assessing the reliability of magnesium in foraminiferal calcite as a proxy for water mass temperatures though many studies on the mg contents in the calcitic tests of foraminifers exist the processes controlling its uptake are still a matter of debate laboratory cultures offer an excellent opportunity to reveal these mechanisms the mg concentrations within single chambers of the planktic foraminifer globigerinoides sacculifer brady maintained under controlled laboratory conditions were measured 1 at variable temperatures 19 5 29 5 c and constant salinity and 2 at variable salinity 22 45 and constant temperature the experimental results suggest that under natural conditions temperature is the leading mechanism controlling the mg ca ratio temperature and magnesium are related proportionally a temperature increase of ca 10 c gives rise to an increase of the magnesium concentrations of ca 130 drastic unnatural salinity changes dominate the effects of temperature a 110 change in the mg ca ratio was observed when salinity was elevated or reduced by more than ca 10 specimens which underwent gametogenesis reveal significantly higher mg concentrations than specimens that did not release gametes partition coefficients for mg in foraminiferal calcite are orders of magnitude lower than values from inorganically precipitated calcite when comparing observed mg ca ratios of foraminiferal tests with predicted mg ca ratios calculated according to empirical equations it becomes evident that foraminiferal tests are undersaturated with respect to mg for the water temperature they have experienced apparently foraminifers are capable of controlling their mg concentration the physiological processes presumably responsible for such depressed mg ca ratios appear to be temperature controlled as deduced from the close relationship of the observed mg ca ratios and water temperature this study demonstrates that variations in temperature and salinity are definitely reflected in the mg content of foraminiferal tests magnesium may thus serve as a paleo proxy for past surface water temperatures as long as postdepositional changes and salinity variations are of subordinate importance or can be excluded

post glacial evolution of the indo pacific warm pool and el nino southern oscillation recent research has revealed new insights into the temperature size and variability of the indo pacific warm pool ipwp and the nature of the el nino southern oscillation enso since the last glacial maximum lgm sea surface temperature sst reconstructions from foraminiferal mg ca alkenone and revised coral sr ca palaeothermometry agree that ssts in the ipwp during the lgm were similar to 3degreesc cooler than at present in the central portion of the ipwf the rapid post glacial rise in sst led the deglaciation by similar to 3000 years to produce near modern ssts by the early holocene in contrast further west and north post glacial shifts in ssts in the south china and sulu seas are synchronous with abrupt climate changes in the north atlantic new evidence for the nature of the little ice age in the tropics has been obtained from a 420 year record of coral sr ca and 6180 from the great barrier reef australia this indicates that ssts and salinity were higher in the 18th century than in the 20th century the results suggest that the tropical pacific played a role as a source region of water vapour during the global expansion of little ice age glaciers the onset of modern enso periodicities is identified by palaeo enso records throughout the tropical pacific region similar to 5000 years ago with an abrupt increase in enso magnitude similar to 3000 years ago individual enso events recorded by corals reveal that the precipitation response to el nino temperature anomalies was subdued in the mid holocene the apparent non linear onset of enso in the late holocene appears to reflect abruptly enhanced interaction between the southern oscillation and the pacific intertropical convergence zone comparisons of precipitation variability recorded by great barrier reef corals with enso indices for the last 350 years confirms that non stationarity of enso teleconnections is a natural characteristic of modern climate c 2003 elsevier ltd and inqua all rights reserved

emplacement of pyroclastic density currents pdcs in a deep sea environment the val d aveto formation case northern apennines italy abstract the occurrence of pdc deposits in a foredeep basin sequence named val d aveto formation 32 29 ma northern apennines italy provides new information on the behavior of pyroclastic density currents entering the water in this work stratigraphic petrographic and mineralogical features that characterize three pyroclastic deposits have been described and analyzed in the field facies and lithological analysis on the blocky size fraction and in the laboratory image analyses on the blocky size detritus optical analyses of the microtextures mineralogical analyses through x ray powder diffraction xrpd and scanning electron microscope with energy dispersive x ray spectometry sem eds the deposits are lapilli to blocky size with a blocky size fraction constituted of accidental detritus in thin sections their groundmass texture varies from porphyritic to eutaxitic where coarser particles become close each others growth rims have been also detected around plagioclase crystals pyrite habits and oxidation and plagioclase albitization are consistent with hydrothermal temperature conditions of 200 c all these results have been compared with the information provided by modern examples of pdc deposits and laboratory experiments on the behavior of water hot particles mixing grain to grain collision has been considered as the main flow mechanism that sustained and avoided the disaggregation of the pdcs entering the water

a study of cleaning procedures used for foraminiferal mg ca paleothermometry the various cleaning steps required for preparation of foraminiferal samples for mg ca and sr ca analysis are evaluated for their relative importance and effects on measured elemental ratios it is shown that the removal of silicate contamination is the most important step for the measurement of mg ca ratios in an example bulk sample mg ca decreases from 10 5 to 2 5 mmol mol 1 during clay removal oxidation of organic material causes a lowering of sample mg ca in the order of 10 or approximately 1 c when converted to temperature use of dilute acid leaching to remove adsorbed contaminants causes partial dissolution of the sample carbonate and a corresponding decrease in mg ca reductive treatment also causes dissolution of the sample and a decrease in the mg ca ratio of up to 10 15 sample preparation for sr ca analysis does not require the same degree of rigor as is necessary for mg ca work the within run reproducibility of the method described here for g ruber in a core top sample from the arabian sea was 1 8 mean sample ratio was 4 72 mmol mol 1 when converted to temperature this becomes 28 0 2 c the equivalent result for sr ca was 0 5 mean ratio 1 44 mmol mol 1

volcanic stratigraphy a review abstract volcanic stratigraphy is a fundamental component of geological mapping in volcanic areas as it yields the basic criteria and essential data for identifying the spatial and temporal relationships between volcanic products and intra inter eruptive processes earth surface tectonic and climatic which in turn provides greater understanding of the geological evolution of a region establishing precise stratigraphic relationships in volcanic successions is not only essential for understanding the past behaviour of volcanoes and for predicting how they might behave in the future but is also critical for establishing guidelines for exploring economic and energy resources associated with volcanic systems or for reconstructing the evolution of sedimentary basins in which volcanism has played a significant role like classical stratigraphy volcanic stratigraphy should also be defined using a systematic methodology that can provide an organised and comprehensive description of the temporal and spatial evolution of volcanic terrain this review explores different methods employed in studies of volcanic stratigraphy examines four case studies that use differing stratigraphic approaches and recommends methods for using systematic volcanic stratigraphy based on the application of the concepts of traditional stratigraphy but adapted to the needs of volcanological environment

a simple evaluation of cleaning procedures on fossil benthic foraminiferal mg ca 1 recent studies suggest that benthic foraminiferal mg ca may be useful in reconstructing deep water temperature changes during the quaternary and on longer timescales rosenthal et al 1997 lear et al 2000 martin et al 2002 because changes in deep water temperature may be small sample preparation could play an important role in reconstructing accurate temperatures from shell mg ca a simple examination of changes in measured shell chemistry of benthic foraminifera from two intervals subjected to increasingly rigorous cleaning reveals that fossil benthic foraminiferal samples cleaned by oxidation yield lower mg ca values than samples only rinsed and weak acid leached reductive cleaning further lowered the shell mg ca of one of the two benthic species examined lower mg ca values following oxidation and reduction appear to reflect removal of contaminant mg associated with remnant organic matter and adsorbed phases

tropical sea surface temperatures during the last glacial period a view based on alkenones in indian ocean sediments abstract the quantification of tropical temperatures during the last glacial cycle 0 150 kyr bp is a controversial issue since different proxies seem to provide conflicting informations to obtain a complementary point of view we use the alkenone method to estimate sea surface temperatures and focus our work on deep sea sediments recovered from the tropical indian ocean we present alkenone data obtained in two cores which cover in detail the last deglaciation and in about twenty cores distributed between 20 s and 20 n that were chosen to evaluate the temperature contrast of the last glacial interglacial transition our results indicate that indian ocean tropical temperatures remained an average within 1 5 2 5 c of their present values during the last glaciation at 10 n the last deglaciation is characterized by two warming steps which is similar to the classical deglacial chronology observed in the north atlantic area at 20 s the deglacial warming occurred at ca 15 cal kyr bp lagging significantly 5 4 kyr behind the antarctic warming but in phase with northern hemisphere time series

submarine pyroclastic deposits formed at the soufriere hills volcano montserrat 1995 2003 what happens when pyroclastic flows enter the ocean the soufriere hills volcano montserrat west indies has undergone a series of dome growth and collapse events since the eruption began in 1995 over 90 of the pyroclastic material produced has been deposited into the ocean sampling of these submarine deposits reveals that the pyroclastic flows mix rapidly and violently with the water as they enter the sea the coarse components pebbles to boulders are deposited proximally from dense basal slurries to form steep sided near linear ridges that intercalate to form a submarine fan the finer ash grade components are mixed into the overlying water column to form turbidity currents that flow over distances 30 km from the source the total volume of pyroclastic material off the east coast of montserrat exceeds 280 106 m3 with 65 deposited in proximal lobes and 35 deposited as distal turbidites

interhemispheric synchrony of the last deglaciation inferred from alkenone palaeothermometry the relative timings of the last deglacial warming in the southern and northern hemispheres are not well constrained but are a crucial component in understanding the mechanisms of deglaciation1 a clearer picture of the degree of interhemispheric synchrony has been obscured by a dearth of high resolution temperature records that can be tied to the absolute calendar timescale moreover the quantification of tropical temperatures during the last glacial cycle is controversial2 8 here we apply the alkenone method of sea surface temperature reconstruction9 10 to several high resolution sediment cores recovered from the tropical indian ocean between 20 n and 20 s the inferred initial sea surface temperature warming 15 000 calendar years ago at 20 s is in phase with northern hemisphere sea this study and air11 temperature changes but lags antarctic warming12 14 by several millennia this finding along with the results of recent modelling studies15 16 provides strong support for the idea that changes in the ocean s global thermohaline circulation were not the only cause of interhemispheric climate teleconnection during the last deglaciation

deep to shallow marine sedimentology and impact of volcanism within the middle triassic palaeo tethyan semantan basin singapore abstract the middle triassic pulau ayer chawan formation is a predominantly deep marine occasionally shallow marine sedimentary succession deposited in the singapore sector of the palaeo tethyan semantan basin the formation provides an important record of the dynamic interplay between a siliciclastic sedimentary system and the products of an adjacent active volcanic arc it is characterised by six sub environments including deep marine turbidite fan deep marine background sedimentation subaqueous debris cone shallow marine volcanically sourced turbidite fan and hyaloclastite mound or ridge turbidite fan deposits preserve the input of both siliciclastic and volcaniclastic sediments from the shelf transported into the deep marine environment by a suite of subaqueous sediment gravity flow processes including turbidity currents mixed flow types hybrid event beds concentrated and hyper concentrated sediment gravity flows and debris flows thick heterolithic successions of debrites were likely sourced through regular collapse of an unstable shelf the presence of hybrid event beds encountered within the deep marine turbidite fans supports a slope that was out of grade and may have been actively retreating towards the hinterland together these factors suggest regional scale uplift of the eastern margins of the semantan basin during triassic times most likely facilitated through volcanic activity in the adjacent palaeo tethys sukhothai arc evidence for contemporaneous arc related magmatism includes ubiquitous volcaniclastic sedimentary rocks within formation including pyroclastic density current deposits and perhaps more strikingly through the hyaloclastites of the nanyang member the hyaloclastites formed through quenching of magmas delivered into the deep marine setting from a series of sub sea vents or mounds

