growth and high resolution paleoenvironmental signals of rhodoliths coralline red algae a new biogenic archive we investigated rhodoliths coralline red algae from a subtropical locality in the gulf of california lithothamnium crassiusculum and a subarctic locality in newfoundland lithothamnium glaciale for their potential as paleoenvironmental archives using microanalytical geochemical techniques to measure variations in 18o mg and ca rhodoliths are potentially well suited as recorders of shallow water paleoenvironmental signals because they 1 have worldwide distribution from the tropics to polar regions 2 are long lived from decades to centuries and 3 display well developed growth bands our results indicate that rhodolith growth bands preserve ultrahigh resolution records of paleoceanographic paleoclimatic change and likely constitute an important new archive for reconstructing the paleoenvironmental history of littoral neritic areas in which these algae are found the 18o content of individually sampled rhodolith growth bands ranges from 2 4 to 4 6 in l crassiusculum and from 3 2 to 0 3 in l glaciale in both cases the range of 18o values suggests a slightly lower amplitude of variation in sea surface temperature than that actually measured in the ocean at the two study sites both l crassiusculum and l glaciale show a negative offset from isotopic equilibrium electron microprobe analysis of magnesium and calcium in growth bands reveals cyclic variations with values ranging between 7 7 18 5 mol mgco3 in l glaciale and 13 2 22 5 mol mgco3 in l crassiusculum in addition electron microprobe element maps highlight individual growth bands provide a powerful approach to study rhodolith formation and indicate that the specimens we analyzed have vertical growth rates of 250 450 m yr

grain fabric of experimental gravity flow deposits abstract grain fabric of deposits accumulated from a high density surge type gravity turbidity current in an experimental flume was measured vertical sequential change 0 2 mm interval in imbrication shows that a bed can be divided into lower middle upper and uppermost parts the lower part is characterized by both up current and down current imbrication with a wide range of angles dominant up current imbrication and rare down current imbrication characterize the middle part the imbrication angle of this part tends to be smaller than in the lower part the upper part is represented by intervals with up current imbrication nearly flat imbrication is dominant in the uppermost intervals statistically significant preferred orientation was observed from the lower middle and upper parts and it deviates up to 13 in both clockwise and anticlockwise directions from the current direction the lower and middle parts of the bed may correspond to the bouma a division judging from the wider range of imbrication angles and the presence of down current imbrication which have been reported from natural turbidite beds the upper part which is characterized by up current imbrication is interpreted to be the bouma b division the uppermost interval may coincide with the d division the episodically appearing down current imbrication in the lower and middle parts can probably be attributed to oscillation of an interface between a denser basal layer and superjacent low density layer of the turbidity current measurement of grain orientations in this and previous studies implies that at least 30 of deviation from the flow axis should be considered for paleoflow analyses based on grain fabrics

assessing the reliability of magnesium in foraminiferal calcite as a proxy for water mass temperatures though many studies on the mg contents in the calcitic tests of foraminifers exist the processes controlling its uptake are still a matter of debate laboratory cultures offer an excellent opportunity to reveal these mechanisms the mg concentrations within single chambers of the planktic foraminifer globigerinoides sacculifer brady maintained under controlled laboratory conditions were measured 1 at variable temperatures 19 5 29 5 c and constant salinity and 2 at variable salinity 22 45 and constant temperature the experimental results suggest that under natural conditions temperature is the leading mechanism controlling the mg ca ratio temperature and magnesium are related proportionally a temperature increase of ca 10 c gives rise to an increase of the magnesium concentrations of ca 130 drastic unnatural salinity changes dominate the effects of temperature a 110 change in the mg ca ratio was observed when salinity was elevated or reduced by more than ca 10 specimens which underwent gametogenesis reveal significantly higher mg concentrations than specimens that did not release gametes partition coefficients for mg in foraminiferal calcite are orders of magnitude lower than values from inorganically precipitated calcite when comparing observed mg ca ratios of foraminiferal tests with predicted mg ca ratios calculated according to empirical equations it becomes evident that foraminiferal tests are undersaturated with respect to mg for the water temperature they have experienced apparently foraminifers are capable of controlling their mg concentration the physiological processes presumably responsible for such depressed mg ca ratios appear to be temperature controlled as deduced from the close relationship of the observed mg ca ratios and water temperature this study demonstrates that variations in temperature and salinity are definitely reflected in the mg content of foraminiferal tests magnesium may thus serve as a paleo proxy for past surface water temperatures as long as postdepositional changes and salinity variations are of subordinate importance or can be excluded

diagenetic stabilization of aragonite and low mg calcite i trace elements in rudists abstract cretaceous rudists with thick multilayered bimineralic aragonite and low mg calcite shells have been studied for the effects of meteoric diagenesis on their textural and chemical attributes the original fine compact prismatic or cellular prismatic microstructures of low mg calcitic layers have been preserved frequently despite the vagaries of their subsequent diagenetic histories these layers usually suffered only partial recrystallization which caused fusion of crystal units rounding of prism comers and partial cementation confined to intercrystalline and intraparticle pore spaces in contrast the originally aragonitic parts of the shell usually suffered either complete dissolution or at best retained some vestiges of their crossed lamellar or complex crossed lamella microstructures synsedimentary submarine diagenetic events such as borings by endolithic fauna internal micritic and or peloidal sedimentation and submarine aragonite and or high mg calcite cements within the primary inter and intraparticle pore spaces were coeval with rudist accretion the subsequent meteoric cementation has been characterized by the formation of bladed and equant ferroan calcites which occluded the residual primary and secondary porosities diagenetic stabilization of aragonite to diagnetic low mg calcite and low mg calcite to diagenetic low mg calcite is believed to have been a two stage process initially sr and na have been partially depleted during an early meteoric diagenetic phase calcitization of metastable phases with expulsion of sr at a slower rate than that of na this stage is followed by incorporation of more mn fe and mg due to precipitation of late ferroan calcite stabilization of aragonite causes more pronounced trace element repartitioning than the stabilization of low mg calcite however the degree of repartitioning depends not only on mineralogy but also on the structural buildup of a given shell layer suggesting that factors such as water rock ratio surface kinetics are of considerable sig ificance for the process of diagenetic stabilization rudist skeletal components with preserved original mineralogy and texture have trace element chemical signatures analogous to holocene marine bivalves this similarity argues for comparable chemical composition of the cretaceous and holocene seawater as well as for similar modes of incorporation of trace elements into mollusc shells

trace and minor element records in aragonitic bivalve shells as environmental proxies abstract investigation of the geochemical composition of bivalve shells can provide information on changes in the marine environment occurring during the lifespan of an organism three species locally abundant in the adriatic sea were chosen in this study namely glycymeris pilosa callista chione and venus verrucosa of these g pilosa has the longest lifespan exceeding 50 years and therefore presents a potential archive of decadal climate variability the other two species c chione and v verrucosa are commercially important samples were collected alive by scuba diving in the north adriatic sea near barbariga istria major growth increments in these shells form on an annual basis and are clearly visible in shell cross sections enabling correct temporal positioning of geochemical data obtained from different shell parts in this study we applied laser ablation inductively coupled plasma mass spectrometry la icp ms in line scan mode to determine the trace and minor element composition along the major growth axis in the hinge area of the shells objectives of this study were to compare signals within and between species and to relate results to available environmental parameters high resolution time series of na cashell mg cashell and sr cashell display characteristic cyclic variations na cashell minima and mg cashell and sr cashell maxima occur near shell annual growth lines in all three studied species results indicate that seawater temperature is not a main driver for incorporation of these elements ba cashell data vary between years and species and have noncyclic sharp peaks callista chione and v verrucosa specimens show higher peaks and background ba cashell values than g pilosa most pronounced peaks in ba cashell occurred at the beginning of the growing season corresponding to the end of year 2011 and beginning of year 2012 and coincided with unusual dense water formation and subsequent changes in the plankton communities in the adriatic sea implications of our study suggest that synchronous peaks in studied specimens are caused by external forcing which could occur on larger regional scales encouraging future studies covering wider area in the adriatic sea and other parts of the mediterranean

emplacement of the 18 may 1980 lateral blast deposit ene of mount st helens washington facies variations east northeast of mount st helens preserve a record of depositional processes in the 18 may 1980 lateral blast cloud this paper reports new field grain size and component data from the ene sector of the timber blowdown zone and presents a model for blast flow and sedimentation the first erupted ejecta was rich in juvenile components and extends to the distal blowdown limit the last erupted ejecta was rich in accidental lithics and reached no further than a few kilometres from the mountain due to waning discharge the blast cloud was a turbulent stratified flow which transported and deposited sediment in the manner of a high density turbidity current the possibility that the blast was emplaced as a giant shearing fluidised bed is not favoured by compositional zoning patterns depositional conditions were strongly influenced by the rate of suspended load fallout from the blast within about 8 km from vent rapid sedimentation caused deposition under moderate to high concentration conditions and formation of a basal hindered settling zone able to detach gravitationally and drain into local depressions the resulting proximal facies resembles a low aspect ratio ignimbrite fines depletion in the proximal facies is attributed to a combination of residual turbulence and rapid gas escape during particle settling and compaction through the hindered settling zone component data suggest that the blast head played no significant role in the generation of fines depletion in the blast deposit as suggested by previous workers with increasing distance from vent the rate of particle fallout declined and sedimentation took place under increasingly dilute and tractional conditions building up antidune like bedforms wavelengths of these bedforms range from 20 to 1 m and decrease away from vent there is a systematic relationship between antidune migration direction and depositional slope the transition from proximal ignimbrite like to distal surge like facies suggests a possible gradation in transport and deposition processes between conventional pyroclastic surges and high velocity pyroclastic flows

preliminary geology mineral chemistry and diamond results from the c29 30 candle lake volcanic complex saskatchewan canada abstract the c29 30 kimberlite is one of two diamondiferous kimberlites in the candle lake cluster located in east central saskatchewan canada approximately 70 km from the fort a la corne kimberlite field the kimberlites are hosted by a cretaceous sequence of marine mudstone and shale of the lower colorado group and underlying siltstone and sandstone of the mannville group this sequence overlies paleozoic carbonates that were deposited over the proterozoic crystalline basement based on the country rock stratigraphy and morphology of the body c29 30 is inferred to be cretaceous in age the elongated kimberlite body has a lateral extent of approximately 2 km with the long axis oriented in a south east to north west direction and an estimated surface expression of 75 3 ha the investigation of 47 drill cores suggests that this body is a single volcanic complex dominated by a single phase of volcaniclastic kimberlite that is characterised by absent to rare phlogopite within the groundmass of preserved juvenile clasts minor amounts of at least one other phase of kimberlite containing conspicuous groundmass phlogopite have also been documented the subsurface shape of c29 30 is complex and is interpreted to result from a combination of explosive volcanic activity that formed two craters from separate feeder vents the formation of the elongated trough is poorly understood it may have formed by a fissure style eruption or erosive processes related to the mass flow of material away from one of the craters or possible the collapse of an eruption column the c29 30 kimberlite is similar to bodies of the fort a la corne kimberlite field with respect to country rock setting pipe morphology and the dominant textural varieties present this contribution presents a preliminary geological model of c29 30 based on data obtained from the drilling programmes completed in 2006 2007 and 2008

