79 ad vesuvius pdc deposits temperatures inferred from optical analysis on woods charred in situ in the villa dei papiri at herculaneum italy abstract determining the deposit temperature of pyroclastic density currents pdcs is a first order priority in the assessment of volcanic hazard for past eruptions in which no direct measurements are possible pdc deposit temperatures have been calculated mainly using magnetic proxies a more recent and innovative approach consists of the determination of the degree of charring of preserved wood fragments by optical analysis in this study we perform optical analyses on wooden beams belonging to the villa dei papiri at the archeological site of herculaneum which was destroyed by pdcs during the 79 ad eruption of vesuvius the new temperature data from this study range between 240 c and 370 c and are in good agreement with literature data for this eruption the large t variation measured can be interpreted as due to the interaction of the pdcs with the local environment i e the impacted buildings of the villa and the sea shoreline the study of in situ charred wood allows to constrain the charring kinetics and to evaluate the sensitivity of the reflectance proxy in recording pdc depositional features we demonstrate that the charcoal reflectance is an excellent proxy for the determination of the pdc deposit temperatures even at a local scale and it can be used in conjunction with or in alternative to other more traditional methodologies especially in case of pre heating effects which may alter the t determinations by thermoremanent magnetization

latest miocene to quaternary horizontal and vertical displacement rates during simultaneous contraction and extension in the southern apennines orogen italy foreland contraction and hinterland extension in the southern apennines orogen of italy produced a complex spatial and temporal pattern of vertical and horizontal displacement remarkably late miocene to mid pleistocene foreland migration of the contractional front at 16 mm yr 1 was not accompanied by uplift and the frontal thrust belt remained at or below sea level only following a mid pleistocene reduction in horizontal displacement did the frontal thrust belt and foreland begin uplift at 0 5 mm yr 1 a rate that increased to 1 mm yr 1 after 125 ka although the extensional hinterland experienced net subsidence during formation of the tyrrhenian basin an extensional transition zone adjacent to the frontal thrust belt records sustained uplift at 0 3 mm yr 1 the interaction of preexisting crustal structure and deep tectonic processes resulted in time integrated displacement rates suggesting steady state deformation for periods of 106 years displacement rate changes were abrupt and occurred over intervals of 105 years or less

column collapse and generation of pyroclastic density currents during the a d 79 eruption of vesuvius the role of pyroclast density the plinian columns formed during the magmatic phase of the a d 79 eruption of vesuvius alternated several times between fully stable buoyantly rising regimes and unstable regimes of partial or total collapse six pyroclastic density currents pdcs were produced during unstable regimes and ultimately caused the destruction of roman towns around the volcano through new measurements of juvenile clast density and estimations of ascent parameters we show that four partial collapses were likely triggered by increases in the abundance of dense juvenile clasts within the eruptive column in contrast the total collapse probably occurred in response to an increase in the wall rock content injected into the plume during a progressive widening of the conduit a sixth low energy small collapse resulted from high abundances in both dense juvenile clasts and wall rock material simulations of eruption column behavior already account for the effects of variations in conduit radius mass discharge rate and particle size but have yet to include variable clast density and wall rock abundance that cause temporal variations in plume density our results suggest that both parameters can exert a significant control on the potential for generation of pdcs

high temperature emplacement of the cerro galan and toconquis group ignimbrites puna plateau nw argentina determined by trm analyses estimates of pyroclastic flow emplacement temperatures in the cerro galan ignimbrite and toconquis group ignimbrites were determined using thermal remanent magnetization of lithic clasts embedded within the deposits these ignimbrites belong to the cerro galan volcanic system one of the largest calderas in the world in the puna plateau nw argentina temperature estimates for the 2 08 ma cerro galan ignimbrite are retrieved from 40 sites in 14 localities 176 measured clasts distributed at different distances from the caldera and different stratigraphic heights additionally temperature estimates were obtained from 27 sample sites 125 measured clasts from seven ignimbrite units forming the older toconquis group 5 60 4 51 ma mainly outcropping along a type section at rio las pitas vega real grande the paleomagnetic data obtained by progressive thermal demagnetization show that the clasts of the cerro galan ignimbrite have one single magnetic component oriented close to the expected geomagnetic field at the time of emplacement results show therefore that most of the clasts acquired a new magnetization oriented parallel to the magnetic field at the moment of the ignimbrite deposition suggesting that the clasts were heated up to or above the highest blocking temperature tb of the magnetic minerals tb 580 c for magnetite tb 600 630 c for hematite we obtained similar emplacement temperature estimations for six out of the seven volcanic units belonging to the toconquis group with the exception of one unit lower merihuaca where we found two distinct magnetic components the estimation of emplacement temperatures in this latter case is constrained at 580 610 c which are lower than the other ignimbrites these estimations are also in agreement with the lowest pre eruptive magma temperatures calculated for the same unit i e 790 c hornblende plagioclase thermometer folkes et al 2011b we conclude that the cerro galan ignimbrite and toconquis group ignimbrites were emplaced at temperatures equal to or higher than 620 c except for lower merihuaca unit emplaced at lower temperatures the homogeneity of high temperatures from proximal to distal facies in the cerro galan ignimbrite provides constraints for the emplacement model marked by a relatively low eruption column low levels of turbulence air entrainment surface water interaction and a high level of topographic confinement all ensuring minimal heat loss

zarqa megafacies widespread subglacial deformation in the sarah formation of saudi arabia and implications for the sequence stratigraphy of the hirnantian glaciation

regional uplift and local tectonic deformation recorded by the quaternary marine terraces on the ionian coast of northern calabria southern italy abstract the setting of a flight of marine terraces along a 65 km long section of the ionian coast of northern calabria is the result of the interaction between interglacial sea levels regional uplift and local fault related elevation changes seven terraces with corresponding palaeoshoreline angles at elevations ranging from 12 m to 420 m were recognised by aerial photo interpretation and field surveying the terraces were correlated to the oxygen isotope stages 1 5a 5c 5e 7 9 15 which correspond to the 7 81 102 124 215 330 and 600 ka highstands of the palaeosea level curve the 600 ka long regional ascent of the terraces took place at an average uplift rate of 0 67 mm yr this value slightly but progressively increases southward along the coastline the elevation of the strandlines is related to the activity of tectonic structures three cases were analysed allowing us 1 to recognise the height anomalies of the terraces on the sibari plain as the result of cumulated coseismic deformation caused by the normal castrovillari fault and on this basis calculate a minimum slip rate and a mean recurrence time for a single event of deformation 2 to exclude the presence of significant vertical deformations and consequently activity on the easternmost section of the normal pollino fault and 3 to hypothesise the presence of an hitherto unknown active fault responsible for the strong vertical displacements of the flight of terraces near the river avena finally we find the ratio of the rate of regional uplift to the average rates of local tectonic deformation to be 2 to 3 1

interferences encountered in the determination of ad of mollusc samples inflexion points interfere with the radiation growth curve of the dating signal at g 2 0014 for mollusc samples several experiments give evidence that the definition of the dating signal at g 2 0014 has to be reconsidered a reliable ad determination very often seems questionable for esr dating of mollusc samples

a recent tectonic reorganization in the south central mediterranean abstract new geodetic data combined with seismicity geologic and geochemical information document a major tectonic reorganization in the central mediterranean around 0 8 0 5 ma when rapid trench migration and consequent tyrrhenian back arc extension which dominated the region s evolution since the tortonian 10 8 ma essentially stopped in response the african convergence in sicily was transferred to a back thrust in the southern tyrrhenian characterized by frequent m5 6 earthquakes in the last 20 years a diffuse transform boundary formed across northeastern sicily to connect the sicilian and calabrian plate boundaries causing opening of the messina straits home to large historical earthquakes and unusual volcanism in the aeolian island arc and the intraplate mount etna a divergence of the ionian region from the main part of africa with northeastward motions that reflect the joint influence of african push and hellenic slab pull and are transmitted to calabria and adria could explain motions observed in the sicily channel calabria and apulia as well as the high level of southeastern sicilian seismic activity

sedimentology of a marine intermontane pleistocene gilbert type fan delta complex in the crati basin calabria southern italy the crati basin is a pliocene holocene extensional basin filled by the progradation of different types of marine fan delta systems coarse grained gilbert type fan deltas developed during the pleistocene they represent the sedimentary response to a strong differential uplift involving the basin margins and the basin itself the differential uplift was responsible for the fragmentation of the basin into several sub basins into which these fan deltas prograded the protection and lateral confinement by structural highs steep coastlines and the absence of strong tidal action in the adjacent ionian sea allowed the regular progradation of these fan deltas in the restricted gulfs and narrow embayments of the crati basin for the classical gilbert type fan deltas in lacustrine settings homopycnal inflow favours a rapid mixing of water masses and deposition of sediment close to the river mouth in the case of the example described here the density contrast between the sea water and the inflowing river water caused the separation of the muddy fraction from the coarse sandy and conglomeratic part of the sediment this allowed the development of steep mud poor coarse grained delta foresets slope instability features slump scars conglomeratic flow slides are fairly scarce in the proximal parts of the san lorenzo del vallo system towards the north where protection from the ionian sea was less they increase in importance

open system coral ages reveal persistent suborbital sea level cycles sea level is a sensitive index of global climate that has been linked to earth s orbital variations with a minimum periodicity of about 21 000 years although there is ample evidence for climate oscillations that are too frequent to be explained by orbital forcing suborbital frequency sea level change has been difficult to resolve primarily because of problems with uranium thorium coral dating here we use a new approach that corrects coral ages for the frequently observed open system behavior of uranium series nuclides substantially improving the resolution of sea level reconstruction this curve reveals persistent sea level oscillations that are too frequent to be explained exclusively by orbital forcing

paleomagnetic determination of emplacement temperatures of pyroclastic deposits an under utilized tool paleomagnetic data from lithic clasts collected from mt st helens usa volcan lascar chile volcan de colima mexico and vesuvius italy have been used to determine the emplacement temperature of pyroclastic deposits at these localities and to highlight the usefulness of the paleomagnetic method for determining emplacement temperatures at mt st helens the temperature of the deposits tdep at three sites from the june 12 1980 eruption was found to be 532 c 509 c and 510 570 c respectively one site emplaced on july 22 1980 was emplaced at 577 c these new paleomagnetic temperatures are in good agreement with previously published direct temperature measurements and paleomagnetic estimates lithic clasts from pyroclastic deposits from the 1993 eruption of lascar were fully remagnetized above the respective curie temperatures which yielded a minimum tdep of 397 c samples were also collected from deposits thought to be pyroclastics from the 1913 2004 and 2005 eruptions of colima at colima the sampled clasts were emplaced cold this is consistent with the sampled clasts being from lahar deposits which are common in the area and illustrates the usefulness of the paleomagnetic method for distinguishing different types of deposit tdep of the lower section of the lithic rich pyroclastic flow lrpf from the 472 a d deposits of vesuvius was 280 340 c this is in agreement with other recently published paleomagnetic measurements in contrast the upper section of the lrpf was emplaced at higher temperatures with tdep 520 c this temperature difference is inferred to be the result of different sources of lithic clasts between the upper and lower sections with the upper section containing a greater proportion of vent derived material that was initially hot our studies of four historical pyroclastic deposits demonstrates the usefulness of paleomagnetism for emplacement temperature estimation

