from greenhouse to icehouse organic walled dinoflagellate cysts as paleoenvironmental indicators in the paleogene abstract dinoflagellates are an important component of the extant eukaryotic plankton their organic walled hypnozygotic cysts dinocysts provide a rich albeit incomplete history of the group in ancient sediments building on pioneering studies of the late 1970s and 1980s recent drilling in the southern ocean has provided a wealth of new dinocyst data spanning the entire paleogene such multidisciplinary studies have been instrumental in refining existing and furnishing new concepts of paleogene paleoenvironmental and paleoclimatic reconstructions by means of dinocysts because dinocysts notably exhibit high abundances in neritic settings dinocyst based environmental and paleoclimatic information is important and complementary to the data derived from typically more offshore groups as planktonic foraminifera coccolithophorids diatoms and radiolaria by presenting case studies from around the globe this contribution provides a concise review of our present understanding of the paleoenvironmental significance of dinocysts in the paleogene 65 25 ma representing earth s greenhouse icehouse transition this episode holds the key to the understanding of extreme transient climatic change we discuss the potential of dinocysts for the reconstruction of paleogene sea surface productivity temperature salinity stratification and paleo oxygenation along with their application in sequence stratigraphy oceanic circulation and general watermass reconstructions

a body wave analysis of the 1966 gisborne new zealand earthquake abstract the ml 6 2 gisborne earthquake of march 4 1966 occurred along the east coast of the north island new zealand modeling of p and s body waves shows that the focal mechanism of this event is consistent with northwestward thrusting of the pacific plate beneath the north island 249 25 and 131 the focal depth is constrained to 18 km significantly less than the values of 25 30 km computed from local network data estimates of the scalar moment source duration and stress drop for the event are 4 1024 dyne cm 2 3 s and 20 120 bar respectively cross correlation errors of synthetic to observed waveforms were computed for all possible p and t axis locations and slip vector orientations and contoured on a projection of the focal sphere the error contour at which the synthetic waveforms distinctly diverged from the observed waveforms was established by eye the procedure shows that the analysis of long period body waves at least in this case provides much better constraint on focal mechanism orientation than does first motion data alone

the hawke s bay new zealand earthquake of 1982 september 02 and deformation in the interior of the subducted pacific plate abstract the most damaging earthquake to occur in new zealand in 1982 was the hawke s bay earthquake of september 02 m b 5 6 an aftershock study using portable microearthquake recorders has established that this event occurred some 20 km south of hastings at a depth of about 47 km this depth places the event in the mantle of the subducted pacific plate this earthquake is a member of a recently recognized class of intraplate shocks occurring along the strike of the subducted plate near the east coast of the north island such events are characterized by normal faulting mechanisms when taken together with activity in the crust of the subducted plate this subcrustal activity resembles a double planed seismic zone restricted in the down dip direction of the subducted plate several lines of evidence suggest that deformation in the mantle of the subducted plate is controlled by the state of coupling of the plate interface at shallow depth 1 1 the subcrustal activity occurs directly beneath the source region of major interplate earthquakes along the east coast of the north island and there appears to be a pairing of interplate and subcrustal events 2 2 stress directions determined for the subcrustal events are concordant with geodetic strain directions and 3 3 the amount of subcrustal activity appears to be related to the state of coupling of the plate interface

