the lilliput effect in the aftermath of the end permian extinction event early triassic animal body fossils and trace fossils are small relative to those in older and younger intervals size decreases sharply through the end permian extinction event and permian triassic boundary and the smallest sizes are encountered in the parvus and isarcica zones of the earliest induan animals appearing within these two zones are also exceedingly small compared to younger congenerics and conspecifics temporary dramatic size decrease of surviving taxa in the immediate aftermath of the extinction event is an example of the lilliput effect coined by urbanek a 1993 biotic crises in the history of upper silurian graptoloids a palaeobiological model historical biology 7 29 50 body size increases somewhat from the carinata zone mid induan but remains depressed for the duration of the early triassic and pre extinction sizes are not commonly recorded until at least the middle triassic marine and terrestrial faunas appear to be similarly affected the lilliput effect and longer term size reduction could be the result of several factors environmental parameters such as marine anoxia due to low atmospheric concentrations of oxygen at this time coupled with sluggish ocean circulation in a greenhouse world and food shortage are the likely proximal causes for the early triassic lilliput effect no single cause can explain all the observations and a combination of factors are likely to be involved

an early lutetian carbon cycle perturbation insights from the gorrondatxe section western pyrenees bay of biscay turbidites and kaolinite a 3 decline in the bulk d 13 c record a 1 decline in benthic foraminiferal d 13 c followed by a gradual recovery a distinct deterioration in foraminiferal preservation high proportions of warm water planktic foraminifera and opportunistic benthic foraminifera and reduced trace fossil and benthic foraminiferal diversity thus recording a significant environmental perturbation the onset of the perturbation correlates with the c21r h6 event recently defined in the atlantic and pacific oceans which caused a 2c warming of the seafloor and increased carbonate dissolution the perturbation was likely caused by the input of 13 c depleted carbon into the ocean atmosphere system thus presenting many of the hallmarks of paleogene hyperthermal deposits however from the available data it is not possible to conclusively state that the event was associated with extreme global warming based on our analysis the perturbation lasted 226 kyr from 47 44 to 47 214 ma and although this duration suggests that the triggering mechanism may have been similar to that of the paleocene eocene thermal maximum petm the magnitude of the carbon input and the subsequent environmental perturbation during the early lutetian event were not as severe as in the petm

faunal turnovers in central pacific benthic foraminifera during the paleocene eocene thermal maximum abstract although it is well known that the paleocene eocene thermal maximum petm coincided with a major benthic foraminiferal extinction event the detailed pattern of the faunal turnover has not yet been clarified our high resolution benthic foraminiferal and carbon isotope analyses at the low latitude pacific ocean shatsky rise have revealed the following record of major faunal transitions 1 an initial turnover which involved the benthic foraminiferal extinction event bfe the bfe marked by a sharp transition from pre extinction fauna to disaster fauna represented by small sized bolivina gracilis expresses the onset of the petm and the abrupt extinction of about 30 of taxa this faunal transition lasted about 45 74 kyr after the initiation of the petm and was followed by 2 the appearance of opportunistic fauna represented by quadrimorphina profunda which existed for about 74 91 kyr after the initiation of the petm these two faunas which appeared after the extinction event are characterized by low diversity and dwarfism possibly due to lowered oxygen condition and decreased surface productivity the second pronounced turnover involved the gradual recovery from opportunistic fauna to the establishment of recovery fauna which coincided with the recovery about 83 91 kyr after its initiation

high palaeolatitude hodh mauritania recovery of graptolite faunas after the hirnantian end ordovician extinction event marine shales directly overlying lower hirnantian uppermost ordovician glacially related sediments in mauritania northwest africa have produced a rich graptolite fauna spanning the ordovician silurian boundary in an area of high palaeolatitude the lowermost transgressive sandy shales are barren of graptolites but overlying shales show a sudden appearance of a diverse fauna indicative of the terminal ordovician persculptus zone suggesting that with improving conditions colonisation by a relatively cold tolerant fauna was possible this fauna is replaced by a low diversity assemblage dominated by long ranging taxa probably representing the basal silurian acuminatus and atavus zones with the extinction of the persculptus zone fauna conditions were still hostile to warm water silurian graptolites and a normalograptus fauna was again established a sudden influx of fairly diverse taxa marks the base of the acinaces zone and the establishment of a typical lower silurian fauna with the establishment of warmer water conditions

the formation of helgafell southwest iceland a monogenetic subglacial hyaloclastite ridge sedimentology hydrology and volcano ice interaction abstract helgafell a little eroded basaltic hyaloclastite ridge in southwest iceland formed in a single eruption under a pleistocene ice sheet the ice thickness at the eruption site was at least 500 m and it was probably located some 15 km from the glacier s snout the eruption created a 2 km long 0 8 km wide and initially 300 m high ridge gravity modelling indicates that helgafell has a bulk density of 1800 kg m 3 and that holocene lavas around it are 40 80 m thick this confirms that helgafell is predominantly made of hyaloclastite with pillow lavas and intrusions only making up a few percent of the total volume the southeast side is made of unsorted eruption fed hyaloclastites considered to have been piled up against an ice wall while moderately to well sorted water transported material is found on the northwest side glacier flow and meltwater drainage was towards the northwest the absence of basal pillow lavas suggests that magma fragmentation occurred from the onset of the eruption until its end the lithofacies preserved indicate a fully subglacial eruption although a final subaerial eruptive phase may have taken place through an ice chimney the volatile contents h 2 o 0 26 0 37 wt of several glass samples from the southeast side of the mountain indicate water pressures of 1 mpa throughout the eruption efficient syn eruptive drainage of meltwater coupled with rapid ice subsidence probably led to partial dynamic support of the ice causing water pressure in the vault to be much lower than the static load of the overlying ice observed lack of correlation between elevation and volatile content may be a consequence of gradual reduction in dynamic support as the eruption rate declined and the edifice grew higher helgafell demonstrates that explosive activity may occur under 500 m thick ice and it may be an analogue to the ridge formed in the gjalp eruption in 1996

a facies model for a quaternary andesitic composite volcano ruapehu new zealand ruapehu composite volcano is a dynamic volcanic sedimentary system characterised by high accumulation rates and by rapid lateral and vertical change in facies four major cone building episodes have occurred over 250 ka from a variety of summit flank and satellite vents eruptive styles include subplinian strombolian phreatomagmatic vulcanian and dome related explosive eruptions and extrusion of lava flows and domes the volcano can be divided into two parts a composite cone of volume 110 km3 surrounded by an equally voluminous ring plain complementary portions of ruapehu s history are preserved in cone forming and ring plain environments cone forming sequences are dominated by sheet and autobrecciated lava flows which seldom reach the ring plain the ring plain is built predominantly from the products of explosive volcanism both the distal primary pyroclastic deposits and the reworked material eroded from the cone much of the material entering the ring plain is transported by lahars either generated directly by eruptions or triggered by the high intensity rain storms which characterise the region ring plain detritus is reworked rapidly by concentrated and hyperconcentrated streams in pulses of rapid aggradation immediately following eruptions and more gradually in the longer intervals between eruptions

evaluating compositional turnover of brachiopod communities during the end triassic mass extinction northern calcareous alps removal of dominant groups recovery and community reassembly abstract this study highlights the role of large scale physical perturbations in mediating biotic replacements and shows that an environmental disturbance at the triassic jurassic t j boundary correlates with abrupt and substantial changes in the composition of brachiopod communities disturbance changed the phylogenetic structure of early jurassic brachiopod communities owing to a removal of higher taxa that were abundant in the late triassic a replacement of brachiopod communities through the rhaetian in the kossen basin northern calcareous alps related to a combination of habitat tracking and immigration local extinction events indicates a high compositional turnover this turnover is of local nature only because early rhaetian communities migrated or tracked their habitats beyond the kossen basin and persisted through to the late rhaetian in other regions a siliciclastic interval that is several meters thick with rare brachiopods dated as the earliest hettangian marks the extinction survival interval this interval is coeval with a negative carbon isotope anomaly implying a correlation with global perturbation of carbon cycle a rapid brachiopod recovery is indicated by a presence of several distinct communities in late early and middle hettangian that show onshore offshore differentiation and beta diversity comparable to pre extinction levels analyses of similarities demonstrate that 1 the compositional turnover of brachiopod communities on generic level at the t j boundary r 0 83 is substantially higher than turnovers between the rhaetian zones r 0 28 0 57 and between the hettangian zones r 0 28 0 53 and 2 the turnover at superfamily level at the t j boundary accounts for differential composition of rhaetian and hettangian communities a global extinction of athyridoid spondylospiroid and dielasmatoid superfamilies characterized by high community level abundances during the late triassic led to a new assembly of jurassic brachiopod communities from surviving superfamilies in addition to persisting rhynchonellids and zeillerioids hettangian brachiopod communities were dominated by terebratuloids spiriferinoids and pennospiriferinoids these superfamilies were characterized in the late triassic by low community level abundance we argue for tracking the phylogenetic structure of communities across mass extinction events because a measurement of the turnover in community level abundance of higher taxa can be highly relevant for estimating the ecologic impact of mass extinctions taxonomic extinction rate metrics or diversity measures can be depressed by surviving taxa that do not re attain their pre extinction community level abundance

detritus feeding as a buffer to extinction at the end of the cretaceous at the end of the cretaceous the principal animals that became extinct such as dinosaurs marine animals that lived in the water column and benthic filter feeders were in food chains tied directly to living plant matter animal groups less affected by extinction including marine benthic scavengers and deposit feeders small insectivorous mammals and members of stream communities were in food chains dependent on dead plant material the proposal that an asteroid or comet impact at the end of the cretaceous produced a dust cloud that cut off photosynthesis for several months is consistent with this pattern of extinction food chains dependent on living plant matter crashed while food chains based on detritus were buffered from extinction because there was a food supply adequate for the interval when photosynthesis was halted