characterizing the mesozoic extension direction in the northern iberian plate margin by anisotropy of magnetic susceptibility ams we present the results of anisotropy of magnetic susceptibility ams analyses carried out on weakly deformed triassic red beds jurassic and lower cretaceous limestones sandstones and shales from several northern iberian mesozoic basins located near the northern iberian plate margin santander cabuerniga and polientes basins in the western part of the basque cantabrian basin and bilbao and aralar basins in the central eastern part cameros basin in the northernmost part of the iberian chain a well defined magnetic lineation of tectonic origin is found at most of the sampled sites and is interpreted as the stretching direction resulting from the extensional deformation characterizing this period during the mesozoic the northern margin of the iberian plate underwent two rifting stages the triassic and late jurassic early cretaceous kimmeridgian albian rifting events both the triassic and the period of the late jurassic early cretaceous rifting event with maximum subsidence rates i e until the barremian are characterized by a ne sw extensional direction in the main subsidence areas this indicates that nw se master faults controlled basin subsidence and sedimentation through these periods in the northern iberia plate margin basins conversely during jurassic and aptian times a lower activity of nw se faults together with more important extension along a nw se direction can be inferred from ams analysis this study indicates the power of ams analysis in basin analysis and geodynamic reconstructions even in subsequently inverted basins

conduction model for the thermal influence of lithic clasts in mixtures of hot gases and ejecta the thermal influence of lithic clasts in mixtures of hot gases and ejecta produced during explosive eruptions is an important aspect of the dynamics of eruption columns and pyroclastic flows in order to study this aspect we present a heat conduction model which considers both the temperature distributions of the lithic clasts and the exchange of thermal energy between the lithic clasts and other constituents gases and juvenile pyroclasts the model quantifies the thermal energy of the system by means of a characteristic energy function that describes the energy absorbed by each lithic clast using this energy function and considering some hypothetical arrangements of lithic clasts it is possible to calculate by means of heat balance the temperature variations in mixtures of hot gases and ejecta as a function of time volume fraction of particles to gas and thermal diffusivity initial temperature diameter and volume fraction of lithic clasts theoretical results show that in an eruption a volume fraction of 12 of cool lithic clasts 20 100 c whose size is less than 5 cm will cause the mixture of hot gases and ejecta to cool by 300 c we suggest therefore that the thermal effects of lithic clasts should be considered in numerical models of eruption columns and pyroclastic flows

depositional model in subglacial cavities killiney bay ireland interactions between sedimentation deformation and glacial dynamics subglacial meltwater drainage and sedimentary processes play a major role in ice sheet dynamic but there is a lack of study of subglacial environment because modern ice sheet beds remain inaccessible previous authors already intended to provide diagnostic criterion and recent investigations suggest that fluid pressure variations are a key factor in subglacial environment this paper investigated the late devensian sedimentary record in order to describe subglacial sedimentological facies associations and deformation features related to fluid overpressures we used an integrated approach based on stratigraphy sedimentology and deformations styles to demonstrate a subglacial depositional model the studied interval is composed of stratified gravel and sand interbedded with diamicton and boulder pavement deposited in depressions formed by irregularity of the upper surface of diamicton deformation structures include convolutes dykes and normal micro faulting dykes show different dip directions from vertical oblique to subhorizontal from which both directions of shortening and extension can be determined vertical dykes are formed under pure shear strain related to ice weight only oblique dykes imply both ice bed coupling and simple shear strain between ice and substrate induced by flowing ice related to progressively increasing meltwater drainage intensity horizontal dykes are formed when minimum strain is vertical and therefore the overpressure exceeds the weight of overburden they are associated with high meltwater drainage intensity and ice bed uncoupling and refer to hydrofracturing overall depositional and deformation sequence also illustrates the increasing intensity of meltwater drainage in small cavity as high energy channelised deposits and in large cavities where subaqueous fan are deposited under hydraulic jump conditions moreover large cavities represent lee side cavities formed by fast flowing ice over an obstacle hydrofracturing is likely to occur when a dense fluid potentially associated with catastrophic drainage of an upstream cavity enters the low pressure confined environment of a downstream cavity and is injected under pressure in the soft substrate the studied glacial sequence represents a regional pattern probably related to an allocyclic control on sedimentation linked to long term glacial dynamics rather than local depositional conditions based on these results we provided a synthetic model linking depositional and deformation processes during ice sheet growth and decay but also valid at different timescales from annual to seasonal scale

mechanisms of hydrovolcanic pyroclast formation grain size scanning electron microscopy and experimental studies pyroclasts produced by explosive magma water interactions are of various sizes and shapes data from analysis of over 200 samples of hydrovolcanic ash are interpreted by comparison with experimentally produced ash grain size and scanning electron microscopy sem reveal information on the formation of hydrovolcanic pyroclasts strombolian explosions result from limited water interaction with magma and the pyroclasts produced are dominantly centimeter sized with increasing water interaction hydrovolcanism increases in explosivity to surtseyan and vulcanian activity these eruptions produce millimeter to micron sized pyroclasts the abundance of fine ash 63 m diameter increases from 5 to over 30 percent as water interaction reaches an explosive maximum this maximum occurs with interactions of virtually equal volumes of melt and water five dominant pyroclast shape types determined by sem result from hydrovolcanic fragmentation 1 blocky and equant 2 vesicular and irregular with smooth surfaces 3 moss like and convoluted 4 spherical or drop like and 5 plate like types 1 and 2 dominate pyroclasts greater than 100 m in diameter types 3 and 4 are typical of fine ash type 5 pyroclasts characterize ash less than 100 m in diameter resulting from hydrovolcanic fragmentation after strong vesiculation fragmentation mechanisms observed in experimental melt water interactions result from vapor film generation expansion and collapse fragments of congealed melt are products of several alternative mechanisms including stress wave cavitation detonation waves and fluid instability mixing all result in rapid heat transfer these mechanisms can explain the five observed pyroclast shapes stress wave fracturing cavitation of the melt results from high pressure and temperature gradients at the melt water interface simultaneous brittle fracture and quenching produces type 1 pyroclasts type 2 develops smooth fused surfaces due to turbulent mixing with water after fracture and before quenching fluid instabilities promote turbulent mixing of melt and water and produce fine ash this kind of fragmentation occurs during high energy explosions the increased melt surface area due to fine fragmentation promotes high efficiency heat exchange between the melt and water shapes of resulting pyroclasts are determined by maximum surface area type 3 and surface tension effects type 4 type 5 pyroclasts result from nearly simultaneous vesicle burst and melt water fragmentation

slickenside and fault surface kinematic indicators on active normal faults of the alpine betic cordilleras granada southern spain abstract twenty four mesoscopic slickenside kinematic indicators are described here for the pliocene quaternary active normal faults of the alpine betic cordilleras granada southern spain the indicators are classified into twelve groups depending on the down or up slope asymmetric orientation of features such as concavities damaged versus sharp grain borders or step edges v shaped markings fractures and trailed material seventeen of the indicators were not previously described in the literature the new kinematic indicators include two types of asymmetric grains a carrot shaped marking six substructures of congruous and incongruous steps trailed fault material a drop shaped figure a v shaped marking three types of synthetic hybrid fractures with congruous steps and two varieties of pluck holes we think that some of these kinematic indicators provide information on the amount of displacement aseismic versus seismic slip rates cataclastic flow frictional wear or surface polishing

influences of urban fabric on pyroclastic density currents at pompeii italy 1 flow direction and deposition 1 to assess ways in which the products of explosive eruptions interact with human settlements we performed volcanological and rock magnetic analyses on the deposits of the a d 79 eruption at the pompeii excavations italy during this eruption the roman town of pompeii was covered by 2 5 m of fallout pumice and then partially destroyed by pyroclastic density currents pdcs anisotropy of magnetic susceptibility measurements performed on the fine matrix of the deposits allowed the quantification of the variations in flow direction and emplacement mechanisms of the parental pdcs that entered the town these results integrated with volcanological field investigations revealed that the presence of buildings still protruding through the fallout deposits strongly affected the distribution and accumulation of the erupted products all of the pdcs that entered the town even the most dilute ones were density stratified currents in which interaction with the urban fabric occurred in the lower part of the current the degree of interaction varied mainly as a function of obstacle height and density stratification within the current for examples the lower part of the eu4pf current left deposits up to 3 m thick and was able to interact with 2 to 4 m high obstacles however a decrease in thickness and grain size of the deposits across the town indicates that even though the upper portion of the current was able to decouple from the lower portion enabling it to flow over the town it was not able to fully restore the sediment supply to the lower portion in order to maintain the deposition observed upon entry into the town

volcanic geology and eruption frequency sao miguel azores six volcanic zones comprise sao miguel the largest island in the azores all are quaternary in age except the last which is partly pliocene from west to east the zones are 1 the trachyte stratovolcano of sete cidades 2 a field of alkali basalt cinder cones and lava flows with minor trachyte 3 the trachyte stratovolcano of agua de pau 4 a field of alkali basalt cinder cones and lava flows with minor trachyte and tristanite 5 the trachyte stratovolcano of furnas and 6 the nordeste shield which includes the povoacao caldera and consists of alkali basalt tristanite and trachyte new radiocarbon and k ar ages augment stratigraphic data obtained during recent geologic mapping of the entire island and provide improved data to interpret eruption frequency average dormant intervals for the past approximately 3000 years in the areas active during that time are about 400 years for sete cidades 145 for zone 2 1150 for agua de pau and 370 for furnas however the average dormant interval at sete cidades increased from 400 to about 680 years before each of the past two eruptions and the interval at furnas decreased from 370 to about 195 years before each of the past four eruptions eruptions in zone 4 occurred about once every 1000 years during latest pleistocene and early holocene time none has occurred for about 3000 years the povoacao caldera truncates part of the nordeste shield and probably formed during the middle to late pleistocene calderas formed during latest pleistocene time at the three younger stratovolcanoes in the sequence outer agua de pau between 46 and 26 5 ka sete cidades about 22 ka inner agua de pau 15 2 ka and furnas about 12 ka normal faults are common but many are buried by holocene trachyte pumice most faults trend northwest or west northwest and are related to the terceira rift whose most active segment on sao miguel passes through sete cidades and zone 2 a major normal fault displaces nordeste lavas 150 250 m and may mark the location of an ancestral terceira rift recent seismicity e g in the 1980s generally has been scattered but some small earthquake swarms have occurred beneath the north eastern flank of agua de pau