micro x ray fluorescence μxrf line scanning on cretaceous rudist bivalves a new method for reproducible trace element profiles in bivalve calcite the reconstruction of palaeoclimate on a sub annual scale requires the measurement of chemical proxies in fossil material at a high spatial resolution while various methods for trace element analysis on the micrometre scale are available they are usually destructive to the sample or not widely accessible this study evaluates the performance of a table top micro x ray fluorescence scanner in obtaining reproducible trace element profiles on bivalve calcite standard calibration and repeatability tests demonstrate the robustness of results obtained with this new generation micro x ray fluorescence device that uses a comparatively high excitation energy of 30 w results show that elemental abundances measured using this fast readily accessible and non destructive analytical setup are reproducible on the g g level and therefore suitable for the analysis of the abundance of commonly studied elements in bivalve calcite for example sr mn and fe spectra obtained in this study show considerable improvement in terms of signal to noise ratio compared to earlier table top xrf studies reliability of the measurements is tested using a conservative detection and quantification limit count rates of ca are used to check for point measurements disturbed by irregularities on the sample surface furthermore the method allows semi quantitative two dimensional element mapping which is a convenient tool for the detection of diagenetic alteration in fossil samples the method reveals records of sr ca fe ca and mn ca ratios in a late campanian vaccinites vesiculosus shell with sr ca ratios showing a trend opposite to mn ca and fe ca resulting trace element records are discussed in terms of seasonal cyclicity in the late cretaceous and diagenetic alteration of the fossil shell this article is protected by copyright all rights reserved

statistical evaluation of elemental concentrations in shallow marine deposits cretaceous lusitanian basin abstract the elemental geochemistry of ancient shallow marine carbonates represents an often underexplored archive of paleoenvironmental change and diagenetic pathways complex multi parameter datasets from a lithologically heterogeneous sedimentary succession in the southern part of the lusitanian basin ericeira portugal are presented and interpreted the section comprises marly carbonate and sandstone rich coastal marine deposits of early albian to early cenomanian age principal component analysis of bulk elemental abundance ca mg sr fe and mn lead to define four geochemical clusters based on common elemental attributes siliciclastics and dolomitized limestones facies yield evidence for significant diagenetic alteration but still preserve information on paleoshoreline position mixed carbonate siliciclastics and limestone facies bear evidence for relative sea level position and relevant paleoclimatic information in their elemental record accordingly mid albian mixed carbonate siliciclastic deposits present variable degrees of continental influx specifically a sharp increase of fe and mn concentrations in relation to continental input is in agreement with periods of enhanced hydrological cycling and increased weathering on adjacent emerged lands the progressive transition towards more marine conditions is accompanied by higher ca and sr content and represented by limestone facies corresponding to a higher sea level position during late albian to early cenomanian times moreover this facies records a trend towards warmer and more arid conditions early diagenetic stabilization and or dissolution of aragonite into low mg calcite can account for major elemental variations including higher sr content strongly coupled with ca content along with lower mg fe and mn concentrations data shown here provide solid evidence that the statistical analysis of the elemental record of ancient marine deposits when combined with conventional sedimentology and thin section petrography allow for elaborate conclusions on their depositional environment and diagenetic pathways cored wells and facies specific reservoir properties can be addressed by these methodologies able to detect and quantify changes in patterns both industry and academy can therefore benefit from approaching such a complex interplay

sedimentary facies of the nova scotian upper and middle continental slope offshore eastern canada a detailed survey of the upper and middle nova scotian continental slope at 42 50 n and 63 30 w indicates a complex morphology dominated by mass movements on various scales and an immature turbidity current channel the range of sediment facies is diverse including hemipelagic and turbidite muds turbidite sands and gravelly sandy muds of debris flow origin deformed units interpreted as slump deposits are also observed several facies associations related to discrete morphological environments are recognized thick turbidite sand units with minor intervening mud beds are characteristic of the high relief uppermost slope and channel margin thinner turbidite sands deformed slump beds and various mud facies are associated with small scale hummocky mid slope topography sand beds are more abundant in the depressions than on intervening hummocks indicating the preferred transport paths of small turbidity currents at the lower end of the main turbidity current channel frequent turbidite sand beds with relatively minor mud beds are deposited on a depositional lobe in areas unaffected by mass movements alternating bioturbated mud and sandy muds make up the core sequences a local model of sedimentation is proposed for this area and illustrates that simple models of continental slope sedimentation only apply to a limited range of settings

discrimination of reworked pyroclastics from primary tephra fall tuffs a case study using kimberlites of fort a la corne saskatchewan canada reworked volcaniclastics are traditionally discriminated from primary tephra fall pyroclastics by an absence of features such as blanketing juvenile lapilli grain welding and poor sorting frequently these features are difficult to identify especially in small outcrops ancient or altered successions debris flows and surge deposits crystal rich volcaniclastics such as kimberlites have a large proportion of coarse euhedral crystals and abrasion leading to rounding can be recognised and classified with relative ease a petrographic method of discriminating reworked material has been devised based on the degree of grain roundness and is illustrated using volcaniclastic kimberlite from fort a la corne saskatchewan canada petrographic thin sections of samples at regular intervals throughout the borehole core and from a nearby crater facies kimberlite show that the percentages of rounded subrounded and euhedral grains define two distinct groupings the first group contains a higher percentage of euhedral grains and includes all the samples from the basal 4 8 m of the 14 1 m thick kimberlite section in borehole 004 and all of the crater facies tephra fall tuffs a second group contains more rounded subrounded and fragmental grains and includes all the data from the upper 6 3 m which are interpreted as reworked strata thus point counting concurs with hand sample interpretation and may be used as a verification tool in discriminating reworked pyroclastic sands from primary tephra fall tuffs

new insights into geochemical behaviour in ancient marine carbonates upper jurassic ammonitico rosso novel proxies for interpreting sea level dynamics and palaeoceanography elemental concentrations in phanerozoic sea water are known to fluctuate both in time and space with regard to carbonates precipitated from marine fluids elemental concentrations in the carbonate crystal lattice are affected by a complex array of equilibrium and non equilibrium as well as post depositional alteration processes to assess the potential of carbonate elemental chemostratigraphy seven upper jurassic sections were investigated along a proximal to distal transect across the south east iberian palaeomargin the aim was to explore stratigraphic and spatial variations in calcium strontium magnesium iron and manganese elemental abundances the epicontinental geochemical record is influenced by the combination of continental runoff and a significant diagenetic overprint in contrast the epioceanic geochemical record agrees with reconstructed open marine sea water values reflecting a moderate degree of syn depositional to early marine pore water diagenesis establishing a fair degree of preservation of matrix micrite a thorough statistical approach was applied and elemental associations tested for their environmental significance principal component and hierarchical cluster analyses revealed a persistent relation between carbonate magnesium iron and strontium abundances processes related to early diagenetic nodulation in ammonitico rosso facies most probably account for the incorporation of these elements in the calcium carbonate lattice the clear decoupling of carbonate manganese abundance with respect to the remaining elements is documented and related to high sea floor spreading rates and hydrothermal activity during the late jurassic the investigation of potential time fluctuation of geochemical patterns was approached through variogram computation the observed temporal behaviour is most likely to be forced by relative sea level dynamics reflecting late jurassic palaeoceanographic conditions and potential planetary interactions the data obtained in this study highlight the utility of elemental data from carbonate matrix micrites as geochemical proxies for studying the influence of remote trigger factors

climate records from a bivalved methuselah arctica islandica mollusca iceland we measured annual shell growth rates of a 374 year old radiometrically confirmed bivalve mollusk specimen of arctica islandica linnaeus this bivalve represents the oldest ever reported individual animal in addition we analyzed 1051 individual powder samples from ontogenetic years two to 40 80 of the entire shell height for isotope analyses oxygen and carbon isotopes exhibit clear intra annual cycles the highest measured carbon isotope values on average 2 73x occurred during summer i e during maximum primary productivity the d 18 oaragonite derived temperature time series cover the period of ad 1496 1533 temperatures calculated from oxygen isotopes ranged from 4 5 to 9 3 8c and exhibit a mean value of 6 2 8c the latter coincides well with the 1854 2003 mean value of 6 81 8c for sea surface temperature between february and september growing season of a islandica neither oxygen nor carbon isotopes exhibit age related unidirectional trends however d 13 caragonite and d 18 oaragonite values fluctuated at decadal periods of four six and eight to nine years nao type periods as well as 12 14 years which may represent teleconnections to cycles in the tropical atlantic annual shell growth is positively correlated to intra annual d 18 oaragonite minima i e warm summer temperatures r 2 0 34 and to intra annual d 13 caragonite minima higher food supply r 2 0 42 using a linear multiregression model 65 of the variation in annual shell growth can be explained by summer temperature and food supply the formation of extremely narrow annual increments coincides with major volcanic eruptions e g tambora 1815 a period of extremely variable growth occurred during the culmination of the little ice age in iceland between ca ad 1550 and 1620 shell growth during ad 1765 1780 however was characterized by very little year to year variability probably as the result of extremely mild climate near the end of the little ice age this study demonstrates that shells of a islandica provide

