slope processes in weathered volcaniclastic deposits within the city of naples the camaldoli hill case we describe the slope processes acting on camaldoli hill the main volcanic feature of the neapolitan area whose geological evolution and setting have been reconstructed the backbone of the hill includes the remnants of two partially superposed tuff cones lying between the campanian ignimbrite ci and the neapolitan yellow tuff nyt this sequence is mantled by pyroclastic anthropogenic and epiclastic deposits with abrupt thickness and facies variations the structural setting of the hill mainly results from several phases of reactivation of the ci caldera faults which were active until about 9 5 ka deformation younger than 15 ka is evidenced by landslide deposits caused by slope instability from volcano tectonism and by a high angle erosional unconformity formed in response to a base level lowering a stratigraphic analysis of the reworked deposits at the foot of the slopes allowed us to define both depositional mechanisms and sedimentation rates the results of combined volcanological geomorphological and engineering geological studies permitted us to constrain and quantify past geological processes and hypothesis about the future evolution of the hill present day slope processes on camaldoli hill are largely controlled by the presence of weathered and reworked deposits whose nature and thickness have been analysed and mapped in detail four main kinds of slope processes have been recognized falls and toppling failures from nyt small scale slides in the weathered and pedogenized loose cover mixed events represented by slides evolving to hyperconcentrated flows mud flows and debris flows and areal and linear erosion consequently a high number of mass movements not previously documented have been mapped at the same time an insight into the sedimentation rate due to the overall slope processes covering a time span of about 5 ka was given some final considerations regarding landslide hazard are presented in the context of the most suitable remedial works

mineralogy and chemistry of massive sulfide deposits from the juan de fuca ridge six hydrothermal vent sites and associated benthic communities were located in the axial valley of the southern juan de fuca ridge using transponder navigated bottom photography the hydrothermal deposits form ledges and shallow mounds within a central zone characterized by a linear bathymetric depression and numerous collapse features the flat valley floor adjacent to the central zone consists of ferrobasalt lobate flows and sheet flows sediment cover is minimal vent sites are characterized by concentrations of tube worms clams benthic siphonophores and several unidentified fauna two types of massive sulfide were dredged from one of the vent sites type a samples are angular slabs of dark gray zn rich sulfide with interlayers and a thin partly oxidized crust of fe sulfide these layered sulfide aggregates appear to be fragments of a sulfide wall enclosing an active hydrothermal vent the outer sulfide wall is composed mainly of colloform fe sulfide and fe poor sphalerite deposited under lower temperature conditions whereby sea water and hydrothermal fluid mix above the discharge point with continued sulfide deposition the wall inhibits mixing of sea water and hydrothermal fluid inside the wall the intensifying hydrothermal system deposits a higher temperature assemblage of granular fe rich sphalerite wurtzite pyrite and minor cu fe sulfide the zonation in wurtzite from fe rich cores to fe poor rims may result from a late stage cooling of the hydrothermal fluid and or a change in fluid chemistry the sulfide wall grows outward where a rupture in it permits the escape of high temperature fluid and then deposition of a secondary shell over the breakthrough point as temperature increases earlier formed minerals dissolve and zn fe and pb migrate toward the outer sulfide wall tube worms flourished in the outer wall of type a samples and abandoned tube structures served as conduits for the late stage hydrothermal fluids type b sulfide samples are subrounded spongy textured fragments composed almost entirely of dendritic aggregates of pale fe poor colloform sphalerite and opaline silica this type of sulfide is deposited in open space by moderate to low temperature fluid discharging at a slow but variable rate the fluid becomes increasingly oxidizing resulting in late stage deposition of hematite barite and sulfur type b samples show little evidence of burrowing animals this type of sulfide may be deposited in settings peripheral to sites of focused discharge

geochemistry of meteorite rich marine limestone strata and fossil meteorites from the lower ordovician at kinnekulle sweden abstract thirteen fossil meteorites 1 5 9 cm have been found in lower ordovician orthoceratite limestone at kinnekulle sweden the meteorites were recovered from a 3 5 m thick quarried interval in the middle of a 30 m thick section of orthoceratite limestone the section formed in an epicontinental sea at very slow sedimentation rates 0 2 cm ka the limestones of the lower two thirds of the section are reddish brown except in the quarried interval where a conspicuous 1 m thick grey limestone bed occurs ten of the meteorites were found in a thin bed below the grey limestone one was found in the grey limestone and two in the red limestone above the meteorites are almost completely pseudomorphosed primarily by calcite and barite they were identified by their content of chromite grains and chondrule pseudomorphs the central part of one of the meteorites shows iridium 800 ppb gold 550 ppb and chromium 4400 ppm concentrations in typical chondritic abundances centimeter resolution profiles for iridium and eight other elements have been established through the quarried interval at a site at 4 km distant from the meteorite producing quarry in the reddish brown parts ir concentrations carbonate free basis lie typically in the range 300 400 ppt compared with 50 ppt ir in average shale in the grey limestone the ir concentrations are lower around 100 150 ppt iridium correlates with iron and appears to be related to sedimentation rate and or iron redox state rather than to any variations in the composition of the siliciclastic fraction with estimated sedimentation rates as above the excess ir flux to the sediment was 30 ng cm 2 ma which is a factor 2 3 higher than the present total ir flux and one order of magnitude higher than the extraterrestrial ir flux to the pacific sea floor our data cannot discriminate to what extent the ordovician ir enrichments are related to extraterrestrial matter or to precipitation of ir from seawater in recent deep sea sediments seawater derived ir enrichments are associated with mn oxides but no similar association occurs in the orthoceratite limestone the ten meteorites in the bed below the grey limestone reflect minimum meteorite accumulation rates of one meteorite per 150 m 2 and 175 ka probably the ten meteorites are related to a local strewn field rather than to background influx minimum accumulation rates calculated on three meteorite finds 20 g in the entire quarried interval give one meteorite per 570 m 2 and 1 17 ma which is one order of magnitude higher than present day large area averaged meteorite influx rates the probability is low that the small area 2 of the sea floor studied would happen to be one where an unusually high number of meteorites struck our results may reflect that meteorite and possibly also extraterrestrial ir influx rates were substantially higher than at the present during a period in the early ordovician enhanced influx rates could be related to an asteroid collision in space