suborbital period sea level oscillations during marine isotope substages 5a and 5c the frequency of oscillations in global ice volume as determined by dating of coral reef deposits provides an important test of the milankovitch model of orbital climate forcing the timing of two episodes of high sea level during marine isotope substages mis 5a and 5c here determined to have occurred at 84 and 101 ka bp are broadly consistent with the milankovitch model however new high precision u series dating of uplifted morphologically distinct coral reef terraces at barbados indicate that mis 5a was both longer and more complex than previously established with an additional sea level highstand occurring at 77 ka bp the u series analysis of a large number of samples for each coral reef deposit reveals a well defined correlation between measured age and initial 234u this correlation is evident even within the uncertainty band of 8 commonly used to exclude diagenetically altered samples and allows a more precise and accurate constraint of the age of these deposits by evaluating where the trend line intersects the modern 234u value other proxy climate records also indicate suborbital period variability during mis 5a and 5c and together imply that as for the last ice age orbital forcing alone cannot account for the observed changes in climate

characterization of various types of deformation and their corresponding deviatoric stress tensors using microfault analysis abstract considering an ideally prefractured material based on mohr s representation and bott s model we define the geometry and the peculiarities of the different theoretical fault domains which are likely to be reactivated under different tectonic regimes the theoretical striations associated with the different types of deformation are also calculated the compressive strike slip extensive strike slip radial extensive and constrictive types of deformation are specified in the second part of this paper using etchecopar s computer aided method a quantitative structural analysis of various types of superficial deformation has been carried out in different study areas southern france greece spain tunisia and nigeria the geometry of the microfault domains as well as the nature of the associated tensors are determined for each type of regional deformation the problem of the spatial homogeneity of the tensors deduced by the microtectonic analysis within the framework of a particular tectonic phase is also discussed

comparison of geodetic and geologic data from the wasatch region utah and implications for the spectral character of earth deformation at periods of 10 to 10 million years the wasatch fault and adjacent fault zones provide an opportunity to compare present day deformation rate estimates obtained from space geodesy with geologic displacement rates over at least four temporal windows ranging from the last millennium up to 10 myr the three easternmost gps sites of the basin and range geodetic network bargen at this latitude define a 130 km wide region spanning three major normal faults extending east west at a total rate of 2 7 0 4 mm yr with an average regional strain rate estimated to be 21 4 nstrain yr about twice the basin and range average on the wasatch fault the vertical component of the geologic displacement rate is 1 7 0 5 mm yr since 6 ka 0 6 mm yr since 130 ka and 0 5 0 7 mm yr since 10 ma however it appears likely that at the longest timescale rates slowed over time from 1 0 to 1 4 mm yr between 10 and 6 ma to 0 2 to 0 3 mm yr since 6 ma the cumulative vertical displacement record across all three faults also shows time variable strain release ranging from 2 to 4 mm yr since 10 ka to 1 mm yr averaged over the past 130 kyr conventional earthquake recurrence models reid type behavior would require an accordingly large variation in strain accumulation or loading rate on a 10 kyr timescale for which there appears to be no obvious geophysical explanation alternatively seismic strain release given a wide range of plausible constitutive behaviors for frictional sliding may be clustered on the 10 kyr timescale resulting in the high holocene rates with comparatively low uniform strain accumulation rates on the 100 kyr timescale wallace type behavior the latter alternative combined with observations at the million year timescale and the likelihood of a significant contribution of postseismic transients implies maxima of spectral amplitude in the velocity field at periods of 10 myr variations in tectonic loading 10 kyr clustered strain release and of 100 years postseismic transients if so measurements of strain accumulation and strain release may be strongly timescale dependent for any given fault system

paleomagnetic evidence for low temperature emplacement of the phreatomagmatic peperino albano ignimbrite colli albani volcano central italy the peperino albano approximately 19 36 ka old is a phreatomagmatic pyroclastic flow deposit cropping out along the slopes of the associated albano maar colli albani volcano italy the deposit exhibits lateral and vertical transitions from valley pond to veneer facies as well as intracrater facies we present the results of a paleomagnetic study of thermal remanent magnetization trm of the lithic clasts of the peperino albano ignimbrite that provide quantitative estimates of the range of emplacement temperatures across the different facies of the ignimbrite emplacement temperatures estimated for the peperino albano ignimbrite range between 240 and 350 c with the temperatures defined in the intracrater facies being generally lower than in the valley pond and veneer facies this is possibly due to the large size of the sampled clasts in the intracrater facies which when coupled with low temperature at the vent were not completely heated throughout their volume during emplacement the emplacement temperatures derived from the paleomagnetic results are in good agreement with the presence of un burnt plants at the base of the ignimbrite indicating that the temperature of the pyroclastic flow was lower than the temperature of ignition of wood paleomagnetic results from the peperino albano confirm the reliability of the paleomagnetic approach in defining the thermal history of pyroclastic flow deposits

tyrrhenian coastal deposits from sardinia italy a petrographic record of high sea levels and shifting climate belts during the last interglacial isotopic substage 5e abstract detailed petrographic and sedimentological analysis of tyrrhenian coastal deposits from four sites in sardinia provides new data about climate and sea level changes during the early part of the last interglacial isotopic substage 5e and shows that facies analysis is not only useful for the identification of ancient depositional environments but also represents a powerful tool for evaluating past climatic conditions and sea level forcing mechanisms two shallowing upward sequences sensu ward w c brady m j 1979 strandline sedimentation of carbonate grainstones upper pleistocene yucatan peninsula mexico am assoc pet geol bull 63 362 369 commonly separated by an erosion surface and displaying complex geometric relationships occur above modern sea level at several locations along the shorelines of sardinia these sequences include upper shoreface to backshore deposits and were formed during separate sea level highstands attributed to isotopic substage 5e our recent revision of these deposits indicates that each sequence presents distinctive petrographic characteristics the older succession essentially contains mixed calcarenites rich in quartz grains and lithic fragments whereas the younger sediments are dominated by carbonate bioclasts such as red algae coral and mollusk fragments both units apparently accumulated in a similar depositional setting but during different climatic regimes the petrography of the lower unit reflects a temperate humid period characterized by increased weathering and continental erosion whereas the composition of the upper one suggests a dryer and possibly warmer climate favoring active carbonate production the disparity in petrographic composition between sequences probably records the migration of atmospheric circulation cells i e a shift of climate belts before and after the 128 ka insolation maximum our climatic data are coherent with the calculated insolation curves for isotopic substage 5e and thus support the milankovitch hypothesis for the origin of pleistocene climates in contrast our sedimentological data clearly show the occurrence of two distinctive highstands of sea level during this time period which does not agree with the hypothesis it follows that the relation between orbitally induced insolation variations climate and sea level is not necessarily straightforward

deposition temperature of the ad 472 pollena pyroclastic density current deposits somma vesuvius italy the deposition temperature of the pyroclastic density current pdc deposits emplaced during the ad 472 pollena eruption somma vesuvius italy has been investigated using the thermal analysis of the magnetic remanence carried by lithic clasts embedded within the deposits a total of 310 lithic clasts were collected from all the pdc units in the pollena stratigraphic succession at different distances from the inferred vent and at different stratigraphic levels the temperature reached by each individual clast during residence in the pdc was estimated through stepwise thermal demagnetization with the values from all clasts collected at each site being used to infer the deposition temperature tdep although the sedimentological features of these pdc deposits show some variation the deposition temperature typically falls in the range 300 to 320 c with a maximum range of 260 to 360 c the fairly uniform temperature observed in both the dune bedded and massive deposits points to homogeneity in attainment of tdep for the different deposits and suggests similarity in the depositional regime of the different pdcs and or in heat transfer to lithic fragments similarity in depositional regime was also favoured by the limited control exerted by topography on the distribution of these pdcs with the northern wall of the somma caldera that did not act as a morphological barrier as a result the currents were capable of moving away from the vent without topographic disturbances and thus significant variations in the cooling regime because the pollena eruption is considered similar to the maximum expected event at somma vesuvius the characteristics of its deposits best simulate the likely maximum hazard for the vesuvius region in this regard pollena produced hot dilute pdcs which were able to travel up to 12 km from the vent maintaining high temperatures across this distance

on the formation of eruption columns following explosive mixing of magma and surface water when magma vents into the sea or a crater lake the ensuing magma water interaction can affect the style of eruption dramatically if the mass of surface water incorporated into the erupting material is small 108 kg s the height progressively decreases with surface water content this occurs when the magma and surface water begin to constitute a significant fraction of the mass at the top of the column so that an increasing fraction of the initial magmatic thermal energy is converted to the surface water rather than the entrained air the transitions in eruption style which result from changes in the mass of surface water mixing with the magma may account for observations of both buoyant plumes and wet surge during the eruptions of taal in 1965 and miyake jima in 1983 and for the changes in the eruptive activity at surtsey in 1963 1964 as the access of seawater to the vent became more restricted we also present calculations which suggest that the accretionary lapilli which are often found in wet flow deposits may result from condensation of vapor in both the cold wet collapsing fountains and in the flows themselves

on the mesozoic ionian basin summary new seismic reflection profiles of the italian deep crust project crop provide new insights on the structure of the ionian sea in spite of the apennines and hellenides neogene subduction zones two conjugate passive continental margins are preserved at the margins of the ionian sea along the malta escarpment to the southwest and the apulian escarpment to the northeast the ionian sea is likely to be a remnant of the mesozoic tethys ocean confined by these two conjugate passive continental margins the transition from continental to oceanic crust appears sharper to the northeast than to the southwest the basin between southeast sicily and southwest puglia was about 330 km wide and suggests a low spreading rate the inferred oceanic ridge should have been flattened by thermal cooling and buried by later sediments based on stratigraphic and structural constraints to the north in the apennines belt the ocean continued to the northwest this palaeogeography is supported by the seismicity of the apennines slab underneath the southern tyrrhenian sea which implies downgoing oceanic lithosphere the adjacent absence or paucity of deep seismicity does not imply absence of subduction but rather it can be interpreted as due to the more ductile behaviour of the subducted continental lithosphere surprisingly we note that where the oceanic inherited basin is subducting underneath the apennines in the hangingwall of the subduction hinge there are outcropping slices of continental crystalline basement previously deformed by the alpine orogen

an inverse problem in microtectonics for the determination of stress tensors from fault striation analysis abstract a method is proposed to compute some characteristics of a possible stress tensor related to striations measured in a given faulted area if several tectonic phases are responsible for the striations the method separates and determines the successive stress tensors the iterative algorithm consists of alternatively a sorting the data attributed to a tectonic phase and b computing the characteristics of the stress tensor of this phase the method is tested using an application to synthetic and actual data

