late pliocene and quaternary glaciations of new zealand abstract evidence of late pliocene glaciations is fragmentary the ross glaciation in northwest south island is correlated with the first marine faunal evidence of marked cooling in the wanganui basin in southern north island it is inferred to be in the 2 6 2 4 ma age range the porika glaciation in a separate area of northwest south island is younger judged by palynology and is correlated with a cooling 2 2 2 1 ma bp inferred from stratigraphic evidence of lowered sea level in the wanganui basin a gap of 1 5 ma in the record of glaciations is largely filled by wanganui basin marine sediments although an unconformity cuts out the record between ca 1 45 and 1 0 ma bp since then the many sedimentary cycles caused by sea level changes are presumed to be glacio eustatic in origin uplifted interglacial marine terraces back to marine oxygen isotope stage 17 and river terraces formed by cold climate aggradation are linked into the cyclic sequence through loess and tephra in their cover beds east of the south island cores from the dsdp site 594 in the southwest pacific record the earliest glaciation and higher in the core nine periods of south island glaciation in the last 0 7 ma onshore because of uplift and erosion only the last four glaciations assigned to oxygen isotope stages 10 8 6 and 4 2 are identified being named nemona waimaunga waimea and otira glaciations they are best known in north westland northwest south island where the relations of glacial outwash and interglacial shoreline deposits are displayed the late otira glaciation stage 2 is radiocarbon dated as beginning somewhat before 22 3 ka bp culminating ca 18 ka bp and ending at ca 14 ka bp when rapid deglaciation began a relatively small advance at ca 12 ka bp may have been followed by little change until after 8 6 ka bp recession was then followed by a period of advance from ca 5 ka bp until recent centuries and a subsequent recession that still continues

on the origin and post depositional history of widespread massive ash deposits the case of intermediate brown tuffs ibt of lipari aeolian islands italy abstract we analysed a widespread massive ash unit outcropping on the island of lipari which belongs to the intermediate brown tuffs ibt succession of the aeolian islands italy the use of a multidisciplinary approach that integrates textural petrological and pedological methods allows us to discriminate between syn eruptive and post depositional features the deposits are dominated by uncrystallised blocky glass fragments of homogeneous shoshonitic composition confirming a provenance from hydromagmatic eruptions on the island of vulcano many glass fragments are surrounded by a coating separated by a thin void of syn eruptive origin due to alteration by aggressive acid gases in the eruptive cloud the lack of this coating in the northern part of lipari can be explained as a progressive dispersion of the gases far from the vent and or to post depositional processes the degree of soil development significantly increases from south soil profiles p1 and p2 at valle muria to north p3 and p4 at madoro and chiesa vecchia sites respectively as a response to a decrease in slope steepness which has brought about a progressive deepening of the pedogenetic front on gentler landforms and conversely its rejuvenation on steep slopes the relatively poor to moderate degree of pedogenic evolution of the studied ibt unit is consistent with its emplacement during part of the last glacial period

an outsider s review of the astronomical theory of the climate is the eccentricity driven insolation the main driver of the ice ages abstract although the astronomical theory of the climate also known as the milankovitch theory explains a number of key features of the paleoclimate time series especially frequency and phase distribution in terms of orbital influence on the waxing and waning of ice sheets it still faces several important unresolved challenges in this review we discuss five main challenges we believe the theory must resolve in order to survive 1 the large amplitude of the 100 ky ice age cycles 2 the switch from 41 ky to 100 ky long glaciations around 0 9 ma bp 3 the absence of significant spectral power at 413 ky over the past 1 2 ma 4 the variation in glacial cycle duration in the last 800 ky and 5 the presence of non orbital spectral peaks in the climate record but in spite of these problems we conclude that the milankovitch theory may still be a viable one at least in the original sense of hays et al science 194 1976 1121 that orbital changes somehow influenced the ice ages many investigators ourselves included appear to see the impact of orbital forcing in the data clear evidence of astronomical forcing as well as evidence which suggests that the climate system responds nonlinearly to all milankovitch orbital frequencies

direct marine terrestrial correlations wanganui basin new zealand the last 1 million years abstract wanganui basin a back arc basin in north island new zealand contains a detailed sequence of interfingering terrestrial and shallow marine sediments spanning the entire quaternary rhyolite tephras erupted from the taupo volcanic zone together with magnetostratigraphy and biostratigraphy facilitate correlations between wanganui basin and the astronomically calibrated oxygen isotope chronology of deep sea cores particularly over the last 1 ma eustatic changes are interpreted from both marine shelf sediments and marine terraces within the basin non marine sediments including loess dunesand and alluvial deposits coupled with pollen analyses are used to interpret climatic changes they can also be directly related to the marine record through stratigraphic relations between marine and non marine deposits in the basin

wet surge deposits at la fossa di vulcano depositional and eruptive mechanisms abstract wet surge deposits of different volcanic cycles of the recent fossa activity at vulcano have been measured on a bed by bed basis with data recorded to millimeter detail the wet surge layers are varicoloured with variable thickness with the most recurrent thickness being about 1 cm the beds consist of fine ash without internal structures textural features include a accretionary lapilli of maximum size of 0 5 cm dispersed thoroughout the layer or forming continuous layers of submillimeter size b vesiculated layers which represent 10 to 65 of the total deposit vesicles have different shapes and smooth walls varying in volume from 1 to 15 20 c soft sediment types of bedding deformation such as gravity flowage ripples load cast and slumps the slope angle has not influenced either the concentration and size of the accretionary lapilli or the shape size and distribution of vesicles only the thickness of the layers decreases with distance from the vent sem investigations show features indicating the hydromagmatic origin of the deposits and stressing the role of the fluid phase noteworthy is the presence of vesiculated grains produced by magmatic exsolution which show chilling effects on the internal walls of the broken bubbles grain size analyses reveal that the layers are not graded and most of the samples have a median size finer than 50 m the grain size distributions are frequently polymodal suggesting several closely timed explosions as all the beds exhibit the same textures grain size and particle morphology a single mechanism can explain their deposition the depositional unit formed at the base of the cloud through the lateral expansion on the ground of a sticky muddy medium consisting of ash and fluid in general each layer lost its plasticity before the deposition of the next layer the deposition occurred in a nearly continuous sequence without periods of rest long enough to permit erosional discontinuity the eruptions are hydromagmatic and occur where magma at least partially fragmented comes into effective contact with subsurface water the process follows a model suggested by wohletz 1983b 1986 developing in more than one fragmentation event in the turbulent surge cloud both severe hydration and alteration of glassy grains and the formation of accretionary lapilli occur

oceanographic and climatic changes over the past 160 000 years at deep sea drilling project site 594 off southeastern new zealand southwest pacific ocean high resolution textural carbonate microfossil and oxygen 18o and carbon 13c stable isotopic analyses are presented for the late quaternary isotopic stages 1 to 6 interval of a core at deep sea drilling project site 594 situated just south of the present subtropical convergence in northernmost subantarctic surface waters on the southern flank of chatham rise in the southwest pacific downcore alternations of pelagic and hemipelagic oozes correspond to interglacial and glacial episodes respectively interglacial oozes contain a northern subantarctic assemblage of planktonic foraminifera with rare cool subtropical species while glacial oozes are characterized by species typical of southern most subantarctic waters and include radiolaria with affinity for antarctic waters the planktonic 18o record for the site supports a 3 6 c temperature change in near surface waters between interglacial and glacial stages and indicates that during stage 5e the near surface waters were about 1 c warmer than at present a pronounced cooling during stage 5d matches that of the vostok ice core d record and negative excursions at the end of stages 2 and 6 support a southern latitude warming preceding northern hemisphere deglaciation benthic foraminifera typical of cold intermediate to deep waters can increase dramatically in abundance in the hemipelagic ooze intervals when 18o results suggest a temperature drop in glacial stage bottom waters of 2 4 c possibly a result of upward displacement of antarctic intermediate water by circumpolar deep water at the site the foraminiferal 13c records support a reduced influence of north atlantic deep water in the southwest pacific during glacial stages when nutrient enhancement occurred in both bottom and surface waters despite the pronounced changes between interglacial and glacial conditions inferred at site 594 contributed to by a substantial northward shift by at least 5 of latitude in the position of the antarctic convergence south of new zealand during glacial episodes we conclude that the subtropical convergence remained locked to chatham rise approximately 44 s throughout stages 1 to 6 major compression of the intervening belt of subantarctic water during glacial episodes and the associated very steep thermal gradients and intensified atmospheric and oceanic circulation patterns that developed in this part of the southwest pacific account for the harsh frigid environment reported for on land southern new zealand at these times

the last glacial maximum in central and southern north island new zealand a paleoenvironmental reconstruction using the kawakawa tephra formation as a chronostratigraphic marker abstract kawakawa tephra formation comprising oruanui ignimbrite flow member and aokautere ash airfall member represents the products of an exceptionally large and widespread volcanic eruption from taupo volcanic centre in the north island of new zealand the eruption occurred during the last glacial maximum and is radiocarbon dated at c 22 6 ka b p thermoluminescence ages are in broad agreement with the radiocarbon age the presence of aokautere ash in loess deposits in alluvial gully fills on river terraces and its absence from unstable sites permits a detailed assessment of geomorphic activity during the last glacial maximum widespread erosion of regolith aggradation of river valleys and deposition of loess particularly in the period following eruption of the kawakawa point to a cold dry variable climate a collation of pollen data for sediments containing aokautere ash and those 14c dated in the range 17 23 ka shows that tall forest was highly restricted in the central and southern parts of the north island an apparently subalpine grassland shrubland was present at sites from present sea level to over 800 m elevation suggesting that factors other than lower temperatures such as exposure to wind and frost fire and reduced rainfall were important in controlling vegetation patterns we conclude that the interval 23 13 ka b p broadly equivalent to oxygen isotope stage 2 represents the period of greatest environmental change in the north island