iron supply and demand in the upper ocean is extraterrestrial dust a significant source of bioavailable iron interplanetary dust particles accrete on the earth at a rate of 40 ktons yr 1 some 90 of this material evaporates in the atmosphere producing a bioavailable iron flux of 3 10 7 mol fe m 2 yr 1 this extraterrestrial fe flux is 30 300 of the eolian flux of bioavailable iron transported from terrestrial sources in remote marine regions and 20 of the upwelled fe flux in the southern ocean extraterrestrial fe may play an important role in regulating the marine carbon cycle in these regions

the age of the neapolitan yellow tuff caldera forming eruption campi flegrei caldera italy assessed by 40ar 39ar dating method abstract the neapolitan yellow tuff nyt is the product of the largest known trachytic phreatoplinian eruption it covered an area larger than 1000 km2 with an estimated volume of about 40 km3 of erupted magma during the course of the eruption a caldera collapsed within the previously formed campanian ignimbrite caldera the resulting nested structure strongly influenced the following volcanic activity in the campi flegrei caldera as previous dating of the nyt does not converge toward a unique result a new set of 40ar 39ar age determinations has been carried out to better constrain the age of the eruption two variants of the 40ar 39ar dating method were applied to determine the age of the nyt eruption 1 single crystal total fusion sctf on an individual phenocryst of feldspar and 2 laser incremental heating lih on bulk aliquots of feldspar phenocrysts the results of the sctf analyses show that the overall sample weighted mean age derived from the conventional age calculation is 15 6 0 8 ka a weighted mean of the isochron age is 15 3 1 2 ka 2 and has been assumed as the best indicator of age to be derived from the sctf analyses the lih analyses results show that plateau ages vary from 15 4 0 5 to 14 5 0 5 ka the overall weighted mean age of the isochron results is 14 9 0 4 ka 2 this result has been assumed as the reference age for the nyt eruption and agrees with the sctf age the new age obtained for the nyt deposits is of great relevance for the understanding of the evolution and the present state of the campi flegrei caldera and collocates the nyt in a crucial stratigraphical position to date the climatic oscillations that occurred between the late glacial and the holocene

asteroid breakup linked to the great ordovician biodiversification event the great ordovician biodiversification event coincides 470 million years ago with the break up of a large asteroid and the resultant frequent bombardment of earth with asteroid fragments

simple shearing block resurgence in caldera depressions a model from pantelleria and ischia abstract similar resurgent blocks occur in caldera depressions at the islands of pantelleria and ischia the two blocks which are tilted show similar deformation patterns and similar distributions of volcanic vents related to resurgence the remaining parts of the floors of the two calderas are not deformed similarities between the two features are so striking that the resurgence mechanism must have been alike a dynamic model for resurgence is presented and called simple shearing block resurgence the triggering mechanism is an increase of the magmatic pressure in the upper part of a shallow magma chamber which results in a vertical direction of the maximum stress applied on the roof rocks the block is first defined by high angle inland dipping marginal detachments and then deformed through a simple shearing mechanism reverse faults on its mostly uplifted side determine an horizontal shortening of the block which is balanced on the opposite side by normal faults oblique movements take place along the other two sides due to this distribution of the stress around the block magmas can reach the surface only through the extensional faults on the less uplifted side

a global rain of micrometeorites following breakup of the l chondrite parent body evidence from solar wind implanted ne in fossil extraterrestrial chromite grains from china previous studies of limestone beds of mid ordovician age from both sweden and china show that the earth saw an at least two orders of magnitude increase in the influx of extraterrestrial material approximately 470 ma following the disruption of an l chondrite parent body in the asteroid belt recovered extraterrestrial material consists of fossil meteorites and sediment dispersed extraterrestrial chromite sec grains both with l chondritic origin ne isotope analysis of sec grains from one of the swedish limestone sections revealed that the vast majority of the grains were delivered to earth as micrometeorites in this study we extend the previous work both in time and geographically by measuring concentrations and isotopic ratios of ne in individual sec grains 60120 mu m in diameter from three different beds from a contemporary middle ordovician limestone section in china all of the chinese sec grains 44 in total contain surface implanted ne of fractionated solar wind composition implying that these grains were as in the case of the swedish sec grains delivered to earth as micrometeorites this gives further compelling evidence that the two to three orders of magnitude increase in the influx of micrometeoritic material following the breakup of the l chondrite parent body was indeed a global event the rain of micrometeorites prevailed for at least 2 myr the estimated time of the deposition of the topmost chinese bed after the breakup event less