a transtensional basin model for the organya basin central southern pyrenees based on magnetic fabric and brittle structures summary the purpose of this paper is to explain the kinematics of the inverted extensional organy basin centralsouthernpyrenees duringitsextensionalevolution thestudyoftheanisotropy of magnetic susceptibility ams and the study of brittle mesostructures are the instruments used to decipher the extensional kinematics separation of magnetic subfabrics analyses of ams at low temperature and anisotropy of the anhysteretic remanence aarm has been also done to properly interpret the obtained magnetic fabric data the combination of all magnetic fabric and brittle mesostructures analyses has provided new information to clarify thestructuralevolutionofthebasin whichsupportanewtectonicmodelfortheaptian albian basinal stage 20 sites for the magnetic fabric analysis were sampled in aptian lower albian marls the ams ellipsoids obtained at room temperature show their kmin axes perpendicular to bedding and kmax axes oriented nw se in 70 per cent of the samples n s in 15 per cent and ne sw in 15 per cent analyses of ams at low temperature show a better clustering of the axes of the magnetic ellipsoid pointing out that phyllosilicates constitute the carriers of the ams whereas the analyses of the aarm confirm the scattering of the ferromagnetic grains these results suggest that the obtained ams in the organy a basin was acquired during or shortly after deposition of the aptian lower albian marls without any subsequent overprint the direction of the magnetic lineation obtained from the ams at room and low temperatures agrees with the orientation of the stress axes obtained from the analysis of brittle mesostructures mainly faults and calcite filled tension gashes indicating its tectonic origin we interpret the orientation of the magnetic ellipsoids related to the transtensional movements linked to the formation of the organy a basin during the aptian albian interval which are consistent with the eastward displacement and rotation of iberia with respect to europe analysis oftensiongashesalsoindicatesamainnw seextensiondirection whereaspalaeostressanalysis of striated faults shows a more n s trending 3 the transtensional model proposed from magnetic fabric and brittle mesostructures for the organy a basin during the aptian albian is consistent with the creation of a strongly subsiding area south of the axial zone during the cretaceous and implies that rotation and separation of iberia respect to europe took place simultaneously

seismites in the fluviatile bima sandstones identification of paleoseisms and discussion of their magnitudes in a cretaceous synsedimentary strike slip basin upper benue nigeria abstract the upper benue basin northeastern nigeria is interpreted as a complex strike slip basin which consists of a set of sub basins controlled by synsedimentary n60 c e trending strike slip faults which were active during early cretaceous times the oblique planar cross beds made of the medium to fine grained sandstones of the upper member of the bima sandstone formation are affected by various soft sediment i e early diagenetic but soft sediment deformational structures these are present not only close to the synsedimentary faults but also on a larger regional scale three main types of structures undulated and recumbent folded cross bedded lamination dislocated convolutions and concordant microbreccias discordant fluidised intrusions are described these are related to processes of sediment deformation favored by sand hydroplasticity liquefaction and fluidization the local organization of these soft sediment intrastratal deformational structures their spatial distribution with respect to synsedimentary faults and their independance with respect to marginal paleoslopes suggest that they cannot be explained by slumping or current drag all the deformations are related to pore water expulsion and it is proposed that the required sand reorganization was triggered by seismic waves the spatial and chronologic distribution and intensity of the various types of deformation structures suggest that they were produced around different epicenters repeated by earthquakes of varying magnitudes associated with the synsedimentary strike slip tectonics

identifying magma water interaction from the surface features of ash particles the deposits from explosive volcanic eruptions those eruptions that release mechanical energy over a short time span1 are characterized by an abundance of volcanic ash2 3 this ash is produced by fragmentation of the magma driving the eruption and by fragmenting and ejecting parts of the pre existing crust host rocks interactions between rising magma and the hydrosphere oceans lakes and ground water play an important role in explosive volcanism4 5 because of the unique thermodynamic properties of water that allow it to very effectively convert thermal into mechanical energy although the relative proportion of magma to host rock fragments is well preserved in the pyroclastic rocks deposited by such eruptions it has remained difficult to quantitatively assess the interaction of magma with liquid water from the analysis of pyroclastic deposits2 3 4 5 here we report the results of a study of natural pyroclastic sequences combined with scaled laboratory experiments we find that surface features of ash grains can be used to identify the dynamic contact of magma with liquid water the abundance of such ash grains can then be related to the water magma mass ratios during their interaction

raised coastal terraces along the ionian sea coast of northern calabria italy suggest space and time variability of tectonic uplift rates abstract a detailed study of uplifted middle late pleistocene marine terraces on the eastern side of northern calabria southern italy provides insights into the temporal and spatial scale variability of vertical displacement rates over a time span of 400 ka calabria is located in the frontal orogen of southern italy above the westerly plunging ionian slab and a combination of lithospheric crustal and surface processes concurred to rapid late quaternary uplift eleven terrace orders and a raised holocene beach were mapped up to 480 m a s l and were correlated between the coastal slopes of pollino and sila mountain ranges across the sibari plain facing the ionian sea side of northeastern calabria precise corrections were applied to the measured shoreline angles in order to account for uncertainty in measurement erosion of marine deposits recent debris shedding and bathymetric range of markers radiometric esr and 14 c dating of shells provides a crono stratigraphic scheme although many samples were found to be resedimented in younger terraces terrace t4 whose inner margin stands at elevations of 94 130 m is assigned to mis 5 5 124 ka based on new esr dating and previous amino acid racemization estimations the underlying terraces t3 t2 and t1 are attributed to mis 5 3 100 ka 5 1 80 ka and 3 60 ka as inferred from their relative position supplemented by esr and 14 c age determinations the age of higher terraces is poorly constrained but conceivably is tracked back to mis 11 400 ka the reconstructed depositional sequence of terraces attributed to mis 5 5 and 7 reveals two regressive marine cycles separated by an alluvial fanglomerate which given the steady uplift regime points to minor sub orbital sea level changes during interstadial highstands based on the terrace chronology uplift in the last 400 ka occurred at an average rate of 1 mm a but was characterized by the alternation of more rapid up to 3 5 mm a and slower down to 0 5 mm a periods of displacement spatial variability in uplift rates is recorded by the deformation profile of terraces parallel to the coast which document the growth of local fold structures

neogene quaternary tectonic evolution of the southern apennines 1 in this paper we present a study of a segment of the southern apennine mountain belt which extends from the pollino mountain range to the south and the sele valley to the north combining regional data and structural information with the results based on the interpretation of several seismic reflection lines and many deep well logs three regional cross sections have been constructed the cross sections highlight the overall architecture of the orogenic belt which is constituted by a thin tectonic layer of allochthonous nappes represented by remnants of the neotethyan accretionary wedge e g liguride and sicilide units resting above a thick imbricated thrust belt this latter comprises distinct units represented by platform carbonates western platform monte alpi costamolina and tempa rossa units and pelagic basin domains lagonegro campomaggiore and faeto units deriving from the late tortonian quaternary deformation of the adria paleomargin the restoration of the three cross sections furnished information on the primary geometry of the adria paleomargin which was characterized by the occurrence of a large platform domain dissected by distinct pelagic basins with complex and irregular margins represented by pelagic embayments and platform promontories developed during the mesozoic and the late cretaceous tertiary times the reconstructed geometry of the paleomargin provided moreover useful insights to evaluate the mode of deformation and the rates of shortening of the thrust belt and to explain the neogene stratigraphy of the distinct platform domains the mode of deformation of this portion of the southern apennines was dominated by the occurrence of crustal thrusts located along previous weakness zones represented by the boundaries between platform and pelagic domains these crustal thrusts caused the complete closure of the basin areas and the direct overthrusting of the different buoyant platform domains with contractional rates characterized by values ranging from 3 1 to 4 3 cm yr finally a geodynamic model in which the southern apennine mountain belt is considered the result of lateral extrusion produced by the indentation of the pelagian block and by the consequent opening of the tyrrhenian sea is also proposed

particle fallout thermal disequilibrium and volcanic plumes we develop a model of a volcanic eruption column that includes the effects of fallout of pyroclasts and thermal disequilibrium we show that clast fallout with no thermal disequilibrium has only a small effect upon the column however disequilibrium changes column behaviour significantly and can even induce collapse our results may explain the lower plume heights and less widely dispersed fallout of cone forming eruptions contrasted with sheet forming eruptions the model also predicts that the transition from the gas thrust to the convective region in a column results in an inflection in dispersal curves that some features of the stratigraphy common to many fall deposits may result from column velocity structure and that there may exist a region near the volcanic vent in which maximum pyroclast size does not decrease significantly with distance

paleomagnetic constraints on a time stratigraphic framework for the evolution of ohachidaira volcano and the summit caldera central hokkaido japan we present a revised stratigraphy of the proximal deposits around ohachidaira volcano and their paleomagnetic directions obtained from 21 sites 193 samples we identify four proximal pyroclastic members from ohachidaira volcano that were produced after the early edifice building effusive volcanism from older to younger 1 vent opening mafic pyroclastic density current pdc deposits kobachidaira ignimbrite 2 maar forming mafic tephra ring deposits mamiyadake tephra ring 3 mafic to silicic caldera forming deposits sounkyo member and 4 mafic pdc deposits kumonotaira ignimbrite well grouped paleomagnetic directions obtained from the kobachidaira ignimbrite and the sounkyo member indicate that each deposit was formed over a short time interval compared to geomagnetic secular variation that is less than a century conversely scattered paleomagnetic directions of the mamiyadake tephra ring record the secular variation of the geomagnetic field that took place over a longer time interval that is at least 750 yr probably more the kumonotaira ignimbrite which has a similar paleomagnetic direction to the underlying sounkyo member may have been produced during the sounkyo eruption from comparison between our data and the previously reported paleomagnetic directions of two petrologically distinct distal ignimbrites we conclude that the sounkyo member is a proximal correlative of the distal pyroxene rich ignimbrite and that the distal hornblende rich ignimbrite may not be of an ohachidaira origin the revised stratigraphy suggests that ohachidaira volcano is a maar caldera complex volcano and that the summit caldera is a flaring funnel formed incrementally by explosive erosion and syn eruptive collapse of the vent walls volume estimates imply that the sounkyo eruption fundamentally enlarged the vent and formed the caldera our data confirm that the comparison of paleomagnetic directions can offer a useful identification and correlation tool for the ohachidaira pyroclastic sequences

age estimates and uplift rates for late pleistocene marine terraces southern oregon portion of the cascadia forearc marine terraces are prominent landforms along the southern oregon coast which forms part of the forearc region of the cascadia subduction zone interest in the cascadia subduction zone has increased because recent investigations have suggested that slip along plates at certain types of convergent margins is characteristically accompanied by large earthquakes in addition other investigations have suggested that convergent margins can be broadly classified by the magnitude of their uplift rates with these hypotheses in mind we generated new uranium series amino acid and stable isotope data for southern oregon marine terrace fossils these data along with terrace elevations and two alternative estimates of sea level at the time of terrace formation allow us to determine terrace ages and uplift rates uranium series analysis of fossil coral yields an age of 83 5 ka for the whisky run terrace at coquille point in bandon oregon a combination of amino acid and oxygen isotope data suggest ages of about 80 and 105 ka for the lowest two terraces at cape blanco these ages indicate uplift rates of 0 45 1 05 and 0 81 1 49 m kyr for coquille point and cape blanco respectively late quaternary uplift rates of marine terraces yield information about deformation in the overriding plate but it is unclear if such data vary systematically with convergent margin type in order to assess the utility of the southern oregon uplift rates for predicting the behavior of the cascadia subduction zone we compared late quaternary uplift rates derived from terrace data from subduction zones around the world on the basis of this comparison the southern oregon rates of vertical deformation are not unusually high or low furthermore late quaternary uplift rates show little relationship to the type of convergent margin these observations suggest that local structures may play a large role in uplift rate variability in addition while the type of convergent margin may place an upper limit on possible uplift rate greater upper limits serve to increase the range of possible uplift rates in the case of the southern oregon coast variability in uplift rate probably reflects local structures in the overriding plate and the rate of uplift cannot be used as a simple index of the potential for great earthquakes along the southern cascadia subduction zone