magnetic fabric and remanent magnetization of pyroclastic surge deposits from vulcano aeolian islands italy abstract tufi di grotte dei rossi inferiori are unwelded fine grained pyroclastic deposits of hydromagmatic origin emplaced between 21 and 11 8 6 ka at vulcano aeolian islands italy by deposition through surges spreading laterally from inside the la fossa caldera in this study the deposit s magnetic properties were investigated and interpreted in terms of eruptive and emplacement dynamics rock magnetism data were supplemented by grain size and textural characteristic analyses as well as scanning electron microscope sem investigations curie point measurements isothermal remanent magnetization and microprobe analyses showed that magnetization is carried by low ti titanomagnetite the size of the grains ranges from about 20 to 300 micrometres their shape from equidimensional to highly elongated the magnetic fabric is typical of fine grained pyroclastics foliation is well developed and in most sites lineation is directed towards the source area of the la fossa caldera the remanent magnetization consists of two components whose blocking temperature spectra partially overlap the direction of the low temperature component is close to that of the axial dipole and consistent with the palaeosecular variation curve for the aeolian islands the high temperature component is systematically shallowed and close to the direction of the magnetic lineation the overall results suggest that the high temperature component was acquired before and the low temperature component after the actual deposition of grains immediately after eruption the grains cooled and moved as free particles in the turbulent cloud during the expansion of the surge flows those particles with high blocking temperatures acquired a thermal remanence they were then deposited and shear at the very base of the flow oriented them and imprinted the rock s fabric and high temperature magnetization component volcanological and magnetic data suggest turbulent transportation and traction deposition of particles finally the rock cooled down and acquired the low temperature magnetization according to this model remanence acquisition in pyroclastic rocks deposited at temperatures lower than the curie point of their ferromagnetic grains depends on both the fluid dynamic forces and cooling history and must therefore be more complex than in pyroclastics deposited at higher temperatures such as welded ignimbrites

dynamics of vulcano island tyrrhenian sea italy investigated by long term 40 years geophysical data abstract vulcano island is a composite volcanic edifice located in the south central sector of the aeolian archipelago tyrrhenian sea italy historic activity has been characterized by frequent transitions from phreatomagmatic to minor magmatic activity the last eruption in 1888 90 saw powerful explosive pulses and this eruption defines what we call vulcanian also for other volcanoes since then volcanic activity has been in the form of fumarolic emanations of variable intensity and temperature mainly concentrated at la fossa crater we investigated vulcano dynamics through ca 40 years of ground deformation and seismicity data collected by the discrete and continuous ingv monitoring networks we considered levelling gps edm seismic and tilt data edm and levelling measurements began in the middle of the 1970s since the late 1990s the edm benchmarks have been measured using gps we performed a data inversion identifying for the 1999 2013 period the action of a deflating magmatic source located under vulcanello at 4 5 km a s l just at the top of a wide regional tectonic tabular source we analyzed data on different time space scales distinguishing the dynamics of different sectors of vulcano piano vulcanello la fossa cone and caldera and three periods 1974 1984 1984 1999 1999 2013 and the time evolution of the dynamics of the island we also show how the regional tectonic stress plays an important role in the transition of the volcanic system from a phase of stability to one of unrest inducing the heating and expansion of shallow hydrothermal fluids

quantitative experiments on phreatomagmatic explosions abstract an experimental set up for controlled generation of thermal explosions fuel coolant interactions has been built by an interdisciplinary research group of volcanologists physicists and engineering scientists the tee haus thermal explosion experiment during the last 3 years more than 500 experimental runs were performed aim of the project was not to build a mini volcano but to produce igniteable mixtures of water and hot melt on a small scale in order to investigate basic physical aspects such small scale mixtures however most probably also occur during phreatomagmatic events in nature mixtures of water and magma on a large scale may be modelled by combination of small elements earlier experimental studies of thermal explosions were carried out with the use of metal melts nearly exclusively therefore a carbonate melt approx 0 3 kg of 1 1 mass ratio na2co3 k2co3 was used for initial experimental series because of easy handling and more magma similarity by injection of water into this melt explosive mixtures were produced and ignited self triggering explosive interactions occurred in a wide melt temperature range 720 to 1040 c at melt temperatures exceeding 1000 c co2 increasingly degassed presence of non condensible gas bubbles in the melt strongly reduced the explosivity the intensity of explosions only slightly increased with higher melt temperatures but strongly increased with higher water injection velocities because of more intensive mixing a minimum injection velocity was found to be approx 0 7 m s 1 experiments with silicate melts derived from diverse remelted volcanic rocks were carried out with a slightly modified set up explosions were ignited by an additional trigger a shock wave of approx 8 j in volcanic systems shock waves of this magnitude are abundant volcanic tremor etc strong explosions with silicate melts were produced at melt temperatures between 1350 and 1750 c the produced explosions exerted repulsion forces of up to 24 000 n with a typical pulse duration of 1 ms carbonate melt resp 1 5 ms silicate melts the ejection velocity was found to be in a range between 200 and 400 m s 1 explosion energy values up to 500 j were calculated the maximum explosion pressure was calculated to be in the range between 10 and 100 mpa only part of the melt so called interactive melt reacts explosively with injected water most of the melt is passively ejected by and after the thermal explosion different fragmentation processes result in specific grain size and grain shape populations that can be distinguished from each other particles resulting from the fine fragmentation process that precedes and causes the thermal explosion are characterized by angular to subrounded shapes and grain sizes ranging from 20 m to 180 m the amount of interactive melt is proportional to the intensity of the explosion the maximum amount of water vapourized at the explosive interaction so called interactive water was estimated thus the water melt mass ratio for explosive interactions could be calculated the values range between 1 25 and 1 35 carbonate melt resp between 1 6 and 1 25 silicate melts

tectonics structural evolution and caldera formation on vulcano island aeolian archipelago southern tyrrhenian sea abstract a detailed structural study and a review of the eruptive history of the island of vulcano aeolian arc southern tyrrhenian sea have been carried out with the purpose of understanding the evolution of both volcanic and tectonic structures the island is composed of four main volcanoes which date from about 120 ka to historical times two calderas occur in the central sector of the island the time space evolution of the volcanism indicates a shifting of the activity from the southeastern sectors towards the northwest two main systems of nw se trending right lateral strike slip faults affect the island ne sw and n s trending normal faults are also present geophysical investigation indicate the nw se trending strike slip faults are likely to be the surface expression of a main regional crustal structure this system of discontinuity is related with the stress field acting in the southern sector of the aeolian archipelago normal n s and ne sw oriented faults represent extensional fractures the ne sw trending structures are related to a local stress field the results of the kinematic analysis as well as the geometric relationships between the faults and the constant subsidence velocities are consistent with the opening of a pull apart basin volcanological and geochronological data are also consistent with the proposed model in the general deformative style affecting the island the calderas can be explained as the consequence of different opening phases of a pull apart basin

the 1245 yr bp asososca maar eruption the youngest event along the nejapa miraflores volcanic fault western managua nicaragua abstract the asososca tephra comprises the asymmetrically distributed well stratified phreatomagmatic products of the 1245 125 120 yr bp asososca maar eruption west of managua nicaragua it is the youngest eruptive unit related to the monogenetic volcanism concentrated along the n s trending nejapa miraflores active fault and intersecting e w to ne sw and nw se minor faults the close relationship between monogenetic volcanism and the structural local tectonic framework is evidenced by the lineament domains and vent alignment patterns identified by remotely sensed images and dems of the research area the asososca maar lake bathymetry suggests that the crater was formed by coalescing vents migrating during the eruptive event the asososca tephra dominantly consists of accidental lithics disrupted from the underlying stratigraphic units observed inside and around the maar crater dry base surge bedsets are dominant throughout the eruptive unit showing facies variation from proximal cross stratified beds to mid distal plane parallel and wavy parallel beds grain size analyses indicate that base surges transported dominantly 1 0 and 1 sized particles at the bedload in form of traction carpets while fine ash material in continuous suspension was minimal juvenile fragments were only identified in the finer fractions varying from vesiculated scoriae to dense sideromelane fragments sem analyses suggest that the asososca eruption resulted from a highly efficient fuel coolant interaction between a tholeiitic basaltic melt and an aquifer hosted in a shallow level between 50 and 200 m of olivine bearing scoria ash and lapilli beds the explosion triggered the country rock comminution and the production of moss like fused shaped and blocky ash shards with stepped surfaces quenching cracks pitting alteration skins and adhered particles all indicative of phreatomagmatic fragmentation the very recent age of the asososca maar eruption confirms that the densely inhabited managua area is volcanically active and that hazard studies should focus on the potential for phreatomagmatic eruptions

influence of late cenozoic mountain building on ocean geochemical cycles in a steady state ocean input fluxes of dissolved salts to the sea must be balanced in mass and isotopic value by output fluxes for the elements strontium calcium and carbon rivers provide the primary input whereas marine biogenic sedimentation dominates removal dissolved fluxes in rivers are related to rates of continental weathering which in turn are strongly dependent on rates of uplift the largest dissolved fluxes today arise in the himalayan and andean mountain ranges and the tibetan plateau during the past 5 m y uplift rates in these areas have increased significantly this suggests that weathering rates and river fluxes may have increased also the oceanic records of carbonate sedimentation level of the calcite compensation depth and delta sup 13 c and delta sup 87 sr in biogenic sediments are consistent with a global increase in river fluxes since the late miocene the cooling of global climate over the past few million years may be linked to a decrease in atmospheric co sub 2 driven by enhanced continental weathering in these tectonically active regions

quantitative hazard assessment of phreatomagmatic eruptions at vulcano aeolian islands southern italy as obtained by combining stratigraphy event statistics and physical modelling abstract the detailed analysis of stratigraphy allowed the reconstruction of the complex volcanic history of la fossa di vulcano an eruptive activity mainly driven by superficial phreatomagmatic explosions emerged a statistical analysis of the pyroclastic successions led to the identification of dilute pyroclastic density currents base surges as the most recurrent events followed by fallout of dense ballistic blocks the scale of events is related to the amount of magma involved in each explosion events involving about 1 million cm 3 of magma occurred during recent eruptions they led to the formation of hundreds of meters thick dilute pyroclastic density currents moving down the volcano slope at velocities exceeding 50 m s the dispersion of density currents affected the whole vulcano porto area the vulcanello area they also overrode the fossa caldera s rim spreading over the piano area for the aim of hazard assessment deposits from la fossa cone and la fossa caldera were studied in detail to depict the eruptive scenarios at short term and at long term by means of physical models that make use of deposit particle features the impact parameters have been calculated they are dynamic pressure and particle volumetric concentration of density currents and impact energy of ballistic blocks a quantitative hazard map based on these impact parameters is presented it could be useful for territory planning and for the calculation of the expected damage