stratigraphic record of the asteroidal veritas breakup in the tortonian monte dei corvi section ancona italy the discovery of elevated concentrations of the cosmogenic radionuclide 3he in deep sea sediments from ocean drilling program odp site 926 atlantic ocean and odp site 757 indian ocean points toward accretion of extraterrestrial matter probably as a result of the catastrophic disruption of a large asteroid that produced the veritas family of asteroids at ca 8 3 0 5 ma and which may have had important effects on the global climatic and ecologic systems here we investigated the signatures possibly related to the veritas event by performing a high resolution multiproxy stratigraphic analysis through the late tortonian early messinian monte dei corvi section near ancona italy closely spaced bulk rock samples through a 36 m thick section approximately spanning from ca 9 9 ma to ca 6 4 ma show an 5 fold 3he anomaly starting at ca 8 5 ma and returning to background values at ca 6 9 ma confirming the global nature of the event we then analyzed at 5 cm intervals bulk rock samples for sedimentary and environmental proxies such as magnetic susceptibility calcium carbonate content total organic carbon and bulk carbonate 18 o and 13 c through a 21 m thick section encompassing the 3he anomaly available high resolution sea surface temperature data via alkenone analyses for this site show a temperature decrease starting exactly at the inception of the 3he anomaly cyclostratigraphic fast fourier transform spectral analyses of the proxies indicate an age of 8 47 0 05 ma for the inception of the 3he anomaly a search for impact ejecta analogous to what is present in the late eocene where both a 3he anomaly and large scale impact events are recorded was not successful detailed cyclostratigraphic analyses of our data suggest that the changes in the stable isotope series and environmental proxy series through this late tortonian time interval had a common forcing agent and that perturbations of orbitally forced climate cycles are present exactly through the interval with the enhanced influx of extraterrestrial 3he thus the chemostratigraphic evidence for a collisional event that created the veritas family of asteroids coinciding with climate perturbations on earth suggests yet another form of interaction between earth and the solar system

beyond black shales the sedimentary and stable isotope records of oceanic anoxic events in a dominantly oxic basin silurian appalachian basin usa abstract episodes of instability in the global climato oceanic system have become the hallmark of the silurian period these events are marked by six large positive carbon isotope excursions associated with major extinctions the widespread environmental consequences of these perturbations of the global carbon cycle remain poorly documented a high resolution chronostratigraphic reconstruction of the appalachian foreland basin afb provides a framework to evaluate environmental signatures of two of these carbon isotope excursions valgu and ireviken events telychian sheinwoodian at a regional scale integration of published biostratigraphic range data mapping of sequence stratigraphic surfaces and facies and generation of high resolution carbon isotope profiles for several transects provides precise correlation of the basin stratigraphy yielding a high resolution temporal framework this chronostratigraphic reconstruction of the afb highlights the importance of time specific facies tsf during these intervals for instance packages of red green and gray marine rocks separately occupied discrete time intervals cutting across local facies belts indicative of shallow to deep marine environments similarly widespread iron mineralization occurred during discreet time slices as bathtub rings rimming the margins of the basin changes from one time specific facies to the next are coincident with changes in carbon isotope values indicating a genetic link between fractionation of the global carbon reservoir and redox changes from generally oxic to anoxic oceanic conditions in parts of the afb the basal part of the study interval was deposited during the valgu event this first event begins with an unconformity marking global lowstand this fall in sea level was coincident with rising carbon isotope values as recorded in adjacent basins a slight sea level rise and flooding of the subaerial unconformity occurred near the peak in carbon isotope values oxidized iron minerals were deposited in a zone that extended from the lower shoreface into the basin center pinching out into shallower parts of the basin thin pyrite phosphorite glauconite layers associated with black shales in the basin center were deposited over these ferruginous strata as the event ended and carbon isotope values shifted negatively to a more stable baseline temperatures warmed sea level reached a silurian high and oxic conditions associated with very low rates of organic carbon oc burial were established these conditions were relatively stable for nearly four million years this long period of stasis was punctuated by the ireviken event which displays a strikingly similar progression of tsf patterns yet more intense and longer lived than the preceding valgu event with the first positive shift in carbon isotopes at the onset of the ireviken event the basin redox system changed from largely oxidizing to reducing coincident with a rapid drop in sea level and an abrupt reappearance of iron mineralization on the basin margins the sea level fall associated with the shift to peak values of the carbon isotope excursion is marked by the progradation of a significant body of sand well out into the basin during this sea level drop conditions in the basin center became highly reducing and periodically sulfidic widespread ironstones and ankeritic carbonates were deposited isochronously rimming the shallow basin margins where they alternated with light gray pyritic shales indicating fluctuating redox conditions a large negative carbon isotope excursion of 3 is coincident with a shift from regression to transgression suggesting glacial melting via methane release continued deposition of ironstones through this time interval suggests a primary link to shallow marine redox processes rather than large scale transgression or regression of the shoreline the ironstones are overlain by gray to black pyritic shales deposited across all environments revealing a final stage of redox progression into sustained sulfidic conditions as peak values of the carbon isotope excursion returned to a high stable baseline near 4 the similar expression of tsfs within the afb of these two global events demonstrates that fractionation of the global atmospheric and oceanic carbon reservoirs had a predictable cascading impact on shallow sea floor environments the associated redox processes reveal the dynamic regional interactions of a shallow oxic epicontinental water mass with a broader anoxic oceanic water mass providing valuable insight into the origin of some of the largest extinctions in the silurian period

l chondrite asteroid breakup tied to ordovician meteorite shower by multiple isochron 40ar 39ar dating radiochronometry of l chondritic meteorites yields a rough age estimate for a major collision in the asteroid belt about 500 myr ago fossil meteorites from sweden indicate a highly increased influx of extraterrestrial matter in the middle ordovician 480 myr ago an association with the l chondrite parent body event was suggested but a definite link is precluded by the lack of more precise radiometric ages suggested ages range between 450 30 myr and 520 60 myr and can neither convincingly prove a single breakup event nor constrain the delivery times of meteorites from the asteroid belt to earth here we report the discovery of multiple 40ar 39ar isochrons in shocked l chondrites particularly the regolith breccia ghubara that allow the separation of radiogenic argon from multiple excess argon components this approach applied to several l chondrites yields an improved age value that indicates a single asteroid breakup event at 470 6 myr fully consistent with a refined age estimate of the middle ordovician meteorite shower at 467 3 1 6 myr according to a geologic time scale 2004 our results link these fossil meteorites directly to the l chondrite asteroid destruction rapidly transferred from the asteroid belt the increased terrestrial meteorite influx most likely involved larger projectiles that contributed to an increase in the terrestrial cratering rate which implies severe environmental stress