dinoflagellate cysts sea level changes and planktonic foraminifers across the cretaceous tertiary boundary at el haria northwest tunisia abstract dinoflagellate cysts and planktonic foraminifers have been studied from the cretaceous tertiary k t boundary interval at el haria northwest tunisia a high resolution integrated biostratigraphy is presented the k t boundary is drawn at the level of extinction of cretaceous planktonic foraminifers and is coincident with the first occurrence of the dinoflagellate cyst species danea californica the final extinction of planktonic foraminifers is foreshadowed by a reduction in their total abundance some 5 kyr earlier at the base of the boundary clay this reduction is coeval with reported anomalies in siderophyle elements and 13 c values in the same area dinoflagellate cysts do not show accelerated rates of extinction at k t time associations of dinoflagellate cysts however change drastically and parallel changes in relative numbers of sporomorphs spores and pollen and in the quantity of land derived organic matter jointly these changes reflect a rapidly falling sea level during the final 17 kyr of the mesozoic which culminates at the level of the k t boundary this steep sea level fall at k t time represents a peak regressive pulse at the end of the well documented latest cretaceous regressive trend this short term sea level fall might show to be a wide spread phenomenon which could have caused an excess shrinking of the already reduced areal extent of marginal seas since deep waters in cretaceous oceans were primarily produced in shallow marginal seas the rate of formation of deep water might have been minimized at k t time minimum rates of formation of deep water might have curtailed the slow upward mixing of relatively cool and nutrient rich deeper water through which the thermocline weakened and surficial waters became depleted in nutrients consequently phytoplankton productivity rapidly diminished which in combination with a weakened thermal gradient pushed the highly depth stratified cretaceous planktonic foraminiferal fauna to extinction over a period of time of some 5 kyr guembelitria cretacea was the sole planktonic foraminifer which could accommodate to the low productivity conditions the oscillating rise in sea level at the beginning of the cenozoic reinforced the upward mixing of relatively cool and nutrient rich deeper water steepened the thermocline and replenished the photic layer with nutrients concomitant niche differentiation in the photic layer progressively stimulated morphological innovation amongst early cenozoic planktonic foraminifers the final return of normally sized planktonic foraminifers and of stable and well balanced dinoflagellate cyst associations at about 125 kyr after the k t boundary seems to indicate that primary productivity and niche differentiation in the photic layer begin to revert to optimum levels the earliest cenozoic planktonic foraminiferal species globoconusa minutula and parvularugoglobigerina fringa are thought to have developed from a benthic foraminiferal species rather than having a planktonic ancestry

seismic geomorphology and sequence stratigraphy as tools for the prediction of reservoir facies distribution an example from the paleocene and earliest eocene of the south buchan graben outer moray firth basin ukcs

spatial clustering and stress drops of foreshocks of the february 1990 tennyson and weber new zealand earthquakes the ability to distinguish foreshocks from background seismicity is very important in short term earthquake prediction to that end we have looked at spatial clustering using waveform cross correlation and stress drops of foreshocks of two new zealand earthquake sequences that occurred in 1990 the tennyson sequence located in a continental margin type strike slip environment consisted of a group of foreshocks an ml 5 8 mainshock and many aftershocks a cross correlation analysis showed five spatially close clusters of activity prior to the mainshock two were event pairs located within the final aftershock zone two were clusters of four events each located outside the aftershock zone and the fifth was a cluster of eight immediate foreshocks loated within the aftershock zone an analysis of two nearby control regions showed that pairs of identical events were not uncommon but larger clusters were stress drops of three events in the 12 days before the mainshock obtained by deconvolving small events as empirical green s functions were lower than for earlier preshocks and aftershocks source time functions derived from the green s function deconvolution indicated that a unilateral rupture model was more appropriate than a circular source model cross correlation values from the ml 5 9 weber sequence also showed spatial clustering but this was well removed from the mainshock in space and time a control area also showed similar clustering suggesting that it is a normal feature of the seismicity at a convergent margin the weber foreshocks only four in all were not highly correlated for both sequences foreshocks did not correlate with the aftershocks indicating that they occurred in a region of complete coseismic stress relief a stress drop of 1650 bars was obtained for a 44 km deep event that occurred within the upper part of the subducting pacific plate nearby but not related to the tennyson sequence

integrating palynological and geochemical data in a new approach to palaeoecological studies upper cretaceous of the banterwick barn chalk borehole berkshire uk abstract the dinoflagellate cyst record from an upper cretaceous uppermost cenomanian upper coniacian chalk core drilled at banterwick barn berkshire is described and statistically correlated with elemental and stable isotope bulk sediment geochemical data from the same core seventy two dinocyst species and subspecies are recorded and stable carbon and oxygen isotopic 13 c 18 o trends are documented lithostratigraphy and chemostratigraphic correlation of the 13 c curve with an expanded section at dover kent are used to identify stratigraphically significant marls and determine the positions of macrofossil zones and stage boundaries in the banterwick barn core these data indicate that 30 m of chalk at dover are represented by senoniasphaera rotundata alveolata is proposed which has a fad in the lower turonian and last appears lad in the lower coniacian senoniasphaera rotundata rotundata autonym herein has its fad in the middle turonian first common occurrence in the uppermost turonian and lad in the upper coniacian an extremely impoverished assemblage of dinocysts in the highest cenomanian to lowest turonian is considered to be largely a preservational artefact of intraclastic nodular and calcarenitic chalks and is not related directly to the well documented global oceanic anoxic event oae2 occurring at that time 93 5 ma a sharp increase in dinocyst abundance in the lower turonian corresponds with a change in lithology to more marly chalks a gradual decrease in the number of species is observed through the middle turonian to upper coniacian 18 o records show that this was associated with global climatic cooling cluster analysis of the dinocyst abundance record with geochemical data indicates four distinct species groups with characteristic geochemical associations i e groups 1 4 groups 1 and 2 are associated with phases of increased siliciclastic supply a positive correlation with higher 13 c values differentiates the latter group 3 is independent of carbonate and detrital input and group 4 is associated with high carbonate flux and low detrital supply these groupings suggest that cyst forming dinoflagellates exhibited a range of ecological niches in the late cretaceous although the relationship between the encystment process and the geochemical associations is unclear key environmental factors are likely to be sea level and climate related including water depth turbidity nutrient supply sea surface temperature and environmental stability predictability integrated geochemical and palynological studies have great potential for inter regional correlation and palaeoenvironmental interpretation

normal faulting through subducted oceanic crust the 19 july 1985 earthquake of hawke s bay new zealand abstract source parameters of the m l 5 7 19 july 1985 earthquake of northern hawke s bay new zealand are determined by modelling the teleseismic p and s body waves a focal depth of 31 1 km scalar moment 5 6 10 17 nm and source duration of 3 0 3 5 s are estimated the focal mechanism strike 224 dip 78 rake 273 shows normal faulting on a nw dipping plane that is parallel to the strike of the subducted pacific plate thirty five aftershocks were recorded by a temporary seismograph network 21 of which were relocated using the jhd method the hypocentres define a northwest dipping plane 20 30 km which extends from the hypocentre of the mainshock to a depth of 47 km the position of the subducted plate in hawke s bay is well defined from previous micro earthquake studies in the region of the mainshock the plate interface is located at a depth of approximately 28 to 30 km placing the hypocentre of the mainshock in the crust of the pacific plate the extent and location of the aftershock distribution suggest that the mainshock ruptured downward and extended through the crust of the plate this event thus differs from other normal faulting events in the region that usually occur in the mantle of the subducted plate the scalar moment at long periods t 45s dziewonski et al 1986 exceeds that determined here by a factor of 2 suggesting a source rich in long period energy an idea supported by the relatively large aftershock area

understanding basin sedimentary provenance evidence from allied phytogeographic and heavy mineral analysis of the palaeocene of the ne atlantic the drilling of hydrocarbon exploration wells in the faroe shetland basin has provided an expanding sample resource that provides material for testing recently developed palynology based sediment transport analysis this technique has been verified by comparison with heavy mineral analysis both approaches have been used to identify sediment sources and input points along the strike of the palaeocene west shetland platform integration of heavy mineral and palynological data has provided a basis for understanding arenaceous and argillaceous sediment distribution and sourcing in addition to a source from the western greenland side of the basin four argillaceous and four arenaceous sedimentary sources have been identified along the strike of the west shetland platform these vary in temporal and spatial distribution and thus provide a history of sediment source evolution this analysis supports a persistent difference in source between the corona basin and the flett and judd sub basins although source variation and overlap between basins is evident transfer zones represent both conduits for and barriers to effective sediment transport both palynological and heavy mineral evidence identifies the former presence of late namurian westphalian strata on the west shetland platform which were removed by subsequent erosion

sage ii measurements of early pinatubo aerosols sage ii satellite measurements of the mt pinatubo eruption cloud in the stratosphere during june july and early august 1991 show that aerosols in the tropics reached as high as 29 km altitude with most of the cloud between 20 and 25 km the most optically thick portions of the cloud covered latitudes from 10 s to 30 n during the early part of this period by late july high stratospheric optical depths were observed to at least 70 n with the high values north of about 30 n from layers below 20 km high pressure systems in both hemispheres were observed to be correlated with the movement of volcanic material at 21 km into the westerly jet stream at high southern latitudes and similarly to high northern latitudes at 16 km by august the entire southern hemisphere had experienced a 10 fold increase in optical depth relative to early july due to layers above 20 km initial mass calculations using sage ii data place the aerosol produced from this eruption at 20 to 30 megatonnes well above the 12 megatonnes produced by el chichon

particle sedimentation and diffusive convection in volcanic ash clouds 1 understanding the longevity of volcanic ash clouds generated by powerful explosive eruptions is a long standing problem for assessing volcanic hazards and the nature and time scale of volcanic forcings on climate change it is well known that the lateral spreading and longevity of these clouds is influenced by stratospheric winds particle settling and turbulent diffusion observations of the recent 2010 eyjafjallajokull and 2011 grimsvotn umbrella clouds as well as the structure of atmospheric aerosol clouds from the 1991 mt pinatubo event suggest that an additional key process governing the cloud dynamics is the production of internal layering here we use analog experiments on turbulent particle laden umbrella clouds to show that this layering occurs where natural convection driven by particle sedimentation and the differential diffusion of primarily heat and fine particles give rise to a large scale instability where umbrella clouds are particularly enriched in fine ash this particle diffusive convection strongly influences the cloud longevity more generally cloud residence time will depend on fluxes due to both individual settling and diffusive convection we develop a new sedimentation model that includes both sedimentation processes and which is found to capture real time measurements of the rate of change of particle concentration in the 1982 el chichon 1991 mt pinatubo and 1992 mt spurr ash clouds a key result is that these combined sedimentation processes enhance the fallout of fine particles relative to expectations from individual settling suggesting that particle aggregation is not the only mechanism required to explain volcanic umbrella longevity

eustatic variations during the paleocene eocene greenhouse world we reconstruct eustatic variations during the latest paleocene and earliest eocene 58 52 ma dinoflagellate cysts grain size fractions and organic biomarkers in marine sections at four sites from three continents indicate an increased distance to the coast during the paleocene eocene thermal maximum petm the same trend is recognized in published records from other sites around the world together the data indicate a eustatic rise during the petm beginning 20 to 200 ka before the globally recorded negative carbon isotope excursion cie at 55 5 ma although correlations are tentative we recognize other global transgressions during chrons c25n and c24n the latter may be associated with eocene thermal maximum 2 53 5 ma or the x event 52 ma these results suggest a link between global sea level and hyperthermal intervals potentially because of the melting of small alpine ice sheets on antarctica thermal expansion of seawater or both however the early onset of sea level rise relative to the cie of the petm suggests contributions from other mechanisms perhaps decreasing ocean basin volume on sea level rise copyright 2008 by the american geophysical union

pollen distribution in marine surface sediments from chilean patagonia abstract southern south america is the only mid to high latitude continental landmass in the southern hemisphere and therefore represents one of the key areas to recover terrestrial records for the study of past and future climate variability at these latitudes during cruise md 159 of r v marion dufresne cores were taken off the chilean coast from 40 to 55 s in the open ocean and the fjords pollen spectra of 32 core top samples illustrate the relationships between pollen distribution in the sampled marine sediments and their transport from the vegetation onshore pollen concentrations show two distinct gradients 1 a north to south gradient controlled by latitudinal vegetation changes and by westerly winds and 2 from the fjords to the open ocean a gradient clearly controlled by wind fluvial inputs and pollen diagenesis linked to the distance from the coast and water depth the distribution of pollen percentages in these marine surface sediment samples reflects the local vegetation from the nearby continental area consequently pollen analyses from older sediments in these marine cores will be reliable tools to reconstruct past vegetational changes

high resolution biostratigraphic zonation for the uk central north sea paleocene abstract this paper presents the high resolution biostratigraphic zonation scheme for the paleocene of the central north sea area uk and the application to formation characterization well correlation reservoir modelling and wellsite activities the scheme is developed from detailed and consistently recorded palynological events supported by microfossil data which have been applied successfully to the majority of proprietary biostratigraphic studies from the basin nine zones and 29 subzones have been defined based on first downhole occurrence fdo or abundance events with chronostratigraphic significance and can be consistently correlated across the studied area the nine biozones are described based on a dominant palynological marker from base upward senoniasphaera inornata and spiniferites magnificus danian isabelidinium viborgense and palaeoperidinium pyrophorum selandian cordosphaeridium gracile spiniferites fentonii spiniferites rhomboideus areoligera gippingensis and base apectodinium spp thanetian the defined bioevents have been consistently linked with the published lithostratigraphy stratigraphic sequences and interpreted depositional environments

stratigraphic and spatial distribution of palynomorphs in deep water turbidites a meta data study from the uk central north sea paleogene abstract the paleogene sele formation spans across the basinal areas of the uk central north sea and comprises a very laterally extensive deep marine fan system namely the forties sandstone member a very important oil and gas reservoir horizon the development of this turbidite system across the basin floor resulted from the response to sea level changes and fluctuating sediment yield from the continental landmass influenced by hinterland uplift and climate in order to understand the distribution of terrestrially sourced and marine palynomorphs in this depositional system comprising stacked turbidite flows statistical analyses of palynology data from 41 wells have been conducted these statistical studies support the division of the microplankton into nine groups clustering taxa depending on their ecology and taphonomy it is observed that the palynological assemblages are influenced by sediment provenance across the turbidite fans the landmass vegetation ecology and the marine microplankton populations varying across the basin the dominant derived cluster groups b peridinioids dominated by apectodinium species and e probably autotrophic gonyaulacoids comprise about 70 of the taxa recorded these dinoflagellates bloomed as a result of low salinity surface waters and an increase in water mass eutrophication resulting from the greenhouse climate optimal conditions of the petm the pollen and spore data although challenging to interpret due to the varied quality of the data set supports the interplay of a coastal wetland vegetation on extensive marginal delta systems with associated wetland and swamp environments

eruption of the eyjafjallajokull volcano in spring 2010 multiwavelength raman lidar measurements of sulphate particles in the lower troposphere 1 a fraction of the volcanic plume that originated from the eyjafjallajokull volcanic eruption on iceland in 2010 reached the southern iberian peninsula in may 2010 the plume was monitored and characterized in terms of optical and microphysical properties with a combination of raman lidar and star and sun photometers our observations showed that the plume arriving at the iberian peninsula was mainly composed of sulphate and sulphuric acid particles to our knowledge this is the first study of optical properties and inverted microphysical properties of volcanic sulphate particles in the lower troposphere boundary layer based on multiwavelength raman lidar measurements a remarkable increase in the particle number concentration in the accumulation mode was determined from the inversion of the aerosol optical properties the large angstrom exponents and low linear particle depolarization ratios 4 7 indicated the presence of small and spherical particles the particle effective radii ranged between 0 30 and 0 55 m in situ instrumentation confirmed an increase of sulphate particles at ground level during this period

a procedure for modelling shallow dislocation sources summary expressions for displacements on the surface of a layered half space due to an arbitrary oriented shear dislocation are given in terms of generalized ray expansions useful approximations of these expressions for shallow events as recorded at teleseismic distances for realistic earth models are presented the results of this procedure are used to generate synthetic p sv and sh waveforms for various assumptions of stress drop

the apectodinium acme and terrestrial discharge during the paleocene eocene thermal maximum new palynological geochemical and calcareous nannoplankton observations at tawanui new zealand manifestations of profound perturbations in biogeochemical systems during the paleocene eocene thermal maximum petm include a prominent global negative 13c and a pronounced increase in the relative abundance of dinoflagellate cysts dinocysts assigned to the genus apectodinium while motile representatives of apectodinium were most likely thermophilic and heterotrophic the underlying causes of this dinoflagellate response are not well understood here we provide new insight by examining the palynology chemistry and calcareous nannoplankton across the petm in a continental slope section at tawanui new zealand across the petm marked changes in the relative abundance of apectodinium vary antithetically with significant changes in the 13c of carbonate and organic matter in general the high relative abundance of apectodinium relates to enhanced concentrations of dinocysts signifying a bloom of apectodinium in surface waters during the petm changes in apectodinium and 13c records correspond to variations in many other parameters including a smaller negative shift in bulk carbonate 13c than expected increased terrestrial palynomorphs elevated toc and c n ratios lower carbonate contents higher sio2 and al2o3 contents and lower si al ratios all of these variations can be explained by an increase in delivery of terrigenous material to the continental margin a peak in the relative abundance of glaphyrocysta dinocysts at the onset of the petm may indicate greater down slope transport of neritic material changes in calcareous nannoplankton abundances suggest increased nutrient availability in surface waters during the petm the combined results show that apectodinium dominated assemblages global perturbations in carbon isotopes and enhanced terrigenous delivery closely correspond in time at tawanui a sudden and massive carbon injection to the ocean atmosphere system may have enhanced weathering and increased terrigenous inputs to continental margins during the petm we further suggest that these inputs caused the apectodinium acme by elevating primary productivity in marginal seas

seismicity structure and tectonics of the wellington region new zealand summary the wellington region lies on the border between the pacific and australian plates the former being subducted the plate interface lies at shallow depth under the region 10 60 km so that detailed and long term monitoring of the seismicity of the zone where large thrust earthquakes are expected to occur is possible hypocentres for events recorded by a 12 station seismic network for the period 1978 1982 7231 events have been refined by the use of a threedimensional velocity model derived from a simultaneous inversion of arrival time data from 129 local events for both hypocentres and velocity the hypocentres show that the subducting pacific plate is defined by a nw dipping zone of relatively intense activity the plate interface as given by the upper envelope of this activity is offset vertically by 7 km on average along a nw se line through cook strait parallel to the direction of absolute motion of the pacific plate rather than to the direction of convergence the strike of the interface at deeper levels also changes across this line this distortion may partly reflect effects of the transition to continent continent type convergence further south within the subducting pacific plate the seismic activity defines two parallel zones separated by about 20 km the lower zone being much less active and perhaps merging with the upper zone at a depth of 80 90 km composite focal mechanisms of events in the upper zone imply predominantly down dip tension with a compression axis perpendicular to the plate interface the mechanism in the lower zone also implies down dip tension but the compression axis has rotated to be horizontal and along strike indicating a component of lateral shearing within the plate these two types of mechanism correlate well with those found previously for events at depths of 150 km or more thus it seems that the large negative buoyancy of the subducted lithosphere dominates the internal stress field throughout the length of the seismically active region the lithosphere acting as a stress guide there is no evidence for a significant number of events with mechanisms indicating thrusting along the plate interface the seismic velocity in the region corresponding to the upper seismic band is close to that typical for oceanic crust which here is probably considerably thicker than normal there is no evidence for a substantial increase in velocity down

caliop observations of the transport of ash from the eyjafjallajokull volcano in april 2010 1 the cloud aerosol lidar with orthogonal polarization caliop is an elastic backscatter lidar carried on the calipso satellite caliop observations between 15 and 20 april 2010 of volcanic ash plumes following the eruption of the icelandic eyjafjallajokull volcano are reported here while caliop has limited spatial coverage due to nadir only sampling ash plumes were observed by caliop over a wide region from the north atlantic ocean to eastern europe during both day and night due to its nadir only view however caliop did not sample the densest ash plumes which were observed by passive satellite sensors and ground based lidar lidar depolarization and spectral backscatter signatures are used to discriminate ash layers from clouds most ash was observed in thin layers of laminar appearance with thicknesses ranging from 0 4 km to a little more than 1 km and at relatively low altitudes between 1 and 7 km most layers reported here produced strong lidar depolarization indicating a predominance of ash over sulfate aerosol in the plumes estimates of lidar extinction to backscatter ratio allow the retrieval of profiles of ash optical properties layers were observed with mean optical extinction ranging from 0 03 km 1 to nearly 1 km 1 combined with an estimate of mass extinction efficiency mass concentration profiles can also be estimated these observations of the three dimensional dispersion of the plume are complementary to observations from passive satellite instruments and ground based lidars and can be useful for verification of dispersion models such as those used by the volcanic ash advisory centers

transport of terrestrial organic matter in the ogooue deep sea turbidite system gabon abstract in order to define the nature and distribution of the organic matter om preserved in the modern ogooue deep sea turbidite system gabon bulk geochemical techniques rock eval pyrolysis elemental and isotopic analyses and palynofacies were applied to three piston cores collected in the cape lopez canyon and lobe and on the continental slope north of the canyon the hemipelagic sedimentation in the study area is characterized by high accumulations of well preserved om 2 3 wt toc bulk geochemical and palynofacies analysis indicate both a marine and terrestrial origin of the om contribution of the marine source is higher on the slope than in the canyon and lobe om accumulation in turbidites is strongly controlled by the combined influence of the cape lopez canyon and littoral drift in the canyon and lobe turbidites show generally low toc content 0 5 wt and om is oxidized the origin of the om is interpreted as both marine and terrestrial with a higher contribution of continental source versus marine source the low toc contents are due to the large siliciclastic fraction transported by the littoral drift and diverted in the cape lopez canyon during high energy processes e g storms which tend to dilute the om in the turbidites transport by long shore currents and or turbiditic flows leads to oxidation of the om on the continental slope located north of the cape lopez canyon large amounts of om are deposited in turbidites up to 14 wt the om is predominantly derived from terrestrial land plants and has not been subjected to intense oxidation these deposits are characterized by high hydrocarbon potential up to 27 kg hc t rock indicating a good potential as gas prone source rock because cape lopez canyon captures a significant part of the sediment transported by the littoral drift the siliciclastic sedimentary flux is reduced north of the canyon om is thus concentrated in the turbidites variation in toc content within turbidite laminae can be explained by the burst and sweep deposition process affecting the boundary layer of the turbulent flow this study confirms that gravity flows play a preponderant role in the accumulation and preservation of om in deep water and that deep sea turbidite systems could be regarded as an environment where organic sedimentation occurs

on the temporal variation of stratospheric aerosol size and mass during the first 18 months following the 1982 eruptions of el chichon baloon borne particle counters at laramie and in southern texas are used to investigate the size and mass distribution of the aerosol which formed in the stratosphere during the first 18 months following the volcanic eruption of el chichon the latter appears to have reached a peak at laramie in early 1983 and began a decline in may measurements of average aerosol radius versus time are used to estimate a sulfuric acid concentration of about 10 to the 7th per cu cm 40 days after the eruption and a net acid vapor lifetime of 25 50 days in the 18 25 km altitude region

marine and terrestrial environmental changes in nw europe preceding carbon release at the paleocene eocene transition environmental changes associated with the paleocene eocene thermal maximum petm 56 ma have not yet been documented in detail from the north sea basin located within proximity to the north atlantic igneous province naip the kilda basin and the northern rain belt paleolatitude 54 1n during the petm this is a critical region for testing proposed triggers of atmospheric carbon release that may have caused the global negative carbon isotope excursion cie in marine and terrestrial environments the cie onset is identified from organic matter d 13 c in exceptional detail within a

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

comparative lidar study of the optical geometrical and dynamical properties of stratospheric post volcanic aerosols following the eruptions of el chichon and mount pinatubo the spatiotemporal evolution of aerosols formed from precursors injected into the stratosphere by major volcanic eruptions such as those of el chichon in 1982 and mount pinatubo in 1991 has been studied using a ground based lidar system located at the observatoire de haute provence ohp in southern france 44 n 5 e from the inversion of the lidar signals the optical geometrical and dynamical properties of the particles have been determined as a function of time after the eruption in immediate post volcanic conditions when the optical thickness of particles in the stratosphere is largely enhanced an estimate of the aerosols backscatter phase function has been evaluated directly from the lidar measurements using a size distribution model adjusted to in situ balloon measurements the precision of this determination lies in the 15 range values of the mean radius of the particles of their integrated content surface areas and sedimentation velocities are then derived from the systematic lidar measurements performed at ohp these values are compared for the two major volcanic eruptions which have occurred over the last decade although the injection of sulphur dioxide was twice as large for the mount pinatubo eruption as compared to the el chichon case the diffusion of the cloud in the two hemispheres due to the interaction of the particular phase of the quasi biennal oscillation with several other dynamical processes at the time of the eruption led to the observation of similar values for the aerosol content over the observatoire de haute provence in the months just following the two events however the residence time of the particles in atmospheric layers below 20 km are 4 months longer after the mount pinatubo eruption caused by the observed difference in the initial vertical distribution of the aerosol cloud

source parameters of large historical 1918 1962 earthquakes south island new zealand we have studied 18 earthquakes of m w 5 5 within the north island new zealand region to determine fault parameters for earthquake hazards and regional tectonic studies since most large m w 6 5 earthquakes in the north island occurred prior to 1961 these events provide important information to supplement studies of more recent seismicity our results indicate that no large plate interface earthquakes have occurred in the central and southern north island for the past 80 years although six strike slip earthquakes of m w 6 8 occurred within the australian upper plate during an extremely active 25 year period that began in 1917 only the m w 7 2 strike slip events were associated with surface faulting indicating the difficulties that may arise in attempting to identify active faults within this region two earthquakes m w 6 9 7 1 off the northeastern north island in 1947 appear to have occurred along the plate interface and were associated with local tsunamis having runup heights of up to 10 m two m w 6 8 events also occurred within the pacific lower plate highlighting the hazards related to intraslab events slip vectors for the earthquakes studied suggest that the majority of transcurrent motion along the plate margin is accommodated within the australian plate similar to the results obtained from studies of more recent smaller earthquakes pure thrusting occurs along the plate interface and t axes of intraslab events indicate downdip tension in the pacific plate

stratospheric aerosol clouds due to very large volcanic eruptions of the early twentieth century effective particle sizes and conversion from pyrheliometric to visual optical depth spectral and pyrheliometric measurements of atmospheric transmission were made by staff members of the astrophysical observatory of the smithsonian institution at washington d c and at mount wilson california during the years 1901 1920 these valuable data are analyzed here with the help of a new inversion method to derive the effective or area weighted radii of stratospheric aerosols formed after three very large volcanic eruptions in this period after the great eruptions of katmai 1912 and santa maria 1902 reff remained close to 0 3 m for at least two years this near constancy of reff has been duplicated in modern times by the aerosols from el chichon 1982 following ksudach s 1907 eruption reff grew from 0 2 0 3 m to 0 4 0 5 m in about 1 year pinatubo s 1991 aerosols grew similarly generally speaking the pyrheliometric optical depth perturbation as measured for the three early eruptions is not equal to the visual optical depth perturbation but in fact the latter is larger by a factor of about 1 6 at least for reff 0 25 0 45 m wider physical implications of the present results are discussed

mid to late eocene organic walled dinoflagellate cysts from odp leg 171b offshore florida mid to late eocene organic walled dinoflagellate cysts from odp leg 171b offshore florida

subduction and back arc activity at the hikurangi convergent margin new zealand the hikurangi margin is a region of oblique subduction with northwest dipping intermediate depth seismicity extending southwest from the kermadec system to about 42 s the current episode of subduction is at least 16 20 ma old the plate convergence rate varies along the margin from about 60 mm a at the south end of the kermadec trench to about 45 mm a at 42 s the age of the pacific lithosphere adjacent to the hikurangi trench is not known

shallow subduction tectonics and fault interaction the weber new zealand earthquake sequence of 1990 1992 a series of four large earthquakes with epicenters very close to one another occurred in 1990 1992 in the weber region of the southeast coast of the north island new zealand the region is one of oblique plate convergence and subduction the plate interface being at about 20 km depth the first event february 19 1990 ml 6 1 mw 6 2 occurred within the upper part of the subducting pacific plate on a steeply northwest dipping normal fault as defined by relocated aftershocks the mechanism of this event reflects downdip tension within the subducting plate due to slab pull forces as is common in new zealand the second event may 13 1990 ml 6 2 mw 6 4 occurred on an imbricate fault in the overlying australian plate dipping shallowly northwest with components of both thrusting and dextral strike slip motion the slip vector is similar to the direction of plate convergence showing no arc normal rotation as observed for subduction thrust events in other areas of oblique convergence it is unlikely that the spatial and temporal closeness of these events is coincidence a similar pair occurred to the south in 1942 but the coupling mechanism is not clear perhaps being related to aseismic slip downdip on the subduction interface two subsequent events both of ml 5 5 occurred on august 15 1990 and march 2 1992 and extended the aftershock zone of the deeper first main shock to the northeast matching the extent of the shallower second main shock mechanisms of aftershocks of the two larger events are quite variable but as a whole are similar to the relevant mainshock the time history of the aftershocks of the first deeper event shows a period of quiescence beginning 35 days before the second shallow event the mean magnitude of those events that did occur was high this observation cannot be explained by station biases weather or changes in analysis methods and may be due to stress changes induced by precursory aseismic slip which would discourage aftershock occurrence

interplate coupling and temporal variation of mechanisms of intermediate depth earthquakes in chile we investigated the temporal variation of the mechanism of large intraplate earthquakes at intermediate depths in relation to the occurrence of large under thrusting earthquakes in chile focal mechanisms were determined for three large events 1 march 1934 m 7 1 d 120 km 20 april 1949 m 7 3 d 70 km and 8 may 1971 m w 7 2 d 150 km which occurred down dip of the great 1960 chilean earthquake m w 9 5 rupture zone the 1971 event is down dip compressional strike 12 dip 80 and rake 100 the 1949 earthquake focal mechanisms is 350 70 and 130 the data available for the 1934 event are consistent with a down dip tensional mechanism thus the two events which occurred prior to the great 1960 chilean earthquake are down dip tensional published fault plane solutions of large intermediate depth earthquakes 28 march 1965 and 7 november 1981 which occurred down dip of the valparaiso earthquakes of 1971 m w 7 8 and 1985 m w 8 0 are also down dip tensional these results suggest that before a major thrust earthquake the interplate boundary is strongly coupled and the subducted slab is under tension at intermediate depths after the occurrence of an interplate thrust event the displacement on the thrust boundary induces transient compressional stress at intermediate depth in the down going slab this interpretation is consistent with the hypothesis that temporal variations of focal mechanisms of outer rise events are due to changes of interplate coupling

revised lower palaeogene lithostratigraphy for the outer moray firth north sea abstract the lower palaeogene lithostratigraphy of the outer moray firth has been revised using wireline log and biostratigraphic data a two fold subdivision into the montrose and moray groups is recognized the montrose group consists of the maureen and lista formations whereas the younger moray group contains the sele balder dornoch and beauly formations the lista formation contains the arenaceous andrew and balmoral members separated by the tuffaceous glamis member the dornoch and beauly formations are prograding shelfal sandstone units that pass basinwards into the age equivalent dominantly argillaceous sele and balder formations the sele formation contains the forties and cromarty members which are locally developed sand rich units stratigraphic analysis has led to the identification of a number of consistently developed high gamma log markers that are interpreted as condensed mudstone horizons these markers are believed to record clastic sediment starvation during periods of maximum marine transgression they often have a strong biostratigraphic fingerprint coinciding with influxes of rich concentrations of microfossils and microflora they are interpreted as the product of synchronous regional transgressive events and have been an important aid to the development of a confident lithostratigraphic framework for the lower palaeogene of the outer moray firth