origin and distribution of terrestrial organic matter in the nw mediterranean gulf of lions exploring the newly developed bit index the branched and isoprenoid tetraether bit index is based on the relative abundance of nonisoprenoidal glycerol dialkyl glycerol tetraethers gdgts derived from organisms living in terrestrial environments versus a structurally related isoprenoid gdgt crenarchaeol produced by marine crenarchaeota the bit index varies between 0 and 1 representing marine and terrestrial organic matter om end members respectively hopmans et al earth planet sci lett 224 107 116 2004 in this study the applicability of the bit index to trace terrestrial om is tested in combination with other organic parameters toc c n ratio 13corg total lipid and n alkane in the gulf of lions a river dominated continental margin of the western mediterranean we analyzed a variety of soils and riverbed sediments from the continent as well as surface sediments from the shelf and canyons the bit index in soils and riverbed sediments shows high values 0 9 while it varies between 0 02 and 0 83 in marine sediments decreasing seaward from the inner shelf to the slope for marine surface sediments high bit values are associated with lower 13corg values as well as higher toc contents and higher n alkane concentrations our results confirm that the bit index can be applied in coastal marine environments in order to characterize terrestrial om as proposed by hopmans et al 2004 therefore the bit index is a useful addition to the proxies presently available for studying the origin and distribution of om in continental margins and especially valuable in multiproxy studies

silica secreting biota and mass extinctions survival patterns and processes abstract high survival and at least regional blooms of siliceous marine groups with coeval retreat of calcareous organisms is known from the frasnian famennian radiolarians silicisponges and end cretaceous diatoms radiolarians mass extinctions a strictly actualistic approach to the palaeoecology of silica secreting biota is of limited significance especially for silica enriched and oligotrophic palaeozoic epeiric seas and in particular during biotic turnovers adaptation among silica secreting marine plankton has led toward more efficient utilization of shrinking dissolved silica resources within surface waters of cenozoic oceans as shown by both radiolarians and diatoms this biosiliceous signal during the major biotic crises is mostly explained by a large scale increase in volcano hydrothermal activity during major plate boundary re arrangements triggering global ecosystem perturbations the cumulative stimulus favoured siliceous versus calcareous biota growth deposition and preservation because of 1 a higher rate of input of silica and other nutrients promoting eutrophication pulses 2 a punctuated or reversed greenhouse climatic effect episodically coupled with 3 vigorous oceanic circulation due to a variety of volcanogenic upwellings and turnovers siliceous communities adapted to more eutrophic conditions have thrived in the stressed niches on the other hand expanding anoxia and nutrification may lead to a stepwise loss of deep water niches and consequent selective decline of more specialized oligotrophic radiolarians and other pelagic biota by contrast siliceous faunas experienced severe non selective losses during the end permian mass extinction recorded as a chert gap thus the greatest environmental disaster of the phanerozoic was driven by a unique set of killing factors extremely effective for radiolarian productivity e g due to the combination of a drastic volcanic winter with expanding superanoxia

glaciovolcanism at volcan sollipulli southern chile lithofacies analysis and interpretation magma ice meltwater interactions produce diverse landforms and lithofacies reflecting the multitude of factors that influence glaciovolcanism including both magmatic e g composition eruption rate and glacial e g ice thickness thermal regime conditions this is exemplified by the walls of the partly ice filled summit caldera of volcan sollipulli a stratovolcano in southern chile which include lithofacies from eruptions of a wide range of magma compositions beneath or in contact with ice here we analyse these lithofacies and hence propose new interpretations of the eruptive and glacial history of sollipulli the facies include a thick laterally extensive sequence of fragmental glaciovolcanic deposits comprising massive mafic lava pillow bearing hyaloclastite overlain by sills and then hyaloclastic debris flow deposits similar to dalsheidi type sequences the distribution and thickness of these units indicate an unusual abundance of magma meltwater interaction for an arc stratovolcano in temperate latitudes perhaps due to eruptions beneath a thick ice cap coherent lava coulees domes lobes and stacks of basaltic andesite trachydacite composition are present around the top of the caldera rim these display morphologies and fracture patterns on caldera facing margins that indicate that the caldera was filled with ice when these lavas were erupted the lithofacies characterised in this study demonstrate the diversity of glaciovolcanism that is possible at arc stratovolcanoes capped by temperate ice or with ice filled calderas and the potential for uncertainties in inference of the palaeoenvironmental conditions of their emplacement

concepts and methods of high resolution event stratigraphy modern geological analyses involving sedimentary rocks require a high resolution system of dating integrating and correlating diverse strati graphic geochemical and paleontological data that also takes into account the possibility that short term phenomena 100 kyr or less exercise a strong control on sedimentation such phenomena may be extraterrestrial tectonic volcanic oceanographic climatic sedimentologic and or bio logic in origin some reflect unpredictable perturbations of local to global scale but most short term phenomena are predictable and may be either autocyclic locally regulated with limited stratigraphic continuity or allo cyclic in nature regionally to globally regulated with extensive strati graphic continuity beerbower 1964 a stratigraphic system based on short term phenomena would ideally be chronostratigraphic involving the identification and regional tracing of time lines isochronous surfaces or very thin event deposits and easily integrated with refined independently derived biostratigraphic and geochronologic systems an intensive search for such a new and revolutionary system of stratig raphy has been prompted in many parts of the phanerozoic by attain ment of plateaus in stratigraphic resolution utilizing the more standard tools of magnetostratigraphy biostratigraphy and geochronology most magnetic reversals have been identified biostratigraphic systems can be no more refined than the maximum evolutionary rates of component taxa and their major structures known for many favored groups and geo chronology is regulated by the analytical confidence limits of radiometric

a model for submarine rhyolite dome growth ponza island central italy abstract the late pliocene rhyolitic submarine volcanic rocks of ponza island italy can be interpreted as the subaqueous equivalent of subaerial dome complexes in terms of geometry and structure three coalescing domes of about 1 km radius and aligned along a ne trending regional fracture have been identified the main difference between subaqueous and subaerial lava domes is that in a subaqueous environment lava is likely to undergo pervasive hyaloclastic brecciation so that domes are mainly composed of variously brecciated in situ to clast rotated hyaloclastite rather than coherent lava we suggest that the shape and rheologic behaviour through time of submarine domes are closely controlled by the development and thickness of the particulate hyaloclastic carapace which assumes the role of the solid crust of domes in subaerial environment the thickness of the hyaloclastic carapace at ponza is greater than 150 m and emplaced during several different pulses or eruptions in the earliest pulses lava is directly extruded on the seafloor and produces hyaloclastite the degree of brecciation of which decreases inward to the coherent flow banded rhyolite lava of the feeder dike once the hyaloclastic carapace is formed further pulses of magma combined with increase in height of the dome result in a local stress pattern characterised by a vertical 1 2 3 producing concentric and radial fractures and normal faults the newly rising magma shielded by the hyaloclastic carapace can intrude along these fault and fracture systems and invade previously emplaced but still water saturated hyaloclastite this produces the characteristic pattern of dikes observed at ponza as a series of concentric dikes that are progressively less inclined outward with respect to the dome centre these late stage dikes in turn produce hyaloclastite at their margins but generally less fragmented than the embedding hyaloclastite probably because the ascending magma is better shielded from direct contact with sea water periodic gravity collapses of the dome maintain the equilibrium between height and radius of the dome as suggested at ponza by the presence of mass flow deposits and the development of small topographic basins on top of the domes probably related to debris removal some of these topographic depressions host subaqueous pyroclastic deposits suggesting that if due to vertical growth of the dome water depth above the dome becomes shallower hydromagmatic explosions may occur

how and why did the lingulidae brachiopoda not only survive the end permian mass extinction but also thrive in its aftermath the end permian mass extinction devastated most of the organisms in the sea and on land however a few late permian taxa survived the mass extinction and also the subsequent early triassic post extinction catastrophic environments among them the lingulidae brachiopods were perhaps one of the most noted conquerors not only had they survived the mass extinction but also they thrived in the early triassic marine realm forming a nearly globally distributed lingulidae fauna characterized by low taxonomic diversity but high abundance of individuals the reasons that this group of brachiopods was able to achieve this remain unclear and could possibly include a number of interacting factors among them are their wide ecological adaptations and their shell composition and appearance the long term evolutionary trends in the shell microstructure and exterior of the lingulidae since the late devonian are thought to have advanced considerably by the end permian to the extent that the shells of the brachiopods were able to sustain stressful e g anoxic environments in addition a variety of short term adaptive changes in the shell size reducing shell size shape shells became more pointed and flatter anteriorly and thickness reducing shell thickness are believed to have also aided the survival of the brachiopods through the highly toxic marine environments from the latest permian to the early triassic the long term unchanged organophosphatic shell composition of lingulidae brachiopods is considered to be another key feature that must have aided the survival of this group in the end permian to the early triassic period for organophosphatic shell composition would have prevented the brachiopods from dissolution in the highly acidic marine environment prevailing globally during the permian triassic transition the ability that the lingulids had to live in a wide range of environmental conditions from high latitude to low latitude and from the shoreface to the relatively deep sea environments is also considered vital for the group to have managed to survive the catastrophic event in the latest permian and then thrive in the vacated ecological space in the ensuing early triassic disaster period 2007 elsevier b v all rights reserved

end cretaceous brachiopod extinctions in the chalk of denmark the results of a detailed study of the brachiopods of the most complete cretaceous tertiary boundary in denmark nye kl v show an extinction pattern for this marine invertebrate group compatible with that reported for pelagic foraminifera and coccoliths and with the impact scenario the extinction is abrupt coinciding with the maastrichtian danian boundary there is no warning in the form of decreasing density decreasing diversity or early extinction of specialized groups the basal few meters of the danian are almost devoid of brachiopods and a danian brachiopod fauna starts almost as abruptly as the maastrichtian fauna disappeared the new fauna is similar to the maastrichtian as regards density and diversity and at maximum six species are common to both stages the northwest european masstrichtian chalk is composed mainly of the remains of coccoliths and pelagic foraminifera the mass extinction of these groups led to a total cessation of chalk production the chalk is overlain by a thin clay bed deposited partly under anoxic conditions this combination of anoxia and clay deposition coupled with a cessation of productivity led to the extinction of specialized groups such as the chalk brachiopods the surviving species included forms that could survive in well aerated shallow marine waters on substrates other than chalk