the influence of water on the strength of neapolitan yellow tuff the most widely used building stone in naples italy neapolitan yellow tuff nyt has been used in construction in naples italy since the greeks founded the city then called neapolis in the sixth century bce we investigate here whether this popular building stone is weaker when saturated with water an issue important for assessments of weathering damage and monument preservation to this end we performed 28 uniaxial compressive strength measurements on dry and water saturated samples cored from a block of the lithified upper member of the nyt our experiments show that the strength of the zeolite rich nyt is systematically reduced when saturated with water the ratio of wet to dry strength is 0 63 complementary experiments show that two other common neapolitan building stones piperno tuff and the grey campanian ignimbrite both facies of the campanian ignimbrite deposit devoid of zeolites do not weaken when wet from these data and previously published data for tuffs around the globe we conclude that the water weakening in nyt is a consequence of the presence of abundant zeolites the block tested herein contains 46 wt of zeolites these data may help explain weathering damage in nyt building stones due to rainfall rising damp and proximity to the sea or water table and the observed link between rainfall and landslides rock falls and sinkhole formation in naples and the weathering of other buildings built from zeolite rich tuffs worldwide

asteroidal source of l chondrite meteorites abstract establishing connections between meteorites and their parent asteroids is an important goal of planetary science several links have been proposed in the past including a spectroscopic match between basaltic meteorites and 4 vesta that are helping scientists understand the formation and evolution of the solar system bodies here we show that the shocked l chondrite meteorites which represent about two thirds of all l chondrite falls may be fragments of a disrupted asteroid with orbital semimajor axis a 2 8 au this breakup left behind thousands of identified 1 15 km asteroid fragments known as the gefion family fossil l chondrite meteorites and iridium enrichment found in an 467 ma old marine limestone quarry in southern sweden and perhaps also 5 large terrestrial craters with corresponding radiometric ages may be tracing the immediate aftermath of the family forming collision when numerous gefion fragments evolved into the earth crossing orbits by the 5 2 resonance with jupiter this work has major implications for our understanding of the source regions of ordinary chondrite meteorites because it implies that they can sample more distant asteroid material than was previously thought possible

hydrothermal petroleum in mineralized mounds at the seabed of guaymas basin petroleum has been dredged from an active hydrothermal mound area in the southern rift of guaymas basin gulf of california this organic matter is composed of gasoline range aliphatic and aromatic hydrocarbons and predominantly residual polar asphaltic material the aliphatic hydrocarbons of two bitumen samples have very different boiling range and composition both samples contain polynuclear aromatic hydrocarbons and olefins which indicate formation at pyrolytic temperatures the overall compositional data indicate an origin from biological detritus by thermal alteration and rapid quenching by hydrothermal removal followed by condensation at the seabed

growth of large sulfide structures on the endeavour segment of the juan de fuca ridge abstract mapping and sampling with dsrv alvin has established that sulfide blocks 0 5 m across dredged from the axial valley of the endeavour segment at 47 57 n are samples of unusually large sulfide structures the steep sided structures up to 30 m in length 20 m in height and 10 15 m across are localized by venting along normal faults at the base of the western axial valley wall and are distributed for about 200 m along strike paralleling the 020 trend of the ridge crest high temperature fluids 350 to more than 400 c pass through the massive sulfide structures and enter seawater through small concentric nozzle like features projecting from the top or the sides of the larger vent structures diffuse low temperature flow is pervasive in the vicinity of the active sulfide structures exiting from basalt and sulfide surfaces alike evidence of recent volcanic activity is sparse the two largest samples taken with the dredge would not have been recoverable using the submersible these samples represent massive complex portions of the sulfide structures which were not closely associated with rapid high temperature fluid flow at the time of sampling they contain textural evidence of sealed hydrothermal fluid exit channels mineralogy is dominated by fe sulfides nnd amorphous silica pyrite marcasite wurtzite chalcopyrite and iss are the most common sulfide phases pyrrhotite galena and sphalerite are present in trace amounts barite amorphous silica and chalcedony are the only non sulfide phases anhydrite is not observed in any of the dredge samples although it is common in the chimney like samples recovered by alvin specific mineralogical textural zones within the dredge samples are anaoogous to individual layers in east pacific rise at 21 n and southern juan de fuca ridge samples with two exceptions a coarse grained highly porous fe sulfide rich interior containing sulfidized tubeworm casts and a 2 5 cm thick zone near the outer margin of the samples dominated by late stage amorphous silica the porous interior may have formed by dendritic crystal growth from a slowly circulating fluid within a large enclosed chamber the amorphous silica deposited from a seawater hydrothermal fluid mixture percolating slowly through the walls of the enclosed chamber conductive cooling of the fluid as it traversed the walls allowed amorphous silica to precipitate these silica rich zones are the densest most durable portions of the structures and may be responsible for the lasting stability of the large sulfide features observations in these samples are consistent with two distinct phases of development phase 1 is analogous to chimney growth and construction at 21 n and ends when flow channels become sealed to rapid flow of through going fluid the flow is evidently redirected within the structure phase 2 includes dissolution of anhydrite and precipitation of amorphous silica during conductive cooling of sluggishly circulating hydrothermal fluid or seawater hydrothermal fluid mixtures evolution of vent structures through phase 2 allows lateral and vertical growth of unusually large structures