eruption processes and facies architecture of the orion central kimberlite volcanic complex fort a la corne saskatchewan kimberlite mass flow deposits in a sedimentary basin abstract the fort a la corne diamondiferous kimberlite field consists of at least 70 bodies of volcaniclastic kimberlite hosted within a contemporaneous non volcanic sedimentary succession this study of the three dimensional stratigraphy and facies architecture across the orion central kimberlite volcanic complex highlights the variations in upper and extra vent processes the sedimentary succession consists of continental to marginal marine quartz sandstones and mudstones overlain by marginal to deep marine dark mudstone and muddy sandstones and siltstones relatively thin conformable volcaniclastic kimberlite packages are interbedded throughout the host rock stratigraphy extremely thick up to at least 211 m thick discordant to concordant volcaniclastic packages series infill at least three elongate northwest trending craters 145a 145b and 219 craters and contain laterally equivalent conformable extra crater deposits bound by marine mudstones indicative of a prevailing dominantly marine environment the volcaniclastic deposits within the 145a and 145b craters respectively are separated by a considerable hiatus whereas the deposit infilling the 219 crater was formed around the same time as 145b crater deposit multiple depositional units of massive to stratified olivine rich sand to pebble sized volcaniclastic facies infill craters and were emplaced by megaturbidite pulses fed by crystal rich eruption fountains which interacted with the crater relief stacked normally graded thick to very thick bedded matrix supported olivine rich facies characterized by brief depositional breaks between some beds represent syn to post eruptive turbidite pulses associated with the early eruptive event in the 145a crater thin layers of light grey kimberlitic mudstone underlie or occur near the base of and above the main volcaniclastic packages associated with the 145b and 219 eruptions crater infilling volcaniclastic deposits were later reworked by storm induced currents into thin to medium graded moderately sorted fine to coarse olivine rich sandstone with intercalated discontinuous muddy laminae laminated to cross laminated olivine rich silt to sand sized volcaniclastic facies constitutes a small volume volcaniclastic turbidite which marks the last preserved kimberlite emplacement event at orion central

rudists as gregarious sediment dwellers not reef builders on cretaceous carbonate platforms abstract it has sometimes been claimed that rudist bivalves competitively displaced corals from reef frameworks during the cretaceous this hypothesis combines two assertions 1 that the autecology of rudists was convergent with that of reef building corals and 2 that rudist formations commonly developed as reefs we dispute both assertions and thus reject the hypothesis of competitive displacement we argue instead that mobile sediments rather than frameworks dominated the margins and tops of most of the extensive carbonate platforms of the period and that it was on these non reefal biotopes that the rudists flourished definitions of reefs tend to combine two major elements 1 a robust biogenic framework with accompanying sedimentary and diagenetic components and 2 topographical relief such definitions are clearly rooted in recent coral reefs in which endosymbiotic zooxanthellae permit the extensive growth of colonial coral frameworks in shallow but relatively nutrient poor waters coralline algae and cementation may contribute significantly to the growth of rigid structures and topography is largely the legacy of pleistocene changes in sea level in rudist formations in contrast individual rudist congregations are volumetrically limited relative to sediment they are often loosely constructed and they evidently showed little if any original relief tabular and small lenticular units predominate these differences in structure and palaeoenvironmental situation between rudist and modern coralgal associations reflect the different autecologies of the constituent organisms the clonal growth of corals predisposes them to the development of frameworks projecting above the sediment surface herein termed superstratal growth by contrast the aclonal development of rudists was better suited to the opportunistic occupation of a variety of temporarily available substrata by large numbers of individuals in particular elevator rudists in which the entire commissure exhibited upward growth evidently grew with their shells largely embedded in and supported by the ambient sediment herein termed constratal growth moreover the tolerances and growth responses of rudists to such factors as water turbidity nutrients and current regime were quite different from those of the majority of reef building corals despite repeated assertions in the literature that rudists possessed zooxanthellae only a few species show any evidence for such a symbiosis and other evidence suggests that most lacked them in view of these differences in their preferred biotopes competition between rudists and corals is doubtful even though members of both groups co occur in many areas the relative decline of coral frameworks in the cretaceous was thus probably independently caused

alteration styles in the orion central volcanic complex fort a la corne kimberlite field saskatchewan and their effects on primary volcaniclastic textures implications for facies mapping and diamond exploration diamond grade distributions within individual kimberlite bodies are controlled by physical emplacement processes which are generally determined from volcaniclastic facies characteristics however the effects and distribution of secondary alteration styles which usually mask primary kimberlite facies have been given little attention at the fort a la corne kimberlite field saskatchewan complex overprinting alteration textures and mineral phases are recognized this study documents the characteristics overprinting relationships and spatial distribution of alteration styles within a crater filling volcaniclastic deposit body 219 of the orion central volcanic complex data were acquired from macroscopic drill core observations microscopic petrography sem imaging eds element mapping and xrd analyses olivine crystals display a mesh fracture pattern and have been replaced by multiple generations of serpentine and magnetite late stage serpentine has migrated into the interstitial medium bulk rock alteration textures include 1 fine grained crystal rich domains which are alteration pseudoclasts and or relict juvenile pyroclasts 2 a heterogeneous interstitial medium varying from early stage disseminated calcite rich serpentine to amorphous serpentine and crystalline calcite and 3 overprinting serpentine carbonate and magnetite veins and serpentine nodules alteration styles defined by unique alteration characteristics are spatially zoned through the body 219 volcaniclastic deposit and this is a result of multiple reaction fronts associated with the influx of fluids of varying composition over time and permeating different parts of the deposit recognition of alteration processes their paragenesis and spatial controls can assist in defining and constraining the distribution of primary kimberlite facies and by consequence the distribution of diamond grades

diagenetic stabilization of aragonite and low mg calcite ii stable isotopes in rudists abstract cretaceous rudists having thick multilayered bimineralic aragonite and low mg calcite shells have been studied for the effects of phreatic vadose meteoric diagenesis on their microstructural and isotopic attributes rudist skeletal components with preserved original mineralogy of aragonite and low mg calcite and with preserved microstructures have isotopic signatures analogous to holocene marine bivalves this similarity argues for a comparable isotopic composition of the cretaceous and holocene seawater as well as for a similar mode of incorporation of stable isotopes into their shells diagenetic stabilization of rudist shells appears to have been a two stage process with low mg calcite diagenetic calcite lmc dlmc and particularly aragonite diagenetic calcite a dlmc transformation as the first step and cementation as a later development the direct a dlmc mineralogical transformation calcitization results in initial depletion in 18o of 2 and the subsequent diagenetic precipitation of ferroan calcite spar causes depletion in 13c as well as an additional decrease in 18o the former due to introduction of organically derived co2 into the diagenetic aquifer in contrast 13o and 13c isotopic depletions in the originally lmc skeletal components are both related to the precipitation of the late diagenetic ferroan sparry calcite cement the earlier calcitization stage being of subordinate importance only

chemical diagenesis of a multicomponent carbonate system 2 stable isotopes abstract this study examines the oxygen and carbon isotopic distribution in the brachiopods crinoids rugose corals and matrix cement from the mississippian burlington limestone iowa and missouri and the silurian read bay formation arctic canada the isotopic data can be reconciled with textural and trace element observations only if the 18o content of ancient oceans differed from that of the present oceans this postulated secular variation in the 18o content of seawater requires a separate evaluation of the mississippian and silurian carbonate components examination of the 18o content of the least altered low mg calcite fossil components of the two formations suggests that the 18o of mississippian seawater was on average about 1 5 lighter and that of silurian seawater was about 5 5 lighter than the 18o of present day ocean water the average diagenetic shift in 18o for the read bay formation which stabilized in a partly closed diagenetic phreatic meteoric system is about 1 for the original low mg calcite and about 2 for the original high mg calcite and aragonite components conversely for the burlington limestone which stabilized in an open diagenetic phreatic meteoric system the average diagenetic shift in 18o is about 3 for the original low mg calcite and about 4 f r the original high mg calcite components the 13c values of the originally low mg calcite or high mg calcite with less than 7 mole mgco3 brachiopods and rugose corals the originally high mg calcite crinoids and the originally aragonite lime mud of the burlington limestone and read bay formation are bimodally distributed this bimodal 13c distribution is independent of geologic age inferred original mineralogy of the component degree of diagenetic alteration and the type of diagenetic meteoric system with components from both the read bay formation and burlington limestone contributing to both 13c groups the mode of the light 13c group is 0 25 and for the heavy 13c group it is 3 25 pdb both 13c groups also show a decrease in 13c of about 1 with increasing diagenetic alteration stabilization

coccolith sr ca as a new indicator of coccolithophorid calcification and growth rate 1 polyspecific coccolith separates from core top sediments in the eastern equatorial pacific show variations of 15 in sr ca ratios across the equatorial upwelling zone with sr ca highest at the equator and decreasing off axis these variations cannot be due to changes in the sr ca of seawater which varies by less than 2 in the surface ocean variations in sr ca of coccolith sediments are similar to variations in primary productivity and alkenone estimated coccolithophorid growth rates in overlying surface waters and to caco3 rain rates measured in sediment traps because of these relationships and because calcification rate exerts a strong control on sr ca in abiogenic calcites we suggest that the observed sr ca variations in coccoliths may be strongly controlled by coccolithophorid growth and calcification rates although temperature may also influence coccolith sr ca to a lesser degree changes in dissolution intensity and coccolith assemblages appear to exert a minor influence if any on coccolith sr ca in these sediment core tops if further work confirms relationships between coccolith sr ca and coccolithophorid productivity sr ca records of past changes in coccolithophorid productivity may be useful in reconstructing past variations in the rain ratio of organic to carbonate carbon an important control on deep ocean ph and partitioning of co2 between the atmosphere and ocean in addition coccolith sr ca might provide an independent record of past changes in coccolithophorid growth rates which in combination with data on the carbon isotopic fractionation in coccolithophorid organic matter may permit more reliable calculations of past dissolved co2 in the surface ocean

a new approach to kimberlite facies terminology using a revised general approach to the nomenclature of all volcanic rocks and deposits descriptive to genetic although kimberlite pipes bodies are usually the remains of volcanic vents in vent deposits and subvolcanic intrusions the terminology used for kimberlite rocks has largely developed independently of that used in mainstream volcanology existing kimberlite terminology is not descriptive and includes terms that are rarely used used differently and even not used at all in mainstream volcanology in addition kimberlite bodies are altered to varying degrees making application of genetic terminology difficult because original components and depositional textures are commonly masked by alteration this paper recommends an approach to the terminology for kimberlite rocks that is consistent with usage for other volcanic successions in modern terrains the eruption and emplacement origins of deposits can often be readily deduced but this is often not the case for old variably altered and deformed rock successions a staged approach is required whereby descriptive terminology is developed first followed by application of genetic terminology once all features including the effects of alteration on original texture and depositional features together with contact relationships and setting have been evaluated because many volcanic successions consist of both primary volcanic deposits as well as volcanic sediments terminology must account for both possibilities