mesozoic cenozoic evolution of the danba dome songpan garze east tibet as inferred from la icpms u pb and fission track data abstract the eastern margin of the tibetan plateau is a key region to understand the formation and tectonic evolution of the plateau most studies concentrated on the longmen shan range that corresponds to the tectonically very active boundary between the tibetan plateau and the sichuan basin this work addresses the deformation and exhumation pattern in the poorly understood metamorphic danba dome situated at the conjunction between the southern longmen shan range and the major strike slip xian shui he fault the early mesozoic and cenozoic evolution of the dome are then compared to the regional evolution of eastern tibet the about 830 ma zircon u pb ages obtained on the gezong and gongcai gneiss as well as u pb ages on inherited zircons in the early mesozoic granites confirm the occurrence of neo proterozoic magmatic episodes in the danba basement at 800 900 ma and 650 750 ma following the closure of the palaeotethys ocean granitoids were emplaced in the danba metamorphic basement and triassic cover from about 230 ma to about 170 ma the western part of the lian he kau granitic massif emplaced between 210 and 200 ma within the triassic cover sequence of the dome was only slightly affected by the early mesozoic deformation however in the eastern deeper level compartment of the massif ductile deformation occurred between 200 and 190 ma contemporaneous with the onset of the barrovian type metamorphism dated at 200 180 ma that deformation is compatible with the early mesozoic deformation observed in the longmen shan range and with the development of the large scale decollement level in the songpan garze area apatite fission track data then indicate that following the oligocene middle eocene onset of eastward motion of the songpan garze terrane the danba dome developed as a crustal scale antiform during the late miocene early pliocene 10 4 ma the exhumation was controlled by the lian he kau fault a major transpressive structure parallel to the xian shui he fault and the associated manai thrust faults regionally while the oligocene middle miocene exhumation phase seems to have been of regional extent the late miocene to present day phase is localised along the longmen shan range thrusts as well as along the back thrusts formed by the lian he kau manai and associated faults

eight glacial cycles from an antarctic ice core the antarctic vostok ice core provided compelling evidence of the nature of climate and of climate feedbacks over the past 420 000 years marine records suggest that the amplitude of climate variability was smaller before that time but such records are often poorly resolved moreover it is not possible to infer the abundance of greenhouse gases in the atmosphere from marine records here we report the recovery of a deep ice core from dome c antarctica that provides a climate record for the past 740 000 years for the four most recent glacial cycles the data agree well with the record from vostok the earlier period between 740 000 and 430 000 years ago was characterized by less pronounced warmth in interglacial periods in antarctica but a higher proportion of each cycle was spent in the warm mode the transition from glacial to interglacial conditions about 430 000 years ago termination v resembles the transition into the present interglacial period in terms of the magnitude of change in temperatures and greenhouse gases but there are significant differences in the patterns of change the interglacial stage following termination v was exceptionally long 28 000 years compared to for example the 12 000 years recorded so far in the present interglacial period given the similarities between this earlier warm period and today our results may imply that without human intervention a climate similar to the present one would extend well into the future

deglaciation in the tropical indian ocean driven by interplay between the regional monsoon and global teleconnections abstract high resolution climate records of the ice age terminations from monsoon dominated regions reveal the interplay of regional and global driving forces speleothem records from chinese caves indicate that glacial terminations were interrupted by prominent weak monsoon intervals wmi lasting a few thousand years deglacial wmis are interpreted as the result of cold temperature anomalies generated by sea ice feedbacks in the north atlantic most prominently during heinrich events recent modeling results suggest however that wmis reflect changes in the intensity of the indian rather than the east asian monsoon here we use foraminiferal trace element mg ca and ba ca and stable isotope records from a sediment core off the malabar coast in the southeastern arabian sea with centennial scale resolution to test this hypothesis and to constrain the nature and timing of deglacial climate change in the tropical indian ocean the malabar deglacial sst record is unique in character and different from other tropical climate records sst at the last glacial maximum was 2 7 0 5 c colder than pre industrial sst deglacial warming started at 18 6 95 ci range 18 8 18 1 kyr bp within error of the onset of warming at other tropical sites as well as in antarctica and the southern ocean and either coeval with or up to 1 kyr before the atmospheric co 2 rise warming took place in two steps separated by an interval of stable sst between 15 7 16 2 14 9 and 13 2 13 9 12 0 kyr bp the 18 o water record and the ba ca record which is a measure of indian sub continent riverine runoff indicate that the last ice age termination was marked by a prominent weak indian monsoon interval interrupted by an intense monsoon phase as seen in speleothem records and predicted by modeling a strong correspondence between the timing of the malabar 18 o sw record and the hulu cave monsoon record suggests that deglacial 18 o changes in both localities dominantly reflect compositional changes in precipitation likely driven by changes in the north atlantic

the riddle of volcaniclastic sedimentation in ancient deep water basins a discussion abstract sedimentary records of deep water basins are useful tools for understanding how volcanism shapes distal environments furthermore these basins represent uncontaminated places where catastrophic eruptions are clearly preserved for these reasons the study of the depositional records of deep sea realms becomes of primary importance to better understand the temporal incidence and the consequences of catastrophic events that may occur on earth however their inaccessible underwater conditions limit the possibility of deep investigations thus ancient analogues represent the best way to integrate direct observations with detailed sedimentological and petrographic analyses this work introduces concepts derived from the study of three sedimentary sequences that form the oligocene foreland and foredeep deep sea basins of the proto alpine belt each succession is characterized by its volcaniclastic detritus and two of them were deposited during volcanic activity we compare their sedimentological and volcanological characteristics highlighting the main features derived from a volcanically controlled sedimentation we emphasize 1 the importance of stratigraphy and petrography in the identification of criteria to recognize volcanism phases in ancient distal deep water sequences 2 the propensity of volcanism to produce detritus during its life rather than after its death and 3 the fundamental role of pyroclastic density currents in delivering particles from source areas to depositional basins these three points suggest that a deep knowledge of ancient sedimentary records integrates our knowledge on the interaction existing between volcanoes and surrounding environments with a hazard assessment perspective

reconstructing sea surface temperature and salinity using δ 18 o and alkenone records the oxygen isotope 18o composition of foraminiferal tests from deep sea sediments is widely used as a palaeoclimate proxy but it includes contributions from sea surface temperature global ice volume and local salinity which are difficult to separate recently a new technique for deriving palaeotemperatures has been developed which is based on the abundance ratios of unsaturated alkenones in phytoplankton algae1 2 here we use a combination of oxygen isotope and alkenone records in a deep sea core from the juncture of the arabian sea and the bay of bengal to extract the salinity signal from the former record variations in salinity are related to the balance between evaporation and precipitation3 and are thus a sensitive indicator of climate change our 170 kyr salinity record enables us to reconstruct changes in the indian monsoon over this period considerably extending earlier studies which reached back to 18 kyr ago 4 8 like these previous studies we find that large variations in the monsoon occurred during the transition from the last glacial period to the present interglacial but our results also provide a view of the monsoon throughout the last glacial and demonstrate the potential of this approach for reconstructing palaeosalinity

sea surface temperature and productivity records for the past 240 kyr in the arabian sea abstract deep sea sediments of two cores from the western ty93 929 p and the southeastern md900963 arabian sea were used to study the variations of the indian monsoon during previous climatic cycles core ty93 929 p was located between the sw monsoon driven upwelling centres off somalia and oman which are characterized by large seasonal sea surface temperature sst and particle flux changes by contrast core md900963 was situated near the maldives platform an equatorial ocean site with a rather small sst seasonality less than 2 c for both cores we have reconstructed sst variations by means of the unsaturation ratio of c37 alkenones which is compared with the 18o records established on planktonic foraminifera in general the sst records follow the 18o variations with an sst maximum during oxygen isotope stage 5 5 the last interglacial at about 120 130 kyr and a broad sst minimum during isotope stage 4 and 3 3 approximately 40 50 kyr the sst difference between the holocene and the last glacial maximum lgm is of the order of 2 c in both cores the ssts during isotope stage 6 are distinctly higher by 1 2 c than the cold sst minima during the last glacial cycle lgm and stage 3 to reconstruct qualitatively the past productivity variations for the two cores we used the concentrations and fluxes of alkenones and organic carbon together with a productivity index based on coccolith species florisphaera profunda relative abundance within each core there is a general agreement between the different palaeoproductivity proxies in the southeastern arabian sea core md900963 glacial stages correspond to relatively high productivity whereas warm interstadials coincide with low productivity all time series of productivity proxies are dominated by a cyclicity of about 21 23 kyr which corresponds to the insolation precessional cycle a hypothesis could be that the ne monsoon winds were stronger during the glacial stages which induced deepening of the surface mixed layer and injection of nutrients to the euphotic zone by contrast the records are more complicated in the upwelling region of the western arabian sea core ty93 929 p this is partly due to large changes in the sedimentation rates which were higher during specific periods isotope stages 6 5 4 5 2 3 and 2 unlike core md900963 no simple relationship emerges from the comparison between the 18o stratigraphy and productivity records the greater complexity observed for core ty93 929 p could be the result of the superimposition of different patterns of productivity fluctuations for the two monsoon seasons the sw monsoon being enhanced during interglacial periods whereas the ne monsoon was increased during glacial intervals a similar line of reasoning also could help explain the sst records by the superimposition of variations of three components global atmospheric temperature and sw and ne monsoon dynamics

seasonal sea surface temperature contrast between the holocene and last glacial period in the western arabian sea ocean drilling project site 723a modulated by monsoon upwelling 1 annual summer and winter sea surface temperatures ssts in the western arabian sea were reconstructed through the last 22 kyr using artificial neural networks anns based on quantitative analyses of planktic foraminifera down core sst estimates reveal that annual summer and winter ssts were 2 1 2 and 2 6 c cooler respectively during the last glacial period than in the holocene a 2 5 c sst increase during termination 1a hereinafter referred as glacial to holocene transition in the western arabian sea the study reveals a strong seasonal sst contrast between winter and summer from 18 to 14 calendar kyr owing to the combined effect of weak upwelling and strong cold northeasterly winds minor or no seasonal sst changes were noticed within the holocene period which is attributed to the intense upwelling during the summer monsoon this causes a lowering of sst to values similar to those of the winter season in analogy with the present day a 3 c rise in winter ssts during the glacial to holocene transition coincides with a strengthening of the monsoon suggesting a link between winter sst and monsoon initiation from the beginning of the holocene strikingly annual summer and winter ssts show a cooling trend from 8 ka to the present day implying tropical cooling in the late holocene

combinations of volcanic flank and seafloor sediment failure offshore montserrat and their implications for tsunami generation recent seafloor mapping around volcanic islands shows that submarine landslide deposits are common and widespread such landslides may cause devastating tsunamis but accurate assessment of tsunami hazard relies on understanding failure processes and sources here we use high resolution geophysical data offshore from montserrat in the lesser antilles to show that landslides around volcanic islands may involve two fundamentally different sources of sediment island flank and larger seafloor sediment failures and can occur in multiple stages a combination of these processes produces elongate deposits with a blocky centre associated with island flank collapse surrounded by a smoother surfaced deposit that is dominated by failed seafloor sediment the failure of seafloor sediment is associated with little marginal accumulation and involves only limited downslope motion submarine landslide deposits with similar blocky and smooth surfaced associations are observed in several locations worldwide but the complex emplacement processes implied by this morphological relationship can only be revealed by high resolution geophysical data such complexity shows that the volume of landslide deposits offshore of volcanic islands cannot simply be used in tsunami models to reflect a single stage collapse of primary volcanic material by applying predictive equations for tsunami amplitude to investigate general scenarios of volcanic island landslide generation we show that the tsunami hazard associated with volcanic island collapse remains highly significant volcanic flank failures even if relatively small may generate large local tsunamis but associated seafloor sediment failures even if they have a much greater volume have a substantially lower potential for tsunami generation