mobility of a large volume pyroclastic flow emplacement of the campanian ignimbrite italy abstract the trachytic campanian ignimbrite originally exposed over a 30 000 km 2 area around naples italy is the product of a highly energetic gas rich eruption the deposit lies in valleys and isolated watersheds and in its medial and distal extent to the south north and east of naples the campanian pyroclastic current encountered mountains exceeding 1000 meters anisotropy of magnetic susceptibility ams measurements indicate that the campanian pyroclastic current the transport system traveled radially outward from the phlegrean fields area but the ignimbrite forming flow the deposition system that developed from the base of the transport system moved downslope from mountainsides to valleys including slopes facing the eruption source and flowed down drainage systems from intermontane basins the campanian pyroclastic current flowed 35 km over the water of the bay of naples to deposit 43 m of ignimbrite on the south shore and also overtopped a 685 1000 m high ridge of the sorrento peninsula to deposit more on the other side the distribution of the ignimbrite and the measured flow directions suggest that the campanian pyroclastic current moved across the landscape as an expanded and therefore turbulent decompressing flow rather than as a high density nonturbulent sheet like current moving over mountains by momentum acquired by eruption column collapse strong expansion is corroborated by shard morphology that indicates derivation from highly inflated pumice and suggests vesicles must have been at least 80 by volume of the original magma

physical chemical and biological investigation of an unconformity between limestone and sandstone in a coastal area iriomote island case study abstract although physical and chemical weathering due to groundwater and or wind flow is frequently observed in outcrops the geological mechanism responsible for these processes is not fully understood in the northern coastal area of iriomote island japan rock collapse caused by weathering of an unconformity between pleistocene limestones and miocene sandstones has been observed the boundary is characterised by distinctive columnar structures in the sandstone possibly induced by preferential weathering along desiccation induced fractures we found that the formation processes of the columns may be closely related to the rock collapse in this study the unconformable layer between the pleistocene ryukyu group and the miocene yaeyama group was investigated to determine the geological processes involved such as the formation weathering mechanisms and alteration of chemical and physical properties consequently the macroscopic and microscopic geometric forms compressive strength and mineral composition of the columnar structures were determined carbon stable isotopic analysis of the columns indicated that microbial solidification phenomena might have been involved in column formation a formation scenario for the columns has subsequently been proposed and we found that past stratification processes based on chemical and biological reactions with desiccation cracks on sandy soil directly influenced the modern dynamic rock collapse

plutonium 238 observations as a test of modeled transport and surface deposition of meteoric smoke particles 1 there are large uncertainties in the transport and surface deposition of upper atmospheric particles used to construct climate proxies here we use a 3 d chemistry climate model ccm to simulate the transport and deposition of plutonium 238 oxide nanoparticles formed after the ablation of a power unit in the upper stratosphere 11 s in 1964 the model reproduces both the observed hemispheric asymmetry and time scale of pu 238 deposition we then use the ccm to investigate the transport of meteoric smoke particles msps from the upper mesosphere the strongest msp deposition is predicted to occur at middle latitudes providing a significant source of fe fertilization to the southern ocean the model also predicts substantially more deposition in greenland than in antarctica by a factor of 15 in agreement with ice core measurements showing that climate proxy measurements from a limited number of sites must be interpreted with care

a rain of ordinary chondritic meteorites in the early ordovician forty fossil meteorites with a total original mass of v7 7 kg have been recovered in the first systematic search for fossil meteorites pursued in an active quarry in lower ordovician 480 ma marine limestone in southern sweden the meteorites represent at least 12 different falls over a seafloor area of v6000 m 2 during 91 75 myr making the quarry one of the most meteorite dense areas known in the world geochemical analyses of relict chromite grains indicate that all or most of the meteorites are ordinary chondrites and probably l chondrites mechanisms for meteorite delivery from the asteroid belt to earth were the same 480 ma as today however the flux was one to two orders of magnitude higher most likely reflecting the disruption of the l chondrite parent body at about that time this is a major event in late solar system history which may also have led to an enhanced flux of asteroids to earth during v30 myr fl 2001 elsevier science b v all rights reserved

ooidal ironstones from ordovician gondwana a review abstract ooidal ironstones occur widely in the ordovician shelf sequences of sw europe the western european platform the avalonian terranes and north africa they form the most important group of deposits of the earlier of the two major periods of phanerozoic ooidal ironstone generation ordovician devonian and jurassic paleogene individual ooidal ironstone horizons are generally thin less than 2 m but may have a very wide lateral extent the ooidal ironstones represent sediments formed under extremely low sedimentation rates and were most commonly developed as the initial deposit above a disconformity ooidal ironstone producing events occurred almost synchronously over wide areas of the gondwanan shelf reflecting the uniform sedimentary conditions across large areas of the shallow low gradient shelf clastic sediments deposited during periods of normal sedimentation show similar remarkable uniformity over large areas this geometry together with the abundant fauna both micro and macro in the ironstone facies means that these thin ironstone beds form important marker horizons for correlation within the region the stratigraphic distribution of the ironstones shows strong correlation with periods of high relative sea level sedimentological study of examples in sw europe indicate that they separate transgressive systems tracts with parasequences bounded by phosphorites from the early part of the following highstand systems tracts without significant parasequences and are therefore interpreted to lie on maximum flooding surfaces such maximum flooding surfaces occur in the early llavirn the late llanvirn the early caradoc and the early ashgill of sw europe outside sw europe the ooidal ironstones may have a different relationship to the sequence stratigraphy possibly reflecting the influence of absolute water depth

