environmental perturbations caused by the impacts of asteroids and comets we review the major impact associated mechanisms proposed to cause extinctions at the cretaceous tertiary geological boundary we then discuss how the proposed extinction mechanisms may relate to the environmental consequences of asteroid and comet impacts in general our chief goal is to provide relatively simple prescriptions for evaluating the importance of impacting objects over a range of energies and compositions but we also stress that there are many uncertainties we conclude that impacts with energies less than about 10 mt are a negligible hazard for impacts with energies above 10 mt and below about 104 mt i e impact frequencies less than one in 6 104 years corresponding to comets and asteroids with diameters smaller than about 400 m and 650 m respectively blast damage earthquakes and fires should be important on a scale of 104 or 105 km which corresponds to the area damaged in many natural disasters of recent history however tsunami excited by marine impacts could be more damaging flooding a kilometer of coastal plain over entire ocean basins in the energy range of 104 105 mt intervals up to 3 105 years corresponding to comets and asteroids with diameters up to 850 m and 1 4 km respectively water vapor injections and ozone loss become significant on the global scale in our nominal model such an impact does not inject enough submicrometer dust into the stratosphere to produce major adverse effects but if a higher fraction of pulverized rock than we think likely reaches the stratosphere stratospheric dust causing global cooling would also be important in this energy range thus 105 mt is a lower limit where damage might occur beyond the experience of human history the energy range from 105 to 106 mt intervals up to 2 106 years corresponding to comets and asteroids up to 1 8 and 3 km diameter is transitional between regional and global effects stratospheric dust sulfates released from within impacting asteroids and soot from extensive wild fires sparked by thermal radiation from the impact can produce climatologically significant global optical depths of the order of 10 moreover the ejecta plumes of these impacts may produce enough no from shock heated air to destroy the ozone shield between 106 and 107 mt intervals up to 1 5 107 years corresponding to comets and asteroids up to 4 and 6 5 km diameter dust and sulfate levels would be high enough to reduce light levels below those necessary for photosynthesis ballistic ejecta reentering the atmosphere as shooting stars would set fires over regions exceeding 107 km and the resulting smoke would reduce light levels even further at energies above 107 mt blast and earthquake damage reach the regional scale 106 km tsunami cresting to 100 m and flooding 20 km inland could sweep the coastal zones of one of the world s ocean basins fires would be set globally light levels may drop so low from the smoke dust and sulfate as to make vision impossible at energies approaching 109 mt 108 years the ocean surface waters may be acidified globally by sulfur from the interiors of comets and asteroids the cretaceous tertiary impact in particular struck evaporate substrates that very likely generated a dense widespread sulfate aerosol layer with consequent climatic effects the combination of all of these physical effects would surely represent a devastating stress on the global biosphere

the last british ice sheet a review of the evidence utilised in the compilation of the glacial map of britain this paper reviews the evidence presently available as at december 2003 for the compilation of the glacial map of britain see clark c d evans d j a khatwa a bradwell t jordan c j marsh s h mitchell w a bateman m d 2004 map and gis database of glacial landforms and features related to the last british ice sheet boreas 33 359 375 and http www shef ac uk geography staff clark chris britice html in an effort to stimulate further research on the last british ice sheet and promote a reconstruction of ice sheet behaviour based on glacial geology and geomorphology the wide range of evidence that has been scrutinized for inclusion on the glacial map is assessed with respect to the variability of its quality and quantity and the existing controversies in ice sheet reconstructions landforms interpreted as being of unequivocal ice marginal origin moraines ice contact glacifluvial landforms and lateral meltwater channels and till sheet margins are used in conjunction with available chronological control to locate former glacier and ice sheet margins throughout the last glacial cycle subglacial landforms drumlins flutings and eskers have been used to demarcate former flow patterns within the ice sheet the compilation of evidence in a regional map is crucial to any future reconstructions of palaeo ice sheet dynamics and will provide a clearer understanding of ice sheet configuration ice divide migration and ice thickness and coverage for the british ice sheet as it evolved through the last glacial cycle

the late devensian periglaciation of upland scotland abstract a wide variety of late devensian periglacial landforms developed on scottish mountains both before ca 13 000 bp and during the loch lomond stadial of ca 11 000 10 000 bp nearly all such features are now inactive late devensian periglacial weathering produced three types of regolith mantle openwork block deposits sandy diamicts and silt rich frost susceptible diamicts each of which supports a characteristic assemblage of relict landforms on upper slopes these include large scale sorted circles and stripes earth hummocks and nonsorted relief stripes sorted and nonsorted solifluction features massive boulder sheets and lobes and nivation benches talus protalus ramparts rock glaciers and alluvial fans also developed at the base of mountain slopes the distribution of late devensian periglacial features on scottish mountains is locally controlled by topography the response of underlying rocks to periglacial weathering and the limits of former glaciers regional variations in the altitude of certain forms of loch lomond stadial age particularly protalus ramparts and rock glaciers indicate a decrease in former snowfall eastwards across the scottish highlands and northwards from the highland boundary fault several upland periglacial features are also diagnostic of former permafrost and complement palaeotemperature reconstructions based on ice wedge casts and the equilibrium firn line altitudes of stadial glaciers these suggest that under stadial conditions mean january temperatures at 600 m and 1000 m on mountains in the western grampians must have been no higher than 20 c and 23 c respectively and possibly several degrees lower