a case study in the new york drumlin field an investigation using microsedimentology resulting in the refinement of a theory of drumlin formation abstract the formation of drumlins remains a major enigma it is accepted that drumlins form under active temperate ice most likely within a soft sediment deforming bed at ephemeral sticky points these sticky points likely lead to the causative mechanism around which sediment nucleation occurs the critical question is under what conditions and where and how do sticky spots form a comparative investigation of a drumlin and mega flute in the new york drumlin field as a case study demonstrates that rheological and sedimentological tills from these different forms are similar it is not therefore rheological change alone that must account for drumlin shape and form but likely the advective subglacial basal sediment flux rate at the ice bed the rate of sediment motion between the upper interface at the ice sediment bed boundary and the lower immobile sediment at depth is crucial at the lower decollement between the mobile and immobile sediment units within the deforming sediment package proto drumlin nucleation is likely to occur and develop into a streamlined form the trigger mechanism for such a perturbation is a derivative of sediment rheology and sediment flux rate driven by the overlying ice stresses recent evidence from antarctica lends credence to this new hypothesis that can be related to all drumlins formed under temperate soft sediment deforming bed conditions

history of subduction and back arc extension in the central mediterranean summary geological and geophysical constraints to reconstruct the evolution of the central mediterranean subduction zone are presented geological observations such as upper plate stratigraphy hp lt metamorphic assemblages foredeep trench stratigraphy arc volcanism and the back arc extension process are used to define the infant stage of the subduction zone and its latest back arc phase based on this data set the time dependence of the amount of subducted material in comparison with the tomographic images of the upper mantle along two cross sections from the northern apennines and from calabria to the gulf of lyon can be derived further the reconstruction is used to unravel the main evolutionary trends of the subduction process results of this analysis indicate that 1 subduction in the central mediterranean is as old as 80 myr 2 the slab descended slowly into the mantle during the first 20 30 myr subduction speeds were probably less than 1 cm year x1 3 subduction accelerated afterwards producing arc volcanism and back arc extension and 4 the slab reached the 660 km transition zone after 60 70 myr this time dependent scenario where a slow initiation is followed by a roughly exponential increase in the subduction speed can be modelled by equating the viscous dissipation per unit length due to the bending of oceanic lithosphere to the rate of change of potential energy by slab pull finally the third stage is controlled by the interaction between the slab and the 660 km transition zone in the southern region this results in an important re shaping of the slab and intermittent pulses of back arc extension in the northern region the decrease in the trench retreat can be explained by the entrance of light continental material at the trench

sea level and deep water temperature changes derived from benthic foraminifera isotopic records we show that robust regressions can be established between relative sea level rsl data and benthic foraminifera oxygen isotopic ratios from the north atlantic and equatorial pacific ocean over the last climatic cycle we then apply these regressions to long benthic isotopic records retrieved at one north atlantic and one equatorial pacific site to build a composite rsl curve as well as the associated confidence interval over the last four climatic cycles our proposed reconstruction of rsl is in good agreement with the sparse rsl data available prior to the last climatic cycle we compute bottom water temperature changes at the two sites and at one southern indian ocean site taking into account potential variations in north atlantic local deep water 18o our results indicate that a last glacial maximum lgm enrichment of the ocean mean oxygen isotopic ratio of 0 95 is the lowest value compatible with unfrozen deep waters in the southern indian ocean if local deep water 18o did not increase during glacials with respect to present such a value of the lgm mean ocean isotopic enrichment would impose a maximum decrease in local bottom water 18o at the north atlantic site of 0 30 during glacials

structural evolution of the lucanian apennines southern italy abstract in this paper we present a study of an entire segment of the southern apennines of italy extending from the pollino mountain range to the south to the agri valley to the north in which all the units of the chain are represented combining regional information with detailed structural data obtained from the different tectonic units forming the orogenic belt the structure as well as the tectonic evolution of this portion of the orogenic belt are proposed the overall architecture of this segment of the southern apennines mountain chain represents the result of a complete orogenic cycle in which oceanic subduction syn collisional and post collisional events are well recorded structurally this segment of the orogenic belt exhibits two distinct structural levels separated by a major detachment surface the sole thrust of the accretionary wedge that occur at the surface in the allochthonous nappes and at depth in the adria continental margin the upper level is characterized by an imbricated fan system affecting the allochthonous terranes emplaced during oceanic subduction and the first stages of continent continent collision the lower level is represented by a duplex geometry that has developed in the post collisional stage during evolution of the foreland migrating thrust system involving the carbonate platform basin system of the adria block during the last stages of the mountain building process when the foreland thrust migration was locked by the thickening of the colliding continental crusts the southern apennines were thus affected by a severe strike slip tectonics that dissects the entire mountain belt deeply modifying the previous thrust geometry

determination of the largest clast sizes of tephra deposits for the characterization of explosive eruptions a study of the iavcei commission on tephra hazard modelling the distribution of clasts deposited around a volcano during an explosive eruption typically contoured by isopleth maps provides important insights into the associated plume height wind speed and eruptive style nonetheless a wide range of strategies exists to determine the largest clasts which can lead to very different results with obvious implications for the characterization of eruptive behaviour of active volcanoes the iavcei commission on tephra hazard modelling has carried out a dedicated exercise to assess the influence of various strategies on the determination of the largest clasts suggestions on the selection of sampling area collection strategy choice of clast typologies and clast characterization i e axis measurement and averaging technique are given mostly based on a thorough investigation of two outcrops of a plinian tephra deposit from cotopaxi volcano ecuador located at different distances from the vent these include 1 sampling on a flat paleotopography far from significant slopes to minimize remobilization effects 2 sampling on specified horizontal area sections with the statistically representative sampling area depending on the outcrop grain size and lithic content 3 clast characterization based on the geometric mean of its three orthogonal axes with the approximation of the minimum ellipsoid lithic fragments are better than pumice clasts when present and 4 use of the method of the 50th percentile of a sample of 20 clasts as the best way to assess the largest clasts it is also suggested that all data collected for the construction of isopleth maps be made available to the community through the use of a standardized data collection template to assess the applicability of the new proposed strategy on a large number of deposits and to build a large dataset for the future development and refinement of dispersal models

pleistocene strike slip tectonics in the lucanian apennine southern italy structural studies carried out in the lucanian apennines southern italy show that strike slip faulting was the principal mode of deformation of this area during middle upper pleistocene time w nw to e se trending left strike slip fault systems dissect the entire apennine mountain belt and affect the preexisting thrust geometry strike slip faults activated by a roughly e w shortening are characterized by different geometries representing the surface response to lateral motion occurring along deep seated structures the occurrence of different structural patterns which characterize different segments of strike slip system is related to 1 the depth of a major decoupling surface which separates the upper tectonic multilayered horizon apennines thrust belt system from the lower rigid horizon apulian belt in which strike slip structures have originated and 2 the geometric relationships between the strike slip faults and the thrust belt pattern which characterize the upper horizon the different segments of the strike slip system are interpreted as internal deformation developed within a crustal shear zone this zone which corresponds to the boundary between the apulian block and the apennine chain is characterized by sinistral movement as a response to the northwesterly convergent motion of the african plate with respect to europe

timing and duration of the last interglacial evidence for a restricted interval of widespread coral reef growth abstract we report new mass spectrometric u series ages for eight last interglacial fossil reefs along the continental margin of western australia corals were selected in growth position from localities that are characterized by apparently low levels of diagenesis and relative tectonic stability so that the fossil reefs provide critical information on last interglacial sea levels without requiring corrections for tectonic movements in addition we have improved the constraint on the timing of onset of reef growth by recovering drill core coral from the base of the reefs uranium and thorium isotopes were measured with high levels of precision leading to improvements in age resolution and allowing samples which have undergone diagenetic exchange of uranium and thorium to be more easily identified and discarded these data supplement our previous results for rottnest island and leander point leading to more than seventy mass spectrometric u series ages from which constraints can be placed on the timing duration and character of the last interglacial sea level highstand reliable ages show that reef growth started contemporaneously at 128 1 ka along the entire western australian coastline while relative sea levels were at least 3 m above the present level because western australia is located far from the former penultimate glacial maximum ice sheets and are not significantly effected by glacial unloading these data constrain the timing of onset of the last interglacial period to 128 1 ka assuming reef growth started soon after sea level approached interglacial levels a unique regressive reef sequence at mangrove bay constrains the timing of termination of the last interglacial period to 116 1 ka the major episode of reef building however both globally and locally along the western australian coast is restricted to a very narrow interval occurring from 128 ka and 121 ka suggesting that global ocean surface temperatures were warm and or sea levels were stable enough to allow prolific reef growth only during the earlier part of the last interglacial

late cenozoic uplift of southern italy deduced from fluvial and marine sediments coupling between surface processes and lower crustal flow abstract we investigate the rates and magnitudes of late pliocene pleistocene uplift at key localities in the southern italian regions of basilicata and calabria using fluvial and marine terraces these rates show strong lateral variations reaching maxima of 1 mm a 1 or more in the southern apennines which have uplifted by many hundreds of metres since the late early pleistocene and by well over 1 km since the middle pliocene integrated study has been facilitated by the realisation that altitudes of river terraces in this region require substantial correction for downstream channel lengthening given the rapid coastal progradation that is occurring before they can be compared with altitudes of marine terraces these high rates of uplift and the corresponding rates of subsidence of the sea floor in adjacent offshore localities are explained as consequences of coupling between erosion and sedimentation by induced flow in the lower continental crust this coupling being particularly strong due to the narrowness of the southern part of the italian peninsula numerical modelling indicates that time averaged and spatially averaged erosion rates in this region have been 0 5 mm a 1 since the early middle pleistocene less than the regional uplift rates indicating that the landscape is not in a steady state although southern italy lies within a plate boundary zone along which the african plate is subducting and within which the continental crust is extending the observed vertical crustal motions are nevertheless controlled by surface processes in particular across much of this region crustal extension is shown to be a much less important factor than onshore erosion in driving the observed rates of vertical crustal motion