the crater facies kimberlite system of tokapal bastar district chhattisgarh india abstract discovery of diamondiferous kimberlites in the mainpur kimberlite field raipur district chhattisgarh in central india encouraged investigation of similar bodies in other parts of the bastar craton the earlier known tokapal ultramafic intrusive body located beyond the 19 km milestone in tokapal village along the jagdalpur geedam road was reinterpreted as crater facies kimberlite its stratigraphic position in the meso neoproterozoic intracratonic sedimentary indravati basin makes it one of the oldest preserved crater facies kimberlite systems ground and limited subsurface data dug tube wells and exploratory boreholes have outlined an extensive surface area 550 ha of the kimberlite the morphological and surface color features of this body on enhanced satellite images suggest that there is a central feeder surrounded by a collar and wide pyroclastic apron exploration drilling indicates that the central zone probably corresponds to a vent overlain by resedimented volcaniclastic epiclastic rocks that are surrounded by a 2 km wide spread of pyroclastic rocks lapilli tuff tuff ash beds and volcaniclastic breccia drill holes also reveal that kimberlitic lapilli tuffs and tuffs are sandwiched between the kanger and jagdalpur formations and also form sills within the sedimentary sequence of the indravati basin the lapilli tuffs are commonly well stratified and display slumping base surges and lava flows occur in the southern part of the tokapal system the geochemistry and petrology of the rock correspond to average group i kimberlite with a moderate degree of contamination however the exposed rock is intensely weathered and altered with strong leaching of mobile elements ba rb sr layers of vesicular fine grained glassy material represent kimberlitic lava flows tuffs containing juvenile lapilli with pseudomorphed olivine macrocrysts are set in a talc serpentine carbonate matrix with locally abundant spinel and sphene garnet has not been observed and phlogopite is very rare very limited microdiamond testing two 18 kg samples proved negative however the composition of chromite grains indicate crystallization in the diamond stability field

geology of the mwadui kimberlite shinyanga district tanzania abstract the mwadui pipe represents the largest diamondiferous kimberlite ever mined and is an almost perfectly preserved example of a kimberlitic crater in fill albeit without the tuff ring the geology of mwadui can be subdivided into five geological units viz the primary pyroclastic kimberlite pk re sedimented volcaniclastic kimberlite deposits rvk granite breccias subdivided into two units the turbidite deposits and the yellow shales listed in approximate order of formation the pk can be further subdivided into two units lithic rich ash and lapilli tuffs which dominate the succession and lithic poor juvenile rich ash and lapilli tuffs the lower crater is well bedded down to at least 684 m from present surface extent of current drill data the bedding is defined by the presence of juvenile rich lapilli tuffs vs lithic rich lapilli tuffs and the systematic variation in granite content and clast size within much of the lithic rich lapilli tuffs four distinct types of bedding have been identified in the pyroclastic deposits diffuse zones characterised by increased granite abundance and size and upward fining units represent the dominant types throughout the deposit lateral heterogeneity was observed in addition to the vertical changes suggesting that the eruption was quite heterogeneous or that more than one vent may have been present the continuous nature of the bedding in the pyroclastic material and the lack of ash partings suggest deposition from a high concentration ejecta sustained eruption column at times e g the massive very diffusely stratified deposits the paucity of tractional bed forms suggest near vertical particle trajectories i e a clear air fall component but the poorly sorted matrix supported nature of the deposits suggest that pyroclastic flow and or surge processes may also have been active during the eruption available diamond sampling data were examined and correlated with the geology data derive from the old 120 37 m 200 61 m 300 92 m and 1200 ft 366 m levels pits sunk during historical mining operations drill logs as well as more recent bench mapping correlating macro diamond sample data and geology shows a clear relationship between diamond grade and lithology localised enrichment and dilution of the primary diamond grade has taken place in the upper reworked volcaniclastic deposits due to post eruptive sedimentary in fill processes clear distinction can be drawn between upper re sedimented and lower pyroclastic crater deposits at mwadui both from a geological and diamond grade perspective finally an emplacement model for the mwadui kimberlite is proposed geological evidence suggests that little or no sedimentary cover existed at the time of emplacement the nature of the bedding within the pyroclastic deposits and the continuity of the bedding in the vertical dimension suggest that the eruption was continuous but that the eruption column may have been heterogeneous both petrologically as well as geometrically volcanic activity appears to have ceased thereafter and the crater was gradually filled with granite debris from the unstable crater walls and re sedimented volcaniclastic material derived from the tuff ring the mwadui kimberlite exhibits marked similarities compared to the orapa kimberlite in botswana

mollusc and brachiopod skeletal hard parts intricate archives of their marine environment the biogenic carbonate hard parts of fossil bivalves cephalopods and brachiopods are among the most widely exploited marine archives of phanerozoic environmental and climate dynamics research the advent of novel analytical tools has led many workers to explore non traditional geochemical and petrographic proxies and work performed in neighbouring disciplines sheds light on the complex biomineralization strategies applied by these organisms these considerations form a strong motivation to review the potential and problems related to the compilation and interpretation of proxy data from bivalve cephalopod and brachiopod hard parts from the viewpoint of the sedimentologist and palaeoceanographer specific focus is on the complex biomineralization pathways of a given dissolved ion or food particle from its aquatic environment via the digestion and biomineralization apparatus in molluscs and brachiopods and its incorporation into a biomineral given that molluscs and brachiopods do not secrete their hard parts from seawater but rather from their mantle and periostracum this paper evaluates differences and similarities of seawater versus that of body fluids cephalopods bivalves and brachiopods exert a strong biological control on biomineralization that to some degree may buffer their shell geochemistry against secular changes in seawater chemistry disordered amorphous calcium carbonate precursor phases later transformed to crystalline biominerals may be significant in carbonate archive research due to expected geochemical offset relative to the direct precipitation of stable phases a reasonable level of understanding of the related mechanisms is thus crucial for those who use these skeletal hard parts as archives of the palaeo environment the impact of what is commonly referred to as biological factors on the geochemistry of mollusc and brachiopod hard parts is explored for conventional isotope systems such as carbon oxygen strontium and traditionally used element to calcium ratios in particular the often used 13ccarb or the mg ca and sr ca elemental proxies are fraught with problems an interesting new research field represents the analysis calibration and application of non traditional proxies to mollusc and brachiopod hard parts examples include the carbonate clumped isotope 47 approach and the analysis of the isotopes of ca mg n li s or element to ca ratios such as li ca or b ca and rare earth elements based on considerations discussed here a series of do s and don ts in mollusc and brachiopod archive research are proposed and suggestions for future work are presented in essence the suggestions proposed here include experimental work also field experiments making use of recent archive organisms or where possible a reasonable recent analogue in the case of extinct groups moreover the detailed understanding of the architecture of mollusc and brachiopod hard parts and their ultra structures must guide sampling strategies for geochemical analyses where feasible a detailed understanding of the diagenetic pathways and the application of multi proxy and multi archive approaches should form the foundation of fossil carbonate archive research the uncritical compilation of large data sets from various carbonate shelled organisms collected at different locations is not encouraged

isotopic and chemical intra shell variations in low mg calcite of rudist bivalves mollusca hippuritacea disequilibrium fractionations and late cretaceous seasonality isotopic 13c 18o and elemental mg sr mn fe compositions were analysed in sclerochronological profiles of several shells of late cretaceous rudist bivalves from greece turkey somalia and the arabian peninsula the preservation of original compositions of low mg calcite of outer shell layers is indicated by constant and high sr generally low fe and mn and the preservation of fibrous prismatic ultrastructures cyclic variations in 18o and mg are interpreted to reflect seasonal temperature salinity cycles and thus annual growth increments in shells of torreites amplitudes of correlated 13c and 18o cycles cannot be related to reasonable palaeotemperatures or salinity this isotopic pattern reflects vital fractionations of an extent which is unknown from modern bivalves in contrast almost identical ranges and amplitudes of 18o cycles are observed in 13 shells of five species from santonian campanian localities in central greece and northern turkey suggesting that seasonal variations in environmental conditions were recorded without significant vital fractionations the effect of seasonal salinity changes on 18o of the shells is evaluated and mean palaeotemperatures are constrained within the range of 30 32 5 c the annual range of temperature was estimated to be 7 c assuming a constant salinity this agrees with other isotopic proxies of late cretaceous palaeotemperatures and with global circulation models which predict higher low latitude sea surface temperatures than the present ones

sedimentologic and stratigraphic constraints on emplacement of the star kimberlite east central saskatchewan abstract diamond bearing kimberlites in the fort a la corne region east central saskatchewan consist primarily of extra crater pyroclastic deposits which are interstratified with lower cretaceous albian and cenomanian marine marginal marine and continental sediments approximately 70 individual kimberlite occurrences have been documented the star kimberlite occurring at the southeastern end of the main fort a la corne trend has been identified as being of economic interest and is characterized by an excellent drill core database integration of multi disciplinary data sets has helped to refine and resolve models for emplacement of the star kimberlite detailed core logging has provided the foundation for sedimentological and volcanological studies and for construction of a regionally consistent stratigraphic and architectural framework for the kimberlite complex micropaleontologic and biostratigraphic analysis of selected sedimentary rocks and u pb perovskite geochronology on kimberlite samples have been integrated to define periods of kimberlite emplacement radiometric age determination and micropaleontologic evidence support the hypothesis that multiple kimberlite eruptive phases occurred at star the oldest kimberlite in the star body erupted during deposition of the predominantly continental strata of the lower mannville group cantuar formation kimberlites within the cantuar formation include terrestrial airfall deposits as well as fluvially transported kimberlitic sandstone and conglomerate successive eruptive events occurred contemporaneous with deposition of the marginal marine upper mannville group pense formation kimberlites within the pense formation consist primarily of terrestrial airfall deposits fine to medium grained cross stratified kimberlitic olivine dominated sandstone in this interval reflects reworking of airfall deposits during a regional marine transgression the location of the source feeder vents of the cantuar and pense kimberlite deposits has not been identified the youngest and volumetrically most significant eruptive events associated with the star kimberlite occur within the predominantly marine lower colorado group joli fou and viking formations kimberlite beds which occur at several horizons within these units consist of subaerial and marine fall deposits the latter commonly exhibiting evidence of wave reworking black shale encased resedimented kimberlite beds likely deposited as subaqueous debris flows and turbidites are particularly common in the lower colorado group during its multi eruptive history the star kimberlite body is interpreted to have evolved from a feeder vent and overlying positive relief tephra ring into a tephra cone initial early joli fou volcanism resulted in formation of a feeder vent 200 m diameter and tephra ring subsequent eruptions dominated by subaerial deposits partly infilled the crater and constructed a tephra cone a late joli fou eruption formed a small 70 m diameter feeder pipe slightly offset to the nw of the early joli fou feeder vent deposits from this event further infilled the crater and were deposited on top of early joli fou kimberlite proximal to the vent and sediments of the joli fou formation distal to the vent the shape of the tephra cone was modified during multiple marine transgression and regression cycles coeval with deposition of the lower colorado group resulting in wave reworked kimberlite sand along the fringes of the cone and kimberlitic event deposits tempestites turbidites debris flows in more distal settings

