxic event during the cenomanian turonian open marine biota such as planktonic foraminifera radiolarians and locally even ammonites associated with and bracketed by successions of typical shallow water carbonates indicate partial drowning of substantial areas of the platform during this time suggestive furthermore that the rate of increase of water depth was locally great enough to outpace carbonate production the presence of carbon rich and fish bearing platy limestones commonly cherty as an associated coeval facies indicates the development of anoxic or euxinic environments and the stromatolitic laminations in such rocks are attributed to the action of bacterial mats it is suggested that an extensive column of deoxygenated water developed in the neighboring marche umbrian adriatic deep water basin and was carried on to the carbonate platform during the cenomanian turonian transgression

cay sal bank bahamas a partially drowned carbonate platform abstract recent high resolution seismic reflection profiling sediment sampling scuba observations and landsat imagery show that cay sal bank csb has very limited reef development no active sand shoals few islands a thin to non existent sedimentary cover and a relatively deep margin 20 30 m and shelf lagoon system 10 20 m windward and leeward margins can be discerned but their general development is poor when compared to the shallower more active margins of little bahama bank lbb and great bahama bank gbb windward margins facing north and east along csb are generally deep rocky sediment barren terraces supporting limited low relief relict reefs leeward margins have small sand bodies maximum thickness 10 m covering reef structures at the bank edge indicating that offbank transport of sands has occurred however these marginal sand bodies are limited in areal extent suggesting that this transport system was not ubiquitous along the south and west facing margins seismic and grab sample data from the deep 200 500 m slopes seaward of the leeward margins show a thin discontinuous unit of periplatform sand containing halimeda molluscs and non skeletal components derived from shallow water the limited basinward extent no deeper than 300 m of this unit recognized by its reflection free seismic facies also indicates that sand production and transport off the bank were never prolific this is in stark contrast to new seismic data from the leeward margins of gbb which clearly show thick 20 m sand bodies covering high reefs 12 15 m along the outer margin and multiple reflection free units extending to great depths 600 m all along the adjacent slope the apparent immature development of normal bank top processes and facies and the absence of key modern depositional environments on csb may be related to the rate at which this platform was submerged due to its comparatively low elevation the initial holocene flooding occurred at approximately 8 10 ka when sea level rise was rapid 6 m ka 1 by comparison the higher lbb gbb were flooded later at a much slower rate 1 5 m ka 1 the relatively rapid flooding of csb provided little time for the shallow depositional environments to start up the continued rapid rate of sea level rise after drowning and offbank transport of sediment and the export of chilled waters formed during winter months prevented the resulting facies from catching up consequently csb appears to be partially drowned particularly when compared to the other healthier rimmed bahamian platforms drowned carbonate banks are very common in the ancient record and potentially provide excellent stratigraphic traps for hydrocarbons csb provides a modern example of a bank that may be in the very early stages of termination final drowning of carbonate platforms may occur as a result of frequent higher order sea level fluctuations superimposed on initial stage of a lower order sea level cycle

cold water stress in florida bay and northern bahamas a product of winter cold air outbreaks abstract during january 1977 three consecutive cold fronts crossed south florida and the northern bahamas which depressed shallow water temperatures below the lethal limit for most reef corals digital thermal infrared data acquired by the noaa 5 meteorological satellite in situ water temperatures and meteorological data were used to study the thermal evolution of florida bay and bahama bank waters the third and most important frontal system depressed florida bay water below 16 c a thermal stress threshold for most reef corals for 8 days the minimum water temperature recorded in situ was 12 6 c satellite data suggest that some florida bay coastal waters were at least 1 c cooler than water at this site cold water plumes detected on satellite imagery suggest that offshelf or offbank movement of cold dense water follows bathymetry controlled routes absence of viable shelf reefs opposite tidal passes supports this contention coral mortality at dry tortugas was up to 91 percent during the 1977 event coral and fish kills were also reported from other parts of the florida reef tract and northern bahamas study results show that cold water stress conditions can exist over vast shallow water areas and have residence times of several days these observations suggest that aperiodic chilling processes have a limiting influence on reef community development throughout the florida reef tract and northern bahamas