interpreting quaternary uplift rates at the mendocino triple junction northern california from uplifted marine terraces analysis of the altitudinal spacing of 14 flights of marine terraces indicates a spatial pattern of varying uplift rates that agrees with that determined from previously dated terraces for the past 3 81 ka and temporal changes in uplift rates from 1 m ka to 3 5 m ka that may reflect response to changes in tectonic regime during passage of the mendocino triple junction mtj a possible mechanism for regional uplift is growth of a slab window south of the mtj the region of most rapid uplift is 25 43 km south of the mtj immediately south of the northern boundary of the slab window the coastline is tilted upward to the south in the region directly above the southern edge of the subducted gorda plate at point delgada 55 km south of the present mtj where the northern edge of the slab window passes approximately 300 ka uplift rates have been 1 2 m ka for at least 330 ka more than 1 4 m y after passage of the southern edge of the subducted slab at the mendocino coast uplift rates have been less than 0 4 m ka for at least 330 ka

thermal interactions of the ad79 vesuvius pyroclastic density currents and their deposits at villa dei papiri herculaneum archaeological site italy abstract pyroclastic density currents pdcs can have devastating impacts on urban settlements due to their dynamic pressure and high temperatures our degree of understanding of the interplay between these hot currents and the affected infrastructures is thus fundamental not only to implement our strategies for risk reduction but also to better understand pdc dynamics we studied the temperature of emplacement of pdc deposits that destroyed and buried the villa dei papiri an aristocratic roman edifice located just outside the herculaneum city during the ad79 plinian eruption of mt vesuvius italy by using the thermal remanent magnetization of embedded lithic clasts the pdc deposits around and inside the villa show substantial internal thermal disequilibrium in areas affected by convective mixing with surface water or with collapsed walls temperatures average at around 270 c min 190 c max 300 c where the deposits show no evidence of mixing with external material the temperature is much higher averaging at 350 c min 300 c max 440 c numerical simulations and comparison with temperatures retrieved at the very same sites from the reflectance of charcoal fragments indicate that such thermal disequilibrium can be maintained inside the pdc deposit for time scales well over 24 hours i e the acquisition time of deposit temperatures for common proxies we reconstructed in detail the history of the progressive destruction and burial of villa dei papiri and infer that the rather homogeneous highest deposit temperatures average 350 c were carried by the ash sized fraction in thermal equilibrium with the fluid phase of the incoming pdcs these temperatures can be lowered on short time less than hours and length scales meters to tens of meters only where convective mixing with external materials or fluids occurs by contrast where the villa walls remained standing the thermal exchange was only conductive and very slow i e negligible at 50 cm distance from contact after 24 hours we then argue that the state of conservation of materials buried by pdc deposits largely depends on the style of the thermal interactions here we also suggest that pdc deposit temperatures are excellent proxies for the temperatures of basal parts of pdcs close to their depositional boundary layer this general conclusion stresses the importance of mapping of deposit temperatures for the understanding of thermal processes associated with pdc flow dynamics and during their interaction with the affected environment

residual topography lithospheric structure and sunken slabs in the central mediterranean abstract the central mediterranean comprises subduction collision and backarc extension all in a relatively small area in this paper we analyze the topography of this region examining the influence of subducting slabs on overriding plates we take the observed surface elevation remove the contribution of the crust to it and use the residual topography to identify regions that are unusually low unusually high or normal then we calculate lithospheric thickness where local isostasy applies the results provide information about the structure of the lithosphere in this complex region and about the vertical tectonics in particular we found a difference between the south tyrrhenian subduction zone and the apennines consistent with the processes of slab rollback and slab break off respectively in the south tyrrhenian the edge of the oceanic plate is strongly pulled down whereas the edge of the overriding plate the calabrian peninsula is uplifted this opposite trend indicates weak plate coupling that is the subducting slab which is rapidly rolling back hangs almost entirely on the oceanic plate and the overriding plate is free in contrast in the apennines high residual topography and uplifting are detected on both sides of the mountain belt consistent with complete break off of the subducted lithosphere

early deformations at a submarine compressive front the quaternary catania foredeep south of mt etna sicily italy abstract in the catania foredeep south of mt etna oil drilling has revealed the existence at depth of an allochthonous complex emplaced during the middle quaternary at the surface outcropping middle quaternary marine marly clays and sands display complex deformations which are partly synsedimentary and which can be correlated with the emplacement of this allochthonous complex most of these deformations are thought to result from gravitational gliding of slope sediment apron this process probably facilitated by high pore pressure would be in particular the cause of a semi penetrative shear deformation with an eastward vergence in the clays thus our study rules out the classical view of a shallow pre etnean gulf that was steadily filled in before emerging some 400 000 to 300 000 years ago this particular example of neotectonics shows the precocity and complexity of deformations occurring in sediments deposited along the compressive margin of a foreland basin or similarly at an accretionary prism front

palaeo stresses inferred from macro and microfractures in the balazuc 1 borehole gpf programme contribution to the tectonic evolution of the cevennes border of the se basin of france abstract the scientific borehole balazuc 1 was drilled on the ardeche margin of the se basin of france for the purpose of studying fluid rock interactions in stratiform reservoirs in a tectonically controlled area a structural study was made of oriented cores from the drill hole between the depths of 1218 and 1729 5 m the various types of fracture that could have been used during fluid transfers have been described and analysed four major faults and 335 minor faults and tension gashes mineralized in carbonates anhydrite and sulphides were intersected at the bottom of the hole one of the major faults brings into contact rocks of triassic age and a formation attributed to the upper palaeozoic the other faults have caused thinning of certain units of the lower middle triassic micro structural study of the fault planes has enabled characterization of the tectonic episodes by which the triassic and lower liassic sedimentary rocks were affected these episodes discussed in the context of the ligurian tethys were 1 e w synsedimentary extension during the early middle triassic that caused tilting to the southeast of the upper palaeozoic and lower middle triassic successions this continued into the late triassic 2 an episode of n s extension during the early lias characterized by hydroplastic type faults probably the result of a local variation of the stress field in a trans tensional regime 3 the major period of activity on the uzer fault with downthrow of more than 1000 m that continued from the lotharingian late sinemurian to the early bathonian it was not possible to calculate the stress tensor for this period because no secondary fault system developed in the lower block traversed by the borehole brittle deformation at this time seems to have been concentrated on the major structures 4 approximately n s extension possibly end jurassic to earliest cretaceous during which the tension gashes mineralized in carbonates and pyrite were formed in the rhaetian and hettangian deposits 5 three compressive and or strike slip episodes attributed to the cenozoic pyrenean and alpine phases of deformation the oligocene extensional phase was not recognized in the borehole

deformation of the 125 ka marine terrace in italy tectonic implications in peninsular italy marine terraces and shorelines created during oxygenisotope substage 5e known historically as the tyrrhenian highstand provide a reliable and homogeneous datum of vertical motions during the past 125 000 years published accounts of 121 locations on the tyrrhenian inner edge were reinterpreted and used to calculate both local and regional uplift rates the data show arching of southern italy between the tyrrhenian and the adriatic coasts and of the calabrian arc between the sangineto and the longi taormina tectonic lineaments at rates of up to 1 2 mm yr for the past 125 ka they also suggest that the present configuration of the southern apennines is the product of post early pleistocene regional uplift superimposed on tortonian to early pleistocene thrusting uplift patterns are characterised by different wavelength in different geodynamic settings suggesting a close link with the depth of the causative tectonic sources

understanding the mesozoic kinematic evolution in the cameros basin iberian range ne spain from magnetic subfabrics and mesostructures abstract analysis of anisotropy of magnetic susceptibility ams and brittle mesostructures hydroplastic synsedimentary faults and tension gashes is applied in this study in order to characterize the mesozoic tectonic events in the cameros basin nw iberian range formed between tithonian and albian times low field ams at room and low temperature lf ams at rt and lf ams at lt respectively together with high field ams hf ams measurements allow separating ferro and paramagnetic fabrics the combination of lf ams at lt and hf ams torque measurements confirms the reliability of both procedures in terms of isolating the paramagnetic contribution to the ams magnetic fabric results combined with the analyses of synsedimentary faults indicate a nw se extension direction during aptian and probably barremian times this extension direction is perpendicular to the main extension direction ne sw prevailing during early and late stages of basin evolution it is also consistent with extension direction deduced from large scale bending folds and tension gashes developed after partial lithification cleavage development during albian enhanced the orientation of the magnetic fabric in lithologies where the previous extensional magnetic lineation is coaxial with the expected one for compression

rapid fluctuations in sea level recorded at huon peninsula during the penultimate deglaciation about 140 000 years ago the breakup of large continental ice sheets initiated the last interglacial period sea level rose and peaked around 135 000 years ago about 14 meters below present levels a record of last interglacial sea levels between 116 000 years to 136 000 years ago is preserved at reef vii of the uplifted coral terraces of huon peninsula in papua new guinea however corals from a cave situated about 90 meters below the crest of reef vii are 130 000 2000 years old and appear to have grown in conditions that were 6 c cooler than those at present these observations imply a drop in sea level of 60 to 80 meters after 130 000 years sea level began rising again in response to the major insolation maximum at 126 000 to 128 000 years ago the early about 140 000 years ago start of the penultimate deglaciation well before the peak in insolation is consistent with the devils hole chronology

problems encountered in the determination of dose and dose rate in esr dating of mollusc shells abstract esr dating has been applied to dating marine mollusc shells for more than 15 years many studies have yielded promising results and contributed to resolving problems in marine and coastal research such as palaeo sea level changes and coastal neotectonic movements however some severe problems remain with respect to the accuracy of the dating results in particular problems encountered in the reliable determination of the equivalent dose de have reduced the merits of the esr dating technique here we present a new approach to obtain more reliable de values inflexion points in the dose response curve are considered to prevent its correct fitting the dating of articulated shells from holocene and last interglacial sediments help to illustrate the potential of this new method of de determination the estimate of the environmental dose has been refined by reconstructing the uranium uptake history of the mollusc shells

the afragola settlement near vesuvius italy the destruction and abandonment of a bronze age village revealed by archaeology volcanology and rock magnetism abstract public works in progress in the campanian plain north of somma vesuvius recently encountered the remains of a prehistoric settlement close to the town of afragola rescue excavations brought to light a bronze age village partially destroyed and buried by pyroclastic density currents pdcs of the vesuvian pomici di avellino eruption 3 8 14c ka bp and subsequently sealed by alluvial deposits volcanological and rock magnetic investigations supplemented the excavations careful comparison between volcanological and archaeological stratigraphies led to an understanding of the timing of the damage the buildings suffered when they were struck by a series of pdcs the first engulfed the village located some 14 km to the north of the inferred vent and penetrated into the dwellings without causing major damage the buildings were able to withstand the weak dynamic pressure of the currents and deviate their path as shown by the magnetic fabric analyses some later collapsed under the load of the deposits piled up by successive currents stepwise demagnetization of the thermal remanent magnetization trm carried by potsherds embedded in the deposits yields deposition temperatures in the order of 260 320 c fully consistent with those derived from pottery and lithic fragments from other distal and proximal sites the fairly uniform temperature of the deposits is here ascribed to the lack of pervasive air entrainment into the currents this in turn resulted from the lack of major topographical obstacles along the flat plain the coupling of structural damage and sedimentological analyses indicates that the currents were not destructive in the afragola area but trm data indicate they were still hot enough to cause death or severe injury to humans and animals the successful escape of the entire population is apparent from the lack of human remains and from thousands of human footprints on the surface of the deposits left by the first pdcs people were thus able to walk barefoot across the already emplaced deposits and escape the subsequent pdcs the rapid cooling of the deposits was probably due to both their thinness and heat dissipation due to condensation of water vapour released in the mixture by magma water interaction