extinction and recovery of benthic foraminifera across the paleocene eocene thermal maximum at the alamedilla section southern spain abstract a complete succession of lower bathyal upper abyssal sediments was deposited across the paleocene eocene thermal maximum petm at alamedilla betic cordillera southern spain where the benthic foraminiferal turnover and extinction event associated with the negative carbon isotope excursion cie across the petm have been investigated detailed quantitative analyses of benthic foraminifera allowed us to distinguish assemblages with paleoecological and paleoenvironmental significance pre extinction fauna extinction fauna survival fauna including disaster and opportunistic fauna and recovery fauna these assemblages have been associated with significant parts of the 13 c curve for which a relative chronology has been established the correlation between the benthic turnover the 13 c curve the calcite and silicate mineral content and sedimentation rates allowed us to establish the sequence of events across the petm at alamedilla the benthic extinction event bee affected 37 of the species and it has been recorded over a 30 cm thick interval that was deposited in c a 10 ky suggesting a gradual but rapid pattern of extinction the beginning of the bee coincides with the onset of the cie 0 ky and with an interval with abundant calcite and it has been recorded under oxic conditions at the seafloor as inferred from the benthic foraminiferal assemblages and the reddish colour of the sediments we conclude that dissolution and dysoxia were not the cause of the extinctions which were probably related to intense warming that occurred before the onset of the cie the bee is immediately overlain by a survival interval dominated by agglutinated species the glomospira acme the low calcite content recorded within the survival interval may result from the interaction between dilution of the carbonate compounds by silicicate minerals as inferred from the increased sedimentation rates and the effects of carbonate dissolution triggered by the shoaling of the ccd we suggest that glomospira species disaster fauna may have bloomed opportunistically in areas with methane dissociation in and around the north atlantic the disaster fauna was rapidly replaced by opportunistic taxa which point to oxic and possibly oligotrophic conditions at the seafloor the ccd gradually dropped during this interval and calcite preservation improved towards the recovery interval during which the 13 c values and the calcite content recovered c a 71 25 to 94 23 ky and stabilized 94 23 ky coeval with a sharp decrease in sedimentation rates

linking distal volcaniclastic sedimentation and stratigraphy with the development of ruapehu volcano new zealand long lived stratovolcanoes are often characterized by cycles that include pulses of explosive and effusive eruptive activity periodic flank collapses and long periods of eruptive quiescence reconstructing these solely from exposures on volcanic edifices is difficult because deposits are dominantly from comparatively recent reconstruction episodes while older sequences are buried or have long been eroded long runout mass flow deposits on the other hand offer insights into the older eruptive history and long term eruptive behavior of composite volcanoes at mt ruapehu new zealand 40ar 39ar dating of lava clasts within distal mass flow sequences combined with new mapping and sedimentological descriptions reveal three hitherto unknown eruptive episodes of the volcano and extend its minimum age to at least 340 ka plinian to subplinian eruptions were followed by periods of subdued volcanic activity voluminous 1 km3 inter eruptive flank failures were precursors to major reconstruction episodes associated with numerous syn eruptive mass flows emplaced up to 90 km from the volcano syn eruptive collapse triggered large plinian eruptions associated with pyroclastic density currents rapid ring plain aggradation dominated during periods of subdued volcanic activity when intensive edifice erosion induced frequent inter eruptive lahars

40ar 39ar geochronology of magmatic activity magma flux and hazards at ruapehu volcano taupo volcanic zone new zealand we have determined precise eruption ages for andesites from ruapehu volcano in the tongariro volcanic centre of the taupo volcanic zone tvz using 40ar 39ar furnace step heating of separated groundmass concentrates the plateau ages indicate several eruptive pulses near 200 134 45 22 and 300 m section of lavas in whangaehu gorge as well as some lavas in ohinepango and waihianoa catchments on eastern ruapehu and this suite of lavas belongs to the waihianoa formation this pulse of activity is not represented on nearby tongariro volcano indicating that the two volcanoes have independent magmatic systems a younger group of lavas yields dates between 50 and 20 ka and includes lava flows from the turoa skifield and in the ohinepango and mangatoetoenui catchments and is consistent with two pulses of magmatism around the time of the last glacial maximum relating it broadly to the mangawhero formation syn and post last glacial activity lavas with ages 15 ka are assigned to the whakapapa formation and include the voluminous flows of the rangataua member on southern ruapehu magma flux integrated over 1000 yr periods averages 0 6 km3 ka 1 assuming a volcano lifespan of 250 ka fluxes for the te herenga waihianoa and mangawhero formations are consistent at 0 93 0 9 and 0 88 km3 ka 1 respectively these fluxes are broadly comparable with those measured at other modern andesite arc volcanoes e g ngauruhoe 0 88 merapi 1 2 and karymsky 1 2 km3 ka 1 the relatively low flux 0 17 km3 ka 1 calculated for the whakapapa formation may derive from underestimates of erupted volume arising from an increase in phreatomagmatic explosive eruptions in postglacial times however using volume estimates for the 1995 1996 eruptions and a recurrence interval of 25 yr has yielded an integrated 1000 yr flux of 0 8 km3 ka 1 in remarkable agreement to estimates for the prehistoric eruptions overall ruapehu shows consistency in magma flux but at time scales of the order of one hundred to some thousands of years field evidence suggests that short bursts of activity may produce fluxes up to twenty times greater this is significant from the perspective of future activity and hazard prediction

stable isotope toc and caco3 record across the cretaceous tertiary boundary at el kef tunisia we report the results of stable oxygen and carbon isotope analysis of carbonate fine fraction and benthic and planktic foraminifers caco3 and toc determinations of sediments across the cretaceous tertiary k t boundary at el kef tunisia we used grain size analysis of the fine fraction carbonate to determine possible compositional effects and smearslide and scanning electron microscope examinations to evaluate possible diagenetic alteration and microfossil preservation the data suggests the following sequence of events upper maastrichtian oxygen and carbon isotope signals indicate relatively warm temperatures a decreasing thermal gradient possibly related to a shallowing sea and relatively high surface water productivity a sharp cooling appears to begin just below the k t boundary the k t boundary is characterized by a sudden 2 negative shift in fine fraction 13c a slight 0 6 enrichment in benthic 13c and a reduction of about 40 in caco3 sedimentation these data imply strongly reduced surface water productivity as also observed in numerous deep sea sequences worldwide the lower danian planktic foraminiferal zones p0 p1a is marked by generally low productivity and unstable environmental conditions as indicated by generally low but fluctuating fine fraction 13c values and low 5 15 carbonate deposition at the base of subzone p1b caco3 benthic and fine fraction 13c values increase gradually and reach near pre k t boundary levels in subzone p1c indicating initial recovery after the k t boundary event about 300 000 400 000 years after the k t boundary the prolonged low productivity episode after the k t crisis and the pre k t boundary cooling associated with a major reduction in planktic foraminiferal diversity are difficult to explain by a single k t boundary bolide impact

radiolarian palaeoecology and radiolarites is the present the key to the past abstract radiolarian productivity pulses and related radiolarite deposition are phenomena difficult to understand from an exclusively actualistic viewpoint evolutionary selection pressure among silica secreting marine plankton both radiolarians and diatoms has led toward more economic usage of rapidly shrinking nutrient resources including dissolved silica of the photic zone in the late cenozoic oceans and in particular a substantial modification of oceanic cycle by the diatom explosive radiation even if there is a proved link between biomineralization and dissolved silica loading among the phytoplankton only the relative independence of modern siliceous planktic biotas from the available silica pool reflects mainly their progressive physiological specialisation during evolutionary history oceanic chemistry and productivity as well as patterns of circulation upwelling have changed radically during the phanerozoic radiolarites apparently represent an anachronistic facies as exemplified by their long lived and ocean wide distribution in palaeo pacific and hitherto highlighted actualistic models of localized intra oceanic wind driven upwelling loci are of largely questionable applicability in addition to plate drift hypersiliceous domains and intervals are explainable mostly by a large scale volcano hydrothermal activity during major plate boundary reconfigurations which in many ways favoured siliceous biotas acme and their skeletal remains accumulation and preservation factors tied to rapid voluminous submarine eruptions such as thermal buoyant megaplumes and basin overturns offer a viable alternative for traditional climatic circulation scenarios in case of hypersiliceous high productivity events irrelevant to greenhouse to icehouse climatic change the evolving carbon and silica cycles were coupled through the greenhouse effect and enhanced chemical weathering volcano hydrothermal and tectonic uplift events related mostly to extensive rifting and or accelerated oceanic spreading were the endogenous driving force that created this perturbation of the exogenous system the present biogeochemical cycle is representative only for the overall silica depleted post eocene oceanic ecosystems which broadly correlates with a major expansion of diatoms groups extremely efficient in silica removal and closely linking the silica budget with phosphorus and nitrogen cycles thus an orthodox uniformitarian approach to biosiliceous sedimentation based on a silica starved vigorous ocean is of limited significance when applied to the pre neogene settings especially in the peculiar planktic habitats of epeiric seas as well as during biotic crises marked by strong geotectonic overprint the major turnovers in marine siliceous biota composition in particular after the end permian radiolarite gap may have been coupled with discernible changes in an increasing biological control on the long term oceanic silica cycling punctuated equilibrium the evolutionary turnovers have induced a stepdown decrease of dissolved silica levels through the phanerozoic contemporaneously with the general secular trend of upward scaling of nutrient related ecological processes and increased effectiveness of resource utilization

patterns of biodiversity and faunal rebound following the k t boundary extinction event in austral palaeocene molluscan faunas palaeocene molluscan faunas are characterised by complex evolutionary histories following the cretaceous tertiary k t boundary extinction event and exhibit dramatic distinct signatures of composition and biodiversity levels relating to extinction and post extinction recovery processes this paper is the first to document and survey the entire palaeocene record of the southern hemisphere which comprises at least 515 recorded molluscan taxa from australia new zealand chatham islands antarctica and south america the record is much richer than previously recognised the k t boundary event was a prime mechanism of change for the composition of palaeocene faunas but palaeocene diversity patterns were shaped also by the final break up of gondwana concomitant changes in climate and in oceanic circulation and faunal recovery processes the flip flop in diversity of bivalves and gastropods across the k t boundary stems from a rapid evolutionary burst of speciation in the danian for gastropods especially carnivorous forms with planktotrophic development which infilled ecospace vacated by the extinction in the southern hemisphere fossil record deposit feeders were less affected by the extinction event and seemingly more extinction resistant but other important factors related to stratigraphic range and spectrum of life habits habitats affected survivorship success suspension feeders especially epifaunal forms were hard hit by the extinction but had bounced back within a few million years by late danian time at the latest but at lower diversity than during the late cretaceous the extinction was not as marked in most southern regions as reflected in the antarctic record in the antarctic k t boundary interval diversity drops suddenly ca 50 m before the boundary and while suspension feeders remain at low diversity for at least 300 kyr gastropods still dominate the molluscan assemblages most of the k t boundary molluscan survivors were bivalve species 66 and all of these were members of representative genera that displayed extensive stratigraphic and geographic ranges in the cretaceous or earlier in the mesozoic the majority of earliest danian antarctic molluscs belong to newly evolved species within surviving genera 58 but by late danian time this trend had changed to a dominance of new species in new genera many new groups arose during the palaeocene especially by late danian time and these faunas are highly distinctive at both genus and species level for example the wangaloa formation fauna of late danian age ca 63 61 ma is dominated by new species in new genera ranging in values from 62 5 to 81 a systematic catalogue of all known palaeocene austral species is presented herein in the appendix for the first time with details of formation recorded age and inferred life habits