subduction related origin of the 750 ma xuelongbao adakitic complex sichuan province china implications for the tectonic setting of the giant neoproterozoic magmatic event in south china

sedimentological and petrographic evolution of a fluvio lacustrine environment during the onset of volcanism volcanically induced forcing of sedimentation and environmental responses

climatology of the eastern arabian sea during the last glacial cycle reconstructed from paired measurement of foraminiferal δ18o and mg ca abstract paired measurements of mg ca and 18 o of globigerenoides sacculifer from an eastern arabian sea eas sediment core indicate that sea surface temperature sst varied within 2 c and sea surface salinity within 2 psu during the last 100 ka sst was coldest 27 c during marine isotope stage mis 4 and 2 sea surface salinity was highest 37 5 psu during most of the last glacial period 60 18 ka concurrent with increased 18 o g sacculifer and c n ratios of organic matter and indicative of sustained intense winter monsoons sst time series are influenced by both greenland and antarctic climates however the sea surface salinity time series and the deglacial warming in the sst record beginning at 18 ka compare well with the lr04 benthic 18 o stack and antarctic temperatures this suggests a teleconnection between the climate in the southern hemisphere and the eas therefore the last 100 ka variability in eas climatology appears to have evolved in response to a combination of global climatic forcings and regional monsoons the most intense summer monsoons within the holocene occurred at 8 ka and are marked by sst cooling of 1 c sea surface salinity decrease of 0 5 psu and 18 o g sacculifer decrease of 0 2

reworked pyroclastic beds in the early miocene of patagonia reaction in response to high sediment supply during explosive volcanic events abstract two meter scale pyroclastic levels are interbedded within the early miocene succession of the estancia 25 de mayo patagoniense transgression and santa cruz formations in the foreland austral or magallanes basin argentina the lower pyroclastic level lpl is a tabular body interbedded within offshore marine deposits laterally continuous for 30 km and varying in thickness from few centimeters to around 4 m grain size grades from coarse to extremely fine ash with upward fining along with a northeastern fining trends structureless fine to very fine tuffs dominate and rare parallel laminations are the only tractive sedimentary structures the upper pyroclastic level upl lies within low energy fluvial deposits and is laterally discontinuous and it is composed by lenticular bodies reaching a maximum of 15 m thick and 100 m wide with a concave up base and a plane top grain size range is similar to the lpl but it coarsens upward the lower portion of the upl shows parallel lamination current ripple lamination and mud drapes with large pumice lapilli and plant debris whereas the upper portion shows parallel lamination and trough cross stratification both pyroclastic levels are composed mainly of pumice grains and glass shards with minor proportions of quartz and plagioclase crystals and lithic fragments the lpl shows no mixing with epiclastic material whereas the upl shows an upward increase in epiclastic material and an upward increment in the scale of cross bedding the large thickness in relation to the possible emission center and the content of plant debris of the lpl does not suggest a direct submarine ash fallout origin the lpl is interpreted as a deposit of hyperpycnal flows generated at the coastal zone when tephra laden rivers plunged into the ocean large amounts of well preserved plant debris support the hypothesis of a terrestrial source of the sediments the upl is entirely composed of tractive deposits so an ash fallout origin is disregarded this together with the lenticular shape and the alluvial plain origin of the encasing sediments suggests accumulation within fluvial channels cycles of upper flow regime parallel lamination current ripple lamination and mud drapes at the lower portion suggest short lived turbulent flows that initially filled semi abandoned channels they were followed by sheet floods and channel reactivation expressed by large scale cross bedding the low degree of particle mixing observed in both levels is explained by the inability of streams to erode the substrate as they are suddenly over saturated with pyroclastic sediments during and after the eruption the grain size distribution of the lpl and geochemical data indicate a contemporaneous volcanic source located to the west southwest in the andean ranges where the south patagonian batholith is presently located

petrogenesis and tectonic implications of neoproterozoic highly fractionated a type granites from mianning south china abstract the origin of neoproterozoic intrusions ca 860 750 ma along the western part of the yangtze craton has been the subject of debate in recent years with two competing models proposed the plume model argues for an extensional setting and emphasizes the role of a superplume in the rodinia breakup whereas the arc model argues for the presence of a subduction zone in the yangtze craton as a contribution to this animated dispute geochronologic and geochemical analyses have been carried out on the mianning granite which is the largest pluton 700 km2 in the northern kangdian rift of the western yangtze craton it is shown that the mianning granites were emplaced at ca 780 ma and display highly fractionated feature i e sio2 75 wt eu eu 0 03 0 50 enrichment of k rb th u zr hf y and rees depletion of nb ta ba sr p eu and ti they are metaluminous to strongly peraluminous a cnk 0 93 1 55 and contain abundant perthite and minor alkali riebeckite and sphene sharing the petrological and geochemical characters of a2 type granites positive nd t 2 97 5 24 and zircon hf t 9 2 12 1 values are consistent with a derivation by partial melting of a relatively young crust formed about 1000 900 ma given the general absence of a type granites in arc settings the mianning a type granites are suggestive of an anorogenic crustal extensional environment for the western yangtze craton during the neoproterozoic the data presented in this study are therefore consistent with an intracontinental rift model but are not sufficient to identify plume involvement in the neoproterozoic magmatism

the oligocene alps domal unroofing and drainage development during early orogenic growth abstract the source of huge volumes of quartzofeldspathic detritus feeding oligo miocene foredeep turbidites of the apennines has long remained an unsolved geological enigma in this article we reinterpret the available sandstone petrography fission track stratigraphic and geomorphological evidence to demonstrate that the adriatic foredeep was dominantly sourced by a himalayan type tectonic aneurysm growing in the central alps since the late oligocene the lepontine dome the lepontine dome is the envelope of distinct subdomes that formed stepwise from east to west during northwestward indentation of adria beneath the axial alps focused erosion of domal culminations cut by antecedent drainage started suddenly in the late oligocene with unroofing of recently emplaced plutons and young amphibolite facies gneisses exhumation was tectonically driven and possibly accelerated by positive feedback between erosion and uplift of hot weak rocks from depth the huge volumes of resulting detritus gonfolite macigno clastic wedge were transported southward for hundreds of kilometers along the rapidly subsiding foredeep formed since middle eocene times in front of the alpine retrobelt and nascent apennine forebelt such massive sediment influx following 15 2 myr of starved foredeep sedimentation testifies to rapid formation of mountain relief in the central alps synchronous to dextral activity along the insubric fault the lepontine dome remains today as the only deeply dissected region in the alps where medium grade metamorphic rocks of the axial belt are extensively exposed the relationships between geological structures and drainage patterns still mirror those formed originally at oligocene times river headwaters have not been significantly displaced since then and their thalwegs constrain finite lateral displacement relative to the southalpine retrowedge to a maximum of 10 20 km our reconstruction has wide implications not only for a better understanding of the tertiary evolution of the alps apennines orogenic couple but also for general relationships among tectonic activity relief formation drainage development erosion distribution and long distance sediment transfer during continental collision and orogenic growth

core top calibration of mg ca in tropical foraminifera refining paleotemperature estimation 1 optimal use of mg ca as a paleotemperature proxy requires establishing calibrations for different species of foraminifera and quantifying the influence of dissolution to achieve this goal we have measured mg ca and 18o in a series of tropical and subtropical core tops including four depth transects the ceara rise the sierra leone rise and the rio grande plateau in the atlantic and the ontong java plateau in the pacific focusing on spinose mixed layer dwelling species globigerinoides ruber and globigerinoides sacculifer and nonspinose thermocline dwelling neogloboquadrina dutertrei shell mg ca in g sacculifer is 5 15 lower than in g ruber while n dutertrei mg ca is 49 55 lower than in g ruber this statistically significant offset has allowed us to establish different calibrations for each species multilinear regression analysis was used to develop calibration equations that include a correction term for the dissolution effect on mg ca in foraminiferal calcite presented in this paper are two sets of calibrations one set using core depth as a dissolution correction and another using co32 as a dissolution parameter the calibrations suggest that g ruber is the most accurate recorder of surface temperature while g sacculifer records temperatures below the surface at 20 30 m the depth habitat of n dutertrei is more uncertain owing to the wide range in habitat depths depending on hydrographic conditions but on average mg ca and 18o data suggest it is at 50 m of the three species n dutertrei is the most sensitive to dissolution up to 23 decrease in shell mg ca per km while g sacculifer is the most resistant

megaturbidite deposits in the holocene basin fill of lake como southern alps italy abstract for the first time limnogeological investigations have been carried out in lake como the deepest lake of the alps combining a bathymetric survey multibeam simrad 3000 with a high resolution seismic reflection study single channel 3 5 khz sub bottom profiler and a coring campaign gravity corer this data set enables detailed characterization of the sedimentary subsurface in the western branch of the lake the como branch which has a typical fjord morphology this paper focuses on the deepest part of the como branch argegno basin in which up to 3 5 m thick turbidite deposits are identified the basin fill of the como branch is characterized by well layered draping and onlapping pelagic sediments that are locally affected by creeping and that are intercalated with mass wasting deposits in particular with two large debris flow deposits evolving into megaturbidites in the deepest part of the basin the multibeam data together with the acoustic facies distributions and the volumes of these two major sedimentary deposits mt1 3 106 m3 and mt2 10 5 106 m3 indicate that they resulted from large slides at the northern tip of the como branch along the steep slopes of a sub lacustrine plateau the estimated ages of these events around the mid 12th mt1 and early 6th mt2 centuries are extrapolated from mean sedimentation rates based on radiocarbon 14c and radionuclide 137cs analyses from short cores in the argegno basin possible trigger mechanisms leading to these catastrophic events in the como branch include a combination of steep slope overloading with significant lake level fluctuations related to holocene climate change and or earthquake shaking the tentative age assignment places the age of both major mass movements near two other events mt1 near the occurrence of a major earthquake in the po plain in 1222 ad intensity ix mcs macroseismically derived magnitude 6 2 and mt2 near a megaturbidite triggered in 700 ad in a proglacial lake in southeastern switzerland blass a anselmetti f grosjean m sturm m 2005 the last 1300 years of environmental history in the sediments of lake sils engadine switzerland eclogae geologicae helvetiae 98 319 332 since dangerous tsunami like waves seiches can be generated by large sub aqueous landslides leading to such megaturbidites in this fjord like basin future studies are required 1 to constrain the age of these catastrophic events 2 to document the stabilities of the steep slopes in the como branch 3 to assess the expected frequency of such catastrophic events and 4 to model the propagation of large waves in the como branch and their potential damage along the highly populated lake shore