the roza member columbia river basalt group a gigantic pahoehoe lava flow field formed by endogenous processes we present studies on the physical volcanology of the 15 ma roza member of the wanapum formation in the columbia river basalt group the roza member represents a compound pahoehoe flood basalt lava flow field with an area of 40 300 km 2 and a volume of 1300 km 3 it consists of 4 major lava flows each composed of numerous decimeter to kilometer long pahoehoe lobes roza lavas feature a wide range of pahoehoe surface structures such as lava rise plateaus tumuli and surface breakouts and we illustrate that the lava morphology is inconsistent with previous proposals of rapid emplacement for these lavas an integral component of the roza flow field is the sheet lobe with internal structures identical to those of inflated pahoehoe sheet lobes from hawaii and iceland both at the same scale and at much larger scales we identify a three part division of the sheet lobes into basal crust lava core and lava crust which are interpreted as the equivalent to the bottom crust the liquid lava core and the surface crust of an active inflating pahoehoe lobe the upper lava crust grows continuously during lava emplacement and its growth rate can be approximated by conductive cooling this relationship is used to calculate the emplacement time for individual roza sheet lobes and to derive a first order estimate on the duration of the roza eruption the results indicate that the emplacement of individual roza lobes lasted for months to years and that the lava flow field was constructed over a period of at least 14 years we propose that the roza flows achieved great areal dimensions and thicknesses by inflation and endogenous growth as the lava flowed from vent to flow front it traveled under an insulating crust which maintained cooling rates of 0 1 c km and allowed for efficient transport of lava over distances up to 300 km

some geological implications of average quaternary glacial conditions analyses of quaternary landscape evolution tend to focus on events associated with culminations of glacial and interglacial ages but for most of quaternary time environments were intermediate in character average quaternary glacial conditions based on assessment of the marine isotope record approximated those near the stage 2 stage 1 transition and during substages 5b and 5d isotope stages 3 and 4 and substages 5a d lie within one standard deviation of the mean value under average glacial conditions ice sheets lying over northern north america and europe were much more contracted than their full glacial counterparts and the distribution of mountain glaciers reflected a snowline depression of some 500 m geomorphic processes operating under average quaternary conditions contributed importantly to landscape evolution examples of landscapes that may represent such average conditions include cirques and fluvial deposits of the pacific northwest the fjords and strandflat of western norway and atolls of the tropical oceans by examining the geologic record from the perspective of average conditions rather than those of climatic extremes added insight can be gained regarding the evolution of quaternary landscapes

volcanological and tectonic control of stratigraphy and structure in the western deccan traps many of the world s flood basalt provinces form elevated plateaux at the margins of continents although in most cases their present large elevation is not the result of mountain building processes several explanations have recently been put forward to explain such occurrences of epeirogeny the deccan trap basalt province forms one such elevated plateau and results are presented here showing how the epeirogenic uplift in this region combined with crustal subsidence probably associated with the rifting of the indian continental margin has affected the structure of the basalt sequence trace element analytical data are used for samples from numerous vertical sections through the deccan traps lava series along and around the western ghats ridge in india the results reinforce the previously defined stratigraphy of the mahabaleshwar area and extend it over a region covering some 36 000 km2 reaching as far south as belgaum and the trap basement contact these results show that the lava pile is not flat lying but forms a very low amplitude anticlinal fold structure plunging southwards by up to 0 3 over most of the area although in the south there is evidence of a reversal of this plunge the fold is interpreted as being the result of two tilting processes 1 westward tilting near the coast due to the foundering of the passive continental margin and 2 epeirogenic uplift along the whole west coast of india producing the observed topography and the peninsula wide drainage patterns and also the easterly component of dip variations in the magnitude of the latter effect along the western continental margin may also be important in generating the plunge of the fold although the possibility of some component of depositional dip may also be important this latter possibility can be modelled using a simple computer program the results of this modelling show that a migrating linear volcanic edifice fits the observations best

biogeochemical constraints on the triassic jurassic boundary carbon cycle event 1 the end triassic mass extinctions represent one of the five most severe biotic crises in earth history yet remain one of the most enigmatic ongoing debate concerns the environmental effects of the central atlantic magmatic province camp eruptions and their linkage with the mass extinction event across the triassic jurassic boundary there is conflicting paleo evidence for changes in atmospheric pco2 during the extrusion of the camp basalts studies on sediments from european and pacific localities have however identified a substantial negative isotopic anomaly up to 3 5 across the tr j boundary providing an important indicator of changes in the operation of the ancient global carbon cycle we sought to explain the paleo evidence by utilizing a carbon cycle model for the hothouse world of the end triassic that emphasizes the chemical weathering of silicate and carbonate rocks and the ocean carbonate chemistry we find that volcanic co2 outgassing fails to fully account for either a sufficient rise in atmospheric pco2 indicated by the stomata of fossil leaves or the sedimentary isotopic fingerprint instead the scenario that best fits all of the geologic evidence is a positive feedback loop in which warming due to a buildup of volcanically derived co2 triggers destabilization of seafloor methane hydrates and the catastrophic release of ch4 palfy et al 2001 we calculate that this carbon cycle perturbation was huge involving the release of 8000 9000 gt c as co2 during the camp basaltic eruptions and 5000 gt c as ch4 in the model the initial isotopic excursion is assumed to take place over 70 kyr while complete reequilibration of the ocean atmosphere system with respect to co2 is accomplished over 700 1000 kyr our results thus provide a preliminary theoretical explanation for the bioevents estimated pco2 changes and isotopic excursions observed in marine and continental sediments at this time