column on column structures as indicators of lava ice interaction ruapehu andesite volcano new zealand abstract lava flows of the mangawhero formation ca 15 60 ka on ruapehu volcano erupted during the last glaciation in a distal flow lobe at tukino on the east side of the mountain small secondary columns 10 20 cm thick have formed on the sides of large rectangular primary 0 5 3 m thick cooling columns thick 10 m zones of such small columns form a lateral and basal outer rind of the lobe as they do not mark glassy zones of quenching these secondary columns are interpreted as being formed by a second cooling event at temperatures below the boundary between the low creep and elastic regimes 600 c by rapid influx of copious amounts of water temperature drops deduced from extensional strains of the two sets of columns were used to gauge the viability of such a two stage process absence of reliable data on andesite contraction coefficients was overcome by using a sliding scale to assess a large range of values the estimates indicate that two stage chilling is feasible after flowing across relatively ice poor terrain the lava flow must have interacted with a valley glacier that provided water for further chilling the already formed primary columns and formation of the outer rind small columns given this evidence for lava ice interaction it is likely that prominent thick flows elsewhere in the mangawhero formation may have been constrained to their ridge top locations by ice conditions similar to those described by lescinsky and sisson lescinsky d t sisson t w 1998 ridge forming ice bounded lava flows at mount rainier washington geology 26 351 354

pleistocene mass flow deposits of basaltic hyaloclastite on a shallow submarine shelf south iceland a pleistocene subaqueous volcanic sequence in south iceland consists of flows of basaltic hyaloclastite and lava with interbedded sedimentary diamictite units emplacement occurred on a distal submarine shelf in drowned valleys along the southern coast of iceland the higher sea level was caused by eustatic sea level change probably towards the end of a glaciation this sequence nearly 700 m thick rests unconformably on eroded flatlying lavas and sedimentary rocks of likely tertiary age a standard depositional unit describing the flows of hyaloclastite starts with compact columnar jointed basalt overlain by cubejointed basalt and or pillow lava this in turn is overlain by thick unstructured hyaloclastite containing aligned basalt lobes and bedded hyaloclastite at the top a similar lithofacies succession is valid for proximal to distal locations the flows were produced by repeated voluminous extrusions of basaltic lava from subaquatic fissures on the eastern rift zone of iceland the fissures are assumed to lie in the same general area as the 1783 laki fissure which produced 12 km3 of basaltic lava due to very high extrusion rates the effective water melt ratio was low preventing optimal fragmentation of the melt the result was a heterogeneous mass of hyaloclastite and fluid melt which moved en masse downslope with the melt at the bottom of the flow and increasingly vesicular hyaloclastite fragments above the upper and distal parts of the flow moved as low concentration turbulent suspensions that deposited bedded hyaloclastite

environmental controls on the post permian recovery of benthic tropical marine ecosystems in western palaeotethys aggtelek karst hungary climate warming during the late permian is associated with the most severe mass extinction event of the phanerozoic and the expansion of hypoxic and anoxic conditions in shallow shelf settings it has been hypothesised that wave aeration provided a habitable zone in the shallowest environments that allowed the survival and rapid recovery of benthic invertebrates during the early triassic we test this hypothesis by studying the rock and fossil records of the aggtelek karst hungary nearshore settings recorded in the bodvaszilas sandstone formation and units a and d of the szin marl formation are characterised by taxonomically homogenous fossil assemblages of low diversity and low evenness ecological and taxonomic recovery in this environmental setting was hampered by persistent environmental stress this stress is attributed to increased runoff related to climate warming during the early triassic that resulted in large salinity fluctuations increased sedimentation rates and eutrophication that led to seasonal hypoxia and an environment only favourable for opportunistic taxa in contrast shoal and mid ramp settings further offshore are characterised by high diversity faunas with a greater functional complexity prior to the late spathian tirolites carniolicus zone the shelly fossils and trace fossils are limited to settings aerated by wave activity which supports the habitable zone hypothesis in the tirolites carniolicus zone however the oxygen minimum zone retreats offshore and the habitable deeper shelf settings are rapidly colonised by shallow water taxa evidenced by the highest levels of diversity and bioturbation recorded in the study locally full recovery of marine ecosystems is not recorded until the illyrian with the establishment of a sponge reef complex

response of early eocene deep water benthic foraminifera to volcanic ash falls in the polish outer carpathians palaeocological implications abstract lower eocene sediments of the subsilesian unit of the polish carpathians contain bentonite layers that were deposited in a deep water basinal environment foraminiferal assemblages occurring within the bentonites and in the surrounding shales show important differences in taxonomical composition the proportions of ecological groups and test composition foraminiferal assemblages collected from bentonites are impoverished display smaller test size are dominated by a single opportunistic taxon and have lower numbers of suspension feeders in comparison with assemblages surrounding sediments in addition bentonite assemblages show a test composition comprised of white fine grained quartz and include a greater number of juvenile forms with test abnormalities the extent of such discrepancies is variable and depends on the thickness of the bentonite layers the deposition of volcanic ash layers bentonites represented catastrophic events for benthic foraminifera after each ash fall event a kill layer was formed and settled by an opportunistic foraminiferal group dominated by specimens of the epifaunal glomospira charoides leading to the formation of nearly monospecific foraminiferal assemblages in the case of thin ash layers some infaunal species are found these organisms probably survived the deposition of volcanic ash and associated unfavourable conditions beneath the surficial sediment layer the studied sections of the subsilesian unit include intervals containing several bentonite layers indicating that the deposition of volcanic ash was a recurrent phenomenon following the deposition of volcanic ash a relatively quick recovery of the foraminiferal community structure took place and changes in the foraminiferal community proceeded each time according to the same sequence

mass extinction and recovery of the early toarcian early jurassic brachiopods linked to climate change in northern and central spain abstract the early toarcian mass extinction event represented the most important mesozoic and cenozoic turnover of the population of brachiopods and severely affected other benthic fauna two main hypotheses have been proposed to explain the synchronous and global mass extinction an oceanic anoxic event or a warming episode to test both hypotheses the dynamics of the brachiopod assemblages below and above the extinction boundary are analyzed and compared with the seawater paleotemperature variations calculated from the 18 o data recorded in belemnite rostra five sections from northern and central spain well dated with ammonites have been selected for this study the sections show no indication of sedimentary breaks and contain abundant brachiopods which have been grouped into four assemblages the changes observed in the brachiopod assemblages show a close correlation with the changes in the seawater paleotemperatures the oldest assemblage assemblage 1 coincides with a cooling interval recorded to have taken place in the latest pliensbachian paleobiogeographical reconstruction shows that this assemblage was distributed at paleolatitudes between 30 and 45 n with a preference for relatively cool waters with the rise of temperatures that took place during the earliest toarcian tenuicostatum zone assemblage 1 was substituted by assemblage 2 which composed of different species of the same genera but considerably restricted to the warmer waters of lower paleolatitudes between 28 and 35 n coinciding with the rapid and pronounced increase in seawater temperature recorded at the tenuicostatum serpentinum zonal boundary all of these brachiopod species disappeared in the studied localities marking clearly the extinction boundary predominant southward currents through the laurasian seaway precluded the possible migration of the brachiopods to cooler northern waters the brachiopods disappearance is independent from the oxygenation degree of the sea bottom and therefore the rapid warming seems to be the most plausible cause of the mass extinction after the extinction event the recovery of the brachiopods was uneven subsequent to a brief pause recovery was rapid in central spain and in other southern areas of western tethys whereas in northern spain and in the whole of europe north of the french central massif brachiopods did not recover until the mid to late toarcian times

early triassic disaster and opportunistic foraminifers in south china survival and recovery are important dynamic processes of biotic evolution during major geological transitions disaster and opportunistic taxa are two significant groups that dominate the ecosystem in the aftermath of mass extinction events disaster taxa appear immediately after such crises whilst opportunists pre date the crisis but also bloom in the aftermath this paper documents three disaster foraminiferal species and seven opportunistic foraminiferal species from lower triassic successions of south china they are characterized by extreme high abundance and low diversity and occurred occasionally in griesbachian smithian and spathian strata the characteristics small size simple morphology and stratigraphic ranges of these groups suggest that r selection is a commonly used strategy for survivors to cope with either harsh post extinction conditions and or environments lacking incumbents

trace fossils in the aftermath of mass extinction events abstract ichnology has great potential to advance our understanding of mass extinction events and yet is currently an underutilized resource in such studies here we review published ichnological studies for the ordovician silurian permian triassic and cretaceous tertiary extinction recovery intervals in addition new information regarding the triassic jurassic ichnological record from england austria and the western usa is presented trace fossils provide important information on the ecological response of the benthic community at such times in the immediate post extinction aftermath the ichnodiversity burrow size depth of bioturbation and ichnofabric index of the sediments are all much reduced there is an increase in all these parameters through the post extinction recovery period in some cases the stepwise reappearance of certain distinctive ichnotaxa e g diplocraterion rhizocorallium and thalassinoides may be of some stratigraphic use evidence from permian triassic studies indicates that recovery took longer at low tropical palaeolatitudes than mid high palaeolatitudes trace fossils also provide important information on palaeoenvironmental change through the extinction recovery interval the application of ichnology to mass extinction studies is in its infancy but should prove a valuable tool in future research

morphological and sedimentological characteristics of the neogene submarine coherent lavas and hyaloclastites in southwest hokkaido japan abstract the neogene formations in southwest hokkaido japan are mostly composed of submarine volcanic products such as submarine coherent lavas and hyaloclastites associated with feeder dikes this paper presents criteria for recognition of submarine effusion products through description of the morphological and sedimentological characteristics of coherent lavas such as pillow lobes sheet flow lava lobes and pseudo pillow lavas and hyaloclastites and feeder dikes and a small amount of associate pyroclastic rocks

evolution of an englacial volcanic ridge pillow ridge tindar mount edziza volcanic complex ncvp british columbia canada abstract glaciovolcanic deposits are critical for documenting the presence and thickness of terrestrial ice sheets and for testing hypotheses about inferred terrestrial ice volumes based on the marine record deposits formed by the coincidence of volcanism and ice at the mount edziza volcanic complex mevc in northern british columbia canada preserve an important record for documenting local and possibly regional ice dynamics pillow ridge located at the northwestern end of the mevc formed by ice confined fissure fed eruptions it comprises predominantly pillow lavas and volcanic breccias of alkaline basalt composition with subordinate finer grained volcaniclastic deposits and dykes the ridge is presently 4 km long 1000 m in maximum width and 600 m high fifteen syn and post eruptive lithofacies are recognized in excellent exposures along the glacially dissected western side of the ridge we recognize five lithofacies associations 1 poorly sorted tuff breccia and dykes 2 proximal pillow lava dykes and tuff breccia 3 distal pillow lava poorly sorted conglomerate and well sorted volcanic sandstone 4 interbedded tuff lapilli tuff and tuff breccia units and 5 heterolithic volcanogenic conglomerate and sandstone given the abundance of pillow lavas and the lack of surrounding topographic barriers capable of impounding water we agree with souther souther j g 1992 the late cenozoic mount edziza volcanic complex geol soc can mem vol 420 320 pp that the bulk of the edifice formed while confined by ice but have found evidence for a more complex and variable eruption history than that which he proposed preliminary estimates of water ice depths derived from ftir analyses of h2o give ranges of 300 to 680 m assuming 0 ppm co2 and 857 to 1297 m assuming 25 ppm co2 variations in depth estimates among samples may indicate that water ice depths changed during the evolution of the ridge which is consistent with our interpretations for the origins of different lithofacies associations given that the age of the units are likely to be ca 0 9 ma souther j g 1992 the late cenozoic mount edziza volcanic complex geol soc can mem vol 420 320 pp pillow ridge may be the best documentation of a regional high stand of the cordilleran ice sheet cis in the middle pleistocene and an excellent example of the lithofacies and stratigraphic complexities produced by variations in water levels during a prolonged glaciovolcanic eruption

the search for the origin of the planktic foraminifera planktic foraminifera are an extremely abundant important and successful group of marine protists they are particularly useful in reconstructing past environments and for biostratigraphic dating despite their importance the origin of the group is uncertain previous work has suggested that they evolved from a benthic ancestor during the triassic or perhaps the mid jurassic bajocian but a reason for their origination has remained unclear here we present evidence from the toarcian early jurassic of nw europe that the origin of the planktic foraminifera may have been one of the results of the early toarcian oceanic anoxic event this event appears to have been associated with a massive dissociation of gas hydrates and other perhaps related water chemistry changes

snow contact volcanic facies and their use in determining past eruptive environments at nevados de chillan volcano chile studies of the eruptive products from volcanoes with variable ice and snow cover and a long history of activity enable reconstruction of erupted palaeoenvironments as well as highlighting the hazards associated with meltwater production such as jokulhlaups and magma water interaction existing difficulties include estimation of ice snow thicknesses and discrimination between ice and snow contact lithofacies we present field evidence from the cerro blanco subcomplex of nevados de chillan stratovolcano central chile which has erupted numerous times in glacial and non glacial periods and most recently produced andesitic lava flows in the 1861 1865 eruption from the santa gertrudis cone on the northwest flank of the volcano the main period of lava effusion occurred during the winter of 1861 when the upper flanks of the volcano were reportedly covered in snow and ice the bases and margins of the first lava flows produced are cut by arcuate fractures which are interpreted as snow contact features formed when steam generated from the melting of snow entered tensional fractures at the flow base in contrast the interiors and upper parts of these flows as well as the overlying flow units have autobrecciated and blocky textures typical of subaerial conditions due to insulation by the underlying lava similar textures found in a lava flow dated at 90 0 0 6 ka that was emplaced on the northwest flank of cerro blanco are also inferred to be ice and snow contact features these textures have been used to infer that a small valley glacier overlain by snow existed in the santa gertrudis valley at the time of the eruption such reconstructions are important for determining the long term evolution of the volcano as well as assessing future hazards at seasonally snow covered volcanoes

a miocene basanite peperitic dyke at stanley northwestern tasmania australia abstract a miocene basanite dyke at stanley northwestern tasmania australia displays well preserved peperite texture the dyke is 2 m wide and has intruded basaltic breccia host sediment one contact of the dyke is fluidally shaped and amoeboid apophyses 10 25 cm long extend into the host sediment whereas the other contact is characterized by blocky peperite texture comprising tabular to wedge shaped clasts up to 30 cm across separated by host sediment the clasts have internal spherical fractures and some show splinter texture vesicles are common in the clasts and those intersected by clast margins have been filled with sediment the interior of the dyke comprises close packed blocky peperite consisting of tabular wedge shaped and polyhedral clasts tens of centimetres across separated by host sediment these clasts show well developed jigsaw fit texture the textures and structures in the basanite dyke are inferred to have formed in two stages an earlier hotter apophysis forming stage and a later cooler angular clast forming stage both of which occurred during the intrusion of magma into wet poorly consolidated sediment in a shallow marine environment during the apophysis forming stage the magma had relatively low viscosity and progressively displaced wet sediment the wet sediment around the dyke was partly fluidized by vaporization of pore water the angular clast forming stage reflects a change in the rheological behaviour of the magma from ductile to brittle most likely in response to decreasing temperature the chilled parts of the dyke were subject to stress arising from cooling contraction and also from continued pulsatory movement of hotter still ductile magma in the interior of the dyke resulting in brittle fragmentation brittle fragmentation was accompanied by movement of host sediment into the newly created open spaces forming blocky peperite spherical fractures splinter texture and sediment filled vesicles formed during the angular clast forming stage because the host sediment is texturally identical either side of the dyke increasing magma viscosity as temperature decreased combined with pulsatory intrusion were evidently important in the production of the blocky peperite

sedimentology and ichnology of the cretaceous tertiary boundary in denmark implications for the causes of the terminal cretaceous extinction abstract trace fossils and other sedimentologic evidence of bioturbation in latest cretaceous and earliest tertiary marine deposits in denmark provide important clues to understanding the ecology of the sea bottom immediately before during and after the terminal cretaceous boundary event trace fossil associations at all the onshore danish boundary sites indicate a general upward shoaling of the late maastrichtian chalk sea which was accompanied by an abrupt shift from a carbonate ooze sea floor to a marly clay rich unstable substrate at the boundary although the substrate condition may have become more stable in the early danian water depths never did return to their former deep level there is evidence of localized anoxia during the deposition of some boundary sediments in the fish clay in shallow parts of the danish maastrichtian sea but no clear evidence of anaerobic conditions occurring at the era boundary was observed in boundary strata deposited in deeper water near the center of the basin in fact earliest danian marl there is totally bioturbated a pulse of calcite dissolution in shallow water coincided precisely with the era boundary and this event played a major role in the formation of the fish clay in eastern denmark which is a condensed series of smectitic clay rich layers from which much calcite has dissolved the effects of this dissolution episode however were not so extreme in the marl that was deposited at the same time in slightly deeper water in northwestern denmark evidence from cretaceous tertiary boundary sequences in denmark and elsewhere suggests that no single catastrophe can account for the major biotic extinctions that occurred at the end of the cretaceous period the primary causal factors of the terminal cretaceous extinction event appear to be drastic global sea level regression occurring simultaneously with extensive volcanism on land and a strong pulse of calcite dissolution in ocean surface waters

high resolution event stratigraphy hires and the quantification of stratigraphic uncertainty silurian examples of the quest for precision in stratigraphy abstract the ability to resolve the stratigraphic record of earth history is critical to understanding past global change events and the range of natural variability within the global paleoclimate the geosphere hydrosphere atmosphere biosphere system operates on geologically very short time scales and we must be able to resolve the stratigraphic record of past events on similar time scales if we are to understand the cause and effect relationships operating within the system global resolution 100 kyr is commonly available when evaluating events from the cenozoic era but such resolution is less common for older portions of earth history the introduction of high resolution event stratigraphy hires more than two decades ago revolutionized the ability to resolve the mesozoic and cenozoic stratigraphic records of global change and a similar revolution is currently underway for the paleozoic as well here we review the application of the principles of hires to the paleozoic stratigraphic record with examples from the silurian system discuss the quantification of chronostratigraphic uncertainty and highlight the current deep time earth history revolution that has the potential to open the entire phanerozoic record to the evaluation of short time scale global climate dynamics

hyaloclastite fragmentation below the glass transition an example from el barronal submarine volcanic complex spain this research has been funded by projects cgl2005 03511 bte hi2006 0073 prin2009 prin 2009h37m59 and prin 2010 11 2010tt22sc and 2010tt22sc 003

stepwise mass extinctions and impact events late eocene to early oligocene abstract species ranges and relative abundances of dominant planktonic foraminifers of eight late eocene to early oligocene deep sea sections are discussed to determine the nature and magnitude of extinctions and to investigate a possible cause effect relationship between impact events and mass extinctions late eocene extinctions are neither catastrophic nor mass extinctions but occur stepwise over a period of about 1 2 million years four stepwise extinctions are identified at the middle late eocene boundary the upperglobigerapsis semiinvoluta zone theg semiinvoluta globorotalia cerroazulensis zone boundary and at the eocene oligocene boundary each stepwise extinction event represents a time of accelerated faunal turnover characterized by generally less than 15 species extinct and in itself is not a significant extinction event relative species abundance changes at each stepwise extinction event however indicate a turnover involving 60 of the population implying major environmental changes there microtektite horizons are present in late eocene sediments one in the upperg semiinvoluta zone 38 2 ma and two closely spaced layers only a few thousand years apart in the lower part of thegloborotalia cerroazulensis zone 37 2 ma each of the three impact events appears to have had some effect on microplankton communities however the overriding factor that led to the stepwise mass extinctions may have been the result of multiple causes as there is no evidence of impacts associated with the step preceding or the step following the deposition of the presently known microtektite horizons

lava ice interaction on a large composite volcano a case study from ruapehu new zealand ice exerts a first order control over the distribution and preservation of eruptive products on glaciated volcanoes defining the temporal and spatial distributions of ice marginal lava flows provides valuable constraints on past glacial extents and is crucial for understanding the eruptive histories of such settings ice marginal lava flows are well displayed on ruapehu a glaciated andesite dacite composite cone in the southern taupo volcanic zone new zealand flow morphology fracture characteristics and 40ar 39ar geochronological data indicate that lavas erupted between 51 and 15 ka interacted with large valley glaciers on ruapehu ice marginal lava flows exhibit grossly overthickened margins adjacent to glaciated valleys are intercalated with glacial deposits display fine scale fracture networks indicative of chilling against ice and are commonly ridge capping due to their exclusion from valleys by glaciers new and existing 40ar 39ar eruption ages for ice marginal lava flows indicate that glaciers descending to 1300 m above sea level were present on ruapehu between 51 41 and 27 15 ka younger lava flows located within valleys are characterised by blocky flow morphologies and fracture networks indicative of only localised and minor interaction with ice and or snow mainly in their upper reaches at elevations of 2600 2400 m an 40ar 39ar eruption age of 9 3 ka 2 error determined for a valley filling flow on the northern flank of ruapehu indicates that glaciers had retreated to near historical extents by the time of emplacement for this lava flow the applicability of 40ar 39ar dating to ice marginal flows on glaciated andesite dacite composite volcanoes makes this technique an additional proxy for paleoclimate reconstructions

comet showers as a cause of mass extinctions if at least some mass extinctions are caused by impacts why do they extend over intervals of one to three million years and have a partly stepwise character the solution may be provided by multiple cometary impacts astronomical geological and palaeontological evidence is consistent with a causal connection between comet showers clusters of impact events and stepwise mass extinctions but it is too early to tell how pervasive this relationship may be

magma water interactions in subaqueous and emergent basaltic in the subaqueous growth and emergence of a basaltic volcano clasts are formed by one or a combination of 1 explosive release of magmatic volatiles 2 explosive expansion and collapse of steam formed at magma water contact surfaces 3 explosive expansion of steam following enclosure of water in magma or entrapment of water close to magma and 4 cooling contraction these processes named respectivelymagmatic explosivity contact surface steam explosivity bulk interaction steam explosivity andcooling contraction granulation can be enhanced by mutual interaction and feedback the first three explosive processes are limited at certain water depths hydrostatic pressures and become increasingly vigorous at shallower levels the depth of onset of magmatic explosivity depends largely on juvenile volatile content it is up to 200 m for tholeiitic magmas and up to 1 km for alkalic magmas at the depth where formation of clastic deposits becomes predominant over effusion of lavas magmatic explosivity is subordinate to steam explosivity as a clast forming process the upward transition to accumulation of dominantly clastic deposits is not simply related to the onset of substantial exsolution of magmatic volatiles and can occur without it contact surface explosivity commonly requires initiation by a vigorous impact between magma and water and although no certain depth limit is known likelihood of such explosivity decreases rapidly with depth clast generation by bulk interaction explosivity appears to be restricted to depths much shallower than that of the critical pressure of water which in sea water is at about 3 km cooling contraction granulation can occur in any depth of water but at shallow levels may be replaced by contact surface explosivity during continuous eruption under water tephra can be ejected and deposited within a cupola of steam such that rapid quenching does not occur emergent volcanoes are characterized by distinctive steam explosive activity that results primarily from a bulk interaction between rapidly ascending magma and a highly mobile slurry of clastic material water and steam the water gets into the vent by flooding across or through the top of the tephra pile and violent explosions cease when this access is sealed the eruptions during emergence of surtsey and capelinhos typify the distinctive explosive activity the style and controls of which are different from those of maar volcanoes

calcareous dinoflagellate associations and maastrichtian tertiary climatic change in a high latitude core odp hole 689b maud rise weddell sea abstract the distribution of calcareous dinoflagellates has been analysed for the maastrichtian miocene interval of ocean drilling project hole 689b maud rise weddell sea the investigation thus represents a primary evaluation of the long term evolution in high latitude calcareous dinoflagellate assemblages during the transition from a relatively warm late cretaceous to a cold neogene climate major assemblage changes during this interval occurred in characteristic steps 1 an increase in relative abundance of tangentially structured species particularly operculodinella operculata at the cretaceous tertiary boundary 2 a diversity decrease and several first and last appearances across the middle late eocene boundary possibly attributed to increased climate cooling 3 a diversity decrease associated with the dominance of calciodinellum levantinum in the late early oligocene 4 the reappearance and dominance of pirumella edgarii in the early miocene probably reflecting a warming trend 5 monogeneric assemblages dominated by caracomia spp denoting strong middle miocene cooling the results not only extend the biogeographic ranges of many taxa into the antarctic region but also indicate that the evolution of high latitude calcareous dinoflagellate assemblages parallels the changing environmental conditions in the course of the cenozoic climate transition therefore calcareous dinoflagellates contribute to our understanding of the biotic effects associated with palaeoenvironmental changes and might possess the potential for reconstructing past conditions the flora in the core includes one new taxon caracomia arctica forma spinosa hildebrand habel and streng forma nov additionally two new combinations are proposed fuettererella deflandrei kamptner 1956 hildebrand habel and streng comb nov and fuettererella flora futterer 1990 hildebrand habel and streng comb nov

trace fossil evidence suggests widespread dwarfism in response to the end cretaceous mass extinction braggs alabama and brazos river texas as a proxy for the body size of the tracemaker burrow diameter provides information on fundamental characteristics such as organism biology and behavior furthermore changes in this endobenthic parameter provide insight into the timing and recovery of burrowing organisms in response to large scale processes operating in ancient trophic systems we herein report a decrease in burrow size in thalassinoides dominated ichnoassemblages across the cretaceous paleogene k pg boundary in well studied shallow marine sections along the brazos river and cottonmouth creek texas and at braggs alabama at the cottonmouth creek and brazos river localities thalassinoides isp occurring above the previously reported negative 13c shift and the first occurrence of unequivocal danian planktonic foraminifera are 17 smaller in short axis diameter and 22 smaller when diameters are corrected for sediment compaction mean k 27 15 7 12 mm mean pg 21 13 6 88 mm n 53 than those excavated and filled prior to deposition of a hummocky cross bedded ejecta bearing sandstone complex commonly interpreted as the chicxulub event deposit across the k pg boundary at braggs diameters dth of simple maze thalassinoides structures from similar recurring depositional facies abruptly decrease by 22 mean k 13 08 1 86 mm mean pg 10 21 1 87 mm n 26 the cretaceous and paleogene burrows were preserved in beds of similar lithology suggesting that the reduction in size is not attributed to sedimentological factors at both localities up section trends in dth are statistically significant 0 05 equal variance t test non parametric mann whitney u test a reduction in dth above the k pg boundary reflects dwarfing within the post extinction endobenthic community these ichnological trends are similar to those recently documented at more impact distal sites along the new jersey coastal plain dwarfing during the early recovery stages of the end cretaceous mass extinction as recorded by trace fossils was widespread and occurred within siliciclastic carbonate and glauconite producing depositional environments since this ichnological signal in shallow marine successions appears to be a general phenomenon across the crisis interval trace fossil analysis provides a potential in situ field method for constraining and correlating the stratigraphic position of the event particularly in the absence of other macroscopic microscopic and geochemical indicators

extinction survivorship and evolution of planktic foraminifera across the cretaceous tertiary boundary at el kef tunisia an expanded sediment record at el kef shows that the k t boundary extinctions of planktic foraminifera extend over an interval from 25 cm below the geochemical boundary ir anomaly to 7 cm above species extinctions appear sequential with complex large ornate forms disappearing first and smaller less ornate forms surviving longer the 14 species extinctions below the boundary appear unrelated to an impact event cretaceous species survivorship is greater than previously assumed about 10 species survive 22 into subzone p1a globigerina eugubina all cretaceous survivors are small primitive forms which are generally smaller than their ancestors in cretaceous sediments species evolution after the k t event occurs in two pulses the first new paleocene species evolve in the basal black clay zone po immediately after the major cretaceous extinctions evolving species are small and primitive similar to cretaceous survivors the second pulse in species evolution occurs in the lower part of subzone p1b with the appearance of larger more diverse species the first major increase in carbonate sedimentation and productivity occurs at this time and signals the recoveyr of the ecosystem nearly 300 000 years after the k t event the species extinctions prior to the generally assumed impact event implied by the ir anomaly and the long recovery period of the ecosystem thereafter cannot be explained by a single impact but suggest that multiple causes may be responsible such as climatic changes volcanism a sea level drop production of warm saline bottom water and the chemical consequences associated with increased salinity

the early evolution and palaeobiogeography of mesozoic planktonic foraminifera this is a digitised version of a thesis that was deposited in the university library if you are the author and you have a query about this item please contact pearl admin pearladmin plymouth ac uk

glaciovolcanic emplacement of an intermediate hydroclastic breccia lobe complex during the penultimate glacial period 190 130 ka ruapehu volcano new zealand

basaltic subglacial sheet like sequences evidence for two types with different implications for the inferred thickness of associated ice abstract subglacially erupted volcanic sequences provide proxies for a unique range of palaeo ice parameters and they are potentially highly useful archives of palaeoenvironmental information particularly for pre quaternary periods they can thus be incorporated by climate and ice sheet modellers in the same way as other environmental proxies yet they remain largely under utilised basaltic volcanic sequences erupted subglacially consist empirically of two major types corresponding to eruptions under thick and thin ice respectively the latter are called subglacial sheet like sequences and only one generic type of sequence has been described so far however there is now evidence that there are at least two generic types with significantly different implications for interpretations of associated palaeo ice sheet thicknesses one type which is relatively well described is believed to be a diagnostic product of eruptions associated with a relatively thin glacial cover 1000 m eruptions that form the dalsheidi type of sequence commence with the injection and inflation of a sill along the ice bedrock interface such interface sills were predicted theoretically but had no known geological example until now subsequent evolution commonly involves floating of the ice cover catastrophic meltwater drainage and emplacement of widespread sheets of hyaloclastite as cohesionless mass flows and hyperconcentrated flows the water saturated hyaloclastite is characteristically intruded by apophyses sourced in the underlying interface sill eruptions are commonly not explosive until their later stages dalsheidi type deposits are outflow sequences probably linked to subglacial pillow volcanoes which in iceland were erupted along fissures they only provide an indication of minimum thicknesses of the associated overlying ice although theoretical considerations suggest substantial ice thicknesses in excess of 1000 m however they are likely to be characteristic products of eruptions under the thick west antarctic ice sheet but are currently inaccessible such eruptions may be capable of destabilising that ice sheet

adaptive strategies and environmental significance of lingulid brachiopods across the late permian extinction abstract linguliform brachiopods are traditionally considered a conservative group which seems to pass through the late permian extinction without any significant loss and even appear to thrive immediately after the extinction peak in the southern alps lingulids are very common in the post extinction mazzin member early induan of the werfen formation sparse occurrences are also known in the overlying siusi and gastropod oolite members late induan and early olenekian in age respectively the recent discovery of well preserved specimens from a pre extinction bed of the bellerophon formation changhsingian has permitted a detailed comparative analysis mostly based on the interior characters preserved in the lingulid succession from across the extinction beds the following effects on the lingulid populations have been analyzed i change in taxonomic assessment ii adaptive strategies during the surviving and recovery phases and iii environmental proxy connected with the killing mechanisms of the late permian extinction the pre extinction individuals belong to lingularia cf smirnovae biernat and emig a species that is characterized by large sized shells with a short lophophoral cavity the post extinction populations belong to different species and probably even to a different genus the first post extinction population early induan with small sized shells and long lophophoral cavity has been referred to lingularia yini peng and shi it records the most severe effects of the late permian extinction on the marine ecosystems the late induan olenekian lingularia borealis bittner with large sized shells and long lophophoral cavity appears during the first phase of the triassic biotic recovery the main adaptive strategies of lingularia yini in comparison with the permian species include i shell miniaturization ii increasing of the lophophoral cavity surface respiratory surface and iii increasing of shell width length ratio these modifications are interpreted as adaptations towards warming and hypoxia two main killing mechanisms of the marine biota the recovery species lingularia borealis maintains a large lophophoral cavity indicating an adaptation towards predominant low oxygenated bottom marine waters the appearance and the great abundance of lingularia yini in the mazzin member early induan represent a proxy of dysaerobic conditions which determined the appearance of the second phase of the lilliput biota characterized by the definitive disappearance of the rhynchonelliform brachiopods and calcareous algae in the southern alps

the smooth brachiopods of the mediterranean jurassic refugees or invaders the jurassic brachiopod fauna of the alpine mediterranean region is dominated by smooth rhynchonellids and spiriferinids and sulcate or perforate terebratulids in contrast to the typical coarsely ribbed brachiopods of the contemporaneous european and african epicontinental areas the best studied example of the mediterranean brachiopod province is the pliensbachian fauna of the bakony mountains hungary there the five most abundant genera are all smooth linguithyris securithyris apringia bakonyithyris pisirhynchia these smooth genera represent different morphological types sulcate axiniform uniplicate phylogenetically related forms are known from several evolutionary lineages of discontinuous record ranging from the triassic to the recent the triassic jurassic and the neogene recent parts of these evolutionary lineages are represented by several genera while in the late cretaceous paleogene interval they seemingly disappear at least they have no record the recent relatives of the above pliensbachian genera live mostly in the deep sea three are shallow bathyal 200 400 m three deep bathyal 800 1200 m and three abyssal 2000 4500 m the abyssal genera occur mainly in the east pacific the geographical distribution of the bathyal genera shows peculiar features they are more or less confined to the western sides of the great ocean basins west pacific west indian ocean caribbean region and they are thalassobathyal i e they are living on submarine plateaus seamounts or island aprons and not on the continental slopes this pattern extrapolated to the past shows good analogy with the jurassic palaeogeographical model developed for the western part of the tethys ocean it is hypothesized that smooth mainly sulcate articulate brachiopods flourished in the bathyal or even abyssal zones during the palaeozoic they were not refugees but formed well adapted communities this stable conservative fauna may have survived the crises manifested in the shelf seas and in cases of appropriate palaeogeographical situations may have implanted its descendants to the shallow bathyal or even sublittoral regions of the western margins of the ocean basins the mediterranean microcontinent system at the western part of the jurassic tethys might have been such an invaded region correlation between plate tectonic changes of ocean continent configurations the presence of ocean basins closed on the west and the occurrence of smooth articulate brachiopod groups in shallow bathyal to sublittoral settings collectively suggest that the deep water forms invaded the shallow environments of the western tethys in early mesozoic times and the w pacific and w indian oceans in the neogene they stayed in the deep sea reservoir when a circum equatorial ocean existed in the late mesozoic

the frasnian famennian biotic crisis how many if any bolide impacts the prime causation of the mid late devonian mass extinction near the frasnian famennian f f boundary remains uncertain nevertheless geochemical evidence has been presented recently as decisive evidence of a giant bolide impact occurring precisely at the f f boundary which promoted the global mortality episode palaeobiological data however imply a gradual global change which is otherwise seen as a record of either multiple extraterrestrial catastrophes or of impact triggered earth bound mechanisms sedimentological mega tsunami physical craters microtektites and geochemical records remain either elusive in many aspects or incompatible with the predicted impact crisis pattern biotic succession across the f f horizon is still poorly known especially in continental domains to evidence a synchronous bedding plane killing event at the close of the crisis instead the commonly documented stepwise loss of biomass and an unproved distinctive dead zone are hard to explain simply as sampling artifacts the assumed mass mortality precisely at the f f boundary may be limited mainly to the pelagic realm the underestimated role of early variscan tectonism and associated volcanic hydrothermal processes resulting in thermal and nutrient pulses as possible prime controls of the f f crisis is suggested as well as resemblances to the superplume conditioned eventful mid cretaceous interval exemplified in the cenomanian turonian mass extinction additional shocks generated by minor cometary strikes are not excluded but may have affected some f f biotas or areas

changes in the pelagic fine fraction carbonate sedimentation during the cretaceous paleocene transition contribution of the separation technique to the study of bidart section abstract the bidart section southwestern france displays an almost complete late maastrichtian early danian transition as the cretaceous paleocene k p crisis mainly affects carbonate producers the aim of this study is to precisely evaluate the evolution of pelagic sediments composition across the boundary a new protocol for separation of fine carbonates into discrete size fractions was used 1 to precisely evaluate in weight of carbonate and not only number of particles per gram of rock the contribution of each carbonate component type foraminifera calcareous nannofossils and nonbiogenic carbonates calcite microparticles and calcareous macrocrystals and 2 to measure their isotopic signature and thus constrain the origin of these carbonate particles the maastrichtian pelagic carbonates are mostly biogenic 70 of the bulk carbonate but also contain nonbiogenic carbonates calcite microparticles 4 m due to their isotopic signature calcite microparticles cannot result from fragmentation and partial dissolution of biogenic remains and the most likely origin appears to be early diagenetic processes and or export from shallow water platforms the calcareous macrocrystals derive from an early diagenetic process the lowermost danian sediments are dominated by nonbiogenic carbonates between 50 and 80 of the bulk carbonate nevertheless two kinds of biogenic components are present thoracosphaera operculata and maastrichtian like calcareous nannofossils thoracosphaera operculata is an opportunistic calcareous dinoflagellate which frequently occurs at high abundances in basal danian sediments and is certainly in situ this is confirmed by it showing a danian isotopic signature the maastrichtian like calcareous nannofossils are nannofossils of taxa that indisputably occur in the maastrichtian but which do not occur consistently in later danian strata they show a maastrichtian type isotopic signature which strongly supports the inference that they are mainly reworked from the maastrichtian this study shows that nonbiogenic carbonates are important components of the pelagic carbonate even during periods of normal sedimentation in the crisis interval the biogenic carbonate production drops sharply while calcite microparticles and carbonate macrocrystals remain almost unaffected and represent the major part of the carbonate in the earliest danian sediments finally the sediments return to a composition similar to that of the maastrichtian in m pseudobulloides foraminifera zone

lava and ice interaction at stratovolcanoes use of characteristic features to determine past glacial extents and future volcanic hazards structures resulting from lava and ice interaction are common at glaciated stratovolcanoes during summit eruptions at stratovolcanoes meltwater is produced and travels freely down steep slopes and thin permeable valley glaciers eroding the ice and enlarging preexisting glacial drainages as a result eruptions in this environment have produced few catastrophic floods lava flowing into the open channels and voids in the glaciers becomes confined and grows thicker filling the available space and producing steep sided bodies with smooth bulbous contact surfaces quenching of lava against ice or by water forms small scale features such as tensional fractures and glass as the amount of meltwater in contact with the lava increases the type and abundance of smaller scale features become similar to those produced during subglacial eruptions into meltwater lakes identification of large and small scale lava ice contact features in the field can be used to reconstruct paleoglacial extent and combined with geochronology of lavas to determine past paleoclimate an understanding of lava ice interaction allows us to better assess the hazards posed by future eruptions at glaciated volcanoes

u pb zircon age constraints on the timing and duration of wenlock silurian paleocommunity collapse and recovery during the big crisis high precision isotope dilution u pb zircon dating was conducted on three volcanic ash fall bentonite samples from the swedish island of gotland and on a fourth bentonite from the west midlands england zircons from the ireviken grotlingbo djupvik gotland and wren s nest hill 15 west midlands bentonites yielded weighted mean pb 206 u 238 ages of 431 83 0 23 0 67 ma 428 45 035 0 73 ma 428 06 0 2110 66 ma and 427 86 032 0 71 ma respectively analytical total uncertainties these biostratigraphically well controlled age dates effectively bracket the wenlock epoch of the silurian period and provide control for the duration of one of the major paleozoic biotic events and associated perturbations to the global carbon cycle the big crisis or lundgreni event graptolites the niulde event conodonts the mulde excursion carbon isotopes these new data suggest an older and shorter duration for the recalibration of the wenlock series and demonstrate that the cascade of biological and chemical events that took place during the big crisis happened on time scales of tens to hundreds of thousands of years less

subglacial intermediate volcanism at kerlingarfjoll iceland magma water interactions beneath thick ice the products of andesite and dacite glaciovolcanism at kerlingarfjoll are unlike others previously described in the literature three sequences of lithofacies are described and interpreted here the andesitic deposits at campsite gully are divided into massive vitriclastic lapilli tuff with intrusions fluidal clast bearing vitriclastic lapilli tuff and stratified pumice rich vitriclastic lapilli tuff at tindur andesitic eruptions produced contorted pillow fragment breccia and the clast supported lithic breccia finally pillow lava with intrusions and crudely bedded vitriclastic lapilli tuff of dacitic composition are described at haraldur abundant vitriclasts the presence of pillow lavas hackly fracturing of lava bodies and lack of oxidation of clasts demonstrate that each of these lithofacies formed in the presence of abundant water this contrasts with all other descriptions of subglacially erupted intermediate magmas which are characterised by jointed and glassy lava flows and domes with a marked scarcity of fragmental material the kerlingarfjoll sequences therefore demonstrate that it is possible for intermediate magmas to generate and interact with significant volumes of water at the base of a glacier preliminary estimates of volatile contents in glassy clasts correspond to quenching pressures equivalent to 500 m water or 550 m ice this is consistent with eruption beneath an ice sheet that was thick enough to overwhelm the underlying topography and where meltwater drainage was controlled by the morphology of the glacier surface it is argued that the drainage of water due to steep topography and or thin and fractured ice as opposed to thermodynamic considerations is the most likely explanation for the absence of evidence for significant magma water interaction in previously described instances of intermediate glaciovolcanism the apparent low viscosity of the kerlingarfjoll magmas may relate to relatively high eruption temperatures and or the inhibition of degassing of the magma due to high ambient pressures and the consequent limitation of groundmass crystallisation

behavior of lophophorates during the end permian mass extinction and recovery abstract the end permian mass extinction devastated most marine communities and the recovery was a protracted event lasting several million years into the early triassic environmental and biological processes undoubtedly controlled patterns of recovery for marine invertebrates in the aftermath of the extinction but are often difficult to single out the global diversity and distribution of marine lophophorates during the aftermath of the end permian mass extinction indicates that stenolaemate bryozoans rhynchonelliform brachiopods and lingulid brachiopods displayed distinct recovery patterns bryozoans were the most susceptible of the lophophorates experiencing relatively high rates of extinction at the end of the permian and becoming restricted to the boreal region during the early triassic the recovery of bryozoans was also delayed until the late triassic and characterized by very low diversity and abundance following the final disappearance of permian rhynchonelliform brachiopod survivors early triassic rhynchonelliform brachiopod abundance remained suppressed despite a successful re diversification and a global distribution suggesting a decoupling between global taxonomic and ecological processes likely driven by lingering environmental stress in contrast with bryozoans and rhynchonelliforms lingulid brachiopods rebounded rapidly colonizing shallow marine settings left vacant by the extinction lingulid dominance characterized by low diversity but high numerical abundance was short lived and they were once again displaced back into marginal settings as environmental stress changed through the marine recovery the presence in lingulid brachiopods of the respiratory pigment hemerythrin known to increase the efficacy of oxygen storage and transport when coupled with other morphological and physiological adaptations may have given lingulids a survival advantage in environmentally stressed early triassic settings

what happens when the ocean is overheated the foraminiferal response across the paleocene eocene thermal maximum at the alamedilla section spain the global warming and major perturbation of the global carbon cycle that occurred during the paleocene eocene thermal maximum petm have been investigated in the lower bathyal upper abyssal alamedilla section spain geochemical anomalies and dramatic faunal changes including the globally recognized extinction event of deep sea benthic foraminifera and the rapid evolutionary turnover of planktic foraminifera and calcareous nannofossils are associated with the petm at alamedilla biotic changes in the plankton and benthos indicate environmental instability 11 14 k y before the onset of carbon isotope excursion that marks the paleocene eocene boundary the reorganization of the planktic ecosystem points to warm and oligotrophic conditions in surface waters during the earliest eocene whereas faunal and geochemical data indicate that the extinctions of benthic foraminifera occurred over an interval with a high caco3 content and oxic conditions at the seafloor the proliferation of disaster taxa glomospira spp after the extinctions has been related to a potential source of isotopically light carbon in the western tethys and north atlantic significant changes in foraminiferal test size are documented across the petm we suggest that increased temperatures played an important role in benthic foraminiferal test size increasing their metabolic rates and consequently their food requirements decreased planktic foraminiferal test size may be related to decreased nutrient availability or surface water density however the differences in test size evolution among different species of both benthic and planktic foraminifera may be related to interspecific competition and ecological adaptations to direct or indirect consequences of the carbon addition during the petm

terrestrial evidence for the lilliput effect across the cretaceous paleogene k pg boundary abstract recent research has demonstrated that the lilliput effect reduction of body size in biota associated with the aftermath of mass extinctions affected all trophic levels in the marine realm following the cretaceous paleogene k pg event however it is unclear if this size change was strictly a marine signal or a global phenomenon that also affected continental ecosystems herein we present the results of an ichnological proxy for body size of soil dwelling insects across the k pg boundary in big bend national park texas u s a quantitative efforts focused on naktodemasis bowni which are characterized as unbranching burrows composed of ellipsoidal packets of backfill menisci these traces were likely produced by beetle larvae or cicada nymphs based on previous comparison with structures generated in modern soils and laboratory experiments as an approximation for the body size of the subterranean insects this dataset indicates that a smaller n bowni diameter dn is statistically correlated

biotic turnover in benthic foraminifera across the cretaceous tertiary boundary at el kef tunisia abstract the cretaceous tertiary boundary section exposed near el kef tunisia is the most complete boundary sequence known to date it contains nearly 1 m of black and gray boundary clay containing planktic foraminiferal zone poa b 2 m of clayey shales of p1a globigerina eugubina zone and 4 m of shales and marls of p1b g taurica zone quantitative analysis of the benthic foraminiferal fauna suggests that deposition during the latest cretaceous occurred in an upper slope to outer shelf environment which shallowed at the k t boundary to an outer to middle shelf depth and shallowed further by p1b time to mid shelf depth a major reduction in benthic diversity occurred near the k t boundary with about 50 of the fauna disappearing diversity remained an average of 37 lower during deposition of the first 3 m of sediment above the boundary poa b p1a and productivity was very low surviving and thriving foraminifers during this interval were primarily low oxygen tolerant epifaunal and infaunal species a sharp decrease in the low oxygen tolerant fauna and appearance of a shallow mid shelf fauna at about 4 m above the boundary p1b zone signals a second regression return to higher oxygen levels and higher productivity although the environmental effects of the k t boundary event can be inferred from benthic faunas the ultimate cause remains elusive faunal changes prior to and the long recovery period after the k t boundary are difficult to explain by a single impact hypothesis

experimental interaction of magma and dirty coolants the presence of water at volcanic vents can have dramatic effects on fragmentation and eruption dynamics but little is known about how the presence of particulate matter in external water will further alter eruptions volcanic edifices are inherently dirty places where particulate matter of multiple origins and grainsizes typically abounds we present the results of experiments designed to simulate non explosive interactions between molten basalt and various coolants ranging from homogeneous suspensions of 0 to 30 mass bentonite clay in pure water to heterogeneous and or stratified suspensions including bentonite sand synthetic glass beads and or naturally sorted pumice four types of data are used to characterise the interactions 1 visual video observations 2 grainsize and morphology of resulting particles 3 heat transfer data from a network of eight thermocouples and 4 acoustic data from three force sensors in homogeneous coolants with 20 sediment heat transfer is by forced convection and conduction and thermal granulation is less efficient resulting in fewer blocky particles larger grainsizes and weaker acoustic signals many particles are droplet shaped or and vesicular containing bubbles filled with coolant both of these particle types indicate significant hydrodynamic magma coolant mingling and many of them are rewelded into compound particles the addition of coarse material to heterogeneous suspensions further slows heat transfer thus reducing thermal granulation and variable interlocking of large particles prevents efficient hydrodynamic mingling this results primarily in rewelded melt piles and inefficient distribution of melt and heat throughout the coolant volume our results indicate that even modest concentrations of sediment in water will significantly limit heat transfer during non explosive magma water interactions at high concentrations the dramatic reduction in cooling efficiency and increase in mingling help to explain globular peperite and provide information relevant to analyses of premixing associated with highly explosive molten fuel coolant interactions in debris filled volcanic vents

subaqueous basaltic lava dome and carapace breccia on king george island south shetland islands antarctica on king george island during latest oligocene earliest miocene time submarine eruptions resulted in the emplacement of a small ca 500 m estimated original diameter basalt lava dome at low head the dome contains a central mass of columnar rock enveloped by fractured basalt and basalt breccia the breccia is crystalline and is a joint block deposit lithic orthobreccia interpreted as an unusually thick dome carapace breccia cogenetic with the columnar rock it was formed in situ by a combination of intense dilation fracturing and shattering caused by natural hydrofracturing during initial dome effusion and subsequent endogenous emplacement of further basalt melt now preserved as the columnar rock muddy matrix with dispersed hyaloclastite and microfossils fills fractures and diffuse patches in part of the fractured basalt and breccia lithofacies the sparse glass rich clasts formed by cooling contraction granulation during interaction between chilled basalt crust and surrounding water together with muddy sediment they were injected into the dome by hydrofracturing local steam fluidisation and likely explosive bulk interaction the basalt lava was highly crystallised and degassed prior to extrusion together with a low effusion temperature and rapid convective heat loss in a submarine setting these properties significantly affected the magma rheology increased the viscosity and shear strength and influenced the final dome like form of the extrusion conversely high heat retention was favoured by the degassed state of the magma minimal undercooling a thick breccia carapace and viscous shear heating which helped to sustain magmatic eruption temperatures and enhanced the mobility of the flow