reconciliation of late quaternary sea levels derived from coral terraces at huon peninsula with deep sea oxygen isotope records a major discrepancy between the late quaternary sea level changes derived from raised coral reef terraces at the huon peninsula in papua new guinea and from oxygen isotopes in deep sea cores is resolved the two methods agree closely from 120 ka to 80 ka and from 20 ka to 0 ka ka 1000 yr before present but between 70 and 30 ka the isotopic sea levels are 20 40 m lower than the huon peninsula sea levels derived in earlier studies new high precision u series age measurements and revised stratigraphic data for huon peninsula terraces aged between 30 and 70 ka now give similar sea levels to those based on deep sea oxygen isotope data planktonic and benthic 18o data using the sea level and deep sea isotopic data oxygen isotope ratios are calculated for the northern continental ice sheets through the last glacial cycle and are consistent with results from greenland ice cores the record of ice volume changes through the last glacial cycle now appears to be reasonably complete

an approach for investigating the depositional mechanism of fine grained surge deposits the example of the dry surge deposits at la fossa di vulcano abstract fine grained thinly laminated surge deposits have been studied in order to understand the physical properties of pyroelastic deposits with a large tractional component and to investigate on type and number of laminae deposited from a single surge cloud the examples are taken from the dry surge deposits of the fossa cone vulcano island where there is a good knowledge of the stratigraphy good exposures of the deposits and an absence of secondary structures analysis of texture and structure allows all the bed facies to be grouped into 4 principal types type 1 is made up of a loose coarse and medium ash in dark grey gently undulating laminae sometimes with cross laminae that alternate with pale grey laminae type 2 consists of grey ash in beds characterized by limited lateral continuity normal grading and a flat non erosive base type 3 is made up of submillimeter ochreous laminae plane parallel or gently undulating type 4 consists of massive beds of fine ash ochre in colour characterized by notably lateral continuity and constant thickness determination of the nature morphology and size of the grains shows that a close relationship exists between the relative abundance and shape of components and the textural and grain size characteristics of the bed facies the results suggest that a single surge event could deposit either a set of plane parallel to transverse laminae as type 1 and type 3 or a pair of laminated beds as type 2 and 4 depending on the flow velocity the effective grain size and density of the solid phase and the particle concentration in the eruptive cloud the almost complete lack of lithics suggests that magma water interaction occurred in sub surface conditions across a fragmented magma surface the efficiency of the interaction was primarily controlled by the ascent velocity of the magma in the conduit and its physical properties

the evolution of pleistocene climate a time series approach abstract in the later part of the pleistocene variations in global ice volume have been dominated by an approximate 100 000 year cycle analysis of 2 myr long oxygen isotope record from an equatorial pacific core indicates that this is true only for the last 900 000 years prior to this time the amplitude of the 100 000 year cycle is much reduced as is the variance of all oscillations with periods greater than 60 000 years based on results of time series analysis of this 2 myr long record the pleistocene glacial cycles can be divided into three sections 1 the late pleistocene 0 900 kyr b p where the variations in the isotope record are dominated by the 100 000 year cycle 2 the middle pleistocene 900 1450 kyr b p in which low frequency components are not as important as in the later period of the pleistocene and 3 the early pleistocene late pliocene 1450 2000 kyr b p where general reductions of importance at all frequencies is seen as compared to the later intervals recent modeling efforts which describe variations in global ice volume show that the dominant low frequency component observed in the late pleistocene can result from different time constants for the rate of glacial growth and decay in response to variations in the earth s orbital parameters it is hypothesized that during the early pleistocene the rate of growth and decay of glaciers were more similar and that continental erosion by successive glacial advances lowered the land surface in areas of ice cap formation to below sea level when the ice caps became marine based more rapid decay of the ice became possible

rates and mechanics of rapid frontal accretion along the very obliquely convergent southern hikurangi margin new zealand analysis of seismic reflection profiles swath bathymetry side scan sonar imagery and sediment samples reveal the three dimensional structure morphology and stratigraphic evolution of the central to southern hikurangi margin accretionary wedge which is developing in response to thick trench fill sediment and oblique convergence between the australian and pacific plates a seismic stratigraphy of the trench fill turbidites and frontal part of the wedge is constrained by seismic correlations to an already established stratigraphic succession nearby by coccolith and foraminifera biostratigraphy of three core and dredge samples and by estimates of stratigraphic thicknesses and rates of accumulation of compacted sediment structural and stratigraphic analyses of the frontal part of the wedge yield quantitative data on the timing of inception of thrust faults and folds on the growth and mechanics of frontal accretion under variable convergence obliquity and on the amounts and rates of horizontal shortening the data place constraints on the partitioning of geological strain across the entire southern hikurangi margin the principal deformation front at the toe of the wedge is discontinuous and represented by right stepping thrust faulted and folded ridges up to 1 km high which develop initially from discontinuous protothrusts in the central part of the margin near 41 s where the convergence obliquity is 50 orthogonal convergence rate is slow 27 mm yr and about 75 of the total 4 km of sediment on the pacific plate is accreted frontally the seismically resolvable structures within 30 km of the deformation front accommodate about 6 km of horizontal shortening at least 80 of this shortening has occurred within the last 0 4 0 1 m y at an average rate of 12 3 mm yr this rate indicates that the frontal 30 km of the wedge accounts for about 33 55 of the predicted orthogonal contraction across the entire plate boundary zone despite plate convergence obliquity of 50 rapid frontal accretion has occurred during the late quaternary with the principal deformation front migrating seaward up to 50 km within the last 0 5 m y i e at a rate of 100 km m y the structural response to this accretion rate has been a reduction in wedge taper and consequently internal deformation behind the present deformation front near the southwestern termination of the wedge where there is an along the margin transition to continental transpressional tectonics the convergence obliquity increases to 56 and the orthogonal convergence rate decreases to 22 mm yr the wedge narrows to 13 km and is characterized simply by two frontal backthrusts and landward verging folds these structures have accommodated not more than 0 5 km of horizontal shortening at a rate of 1 mm yr which represents 5 of the predicted orthogonal shortening across the entire plate boundary in southern north island the landward vergent structural domain may represent a transition zone from rapid frontal accretion associated with low basal friction and high pore pressure ratio in the central part of the margin to the northern south island region where the upper and lower plates are locked or at least very strongly coupled

rock magnetism and compositional investigation of brown tuffs deposits at lipari and vulcano aeolian islands italy abstract a rock magnetic investigation was carried out on the nonwelded ash deposits of the brown tuffs aeolian islands southern tyrrhenian sea to improve the stratigraphic correlation between the deposits cropping out on lipari and vulcano islands and locate their source area the study was supplemented by petrographical and geochemical analyses on selected strata with the intent to compare the brown tuffs to other rocks emplaced at vulcano in the same time span more than 30 levels were sampled in the intermediate 56 4 ka ibt 21 22 ka and upper 21 22 ka ubt parts of the brown tuffs sequences on the two islands their characteristic remanent magnetization chrm directions were derived from stepwise thermal demagnetization and the magnetic fabric from measurements of the anisotropy of magnetic susceptibility the levels with indistinguishable chrm directions were regarded as coeval and to form an individual stratigraphic unit the units were referred to the brown tuffs sequence of lucchi et al 2008 on the grounds of their emplacement age provided by comparison of their mean paleomagnetic direction with the paleosecular variation curves of the southern tyrrhenian region as well as the field constraints the closer correlation between the sequences of lipari and vulcano contributes to a better understanding of the volcanic activity that produced the brown tuffs and shows that most of the ibt and the oldest ubt levels were emplaced in a short time span between 24 and 20 17 ka the magnetic fabric is typically well developed but at most sites the magnetic foliation is very close to horizontal and no imbrication is defined the source area of the brown tuffs parent pyroclastic flows as constrained from the intersection of the magnetic lineations falls in the northeastern part of la fossa caldera structure although limited to major elements compositional data provide further indication about the parent plumbing system and its behaviour magma batch es involved in the ibt eruptions have homogeneous features and underwent frequent refilling and tapping processes conversely those involved in the early ubt eruptions are compositionally more variable this suggests more complex evolution and plumbing system activity the ubt eruptions represent either residual mafic magmas from the previous eruptions or the arrival of new fresh shoshonitic magma in the system

subduction of seafloor asperities revealed by a detailed stratigraphic analysis of the active margin shelf sediments of central ecuador the uplift of the coastal cordillera of central ecuador is a likely consequence of the subduction of the carnegie ridge a 400 km long and 2 km high topographic asperity this study aims at analyzing the impact of the subduction of the carnegie ridge on the continental shelf sedimentation during the quaternary we interpret high resolution 50 450 hz frequency multi channel 72 channels and single channel sparker seismic data piston cores sediment profiles 3 5 khz and high resolution multibeam bathymetry acquired during the atacames cruise with the rv l atalante in 2012 in the la plata island cabo san lorenzo peninsula region the results show a full and detailed record of the last ten quaternary sedimentary sequences deposited in intra shelf basins at and just seaward of the shelf break these 100 ka scale sequences are tied to piston core data to well dated quaternary onshore exposures and to a flight of coastal marine terraces on cabo san lorenzo peninsula and la plata island these sequences correlate with the global ice volume and deep marine temperature changes d18o for the last 0 7 ma which points to a strict climatic control on depositional sequence development and preservation however the subsidence of the continental shelf acoustic basement estimated by the stepwise backstripping of the sedimentary record exhibits a complex deformation pattern with uplifting and subsiding regions deep marine seismic data currently under processing show evidence for a subducted seamount beneath la plata island and gps data indicate an important interplate coupling in the same area with the potential to generate a mw 7 7 5 earthquake the pattern of the continental shelf deformation is consistent with the shape of this seamount we tested the hypothesis of a link between the margin deformation and the subduction of the seamount by comparing a stepwise subduction of the seamount to the palinspastic restoration of the deformation of the continental shelf for the last 1 ma this comparison shows that the collision probably started c 500 ka ago together with the syntectonic sedimentation and drastically slowed down by c 50 ka with the sealing of most of the deformation on the shelf

volcanic hazards at fossa of vulcano data from the last 6 000 years stratigraphic reconstruction of the complete sequence of deposits that formed the fossa cone of vulcano has distinguished four principal eruptive cycles punte nere palizzi commenda and pietre cotte at least three additional eruptive cycles one of which ends with the campo sportivo lava occur between deposits of the punte nere and palizzi cycles however exposure is inadequate for their characterization the assignment of the modern deposits that follow the pietre cotte lava is uncertain