sediment distribution dispersal and budget in the yellow sea abstract information on the surface sediment distribution in the yellow sea is newly compiled based on all available data produced by chinese and korean workers and is used to refine the dispersal patterns and budget of sediments derived from the adjoining landmass the central yellow sea is largely covered with fine grained sediments originating from the huanghe river 2 2 10 8 t yr about 20 of the total discharge thick sediment accumulation exceeding 5 mm yr occurs in the gulf of bohai and around the shandong peninsula about two thirds of the total huanghe river discharge the old huanghe delta suffers from reworking by strong tides and waves and forms a mud patch southwest of cheju island accumulation rate 2 10 7 t yr more than half of the sediments derived from the changjiang river are deposited along the coast of the east china sea the remainder accumulate on the inner shelf off the river mouth in the southeastern yellow sea the keum river dominates sediment discharge forming a holocene mud belt along the southwestern coast of korea accumulation rate 5 10 6 t yr turbid water plumes occur nearshore throughout the year and their suspended sediments are transported along the tip of the peninsula to the western coastal embayments in the south sea the nakdong river discharge of 1 10 7 t yr is responsible for the eastern nearshore mud of the south sea relict sands occur in the northern part of the yellow sea in the northern east china sea and in the korea strait

further evidence of fine grained sediment dispersal in the southeastern yellow sea abstract a large portion of the yellow sea is floored by fine grained clastics derived largely from the hwangho and yangtze rivers coarse grained sediments only prevail in the eastern part of the sea derived probably from the short and steep korean rivers near the keum estuary the coarse grained sediments contain substantial amounts of fine fractions detrital clays such as kaolinite and chlorite are abundant in the fine fractions and this trend extends for about 120 km both toward the northwest and the southwest the distributions of some trace elements in the bulk sediments also follow the same trend the close correspondence between mineralogical and geochemical evidence and hydrographic data suggests that the bulk of fine grained sediments in the southeastern yellow sea originates from the keum river and is subsequently transported by prevailing nearshore currents both northwestward during summer and dominantly southwestward in winter illite is dominant in the rest south of 35 n of the sea influenced by the discharge of hwangho river and possibly yangtze river the effect of the kuroshio in transporting illite into the southeastern yellow sea appears to be minimal

the permo triassic extinction the end permian mass extinction brought the palaeozoic great experiment in marine life to a close during an interval of intense climatic tectonic and geochemical change improved knowledge of latest permian faunas coupled with recent advances in isotopic studies and biostratigraphy have greatly enhanced our understanding of the events of 250 million years ago and have begun to provide answers to many questions about the causes of extinction

non climatic factors and the environmental impact of volcanic volatiles implications of the laki fissure eruption of ad 1783 studies of the potential of icelandic volcanic eruptions to modify the environment of the british isles have primarily concentrated on the degree of induced climate change but models and temperatu

a lava flow without a source the cohassett flow and its compositional components sentinel bluffs member columbia river basalt group abstract the eruption of sentinel bluffs member lava flows at approximately 15 5 ma marked the end of grande ronde basalt volcanism the most voluminous period of the columbia river basalt group more than 10 000 km3 of lava erupted from northerly trending feeder dikes in eastern washington and northern oregon and flowed westward down an ancestral paleoslope covering more than 169 700 km2 of the flood basalt province the sentinel bluffs member consists of six phases or types defined by their compositions lava flows having the first compositional type were the most voluminous and reached the pacific ocean the volume of later lava flows having the other compositional types declined with time until the final eruption produced the second largest volume of basalt at the source area compositional variation in sentinel bluffs lava flows is relatively small this homogeneity allows the individual compositional types and thus phases of the eruption to be easily recognized farther west however composition

an ice cap landsystem for palaeoglaciological reconstructions characterizing the younger dryas in western scotland abstract this paper reviews the contrasting behaviours of ice caps and icefields defines a generic landsystem model that can effectively discriminate between them and applies the model to landform sediment assemblages in an area of western scotland such a model is necessary since many palaeoenvironmental inferences from formerly glaciated terrains are based on the geometry extent and dynamics of reconstructed ice masses the validity of these glacier reconstructions is dependent on the accurate initial interpretation of relict landforms and sediments and their inter relationships a new landsystems model is presented here in which individual geological and geomorphological elements are checked against a set of eight theoretical diagnostic criteria that characterize the style of former glaciation when applied to a 1200 km 2 area of the western scottish highlands the landsystem tool predicts 1 an extensive younger dryas ice cap with a maximum surface elevation of 900 m above sea level implying colder or wetter conditions than previously thought and 2 the survival of an independent mountain icefield in part of the area during deglaciation glaciological theory proxy palaeoenvironmental data and established glacier climate topography relationships support these predictions thereby giving credibility to the landsystem methodology as a generic tool for palaeoglaciological reconstructions

the last ice sheet in north west scotland reconstruction and implications recent models of the last scottish ice sheet suggest that nunataks remained above the ice surface in areas peripheral to the main centres of accumulation this proposition has been investigated on 140 mountains over an area of 10 000 km2 in nw scotland outside the limits of the later loch lomond readvance in this area there is evidence for a single high level weathering limit that separates glacially eroded terrain from higher areas of in situ frost debris this limit occurs at altitudes ranging from 425 to 450 m in the outer hebrides to 950 m on the mainland and is best developed on lithologies that resisted breakdown after ice sheet downwastage interpretation of this weathering limit as a periglacial trimline cut by the last ice sheet at its maximum thickness is supported by 1 joint depth and schmidt hammer measurements that indicate significantly more advanced rock breakdown above the weathering limit 2 a much greater representation of gibbsite a pre late devensian weathering product in the clay fraction of soils above the limit 3 cosmogenic isotope dating of the exposure ages of rock outcrops above and below the limit 4 the sharpness of the limit at some sites and its regular decline along former ice flowlines and 5 shear stress calculations based on the inferred altitude and gradient of the former ice surface reconstruction of the ice surface based on trimline evidence indicates that the mainland ice shed lay near or slightly east of the present watershed and descended northwards from 900 m to ca 550 m at the north coast independent dispersion centres fed broad ice streams that occupied major troughs on skye an ice dome 800 m deflected the northwestwards movement of mainland ice but the mountains of rum were over ridden by mainland ice up to an altitude of ca 700 m the outer hebrides supported an independent ice cap that was confluent with mainland ice in the minches extrapolation of the trimline evidence indicates that most reconstructions of ice extent are too conservative and suggests that low gradient ice streams extended across the hebridean shelf offshore wider implications of this research are 1 that blockfields and other periglacial weathering covers are not all of the same age or significance depending on the resistance of different lithologies to frost weathering 2 that the contrasting degree of glacial modification in the western and eastern highlands of scotland may reflect a former cover of predominantly warm based ice in the former and predominantly cold based ice in the latter and 3 that the approach and techniques developed in this study have potential application for constraining ice sheet models not only in areas peripheral to the main centres of ice accumulation in britain and ireland but also in other mountain areas where nunataks protruded through warm based late pleistocene ice masses