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

tectonic history of a jurassic backarc basin sequence the gran canon formation cedros island mexico based on compositional modes of tuffaceous deposits the jurassic gran canon formation cedros island baja california mexico constitutes an unusually well preserved and exposed example of ancient backarc basin fill petrofacies analysis conducted on tuff aceous sandstone and tuff samples from this formation complement and reinforce prior lithofacies interpretations but with some modification when temporal and spatial trends in petrographic data detrital modes are analyzed and compared to mod els based on data collected from deep sea drilling project and ocean drilling pro gram cores the trends indicate a second heretofore unrecognized phase of backarc rifting basalt lavas interstratified with da citic pyroclastic rocks of the primary vol canic lithofacies previously interpreted to record the eruption of differentiated mag mas at the climax of growth of the gran canon island arc are now as a result of this study considered to be the product of arc extension and rifting our method of modal analysis uniquely combines the quantification of textural at tributes of pyroclastic and epiclastic debris that reflect eruption style and magma com position as well as the effects of reworking and mixing in marine settings this study demonstrates that detailed petrographic analysis is useful in the interpretation of ancient volcaniclastic deposits suspected of having formed in backarc basin settings

a first look at past sea surface temperatures in the equatorial indian ocean from mg ca in foraminifera 1 sea surface temperature sst for the central equatorial indian ocean has been reconstructed over the last 137 kyr from mg ca of the planktonic foraminiferal species globigerinoides ruber according to our record the equatorial indian ocean sst was 2 1 c colder during the last glacial maximum as compared to present times the data further shows that the surface equatorial indian ocean was comparatively warmer during isotopic stage 5e than at present 29 9 vs 28 5 c comparison of the equatorial indian ocean sst with the antarctic d and greenland 18o records shows that the major high latitude cooling warming events are also present in the equatorial indian ocean sst variation record similarity between the equatorial indian ocean sst and the equatorial pacific sst suggests the possibility of a common mechanism controlling the ssts in both the equatorial indian ocean and the pacific ocean

organic carbon preservation in southeastern arabian sea sediments since mid holocene implications to south asian summer monsoon variability the earlier studies show a contrasting long term trend of the south asian summer monsoon sasm after attaining the precessional forcing induced mid holocene maximum the increasing total organic carbon toc concentration of marine sediments in the southeastern arabian sea seas has been interpreted to imply strengthening sasm since mid holocene by a few studies however toc concentration is also influenced by redox conditions sedimentation rate and an influx of terrigenous matter depending on the regional settings so it needs to be ascertained whether the toc concentration of the sediments in the seas is a signal of productivity related to the sasm strength or preservation therefore we studied multiple proxies toc total nitrogen atomic c n 13corg caco3 and major and trace elements concentration for determining the productivity redox conditions detrital supply and provenance in a sediment core from the upper continental slope of the seas spanning the past 4700 years at centennial scale resolution the present study shows that the observed toc increase is not a result of enhanced productivity but is because of better preservation due to the increased sedimentation rate along with increasingly reducing conditions since mid holocene we further show that the sasm has been declining since mid holocene after attaining a precession forced maximum which corroborates the earlier model ensemble studies

rainfall triggered lahars at volcan de colima mexico surface hydro repellency as initiation process article volcan de colima is currently the most active volcano in mexico since 1998 intermittent activity has been observed with vulcanian eruptions lava flows and growing domes that have collapsed producing several block and ash flow deposits during the period of heightened activity since 1998 at volcan de colima pyroclastic flows from dome or column collapse have not reached long distances most of the time less than 6k m from the crater in contrast rain induced laharswere more frequent and have reached relatively long distances upto 15 km causing damage to infrastructureand affecting small villages in 2007 tworain gauge stationswereinstalledonthesouthern flankofthevolcanoregisteringeventsfromjunethroughtooctober the period when rains are intense and lahars frequent by comparing lahar frequency with rainfall intensity and the rainfall accumulated during the previous 3 days lahars more frequently occur at the beginning of the rainfall season with low rain accumulation 10 mm and triggered by low rain intensities 20 mm h during the months with more rainfall july and august lahars are less frequent and higher peak intensities up to 70 mm h are needed to trigger an event in both cases lahars were initiated as dilute sediment laden streamflows which transformed with entrainment of additional sediment into hypercon centratedanddebris flows withalternationsbetweenthesetwo flowtypes ahydro repellencymechanism in highly vegetated areas i e evergreen tree types with considerable amount of resins and waxes such as pines with sandy soils can probably explain the high frequency of lahars at the beginning of the rain season during low rainfall events under hydrophobic conditions infiltration is inhibited and runoff is facilitated at more highly peaked discharges that are more likely to initiate lahars

generation of block and ash flows during the 1990 1995 eruption of unzen volcano japan processes generating block and ash flows by gravitational dome collapse merapi type pyroclastic flow were observed in detail during the 1990 1995 eruption of unzen volcano japan two different types were identified by analysis of video records and observations during helicopter flights most of the block and ash flows erupted during the 1991 1993 exogenous dome growth stage initially involved crack propagation due to cooling and flowage of the dome lava lobes the mass around the crack became unstable locally decreasing in tensile strength finally a slab separated from the lobe front fragmented progressively from the base to the top within a few seconds and became a block and ash flow rock falls immediately followed in response to local instability of the lobe front clasts in these rock falls fragmented and merged with the preceding flow in contrast block and ash flows during the endogenous dome growth stage in 1994 were generated due to local bulge of the dome unstable lava blocks collapsed and subsequently fragmented to produce block and ash flows

the late triassic rift related volcanic rocks from eastern qiangtang northern tibet china age and tectonic implications abstract the late triassic nadi kangri volcanic rocks with nearly ew trending outcrops within the qiangtang basin northern xizang tibet china are composed mainly of acid tuff dacite rhyolite and minor basic volcanic rocks there exists a significant depositional hiatus between the nadi kangri volcanic rocks and underlying strata therefore the nadi kangri volcanic rocks represent a new evolution history of the mesozoic qiangtang basin the magma emplacement age of the nadi kangri volcanic rocks in the geladaindong area is 220 4 2 3 ma representing the onset of the mesozoic qiangtang basin the nadi kangri basalts have high nb zr 0 049 0 058 ta hf 0 12 0 15 and zr y 4 95 6 01 ratios in the tectonic discrimination diagrams such as zr vs zr y and th hf vs ta hf the nadi kangri basaltic rocks mostly plot in the within plate setting field the geological background and the geochemical characteristics suggest that the nadi kangri volcanic rocks were formed in a continental rift setting

discrimination of ophiolitic from nonophiolitic ultramafic mafic allochthons in orogenic belts by the al ti ratio in clinopyroxene in mafic igneous suites typical of anorogenic igneous provinces mid ocean ridges back arc basins continental rifts and hotspots clinopyroxenes of tholeiitic and silica undersaturated rocks incorporate al in clinopyroxene chiefly via the charge coupled substitution vimgivsi2 vitiival2 as the catial2o6 molecule this substitution is promoted by high titania activity relative to silica in the melt and hence is particularly characteristic of silica undersaturated mafic rocks mafic igneous suites of convergent plate margins i e arc tholeiites and calc alkalic gabbros and basalts characteristically incorporate al in clinopyroxene largely as the cafe3 alsio6 molecule the vimgivsi vife3 ival substitution is promoted by relatively high fugacities of h2o and o2 a characteristic feature of arc axis magmas recognition of cumulates that are complementary to compositions of eruptive rocks in arcs is crucial to development of valid petrogenetic models for arc magmas plots of tetrahedrally coordinated al vs octahedral ti in augite of gabbroic and ultramafic cumulates show that augite data arrays for arc related cumulates have a trend of substantially higher al ti in clinopyroxene than do those from rift related tholeiites the al ti ratio in clinopyroxene may be utilized to discriminate ophiolitic from nonophiolitic ultramafic mafic allochthons in orogenic belts

widespread syn eruptive volcaniclastic deposits in the pleistocenic basins of south western calabria abstract since late tortonian depositional sequences developed along the southern calabrian forearc inside the half graben depressions of the mesima gioia tauro and reggio calabria basins in these basins volcaniclastic sedimentation took place during lower to middle pleistocene volcaniclastic deposits consist of isolated pumice swarms ash layers and thick successions of lapilli and ash in this paper we describe and discuss the depositional characteristics of these volcanogenic sediments and the morphology mineralogy and chemistry of pumices shards lithics and crystal fragments these deposits all have the characteristics of a proximal tephra fall deposit from a plinian plume which has been reworked in a shore environment in the mesima basin the deposits reach 6 m in thickness and in the gioia tauro plain 21 m of pumiceous sediments have been cored in a drill hole the compositional homogeneity of fragments and the absence of non volcanic detritus as well as of soil or organic matter suggest that the deposits were quickly reworked after their primary emplacements all the tephra deposits exhibit calc alkaline affinity and dacitic to rhyolitic composition the mineralogical assemblage including orthopyroxene as phenocryst indicates provenance from magmatic arc volcanism icp ms and la icp ms analyses of crystals and glass point to a common origin probably from a single eruption this makes these volcaniclastic layers a very useful tool for stratighaphic reconstructions at a regional scale the geological setting of the deposits their petrological and geochemical signature and the occurrence of large size clasts suggest a provenance from explosive eruptions preceding the emplacement of the 50 ka dacitic lava dome of the island of panarea aeolian archipelago however a provenance from a different calc alkaline volcanic system cannot be excluded these deposits can therefore represent the only evidence of a large explosive eruption in the southern tyrrhenian sea whose very proximal equivalent is not preserved

petrogenesis of adakitic porphyries in an extensional tectonic setting dexing south china implications for the genesis of porphyry copper mineralization the dexing adakitic porphyries quartz diorite granodiorite porphyries associated with giant porphyry cu deposits are located in the interior of a continent south china they exhibit relatively high mgo cr ni and sr contents high la yb and sr y ratios but low yb and y contents similar to adakites produced by slab melting associated with subduction however they are characterized by bulk earth like nd sr isotope compositions end t 1 14 to 1 80 and 87 sr 86 sr i 0 7044 0 7047 and high th 12 6 27 2ppm contents and th ce 0 19 0 94 ratios which are different from those of cenozoic slab derived adakites sensitive high resolution ion microprobe shrimp geochronology studies of zircons reveal that the dexing adakitic porphyries have a crystallization age of 171 3ma this age is contemporaneous with middle jurassic extension within the shi han rift zone and within plate magmatism elsewhere in south china indicating that the dexing adakitic porphyries were probably formed in an extensional tectonic regime in the interior of the continent rather than in an arc setting their high th contents and th ce ratios and middle jurassic age argue against an origin from a neoproterozoic 1000ma stalled slab in the mantle taking into account available data for the regional metamorphic magmatic rocks and the present day crustal thickness 31km in the area we suggest that the dexing adakitic porphyries were most probably generated by partial melting of delaminated lower crust which was possibly triggered by upwelling of the asthenospheric mantle due to the activity of the shi hang rift zone moreover the dexing adakitic magmas must have interacted with the surrounding mantle peridotite during their ascent which elevated not only their mgo cr and ni contents but also the oxygen fugacity fo2 of the mantle the high fo2 could have induced oxidation of metallic sulfides in the mantle and mobilization of chalcophile elements which are required to produce associated cu mineralization therefore the cu metallogenesis associated with the dexing adakitic porphyries is probably related to partial melting of delaminated lower crust similar to the metallogenesis accompanying slab melting

detrital fingerprints of fossil continental subduction zones axial belt provenance european alps abstract collision orogens such as the alps or the himalayas are generated by plate convergence culminating in attempted subduction of a thinned continental margin massive amounts of metamorphic rocks displaying high pressure parageneses are produced during such relatively brief tectonic events and then rapidly exhumed to form the axial backbone of the new orogen sediment composition provides a fundamental key to identify past events of continental subduction although coupled detrital geochronology techniques are needed to discriminate neometamorphic and paleometamorphic sources of detritus within the austroalpine cretaceous and penninic eocene axial belts of the alps we ideally distinguish three structural levels each characterized by diagnostic detrital fingerprints the shallow level chiefly consists of offscraped remnant ocean turbidites and unmetamorphosed continental margin sediments and mostly produces lithic to quartzolithic sedimentaclastic sands yielding very poor heavy mineral suites inc