calcite in fractures in a volcanic environment vulcano island italy contribution of geochronological and isotopic studies to volcanotectonics abstract the southern and southeastern rim of the present caldera la fossa caldera at vulcano island aeolian islands italy is crosscut by a network of fractures filled with calcite and minor chalcedony fluid inclusion studies indicate that both mineral phases were deposited from hydrothermal solutions several calcite samples were analyzed and their u sr nd o and c isotopic composition was determined u th geochronological data suggest two discrete depositional episodes one at 50 ka southern rim and the other at 25 ka southeastern rim oxygen isotopic compositions 87 sr 86 sr and 234 u 238 u ratios exclude that seawater was involved significantly in the hydrothermal system in agreement with fluid inclusion studies which did not document the presence of nacl the nd and sr isotopic composition of calcite reflects the composition of the host rocks the oxygen isotopic composition excludes a post depositional interaction with meteoric water and suggests a depositional temperature consistent with that obtained from the fluid inclusion study 160 170 c assuming equilibrium conditions and a fluid isotopic composition close to present day steam emissions the positive correlation between u content and c isotopic composition indicates a rapid change in co 2 pressure during calcite deposition this observation is consistent with a rapid fluid ascent likely connected to two phases of collapse of the la fossa caldera the ages of the calcites which fill the fractures at the la fossa caldera indicate the activation time of the fracture systems which in turn are connected to the above mentioned phases of the caldera collapse

occurrence of somma vesuvio fine ashes in the tephrostratigraphic record of panarea aeolian islands ash rich tephra layers interbedded in the pyroclastic successions of panarea island aeolian archipelago southern italy have been analyzed and related to their original volcanic sources one of these tephra layers is particularly important as it can be correlated by its chemical and morphoscopic characteristics to the explosive activity of somma vesuvio correlation with the pomici di base eruption that is considered one of the largest explosive events causing the demolition of the somma stratovolcano seems the most probable the occurrence on panarea island of fine ashes related to this eruption is of great importance for several reasons 1 it allows to better constrain the time stratigraphy of the panarea volcano 2 it provides a useful tool for tephrochronological studies in southern italy and finally 3 it allows to improve our knowledge on the distribution of the products of the pomici di base eruption giving new insights on the dispersion trajectories of fine ashes from plinian plumes other exotic tephra layers interbedded in the panarea pyroclastic successions have also been found chemical and sedimentological characteristics of these layers allow their correlation with local vents from the aeolian islands thus constraining the late explosive activity of panarea dome

a one dimensional model of continental ice volume fluctuations through the pleistocene implications for the origin of the mid pleistocene climate transition abstract a new one dimensional zonally averaged high resolution spherical model of the accumulation and flow of continental ice sheets in response to variations in insolation forcing has been constructed the model includes a detailed representation of the influence of the isostatic adjustment of the earth under the weight of the ice at a rate determined by the viscosity of the planetary mantle with this model we address the issue as to whether the combination of physical processes that it includes is sufficient to allow us to reconcile the variations of continental ice volume that are inferred to have dominated the pleistocene epoch on the basis of the analysis of 18o data from deep sea sedimentary cores we use high resolution data from the newly analyzed odp site 677 and from dsdp site 607 as principal observational constraints these datasets reveal a marked transition in climate to have occurred at mid pleistocene time about 900 000 years bp in order to understand this transition we find that we

pleistocene unconformity bounded shelf sequences wanganui basin new zealand correlated with global isotope record abstract eleven successive unconformity bound sequences in the castlecliff section wanganui basin each typically composed of a lower variably conglomeratic 0 1 2 m thick shell bed and an upper 5 20 m thick barren siltstone are identified in the stratotype of the local new zealand middle pleistocene castlecliffian stage based on magnetostratigraphy the section is correlated with the published benthonic oxygen isotope curve for dsdp core 552a from the north atlantic each of the sequences accumulated during one of the odd numbered interglacial isotope stages in the interval 31 to 11 inclusive the unconformities developed during intervening glacial ages when the shelf was exposed through glacio eustatic lowering the correlation provides a geochronologic framework for assessment of the eustatic contribution to the generation of the sequences in a situation where the paleoshorelines and related shelf sequences are preserved and for which an independent approximation of the sea level history is available in the form of an oxygen isotope curve

inner forearc sequence architecture in response to climatic and tectonic forcing since 150 ka hawke s bay new zealand the influence of eustasy tectonic deformation and sediment flux as controlling parameters on basin stratigraphy and depositional sequence development are largely accepted eustasy is usually considered as the dominant mechanism of sequence generation especially for pleistocene successions in active subduction margin settings the high rates of tectonic deformation are expected to have a stronger influence on basin fill architecture while sediment flux is generally less well constrained and therefore less frequently considered the active hikurangi subduction margin in new zealand offers the opportunity to quantitatively assess the relative roles of tectonic climatic and eustatic drivers we present a quantitative source to sink like study of the late pleistocene succession from the hawke s bay sector of the inner forearc domain c 150 ka to present the interpretation of a grid of high resolution marine seismic data onland and offshore core and well descriptions and the integration of geomorphic studies enabled identification of system tracts in turn these comprise two sea level cycle depositional sequences lps1 and lps2 including one complete 100 ka sequence lps1 isopach maps of both sequences reveal changes in sediment distribution and preservation that reflect the relative roles of tectonic deformation and eustasy eustasy dominates development of sequence architecture at relatively short time scales i e 100 kyrs four long lasting depocenters are identified over the inner forearc domain and located in four subsiding basins kidnappers mahia lachlan and motu o kura basins significant shifts of the depocenter location in the basins are correlated with eustatic sea level changes estimates of sediment volumes and masses from isopach maps indicate higher mass accumulation rates during climato eustatic extremes which we correlated to the onland erosional response sediment distribution and landscape evolution are strongly influenced by the interaction of the structural deformation and sediment flux we present paleogeographic reconstructions for the inner forearc domain coincident with two paleoclimatic extremes last glacial maximum and holocene optimum these illustrate the importance of eustatic changes structural deformation and sediment flux on the pattern of sediment distribution accumulation and sequence architecture

the mid pleistocene climate transition onset of 100 ka cycle lags ice volume build up by 280 ka the mid pleistocene climate transition mpt is the complex climatic change which brought the late pleistocene ice ages we explore the mpt in the time and frequency domains by new methods of time series analysis high resolution oxygen isotope records reveal that the ice volume related increase in 18o mean amplitude 0 29 0 05 1 transition midpoint 922 12 ka duration 40 9 ka significantly preceded the abrupt increase in the amplitude of the 100 ka cycle at 641 9 ka this finding can be quantitatively simulated using a simple ice bedrock model in which due to the additional ice the calving threshold is exceeded the simulated calving events prior to 650 ka are separated by 77 ka whereas after 650 ka they occur pseudo periodically with a mean period of nearly 100 ka the cause for the delay of the 100 ka calving cycle was not a slow bedrock relaxation rather the coincidental combination of insolation existing ice mass and bedrock depression

fragmentation versus transportation mechanisms in the pyroclastic sequence of monte pilato rocche rosse lipari italy abstract monte pilato is a rhyolitic pumice cone formed about 1400 years ago during the last volcanic activity which occurred at lipari its activity consisted of numerous explosive episodes ending with the extrusion of the rocche rosse obsidian lava flow we have identified nine different pyroclastic lithofacies of which four main lithofacies represent 90 of the erupted products they include 1 deposits consisting of decimeters to meters thick well sorted graded beds of pumice lapilli which are of fall origin 2 massive deposits consisting of decimeters thick beds of pumice lapilli in an ash matrix interpreted as being of pyroclastic flow origin 3 deposits of centimeters thick ash beds of surge origin 4 decimeter thick fine ash layers with scattered subcentimetric accretionary lapilli of turbulent flow origin the complex grain size distributions of the main lithofacies were distinguished using a multivariate statistic analysis r mode factor analysis variations of the grain size characteristics in relation to the distance from the vent area have been investigated in order to discriminate the roles played by fragmentation and transportation processes in the lithofacies 1 fall deposits the grain size distribution is always unimodal and varies from a rosin type distribution near the vent to a gaussian one in the distal outcrops this is caused by the transport process and the different particle trajectories in lithofacies 2 3 and 4 the grain size distributions are always polymodal the polymodality is not caused by preferential processes occurring during transportation but seems rather to be connected with the original fragmentation of the pyroclastic material the pumice lapilli present both in lithofacies 1 and 2 have mean vesicularity index values always in excess of 65 and the value is homogeneous throughout the sample these data suggest that for these two lithofacies the pumice lapilli originated from exsolution of magmatic gases in contrast the fine ash particles in lithofacies 2 and also the main mode of lithofacies 3 and 4 deposits show typical features of hydromagmatic fragmentation processes the grain size population is always centered at 4 5 0 032 0 064 mm and interestingly the same grain size has been obtained recently zimanowski et al 1991 for fragments produced by experimental magma water interaction field and laboratory data suggest that during monte pilato rocche rosse eruptions magmatic and hydromagmatic mechanisms were frequently operative at the same time

frequent activity on vulcano italy spanning the last 80 ky new insights from the chemo stratigraphy of the brown tuffs abstract the brown tuffs bt are widespread reddish brown to grey ash rich pyroclastic deposits recognized in the stratigraphic sequences of the aeolian islands and capo millazzo peninsula sicily that span the last 80 ky they have very homogeneous lithological textural and sedimentological features which make it difficult to reliably correlate units on the islands to proximal units in the source areas here we carefully re interpret the stratigraphic profiles of the bt on vulcano and lipari where the deposits are thickest and present the most complete succession the investigation is based on a large dataset of major and minor element geochemistry of juvenile glass components for the majority of the recognized bt depositional units whilst also providing new radiocarbon ages the distinctive chemical groupings observed within the glass analyses both temporally and spatially allow us to fingerprint the three main stratigraphically defined macro units in which the bt succession can be sub divided using prominent tephra marker beds the ischia tephra monte epomeo green tuff 56 ky and monte guardia pyroclastics from lipari herein radiocarbon dated to 27 26 ky the lower 80 56 ky lbt intermediate 56 27 ky ibt and upper bt here dated at 24 6 ky ubt macro units display k series volcanic glasses ranging from basaltic trachy andesites through trachy andesites to more evolved trachytes all consistent with an origin on vulcano the ubt are clearly distinguished from the lower macro units by their higher sio2 trachy andesite to trachytic glasses which extend to noticeably lower tio2 cao and mgo contents these features make it possible to re define the geochemical evolutionary boundary between ibt and ubt as corresponding to the 24 ky spiaggia lunga scoria bed on vulcano which is stratigraphically higher and younger than the previous boundary marker monte guardia the glass compositions of the lbt ibt and ubt are used to 1 assess links to known proximal eruption units outcropping on vulcano 2 validate medial distal bt occurrences across the aeolian archipelago salina filicudi and panarea and on capo millazzo 3 confirm that the bt are responsible for distal volcanic ash layers preserved in central mediterranean marine sedimentary archives interestingly the glass compositions of the ubt are very similar to those of the punte nere unit the earliest pyroclastic products erupted from the currently active la fossa cone on vulcano indicating the corresponding magmatic system has likely erupted similar melts and products over the last 24 ky and thus extending its life cycle such information is crucial for evaluating the long term eruption scenarios underpinning hazard assessment of the la fossa caldera magmatic system

controls on active forearc basin stratigraphy and sediment fluxes the pleistocene of hawke bay new zealand detailed high resolution documentation of forearc basin fi ll is scarce in the literature in this geological and geophysical study we investigated the pleistocene sedimentary record of the tectonically active hawke bay forearc domain of the hikurangi subduction margin of new zealand interpretation of an extensive seismic refl ection data set that is correlated with marine cores and onshore geological maps identifi es the detailed stratigraphic architecture of the last 1 1 m y this analysis reveals the infl uences and interactions of tectonic deformation climate eustasy and isostasy on forearc basin sedimentation eleven 100 k y depositional sequences are recognized in the basin fi ll thus highlighting the dominance of pleistocene climate eustasy on sequence development the stacking pattern and isopach maps of sequences exhibit an overall retrogradational trend and an arcward migration of depocenters these trends progressively develop a basinwide diachronous and composite erosion unconformity formed by the lateral succession and landward encroachment of the 12 sequence bounding unconformities s12 to s1 among these the s5 surface ca 430 ka is an angular unconformity that separates major megasequences of the sedimentary record the forearc domain evolved from a series of ridge parallel basins to a succession of connected basins that have progressively developed around major growing thrust faulted ridges since ca 430 ka this change in basin confi guration and associated signifi cant increase of the preserved sediment fluxes occurred synchronous with the reactivation of major out of sequence thrusts and the completion of the mid pleistocene transition

isothermal plateau fission track ages of hydrated glass shards from silicic tephra beds abstract the age of silicic tephra beds that have experienced a simple thermal history can be accurately and precisely determined by application of the isothermal plateau fission track technique to hydrated glass shards age estimates obtained by this means compare very well with those based on co existing mineral phases using the k ar 40ar 39ar external detector fission track and thermoluminescence techniques this concordance contradicts the popular belief that hydrated glass shards give unreliable ages distal tephra beds many of which are difficult to date because of their fine grainsize low abundance of crystals and common presence of detrital grains are readily dated by the isothermal plateau glass fission track method this new advance should greatly facilitate the development of detailed chronologies of tephra bearing sedimentary sequences located far from volcanic centres

the mid pleistocene climate transition as documented in the deep south atlantic ocean initiation interim state and terminal event abstract the mid pleistocene transition mpt of the global climate system initiated by a shift towards much larger northern hemisphere ice shields at around 920 ka and ending with predominance of 100 kyr ice age cyclicity since about 640 ka is one of the fundamental enigmas in quaternary climate evolution climate proxy records not exclusively linked to global ice volume are necessary to advance understanding of the mpt here we present a high resolution pleistocene magnetic susceptibility time series of 12 sediment cores from the subtropical south atlantic essentially reflecting dissolution driven variations in carbonate accumulation controlled by changes in deep water circulation in addition to characteristics known from 18o records the data sets reveal three remarkable features intimately related to the mpt 1 an all pleistocene minimum of carbonate accumulation in the south atlantic at 920 ka 2 a mpt interim state of reduced carbonate deposition indicating that the mpt period may have been a discrete state of the pleistocene deep water circulation and climate system and 3 a terminal mpt event at around 540 530 ka documented in several peculiarities such as thick laminated layers of the giant diatom ethmodiscus rex

evolution of the fossa cone vulcano abstract in decreasing order of abundance the principal emplacement mechanisms for deposits of the fossa edifice of vulcano include dry surge wet surge pyroclastic fall lahar lava flow pyroclastic flow and epiclastic processes most samples from pyroclastic beds on fossa contain two grain size populations the coarser mode at 0 5 1 5 resulted from modified ballistic transport whereas the finer mode at 2 5 3 5 is related to surge transport reconstruction of the entire stratigraphy of the cone permits the beds to be grouped into five principal eruptive cycles all of which postdate the lower pilato ash of lipari dated at 11 000 to 8 500 y b p pte nere cycle palizzi cycle commenda cycle pietre cotte cycle and the modern cycle additional cycles may be present but exposures on the cone are insufficient for their adequate definition all cycles follow a similar stochastic pattern starting with surge eruptions and ending with effusion of lava from the crater rim the frequency of pyroclastic fall events increases with time throughout each cycle this progressive decrease in the efficiency of water melt interaction through the duration of each cycle may be due to a gradual rise of each new magma column coupled with an increase in magmatic volatiles tectonism and magma mixing both play a role in triggering eruptions on fossa the present crater lies at the intersection of two prominent tectonic trends a nnw fracture system parallels the main eruptive centers and an ene set aligns with the migration of minor vents the silicic lavas of fossa contain a mixture of two components xenocrysts of plagioclase augite and olivine surrounded by a dark glass are intimately dispersed into an evolved rhyolitic matrix

marine continental tephra correlations volcanic glass geochemistry from the marsili basin and the aeolian islands southern tyrrhenian sea italy abstract major minor and trace element analysis of volcanic glass in proximal and distal it is evident that correlation of proximal continental and distal marine tephras at a high level of confidence requires a full complement of major minor and trace element data in conjunction with considerations of the mineralogy and morphology of juvenile deposits these data help define petrological lineages such that precise provenance can be established whilst a precise proximal distal match must be based on identical major minor and trace element concentrations it is clear that resurgent activity from a single volcano can produce magmas with identical compositions in such cases stratigraphic relationships must complement any geochemical study occasionally proximal stratigraphies may be unrepresentative of the complete eruptive history because of a lack of exposure due to burial by more recent effusive and explosive activity or sector collapse which can remove vital stratigraphy particularly on volcanic islands

sedimentary architecture of a plio pleistocene proto back arc basin wanganui basin new zealand the sedimentary architecture of active margin basins including back arc basins is known only from a few end members that barely illustrate the natural diversity of such basins documenting more of these basins types is the key to refining our understanding of the tectonic evolution of continental margins this paper documents the sedimentary architecture of an incipient back arc basin 200 km behind the active hikurangi subduction margin north island new zealand the wanganui basin wb is a rapidly subsiding plio pleistocene sedimentary basin located at the southern termination of the extensional back arc basin of the active central volcanic region tvz the wb is asymmetric with a steep thrust faulted outer arc ward margin and a gentle inner craton ward margin it contains a 4 km thick succession of plio pleistocene sediments mostly lying offshore composed of shelf platform sediments it lacks the late molasse like deposits derived from erosion of a subaerial volcanic arc and basement observed in classical back arc basins detailed seismic stratigraphic interpretations from an extensive offshore seismic reflection data grid show that the sediment fill comprises two basin scale mega sequences 1 a pliocene 3 8 to 1 35 ma sub parallel regressive bpre growthq sequence that overtops the uplifted cratonward margin above the reverse taranaki fault and 2 a pleistocene 1 35 ma to present divergent transgressive bsyn growthq sequence that onlaps i the craton ward high to the west and ii uplifted basement blocks associated with the high angle reverse faults of the arc ward margin to the east along strike the sediments offlap first progressively southward mega sequence 1 and then southeastward mega sequence 2 with sediment transport funnelled between the craton and arc ward highs towards the hikurangi trough through the cook strait the change in offlap direction corresponds to the onset of arc ward thrust faulting and the rise of the axial ranges at ca 1 75 ma resulting in 5100 5700 m of differential subsidence across the fault system sedimentation has propagated south to southeast ward over the last 4 myrs at the tip of successive back arc graben volcanic arcs and the associated thermally uplifted parts of the north island following the southward migration of the hikurangi subduction margin subsidence occurred by mantle flow driven flexure the result of active down drag of the lithosphere by locking of the hikurangi subduction interface and sediment loading the wb is considered to be a proto back arc basin that represents the intermediate stage of evolution of an epicratonic shelf platform impacted by active margin processes

the pleistocene cape kidnappers section in new zealand orbitally forced controls on active margin sedimentation high sedimentation rates in pleistocene active margin basins can provide a very detailed record of tectonic and climatic controls on sediment preservation a 500 m thick pleistocene rock section exposed in northeastern north island of new zealand kidnappers group provides the opportunity to discuss these controls the section is composed of conglomerate sandstones siltstones and minor shales interbedded with tephra layers the sediments were deposited in alluvial to shallow marine environments and preserved in stacks of depositional units decimetres to hundreds of metres thick as a result of base level changes through time the correlation of base level changes in the section with the deep sea oxygen isotope stratigraphy shows that the sequences at 10 m and 80 m scales can correlate respectively to the 20 and 100 kyr changes in eustatic sea level but that the 80 m thick sequences correlate also to changes in tectonic uplift rates a major change in the stratigraphical architecture occurs at the mid pleistocene transition mpt when the 40 kyr ice volume variations shifted to a dominant 100 kyr variation this change includes an increase in the amplitude of the shifts in depositional environments and an overall simplification of the stacking pattern of the depositional units through the mpt this study illustrates that active margin basins can record orbitally forced sedimentary cycles and points to a possible leading influence of eustasy on the pattern of sediment preservation in tectonically active areas copyright 2004 john wiley sons ltd

experimental soft sediment deformation structures formed by the liquefaction of unconsolidated sands and some ancient examples the effects of liquefaction in saturated sand bodies under a variety of driving forces are described from shaking table experiments and structures from the geological record are presented which are analogous to the experimental structures the collapse of sloping heaps of cross bedded sand under a gravitational body force generates low angle essentially uncontorted stratification a basal zone of shearing may be present with steepened and folded foresets stretching of foresets may be accommodated on normal faults and bottomsets may be contorted into inclined folds in natural systems the substrate may also liquefy causing deformation driven by an unevenly distributed confining load stratification in the surface bedform is flattened and stratification in the substratum contorted experiments failed to produce relative displacement at the interface between stacked sand bodies liquefaction of gravitationally unstable systems in sands generates load structures comparable to those from sand mud systems recumbent folded deformed cross bedding is formed by current shear over a liquefied bed as has been inferred from field and theoretical analyses shear of nonliquefied sand forms angular folds other deformation mechanisms such as fluidization or seepage may generate structures similar to all of these local water escape structures driven by fluidization occur in the upper parts of some liquefied sand bodies they include cusps sand volcanoes and clastic dykes transient cavities formed in some experiments and seemed to be preserved as breached cusps although the experiments tried to isolate individual driving forces driving forces may operate together and there may be a continuum between deformation driven by water escape and deformation driven by loading different structures from those described here may form where liquefaction develops in a buried layer as opposed to at the sediment surface

quaternary and upper pliocene glaciations and forest development in the tropical andes evidence from a long high resolution pollen record from the sedimentary basin of bogota colombia pollen analysis of 1230 samples from a 357 m long core of lake sediments from the sedimentary basin of bogota eastern cordillera colombia alt 2550 m above sea level has provided a high resolution record of changes in the andean vegetation belts and long range climatic fluctuations during the last 3 5 ma direct time control is provided by k ar datings and fission track datings of 14 intercalated volcanic ash layers the resulting pollen diagram has been divided into 55 pollen zones representing 27 complete major climatic cycles glacial interglacial cycles a tentative correlation with the marine oxygen isotope chronology and the european stratigraphical climatic subdivision could be established the altitudinal position of the forest line which corresponds with the 9 5 c isotherm shifted between minimal c 1700 1800 m and maximal c 3400 3700 m alt at present situated at c 3100 m alt which rendered the altitudinal position of the high plain of bogota the dry bed of a former lake at 2550 m a sensitive recorder of temperature changes the estimated fluctuations in mean annual temperature at the level of the high plain of bogota are from 15 c a distinct change in the nature of the climatic cycles occurs around 2 5 ma b p the interval of 3 5 2 5 ma b p shows high frequency low amplitude climatic oscillations whereas the last 2 5 ma is characterized by low frequency high amplitude climatic oscillations with a superposed high frequency oscillation it is assumed that these oscillations correspond mainly with the variations in orbital eccentricity and obliquity the major constituents making up the andean forest have been subjected to considerable changes in the course of time in the early pliocene forests vallea and myrica are prominent elements weinmannia was almost absent the role of polylepis in the timberline forests increased markedly around 3 1 ma b p and also migrated by adaptation from the upper andean forest line to higher elevations the closure of the isthmus of panama during the pliocene enabled northern hemisphere elements to migrate into south america alnus reached the area of bogota around 2 7 ma b p and dramatically changed the vegetation especially on the flats around the lake of bogota where alnus swamp forests replaced myrica carr around 2 9 ma b p weinmannia became an important constituent of the upper andean forest but slightly later slope forests of alnus replaced parts of the area which had previously been covered by weinmannia forest the marked role of vallea in the andean forest diminished definitively after 2 5 ma b p quercus migrated more recently to south america and reached the area of bogota 1 ma b p it changed for the last time drastically the aspect of the andean forest all palynologically recognizable elements of the modern andean forest were present from now on and the subsequent adaptation and speciation of quercus and many other elements must have mainly taken place at the species level

age and petrology of the late pleistocene brown tuffs on lipari italy late pleistocene volcanic products on lipari consist mainly of pyroclastic surge deposits monte guardia sequence and fine grained brown tuffs radiometric age determination on carbon from thin soils at the top of the tuffs indicate that they have several ages of emplacement ranging from more than 35 000 to 16 800 years ago chemical and microprobe data on glass and mineral fragments from these tuffs show that they belong to a shoshonite or high k series this composition is compatible with an origin related to the magma system of vulcano but not with the magma system on lipari

the stratigraphic role of marine deposits in the geological evolution of the panarea volcano aeolian islands italy using reconstructed unconformity bounded stratigraphy the geological evolution of panarea and surrounding islets can be described in terms of the interaction between the growing volcano and sea level fluctuations from the recognition of marine deposits corresponding to marine oxygen isotope stage mis 5 and of widespread brown tuff type pyroclastic deposits on panarea two first order unconformities u i and u ii of regional stratigraphic significance can be correlated with the island of lipari and adopted as a means of correlation on an inter island scale in the aeolian volcanic district then two second order and three third order unconfomities consisting of erosional surfaces related to minor sea level fluctuations or to subaerial reworking operating during the phases of volcanic inactivity are introduced the construction of the volcanic edifice occurred during seven successive eruptive epochs of local volcanic activity between 150 and 10 ka with intervening dormant periods characterized by the activation of reworking processes in subaerial and marine environments and by the emplacement of widespread pyroclastic deposits of external provenance

expressions for the formation of load casts in soft sediment abstract a simple equation predicting the dimensions of sediment load casts is obtained from the fluid mechanics literature the equation relates the density and viscosity of the upper and lower sedimentary materials to the size of the expected load cast these results are extended to predicting load cast size as a function of median grain size and sediment concentration which are of more utility in geological studies the results are based on the assumption of newtonian fluid behavior and predict load cast dimensions of less than 10 cm for a wide range of sediment conditions it is hypothesized that although the results are of the correct order of magnitude non newtonian rheologic properties are important to load cast formation given the common occurrence of load casts larger than those pr dicted

geology and volcanology of san venanzo volcanic field umbria central italy the purpose of this paper is to integrate or even modify where necessary the geovolcanological setting outlined by other authors on the history of the small volcanic field of san venanzo umbria central italy to attain this goal new accurate field investigations were carried out in that area coupled with detailed stratigraphic studies and laboratory analyses to support field evidence with experimental results the first objective was to stress the importance of a groundwater reservoir whose interaction with magma at various degrees was responsible not only for the explosive character of volcanism in that area but also for the complex morphology of the volcanic deposits that are widely scattered on the underlying sedimentary basement another objective was to clarify the role played by tectonic activity in enhancing the fast and discontinuous ascent of batches of magma from the mantle to the surface through two different sets of faults opened by tectonic unrest into the crust that were also responsible for the morphology and spatial distribution of volcanic centres this was considered to be very important in consideration of the still active stress field of the region finally special attention was focused on the presence of a palaeosol between two eruptive sequences as it most likely denoted a split in the volcanic activity of this site into two separate phases this observation leads to the conclusion that in spite of its eruptive characteristics the small volcano of san venanzo is not monogenic for all of these topics a number of conclusions have been drawn and they are reported with more data in the following sections of this paper

recycling of magmatic clasts during explosive eruptions estimating the true juvenile content of phreatomagmatic volcanic deposits the juvenile content of phreatomagmatic deposits contains both first cycle juvenile clasts derived from magma at the instant of eruption and recycled juvenile clasts which were fragmented and first ejected by earlier explosions during the eruption but fell back or collapsed into the vent recycled juvenile clasts are similar to accessory and accidental lithics in that they contribute no heat to further magma water interaction but previously no effective criteria have been defined to separate them from first cycle juvenile clasts we have investigated componentry parameters vesicularity clast morphology and extent of mud coating which in specific circumstances can distinguish between first cycle juvenile clasts involved in only one explosion and such recycled juvenile clasts phreatomagmatic fall deposits commonly show gross grainsize and sorting characteristics identical to deposits of purely dry or magmatic eruptions however the abundance of non juvenile clasts in pyroclastic deposits is a sensitive indicator of the involvement of external water if this component is calculated including recycled juvenile clasts with accidental and accessory clasts the contrast is even more striking data from a holocene maar deposit in taupo volcanic zone new zealand suggest that the first cycle juvenile component of the deposits is less than one third of that determined by simple juvenile lithic crystal componentry

clinker formation in basaltic and trachybasaltic lava flows clinker is a term used to describe massive or scoriaceous fragments commonly associated with a lava flows clinker is generally considered to form by fragmentation of an upper vesiculated crust due to an increase in apparent viscosity and or to an increase in shear strain rate surface clinker is considered to be transported to the flow front and incorporated at the base by caterpillar motion clinker that we have observed on a variety of lava flows has very variable textures which suggests several different mechanisms of formation in order to study clinker formation we examined several lava flows from the chaine des puys central france where good sections surface morphology and surface textures are widespread and clearly visible we observed basal and surface a clinker that has fragmentation textures similar to those observed in ash formed in eruptions under dry conditions in two p hoehoe flows we have observed basal clinker that formed in situ two other flows display clinker features identical to those commonly observed in phreatomagmatic ash such as adhering particles blocky shapes spherical glass and attached microphenocrysts another p hoehoe flow has a flakey angular basal breccia with microfaulted and abraded clasts these were probably formed at a cooled lava base by large amounts of simple shear and consequent intra lava brittle faulting using these observations we propose three different ways of fragmentation 1 clinker can form at the surface and eventually produce roll over basal breccia 2 water lava interactions can form basal clinker by phreatomagmatic fragmentation water lava ratio variations may produce different clinker structures in a manner similar to observed textural changes in phreatomagmatic eruptions 3 clinker can be formed by brittle brecciation during basal simple shear the different clinker can provide information about the mechanisms and environmental conditions during lava flow emplacement

fluvial responses to climate and sea level change a review and look forward summary fluvial landforms and deposits provide one of the most readily studied quaternary continental records and alluvial strata represent an important component in most ancient continental interior and continental margin successions moreover studies of the long term dynamics of fluvial systems and their responses to external or allogenic controls can play important roles in research concerning both global change and sequence stratigraphy as well as in studies of the dynamic interactions between tectonic activity and surface processes these themes were energized in the final decades of the twentieth century and may become increasingly important in the first decades of this millennium this review paper provides a historical perspective on the development of ideas in the fields of geomorphology quaternary geology vs sedimentary geology and then summarizes key processes that operate to produce alluvial stratigraphic records over time scales of 103 106 years of particular interest are changes in discharge regimes sediment supply and sediment storage en route from source terrains to sedimentary basins as well as changes in sea level and the concept of accommodation late quaternary stratigraphic records from the loire france mississippi usa colorado texas usa and rhine meuse the netherlands rivers are used to illustrate the influences of climate change on continental interior rivers as well as the influence of interacting climate and sea level change on continental margin systems the paper concludes with a look forward to a bright future for studies of fluvial response to climate and sea level change at present empirical field based research on fluvial response to climate and sea level change lags behind a the global change community s understanding of the magnitude and frequency of climate and sea level change b the sequence stratigraphic community s desire to interpret climate and especially sea level change as forcing mechanisms and c the modelling community s ability to generate numerical and physical models of surface processes and their stratigraphic results a major challenge for the future is to catch up which will require the development of more detailed and sophisticated quaternary stratigraphic sedimentological and geochronological frameworks in a variety of continental interior and continental margin settings there is a particular need for studies that seek to document fluvial responses to allogenic forcing over both shorter 102 103 years and longer 104 106 years time scales than has commonly been the case to date as well as in larger river systems from source to sink studies of quaternary systems in depositional basin settings are especially critical because they can provide realistic analogues for interpretation of the pre quaternary rock record

extensional deformation across an active margin relations with subsidence uplift and rotations the hikurangi subduction new zealand on the basis of field studies in the forearc domain of the hikurangi subduction margin in the eastern north island of new zealand we analyze the evolution of the subduction since its onset 25 myr ago analyses of brittle deformation within this forearc domain have revealed evidence of extensional deformation contemporaneous with the subduction of the pacific plate beneath the north island the type and origin of extensional deformation during the development of the active margin are discussed the problem is crucial because this forearc domain was previously considered as having undergone almost continuous compression during the late cenozoic two distinct events of late cenozoic extensional deformation are identified the youngest one is quaternary in age it affects limited areas where important uplift prevails the orientation of extensional paleostress axes is perpendicular to that of uplift axes hence consistent with the classical hypothesis of gravitational collapse affecting the upper part of the margin of particular interest is the older extensional event middle late miocene in age it affected most of the forearc domain during a long time span that was also characterized by widespread margin subsidence some structures attributed to this event are syndepositional including rollover structures and there are mainly high angle normal faults that affect not only the miocene sediments but also the pre miocene basement the orientations of paleostress axes obtained by inversion of fault data sets are multiple after corrections taking into account the rotational history of the margin during the late cenozoic they are found to be generally consistent with two major trends because these extensional structures developed throughout a long period of the margin subsidence it is proposed that they reflect the process of tectonic erosion that affected the hikurangi active margin during the middle and late miocene between about 15 and 5 myr ago

amino acid geochronology of pleistocene marine sediments in the wanganui basin a new zealand framework for correlation and dating amino acid analysis of indigenous protein preserved in fossil marine bivalves from plio pleistocene sediments in the wanganui basin north island new zealand has provided an aminostratigraphy d alloisoleucine l isoleucine d aile l ile ratios were measured in the venerid marine bivalves tawera spissa and austrovenus stutchburyi that show progressively increasing d aile l ile ratios with increasing stratigraphical age when calibrated by magnetostratigraphy fission track dating radiocarbon dating and coccolith biostratigraphy these relative d aile l ile ages range up to c 1 ma the aminostratigraphy provides a framework of correlation and dating for other sites in the new zealand area where other methods of dating are unavailable as well as facilitating correlation with oxygen isotope stratigraphy this is the first calibrated aminostratigraphical sequence from a long sequence of sediments that cover a significant proportion of the pleistocene

eruptive and emplacement mechanisms of widespread fine grained pyroclastic deposits on vulcano island italy tufi di grotte dei rossi inferiori are thick ash deposits representing the most voluminous stratigraphic unit on vulcano island the deposits are related to hydromagmatic eruption which occurred under shallow water inside a caldera depression grain size data and results of sem investigation allow the character of the transporting medium solid material concentration in the cloud during the lateral expansion and the nature and role of the fluids present at the time of deposition to be constrained we suggest that the eruption was characterized by closely timed hydromagmatic pulses giving rise to eruption clouds rich in water vapor and steam the coarser material was not significantly transported in the eruptive cloud and it probably deposited in the caldera depression area the finer material was extensively transported in the cloud creating turbulent flows which surmounted the caldera rim barrier and dispersed in a southward direction forming widespread deposits in the piano area lower concentrated flows produced laminated deposits of more limited dispersion whereas higher concentrated flows formed more dispersed thicker massive layers

stratigraphy and significance of brown tuffs on the aeolian islands southern italy abstract brown tuffs bt are volcaniclastic ash deposits prominently represented in the stratigraphic profiles of all the aeolian islands and capo milazzo on the northern coast of sicily detailed stratigraphy and tephrochronology together with available radiometric ages suggest that they were emplaced over a long time interval spanning from the end of the last interglacial period ca 80 ka bp up to 4 5 ka bp age of the overlying punte nere pyroclastic products on vulcano the most complete bt succession is documented on lipari where 14 distinct and successive units are subdivided by the interbedding of widespread tephra layers local volcanic products paleosols and epiclastic deposits and the occurrence of local erosive surfaces inter island occurrence of ischia tephra a widely known tephra layer in the aeolian archipelago dated at 56 ka bp and monte guardia pyroclastics from lipari dated at 22 20 ka bp subdivides the bt succession in upper ubt intermediate ibt and lower bt units lbt which can be correlated at regional level the lbt was emplaced between 80 and 56 ka bp the ibt between 56 and 22 ka bp and the ubt between 20 and 4 5 ka bp on the basis of stratigraphy similarity in lithology and textural features morphology of glass fragments composition and consistency of thickness and grain size variations ubt units correlate with piano grotte dei rossi tuffs on vulcano island they were generated by pulsating hydromagmatic explosive activity giving rise to pyroclastic density currents spreading laterally from a source located inside the la fossa caldera on vulcano island composition is in agreement with this hypothesis since ubt compositional features match those of vulcano magmas erupted in that period the effect of co ignimbrite ash clouds or associated fallout processes from sustained eruptive columns is seen to explain the presence of ubt in areas further away from the suggested source e g salina and lipari islands and capo milazzo the origin of ubt exposed on panarea island is still a matter of debate due to contrasting compositional data due to large uniformity of lithological textural and componentry characters with respect to the ubt the lower portions of the bt succession lbt ibt are considered to be the result of recurrent large scale hydromagmatic eruptions of similar type moreover for the ibt units the correlation with monte molineddo 3 pyroclastics of vulcano island on the basis of lithological compositional and stratigraphic matching again suggests source s related to the vulcano plumbing system and located within the la fossa caldera

aeromagnetic data provide new insights on the volcanism and tectonics of vulcano island and offshore areas southern tyrrhenian sea italy 1 the active vulcano island southern tyrrhenian sea represents the southernmost portion of a nw se elongated volcanic ridge that includes also lipari and salina islands the ridge is affected by a regional nw se to n s striking fault system the elaboration and analysis of data from three high resolution aeromagnetic surveys carried out between 1999 and 2004 on vulcano and offshore allow us to recognize high intensity magnetic anomalies related to volcanic centers conduits or shallow intrusions previously unreported offshore submarine vents have been also recognized some of them may correspond with source areas of outcropping exotic pyroclastics on vulcano the spatial analysis of the recognized magnetic anomalies and volcanic structures shows that they are preferably aligned along the strikes of the main regional faults that affect the volcanic ridge submarine volcanic conduits revealed by the aeromagnetic survey might represent potential sources for future submarine effusive or explosive activity

isothermal plateau fission track ages of tephra beds in an early middle pleistocene marine and terrestrial sequence cape kidnappers new zealand abstract at least nine rhyolitic eruptive events or sequences are interbedded with alternating marine and terrestrial sediments of early middle pleistocene age at cape kidnappers new zealand the sediments represent one of the few high resolution glacio eustatic sea level records in new zealand we have obtained ages of 0 99 0 09 1 00 0 10 0 86 0 05 and 0 79 0 06 ma in ascending stratigraphic order for four prominent tephra beds from isothermal plateau fission track dating of their glass shards these ages are older than previous fission track determinations but are in agreement with tephra correlations to other sections ar ar data and magnetostratigraphy however the upper part of the sequence previously interpreted as the brunhes chron may have been affected by normal overprinting and is instead older the tephra record suggests a higher frequency of eruptions than is indicated by the proximal ignimbrite record in the taupo volcanic zone the new tephra ages indicate that the section was deposited in the interval 1 0 0 65 ma at a rapid average sedimentation rate of ca 1 m ka

latest cretaceous early neogene oxygen and carbon isotopic record at dsdp sites in the indian ocean abstract stable isotopic data of calcareous nannofossil monogeneric and monospecific planktic and benthic foraminifera from five indian ocean dsdp sites 212 217 220 237 and 253 leads to the following paleoclimatic and paleoceanographic conclusions the latest cretaceous oxygen isotopic record implies a cooling 3 4 c during the maastrichtian at the cretaceous tertiary boundary only a minor warming about 2 c has been recorded the parallel 13 c decrease of more than 1 indicates a significant decrease in productivity during the latest paleocene a positive 13 c excursion was detected in sites 217 and 237 this transient enrichment in 13 c may be due to productivity changes on continents and or a change in the storage rate of organic matter in marginal basins or shelf areas the most striking feature in the oxygen isotopic record is noted at the early middle eocene transition the shift towards more positive values which were probably enhanced to a certain extent by a preceding diagenetic alteration delineates a dramatic climatic deterioration at high and mid latitudes during the earlier tertiary near the eocene oligocene boundary a cooling is evident within the latest eocene interval during the earliest oligocene time a hiatus at sites 217 and 253 partially obscures the climatic record several climatic fluctuations have been noted during the oligocene a cooling at the base of zone np 23 a warming at the top of zone np 23 through np 24 and a cooling during zone np 25 the miocene oxygen isotopic record is dominated by changes in surface and bottom water environments during zone nn5 the decreasing and then increasing 18 o values together with the subsequent steepening of the vertical 18 o gradient point towards major climatic instabilities these events coincide with the mid miocene build up of antarctic ice sheets during the latest miocene to the earliest pliocene the 18 o record of planktic foraminifera indicates a significant warming of the indian ocean at mid latitudes the 13 c record during the oligocene and miocene reveals several cycles 13 c enrichments np 24 nn2 nn5 nn9 and base nn 11 which are most likely related to changes in storage rates of organic matter and biological productivity due to climatic changes and transgression regression cycles in addition changes in the circulation patterns may also have influenced the carbon isotopic record

deep water gravity core from the marsili basin tyrrhenian sea records pleistocenic holocenic explosive events and instability of the aeolian archipelago italy abstract a 4 8 m long gravity core was recovered on a relative topographic high in the northern part of the marsili basin southern tyrrhenian sea at a water depth of 3200 m the core was taken in order to decipher the sedimentary record of the past volcanic events of the nearby aeolian arc a succession of thin 2 cm to 5 cm thick fine grained turbidites mainly of volcaniclastic origin topped by hemipelagic mud layers and a number of primary tephra layers were recovered by the core the most prominent turbidite occurs in the lower part of the core at 385 cm it consists of a 20 cm thick thinning upward pebble to sand sized bed grain size analysis and component compositions in the 0 063 0 250 mm size fractions were determined on thirty samples taken from primary tephra beds and the silty sandy basal part of the volcaniclastic turbidite units sem scans and glass fraction chemical analyses were successively carried out on a selection of 17 samples to aid source correlation and comparison sub aerial tephras of the lower pollara salina 24 3 6 ka gabellotto fiumebianco lipari 8 5 or 11 5 ka monte pilato lipari 749 or 580 ad and secche di lazzaro stromboli 5 ka eruptions were also analyzed with the same procedure primary tephra respectively belonging to the eruptions of lower pollara gabellotto fiumebianco and vesuvius ap eruptions 3 5 ka 79 ad were identified in the core at the expected relative stratigraphic depths two turbidite beds composed of monogenic glass shards were also identified and interpreted as the remobilisation of primary tephras of secche di lazzaro stromboli 5 ka and pilato lipari 580 or 749 ad tephrochronology results indicate that the cored sequence formed in the last 30 ka suggesting an average sedimentation rate of 0 15 0 17 mm y the thick pebbly sandy turbidite unit in the lower part of the core has component and glass composition compatible with the lower pollara volcanic sequence of salina island in view of the grain size and thickness of the turbidite unit we suggest that it represents the deposit of a large failure event the tephra corresponding to the lower pollara event lies below the turbidite unit separated by 16 cm of hemipelagic mud indicating that the collapse took place sometime after the eruption

composite detrital and thermal remanent magnetization in tuffs from aeolian islands southern tyrrhenian sea revealed by magnetic anisotropy this paper reports on the complex relation between rock emplacement and remanence acquisition in tuffs deposited by pyroclastic density currents disclosed by systematic measurements of the anisotropy of magnetic susceptibility and natural remanent magnetization nrm thermal demagnetization shows that the nrm consists of two components with different blocking temperature spectra the direction of the low temperature component is consistent with the geocentric axial dipole value whereas the high temperature component has dispersed directions the magnetic fabric is oblate the magnetic foliation is close to the bedding and the lineations are generally dispersed along a girdle within the foliation plane the directions of the magnetic lineation and the high temperature remanence component of individual specimens are close to each other this correspondence suggests that the high blocking temperature grains acquired a remanence aligned to their long dimension before deposition while cooling within the explosive cloud and the moving pyroclastic current thereafter during deposition the traction processes at the base of the current oriented the grains along the flow direction and affected both fabric and high temperature remanence this nrm component results from mechanical orientation of previously magnetized grains and is thus detrital in origin a second thermal component was then acquired during the cooling of the low blocking temperature grains after deposition these results show that nrm in fine grained pyroclastic rocks is affected by the earth s magnetic field as well as the emplacement processes and that magnetic fabric data are essential to unravel its complex nature

sequence concepts at seismic and outcrop scale the distinction between physical and conceptual stratigraphic surfaces abstract the sequence stratigraphic terms maximum flooding surface and downlap surface as currently applied are ambiguous examples of these intra sequence surfaces are summarised from high frequency mid pleistocene sequences and from a cretaceous recent seismic megasequence both from new zealand at any one locality a mid pleistocene sequence contains up to four stratal discontinuities in ascending order the sequence boundary ravinement surface local flooding surface and downlap surface these physical surfaces which occur in outcrop are regionally diachronous and should be differentiated from theoretical isochronous horizons such as the time of maximum flooding horizon corresponding to maximum shoreline transgression and the time of peak eustatic or local relative sea level horizons corresponding to the highpoint of the eustatic and relative sea level cycles respectively in seismic studies the boundary between the transgressive and highstand systems tracts is usually located at the downlap surface on the basis of a major thermo tectonic sea level cycle in the canterbury basin it is shown that the downlap surface is not a single regional surface and that the change in slope associated with toes of successive prograding clinoforms rises in stratigraphic height basinwards the downlap surface therefore does not usually coincide with the maximum flooding horizon in plio pleistocene cyclothems a discrete unit the mid cycle shellbed straddles the contact between the transgressive and highstand systems tracts this unit might be classified within its own systems tract the condensed section systems tract csst alternatively the position of the boundary between the transgressive and highstand systems tracts can remain unspecified or unknowable

correlation of fluviodeltaic aggradational sections with glacial climate history a revision of the pleistocene stratigraphy of rome volcanic horizons interbedded with fluviodeltaic clastic sediments of the tiber and fosso galeria river valleys near rome provide a unique opportunity to date five middle pleistocene fining upward aggradational sections 40 ar 39 ar ages from the interbedded volcanic beds illustrate that aggradation occurred on an approximate 100 k y cycle and was initiated by sea level rise associated with glacial melting the age constraint additionally shows that aggradation occurs rapidly in response to sea level change and thus ages from volcanic strata within the aggradational sections provide high resolution constraint on the timing of relative sea level rise the established chronology is consistent with other glacial proxies and their radioisotopically or orbitally based time scales for the timing of glacial terminations vi and v but is significantly older than most records for the timing of termination iii ultimately the age of each termination should be determined by radioisotopic means and to that end the work here shows that fluviodeltaic sedimentology provides valuable information for middle pleistocene time scale calibration

glass geochemistry of pyroclastic deposits from the aeolian islands in the last 50 ka a proximal database for tephrochronology abstract volcanic ash 1000 analyses provides a basis for proximal distal and distal distal tephra correlations tephra deposits from the different aeolian islands are geochemically diverse with some individual eruptions showing diagnostic geochemical heterogeneity recognised both stratigraphically and or spatially major element glass analyses reveal that vulcano 0 21 ka and stromboli 4 13 ka have erupted potassic shoshonitic and k series tephra with broadly overlapping compositions but data presented here demonstrates that their eruptive products can be distinguished using either tio2 contents or their hfse th ratios whilst individual volcanic sources often produce successive tephra deposits with near identical major and minor element compositions through time i e lipari vulcano trace element glass data can help to decipher successive eruptions changes in lree and th concentrations of volcanic glasses erupted spanning approximately the last 50 ka greatly enhance the potential to discriminate successive eruptive units on lipari the new proximal glass database has been used to verify new ionian sea core m25 4 12 and existing distal occurrences of aeolian island derived tephra enabling the reassessments of past ash dispersals finally proximal and distal data have been used to establish an integrated proximal distal eruptive event stratigraphy for the aeolian islands

volcanological and petrological evolution of vulcano island aeolian arc southern tyrrhenian sea petrological and geochemical data are reported for volcanic rocks from vulcano island the subaerial volcanism 120 ka to present built up a nw se elongated composite structure affected by two intersecting multistage calderas volcanics older than 20 ka consist mostly of high k calc alkaline hkca to shoshonitic sho mafic rocks these magmas interacted significantly with the continental crust which generated variable sr isotopic ratios 0 70412 0 70520 however a major role was also played by input of parental liquids into the magma chamber which prevented further evolution of the magmas hkca sho and potassic ks rocks formed from 20 to 8 ka display a much larger range of sio2 from shoshonites to rhyolites and higher concentrations of incompatible elements with respect to the previous stage sr isotopic ratios show small variations 0 70448 0 70486 mixing of silicic and mafic liquids and fractional crystallization processes fc were the main evolutionary processes during this stage volcanics younger than 8 ka consist of sho and leucite bearing ks mafic rocks with abundant intermediate and silicic products mafic and intermediate rocks display similar incompatible element abundances and sr isotopic ratios as the previous stage volcanics whereas higher 87sr 86sr 0 70494 0 70583 are observed in some rhyolites these products originated from a complex interplay of fc crustal assimilation and magma mixing processes the most mafic rocks show increasing incompatible element abundances rb sr rb ba mg al mg ca and a decrease in large ion lithophile to high field strength element ratios passing from older hkca sho to the younger sho ks volcanics these variations suggest a shifting of magma sources from a slightly metasomatized asthenosphere fertile peridotite to a more strongly metasomatized lithospheric mantle residual peridotite time related petrological and geochemical variations have been used to develop a model for the evolution of the vulcano plumbing system

comparison of isotopic composition of planktonic foraminifera in plankton tows sediment traps and sediments planktonic foraminifera from plankton tows sediment traps and sediments in the central north atlantic were studied in order to understand what determines their oxygen and carbon isotope composition a clear separation of species and genera on a 18o vs 13c plot for all samples suggests that their isotopic composition is controlled to a certain degree by biological factors within a species population the globorotaliids show a positive linear correlation between 18o and 13c while the shallow dwelling spinose species mostly globigerinoides species do not show a definite trend the latter species when collected in plankton tows often show slight negative deviations from isotopic equilibrium with respect to oxygen all species deviate from carbon isotope equilibrium by 1 5 to 6 these deviations from equilibrium are probably caused by incorporation of isotopically light metabolic co2 into the skeleton which is enhanced by the activity of symbiotic algae during their ontogeny the average weight per individual of most species increases which indicates that calcification continues to a depth of about 100 m this additional skeleton roughly 50 by weight is isotopically heavier because temperatures are lower and photosynthesis of symbiotic algae stops below the photic zone therefore the skeleton of foraminifera collected in sediment traps below 400 m has an overall oxygen isotope composition that seems to be in equilibrium for caco3 deposited in the upper 100 m