carbonate mounds in the santaren channel bahamas a current dominated periplatform depositional regime abstract new hydroacoustic data high resolution multichannel seismic reflection data ctd casts and sampling document the dominance of bottom currents and the occurrence of carbonate mounds in the santaren channel off great bahama bank and cay sal bank based on these data sets three types of carbonate mounds have been identified in water depths between 285 and 685 m their distribution is strongly related to the present current regime bank driven sediments are caught up by the currents and redeposited mainly in the channel center resulting in the accumulation of giant confined drifts flanked by moats the moats at the banks toe of slope are formed by a southward and northward flowing water mass respectively mainly antarctic intermediate water and subtropical underwater the observed carbonate mounds are concentrated in these moats mound type 1 has an elongated shape parallel to the prevailing bottom current direction a gently inclined flank facing the water flow and a steep flank in its current shadow its upstream flank is covered by a thin sediment wedge whereas the lee side is marked by a parabolic scour type 1 occurs at both bank margins but mainly off great bahama bank consisting of cold water coral rubble floating in a sediment matrix and is thus interpreted as cold water coral mound by contrast type 2 mounds are restricted to the cay sal margin and have a predominately conical outline bottom samples including living sessile crinoids show that its surface must be lithified and colonized by macroepibenthos except corals the mounds are situated in pockmark like depressions that are underlain by fluid escape structures like pipes and chimneys these fluid pathways are generated by a network of fractures mound type 2 is probably formed by abiotic carbonate precipitation however a chemoherm nature cannot be ruled out mound type 3 has a conical to polygonal shape and occurs off cay sal bank and great bahama bank it is surrounded by a scour which is elongated in downcurrent and crescent in upcurrent direction a sediment bulge formed at its front this type is consistent with blocks and boulders colonized by macroepibenthos and related to gravity controlled mass movements at the steep bank slopes principally two habitats can be distinguished the great bahama bank periplatform deep water province dominated by mound type 1 and the cay sal bank slope to basin province occupied by mound type 2 that is associated with pockmark like structures mound type 3 occurs in both habitats physical water mass properties for the existence of cold water corals are limited to a depth range of ca 430 to 685 m with seawater densities of 26 93 to 27 29 kg m and temperatures below 13 c their dominance off great bahama bank might be addressed to a more effective food supply induced by local downwelling

carbonate platform depositional sequences upper cretaceous south central pyrenees spain abstract the upper cretaceous cenomanian maastrichtian of the south central pyrenees shows five carbonate platform sequences where the major parameters are tectonism relative sea level fluctuations and inherited depositional profile depositional geometries and basin analysis permit an understanding of the depositional history five depositional sequences have been recognized 1 the santa fe sequence middle upper cenomanian a ramp to a skeletal rimmed shelf with an escarpment bypass margin the lower boundary is an angular unconformity and the upper one records a sea level drop the platform location of the margin was determined by a listric normal fault 2 an abrupt sea level rise drowned the former platform the congost sequence turonian lower coniacian a distally steepened ramp with erosional distal deep slope the depositional model was largely controlled by pre existing basin morphology cessation of platform development was due to a relative sea level drop 3 the sant corneli sequence upper coniacian lower santonian a mixed terrigenous skeletal homoclinal ramp with upright margin deep slope and dysaerobic basin the slope results from the backstepping by 24 km of the previous margin and gentle basin tilting the platform margin remained more or less at the same position and relief between platform and slope increased indicating continuous relative sea level rise the upper boundary is an angular unconformity at the platform margin produced by an abrupt sea level rise and platform drowning and by listric normal faulting 4 the vallcarga sequence upper santonian campanian a distal steepened skeletal homoclinal ramp erosional escarpment and turbidite basin which corresponds to the mesozoic maximum marine expansion a listric normal fault created two depositional areas a more or less flat footwall block with a north northwest prograding carbonate ramp

origin of temporal compositional variations during the eruption of lake purrumbete maar newer volcanics province southeastern australia the pleistocene lake purrumbete maar eruption sequence of the newer volcanics province of southeastern australia records stratigraphic temporal and geochemical variations that cannot be explained by crustal processes such as fractional crystallisation and crustal contamination samples from the lake purrumbete maar have distinct trace element trends that correlate with stratigraphic height with decreasing incompatible element concentrations from the bottom of the sequence to the top indicating that the most enriched melts were ejected during the earliest eruption stages with the least enriched melts erupted in the final stages variations in rare earth element ratios indicate that these melts were formed by dynamic melting of garnet lherzolite mantle material consistent with other volcanic centres within the basaltic cones subprovince of the newer volcanics province the geochemistry of the erupted units at lake purrumbete also record minor differentiation of the melts by olivine fractionation although these processes alone cannot explain the observed geochemical variations in the eruption sequence further differentiation of the melts by different processes such as deep clinopyroxene fractionation or assimilation of metasomatised lithosphere may be responsible for the observed geochemical trends at lake purrumbete this shows the complexity of the plumbing system of monogenetic volcanoes but also shows the opportunities that these volcanoes provide to study these processes in detail as the geochemical variations that are preserved in this type of volcanism by fast magma ascent through the crust as evidenced by the presence of fresh mantle xenoliths predominantly reflect processes that occurred in the mantle rather than in the crust