transition from steady to unsteady plinian eruption column the vei 5 4 6 ka fogo a plinian eruption sao miguel azores abstract the 4 6 ka fogo a trachytic plinian eruption on sao miguel island azores portugal is composed by four main phases 1 initial phreatomagmatic activity which emplaced thin surge deposits with accretionary lapilli 2 fully buoyant steady plinian activity which generated a prominent trachytic basal fall out deposit 3 partial collapsing activity which led to the emplacement of two trachytic trachydacitic intra plinian ignimbrites pink and black ignimbrites and associated surge deposits inter stratified within two fall out deposits 4 vent widening and fully collapsing activity which caused the emplacement of the climactic brown trachydacitic ignimbrite the deposits of these four main phases have been organised into three members fga1 fga2 and fga3 sub divided into 15 stratigraphic or emplacement units the fluctuations from a steady to unsteady plinian eruption column parallel the change in composition of the magma from trachytic to trachydacitic although minimal the change in composition resulted in a marked change in colour of the juvenile clasts from white at the base first phase to pink and light dark grey banded and black second and third phases and to dark brown fourth phase density analysis of juvenile clasts revealed that the change in composition did not significantly affect the density of the juvenile pumice pyroclasts the vesicularity of which increases from 70 to 85 up through the sequence the pink and the black intra plinian ignimbrites were emplaced only within the narrow paleo valleys of the southern flank with maximum thicknesses of 9 m and 5 m respectively transitioning onto adjacent topographic highs where thin veneer surge layers were deposited the fall out deposits inter bedded between the ignimbrites lack basal reverse grading indicating that the eruption column continued to be sustained during the partial collapses generating the intra plinian ignimbrites the climactic dark brown ignimbrite was emplaced radially with a maximum thickness of 40 m the absence of oxidation surfaces or evidence of reworking within the fogo a deposits indicates that there were no time breaks during the different phases of the eruption the on land bulk volume of the three ignimbrites has been estimated around 3 2 km3 while the volume of the intra plinian fall out deposits is 0 003 km3 these bulk volume estimations summed with the basal fall out volume calculated by walker and croasdale 1970 makes a total bulk volume for the fogo a deposits of 4 4 km3 indicating a volcanic explosively index of 5 higher than previously estimated this result is fundamental for the forecasting a possible scenario for a future eruption

syn diagenetic evolution of shear structures in superficial nappes an example from the northern apennines nw italy abstract in the superficial nappes of the northern apennines meso and microstructures in sheared mudstones and fine grained turbidites consist mainly of networks of striated faults and calcite vein arrays the striated faults correspond to the first generation of structures they form two sets respectively synthetic and antithetic to the general shearing locally a sigmoidal microfabric is associated with the synthetic faults in scaly deformation bands up to a few metres thick late laterally extensive calcite veins are superposed on these structures they result from the opening of multiple releasing oversteps between shear surfaces the crack seal mechanism of deformation played a major role in their formation structures of the first generation result from heterogeneous ductile deformation of initially poorly lithified and water rich sediments the late formation of the calcite veins corresponds to a transitional ductile brittle behaviour in sufficiently lithified sediment evolution of structures probably depended on a strain hardening process and was dependent on the progressive compaction and dewatering of the sediment the gently dipping faults and veins probably formed the main pathway for the interstitial fluids possibly overpressured expelled from the sediment we emphasize that the geometry of the structures described provides important shear sense criteria for the study of superficial nappe tectonics

synlithification deformation processes of the cretaceous sediments of the ivory coast ghana transform margin a way to detail the margin history the ivory coast ghana margin is a typical transform margin along which large scale tectonism has been well documented the cretaceous sediments of the ivory coast ghana transform margin were subjected to numerous tectonic gravitational and hydrothermal forces during lithification in this paper we infer the order of occurrence of deformation regimes from characteristic deformations observed in samples of ocean drilling program odp leg 159 three main types of minor scale deformation are identified and characterized in terms of geometry rheology and kinematics 1 extensional structures such as normal faults and irregular veins with angular indented walls that are widely recorded at all odp sites 2 compressional structures that are confined to the marginal ridge of the ivory coast ghana transform margin and include reverse faults folds and vertical crenulation cleavage and 3 various types of shear zone at low angles with respect to bedding which are continuous throughout the cretaceous succession of the ridge structural analysis combined with thin section observation shows that most of these deformations occurred in water rich sediments the extensional minor scale structures are related to the early cretaceous rifting stage of the margin as characterized at regional scale by half grabens and tilted blocks the compressional structures observed in the samples are attributed to turonian santonian positive inversion tectonics and related to the occurrence of large scale flower structures and inverted extensional blocks in contrast the shear zones at low angles with respect to bedding observed throughout the cretaceous series are linked to local gravity induced tectonics

thermal state and implications for eruptive styles of the intra plinian and climactic ignimbrites of the 4 6 ka fogo a eruption sequence sao miguel azores the 4 6 ka fogo a plinian eruption was a caldera forming volcanic event on sao miguel island azores the deposit succession is very complex composed of a thick trachytic plinian fallout deposit interstratified with two intra plinian ignimbrites named pink ignimbrite and black ignimbrite sequentially the succession ends with a main ignimbrite named dark brown ignimbrite which represents the deposit of complete collapse of the eruption column and the end of the eruption in this work emplacement temperatures of the three ignimbrites are estimated by study of partial thermal remanent magnetization ptrm of lithic clasts a total of 140 oriented lithic clasts were collected from 15 localities distributed along the northern and southern flanks of fogo volcano the paleomagnetic data reveal different emplacement temperatures and thermal histories that were experienced by each ignimbrite the results indicate the presence of five different paleomagnetic behaviours that suggest emplacement temperatures of 350 400 c for the first pink intra plinian ignimbrite temperatures higher than 580 600 c for the second black intra plinian ignimbrite and 250 370 c for the last dark brown climactic ignimbrite the thermal history experienced by each pyroclastic flow and its ignimbrite deposit was also assessed by the use of the magnetite ilmenite geothermometer to determine the pre eruptive magma temperature estimated to be around 900 c we interpret the different emplacement temperatures of the fogo a ignimbrites as being due to a combination of factors these include i collapse from different heights of the eruption column and the resultant different amounts of air entrainment into the gas particle mixture ii variable content of lithic clasts and iii different types of juvenile clasts in the ignimbrites

forced transport of thermal energy in magmatic and phreatomagmatic large volume ignimbrites paleomagnetic evidence from the colli albani volcano italy abstract few studies have detailed the thermal architecture of large volume pyroclastic density current deposits although such work has a clear importance for understanding the dynamics of eruptions of this magnitude here we examine the temperature of emplacement of large volume caldera forming ignimbrites related to magmatic and phreatomagmatic eruptions at the colli albani volcano italy by using thermal remanent magnetization analysis on both lithic and juvenile clasts results show that all the magmatic ignimbrites were deposited at high temperature between the maximum blocking temperature of the magnetic carrier 600 630 c and the glass transition temperature about 710 c temperature estimations for the phreatomagmatic ignimbrite range between 200 and 400 c with most of the clasts emplaced between 200 and 320 c because all the investigated ignimbrites magmatic and phreatomagmatic share similar magma composition volume and mobility we attribute the temperature difference to magma water interaction highlighting its pronounced impact on thermal dissipation even in large volume eruptions the homogeneity of the deposit temperature of each ignimbrite across its areal extent which is maintained across topographic barriers suggests that these systems are thermodynamically isolated from the external environment for several tens of kilometers based on these findings we propose that these large volume ignimbrites are dominated by the mass flux which forces the lateral transport of mass momentum and thermal energy for distances up to tens of kilometers away from the vent we conclude that spatial variation of the emplacement temperature can be used as a proxy for determining the degree of forced convection flow

interaction of pyroclastic density currents with human settlements evidence from ancient pompeii integrating field observations and rock magnetic measurements we report how a turbulent pyroclastic density current interacted with and moved through an urban area the data are from the most energetic turbulent pyroclastic density current of the a d 79 eruption of vesuvius italy which partially destroyed the roman city of pompeii our results show that the urban fabric was able to divide the lower portion of the current into several streams that followed the city walls and the intracity roads vortices revealed by upstream particle orientations and decreases in deposit temperature formed downflow of obstacles or inside cavities although these perturbations affected only the lower part of the current and were localized they could represent in certain cases cooler zones within which chances of human survival are increased our integrated field data for pyroclastic density current temperature and flow direction collected for the first time across an urban environment enable verification of coupled thermodynamic numerical models and their hazard simulation abilities

sedimentation of tephra by volcanic plumes i theory and its comparison with a study of the fogo a plinian deposit sao miguel azores sedimentation of ejecta from volcanic plumes has been studied as a function of distance from the source in the fogo a plinian deposit sao miguel azores the fogo a trachytic pumice deposit is reversely graded and can be divided into two parts on the basis of pumice colour abundance of syenite accessory lithic clasts and distribution the lower syenite poor part was dispersed to the south and was clearly influenced by wind the upper syenite rich part is coarsegrained and has a nearly symmetrical distribution around the vent elongation of isopachs to the east indicate a weak wind influence the grain size variations of lithic and crystal components in the upper coarse part were studied total accumulation and accumulation per unit area expressed in kg m2 show good fits to a gaussian function at distances greater than 7 km for grain diameters less than 2 cm these results agree with a theoretical model for a radially spreading turbulent current moving over a quiescent fluid the gaussian coefficient is shown to be a function of grain size and the flow rate of material into the umbrella region of the eruption column the coefficient is therefore also a function of column height the column height deduced from these data is 21 km which is in broad agrrement with the column height of 27 km deduced from maximum clast dispersal using the method of carey and sparks 1986 the accumulation of clasts larger than 2 cm agrees with a theory for the fallout of clasts from the margins of the ascending eruption column which treats the plume as a succession of large eddies that decrease their mass of particles as an exponential function of time calculations are also presented for the influence of the radial inflow of surrounding air into the column on the deposition of clasts these calculations constrain the wind speed during the later part of the fogo a eruption to be at most a few metres per second the study has allowed four different dynamic categories of clast behaviour to be recognised in eruption columns