source rock versus sedimentary control on the mineralogy of deltaic volcanic arenites upper triassic northern italy abstract the carnian sandstones of the southern alps are fluviodeltaic and lagoonal clastic wedges derived from volcanic source rocks changing with time from mesosilicic to persilicic lavas and pyroclastics two thirds of the variance in detrital modes reflect this petrologic evolution of the source the effect of sedimentary processes is never strong enough to obscure the fundamental relationship of sandstone composition to provenance but it accounts for most short term variability in quartz feldspar and feldspar volcanic rock fragment ratios plagioclase and quartz grains are concentrated respectively in the very fine to fine fractions and in medium grained sandstones the quartz feldspar ratio q f thus decreases through delta plain upward fining sequences from channel lag sediments f 1 3 to overbank sands q f 1 8 the sedimentary control on the composition of fluviodeltaic sands results from the coupling of mechanical effects in high gradient headwater streams and hydraulic sorting in low gradient depositional environments assuming that the effectiveness of mineralogical segregation in different grain size fractions during transport depends primarily on paleorelief a decrease in altitude during carnian times is inferred within the triassic volcanic source which lay south of the sedimentary depocenter reworking by weak traction currents in lagoonal settings has further increased the textural maturity and the mineralogical stability of the sands volcanic rock fragments were reduced by selective destruction in marine environments but the q f ratio was no affected and a common value of 1 6 characterizes all lagoonal strata

change in the intensity of low salinity water inflow from the bay of bengal into the eastern arabian sea from the last glacial maximum to the holocene implications for monsoon variations a 100 400 km wide region of the coastal eastern arabian sea eas off the west coast of india is characterized by a low salinity tongue formed by the inflow of low salinity surface water from the bay of bengal bob this low salinity tongue is largely driven by the sea level higher in bob than in the arabian sea and by alongshore pressure gradient between southern and northern eas and is expected to respond to summer monsoon freshwater flux to the bay here we report past variation in the relative intensity of summer and winter monsoons based on changes in the north south salinity gradient within this low salinity tongue the salinity gradient is estimated from paired measurement of 18 o and mg ca in globigerinoides sacculifer extracted from sediment cores collected at northern high salinity and southern low salinity locations within this tongue the last glacial maximum lgm to peak holocene 18 o and sea surface temperature gradients at both locations are 2 and 2 o c respectively while the sea surface salinity gradient at northern eas is 0 5 psu higher than in the southern eas suggesting distinctly different sss structure in the lgm eas the north south surface salinity gradient was also larger by 0 5 psu during the lgm 1 2 psu as compared to the gradient during the holocene 0 7 psu increased north south surface salinity gradient during the lgm suggests diminished flow of low salinity water into the coastal eas caused by combined effect of decreased freshening of the bob and reduced seasonal mountain rivers discharge into the eas such surface hydrographic conditions in the coastal eas clearly indicate significantly weakened summer monsoons and strengthened winter monsoons during the lgm

the yanbian terrane southern sichuan province sw china a neoproterozoic arc assemblage in the western margin of the yangtze block abstract the magmatic and tectonic history of the yangtze block and its possible affinity with other neoproterozoic arc terranes are important elements in the reconstruction of neoproterozoic plate tectonics the yanbian terrane in the western margin of the yangtze block is a typical arc assemblage composed of a flysch type sedimentary sequence intruded by gabbroic and granodioritic plutons the sedimentary sequence consists chiefly of tuffaceous material with interlayered chert sandstone and pillow basalts laser ablation icp ms u pb dating of detrital zircons from the sandstones yield ages as young as 840 ma the gaojiacun and lengshuiqing mafic intrusions are dated at 812 3 ma and 806 4 ma respectively using the shrimp zircon u pb technique geochemical data show that both the gaojiacun and lengshuiqing intrusions have arc signatures with nd t values of 1 5 to 6 0 initial 87 sr 86 sr ratios of 0 705 0 706 and pronounced negative nb ta and zr hf anomalies their geochemical variations are best explained by fractional crystallization without major crustal contamination the yanbian terrane represents a typical arc assemblage formed on the western edge of the yangtze block during neoproterozoic time the sedimentary sequence was deposited in an oceanic setting probably in a back arc basin environment the depleted subduction modified lithospheric mantle wedge above the subduction zone was the source of melts from which the mafic plutons were crystallized this scenario suggests subduction of oceanic lithosphere eastward present day orientation underneath the yangtze block

provenance of volcaniclastic beach sand in a magmatic arc setting an example from lipari island aeolian archipelago tyrrhenian sea lipari an active volcanic island in the aeolian magmatic arc is an excellent area to determine the effects of multiple source lithology climate weathering transport and depositional environment on epiclastic sand composition volcaniclastic sand samples from 12 modern beaches were petrographically characterized using the gazzi dickinson method and the proportions of source rocks in combination with topography in associated coastal drainage basins were quantified using gis several types of bedrock in the 12 drainage basins that are the likely prominent sources for sand at each sampled beach were recognized and divided into two categories of provenance lithotypes lavas and pyroclastic rocks ranging in composition from basaltic andesitic to andesitic to rhyolitic volcanic lithic fragments from lipari beach sand consist of colourless and black glassy volcanic fragments with lathwork felsitic vitric and microlitic textures moreover high amounts of detrital less durable minerals such as pyroxene olivine and fe oxides illustrate how the analysed sands preserve the source rock s provenance signals applying the concept of sand generation index we see that these lithotypes have different propensities to create detritus in terms of both grain size and composition clastic contribution from pyroclastic rock outcrops such as pumice is not found in the size ranges studied suggesting that these pumiceous source rocks probably only produce gravel or very fine sand and silt this finding has implications for the stratigraphic record because pumice clasts ranging from medium to fine grain size could be underrepresented in older volcaniclastic deposits and overrepresented in other size fractions

the interaction of volcanism and sedimentation in the proximal areas of a mid tertiary volcanic dome field central arizona u s a abstract exposures of an oligocene small volume dome field in central arizona usa provide an excellent example of the interaction of volcanism and sedimentation in a proximal volcanic setting volcanism in the field began with eruption of a shoshonite cinder cone and lava flows which were emplaced onto braided stream gravels stream sediments aggraded to the top of the lava flows before eruption of an amphibole trachyte dome and its derivative pyroclastic flows deposition from the pyroclastic flows was punctuated by fluvial sedimentation which took the form of both sheetflow reworking and debris flow and hyperconcentrated flow deposition the lack of pronounced channel formation may indicate that inter eruptive periods were brief two principles of volcaniclastic sedimentation are well documented in this study first active aggradation may preserve proximal deposits that are normally eroded quickly from a volcano this aggradation is seen in the interstratification of braided stream gravels derived from outside the area of volcanism with dome derived primary pyroclastic deposits the growing dome apparently did not form a large topographic feature and thus did not overwhelm the preservation caused by regional aggradation the landscape response to volcanism was highly complex and the response of the stream system to short term volcanic processes merely accentuated the effects occurring due to longer term tectonic subsidence second because sediments in the proximal areas of the dome were preserved the interaction of the regional dispersal system with the dome complex is clear pyroclastic deposits were in some cases localized in channels reworked pyroclastic deposits have structures indicative of sheetflow or mass flow but are entirely pyroclastic in composition deposits strongly influenced by the regional system are also mass flows or sheetflows but they contain appreciable concentrations of non volcanogenic material and were deposited by debris choked braided streams

evolving history of the east asian summer monsoon intensity during the mis5 inconsistent records from chinese stalagmites and loess deposits as an important component of the global monsoon system the intensity of east asian summer monsoon easm influences lives and economic development of more than 2 billion people the last interglacial period also known as marine isotope stage 5 mis 5 has been thoroughly investigated due to its similarity to the modern interglacial period mis 1 according to records from chinese stalagmites and loess deposits evolving history of easm intensity during mis5 can be divided into 5 sub stages i e 5a 5e however during the 3 warm sub stages 5a 5c and 5e evolving history of easm intensity recorded by chinese stalagmites and loess deposits is apparently different oxygen isotope 18o records of stalagmites demonstrate that the easm intensity during mis5e 5c and 5a is not obviously different on the other hand easm intensity apparently decreased from mis5e to 5c and 5a based on chinese loess deposits records the discrepancy between chinese stalagmite and loess deposits reveals that 18o records of stalagmites may not be a pure indicator of easm intensity the relationship between 18o and easm intensity is not linear based on 18o data of modern precipitation from 21 weather stations within major monsoon area in china mmac ca 110 e to 122 e 18 n to 41 n we speculate that chinese stalagmite 18o values recorded changes of 18o of summer precipitation as well as adjustment from 18o of winter precipitation inconsistent records from chinese stalagmites and loess deposits indicate that further investigations are needed to study the mechanism and fractionation of 18o in stalagmites collected in china

chronology and climatic implications of late quaternary glaciations in the goriganga valley central himalaya india abstract goriganga valley which is located in the transition zone between the dry steppe of the tibetan plateau in the north and the sub humid himalayan climate in the south has preserved four events of glaciation with decreasing magnitude the oldest stage i glaciation is represented by a 12 5 km long discontinuous diamictite ridge which terminates north of rilkot 3100 m asl the stage ii glaciation is represented by sub rounded and partially eroded lateral moraines and terminates around martoli village 3240 m asl the stage iii and iv glacial moraines are sharp crested unstable and terminate proximal to the present day glacier at 3640 m asl and 3740 m asl respectively the stage ii moraines have been optically dated between 25 2 ka and 22 1 ka implying that glacier expanded during the global last glacial maximum lgm this is contrary to the suggestion that during last glacial maximum lgm glaciation was limited in extent due to weak indian summer monsoon ism in the monsoon dominated regions of the himalaya we ascribe the lgm glaciations to a combination of the lowered temperature and enhanced mid latitude westerlies following the lgm glaciation goriganga valley experienced two major pulses of deglaciation the older event is dated between 16 and 12 ka and is coeval with the initiation of the ism whereas the younger events 10 8 ka represent the early to mid holocene strengthened ism the stage iii and iv glaciations which terminated proximal to the modern glacier are speculated to occur during the mid holocene and little ice age lia respectively

interpretation of neovolcanic versus palaeovolcanic sand grains an example from miocene deep marine sandstone of the topanga group southern california despite abundant data on volcaniclastic sand stone the compositional spatial and temporal distribution of volcanic detritus within the sedimentary record is poorly documented one of the most intricate tasks in optical analysis of sand stone containing volcanic particles is to distinguish grains derived by erosion of ancient volcanic rocks i e palaeovolcanic noncoeval grains from grains generated by active volcanism subaqueous and or subaerial during sedimentation neovolcanic coeval grains deep marine volcaniclastic sandstones of the middle topanga group of southern california are interstratified with 3000 m thick volcanic deposits both subaqueous and subaerial lava and pyroclastic rocks ranging from basalt andesite to dacite these rocks overlie quartzofeldspathic sandstones petrofacies 1 of the lower topanga group derived from deep erosion of a mesozoic magmatic arc changes in sandstone composition in the middle topanga group provide an example of the influence of coeval volcanism on deep marine sedimentation volcaniclastic strata were deposited in deep marine portions of a turbidite complex volcaniclastic apron built onto a succession of intrabasinal lava flows and on the steep flanks of subaerially emplaced lava flows and pyroclastic rocks distinctive petrofacies 2 5 directly overlying basalt and basaltic andesite lava flows petrofacies 2 is a pure volcanolithic sandstone including vitric microlitic and lathwork volcanic grains and neovolcanic crystals plagioclase pyroxene and olivine the abundance of quenched glass palagonite fragments suggests a subaqueous neovolcanic provenance whereas sandstones including andesite and minor basalt grains suggest subaerial neovolcanic provenance this petrofacies probably was deposited during syneruptive periods testifying to provenance from both intrabasinal and extrabasinal volcanic events deposited during intereruptive periods impure volcanolithic petrofacies 3 includes both neovolcanic 85 and older detritus derived from plutonic metamorphic and palaeovolcanic rocks during post eruptive periods the overlying quartzofeldspathic petrofacies 4 and 5 testify to progressive decrease of neovolcanic detritus 48 14 and increase of plutonic metamorphic and palaeovolcanic detritus the upper topanga group calabasas formation conformably overlying the middle unit has dominantly plutoniclastic sandstone petrofacies 6 neovolcanic detritus is drastically reduced 4 whereas palaeovolcanic detritus is similar to percentages of the lower topanga group petrofacies 1 the middle topanga group sandstones are vertically organized into four