the influence of palaeotopography on facies architecture and pyroclastic flow processes of a lithic rich ignimbrite in a high gradient setting the abrigo ignimbrite tenerife canary islands abstract the late pleistocene 188 19 ka abrigo ignimbrite represents the last major explosive caldera forming eruption on tenerife it consists almost entirely of a moderate volume 1 8 km 3 light grey phonolitic lithic rich ignimbrite deposit although a possible abrigo member thin fall deposit is locally preserved beneath the ignimbrite suggesting an initial short lived stable plinian eruption column the ignimbrite deposit is dispersed radially around the lower flanks of the las canadas edifice and correlates to a clast supported lithic breccia on the eastern and northern caldera wall much of the ignimbrite was probably deposited offshore or within the caldera now buried by more recent lavas two major depositional units separated by a co ignimbrite ash cloud deposit and which display dramatic variations in thickness pyroclastic flows were channelised along and deposited within the same valleys that exist today and were commonly continuous and sheet like across the interfluves the basal zones of pyroclastic flows are envisaged as a bed load of coarse lithic lapilli and blocks transported under their own momentum and with the support of the surrounding fine ash gas granular flow

development of foliation and fold interference patterns produced by sedimentary processes penecontemporaneous folds lineations foliation and fold interference patterns are found in part of the pigeon point formation a turbidite sequence occurring along the central california coast these structures are associated with slumped sheets and they formed while the rocks were largely unlithified the foliation which is commonly roughly axial planar to folds is clearly shown in the hinges of slump folds and is defined by preferred alignment of inequant grains and silt sand domains the latter having formed from disrupted bedding laminae models that attempt to explain the genesis of penecontemporaneous foliation involve simple load compaction superimposed on pre existing slump folds model 1 or rotation of grains facilitated by slump folding model 2 evidence from this study indicates that a modified version of model 2 is commonly active it is suggested that a critical content of interstitial water is necessary whereby sufficient water pressure can build to decrease grain cohesion and induce liquefaction of layers further compaction in the hinge areas of slump folds then expels water during slumping such that preferred alignment of silt sand domains and inequant grains is facilitated all three of the basic fold interference patterns normally attributed to hard rock folding occur in these slumped sheets and along with foliation and related structures strongly resemble features generated by tectonic movement these structures can persist into the higher metamorphic grades where they may be misidentified as evidence for early repeated folding in this case the structural history of that part of the orogen may be reported as more complicated than it actually is

settling behaviour of concentrated dispersions and some volcanological applications abstract experiments have been carried out on the settling of non aggregating poorly sorted aqueous dispersions laced with lowdensity particles in order to gain insight into the sedimentation behaviour of volcaniclastic flows which contain pumice two poorly sorted dispersions of silicon carbide particles with continuous size distributions were studied plastic beads were added as a light component experiments were carried out at solids concentrations between 10 and 60 vol dispersions of low concentration generated normally graded deposits in which particles of different densities were in approximate hydraulic equivalence above a critical concentration 45 to 60 depending on the grain size distribution particle segregation was suppressed and the dispersion settled to form a virtually ungraded bed hindered settling at intermediate concentrations generated normally graded deposits with elutriation pipes floating rafts of plastic and capping layers of fines elutriated by escaping pore fluid buoyancy forces resulted in strong hydraulic inequivalence between light and dense components in the deposits from intermediate concentrations two mechanisms of elutriation pipe growth were observed at intermediate concentrations pipes grew progressively upwards in the deposit as the latter aggraded whereas at high concentrations they nucleated and grew uniformly throughout the whole dispersion elutriation pipes form readily during sedimentation of some poorly sorted aqueous dispersions the presence of elutriation pipes cannot be used alone to distinguish between deposits of epiclastic and pyroclastic flows reverse grading of pumice pumice rafts elutriation pipes and layers of elutriated fines should characterise deposits from pumice rich submarine mass flows despite differences in the fluid phase the experiments also have implications for fluidization mechanisms in pyroclastic flows hindered settling of a concentrated poorly sorted dispersion is a type of self fluidization in which the sedimentation of large particles causes a sufficiently strong vertical fluid flux to fluidize or elutriate smaller ones hindered settling is intrinsic to all pyroclastic flows as they spread out and deflate across the landscape and may reinforce other gas sources as an effective fluidization mechanism during emplacement of type 2 and type 3 ignimbrites and of coignimbrite lag breccias

stable isotope sclerochronology of rudist bivalves growth rates and late cretaceous seasonality the almost complete translation of shell accretion to vertical growth was a successful morphogenetic adaptation of rudist bivalves which replaced coral algal hydrozoan communities in most tethyan shallow marine environments during the cretaceous growth rates of rudist shells are therefore important in reconstructions of cretaceous shallow marine benthic communities carbon and oxygen isotopic compositions were analyzed in sclerochronological profiles through the shells of two late cretaceous rudist bivalves from greece and turkey values of 13 c vary between 0 8 and 2 2 in the hippuritid vaccinites ultimus and between 0 8 and 2 6 in the radiolitid gorjanovicia cf costata ranges in 18 o are 5 3 to 2 9 and 4 6 to 2 1 respectively a distinct cyclicity of 13 c and 18 o in both shells reflects late cretaceous seasonality and indicates annual vertical growth increments of 45 mm in v ultimus and 54 mm in gorjanovicia the concentrations of minor elements are similar to those of extant bivalves with low mg calcite shells

fragmentation in kimberlite products and intensity of explosive eruption the explosive eruption of kimberlite magma is capable of producing a variety of pyroclast sizes shapes and textures however all pyroclastic deposits of kimberlite comprise two main types of pyroclasts 1 pyroclasts of kimberlite with or without enclosed olivine crystals and 2 olivine crystals which lack coatings of kimberlite here we propose two hypotheses for how kimberlite magmas are modified due to explosive eruption 1 olivine crystals break during kimberlite eruption and 2 kimberlite melt can be efficiently separated from crystals during eruption these ideas are tested against data collected from field study and image analysis of coherent kimberlite and fragmental kimberlite from kimberlite pipes at diavik nt olivines are expected to break because of rapid pressure changes during the explosive eruption disruption of kimberlite magma and pyroclast production is driven by ductile deformation processes rather than by brittle fragmentation the extent to which melt separates from olivine crystals to produce kimberlite free crystals is a direct consequence of the relative proportions of gas melt and crystals lastly the properties of juvenile pyroclasts in deposits of pyroclastic kimberlite are used to index the relative intensity of kimberlite eruptions a fragmentation index is proposed for kimberlite eruption based on a crystal size distributions of olivine and on b ratios of selvage free olivine pyroclasts to pyroclasts of kimberlite with or without olivine crystals

a shallow marine volcaniclastic facies model an example from sedimentary rocks bounding the subaqueously welded ordovician garth tuff north wales u k abstract volcaniclastic sedimentary rocks bounding the ordovician garth tuff in north wales were deposited in a shallow marine setting adjacent to a magmatic arc the volcaniclastic sedimentary rocks are primarily of angular to euhedral quartz angular euhedral feldspar and volcanic rock fragments these grains are of a pyroclastic origin but have been reworked to various degrees sedimentary rock fragments rounded quartz muscovite biotite iron rich chlorite and various clay minerals occur in lesser amounts the sedimentary rocks can be divided into a proximal offshore to foreshore facies association poffa and an offshore to lower shoreface facies association olsfa the sand dominated poffa exposed near capel curig is characterized by large wave ripples hummocky cross stratification co sets of trough cross beds reactivation surfaces plane beds and graded turbidite layers in suspension deposited mudstone water depths calculated from bedding plane exposure of large wave ripples and determined by the presence of hummocky cross stratification and by facies association vary from a few meters to around 30 m 45 50 m theoretical maximum in a 45 m thick stratigraphic section beneath the tuff eight kilometers to the southeast the garth tuff is bounded by a thick sequence of suspension deposited laminated mudstone with thin graded beds of siltstone and fine grained sandstone this facies association olsfa represents the introduction of material by distal turbidites and by pelagic sedimentation the olsfa was deposited in water depths well below storm wave base possibly in excess of 200 m no evidence of storm waves or surface generated currents occur until over 40 m above the tuff this study documents marine sedimentary rocks deposited in water depths ranging from foreshore to offshore as the bounding facies of the garth tuff it is thus reasonable to conclude that the garth tuff was emplaced and welded in water depths greater than the thickness of the tuff in the area of this study

the submarine eruption and erosion of surtla surtsey iceland abstract surtla is the site of a short lived submarine vent which built basaltic elastic deposits almost to sea level in 1963 early in the eruption of surtsey since then wave and current activity have eroded the volcanic pile such that in july 1981 its top was a fairly level plateau 45 m below sea level and its surface comprised a lag deposit of sparse blocks of lava in a bed mainly of glass granules this winnowed layer was underlain by a nonreworked poorly sorted and finer deposit of glassy clasts formed by a combination of disruption by magmatic volatiles steam explosions and quench brecciation during the eruption the explosion violence and associated comminution increased as the pile built up to shallower water depths it is argued that at times of continuous effusion a cupola of steam was situated over the vent as indicated by scoriaceous spatter which shows agglutination and bread crust features that can only have developed in conditions more akin to subaerial than hitherto envisaged in a subaqueous eruption

oxygen isotope fluctuations in a modern north sea oyster crassostrea gigas compared with annual variations in seawater temperature implications for palaeoclimate studies abstract a total of 181 oxygen isotope values from sequential samples of the left shell of a modern pacific oyster crassostrea gigas that lived on a sub tidal oyster bank in the list basin north sea germany shows periodically varying values between 1 3 and 2 5 in order to test whether these 18 o fluctuations reflect seawater temperature changes the isotope values of the shell were compared to actual seawater temperature variations from the region c gigas serves as an excellent proxy for temperature of palaeoseawater and the results show that the examined oyster precipitated its shell in 18 o equilibrium with the ambient seawater a cessation of the oyster shell calcification starts at water temperatures below 6 c at lower temperatures than previously thought for crassostrea for palaeoclimate investigations the termination of shell production is important because the lowest temperatures might not be represented in the shell higher water temperatures are therefore potentially over represented in time spans when the shell grows faster and mean oxygen isotope values may potentially bias the mean seawater temperatures of annual variations towards higher temperatures