phanerozoic oolitic ironstones geologic record and facies model oolitic ironstonesl composed predominantly of ooidsl of ferric oxide and chamosite accumulated throughout much of phanerozoic time figure 1 and some of them have been important ore deposits they are built of two very common products of weathering iron oxide and clay but they constitute a distinctive and subordinate sedimentary facies for which there is no simple modem analogue as a result considerable disagreement has attended more than 125 years of discussion about their origin early analyses of these rocks for example the minette are of france focused mainly on their chemical and mineral composition and on processes of diagenesis more recent work has described their sedimentary textures and structures as well as their general facies and depositional environments ad eleye 1973 brookfield 1973 corbin 1980 hallam 1975 karpov et a11967

the restless resurgent campi flegrei nested caldera italy constraints on its evolution and configuration abstract we have collected new stratigraphic data in the campi flegrei caldera through surface geological mapping and study of cores drilled to various depths we integrate these data with geological geochronological and geophysical constraints available in the literature to reconstruct the volcanic and deformational history of the caldera the caldera is a resurgent nested structure resulting from two main collapses related to the campanian ignimbrite 37 ka and the neapolitan yellow tuff 12 ka eruptions while the structure is affected by a broad subsidence ongoing local resurgence and unrest occur inside the younger nested caldera structure although most of the caldera floor consists of multiple structural blocks due to long term deformations magmas were able to erupt only in one sector of the resurgent part the caldera has shown signs of unrest during the past 25 years with short term deformations that have generated a net uplift of 3 5 m the short term deformations are related to the neapolitan yellow tuff caldera resurgence and interpreted as the net result of brittle and ductile components the long term deformations likely represent the sum of the permanent brittle component of each short term deformational event

gold in sea floor polymetallic sulfide deposits bulk chemical analyses of 48 samples of hydrothermal precipitates from seven polymstallic sulfide deposits at sea floor spreading centers in the eastern pacific reveal distinct patterns of gold enrichment high gold contents are found in samples from two sulfide deposits the axial seamount 45057 n 130002 w and the southern explorer ridge 49045 6 n 130016 2 w a large 160 kg sample composed of silica barite and sphalerite from the top of the axial seamount deposit gives analyses up to 6 700 ppb au averaging 4 900 ppb au similar material from the southern explorer ridge gives analyses up to 1 500 ppb au averaging 660 ppb au detailed mineralogical studies together with bulk chemical analyses of a wide range of samples from these two sites reveal strong elemental associations and paragenetic controls on gold deposition gold at concentrations of about 200 ppb is associated with high cu 1 wt and mo up to 470 ppm at concentrations 800 ppb with high zn 10 wt ba 3 wt and sio 20 wt and at concentrations 1 200 ppb with high pb 0 1 wt ag 100 ppm as 300 ppm and sb 50 100 ppm samples with the highest gold values from both locations contain late sinterlike low temperature sulfosalts of pb as sb ag and s in a matrix of amorphous silica these sulfosalts are the probable repositories of the gold published analyses of au poor 300oc cu fe rich sulfides and subsequently remobilized by late sustained low temperature 250oc fluids and concentrated in sio ba zn rich precipitates near the surface suitable fluid chemistry is required to mobilize the gold and a favorable precipitation mechanism is needed to concentrate it these observations could explain the occurrence of high gold concentrations in selected ore types of some ancient massive sulfide deposits on land

magnitude and frequency of rock falls and rock slides along the main transportation corridors of southwestern british columbia the two main transportation corridors of southwestern british columbia are subject to a range of rock slope movements rock falls rock slides and rock avalanches that pose significant risks to r

late miocene carbon isotope records and marine biological productivity was there a dusty link 1 we examine whether or not a relationship exists between the late miocene carbon isotope shift 7 6 6 6 ma and marine productivity at four sites from the indian and pacific oceans ocean drilling program sites 721 1146 1172 and 846 we use a multiproxy approach based on benthic foraminiferal accumulation rates elemental ratios and dissolution indices and we compare these data to benthic foraminiferal 13c values measured on the same samples although some of these sites have been targeted previously in studies of either the late miocene early pliocene biogenic bloom sites 721 and 846 or the late miocene carbon isotope shift site 1172 our records are the first to establish paired proxy records of carbon isotopes and paleoproductivity allowing a direct assessment of a potential link our results indicate that at all sites productivity increased sometime during the 13c shift at three sites 721 1146 and 846 productivity increased at the beginning of the shift the correlation coefficients derived from linear regression between micropaleontologically derived productivity and foraminiferal 13c values are relatively high during the time interval containing the late miocene 13c shift and statistically significant at three of the sites carbon flux and isotope mass balance considerations illustrate that transfer of organic matter between the terrestrial and marine reservoirs together with enhanced oceanic upwelling best approximates observed changes in carbon isotope records and paleoproductivity we note that long term trend in the site 846 paleoproductivity record can be correlated to the long term trend in the site 848 eolian flux reconstructions of hovan 1995 hinting at a link between strengthened wind regime and productivity during the late miocene

accretion rates of meteorites and cosmic dust in the early ordovician abundant fossil meteorites in marine condensed lower ordovician limestones from kinnekulle sweden indicate that accretion rates of meteorites were one to two orders of magnitude higher during an interval of the early ordovician than at present osmium isotope and iridium analyses of whole rock limestone indicate a coeval enhancement of one order of magnitude in the influx rate of cosmic dust enhanced accretion of cosmic matter may be related to the disruption of the l chondrite parent body around 500 million years ago

late miocene global cooling and the rise of modern ecosystems a period of continental aridification and ecosystem change occurred about seven million years ago a global sea surface temperature reconstruction identifies cooling temperatures and a strengthened meridional temperature gradient at this time

the late eocene 187os 188os excursion chemostratigraphy cosmic dust flux and the early oligocene glaciation abstract high resolution records ca 100 kyr of os isotope composition 187os 188os in bulk sediments from two tropical pacific sites odp sites 1218 and 1219 capture the complete late eocene 187os 188os excursion and confirm that the late eocene 187os 188os minimum earlier reported by ravizza and peucker ehrenbrink earth planet sci lett 210 2003 151 165 is a global feature using the astronomically tuned age models available for these sites it is suggested that the late eocene 187os 188os minimum can be placed at 34 5 0 1 ma in the marine records in addition two other distinct features of the 187os 188os excursion that are correlatable among sections are proposed as chemostratigraphic markers which can serve as age control points with a precision of ca 0 1 myr we propose a speculative hypothesis that higher cosmic dust flux in the late eocene may have contributed to global cooling and early oligocene glaciation oi 1 by supplying bio essential trace elements to the oceans and thereby resulting in higher ocean productivity enhanced burial of organic carbon and draw down of atmospheric co2 to determine if the hypothesis that enhanced cosmic dust flux in the late eocene was a cause for the 187os 188os excursion can be tested by using the paired bulk sediment and leachate os isotope composition 187os 188os were also measured in sediment leachates results of analyses of leachates are inconsistent between the south atlantic and the pacific sites and therefore do not yield a robust test of this hypothesis comparison of 187os 188os records with high resolution benthic foraminiferal 18o records across the eocene oligocene transition suggests that 187os flux to the oceans decreased during cooling and ice growth leading to the oi 1 glaciation whereas subsequent decay of ice sheets and deglacial weathering drove seawater 187os 188os to higher values although the precise timing and magnitude of these changes in weathering fluxes and their effects on the marine 187os 188os records are obscured by recovery from the late eocene 187os 188os excursion evidence of the global influence of glaciation on supply of os to the ocean is robust as it has now been documented in both pacific and atlantic records

a russian record of a middle ordovician meteorite shower extraterrestrial chromite at lynna river st petersburg region numerous fossil meteorites and high concentrations of sediment dispersed extraterrestrial chromite ec grains with ordinary chondritic composition have previously been documented from 467 1 6 ma middle ordovician darriwilian strata these finds probably reflect a temporarily enhanced influx of l chondritic matter following the disruption of the l chondrite parent body in the asteroid belt 470 6 ma in this study a volkhovian kundan limestone marl succession at lynna river northwestern russia has been searched for ec grains 63 mu m eight samples forming two separate sample sets were collected five samples from strata around the asaphus expansusa raniceps trilobite zone boundary in the lower middle kundan yielded a total of 496 ec grains in 65 5 kg of rock average 7 6 ec grains kg 1 but up to 10 2 grains kg 1 these are extremely high concentrations three orders of magnitude higher than background levels in similar condensed sediment from other periods ec grains are typically about 50 times more abundant than terrestrial chrome spinel in the samples and about as common as terrestrial ilmenite three stratigraphically lower lying samples close to the a lepidurusa expansus trilobite zone boundary at the volkhov kunda boundary yielded only two ec grains in 38 2 kg of rock 0 05 grains kg 1 the lack of commonly occurring ec grains in the lower interval probably reflects that these strata formed before the disruption of the l chondrite parent body the great similarity in ec chemical composition between this and other comparable studies indicates that all or most ec grains in these russian mid ordovician strata share a common sourcethe l chondrite parent body less

the neapolitan yellow tuff a large magnitude trachytic phreatoplinian eruption eruptive dynamics magma withdrawal and caldera collapse the results of a detailed stratigraphical and volcanological study has allowed the definition of the neapolitan yellow tuff nyt as the largest known trachytic phreatoplinian eruption with an estimated volume of not less than 30 km3 dre the nyt sequence can be subdivided in a lower and an upper member sedimentological and textural variations in time and space indicate that different eruptive and depositional mechanisms operated during the eruption the lower member eruptive phase was characterized by alternating phreatoplinian and magmatic explosions while the upper member eruptive phase was characterized by a random sequence of phreatomagmatic and magmatic explosions particles produced by the same explosion were deposited contemporaneously by fallout and surge mechanisms either at different or at the same distance from the vent compositional variations show that the nyt sequence cannot be modeled as an inverted compositionally zoned magma body with magma becoming more basic in the course of the eruption the chamber composed of three geochemically distinct magma layers was tapped at different depths according to the eruption dynamics each phreatoplinian explosion tapped concurrently all the magma layers while magmatic explosions tapped only one of them the onset of the nyt caldera collapse is well constrained between lower and upper member eruptive phases the collapse which is only gravimetrically detectable occurred inside the larger phlegrean fields caldera which therefore can be defined as a nested caldera

deposition and diagenesis of clinton ironstones silurian in the appalachian foreland basin of pennsylvania clinton ironstones mid silurian on the southeastern margin of the appalachian foreland basin in central pennsylvania consist largely of skeletal grainstone storm beds whose skeletal fragments are extensively impregnated and replaced by ferric oxide other forms of iron mineralization consist of ooids superficial ooids cavity fillings and cements composed of ferric oxide and or chamositic clay and two generations of iron rich carbonate spar true oolite is rare small proportions of ferruginized grains are present in coarse lags at tops of some small scale 1 to 5 m coarsening upward sequences which are the record of mid shelf shoals from which the skeletal grainstone storm beds were derived ooids and superficial ooids are likely to have formed in dysaerobic conditions where the pycnocline of a highly stratified sea intersected shoal flanks ferrous iron from anaerobic deeper waters precipitated on quartz and skeletal fragment nuclei in weakly reducing conditions with episodic gentle agitation several stages of early diagenetic ferruginization affected skeletal grainstone storm beds and sequence capping coarse lags chamositic clay precipitated in pores and cavities of skeletal fragments within quartz sand adjacent to crinoid ossicles and as bed parallel connectors of large skeletal fragments as diagenesis progressed with further burial many skeletal fragments were extensively replaced by ferric oxide most chamositic clay altered to ferric oxide other chamositic clay matured from berthierine to chamosite and clusters of bladed specularite replaced parts of primary grains and secondary carbonate cements paleomagnetic and fluid inclusion analysis indicates that many late diagenetic changes took place at elevated temperatures during deen burial in an early phase of the alleghanian orogeny

conditions for generation of fire related debris flows capulin canyon new mexico comparisonoftheresponsesofthreedrainagebasinsburnedbythedomefireof1996innewmexicoisusedtoidentifythe hillslope channelandfirecharacteristicsthatindicateasusceptibilityspecificallytowildfire relateddebrisflow summer thunderstorms generated three distinct erosive responses from each of three basins the capulin canyon basin showed widespreaderosivesheetwashandrillingfromhillslopes andseverefloodingoccurredinthechannel thenorthtributary basin exhibited extensive erosion of the mineral soil to a depth of 5 cm and downslope movement of up to boulder sized material andatleastonedebrisflowoccurredinthechannel negligiblesurfacerunoffwasobservedinthesouthtributary basin thenegligiblesurfacerunoffobservedinthesouthtributarybasinisattributedtothelimitedextent andseverityof the fire in that basin the factors that best distinguish between debris flow producing and flood producing drainages are drainage basin morphology and lithology a rugged drainage basin morphology an average 12 per cent channel gradient andsteep roughhillslopescoupledwithcolluviumandsoilweatheredfromvolcaniclasticandvolcanicrockspromotedthe generation of debris flows a less rugged basin morphology an average gradient of 5 per cent and long smooth slopes mantled with pumice promoted flooding flood and debris flow responses were produced without the presence of waterrepellentsoils thecontinuityandseverityoftheburnmosaic theconditionoftheriparianvegetation theconditionofthe fibrous root mat accumulations of dry ravel and colluvial material in the channel and on hillslopes and past debris flow activity appearedtohavelittlebearingonthedistinctiveresponsesofthebasins publishedin2000byjohnwiley sons ltd

wildfire related debris flow initiation processes storm king mountain colorado a torrential rainstorm on september 1 1994 at the recently burned hillslopes of storm king mountain co resulted in the generation of debris flows from every burned drainage basin maps 1 5000 scale of bedrock and surficial materials and of the debris flow paths coupled with a 10 m digital elevation model dem of topography are used to evaluate the processes that generated fire related debris flows in this setting these evaluations form the basis for a descriptive model for fire related debris flow initiation the prominent paths left by the debris flows originated in 0 and 1st order hollows or channels discrete soil slip scars do not occur at the heads of these paths although 58 soil slip scars were mapped on hillslopes in the burned basins material derived from these soil slips accounted for only about 7 of the total volume of material deposited at canyon mouths this fact combined with observations of significant erosion of hillslope materials suggests that a runoff dominated process of progressive sediment entrainment by surface runoff rather than infiltration triggered failure of discrete soil slips was the primary mechanism of debris flow initiation a paucity of channel incision along with observations of extensive hillslope erosion indicates that a significant proportion of material in the debris flows was derived from the hillslopes with a smaller contribution from the channels because of the importance of runoff dominated rather than infiltration dominated processes in the generation of these fire related debris flows the runoff contributing area that extends upslope from the point of debris flow initiation to the drainage divide and its gradient becomes a critical constraint in debris flow initiation slope area thresholds for fire related debris flow initiation from storm king mountain are defined by functions of the form acr tan 3 s where acr is the critical area extending upslope from the initiation location to the drainage divide and tan is its gradient the thresholds vary with different materials

velocity and runout simulation of destructive debris flows and debris avalanches in pyroclastic deposits campania region italy the campanian apennines are characterized by the presence of monocline ridges mainly formed by limestone during the periods of volcanic activity of the somma vesuvius and phlegrean fields the ridges were mantled with pyroclastic materials in varying thickness the pyroclastics have been involved in destructive landslides both in historical time and in the recent past 1997 1998 1999 the landslides occur following intense and prolonged rainfalls in some cases landslides extended up to 4 km into the surrounding lowlands and reached towns causing severe destruction and over 200 deaths generally the landslides begin as small debris slides that develop into large shallow debris avalanches or debris flows involving pyroclastic horizons and colluvial soils 0 5 2 m thick on steep and vegetated slopes often at the heads of gullies during motion the landslide materials eroded vegetation and soils from the slope so that the moving material volume tended to increase then proceeding towards and beyond the base of the slopes the phenomena evolved into hyperconcentrated streamflow due to dilution by incorporating water the results of motion analyses are described an empirical rheological relationship was used including two principal terms that depend on the total normal stress and on the flow velocity on this basis the model has simulated the velocity and duration of debris avalanches and the distribution of the deposits the selected areas were those of sarno quindici and cervinara where a large amount of data is available both on the material properties and geomorphological setting it was found that the majority of the cases at the two sites can be simulated successfully with only one specific pair of rheologic parameters this provides the possibility for first order predictions to be made of the motion of future landslides such predictions will be a valuable tool for outlining potential hazard areas and designing remedial measures