comments on deccan flood basalts at the cretaceous tertiary boundary by v courtillot j besse d vandamme r montigny j j jaeger and h cappetta the age of the flood basalts of the deccan area and the length of the interval during which the outpourings took place are not known precisely the authors have tried to date those basalts and estimate how long the volcanic activity lasted on the basis of new paleomagnetic paleontological and geochronological data of the deccan effusives they came to the preliminary conclusion that the volcanic activity may have lasted less than 1 ma and that the majority of the lavas poured out during chron 29r unfortunately the authors were not familiar with our paper on paleomagnetism and radiomettic age determinations of deccan trap lavas 2 in our paper we presented the paleomagnetic data derived from 223 individual lava flows from 16 sections all over the deccan area and gave the k ar age determinations for 13 selected unaltered lava flows we agree that the enormous volume of deccan extrusives poured out in a relatively short interval and that the volcanic activity was probably concerned with the spreading in the central indian ocean in late cretaceous and early tertiary time

distribution and origin of clay minerals in surficial shelf sediments western north island new zealand abstract western shelf surficial sediments are mainly terrigenous muds and variably muddy fine and very fine sands of mixed modern relict heritage overall their clay fraction is dominated by illite and smectite lesser amounts of chlorite and mixed layer clays and some kaolinite the close similarity of shelf clay mineral assemblages with those in adjacent river and harbour sediments demonstrates that offshore north south regional trends in clay mineralogy parallel regional changes in onshore geology involving both western north island and more distant northwestern south island sources the same detrital clay mineral patterns on the shelf have persisted during the sea level rise following the last glaciation and are complicated only by local concentrations of authigenic smectite from volcanogenic material on the basis of the distribution and origin of the major clay minerals five north south clay petrologic zones occur on the shelf 1 hamilton shelf abundant smectite and common poorly crystalline illite primarily detrital from oligocene mudstones some smectite authigenic from quaternary volcanogenic material 2 north taranaki shelf abundant crystalline illite and common mixed layer clays and crystalline chlorite primarily detrital from miocene mudstones 3 central taranaki shelf abundant crystalline illite and common smectite and chlorite smectite is authigenic from egmont derived andesitic material contemporaneous with deposition of detrital illite and some chlorite derived from northwestern south island via the westland current and from adjacent shelf zones 4 south taranaki shelf abundant crystalline illite and chlorite detrital via the westland current from northwestern south island rivers that drain an actively eroding granitic schistose provenance and 5 north cook strait basin abundant crystalline illite and common mixed layer clays and crystalline chlorite detrital from pliocene quaternary mudstones of the south taranaki wanganui region as well as from northwestern south island sources via the d urville current

drumlins in ice sheet reconstructions with reference to the western pennines northern england abstract drumlin morphology and distribution can be used to determine the palaeoglaciological conditions under which subglacial bedforms were created by late pleistocene ice sheets detailed field mapping of part of the large drumlin fields in northern england in particular the identification of areas of superimposed drumlins has been shown to be of significance in the delimitation of the ice divide within the area the overall distribution of the subglacial bedforms has also been used to define the extent of ice streams within this part of the late devensian dimlington stadial ice sheet based on the physical principles which underlie the deformational model of drumlin formation and present day glaciological information on subglacial ice sheet conditions variations in drumlin morphology have allowed a first attempt at reconstructing areas of high 100 kpa and low

evidence for errors in the geomagnetic polarity time scale at 17 15 ma 40ar 39ar dating of basalts from the pacific northwest usa 40ar 39ar incremental heating studies have been carried out on whole rock basalt samples from the columbia river basalt crb and the steens basalt to obtain crystallization ages with a standard error 1 these high precision accurate ages are utilized with the known magnetostratigraphy of the crb to test the accuracy of the early to middle miocene section of the geomagnetic polarity time scales currently in use we conclude that these time scales underestimate the ages of various chrons within this time range by 0 9 m y

the distribution of clay minerals in recent sediments of the korea strait abstract the bottom sediments of the korea strait contain on average 50 illite 21 kaolinite 17 intergrade clay 8 chlorite and 4 smectite the geographical distribution of the clay minerals shows an increase in illite a decrease in kaolinite and a slight decrease in chlorite seawards the distributional patterns of smectite and intergrade clay are irregular the clay fractions of the sediments near the land are supplied by river borne sediments and are mixed with sediments transported landwards from offshore the distribution of clay minerals in the korea strait appears to have been influenced by the supply or and redistribution of fine grained sediments by the tsushima warm current from the east china sea kaolinite seems to be transported mainly by river runoff and illite chlorite and smectite might have been derived partly from the east china sea by the tsushima warm current intergrade clay seems to have a complex origin