climate impact of late quaternary equatorial pacific sea surface temperature variations magnesium calcium data from planktonic foraminifera in equatorial pacific sediment cores demonstrate that tropical pacific sea surface temperatures ssts were 2 8 0 7 c colder than the present at the last glacial maximum glacial interglacial temperature differences as great as 5 c are observed over the last 450 thousand years changes in sst coincide with changes in antarctic air temperature and precede changes in continental ice volume by about 3 thousand years suggesting that tropical cooling played a major role in driving ice age climate comparison of sst estimates from eastern and western sites indicates that the equatorial pacific zonal sst gradient was similar or somewhat larger during glacial episodes extraction of a salinity proxy from the magnesium calcium and oxygen isotope data indicates that transport of water vapor into the western pacific was enhanced during glacial episodes

primary or secondary distal volcaniclastic turbidites how to make the distinction an example from the miocene of new zealand mahia peninsula north island abstract miocene marine volcaniclastic deposits occur in mahia peninsula north island new zealand and were sedimented in a forearc setting related to the hikurangi trench subduction system these deposits are interbedded with hemipelagic marls and correspond to simple or amalgamated centimetric to metric thick turbiditic sequences volcaniclastic material is mainly composed of vitric particles with crystals quartz plagioclase with minor biotite amphibole pyroxene and oxides which are well represented in the coarse grained fraction the glass shards are mainly rhyolitic in composition three types of volcaniclastic turbidites were distinguished with geochemical data because distinction is impossible on sedimentary characteristics 1 primary monomagmatic turbidites contain both magmatic bubble wall pumice and shards and phreatomagmatic blocky shards with few vesicles and hydroclastically fragmented pyroclasts vitric particles the chemical compositions of the vitric particles and the crystals are very homogeneous suggesting a cogenetic origin these turbidites directly result from unique eruptive events and are probably related to the entrance of hot subaerial pyroclastic flows into the sea which also led to their transformation into subaqueous gravity flows 2 secondary monomagmatic turbidites never contain phreatomagmatic pyroclasts and the glass compositions display a trend from andesites to rhyolites there is a strong linear correlation in the compositions that suggest that the glass particles are derived from the same magma crystals also show a compositional homogeneity these deposits reflect the succession of several eruptions related to a unique magmatic system and result of the reworking of volcaniclastic material after relatively short storage on the shelf 3 secondary multimagmatic turbidites do not display compositional homogeneity of their vitric and mineral components this implies that the volcaniclastic material has been stored during a relative long period on the shelf before remobilization and that this sedimentation records the volcanic activity of multiple magmatic sources consequently it has been possible to distinguish primary volcaniclastic turbidites that are directly related to the volcanic activity from secondary turbidites that result from reworking of previously deposited material on the shelf monomagmatic turbidites can be used as stratigraphic and magmatic markers whereas multimagmatic cannot multimagmatic turbidites however record the evolution of the volcanic arc during longer periods this leads to the conclusion that the mahia peninsula volcaniclastic turbidites distally record the evolution of the source volcanic arc

climatic tectonic and volcanic controls of sediment supply to an oligocene foredeep basin the val d aveto formation northern italian apennines abstract the val d aveto formation is a turbidite sequence deposited in the northern apennines during the oligocene 32 29 ma the occurrence of calcareous siliciclastic volcaniclastic and carbonatoclastic deposits makes the val d aveto formation a natural laboratory to study the interplay among climate tectonics and volcanism in a subduction related context eight logs have been studied in order to reconstruct the stratigraphic architecture of the succession ten different facies one limestone senso lato facies four siliciclastic facies four volcaniclastic facies and one carbonatoclastic facies have been recognized on the basis of their different sedimentary features microtextures and matrix compositions through thin section analysis and x ray powder diffraction for the first time syn volcanic facies pyroclastic density current and epiclastic deposits have been distinguished from post volcanic facies in the volcaniclastic facies compositional trends of sandy to muddy detritus together with image analyses on gravel dimensions highlight spatial and temporal persistence of the syn depositional volcanic activity across the source to sink system lithological and petrographic analyses on the gravel size fraction of the siliciclastic and volcaniclastic detritus point out a se france provenance and reveal the strong influence that tectonics has on sediment production the comparison between the geodynamic evolution of the source area and the stratigraphic evolution of the val d aveto formation can help unravel the importance of climate on the redistribution of tectonically produced sediments and shaping of the resulting submarine fan

assessing influence of diagenetic carbonate dissolution on planktonic foraminiferal mg ca in the southeastern arabian sea over the past 450 ka comparison between globigerinoides ruber and globigerinoides sacculifer 1 the influence of supralysoclinal calcite dissolution on the mg ca thermometer over the last 450 ka is assessed using globigerinoides ruber and globigerinoides sacculifer from a core site in the eastern arabian sea the studied site is characterized by precession cycled paleoproductivity changes that have induced calcite dissolution in the sediments although the core still contains 40 80 caco3 during high productivity periods the narrow sized test weights of both foraminiferal species tend to decrease with increasing mn ca ratio indicating corrosive pore water conditions scanning electron microscope observations show that g sacculifer maintains a better preserved test ultrastructure than g ruber microprobe mapping reveals that mg rich bands in g ruber chamber walls are preserved despite reduced ca content assuming that the low test weight and offset in mg ca temperature between g sacculifer and g ruber are exclusively produced by calcite dissolution the bias in mg ca temperature determination can be estimated at around 1 c comparable to uncertainty of this thermometry despite the evidence for test dissolution foraminiferal mg ca seems to preserve initial temperature signals under the studied conditions

a glimpse of the quaternary monsoon history from india and adjoining seas abstract the evolution of the monsoon is briefly summarized taking into account previous studies conducted on both terrestrial and marine records recovered from the indian subcontinent and the adjoining seas while the initiation of the monsoon is debated it seems clear that a major intensification of the summer monsoon occurred at 8 2 ma a seasonal monsoon circulation with distinct summer and winter monsoon phases was established at 2 8 ma in the late quaternary the summer monsoon weakens during glacial periods as compared to interglacial periods the centennial to sub centennial scale changes in the monsoon during both glacial and interglacial periods suggest strong links between high latitude processes and the tropical monsoon and its role in modulating northern hemispheric climate the glacial terminations are marked by weak monsoon activity the summer monsoon weakened during the middle holocene after the early holocene optimum a change in the monsoon intensity though alters the salinity of the seas surrounding india the quantitative paleosalinity reconstructions still have large associated uncertainties and an effort should be made to lower them

chemistry of surface sediment along a north south transect across the equator in the central indian basin an assessment of biogenic and detrital influences on elemental burial on the seafloor nineteen surface sediment samples collected along a north south transect across the equator in the central indian basin cib were analysed for their major minor and rare earth element ree composition in absence of the element flux data we demonstrate here the association of various elements and their preferential sinks using inter elemental associations in sediment exhibiting latitudinal dissimilarity biogenic sedimentation north of the equator 1 to 4 n latitudes is dominated by carbonate ooze whereas south of the equator 4 to 14 s latitudes is dominated by siliceous ooze carbonate ooze deposition 60 caco3 above 4400 m and its drastic reduction to 80 of their respective total content in all the three sediment zones these observations suggest a close link between ba and a mn oxide phase on the other hand nearly overlapping latitudinal trends of alxs with carbonate in areas north of the equator and opal south of the equator strong positive correlation of alxs with opal r 0 8 similar ratios between carbonate free opal and alxs 16 in both biogenic sediments suggest a close link between productivity and alxs the alxs proportion in both biogenic sediment types is around 28 of the total al suggesting nearly the same level of primary productivity along the transect 4 n to 14 s which supports the estimates of berger berger w h 1989 global maps of the ocean productivity in w h berger v s smetacek g wefer eds productivity of the ocean present and past dahlem workshop reports wiley chichester pp 429 455 and kabanova kabanova j g 1968 primary production of the northern part of the indian ocean oceanology 8 214 255 i e 70 g cm 2 y 1 the rees exhibit mutual coherence in the sediment r 0 7 however they display an increasing affinity towards mn r increases from 0 6 to 0 8 and decreasing affinity towards ti r decreases from 0 8 to 0 3 with increasing atomic number such a subtle but systematic variation within ree group suggests preferential burial of heavy ree by mn oxide phase and light ree by detrital phase

erosion transport and segregation of pumice and lithic clasts in pyroclastic flows inferred from ignimbrite at lascar volcano chile abstract investigations have been made on the distribution of pumice and lithic clasts in the lithic rich soncor ignimbrite 26 5 ka and the 1993 pumice flow deposits of lascar volcano chile the soncor ignimbrite shows three main lithofacies which grade into one another coarse lithic breccias range from matrix poor stratified varieties irregular shaped sheets and elongate hummocks in proximal environments to breccia lenses with pumiceous ignimbrite matrix massive lithic rich facies comprise the bulk of the ignimbrite pumice rich facies are bimodal with abundant large pumice clasts often with reverse grading rare lithic clasts and occur distally and on high ground adjacent to deep proximal valleys in the 1993 pyroclastic flow deposits lithic rich facies are deposited on slopes up to 14 whereas pumice rich facies are deposited only on slopes

anatomy of a submarine pyroclastic flow and associated turbidity current july 2003 dome collapse soufriere hills volcano montserrat west indies the 12 to 13 july 2003 andesite lava dome collapse at the soufriere hills volcano montserrat provides the first opportunity to document comprehensively both the sub aerial and submarine sequence of events for an eruption numerous pyroclastic flows entered the ocean during the collapse depositing approximately 90 of the total material into the submarine environment during peak collapse conditions as the main flow penetrated the air ocean interface phreatic explosions were observed and a surge cloud decoupled from the main flow body to travel 2 to 3 km over the ocean surface before settling the bulk of the flow was submerged and rapidly mixed with sea water forming a water saturated mass flow efficient sorting and physical differentiation occurred within the flow before initial deposition at 500 m water depth the coarsest components 60 of the total volume were deposited proximally from a dense granular flow while the finer components 40 were efficiently elutriated into the overlying part of the flow which evolved into a far reaching turbidity current

fluvial responses to volcanism resedimentation of the 1800a taupo ignimbrite eruption in the rangitaiki river catchment north island new zealand abstract the potential for the generation of dangerous and damaging lahars and floods in response to the eruption of voluminous pyroclastic debris has become increasingly appreciated in recent years the style and tempo of this response varies both between eruptions and between individual catchments impacted by a single eruption so that an understanding of the factors controlling this variation is necessary for precise hazard assessment the 1800a taupo eruption from the taupo volcanic centre in the central north island of new zealand devastated an area of 20 000 km 2 during eruption of a climactic ignimbrite impacting the headwaters of all major rivers draining radially from this region the rangitaiki river the subject of this paper differs from other catchments in that the taupo ignimbrite buried an essentially flat land surface inherited from a suite of welded ignimbrite sheets erupted between 320 340 and 230 ka the middle reaches of the catchment are characterised by narrow steep gorges alternating with low gradient basins developed in tectonic half grabens initially remobilisation of pyroclastic material in the headwaters was dominated by hyperconcentrated sheet flows resulting in shallow reworking in higher gradient areas reintegration of drainage networks was achieved by incision of deep channels and gullies assisted by breakouts from ephemeral lakelets developed in ignimbrite dammed depressions braided and later meandering streams superseded this pattern as rill and gully systems stabilised and sediment yields fell leading to a decline in drainage density gorge reaches acted as efficient conduits for remobilised material while the basins acted as local depocentres for the temporary storage of volcaniclastic sediments mediating the transfer of pyroclastic debris to the bay of plenty coast 100 km to the north reworking and resedimentation of pyroclastic debris began immediately after the eruption peaking early and then rapidly declining so that most geomorphic adjustments occurred within one or two decades of the initial disturbance