evidence of two holocene phreatomagmatic eruptions at stromboli volcano aeolian islands from paleomagnetic data 1 we present detailed stratigraphic sedimentological and paleomagnetic analyses of holocene phreatomagmatic deposits at stromboli volcano aeolian islands italy the investigated deposits belong to the secche di lazzaro succession sdl and to the advanced operations center of the department of civil defense coa succession both lying on the neostromboli lavas ca 13 5 ka the two stratigraphic successions have similar stratigraphic position and show a phreatomagmatic origin likely related to catastrophic magma water interaction processes during sector collapse events however the thermal remanent magnetization data of the lava lithics indicate that deposits of the sdl succession were emplaced at very low temperatures less than 140 c whereas the basal part of the coa deposit was emplaced at temperatures between 300 340 c paleomagnetic results indicate that the two investigated deposits may be related to two distinct eruptive events occurred during the holocene recent phreatomagmatic activity at stromboli apparently has occurred more frequently than previously believed consequently we must reconsider the recurrence interval of this dangerous eruptive scenario for stromboli

glass transition temperatures of natural hydrous melts a relationship with shear viscosity and implications for the welding process abstract glass transition temperatures tg have been determined for natural multicomponent melts using differential scanning calorimetry trachytic dacitic phonolitic and basaltic base compositions have been analysed over a range of water contents up to 3 75 wt for each sample tg has been obtained over a range of cooling heating rates using the extrapolated onset and the peak temperatures in heat capacity temperature curves tg of all compositions are strongly reduced by increasing water content particularly for the first 1 wt added base composition also has an effect with the lowest tg occurring in the peralkaline phonolite suite for all samples a clear dependence on the cooling heating rate has been recorded these results have been compared with rheological investigations on the same samples on the basis of the equivalence of the shear and enthalpic relaxation process timescales we provide a method to predict the shear viscosity at the glass transition for all the melts investigated in this study both dry and hydrous our determinations of tg provide a lower limit for the time temperature envelope that gives rise to densely welded deposits and constraints on their emplacement temperature furthermore by using the viscosity values predicted at the glass transition we suggest that welding processes may occur over timescales on the order of tens of seconds to tens of minutes at tg

emplacement temperature estimation of the 2015 dome collapse of volcan de colima as key proxy for flow dynamics of confined and unconfined pyroclastic density currents abstract the recent 10th 11th of july 2015 volcan de colima eruption involved the collapse of the summit dome that breached to the south generating pyroclastic density currents pdcs along the montegrande ravine on the southern flank of the volcano trees within the valley were buried uprooted and variably transported by the pdcs while the trees on the edges of the valley and on the overbanks were mainly burned and folded the emplacement temperature of valley confined and overbank pdc deposits were reconstructed using partial thermal remanent magnetization ptrm analysis of lithic clasts and charcoal reflectance analysis ro applied to the charred wood a total of 13 sites were sampled for the ptrm study and 39 charcoaled wood fragments were collected for the charcoal optical analysis along the entire deposit length in order to detect temperature variation from proximal to distal zone the result overlap from both data sets display a t max from 345 385 c in valley confined area from 3 5 to 8 5 km from the vent and 170 220 c from 8 0 to 10 5 km from the vent in unconfined distal area the emplacement temperature pattern along the 10 5 km long deposit appears related to the degree of topography confinement valley confined and unconfined in particular the valley confined setting is very conservative in terms of temperature while the major drop occurs in a very narrow space where the pdc expanded over unconfined flat topography just at the exit of the main valley this study represents the first attempt in determining the relationship between pdcs flow dynamics variation and topographic confining using deposit emplacement temperature as key proxy

pedogenic slickensides indicators of strain and deformation processes in redbed sequences of the appalachian foreland pedogenic slickensides are convex concave slip surfaces that form during expansion contraction in expansive clay soils such as vertisols in the central appalachians they occur near the tops of fining upward cycles in paleozoic redbeds such as the bloomsburg catskill and mauch chunk formations pedogenic slickensides are found in association with other pedogenic or paleosol features such as clay skinned peds in situ calcareous nodules and root impressions repeated movements along these shear planes during pedogenesis produce strongly aligned clay particles adjacent to pedogenic slickensides as a result they are preserved as discrete fractures throughout diagenesis compaction and superimposed tectonic deformation during whole rock deformation pedogenic slickensides segregate penetratively deformed rocks into independent foliated packets and serve as discontinuities that are followed by later structural features because the original morphology of pedogenic slickensides is known they can be used as crude strain markers

a new interpretation of terraces in the taranto gulf the role of extensional faulting abstract the taranto gulf of southern italy provides an excellent case where it is possible to document the importance of normal faults in displacing terraced deposits the study area is located at the front of the southern apennines that is a fold and thrust belt developed following the closure of the mesozoic tethys ocean and the deformation of the adriatic passive margin during tertiary and quaternary times the outer eastern parts of the belt were structured in quaternary i e up to middle pleistocene times the front of the chain is partially sealed by pliocene pleistocene foredeep deposits which represent the infill of the bradanic trough the upper portion of the middle pleistocene succession consists of marine sands and conglomerates that in the previous literature have been arranged in several orders of terraces analysis of aerial photographs and geomorphological mapping has shown the occurrence of prominent geomorphic lineaments which appear to control the local drainage pattern some of these structures coincide with the map trace of normal faults that produce vertical offsets of the marine terrace surfaces in the order of ca 10 m each many of the fault escarpments reduce their elevation and terminate laterally in other cases fault escarpments are laterally continuous and can be traced for up to 3 4 km scarp height is between 2 and 10 m their mean trend ranges from nne ssw to ene wsw and defines an arcuate pattern that mimics the present coastline an accurate geomorphological sedimentological and stratigraphic analysis has been carried out in a selected area of the bradanic trough pisticci transect to investigate in detail the relationships between normal faults and the development of the terraces this analysis allowed us to recognise five facies associations related to the upper and lower beachface and to the neritic clays which represent the substratum of the terraces more importantly we observed that all the terraced deposits in the pisticci transect could be referred to a single sedimentary body displaced by faults the terraced deposits are related to an event of beach progradation of middle pleistocene age which has been documented in other areas of the italian peninsula these results outline an intimate relationship between the arcuate trend of the recognised fault set and the present coastline pattern the development of the normal faults can be related to large scale gravitational processes developed after the general tilting towards the se of the bradanic trough

subglacial deformation and water pressure cycles as a key for understanding ice stream dynamics evidence from the late ordovician succession of the djado basin niger subglacial deformation is crucial to reconstructing glacier dynamics sediments associated with the late ordovician ice sheet in the djado basin niger exhibit detailed structures of the subglacial shear zone three main types of subglacial shear zones ssz are discriminated the lowermost ssz developed on sandstones displays riedel macrostructures and cataclastic microstructures these resulted from brittle deformation associated with strong glacier bed coupling and low pore water pressure where they developed on a clay rich bed the overlying ssz display s c to s c fabrics sheath folds and dewatering structures these features indicate high ductile shear strain and water overpressure on fine grained sand beds the ssz exhibit homogenized sand units with sand stringers interpreted as fluidized sliding beds the succession of subglacial deformation processes depends on fluid pressure behavior in relation to subglacial sediment permeability fluid overpressure allows subglacial sediment shear strength and ice bed coupling to be lowered leading to ice streaming

does porewater or meltwater control tunnel valley genesis case studies from the hirnantian of morocco several ordovician tunnel valleys are exposed in the moroccan anti atlas mountains including the alnif and the foum larjamme tunnel valleys located 150 km away from each other sedimentological and deformational analyses of these two glacial troughs reveal that differing processes lead to their formations the alnif tunnel valley contains numerous deformation structures within sediments both below and above the main glacial erosion contact surface ball structures and clastic dykes occur within preglacial sediments down to 35 m below glacial incisions while overlying glacial sediments contain fluted surfaces clastic dykes dewatering structures folds and radial step normal faults the characteristics of the alnif tunnel valley can be explained by a porewater pressure driven model of formation where the localized increase of basal shear stress and porewater pressure underneath subglacial deforming zones lead to the development of a dense hydrofracture network in the preglacial bed these processes of hydraulic brecciation promoted subglacial remobilization of the preglacial material and contributed to the formation of the tunnel valley the foum larjamme tunnel valley displays undisturbed preglacial sediments and few dewatering structures at the base of the glacial sedimentary infill which suggests relatively low porewater pressures within the tunnel valley during formation this second type of tunnel valley where porewater pressure remained relatively low appears to have been formed by meltwater erosion the undulating base of the foum larjamme tunnel valley implies progressive erosion by a stable subglacial braided network of nye channels or alternatively by channels migrating laterally during episodic minor subglacial outbursts these two tunnel valleys highlight the regional variability of processes involved in the formation of tunnel valleys the distribution of palaeo ice streams in north africa illustrate that morphologies and processes involved in the formation of tunnel valleys vary between ice stream and inter ice stream zones due to variations in meltwater availability the topography and bed lithological properties

role of synsedimentary strike slip faults in the formation of moroccan triassic basins upper triassic sandstone and siltstone infilled basins in the massif ancien of the high atlas morocco are distributed along a complex east northeast trough at the boundary between the hercynian orogen and the west african craton the formation of these basins involved a dense pattern of pre existing faults hydroplastic slickensides which affect nonlithified sediments help identify not only dip slip but also strike slip faults together with other tectonic and sedimentary structures the directional distribution of these faults leads to a model in which extension varies from north northwest during lower unit sandstone infilling to northwest during upper unit siltstone infilling the latter direction is compatible with the formation of the lower liassic intrusional doleritic dikes of the anti atlas

neogene to quaternary sedimentary basins in the south adriatic central mediterranean foredeeps and lithospheric buckling up to several kilometers deep sedimentary basins of neogene to quaternary age are found in the south adriatic between the apennines and the dinarides albanides they are the apennines foredeep the central adriatic basin and the south adriatic basin two regional seismic lines 260 and 170 km long across the entire system provide hitherto unavailable constraints on the kinematics and dynamics of basin development the apennine foredeep imaged along the lines formed in middle to late pliocene times through a rapid westward tilting of the basin floor a paleobathymetry of few kilometers was created in which allochthonous bodies were emplaced and sediments deposited unaffected by deformation and farther rotations the central and south adriatic basins formed in neogene to quaternary times and are both characterized by strong subsidence in their central parts gradually diminishing toward the edges in the sw and ne depocenters did not shift laterally through time subsidence rates increase through time and subsidence continued also following the end of main shortening episodes in the dinarides albanides the central and south adriatic basins form two crustal scale synclines with subsidence concentrated in their central parts basins geometries and subsidence patterns indicate that the adriatic crust has undergone episodes of buckling since miocene times wavelengths and amplitudes of such folds change along strike corresponding to mechanical changes of the folded medium

on the post 25 ma geodynamic evolution of the western mediterranean during the neogene and quaternary western mediterranean geodynamics were dominated by the eastward migration of the apenninic arc and associated back arc basins the migration was controlled by retreat of the apenninic slab and was associated with boudinage of the lithosphere in the back arc area palaeo reconstruction of the kinematics of the arc suggests about 775 km of migration from the late oligocene to present along a transect from the gulf of lions to calabria a maximum of 135 km of n s converge occurred between africa and europe during the same time span the western mediterranean was thus mainly shaped by the migration of the slab related to west directed subduction it is hypothesized that minor n s convergence deformed the arc but was not the cause of its formation 1998 elsevier science b v all rights reserved