physical properties and geoacoustic provinces of surficial sediments in the southwestern part of the ulleung basin in the east sea abstract a total of 157 piston and box core samples were collected and analyzed to characterize physical properties and geoacoustic provinces of surficial sediments in the southwestern part of the ulleung basin in the east sea the results and distribution patterns of surficial sediment texture physical and acoustic properties reflect well the sedimentary environment like distribution and composition of sediment in the study area the inner shelf and basin slope in this study are dominated by fine grained sediments and show high porosity and water content with low bulk density and velocity as well the trough of the korea strait and outer shelf which is composed of coarse grained sediments shows low porosity and water content and high bulk density and velocity based on in situ velocity and sediment properties the study area is divided into five provinces 1 province ia is hemi pelagic mud partially mixed with intermittent sandy sediments which are derived from the outer shelf due to slide slump or mass flows in situ velocity 1445 m s mean grain size 8 4 porosity 84 and bulk density 1 24 g cm3 2 province ib is covered with muddy sediments that were deposited during the holocene in situ velocity 1445 m s mean grain size 7 9 porosity 78 and bulk density 1 35 g cm3 3 province ii is marked by mixed recent and relict sediments in situ velocity 1477 m s mean grain size 6 1 porosity 68 and bulk density 1 53 g cm3 4 province iii is dominated by coarse grained relict sediments formed during the pleistocene in situ velocity 1564 m s mean grain size 3 8 porosity 54 and bulk density 1 77 g cm3 and 5 province iv consists of coarser sediments than province iii in situ velocity 1671 m s mean grain size 3 0 porosity 46 and bulk density 1 91 g cm3 the compressional wave velocity mean grain size and bulk density increase from province ia to province iv whereas the porosity and water content decrease from province ia to province iv variability of the physical and acoustic properties tends to follow the general trend of the mean grain size the classification of each province using the in situ velocity corrected with the temperature and pressure provides a better reflection of the sediment properties and sedimentary environment

volatile fluxes during flood basalt eruptions and potential effects on the global environment a deccan perspective abstract we examine the role that flood basalt eruptions may have played during times of mass extinction through the release of volcanic gases continental flood basalt provinces have formed by numerous eruptions over a short period of geologic time characteristically a few million years within this period a short lived climactic phase that lasts about 1 ma typically emplaces a large proportion of the lava volume this phase consists of a series of huge eruptions each yielding 10 3 10 4 km 3 of magma each eruption lasted on the order of a decade or more and built an immense p hoehoe dominated lava flow field by eruptive activity along fissures tens to hundreds of km long high fire fountains emanating from vents along the fissures at times sustained eruption columns that lofted gas and ash into the upper troposphere and lower stratosphere while the lava flows covered huge areas the combination of large eruption magnitudes maintained high effusion rates during eruptions and the repeated nature of the characteristic large scale eruptive activity occurs in earth history only during periods of flood basalt volcanism based on recent analogs and determination of volatile contents of ancient flood basalt lavas we estimate that individual eruptions were capable of releasing 10 000 tg of so 2 resulting in atmospheric loadings of 1000 tg a 1 during a sustained decade long eruptive event we apply this model of flood basalt volcanism to estimate the potential mass of co 2 and so 2 released during formation of the 65 ma deccan province the deccan lava pile contains the record of hundreds of enormous p hoehoe flow fields erupted within a period of about 1 ma consequently atmospheric perturbations associated with so 2 emissions from just one of these long lasting eruptions were likely to have been severe and constantly augmented over a decade or longer by contrast the amounts of co 2 released would have been small compared with the mass already present in the atmosphere and thus much more limited in effect individual eruptions were followed by hiatuses of hundreds to thousands of years during which the gas contributions to the atmosphere would be recycled it is clear that the nature and potential atmospheric impact of a series of huge volume repeated long term degassing events requires further investigation in conjunction with appropriate climate models

multiple factors in the origin of the cretaceous tertiary boundary the role of environmental stress and deccan trap volcanism a review of the scenarios for the cretaceous tertiary k t boundary event is presented and a coherent hypothesis for the origin of the event is formulated many scientists now accept that the event was caused by a meteorite impact at chicxulub in the yucatan peninsula mexico our investigations show that the oceans were already stressed by the end of the late cretaceous as a result of the long term drop in atmospheric co2 the long term drop in sea level and the frequent development of oceanic anoxia extinction of some marine species was already occurring several million years prior to the k t boundary the biota were therefore susceptible to change the eruption of the deccan traps which began at 66 2 ma coincides with the k t boundary events it erupted huge quantities of h2so4 hcl co2 dust and soot into the atmosphere and led to a significant drop in sea level and marked changes in ocean temperature the result was a major reduction in oceanic productivity and the creation of an almost dead ocean the volcanism lasted almost 0 7 m y extinction of biological species was graded and appeared to correlate with the main eruptive events elements such as ir were incorporated into the volcanic ash possibly on soot particles this horizon accumulated under anoxic conditions in local depressions and became the marker horizon for the k t boundary an oxidation front penetrated this horizon leading to the redistribution of elements the eruption of the deccan traps is the largest volcanic event since the permian triassic event at 245 ma it followed a period of 36 m y in which the earth s magnetic field failed to reverse instabilities in the mantle are thought to be responsible for this eruption and therefore for the k t event we therefore believe that the k t event can be explained in terms of the effects of the deccan volcanism on an already stressed biosphere the meteorite impact at chicxulub took place after the onset of deccan volcanism it probably played a regional rather than a global role in the k t extinctions