physical controls on sand composition and relative durability of detrital minerals during ultra long distance littoral and aeolian transport namibia and southern angola 2014 international association of sedimentologists sediment in coastal namibia to southern angola is supplied dominantly from the orange river with minor additional fluvial input and negligible modifications by chemical processes which makes this a great test case for investigating physical controls on sand texture and composition this study monitored textural mineralogical and geochemical variability in beach and aeolian dune sands along a ca 1750 km stretch of the atlantic coast of southern africa by using an integrated set of techniques including image analysis laser granulometry optical microscopy raman spectroscopy and bulk sediment geochemistry these results contrast with previous reports that feldspars and volcanic detritus break down during transport that sand grains are rounded rapidly in shallow marine environments and that quartzose sands may be produced by physical processes mechanical wear is unable to modify the relative abundance of detrital components including pyroxene and mafic volcanic rock fragments traditionally believed to be destroyed rapidly the sole exceptions are poorly lithified or cleaved sedimentary metasedimentary rock fragments readily lost at the transition to the marine environment and slow settling flaky micas winnowed and deposited offshore coastal sediments tend to be depleted in relatively mobile amphibole preferentially entrained offshore or re deposited in sheltered beaches while less mobile garnet is retained onshore no detrital mineral displays a significant increase in grain roundness after 300 to 350 km of longshore transport in high energy littoral environments from the orange mouth to south of the namib erg but all minerals get rapidly rounded after passing into the dunefield pyroxene and opaques get rounded faster than harder quartz and garnet but sand mineralogy remains unchanged excepting strong transient selective entrainment effects physical processes are unable to modify sand composition significantly selective mechanical breakdown can be largely neglected in quantitative provenance analysis of sand and sandstone even in the case of ultra long distance transport in high energy environments dominated by strong persistent winds and waves

evidence for global teleconnections in a late pleistocene speleothem record of water balance and vegetation change at sudwala cave south africa abstract understanding the global response to millennial scale climatic events is essential to our comprehension of climatic teleconnections and projection of future change however the extent and nature of their expression in areas of the southern hemisphere is often viewed as equivocal here we report uranium thorium dating of speleothem formations sampled at sudwala cave in the north eastern lowveld region of south africa s summer rainfall zone srz the growth intervals of multiple formations alongside a detailed chronology and multi proxy analysis of two periods of growth 40 35 ka and 13 8 12 8 ka in a stalagmite sc1 provide information regarding key fluctuations in the palaeoclimatic and palaeoenvironmental conditions during the late pleistocene high resolution stable isotope trace element and micro raman analysis are used alongside petrographic investigation to provide a detailed assessment of the climatic conditions associated with the onset and termination of growth in sc1 the combined raman and petrographic analysis represents a rare approach enabling the identification of aragonite calcite shifts both within and across growth intervals and diagenetic events potentially significantly influencing the recorded signal and often resulting in the major loss of chemical information consequently the identification of this post depositional chemical alteration could become a crucial prerequisite in speleothem palaeoclimatology particularly in areas prone to aragonite speleothem deposition susceptible to calcite conversion such as cave sites hosted by dolomitic karst systems the multiple proxies used in this study highlight the complex forcing relationships between climatically related environmental change and local cave conditions on speleothem precipitation contesting a common paradigm by associating drier conditions at sudwala with the initiation of speleothem growth the growth interval identified in stalagmite sc1 during the late deglaciation 13 85 12 79 ka coincides convincingly with both the southern hemispherically forced antarctic cold reversal 14 1 12 8 ka and the younger dryas 12 9 11 5 ka of northern hemispheric origin identifying southern africa as a vital location for the investigation of the hemispheric to global expression of the millennial scale fluctuations of the last deglaciation

energy growth in laharic mass flows lahars debris flows and sediment rich floods are frequent and deadly hazards at all mountain forming volcanoes their hazard potential is traditionally assessed through mass conserving closed system models where peak conversion rates of potential energy to mechanical energy and hence maximum destruction potential are predicted to occur on the steepest volcano flanks this belies evidence of extremely high energy and deadly catastrophes caused by such flows at large distances from volcanoes here we use the first high resolution record of a moving lahar to develop a new model of the temporally and spatially variable mass flow structure we show that bulk flow energy can grow dramatically in such systems over tens to hundreds of kilometers via momentum transfers from the lahar into water and particles along its path we also demonstrate that dynamic transformations of such flows and their ultimate runout are primarily controlled by the mass flow front

reply to the comment by zhou et al on revisiting the yanbian terrane implications for neoproterozoic tectonic evolution of the western yangtze block south china precambrian res 151 2006 14 30 precambrian res 154 2007 153 157

application of actualistic models to unravel primary volcanic control on sedimentation taveyanne sandstones oligocene northalpine foreland basin abstract this work is focused on the taveyanne sandstones gres de taveyanne an oligocene volcaniclastic turbidite sequence cropping out in the northern alpine molassa between se france and central switzerland with the aim to investigate the temporal relationship between volcanic activity and sediment supply detailed stratigraphic sedimentological and petrographic xrd analyses on mudstones and point counts on sandstones studies conducted on three sections col de l oulette and flaine in se france taveyanne in sw switzerland allow a discrimination of three main facies among which only one is extremely enriched in volcaniclastic detritus and characterized by features similar to those of disaggregated pyroclastic density current deposits the other two facies are characterized by variable to no volcanic detritus but supplied by crystalline and sedimentary detritus such sediment trends are similar to those of modern volcanically controlled source to sink systems this allows a reinterpretation of the taveyanne sandstones as a syn volcanic turbidite system episodically supplied by large amounts of volcanic detritus which periodically modified the drainage paths moreover the well known temporal and spatial persistence of such modifications in modern settings leads to conciliate the syn volcanic supply with the location of the volcanic centers in the internal part of the alps without invoking particular climatic and tectonic conditions controlling foreland sedimentation

timing cause and consequences of mid holocene climate transition in the arabian sea abstract we reconstruct centennial scale quantitative changes in surface seawater temperature sst evaporation precipitation from mg ca and 18o of surface dwelling planktic foraminifera productivity from relative abundance of globigerina bulloides carbon burial from caco3 and organic carbon corg and dissolved oxygen at sediment water interface covering the entire holocene from a core collected from the eastern arabian sea from the multi proxy record we define the timing consequences and possible causes of the mid holocene climate transition mhct a distinct shift in evaporation precipitation e p is observed at 6 4 ka accompanied by a net cooling of sst the shift in sst and e p is synchronous with a change in surface productivity a concurrent decrease is also noted in both the planktic foraminiferal abundance and coarse sediment fraction a shift in carbon burial as inferred from both the caco3 and corg coincides with a change in surface productivity a simultaneous decrease in dissolved oxygen at the sediment water interface suggests that changes affected both the surface and subsurface water a similar concomitant change is also observed in other cores from the arabian sea as well as terrestrial records suggesting a widespread regional mhct the mhct coincides with decreasing low latitude summer insolation perturbations in total solar intensity and an increase in atmospheric co2

long runout pyroclastic surge on a cretaceous alluvial plain republic of korea pyroclastic surge is a dilute and turbulent flow of volcanic gas and tephra that is commonly generated during explosive volcanic eruptions and can threaten lives along its flow paths assessing its travel distance and delineating future volcanic hazards have therefore been major concerns of volcanologists historical eruptions show that most pyroclastic surges travel a few tens of kilometres or less from their sources aeolian or aquagene processes have therefore been evoked for the emplacement of supposed surge deposits much beyond this distance here we show that a cretaceous tuff bed in korea was emplaced by an exceptionally powerful pyroclastic surge that flowed as far as the most powerful pyroclastic flows that formed the low aspect ratio ignimbrites lari this has significant implications for interpreting ancient volcanic eruptions and delineating volcanic hazards by pyroclastic surges and casts intriguing questions on the eruption dynamics and physics of long runout pyroclastic surges and their distinction from lari forming pyroclastic flows

construction of volcanic records from marine sediment cores a review and case study montserrat west indies detailed knowledge of the past history of an active volcano is crucial for the prediction of the timing frequency and style of future eruptions and for the identification of potentially at risk areas subaerial volcanic stratigraphies are often incomplete due to a lack of exposure or burial and erosion from subsequent eruptions however many volcanic eruptions produce widely dispersed explosive products that are frequently deposited as tephra layers in the sea cores of marine sediment therefore have the potential to provide more complete volcanic stratigraphies at least for explosive eruptions nevertheless problems such as bioturbation and dispersal by currents affect the preservation and subsequent detection of marine tephra deposits consequently cryptotephras in which tephra grains are not sufficiently concentrated to form layers that are visible to the naked eye may be the only record of many explosive eruptions additionally thin reworked deposits of volcanic clasts transported by floods and landslides or during pyroclastic density currents may be incorrectly interpreted as tephra fallout layers leading to the construction of inaccurate records of volcanism this work uses samples from the volcanic island of montserrat as a case study to test different techniques for generating volcanic eruption records from marine sediment cores with a particular relevance to cores sampled in relatively proximal settings i e tens of kilometres from the volcanic source where volcaniclastic material may form a pervasive component of the sedimentary sequence visible volcaniclastic deposits identified by sedimentological logging were used to test the effectiveness of potential alternative volcaniclastic deposit detection techniques including point counting of grain types component analysis glass or mineral chemistry colour spectrophotometry grain size measurements xrf core scanning magnetic susceptibility and x radiography this study demonstrates that a set of time efficient non destructive and high spatial resolution analyses e g xrf core scanning and magnetic susceptibility can be used effectively to detect potential cryptotephra horizons in marine sediment cores once these horizons have been sampled microscope image analysis of volcaniclastic grains can be used successfully to discriminate between tephra fallout deposits and other volcaniclastic deposits by using specific criteria related to clast morphology and sorting standard practice should be employed when analysing marine sediment cores to accurately identify both visible tephra and cryptotephra deposits and to distinguish fallout deposits from other volcaniclastic deposits

posteruption suspended sediment transport at mount st helens decadal scale relationships with landscape adjustments and river discharges received 11 december 2002 revised 30 september 2003 accepted 18 november 2003 published 17 january 2004 1 widespread landscape disturbance by the cataclysmic 1980 eruption of mount st helens abruptly increased sediment supply in surrounding watersheds the magnitude and duration of the redistribution of sediment deposited by the eruption as well as decades to centuries old sediment remobilized from storage have varied chiefly with the style of disturbance posteruption suspended sediment transport has been greater and more persistent from zones of channel disturbance than from zones of hillslope disturbance despite the severe landscape disturbances caused by the eruption relationships between discharge magnitudes and frequencies and suspended sediment transport have been remarkably consistent discharges smaller than mean annual flows generally have transported 5 but locally 15 of the annual suspended sediment loads and infrequent p 0 01 large floods have transported as much as 50 of the annual suspended sediment loads in a single day however moderate magnitude discharges those greater than mean annual flows but less than 2 year floods have transported the greatest amounts of sediment from all disturbance zones such discharges have transported on average 60 to 95 of the annual suspended sediment loads usually within cumulative periods of 1 3 weeks each year although small magnitude and largemagnitude discharges have locally and episodically transported considerable amounts of suspended sediment there has not been any notable change in the overall nature of the effective discharges moderate magnitude flows have been the predominant discharges responsible for transporting the majority of suspended sediment during 20 years of posteruption landscape adjustment index terms 1824 hydrology geomorphology 1625 1815 hydrology erosion and sedimentation 1860 hydrology runoff and streamflow keywords sediment yield suspended sediment transport mount st helens erosion volcano geomorphology