mid jurassic volcanic structures in the outer moray firth basin uk 3d seismic mapping in the southern part of quadrant 15 in the outer moray firth basin reveals an array of circular to oval downthrown blocks bound by steep ring faults these lows affect triassic and older strata are approximately 1 5 2 km in diameter and 0 5 1 km deep the footwall crests of the structures now lie at a depth of c 2 5 km several alternative causal mechanisms for these circular fault blocks are examined including salt dissolution strike slip pull apart and impact cratering but in terms of geological and geometrical criteria the most likely mechanism appears to be small calderas or diatreme conduit collapse seismic data indicates that the circular structures cut triassic permian and devono carboniferous strata and are infilled with pre upper oxfordian sediments therefore they are broadly synchronous with mid jurassic volcanism local well control demonstrates the presence of several thousand feet of basalt tuffs and lavas the model proposed here to account for the circular structures consists of an initial phase of diatreme maar cratering as magmas associated with the rattray volcanics member intruded shallow aquifers in the pentland formation fluviodeltaic rocks these maars enlarged and deepened via conduit wall collapse supplemented by downsag faulting due to magma withdrawal the post volcanic evolution of the structures included 1 differential erosion creating accommodation space which may have been infilled with oxfordian reservoir sands and 2 local reactivation by underlying basement faults in the kimmeridgian

tropical seasonality in the late campanian late cretaceous comparison between multiproxy records from three bivalve taxa from oman abstract geochemical proxy records from calcite shells of bivalves constitute an important archive for the reconstruction of palaeoenvironmental conditions on sub annual timescales however the incorporation of these trace element and stable isotope proxies into the shell is influenced by a multitude of physiological and environmental factors that need to be disentangled to enable reliable reconstruction of palaeoclimate and palaeoenvironment in this study records of multiple proxies in three bivalve taxa from the same late campanian locality in oman are used to study the expression of various geochemical proxies in relation to each other and to the palaeoenvironment micro x ray fluorescence mapping allows the localization discussion and evasion of diagenetically altered parts of the fossil shells x ray fluorescence line scanning calibrated with laser ablation inductively coupled plasma mass spectrometry is used to measure trace element profiles through well preserved calcitic parts of the shells records of stable carbon and oxygen isotope ratios of shell calcite are combined with these high resolution trace element concentration profiles to study sub annual variations in shell chemistry and reconstruct changes in the palaeoenvironment of the bivalves on a seasonal scale spectral analysis routines are used to detect cyclicity in stable isotope 18o and 13c and trace element mg ca sr ca s ca and zn ca records differences in seasonal expression between these chemical proxies and between individual shells are discussed in terms of the relative influence of palaeoenvironment and potential species specific physiological effects stable oxygen isotope ratios between shells suggest a local palaeotemperature seasonality of 8 c around an annual mean of 28 c with the shell of the rudistid torreites sanchezi milovanovici yielding slightly higher average temperatures the discussion of the application of various mg ca palaeotemperature calibrations on mg ca records in these bivalve species emphasizes the complexity of using trace element proxies in extinct bivalve species it shows that long term changes in mg ca ratios in ocean water need to be taken into account and that mg ca ratios in bivalves might be influenced by vital effects sr ca and s ca ratios in these fossil taxa are likely controlled by growth and metabolic rates of the shell although an influence of local salinity on strontium to calcium ratios cannot be excluded sub annual variations in zinc concentrations in shell calcite may reflect seasonal variations in palaeoproductivity and redox conditions in the water column

ocean circulation connecting fram strait to glaciers off northeast greenland mean flows topographic rossby waves and their forcing abstractfrom 2014 through 2016 we instrumented the 80 km wide norske trough near 78 n latitude that cuts across the 250 km wide shelf from fram strait to the coast our measurements resolve a 10

particle fabric in a small type 2 ignimbrite flow unit laacher see germany and implications for emplacement dynamics ignimbrites of the 13 ka upper laacher see tephra were deposited from small highly concentrated moderately fluidized pyroclastic flows their unconsolidated nature and the prominence of accidental devonian slate fragments make these ignimbrites ideal for clast fabric studies the upper flow unit of ignimbrite m14 has characteristics typical of a type 2 ignimbrite layer 2a and the lower part of layer 2b of the flow unit have strong upstream inclined a p fabrics a p means long particle axes parallel to flow direction only clasts with a b axial ratios of 2 5 or greater preserve good a p fabrics whereas the a b planes of flat fragments dip upstream irrespective of axial ratio the a axis fabric becomes weaker flatter and more girdle like in the upper half of layer 2b at one locality the a axis fabric appears to rotate 40 up through the flow unit suggesting either shear decoupling of different levels in the moving flow or unsteadiness effects in a flow depositing progressively at its base the existence of similarly strong a p fabrics in layer 2a and the lower half of layer 2b appears inconsistent with the common interpretation that ignimbrite flow units are emplaced as a plug of essentially non shearing material layer 2b on a thin shear layer layer 2a and that the entire flow freezes en masse to form the deposit the data suggest that if the flow froze en masse it was shearing pervasively through at least half its thickness another possibility is that the flow unit aggraded progressively from the base up and that the fabrics record the integrated history of shear directions and intensities immediately above the bed throughout the duration of deposition

an ignimbrite veneer deposit the trail marker of a pyroclastic flow abstract the term ignimbrite veneer deposit ivd is proposed for a new kind of pyroclastic deposit which is found associated with and passes laterally into taupo ignimbrite of valley pond type in new zealand it forms a thin layer mantling the landscape over 15 000 km 2 and is regarded as the deposit from the trailing tail of a pyroclastic flow where a relaxation of shear stress favoured the deposition of the basal part of the flow the ivd differs little in grain size from the associated ignimbrite but it shows a crude internal stratification attributed to the deposition of a succession of layers one after the passage of each pulse of the pyroclastic flow it locally contains laterally discontinuous lenses of coarse pumice lee side lenses on the far vent side of topographic obstacles in nearvent exposures the taupo ivd shows lensoid and cross stratified bed forms even where it stands on a planar surface attributed to deposition from a flow travelling at an exceedingly high velocity an ivd can be distinguished from a poorly sorted pyroclastic fall deposit because the beds in it show more rapid lateral variations in thickness it may show a low angle cross stratification and it contains carbonised wood from trees not in the position of growth from the deposit of a wet base surge because it lacks vesicles and strong antidune like structures and contains carbonised vegetation and from a hot and dry pyroclastic surge deposit because it possesses a high content of pumice and fines the significance of an ivd is that it records the passage of a pyroclastic flow where the flow itself has moved farther on

volcaniclastic sedimentation in a shallow water marginal basin the early miocene koura formation sw japan abstract the early miocene koura formation sw japan is composed mainly of reworked volcaniclastics and andesite to rhyolite pyroclastics and constitutes part of the volcanic zone of sw japan of that time reworked volcaniclastic sequences are thick and mostly coarse grained and based on conventional facies concepts are interpreted as shoreface to beach deposits turbidites and debris flow deposits thick acid tuffs intercalated in the volcaniclastic sequences individually show internal features characteristic of either subaerial or subaqueous ash flow emplacement or in some cases both andesite pyroclastic facies include surge and fall deposits facies relationships together with the fossil record indicate deposition in a shallow lacustrine environment the deposition rate of the koura formation was probably high enough to rapidly fill the shallow lake but sedimentation was balanced by rapid subsidence of the lake similar to lakes present within the modern volcanic zones of taupo new zealand and hohi japan the koura formation grades upward into marine deposits and may represent the initial volcanism and volcaniclastic sedimentation during the early stages of back arc or intra arc rifting

pebble orientation on large experimental debris flow deposits abstract replicable pronounced orientation of discoid pebbles 8 mm embedded on surfaces of large 10 m3 experimental debris flow deposits reveals that strongly aligned imbricate fabric can develop rapidly over short distances in mass flows pebble long axes aligned subparallel to deposit margins as well as subparallel to margins of surge waves arrested within the deposits pebble alignment exhibited modes both parallel to a p the primary flow direction intermediate axes dipped preferentially inward from surge wave margins b i orientation repetitive development of margin parallel imbricate fabric distributed across deposit surfaces provides compelling evidence that deposits formed dominantly through progressive incremental accretion rather than through simple en masse emplacement pronounced fabric along deposit and arrested surge wave margins reflects significant grain interaction along flow margins this sedimentological evidence for significant marginal grain interaction complements theoretical analyses iverson 1997 and other experimental data major 1996 iverson 1997 that indicate that resistance along flow margins is an important factor affecting debris flow deposition the fabric on the experimental deposits demonstrates that debris flows can develop strongly imbricate particle orientation that mimics fabric developed during fluvial deposition particle shape and local stress fields appear to have more control over fabric development than does general depositional process other criteria in addition to particle orientation are needed to discriminate mass flow from fluvial gravel deposits and to unravel depositional history

the geochemistry of carbonate diagenesis the past present and future stable carbon and oxygen isotopes 18o and 13c values and trace elements have been applied to the study of diagenesis of carbonate rocks for over 50 years as valuable as these insights have been many problems regarding the interpretation of geochemical signals within mature rocks remain for example while the 18o values of carbonate rocks are dependent both upon the temperature and the 18o value of the fluid and additional information including trace element composition aids in interpreting such signals direct evidence of either the temperature or the composition of the fluids is required such information can be obtained by analysing the 18o value of any fluid inclusions or by measuring the temperature using a method such as the clumped isotope technique such data speak directly to a large number of problems in interpreting the oxygen isotope record including the well known tendency for 18o values of carbonate rocks to decrease with increasing age unlike the 18o 13c values of carbonates are considered to be less influenced by diagenesis and more a reflection of primary changes in the global carbon cycle through time however many studies have not sufficiently emphasized the effects of diagenesis and other post depositional influences on the eventual carbon isotopic composition of the rock with the classic paradigm that the present is the key to the past being frequently ignored finally many additional proxies are poised to contribute to the interpretation of carbonate diagenesis although the study of carbonate diagenesis is at an exciting point with an explosion of new proxies and methods care should be taken to understand both old and new proxies before applying them to the ancient record

maar diatreme volcanoes a review maar diatreme volcanoes are produced by explosive eruptions that cut deeply into the country rock a maar is the crater cut into the ground and surrounded by an ejecta ring while the diatreme structure continues downward and encloses diatreme and root zone deposits here we attempt an evenhanded review of maar diatreme volcanology that extends from mafic to kimberlitic varieties and from historical maar eruptions to deeply eroded or mined diatreme structures we conclude that maar diatreme eruptions are episodic ejecta rings provide invaluable insight into eruption processes and sequence but are incomplete records of diatreme formation deposits within the diatreme structure include in varying proportions lower unbedded deposits sometimes typified by subvertical contacts among domains of debris emplaced sequentially and upper bedded deposits formed by sedimentation on surfaces open to the atmosphere a basal root zone comprises the transition from coherent magmatic feeder dike to clastic deposits formed by fragmentation of magma and enclosing country rock root zones are irregular in form and the clastic deposits are typically intruded by contorted dikes irregular root zone like chaotic breccias cut by contorted dikes are also present within diatreme deposits where they represent intra diatreme fragmentation zones and record changes in the location of the explosion locus during eruption

shallow water volcaniclastic deposition in the early archean panorama formation warrawoona group eastern pilbara block western australia abstract the panorama formation of the 3 3 3 5 ga warrawoona group in the eastern pilbara block western australia is a regional unit composed largely of silicified felsic volcaniclastic sandstone and tuff deposited at the close of a major period of early archean felsic volcanism it is divided into eight lithofacies a volcaniclastic tuff and tuff breccia b chert clast conglomerate c well bedded tuff and tuff breccia d cross stratified volcaniclastic sandstone e laminated and cross laminated siltstone f banded chert g silicified evaporite and h felsic lava wave formed features occur in lithofacies b c d and e the eight lithofacies occur in four facies associations 1 sequences of banded chert with lesser amounts of tuff representing clastic starved probable basinal environments 2 sequences of siltstone with variable amounts of tuff representing lower shoreface and prodelta environments 3 sequences of cross stratified sandstone with one or more other facies representing upper shoreface fan delta front and braided stream environments and 4 sequences of turbiditic and ash fall tuff representing subaqueous settings under the direct influence of pyroclastic volcanism in the north pole dome the panorama formation is developed directly over basalt and consists of shoaling upward sequences from base to top of associations 1 2 and 3 interpreted as sedimentation in prograding fan delta complexes flanked laterally by shoreface environments in other areas associations 3 and 4 are developed over thick sections of felsic lava and breccia of the duffer formation felsic volcanism controlled sediment composition sediment size and the rate of sediment supply to surrounding epiclastic systems deposition took place under regionally developed shallow water to subaerial conditions in which deep water distal facies were not well developed despite the abundance of wave influenced shallow water environments evidence for tides is rare probably because deposition took place under regionally microtidal marine conditions

deep seismic profile across a proterozoic collision zone surprises at depth collisions between continents generate the world s most striking mountains the deep structure of these collision zones inferred from seismic reflection profiles1 3 can be equally dramatic if less well understood improved knowledge of the structure of ancient collisional belts now known to have developed through plate tectonic processes4 5 can provide important new insights into the mechanisms of crustal growth although many such belts have been partly destroyed by severe post collisional deformation6 7 or magmatism8 some have been preserved in the stable interiors of continents9 one example is the early proterozoic trans hudson orogen9 10 in western canada here we present seismic reflection images across the entire orogen which reveal a broadly symmetric structure with reflections linked to island arc rocks dipping beneath both bounding archaean cratons the observed reflection geometries imply a doubling of crustal thickness during the collision along crust penetrating faults the presence of a significant amount of archaean crust at depth the extent of which could not have been determined from surface mapping suggests the need for caution in inferring crustal growth rate from the surface area of juvenile crust11 12

geology and diamond distribution of the 140 141 kimberlite fort a la corne central saskatchewan canada abstract the cretaceous age fort a la corne falc kimberlite province comprises at least 70 bodies which were emplaced near the edge of the western canadian interior seaway during cycles of marine transgression and regression many of the bodies were formed during a marine regression by a two stage process firstly the excavation of shallow but wide craters and then subsequent infilling by xenolith poor crater facies subaerial primary pyroclastic kimberlite the bodies range in size up to 2000 m in diameter but are mainly less than 200 m thick and thus comprise relatively thin but high volume pyroclastic kimberlite deposits each body is composed of contrasting types of kimberlite reflecting different volcanic histories and therefore are considered separately the 140 141 kimberlite is the largest delineated body in the province estimated to have an areal extent below glacial quaternary sediments in excess of 200 ha the infilling of the 140 141 crater is complex resulting from multiple phases of kimberlite the central part of the infill is dominated by several contrasting phases of kimberlite one of these phases is a primary pyroclastic airfall mega graded bed up to 130 m in thickness the constituents grade in size from very fine to coarse macrocrystic kimberlite through to a basal breccia the mega graded bed is a widespread feature within parts of the body examined to date and at this current stage of evaluation appears to explain a variable diamond distribution within a tested portion of the pipe a second different phase of kimberlite is interpreted as representing a younger nested crater within the mega graded bed centrally located thicker intersections 450 m of this younger kimberlite may indicate a vent for the kimberlite crater the thickness of the mega graded bed increases with proximity to the younger kimberlite in the study area macrodiamond minibulk sample grades from the mega graded bed have been obtained from nine large diameter drill holes located within the northwest part of the body from an area of 20 ha which represents approximately 10 of the currently modeled kimberlite outline diamond grade increases with depth within the mega graded bed and also increases within the same unit towards the centrally positioned younger kimberlite macrodiamond sample grades vary from low at the top of the mega graded bed to considerably higher grades near the base total sample grade per drill hole varies from moderate near the vent feature to lower grades 200 300 m from the vent feature macrodiamond stone frequency measured in stones per tonne shows a pronounced relationship with depth and proximity to the vent feature within the mega graded bed there is a strong correlation between depth and increased stones per tonne and a similar correlation between stones per tonne and proximity to the vent feature the data supports the emplacement model of the mega graded bed and in turn this information is useful in understanding the macrodiamond distribution within this bed

emplacement and reworking of cretaceous diamond bearing crater facies kimberlite of central saskatchewan canada in central saskatchewan canada kimberlites were emplaced into cretaceous marine and nonmarine clastic sediments core recovered from one drill hole that intersects kimberlite smeaton fac uk core 169 8 was selected for an integrated study involving sedimentology volcanology mineralogy geochemistry palynology micropaleontology organic petrology and radiometric age determination only crater facies kimberlite has been observed there is no indication of the locations of feeder dikes four varieties of kimberlite occur all originating from subaerial volcanism 1 fluvial reworked kimberlite 2 diamondiferous kimberlite lapillistone air fall deposits 3 kimberlite olivine crystal tuff air fall deposits and 4 diamondiferous marine wave reworked kimberlite within the multiple primary eruptive phases of the kimberlite air fall deposits the volcanic style changed upward with time from violent strombolian to more explosive volcanism the bulk of the volcanism formed conformable air fall deposits on terrestrial sediments of the cantuar formation resulting in the development of positive relief tephra cones subsequent marine transgression associated with the westgate formation partially beveled the top of the cone the kimberlite air fall deposits contain microdiamonds 5 to 25 m in diameter the maximum temperature and vitrinite reflectance values of coaly matter in the kimberlites indicate that these deposits although originally derived from magma at high temperatures did not thermally affect entrained surficially derived clasts or the country rock during emplacement the chemical content of intrakimberlite shale clasts is markedly different from the marine and nonmarine shales and indicates significant synemplacement and postemplacement fluid movement through the volcanic pile at least two episodes of kimberlite volcanism occurred in the middle and late albian paleontologically assigned a u pb perovskite radiometric age of 101 1 2 2 ma from a kimberlite lapillistone from the younger episode of volcanism is internally consistent with biostratigraphic studies that constrain the kimberlite volcanism as post middle albian and pre late albian to late albian

growth of phreatomagmatic explosion craters a model inferred from suoana crater in miyakejima volcano japan abstract a subvertical cross section of a maar diatreme volcano is exposed in the wall of the a d 2000 caldera on miyakejima volcano the maar suoana is one of the lateral vents of this volcano and it was inferred to be formed in the 7th century the subvertical wall of the a d 2000 caldera truncated the suoana maar crater at its center revealing the near comlete cross section of this small maar diatreme volcano exposed in the cross section are a 400 m wide maar crater an associated tuff ring with a maximum thickness of 20 m a diatreme extending vertically to a depth of about 220 m from the floor of the maar crater and a feeder dike connected to the base of the diatreme the depth of the diatreme structure is about 260 m from the original ground surface the outline of the diatreme resembles an upward opening funnel with an almost vertical wall below 560 m asl and an upward flaring wall above 560 m asl coarse grained volcanic breccia fills the diatreme the deposits of which can be divided into 6 units based on lithological and structural characteristics the upper half of the diatreme is filled with landslide deposits mainly derived from the surrounding crater wall the bottom of the diatreme is occupied by massive explosion breccia some coherent blocks were detached from the wall of the diatreme and preserved in the diatreme fill the y shaped cross sectional geometry of the suoana diatreme is the result of a combination of an underground subsidence in the lower part of the diatreme and the surface landslide in its upper part the inwardly inclined stratification of pyroclastic rock units and development of many small faults in the diatreme filling breccia indicate successive collapse and deformation of these materials within the diatreme during the eruption the upper part of the diatreme was formed by the landslides of the crater wall induced by the subsidence of the crater floor discharge of tephra from the bottom of the diatreme caused infill subsidence which induced sliding of the inner wall of the crater as a result the topographic diameter of the crater became much larger than that of the diatreme itself the tephra ring surrounding the crater consists mainly of pyroclastic fall deposits

freshening of the alaska coastal current recorded by coralline algal ba ca ratios arctic ocean freshening can exert a controlling influence on global climate triggering strong feedbacks on ocean atmospheric processes and affecting the global cycling of the world s oceans glacier fed ocean currents such as the alaska coastal current are important sources of freshwater for the bering sea shelf and may also influence the arctic ocean freshwater budget instrumental data indicate a multiyear freshening episode of the alaska coastal current in the early 21st century it is uncertain whether this freshening is part of natural multidecadal climate variability or a unique feature of anthropogenically induced warming in order to answer this a better understanding of past variations in the alaska coastal current is needed however continuous long term high resolution observations of the alaska coastal current have only been available for the last 2 decades in this study specimens of the long lived crustose coralline alga clathromorphum nereostratum were collected within the pathway of the alaska coastal current and utilized as archives of past temperature and salinity results indicate that coralline algal mg ca ratios provide a 60 year record of sea surface temperatures and track changes of the pacific decadal oscillation a pattern of decadal to multidecadal ocean atmosphere climate variability centered over the north pacific algal ba ca ratios used as indicators of coastal freshwater runoff are inversely correlated to instrumentally measured alaska coastal current salinity and record the period of freshening from 2001 to 2006 similar multiyear freshening events are not evident in the earlier portion of the 60 year ba ca record this suggests that the 21st century freshening of the alaska coastal current is a unique feature related to increasing glacial melt and precipitation on mainland alaska

experiments on deaerating granular flows and implications for pyroclastic flow mobility 1 granular flows were generated by the release of beds of particles in various fluidized states which then deaerated in a horizontal channel we describe characteristics of the flows and their deposits morphological similarities between deposits in experiments and in the field suggest that pyroclastic flow deposits form from a fluidized mixture the experiments show that slightly expanded fluidized flows are more mobile than non fluidized flows of equivalent volume and material composition they travel to a fixed distance from their source which depends only weakly on their initial degree of fluidization flows of fine particles 100 m deaerate slowly and are highly mobile pyroclastic flows commonly have large amounts of fine ash which may have a controlling influence on their high mobility

eruption of kimberlite magmas physical volcanology geomorphology and age of the youngest kimberlitic volcanoes known on earth the upper pleistocene holocene igwisi hills volcanoes tanzania the igwisi hills volcanoes ihv tanzania are unique and important in preserving extra crater lavas and pyroclastic edifices they provide critical insights into the eruptive behaviour of kimberlite magmas that are not available at other known kimberlite volcanoes cosmogenic 3he dating of olivine crystals from ihv lavas and palaeomagnetic analyses indicates that they are upper pleistocene to holocene in age this makes them the youngest known kimberlite bodies on earth by 30 ma and may indicate a new phase of kimberlite volcanism on the tanzania craton geological mapping global positioning system surveying and field investigations reveal that each volcano comprises partially eroded pyroclastic edifices craters and lavas the volcanoes stand 102 to 106 pa s for kimberlite attributed to degassing and in vent cooling each volcano is inferred to be the result of a small volume short lived days to weeks monogenetic eruption the eruptive processes of each igwisi volcano were broadly similar and developed through three phases 1 fallout of lithic bearing pyroclastic rocks during explosive excavation of craters and conduits 2 fallout of juvenile lapilli from unsteady eruption columns and the construction of pyroclastic edifices around the vent and 3 effusion of degassed viscous magma as lava flows these processes are similar to those observed for other small volume monogenetic eruptions e g of basaltic magma

structure and eruptive mechanisms at surtsey volcano iceland glassy basalt tuff was the primary material cored in 1979 from a 181 m deep drill hole on the east tuff ring of surtsey volcano despite the fact that the hole extends 122 m below sea level all the core is similar to the exposed tephra composing the two tuff rings of the island the tuff includes abundant accretionary lapilli and tuff vesicles indicating that it was all deposited subaerially during the growth of the tuff rings repeated hydromagmatic explosion cycles began with a series of intermittent tephra finger explosions leading up to continuous uprush explosions which lasted for several minutes to several hours this nozzle like continuous activity produced eruption columns 100 250 m in diameter and 500 2000 m in height which probably quarried several hundred metres below the ground surface the continuous uprush explosion type provides a reasonable mechanism to excavate a diatreme from the top down during construction of the tuff rings concentric faults repeatedly downdropped a funnel like structure 400 800 m in diameter several hundred metres thus accounting for the presence of subaerially deposited tephra in the drill core far beneath sea level ring dykes later intruded upward along these faults and fed small lava flows heat in the surface tephra probably originated primarily from these shallow intrusions

improving the detection of shell alteration implications for sclerochronology abstract sclerochronology makes use of fossil shell archives to establish records allowing for investigation of high resolution environmental dynamics nevertheless this potential can often not be fully exploited due to the interplay between paleoenvironmental variability vital effects and the potential diagenetic modification of skeletal materials which often results in highly complex records a novel dynamic approach aiming to separate pristine from altered shell material for paleoclimate and paleoenvironmental reconstructions is proposed seventeen fossil bivalve shells requieniid rudists pectinids and chondrodonts from two neighbouring lower cretaceous albian shallow water sections lusitanian basin western portugal were analysed for their major and trace elemental compositions using high resolution quantitative xrf line scans their complex records were subject to a novel statistical analysis protocol which tested mono and multi species datasets as well as comparing shells from both locations characteristic elemental associations reveal the differential impact of early and late diagenetic alteration processes the incorporation of elements associated with detrital contribution fe si al is attributed to syn depositional bioerosion shell boring in clear contrast shell portions showing a strong correlation between fe and mn are indicative of later diagenetic alteration the influence of each process is different at each site revealing local differential alteration pathways mono specific comparisons provides identical geochemical responses suggesting that intra specific differences do not control the observed elemental patterns in contrast inter species tests rendered a clear separation in the way elements are incorporated in the shells of pectinids and requieniids e g as evidenced by differences in mg or sr content such differences can be linked to differential biomineralization pathways easily detected by the applied method we present a new dynamic method for distinguishing pristine from altered shell material not relying on arbitrary diagenetic thresholds for trace element content by clearly identifying shell alteration pathways syn to post depositional processes are recognized a progressive cleaning of the elemental dataset allows paleoenvironmental studies to be based on the most pristine data contributing to unravelling the complex interplay between climate environmental dynamics and their impact on biomineralization processes and sclerochronological archives

the relationship between shell size and mg ca sr ca δ18o and δ13c of species of planktonic foraminifera the relationship between shell size and mg ca sr ca 18o and 13c of planktonic foraminiferal calcite has been investigated using seventeen species in six different size fractions mg ca increases and sr ca decreases with increasing size except for two globorotaliid species which show the opposite trend the changes in mg ca broadly follow 18o calcification temperatures except that surface and near surface dwelling species show larger changes in mg ca than can be accounted for by differences in calcification temperature derived from 18o the increases in mg ca and decreases in sr ca vary linearly with the well established increase in 13c with size this is consistent with smaller individuals calcifying faster than larger individuals and larger individuals forming calcite that more closely reflects seawater temperature and composition it appears that variations in calcification rate affect mg and sr shell chemistry the observations may account for part of the temporal variability in foraminiferal sr ca within a single size fraction that has been attributed to changes in seawater sr ca

submarine crystal tuffs their origin using a lower devonian example from southeastern australia summary the submarine crystal rich volcaniclastics of the lower devonian merrions tuff contain concentrations of angular to euhedral volcanic quartz plagioclase and orthoclase lithic fragments largely altered vitriclasts are minor components and the average matrix content is 37 6 associated dacite andesite and rhyodacitic lavas have average groundmass contents of 64 2 rare shards in the graded pelitic tops of the thick volcaniclastic sedimentation units suggest that the mode of fragmentation originally was by explosive magmatic eruptions the sedimentology of the volcaniclastics suggests subsequent redeposition by cold state mass flow processes the volcaniclastics form an isotopically coherent suite and so redeposition must have occurred essentially contemporaneously with eruption the high crystal fragment concentration in these volcaniclastics is higher than lavas and ignimbrites and suggests some process whereby the groundmass fraction of the erupting magma is selectively removed so concentrating the crystal fraction the crystal rich character of the crystal tuffs is not simply due to explosive eruption several primary and secondary factors processes could have interacted to ultimately produce the crystal rich character these being i eruption of highly crystallized magmas 65 phenocrysts ii concentration of crystals in primary eruption columns iii concentration of crystals in any resulting pyroclastic flows fine vitric ashes being elutriated out and being carried away in accompanying trailing ash clouds iv concentration of crystals in secondary eruption columns generated by the flow of hot pyroclastic flows into the ocean and v concentration of crystals by the elutriation of fines into the trailing fine sediment cloud accompanying submarine mass flows resulting from the slumping of volcaniclastic aggregates from shallow marine subaerial settings

contained reflected turbidity currents from the middle ordovician cloridorme formation quebec canada an alternative to the antidune hypothesis the parautochthonous cloridorme formation is a syn orogenic flysch succession that was deposited in an elongate foredeep basin as mainly lower middle fan outer fan and basin floor deposits the basin floor deposits about 1 5 km thick are confined to members 1 2 and 1 and are characterized by graded thick 1 10 m mud rich calcareous greywacke beds previously interpreted as deposits of concentrated muddy unidirectional turbidity currents that locally generated backset antidune lamination in internally stratified flows the dominant flow directions were from east to west but west to east transport also occurred as seen in the orientation of ripples climbing ripples flutes consistently overturned flames and grain imbrication we believe that the flows that deposited these thick calcareous greywacke beds reversed by roughly 180 one or more times during deposition of the lower sandy part of the beds flow reversals are consistent with the sharp grain size breaks and mud partings within sandy divisions measurement of grain fabric relative to stratification in the most celebrated antidune bedforms indicates flow from west to east thus the bedforms were produced by west to east migration of megaripples not by the upcurrent migration of antidunes the thick muddy beds were deposited by large volume muddy flows that were deflected and reflected from the side slopes and internal topographic highs of a confined basin floor much like the contessa and similar beds of the italian apennines large quantities of suspended mud were ponded above the irregular basin floor and settled to produce the thick silty mudstone caps seen on each bed because of their mode of emplacement we propose that these beds be called contained turbidites

lithic breccias in intermediate volume phonolitic ignimbrites tenerife canary islands constraints on pyroclastic flow depositional processes abstract lithic occurrences within quaternary phonolitic ignimbrites on tenerife canary islands fall into three broad groupings 1 massive ignimbrite with large floating lithics 2 basal lithic rich bedforms and 3 matrix to clast supported lithic breccias within ignimbrite massive ignimbrite divisions commonly contain large outsized either solitary or scattered lithics which are mostly monomictic and derived locally from substrate erosion by pyroclastic density currents low and high aspect ratio lithic rich bedforms occur at the base of several ignimbrites most bedforms are asymmetric with steeper lee sides and they are buried by stratified and or massive ignimbrite internally most bedforms are massive some however exhibit an upstream inclined stratification indicating upcurrent migration of the bedform which is interpreted to record antidune like flow regimes locally derived basalt clasts are important constituents of some of these bedforms which have also been sourced through substrate erosion matrix to clast supported pebble to boulder sized lithic breccias occur at various heights within massive ignimbrite lithic breccias at or near the top of most ignimbrites contain vent derived lithics and record a late flux of lithic material from the vent during a sustained pyroclastic flow event extensive boulder sized breccias at the top of two ignimbrites are interpreted to record the onset of caldera collapse late in the pyroclastic flow forming eruptions some breccias contain boulders that are oriented with long axes transverse to flow indicating late stage tractional transport thin bedded matrix supported lithic breccias or lithic trains and stratified ignimbrite are commonly developed adjacent to or immediately above topographic highs these facies laterally merge into massive ignimbrite infilling topographic lows massive ignimbrite is interpreted to be deposited from a high particle concentration hindered settling zone inverse grading and long axis parallel to bedding imbrication of lithics within the thin bedded breccia facies are interpreted to record deposition under modified grain flow conditions a variety of depositional processes are thus recorded and the relationship between lithic breccias ignimbrite facies and topography indicates that there were spatial variations in depositional mechanisms at any one instant the vertical sequence of bedform stratified ignimbrite massive ignimbrite characterises the lower part of several ignimbrites and is interpreted to record increasing rates of deposition from a sustained current multilayered lithic breccias at various heights within massive ignimbrite are a form of clast compositional zonation and reflect temporal changes in supply flow competence and capacity