sulphur release from flood lava eruptions in the veidivotn grimsvotn and katla volcanic systems iceland book description humans have long marvelled at and feared the odorous and colourful manifestations of volcanic emissions and in some cases have harnessed them for their economic value the degassing process responsible for these phenomena is now understood to be one of the key factors influencing the timing and nature of volcanic eruptions moreover the surface emissions of these volatiles can have profound effects on the atmospheric and terrestrial environment and climate even more fundamental are the relationships between the history of planetary outgassing differentiation of the earth s interior chemistry of the atmosphere and hydrosphere and the origin and evolution of life this book provides a compilation of 23 papers that investigate the behaviour of volatiles in magma the feedbacks between degassing and magma dynamics and the composition flux and environmental atmospheric and climatic impacts of volcanic gas emissions

determination of total h2o and co2 budgets in evolving magmas from melt inclusion data 1 numerical simulations of volcanic processes show that the preeruptive and eruptive dynamics depend substantially on the amount and composition of volatiles present in magma either dissolved in the liquid or separated in a gas phase although the investigation of melt inclusions within crystals is providing increasingly abundant data on the amount of volatiles dissolved in magmatic liquids classic approaches involving phase relationships and experimental petrology cannot provide the relative mass of gas and liquid phases in magma this represents a serious limit to the simulation of the dynamics of magmatic and volcanic processes here a theoretical framework based on mass balance equations for the volatile species water and carbon dioxide in crystallizing degassing magmas is developed the theory presented offers a systematic description of the mass relationships between dissolved and total volatiles in magma and leads to the definition of the total volatile tv line concept the tv line represents the locus of total volatile contents consistent with the amounts dissolved in the liquid and measured in melt inclusions appropriate expressions for tv lines for closed and open system conditions with respect to the gas phase and for crystallizing and noncrystallizing magmas are developed the tv line approach allows discrimination between melt inclusions formed in closed versus open system conditions and determination of total volatile budgets for magmas evolving under closed system conditions and it can constrain the degassing history of magmas evolving in open system conditions several examples of the use of the tv line approach to determine total h2o and co2 budgets in evolving magmas starting from melt inclusion data are provided applications to real cases suggest that total dissolved plus exsolved carbon dioxide contents in magmas can be in some cases from 1 to more than 2 orders of magnitude greater than the dissolved amounts

did paleogene north atlantic rift related eruptions drive early eocene climate cooling abstract the delivery of volcanogenic sulphur into the upper atmosphere by explosive eruptions is known to cause significant temporary climate cooling therefore phreatomagmatic and phreatoplinian eruptions occurring during the final rifting stages of active flood basalt provinces provide a potent mechanism for triggering climate change during the early eocene the northeast atlantic margin was subjected to repeated ashfall for 0 5 m y this was the result of extensive phreatomagmatic activity along 3000 km of the opening northeast atlantic rift these widespread predominantly basaltic ashes are now preserved in marine sediments of the balder formation and its equivalents and occur over an area extending from the faroe islands to denmark and southern england these ash bearing sediments also contain pollen and spore floras derived from low diversity forests that grew in cooler drier climates than were experienced either before or after these highly explosive eruptions in addition coeval plant macrofossil evidence from the bighorn basin wyoming usa also shows a comparable pattern of vegetation change the coincidence of the ashes and cooler climate pollen and spore floras in northwest europe identifies volcanism as the primary cause of climate cooling estimates show that whilst relatively few phreatomagmatic eruptive centres along the 3000 km opening rift system could readily generate 0 5 1 c cooling on an annual basis only persistent or repeated volcanic phases would have been able to achieve the long term cooling effect observed in the floral record we propose that the cumulative effect of repeated balder formation eruptions initiated a biodiversity crisis in the northeast atlantic margin forests only the decline of this persistent volcanic activity and the subsequent climatic warming at the start of the eocene thermal maximum allowed the growth of subtropical forests to develop across the region

periglacial trimlines in the scottish highlands abstract two periglacial weathering limits have been identified on mountains in the highlands of scotland the lower has been interpreted as a periglacial trimline marking the upper limits of loch lomond younger dryas stade glaciers and has been employed to reconstruct the dimensions of parts of the main west highland icefield and certain smaller glaciers and icefields interpretation of the upper weathering limit has been more contentious but recent research has demonstrated 1 significant contrasts in the degree of bedrock weathering above and below this limit 2 that gibbsite a pre devensian weathering product is abundant above the limit but rare in soils farther downslope 3 that the isotopic 26al age of bedrock exposures above the limit greatly exceeds that at lower altitudes and 4 that the altitude of the weathering limit descends regularly along former ice sheet flowlines collectively these attributes suggest that the upper weathering limit is a periglacial trimline defining the maximum altitude of the last ice sheet calculated basal shear stress values are consistent with this interpretation which implies that the mainland ice shed lay at ca 900 m in wester ross and descended gently northwards whilst harris and lewis in the outer hebrides supported an independent ice cap that achieved a maximum altitude of ca 700 m wider implications of this interpretation and the future potential for ice sheet reconstruction are explored

the quaternary deposits and landforms of scotland and the neighbouring shelves a review abstract a thick sequence of quaternary sediments up to 1000 m has been deposited in the north sea basin and perhaps five major glacial episodes the first occurring prior to ca 1 8 2 1 ma bp and the last during the late devensian can be recognised between the glacial events periods of low salinity arctic marine or glacio marine sedimentation have been dominant although episodes of ameliorated climate when north atlantic drift waters had access to the north sea have been identified a number of horizons in separate boreholes have been correlated with the last interglacial oxygen isotope stage 5e and a sequence of water mass movements around the scottish coasts can be reconstructed for the last ca 125 ka on land sequences of quaternary deposits relating to several glacial and non glacial terrestrial and marine events occur in different areas but due to poor dating correlation between these sequences cannot yet be achieved in particular north east scotland has a complex glacial history with evidence for ice sheet glaciation on at least four occasions evidence from the outer hebrides north east scotland and the north sea basin indicates that the late devensian scottish ice sheet had a rather restricted extent only reaching a short distance offshore along much of the east and west coasts at this time ice free areas existed in north east scotland on the isle of lewis and probably in caithness and orkney whilst part of the outer shelf around st kilda was dry land a marine embayment extended down the east coast of scotland between the scottish and scandinavian ice sheets and independent ice caps existed on the outer hebrides and probably on shetland deglaciation of the greater part of the country took place prior to ca 13 ka bp whilst the climate was still very cold the ice retreat appears to have been orderly with stagnant ice masses being trapped only in topographically suitable locations a number of retreat stages or minor readvances occurred during the general deglaciation the firth of clyde was one of the last areas outside the highlands to be deglaciated and this occurred in a rapid possibly catastrophic fashion shortly prior to ca 13 ka bp despite the mild climate at the start of the lateglacial interstadial it is not known if there was complete deglaciation prior to the loch lomond readvance the readvance glaciers however may have started to advance during the latter part of the interstadial when declining terrestrial temperatures coincided with a period of mild marine conditions the loch lomond readvance maximum can only be dated to some time after ca 10 9 ka bp and it is likely that final ice free conditions were not achieved until the earliest holocene

a geological map of the southern deccan traps india and its structural implications a geological map of an area of over 125 000 km 2 within the southern deccan traps india is presented which is based upon variations in the basalt geochemistry it represents a synthesis of new data and earlier work the use of large data sets has allowed stratigraphic boundaries to be established with greater accuracy over a much larger area than before the geochemical sections demonstrate that the southward overstepping stratigraphic style encountered along the ghats ridge has an essentially north to south polarity and that there appears to be detectable overstep in an east to west sense however the stratigraphy defines a pronounced coastward dipping monoclinal flexure across the western ghats ridge between 16 n and 18 n the data are consistent with two models of eruption the first considers the deccan eruptive focus to have been fixed throughout the volcanic episode producing an essentially annular flow pattern the second considers the flow pattern to have been generated from a southerly migrating eruptive centre resulting from the northerly drift of india over a fixed hotspot both hypotheses are consistent with recent quantitative models which suggest that rapid and voluminous flood basalt eruptions are the result of continental rifting events associated with plume generated thermal 9highs9 until a causal link between established plume hotspot trails and impact sites can be satisfactorily demonstrated we find it unnecessary to invoke a cataclysmic impact event as an explanation for the deccan eruptions

late devensian ice sheet in the western grampians scotland a radial pattern of ice flow of the last ice sheet in the largest source area of ice c 5000 km2 in the british isles in western scotland is demonstrated by the dispersal of indicator erratics and by patterns of striae friction cracks and ice moulded landforms three major ice domes and the principal ice divide are identified in the western grampians the ice domes coincided with the highest mountain blocks while it is inferred that the alignment of many of the pre existing valleys controlled much of the outflow of ice forming ice streams within the ice sheet the importance of the rannoch moor basin as a radial provider of ice to surrounding areas was apparently less significant than has hitherto been considered ice flowed into and across the southern part of the basin from the principal ice divide located to the west and south no evidence has yet been found that would support a model of an eastward migrating ice divide either during the build up or during the deglaciation of the late devensian ice sheet

lateglacial surface exposure dating in the monadhliath mountains central highlands scotland we constrain the deglaciation history of the monadhliath mountains since the last glacial maximum using glacial geomorphology and surface exposure dating collectively these data clarify the glacial history of the monadhliath mountains at the close of the devensian cold period 10be exposure ages indicate deglaciation of the last devensian ice sheet at 15 1 1 4 ka at ca 640 m od the exposure ages are consistent with basal radiocarbon ages from nearby loch etteridge 5 km to the south east 15 3 0 2 kcal bp1 boulders from moraines in three monadhliath corries yielded exposure ages between 11 8 ka and 9 8 ka 470 600 m od suggesting that a lateglacial advance occurred during the younger dryas stadial the limited extent of these younger dryas glaciers in the monadhliath mountains results from the combined effect of a drier climate experienced in the eastern part of the central highlands ice cap and topographical factors our reconstruction largely supports the deglaciation model of golledge et al 2008 and confirms that a sw to ne precipitation gradient dominated scotland during the younger dryas

gibbsitic soils on former nunataks implications for ice sheet reconstruction x ray diffraction analyses of soils above and below a periglacial trimline developed across the basalts of the trotternish escarpment isle of skye scotland demonstrate that gibbsite is restricted to soils above the trimline this suggests that the gibbsite is a relict of pre late devensian weathering and that the trimline did not develop after the last ice sheet achieved its maximum thickness the sharpness of the boundary between frost weathered regolith and gibbsitic soils upslope and ice scoured bedrock associated with gibbsite free soils downslope suggests that the trimline represents the altitude of the last ice sheet at its maximum thickness rather than a former boundary between passive cold based ice and erosive warm based ice these findings illustrate how identification of high level periglacial trimlines and associated contrasts in clay mineralogy provide a means for constraining reconstructions of the form of the last ice sheets

eocene succession on the east shetland platform north sea abstract a sand prone middle eocene sequence is recognized in three cored boreholes on the east shetland platform three lithostratigraphic divisions are recognized lower sand unit main sand unit and upper claystone unit the lower sand unit is of fluvio deltaic origin occurring on the southern part of the east shetland platform the main sand unit represents the subsequent transgression of the delta the unit comprises a set of highstand shelf systems tracts separated by glauconitic bands and reflected by palynological assemblage breaks the presence of reworked palynofloras in sediments of late middle eocene age implies derivation of sediment from the north west part of the east shetland platform although it is tempting to ascribe sea level changes to the sediment pattern a tentative correlation with the hampshire basin only highlights the difficulties involved

geochemistry of surface sediments off the southern and western coasts of korea abstract the continental shelf off the southern and western side of the korean peninsula is part of a modern epicontinental sea and is an effective sediment trap for clastic material derived from china and korea we have analyzed 179 surface sediment samples from this shelf for al fe na k mg ca ti p mn sr ba v cr co ni cu zn organic carbon and calcium carbonate in order to determine the geochemical characteristics of these sediments results showed a wide range of element contents which are mainly related to the textural variability of sediments exceptions to this were found in the contents of ca k sr and ba the ca and sr contents were largely determined by the amounts of carbonate present the k content on the other hand appeared to be influenced by both the contents of illite and feldspar and ba of potassium feldspar for muds i e sediments deposited under present day conditions it is possible to distinguish those in the central yellow sea from those in the keum estuary the former are characterized by high contents of fe na k mg ca and v and the latter by high contents of mn ba and co these differences become more apparent when these elements are normalized relative to al in order to minimize grain size effects the distribution of v al ratios is different from that of other elements the highest v al values occur in muds from the central yellow sea derived from the huanghe the yellow river in china whereas the highest values of mn al are found in the nearshore area adjacent to the korean peninsula based on these results it is suggested that the sources of fine sediments in the yellow and south seas can be distinguished from the geochemical characteristics of the surface sediments in the yellow sea two different sources of fine grained sediments can be seen the huanghe and the keum river the former is characterized by higher v contents and the latter by higher mn contents using the v al ratio as an end member component of the two source materials the dispersal patterns of the fine sediments 6o were also derived

the geochemistry of indian bole horizons palaeoenvironmental implications of deccan intravolcanic palaeosurfaces deccan intravolcanic bole horizons represent weathering products formed during major hiatuses of a major volcanic episode in these quiescent periods weathering processes pervasively altered the newly formed volcanic landscape and subsequent flows covered and effectively fossilized the resulting weathered palaeosurfaces the current work is a detailed geochemical study which examines patterns of element mobilization during these intravolcanic weathering events the bole horizons normally rest on top of altered basaltic lavas both boles and altered lavas represent a comparatively early stage in weathering because the content of chemically residual elements such as aluminium and iron are closer to fresh basalt than laterite nevertheless these is clear evidence for significant chemical alteration because the more mobile elements such as calcium and sodium have been substantially removed a chemically distinctive nature for some boles can be demonstrated from chondrite normalized ree plots and in these instances strontium and neodymium isotopic compositions demonstrate that the fine grained bole material is derived from a chemically distinct source in addition thin sections reveal that these fine grained portions commonly contains glass shards and occasionally fresh phenocrysts it is therefore suggested that many deccan boles are in fact weathered pyroclastic material and that the pyroclastic content of the basaltic succession may be greater than previously supposed a significant pyroclastic input during the deccan eruptions has important palaeoenvironmental implications for the fate of late cretaceous flora and fauna in peninsular india

glacial trimlines to identify former ice margins and subglacial thermal boundaries a review and classification scheme for trimline expression abstract reconstructions of former ice sheets and glaciers provide important palaeoglaciological information about their behaviour in response to climate changes glacial trimlines record both the margin positions and palaeo ice thickness enabling the production of empirically constrained 3 dimensional reconstructions however the literature review into the characteristics interpretation and use of glacial trimlines here presented shows that these features have been under utilised and are poorly described in the existing literature with a confusing terminology currently in use a new classification scheme and terminology for trimline identification and interpretation is developed to better facilitate further research into these common features of glacierised and formerly glaciated landscapes

new geochemical evidence for the onset of volcanism in the central atlantic magmatic province and environmental change at the triassic jurassic boundary the late triassic early jurassic was a time of major global change however the fundamental processes driving these changes are less than clear we have determined the re and os abundances and os isotope compositions of marine mudrock samples that span the triassic jurassic boundary in the uk and have established that major isotopic and geochemical shifts in the composition of seawater took place in the latest triassic we argue that these shifts were caused by the sudden initiation of widespread igneous activity within the central atlantic magmatic province associated with rifting of the supercontinent pangea the os isotope composition of seawater responded rapidly to these events demonstrating that the seawater os isotope system has great potential in identifying the nature and precise timing of major environmental change

sedimentology stratigraphy and glacier dynamics western scottish highlands glacial sediments of the western scottish highlands are comprehensively described and characterized here for the first time enabling the first glacial stratigraphy for the area to be proposed this classification is based on the results of extensive geological mapping and field investigation of sedimentary sequences and their structures x ray diffraction and particle size distribution analyses and comparison with deposits formed in contemporary glaciated environments these new data are subsequently appraised in terms of their implications for late pleistocene glacier evolution and dynamics together the data suggest that much of the landscape is palimpsest and can be attributed to the weichselian late devensian glaciation subsequent glacier advance during the younger dryas did little to modify the area suggesting that ice flow was dominated by sliding on a meltwater lubricated rigid bed with deformation of basal sediments playing a more limited role final deglaciation was marked by a significant increase in basal meltwater flux reflecting the warming climate and increasing precipitation these new palaeoglaciological and palaeoenvironmental insights advance our understanding of former glacier dynamics in the western scottish highlands improve our knowledge of pleistocene landscape evolution of this area and enable comparisons to be made with sedimentary sequences elsewhere