hydrographic changes in the southern bay of bengal during the last 65 000 y inferred from carbon and oxygen isotopes of foraminiferal fossil shells abstract we present 13 c and 18 o records of planktonic globigerinoides ruber and benthic foraminifera cibicidoides spp from two deep sea sediment cores sk157 15 and sk157 16 from the southern bay of bengal the chronology of these gravity cores was established using eleven ams radiocarbon ages from mixed species of planktonic foraminifera globigerinoides ruber and globigerinoides sacculifer and oxygen isotope stratigraphy large variations in 13 c and 18 o of planktonic and benthic foraminifera in these cores are suggestive of significant changes in surface and deep water masses for the 65 ka bp the 18 o values in planktonic foraminifera in both these cores are significantly higher relative to sediment cores from the western bay of bengal and the andaman sea because of the reduced influence of riverine fresh water fluxes benthic 13 c values in cores sk157 15 and sk157 16 exhibit significant variations in source water characteristics during the holocene and the last glaciation large decrease in 13 c values of bottom dwelling benthic foraminifera cibicidoides spp during the last glacial maximum lgm and 50 65 ka bp suggest drastic reduction in north atlantic deep water nadw fluxes into the southern bay of bengal and concurrent increase of deep water formed in the southern ocean sodw with significantly low 13 c values

volcaniclastic stratigraphy of gede volcano west java indonesia how it erupted and when abstract gede volcano west java indonesia is located 60 km south of jakarta within one of the regions with highest population density in the world therefore knowledge of its eruption history is necessary for hazard evaluation because even a small eruption would have major societal and economic consequences here we report the results of the investigation of the stratigraphy of gede with the focus on its volcaniclastic deposits of holocene age and include 23 new radiocarbon dates we have found that a major part of the volcanic edifice was formed in the pleistocene when effusions of lavas of high silica basalt dominated during this period the volcano experienced large scale lateral gravitational failure followed by complete reconstruction of the edifice formation of the summit subsidence caldera and its partial refilling after a repose period of 30 000 years the volcanic activity resumed at the pleistocene holocene boundary in the holocene the eruptions were dominantly explosive with magma compositions ranging from basaltic andesite to rhyodacite many deposits show heterogeneity at the macroscopic hand specimen scale and also in the minerals which indicates interactions between mafic basaltic andesite and silicic rhyodacite magmas significant eruptions of the volcano were relatively rare and of moderate violence the highest vei was 3 4 the largest volume of erupted pyroclasts 0 15 km3 there were 4 major holocene eruptive episodes ca 10 000 4000 1200 and 1000 yr bp the volcanic plumes of these eruptions were not buoyant and most of the erupted products were transported in the form of highly concentrated valley channelized pyroclastic flows voluminous lahars were common in the periods between the eruptions the recent eruptive period of the volcano started approximately 800 years ago it is characterized by frequent and weak vei 1 2 explosive eruptions of vulcanian type and rare small volume extrusions of viscous lava we estimate that during last 10 000 years gede erupted less than 0 3 km3 dre dense rock equivalent of magma such small productivity suggests that the likelihood of future large volume vei 5 eruptions of the volcano is low although moderately strong vei 3 4 explosive eruptions capable of depositing pyroclastic flows and lahars onto the ne foot of the volcano are more likely

interpreting provenance relations from sandstone detrital modes southern italy foreland region stratigraphic record of the miocene tectonic evolution abstract the southern italy orogen preserves deep marine turbitic clastic wedges that record the key tectonic events during structural growing over the adria margin the regional tectonic transition from thick skinned calabrian accretion and deformation during late paleogene to middle miocene to thin skinned southern apennines thrusting since early middle miocene is recorded by diverse contrasting petrofacies in uppermost paleogene and miocene sandstones of dominantly turbiditie deposits most of these sandstones reflect in time quartzolithic and quartzofeldspathic and arkosic petrofacies derived from growing and unroofing calabrian terranes quartzose petrofacies mainly indicate provenance from cratonal african margin during langhian and or from lowland internal domains before its deformation during the cretaceous to paleogene volcaniclastic sandstone petrofacies also testify active volcanism during the late paleogene to early miocene these variable compositions indicate strong palaeogeographic constraints for the central western mediterranean during the neogene reflecting provenance relationships from differentiate source rocks these include interplays between ophiolitiferous uplifted continental shallow to deep crust terranes volcanic and sedimentary mostly carbonate source rocks sandstone detrital modes provide an example of the close relations between clastic compositions and growing orogen in southern italy and may contribute to unravel the geodynamic history of other major orogens

detrital geochronology of unroofing magmatic complexes and the slow erosion of oligocene volcanoes in the alps abstract tectonic reconstructions and quantitative models of landscape evolution are increasingly based on detailed analysis of detrital systems since the definition of closure temperature in the 1960s mineral ages of low temperature geochronometers are traditionally interpreted as the result of cooling induced by erosion whose rate is a simple unique function of age patterns such an approach can lead to infer paradoxically high erosion rates that conflict with compelling geological evidence from sediment thickness in basins this indicates that tectonic and landscape models that solely interpret mineral ages as due to cooling during exhumation may not be valid here we propose a new approach that takes into account the effects of both crystallization and exhumational cooling on geochronometers from u pb on zircon to fission tracks on apatite we first model the mechanical erosion of an unroofing magmatic complex and the resulting accumulation and burial of the eroded units in reverse order in the basin detrital mineral ages follow a regular pattern downsection some mineral ages such as e g u pb ages of zircons cluster around the magmatic age i e the crystallization of the magma its value is constant along the stratigraphic column in the sedimentary basin we refer to this behavior as stationary age peak some other mineral ages such as e g apatite fission track ages are often younger than the magmatic age when they vary smoothly with depth they define a moving age peak which is the only possible effect of undisturbed cooling during overburden removal and can therefore be used to calculate an erosion rate the predictions of our model were tested in detail on the extremely well studied bregaglia bergell orogenic pluton in the alps and on the sedimentary succession derived from its erosion the gonfolite group the consistency between predicted and observed age patterns validates the model our results resolve a long standing paradox in quantitative modelling of erosion sedimentation namely the scarcity of sediment during apparently fast erosion starved basins are the observational baseline and modelling must be tuned to include a correct analysis of detrital mineral geochronology in order to reconcile perceived discrepancies between stratigraphical and geochronological information in addition our data demonstrate that volcanoes were active on top of the growing oligocene alps this study illustrates rigorous criteria for detrital mineral geochronology that are applicable to any geological setting including magmatic arcs and collision orogens and provides fundamental interpretive keys to solve complex puzzles and apparent paradoxes in geological reconstructions

timing and emplacement dynamics of newly recognised mass flow deposits at 8 12ka offshore soufriere hills volcano montserrat how submarine stratigraphy can complement subaerial eruption histories this contribution describes two mass movement deposits total volume 0 5 km3 identified in seven marine cores located 8 to 15 km offshore southern montserrat west indies the deposits were emplaced in the last 35 ka and have not previously been recognised in either the subaerial or distal submarine records age constraints provided by radiocarbon dating show that an explosive volcanic eruption occurred at ca 8 12 ka emplacing a primary eruption related deposit that overlies a large 0 3 km3 reworked bioclastic and volcaniclastic flow deposit formed from a shelf collapse between 8 and 35 ka the origin of these deposits has been deduced through the correlation of marine sediment cores component analysis and geochemical analysis the 8 12 ka primary volcanic deposit was likely derived from a highly erosive pyroclastic flow from the soufriere hills volcano that entered the ocean and mixed with the water column forming a water supported density current previous investigations of the eruption record suggested that there was a hiatus in activity at the soufriere hills volcano between 16 and 6 ka the ca 8 12 ka eruptive episode identified here shows that this hiatus was shorter than previously hypothesised and thus highlights the importance of obtaining an accurate and complete marine record of events offshore from volcanic islands and incorporating such data into eruption history reconstructions comparisons with the submarine deposit characteristics of the 2003 dome collapse also suggests that the 8 12 ka eruptive episode was more explosive than eruptions from the current eruptive episode

el escondido a newly identified silicic quaternary volcano in the ne region of the northern volcanic segment central cordillera of colombia abstract el escondido 1650 m a s l is a silicic quaternary volcano recently identified on the central cordillera of colombian andes it is located about 50 km ne from the northern segment of active volcanoes it has been recognized as a polygenetic pyroclastic dome ring complex structure whose eruptive products derived from a crater like semi circular depression of 1 7 km in diameter this crater formed at the contact of the granitic florencia stock 54 9 1 8 my with the paleozoic metamorphic basement and at the intersection of the nnessw trending palestina fault system with an ew trending fault the preserved volcano morphology and the volcanic succession associated with it were defined as the el escondido volcanic center the eruptive products are alternating silicic mostly dacitic pyroclastic density current deposits pumice fall deposits and ballistic projectiles which suggest high explosiveness two 14c radiogenic dates obtained on carbonized wood fragments of the middle part of the eruptive sequence displayed ages of 36 030 380 bp and 33 550 280 bp suggesting two major eruptive episodes of the volcano about 2500 years apart the latest eruptive activity is inferred to be the emplacement of lava domes to the south of the crater like structure which are responsible for the partial destruction of the pyroclastic ring in that sector the products emitted by el escondido correspond to medium k andesites to dacites of the calc alkaline series and petrographically to amphibolic andesites towards the western and eastern sector of the volcano there are chlorinated thermal waters with temperatures up to 45 c the first monitoring of the volcanic activity carried out by the colombian geological survey cgs through the volcanological and seismological observatory of manizales vsom has not detected so far unusual volcano seismic activity the previously unreported el escondido volcano represents one of the northernmost occurrence of quaternary volcanism in the whole andean cordillera thus its study may have wide implications regarding the geodynamics of the region and subduction zone the correct assessment of geologic hazards and the identification of natural resources like geothermal reservoirs and mineral deposits of economic interest

adakitic granites within the ne jiangxi ophiolites south china geochemical and nd isotopic evidence geochemical and nd isotopic data are reported for the ca 970 ma albite granites within the neoproterozoic ne jiangxi ophiolite south china these granites are high in al2o3 15 17 na2o 7 3 8 5 mg 43 62 sr 383 920 ppm sr y 166 444 and y yb 12 14 but low in k2o 0 2 0 6 tio2 0 3 p2o5 0 1 furthermore they display consistently high morb like initial end values of 4 6 to 6 7 at ca 970 ma these geochemcial and isotopic characters are similar to those of the modern adakites compared with the modern adakites the xiwan albite granites are depleted in middle to heavy ree with y yb ratio of 12 14 which can be attributed to residual amphibole and garnet in the source geological and geochemical features suggested that the granites were generated by low degrees of partial melting of subducted spilitized oceanic crust at pressures high enough to stabilize garnet and amphibole these are the first adakitic granites identified within the ne jiangxi ophiolite their presence shows that granitic rocks that intrude ophiolites can be generated not only during the processes of sea floor spreading oceanic crust shearing and obduction of fragmented oceanic lithosphere as previously thought but also during the process of subduction of oceanic lithosphere the shrimp u pb zircon age of 968 23 ma for the xiwan adakitic granite geochimica 23 1994 117 should be re interpreted as the timing of subduction of oceanic crust rather than as the age of oceanic crustal formation as previously interpreted

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr