paleovegetation simulations of lowland amazonia and implications for neotropical allopatry and speciation paleovegetation modeling simulations of the lowland amazon basin were made to assess the relative importance of glacial climate and atmospheric co2 for altering vegetation type and structure as well as to explore the potential physiological mechanisms underlying these ecosystem level responses modeling results support the view that widespread invasion of grasslands into the amazon lowlands during the last glaciation was not likely glacial cooling was probably responsible for maintaining glacial forest cover via its effects in reducing photorespiration and decreasing evapotranspiration which collectively improve plant carbon and water relations modeling results confirm that leaf area index lai a common proxy for canopy density is highly sensitive to independent and interactive changes in climate and low concentration of atmospheric co2 and the results show considerable region to region variation during the last glaciation heterogeneous variations in glacial vegetation lai may have promoted allopatric speciation by geographically isolating species called vicariance in the forest sub canopy the proposed vicariance hypothesis incorporating spatial variations in canopy density conforms to many of the essential tenets addressed by previous neotropical speciation models but also helps to overcome some of their inconsistencies c 2001 university of washington

neogene and quaternary history of vegetation climate and plant diversity in amazonia the neotropical amazonian and andean plant diversity developed mainly during the tertiary in amazonia miocene oral diversity seems considerably higher than today during the neogene tropical taxa entered newly created montane area and montane taxa entered the tropical lowlands the general decrease of temperature during the upper neogene and especially during the quaternary glacial periods may have caused considerable extinctions in the lowlands representation of pollen of apparently principally montane taxa podocarpus hedyosmum in miocene pliocene and quaternary sediments of amazonia and surroundings is still di cult to interpret in terms of temperature decrease at low elevation changes in precipitation may have profound impact on the composition of vegetation communities ilex and melastomataceae increase signi cantly in many glacial pollen records increase of weinmannia in amazonian pollen records seems the best indicator of downward migration of montane vegetation belts a temperature lowering at sea level of 4 5 13c during the last glacial maximum lgm seems reasonable it may have caused a downslope migration of some 700 m of the lower montane vegetation belt lower montane arboreal species may have been able to grow in higher elevation areas 500 m of amazonia increasing background pollen values of montane taxa in the area di erence between a cool and wet middle pleniglacial 60 28 ka bp and a cold and dry upper pleniglacial 28 14 ka bp thus including the lgm is evident in andean and amazonian records statements about environmental conditions of the ice age amazon should be speci ed chronologically the middle pleniglacial is a time of accumulation of uvial sediments the upper pleniglacial is a time of incision of the rivers in their sediments sedimentation started again in the lateglacial since ca 13 ka bp and the holocene when lake levels rose again based on simpli ed considerations of precipitation changes and evaporation we estimate that lgm rainfall may have been reduced by values of ca 45 10 amazonian and cordilleran lakes dried up dry rain forest was locally replaced by savanna savanna forest or cerrado type vegetation dry rain forest savanna forest and pure savanna was locally replaced by extensive semi desert dune formations lower rio branco area in present day central amazonia the present day centers of higher rainfall 2500 mm surrounded by areas of lower rainfall are refuge areas of the very wet rain forest and of the very high plant diversity 300 plant species per 0 1 ha and they should have been that equally or more during the dry climate intervals plant diversity of drier forests is in the order of 100 150 species per 0 1 ha both extinction and speciation in isolation under precipitation and temperature stress may have taken place in these refugia 2000 elsevier science ltd all rights reserved

local site effects in atakoy istanbul turkey due to a future large earthquake in the marmara sea summary since the 1999 izmit and duzce earthquakes in northwest turkey many seismic hazard studies have focused on the city of istanbul an important issue in this respect is local site effects strong amplifications are expected at a number of locations due to the local geological conditions in this study we estimate the local site effects in the atakoy area southwestern istanbul by applying several techniques using synthetic data hybrid 3 d modelling and 1 d modelling and comparing to empirical data we apply a hybrid 3 d finite difference method that combines a complex source and wave propagation for a regional 1 d velocity model with site effects calculated for a local 3 d velocity structure the local velocity model is built from geological geotechnical and geomorphological data the results indicate that strongest spectral amplifi cations sa in the atakoy area occur around 1 hz and that amplification levels are largest for alluvial sites where sa reaching a factor of 1 5 2 can be expected in the case of a large earth quake we also compare our results to h v horizontal to vertical component of the recorded signal spectral ratios calculated for microtremor data recorded at 30 sites as well as to ambient noise synthetics simulated using a 1 d approach because the applied methods complement each other they provide comprehensive and reliable information about the local site effects in atakoy added to that our results have significant implications for the southwestern parts of istanbul built on similar geological formations for which therefore similar sa levels are expected

palaeoreconstruction of the amazon river freshwater and sediment discharge using sediments recovered at site 942 on the amazon fan a continuous reconstruction of palaeoclimate has been generated for the last 12 000 c 14 yr bp from odp site 942 5 degrees 45 n 49 degrees 6 w at a water depth of 3346 m drilled to the west of the amazon fan records from the site suggest that during the younger dryas the amazon basin was extremely dry and amazon river discharge was low this increased aridity is hypothesised to be due predominantly to reduced precipitation in addition there is evidence for a discharge event at the end of the younger dryas coeval with termination 1b that produced an estimated amazon river outflow equivalent to present day values and an increase in sediments derived from the andes the timing of this event coincident with the warming of the andean ice sheet suggests that it was at least partly driven by meltwater produced by the retreat of andean glaciers but also required an increase in regional rainfall resulting from changes in climate site 942 also demonstrates that the sediment input to the western part of the amazon fan from the river ceased between 9900 and 9500 c 14 yr bp at a time when sea level was 40 50 m below the present level if this value is truly indicative of the sea levels at which the sediment supply to the fan switched off then it is far greater than the 30 m below current sea level suggested previously copyright c 2000 john wiley sons ltd

late glacial cooling in amazonia inferred from pollen at lagoa do caco northern brazil new pollen data from a core at lagoa do caco maranhao state brazil 2 58 s 43 25 w 120 m elevation show higher frequencies of podocarpus at the end of the pleistocene than today the increase in podocarpus which follows the successive increase of various pioneer species such as didymopanax melastomataceae combretaceae and cecropia implies a progressive late glacial increase of moist and cool climatic conditions a comparable increase in podocarpus is found in other lowland records in amazonia a review of published pollen data from amazonia suggests that the moisture source was from the southeast by contrast present day moisture comes from the tropical atlantic and from the amazon basin with its convective precipitation the likely cause for the southeastern moisture source between ca 15 000 and 14 500 cal yr b p was enhanced polar antarctic advection that reached low latitudes and maintained year round the meteorological equator in its austral winter position at northern latitudes or reduced drastically its southward summer displacement this hypothesis is consistent with marine and ice core records

basement hosted quartz barite sulfide veins in the french alps a record of alpine tectonic fluid expulsion in the external crystalline massifs structural fluid inclusion and isotope s and sr evidences quartz barite sulfide veins hosted by a late variscan monzonite in the polymetamorphic basement of the aiguilles rouges massif western alps france have been the subject of a combined structural microthermometric fluid inclusion and sulfur and strontium isotope study the mineralized veins have a maximum age of 40 ma and were emplaced along vertical tension fractures formed or possibly reopened during the mesoalpine thrust phase two mineralization stages have been recognized a major stage of quartz barite veins with minor and irregularly distributed sulfides and sulfosalts and a minor crosscutting stage of quartz stibnite veins fluid inclusion microthermometry homogeneous 87 sr 86 sr ratios of the barite and the texture and mineralogical composition of the polymetallic quartz barite veins indicate that they were formed mainly due to the cooling of a single aqueous fluid with a salinity around 9 wt percent nacl equiv contemporaneous pressure variations cannot be excluded sulfur isotope thermometry yields formation temperatures between 255 degrees and 270 degrees c and combined with the fluid inclusion isochores they indicate pressures of 0 45 to 1 55 kbars corresponding to a depth of 3 6 super 2 3 sub 1 9 km assuming lithostatic conditions sulfur in the fluid was dominated by h 2 s which was oxidized at the ore site due to cooling of the fluid the vein barites are enriched in 87 sr with respect to the host rocks and indicate that the strontium and the barium were leached from deeper lithologies after the emplacement of the quartz barite veins the hydrothermal system was opened toward shallower structural levels allowing the ingress of meteoric water the late quartz stibnite veins are associated with a distinct and warmer co 2 bearing fluid we conclude that the h 2 o nacl ore bearing fluid originated at a depth of about 15 km by dewatering of mesozoic sedimentary rocks during the collisional thrust mesoalpine phase subhorizontal thrust planes between the basement crystalline rocks and overlying sedimentary units inhibited mixing or regeneration of the system with superficial fluids subvertical fluid migration was restricted to faults in the polymetamorphic basement late alpine extension tectonics allowed the upward migration of deep co 2 bearing fluids and also favored the influx of surface fluids that had remained isolated from the h 2 o nacl hydrothermal system

observations on late pleistocene cooling and precipitation in the lowland neotropics although accurate reconstructions of amazonian palaeoclimates are central to under standing the distribution and history of neotropical biodiversity current reconstructions based on proxy data are discordant and subject to intense debate we review some current thinking in amazonian climatology and incorporate some new ideas in an attempt to explain the apparently con tradictory records of palaeoprecipitation from across the amazon basin we suggest that palaeoecol ogists need to recognise that organised convective radiation the process that induces most wet season rainfall in amazonia should be treated as a phenomenon related to but separate from the passage of the inter tropical convergence zone itcz decoupling itcz migration from larger con vective activity provides a mechanism to account for observed palaeoclimatic heterogeneity patterns of observed precipitation change are consistent with the long term persistence of closed forest across much of amazonia indicating that the greatest changes in precipitation during the last glacial max imum came during the wet season which would have little negative impact on forest extent neo tropical cooling at the last glacial maximum lgm is widely accepted although the estimates of that cooling range between 1 c and 5 c in answering the basic question what is meant by cooling we observe that interhemispheric ice mass asymmetry may have caused cooling to be manifested differently according to location a terrestrial cooling of ca 5 c as well as radiative cooling and event based cooling combined to induce vegetation change probably both absolute temperature and mean monthly minima were reduced by polar air incursions in the northern neotropics how ever in the southern neotropics mean monthly minima were reduced by more frequent incursions of patagonian air masses but absolute minima may have been largely unchanged copyright 2004 john wiley sons ltd

eastern tropical pacific vegetation response to rapid climate change and sea level rise a new pollen record from the gulf of tehuantepec southern mexico abstract a 30 000 year long pollen record from the gulf of tehuantepec southern mexico shows the varying influence of air temperature precipitation and eustatic sea level rise on changes in coastal and upland vegetation patterns during the late glacial period pine juniper forests grew in the sierra madre del sur along the pacific slope with broadleaf forests present at low elevations coastal wetland and riparian vegetation were limited in distribution significant cooling associated with heinrich 1 17 000 15 000 cal yr bp resulted in an expansion of pine juniper woodland by the time of bolling allerod warming 14 700 13 000 cal yr bp extensive mangrove forest development was assisted by sea level rise and reduced precipitation associated with a more southerly position of the intertropical convergence zone itcz than at present concurrently the expansion of oak into pine woodlands was promoted by warmer conditions than before increased summer precipitation in the early holocene and stabilizing sea levels limited mangrove forests along the coast and allowed mixed conifer and hardwood forest to become more widespread inland the onset of a more seasonal climate driven by a weakening of the mexican monsoon and a southerly shift in itcz position led to the establishment of modern open forests of pine and oak after 4300 cal yr bp

discussion of an attenuation relationship based on turkish strong motion data and iso acceleration map of turkey by ulusay et al eng geol 74 265 291 2004

2 d p sv and sh spectral element modelling of seismic wave propagation in non linear media with pore pressure effects it has long been recognized that the effects of superficial geological layers or site effects can play a major role on the seismic ground motion at the free surface in this study we compute wave propagation in a 2 d asymmetrical basin considering both soil non linearity and pore pressure effects equations of elastodynamics of wave propagation are solved using the spectral element method sem the geometry of the basin gives rise to basin edge generated waves that are different for in plane p sv and out of plane sh wave propagation and resulting in different non linear response moreover the excess pore pressure development in superficial liquefiable layers effective stress analysis brings larger deformation and loss of strength than the analysis without pore pressure effects total stress analysis the coupling of vertically propagating waves and the waves specifically generated in 1 d model leads to waves whose amplitude and duration are higher than the 1 d case this multidimensional effect increases material non linearity such complex wavefield provokes larger deformation and higher pore pressure rise that cannot be predicted by 1 d modelling therefore our paper suggests the use of multidimensional modelling while studying seismic wave propagation in both linear and non linear complex media

geochronology of the porgera gold deposit papua new guinea resolving the effects of excess argon on k ar and age estimates for magmatism and mineralization abstract mesothermal epithermal gold mineralization at porgera in the highlands of papua new guinea png occurs in structurally controlled veins and disseminations which overprint and cross cut a suite of shallow level comagmatic mafic alkaline stocks and dykes the porgera intrusive complex pic and their sedimentary host rocks conventional k ar apparent ages of twelve hornblende separates from eight different intrusions scatter between 7 and 14 ma but four biotite separates are concordant at 6 02 0 29 ma 2 40 ar 39 ar step heating experiments on six of the hornblende separates reveal saddleshaped age spectra which indicate the presence of excess 40ar one of these samples yields a well defined plateau with an apparent age of 5 96 0 25 ma 2 this age is identical to that of the biotites and suggests an age of 6 0 0 3 ma 2 for emplacement of the pic older apparent ages obtained from conventional k ar and 40 ar 39 ar analyses are explained by excess 40ar contamination conventional k ar analyses of six separates of hydrothermal illite and roscoelite associated with gold mineralization yield apparent ages of between 5 1 and 6 1 ma and indicate that ore deposition occurred within 1 ma of magmatism at porgera evidence for the evolution of a magmatic volatile phase and the presence of excess 40ar both in the intrusives and in hydrothermal fluids associated with the orebody suggest that magmatic fluids may have had some involvement in metallogenesis but the exact nature of this involvement is not yet clear late miocene magmatism and mineralization at porgera are thought to have occurred shortly prior to or during the initiation of continent arc collision and to pre date associated pliocene uplift and foreland deformation in the highlands

stable isotope study of the mineralization and alteration in the madjarovo pb zn district south east bulgaria the madjarovo ore district is centred on the exposed section of a lower oligocene volcano and consists of radially disposed pb zn precious metal veins and attendant intermediate sulfidation wallrock alteration earlier high sulfidation and potassic porphyry style alterations are found in the centre of the district spatially associated with monzonitic intrusions the total duration of all mineralization and alteration was ca 300 ka stable isotope analyses s o h have been carried out on a suite of sulfides sulfates and silicates from the mineralization high and intermediate sulfidation alterations and a suite of basement rocks these data range between the following limits delta 34 s sulfides 1 2 operatorname to 6 8 text delta 34 s sulfates 21 4 text to 24 9 delta 18 o sulfates 5 8 operatorname to 11 6 delta d sulfates 35 1 operatorname to 67 1 delta 18 o silicates 5 2 text to 13 5 delta d operatorname silicates 36 3 to 77 0 we also analysed d of fluid inclusions in quartz and barite for which we obtained respectively the ranges of 43 6 to 78 6 and 58 4 to 67 1 the data show that high sulfidation alteration was dominated by magmatic fluids with minor meteoric water whereas the fluids responsible for the intermediate sulfidation alteration were essentially magmatic the fluids responsible for the intermediate sulfidation pb zn mineralization were mixed magmatic meteoric and certainly contained a significant meteoric component sulphur is likely derived from basement and or igneous sources the evolution of alteration and mineralization styles from potassic porphyry copper style to high sulfidation to intermediate sulfidation can be understood in terms of changing ore fluid composition resulting from an increasing permeability of the system and an increasingly remote source of magmatic fluid with time these changes link directly to the geological evolution of this volcanic centre

environmental changes in southeastern amazonia during the last 25 000 yr revealed from a paleoecological record abstract new pollen micro charcoal sediment and mineral analyses of a radiocarbon dated sediment core from the serra sul dos carajas southeast amazonia indicate changes between drier and wetter climatic conditions during the past 25 000 yr reflected by fire events expansion of savanna vegetation and no analog amazonian forest communities a cool and dry last glacial maximum lgm and late glacial were followed by a wet phase in the early holocene lasting for ca 1200 yr when tropical forest occurred under stable humid conditions subsequently an increasingly warm seasonal climate established the onset of seasonality falls within the early holocene warm period with possibly longer dry seasons from 10 200 to 3400 cal yr bp and an explicitly drier phase from 9000 to 3700 cal yr bp modern conditions with shorter dry seasons became established after 3400 cal yr bp taken together with paleoenvironmental evidence from elsewhere in the amazon basin the observed changes in late pleistocene and holocene vegetation in the serra sul dos carajas likely reflect large scale shifts in precipitation patterns driven by the latitudinal displacement of the inter tropical convergence zone and changes in sea surface temperatures in the tropical atlantic

sources of metals in the porgera gold deposit papua new guinea evidence from alteration isotope and noble metal geochemistry the porgera gold deposit is spatially and temporally associated with the late miocene mafic alkalic epizonal porgera intrusive complex pic located in the highlands of papua new guinea png the highlands region marks the site of a tertiary age continent island arc collision zone located on the northeastern edge of the australasian craton the pic was emplaced within continental crust near the lagaip fault zone which represents an oligocene suture between the craton and volcano sedimentary rocks of the sepik terrane magmatism at porgera probably occurred in response to the late miocene elimination of an oceanic microplate and subsequent early pliocene collision between the craton margin and an arc system located on the bismarck sea plate gold mineralization occurred within 1 ma of the time of magmatism metasomatism accompanying early disseminated au mineralization in igneous host rocks resulted in additions of k rb mn s and co2 and depletions of fe mg ca na ba and sr rare earth and high field strength elements remained largely immobile pervasive development of illite k feldspar quartz carbonate alteration assemblages suggests alteration by mildly acidic 200 to 350 c fluids at high water rock ratios strontium and lead isotopic compositions of minerals from early base metal sulphide veins associated with k metasomatism and later quartz roscoelite veins carrying abundant free gold and tellurides are remarkably uniform e g 87sr86sr 0 70745 0 00044 n 10 207pb204pb 15 603 0 004 n 15 these compositions fall between those of unaltered igneous and sedimentary host rocks and specifically sedimentary rocks from the jurassic om formation which underlies the deposit igneous rocks 87sr86sr 0 7035 207pb204pb 15 560 om formation 87sr86sr t 0 7153 207pb204pb 15 636 it is therefore suggested that the hydrothermal fluids acquired their sr and pb isotopic signatures by interaction with or direct derivation from a plutonic root of the pic and host sedimentary rocks of the om formation it is likely that au was also derived from one or both of these two sources concentrations of au in unaltered igneous and sedimentary rocks from porgera 10 ppb au do not indicate that either lithology represents a significantly enriched protore although au and platinum group element pge abundances in the igneous rocks suggest a mild primary magmatic enrichment of au relative to the pge average au pt pd mantlenormalized 14 0 6 5 n 8 evidence that the porgera magmas were rich in volatiles permits speculation that au may have been concentrated in a magmatic fluid phase but alternative possibilities such as derivation of au by hydrothermal leaching of solidified igneous materials or sedimentary rocks cannot be excluded at this time

simplified empirical method for predicting earthquake induced settlements and its application to a large area in spain abstract most of the commonly used existing empirical methods to predict earthquake induced settlement s in sandy soils require numerous iterations or the use of charts tables and diagrams in general these methods estimate the one dimensional settlement of dry sandy soil on level ground by using a well known step by step procedure based on standard penetration test spt values which is particularly effective for practical applications a review of the state of the art methods shows that seismic settlement in all cases increases as the layer thickness h of sandy soils increases and corrected spt blow count n 1 60 decreases with that in mind we propose a novel simple way to estimate s based on the h n 1 60 ratio for a reference earthquake magnitude this approach provides a tool that can rapidly obtain s in numerous sites and can be applied to large areas in the last fifty years the population of the metropolitan area of granada mag has doubled the amount of developed land has increased by approximately 4650 ha and the areas with the greatest population and construction growth are located on sedimentary deposits the land beneath the urbanized areas of the mag is located on alluvial colluvial silt and clay deposits with different thicknesses of granular soils and varying water table depths the mag is acknowledged to be the most seismically active zone in spain and seismically induced phenomena such as liquefaction and ground settlement were reported in specific zones during moderate 1806 and strong 1431 historical local earthquakes the present study focuses on differential vertical displacement assessment in this large area of southern spain for two earthquakes of magnitude mw 6 6 and 7 0 the maximum expected settlement due to earthquake shaking of alluvial soils sandy soils and fine soils clay and or silt was obtained by correlating the mentioned h n 1 60 ratio with the s predicted by two well known methods v s values have been estimated from n 1 60 data using methods proposed in the literature and tested with v s local data from spac and refraction profiles the results from the new formula proposed here show predictable settlement ranging from 0 1 to 21 4 cm and up to 24 7 cm for the 6 5 and 7 0 earthquakes respectively these were greater than 2 0 cm and 3 3 cm in the north central and north western sectors of the study area especially in the town of atarfe and along the road between pinos puente and atarfe the same zones where settlements were observed in the 1806 earthquake zones where earthquake building damage may appear have been detected by comparing the maximum s and the maximum permitted settlements derived from different angular distortion values considering 5 and 6 m as typical distances between supporting structures

planetary and synoptic scale signatures associated with central american cold surges abstract motivated by outstanding issues from a previous case study of a midlatitude cold surge that affected mexico and central america the climatology of central american cold surges is examined in this paper an independently derived listing of 177 cold surge events is employed for which the following properties are tabulated onset date duration time between cold surge events latitude of maximum equatorward penetration min and 48 h maximum surface temperature change at merida mexico t these data show that 75 of the cold surges have durations of 2 6 days the same timescale as mobile disturbances in the westerlies also there does not appear to be any relationship between t and the duration of the event although cold surges that penetrate to low latitudes min 7 10 n have a weak tendency to persist longer than those that do not penetrate to low latitudes min 15 20 n in addition the reding data indicate that the cold surges tend to reach their most equatorward extent where

the climate of the altiplano observed current conditions and mechanisms of past changes abstract the large scale controls on the climate of the south american altiplano are investigated using local observations reanalysis data and general circulation model experiments the objective is to gain understanding of causes of climate variability and climate change by relating mechanisms that operate on timescales ranging from the intraseasonal to the glacial interglacial our results suggest that on all timescales the climatic conditions on the altiplano are closely related to the upper air circulation with an easterly zonal flow aloft favoring wet conditions and westerly flow causing dry conditions different factors influence the upper air circulation on the different timescales intraseasonal variability is a reflection of the position and intensity of the bolivian high which is modulated by rossby waves emanating from the midlatitude south pacific the annual cycle of dry winter and wet summer conditions is caused by the seasonal expansion of the equatorial easterlies in the upper troposphere rather than direct insolation forcing over the altiplano or moisture changes in the source area interannual variability is primarily related to changes in the mean zonal flow over the altiplano reflecting changes in meridional baroclinicity between tropical and subtropical latitudes which in turn is a response to sea surface temperature changes in the tropical pacific orbitally forced changes in the land sea contrast drive continental scale circulation changes which significantly alter the zonal flow over the altiplano on glacial interglacial timescales the contrast in heating between northern and southern hemispheres during the glacial leads to upper air easterly anomalies throughout the tropics on modern timescales the marked submonthly seasonal and interannual changes of moisture over the altiplano cannot be accounted for by moisture changes in the humid tropical lowlands however the model experiments suggest that cooler conditions during a glacial reduce moisture availability from the tropical lowlands which counteracts the effect of the upper level circulation resulting in little overall change in precipitation this observational and modeling analysis provides a physical framework for relating the mechanisms of both internal and forced climate change on the altiplano on a wide range of timescales

evolution and geodynamic significance of the tertiary orogenic volcanism in northeastern greece the tertiary volcanism of eastern macedonia and western thrace greece developed in association with the sedimentary basin which formed from eocene to oligocene along the southern margin of the rhodope massif the volcanic products ranging in composition from basaltic andesites to rhyolites show an overall calc alkaline orogenic affinity while chemical characteristics identify different groups of rocks probably reflecting minor differences among parent magmas the observed evolution within any group of rocks is compatible with fractional crystallization processes acting on relatively shallow magma bodies the sr isotopic composition of rhyolitic member shows an initial87sr 86sr ratio comparable with that of basaltic andesites reinforcing the hypothesis of a crystal liquid line of descent geochemical and petrographic evidence on the whole suggests that the investigated orogenic association developed on an active continental margin characterized by a relatively thick crust acting as a density filter for the basic magmas and facilitating their storage and fractionation within the crust itself minor contamination by interaction with host materials may also have occurred stratigraphic and k ar geochronological data indicate that the volcanic activity started in upper eocene and reached its maximum development in upper oligocene from lower miocene the volcanism shifted southward in the central aegean area and in part of western anatolia coming to an end by middle miocene the southward migration of the volcanic front has been interpreted as a consequence of the increase in the dipping of the benioff zone due to the decrease of penetrative strength after the main phase of continental collision

a multi proxy palaeoecological record of late holocene forest expansion in lowland bolivia abstract pollen charcoal and bulk sediment stable carbon isotope analysis of a 2 4 m sediment core from laguna yaguaru in eastern bolivia located near the modern ecotone between the humid evergreen amazon rainforest and the seasonally dry semi deciduous chiquitano dry forest provides a 5600 year record of environmental change in an area sensitive to changes in the strength of the south american monsoon the core consists of organic sediment interrupted by a 15 cm mineral facies deposited 5270 yr bp in a low energy flood event in the yaguaru basin pollen data indicate that the basin contained a cattail typha marsh prior to the flood some dry forest elements were present probably growing within small patches of forest within a matrix of generally open vegetation including marsh savanna and savanna woodland above the flood layer typha pollen is absent indicating open water conditions and pollen assemblages are similar to modern pollen spectra from bolivian dry forests around 1200 bp charcoal concentrations decrease carbon isotope ratios become more negative and celtis pollen rises dramatically signaling forest expansion and the development of the modern closed canopy dry forest at laguna yaguaru the wetter conditions implied by this forest expansion suggest the region was affected by the strengthening south american monsoon at this time the timing of the arrival of monsoon moisture at yaguaru is consistent with nearby records allowing a 700 year delay for the migration of the monsoon to reach the more southerly location of yaguaru

evidence of a late glacial warming event and early holocene cooling in the southern brazilian coastal highlands a high resolution pollen record of the atlantic rain forest arf biome from the coastal serra do tabuleiro mountains of southern brazil documents an 11 960 yr history of vegetation and climate change a marked expansion of weinmannia into the grassland vegetation marks the latter part of the younger dryas reflecting warm and relatively wet conditions between 11 490 and 9110 cal yr bp grasslands became dominant again indicating a long cold and dry phase probably in response to the stronger influence of cold south atlantic seawater and to antarctic cold fronts between 9110 and 2640 cal yr bp four distinct phases with strong or moderate expansions of different arf biome taxa were recorded reflecting warmer and relatively dry conditions with changes in rainfall and length of the annual dry season after 2640 cal yr bp the modern arf biome became established with high amounts of ferns reflecting somewhat cooler and wetter conditions with a reduced annual dry season in particular after 1000 cal yr bp tree ferns increased reflecting wetter conditions with no dry season

40ar 39ar geochronology of magmatism and hydrothermal activity of the madjarovo base precious metal ore district eastern rhodopes bulgaria the madjarovo volcanic complex and ore district comprise alteration styles from potassium silicate advanced argillic and sericite alteration to adularia sericite alteration mineralization with a close and unambiguous spatial relationship to specific magmatic events new 4 ar 39ar laser fusion and incremental heating experiments on nine sanidine biotite adularia k feldspar and alunite samples constrain the ages and time span of lavas and tepluas comprising the complex and their relationship to the hydrothennal activity these results demonstrate that high k calc alkaline to shoshonitic volcanic activity began c 32 7 ma and terminated c 500 ka later with the extrusion of quartz latite lavas at 32 2 ma the final stage of volcanism was accompanied by intrusion of cornpositionally similar monzonite stocks and trachytic dykes c 32 2 32 1 ma and associated barren advanced argillic and sericite alteration lithocap and adularia sericite base precious metal vein mineralization a probable thermal event at c 12 13ma disturbed the ages of alunite and sericite bearing alteration at low stratigraphic levels however field relations combined with a plateau age of 32 1 0 2 ma from adularia in low sulphidation veins that cross cut lithocap indicate that hydrothermal activity including baseand precious metal vein deposition was coeval with the youngest magmatic activity although most recent models of epithermal systems emphasize close spatial association among volcanic and plutonic events alteration and deposition of ore hedenquist lowenstern 1994 sillitoe 1993 1995 only rare combinations of geological events provide examples where relationships between igneous rocks porphyry and epithermal systems both high and low sulphidation are exposed this is mainly because young epithermal systems are poorly exposed whereas older deposits are eroded or deformed hedenquist arribas 1999 cooke simmons 2000 most economic epithermal ore deposits are tertiary and conventional k a r dating cannot precisely constrain the timing of magmatism alteration and mineralization at the 95 confidence level the precision of 4 ar 39ar age determinations of krich minerals is typically better than i0 5 thus for the oligocene materials of this investigation differences in age of about 200 ka may be distinguished e g marsh et al 1997 singer march

quantitative estimates of glacial and holocene temperature and precipitation change in lowland amazonian bolivia quantitative estimates of temperature and precipitation change during the late pleistocene and holocene have been difficult to obtain for much of the lowland neotropics using two published lacustrine pollen records and a climate vegetation model based on the modern abundance distributions of 154 neotropical plant families we demonstrate how family level counts of fossil pollen can be used to quantitatively reconstruct tropical paleoclimate and provide needed information on historic patterns of climatic change with this family level analysis we show that one area of the lowland tropics northeastern bolivia experienced cooling 1 3 c and drying 400 mm yr relative to present during the late pleistocene 50 000 12 000 calendar years before present cal yr b p immediately prior to the last glacial maximum lgm ca 21 000 cal yr b p we observe a distinct transition from cooler temperatures and variable precipitation to a period of warmer temperatures and relative dryness that extends to the middle holocene 5000 3000 cal yr b p this prolonged reduction in precipitation occurs against the backdrop of increasing atmospheric co2 concentrations indicating that the presence of mixed savanna and dry forest communities in northeastern bolivia durng the lgm was not solely the result of low co2 levels as suggested previously but also lower precipitation the results of our analysis demonstrate the potential for using the distribution and abundance structure of modern neotropical plant families to infer paleoclimate from the fossil pollen record

does a monsoon climate exist over south america the climatology and the basic state of the summertime circulation and rainfall over south america are studied using assimilation products from the data assimilation system of goddard earth observing system 1 geos1 and satellite derived rainfall results indicate the existence of a regional summer monsoon circulation regime induced by strong diabatic heating over the subtropical south american highland centered at the altiplano plateau sensitivity of the results to the assimilation scheme is tested by comparing that with the national centers for environmental prediction ncep reanalysis and with satellite rainfall estimates results show general agreement between the model produced rainfall anomaly and the satellite estimates as well as consistency between the basic circulation features in the geos 1 and the ncep reanalyses a case study of 1989 90 south american summer monsoon sasm reveals the following characteristics 1 in late spring the onset of sasm is signaled by an abrupt merging of the upper tropospheric double westerly jets one in the subtropics and the other in the subpolar region into a single jet in the midlatitudes this is followed by the establishment of a vortex to the southeast of altiplano and occurrence of heavy precipitation over subtropical eastern brazil 2 during the mature phase of sasm the heavy rainfall zone moves over the altiplano plateau and the southernmost brazilian highland the fully established sasm features are the following a an enhancement of equatorial north atlantic trade wind which emanates from the sahara high and crosses the equator over the south american continent b a buildup of strong northwesterlies along the eastern side of the tropical andes and c development of the south atlantic convergence zone in the southernmost position with strong convective activity meanwhile the upper tropospheric return flow emerges from an anticyclone formed over the altiplano plateau crosses the equator and sinks over northwestern africa 3 the withdrawal of sasm in late summer is signaled by the resplitting of the midlatitude westerly jet at the same time the low level northwest monsoon flow diminishes reducing the moisture supply and leading to the termination of heavy precipitation over the subtropical highland results also show that the above mentioned characteristics of sasm are clearly linked to the tropospheric temperature changes over the central south american highland sensible versus latent heating over the highland are bound to play an important role in the evolution of sasm to provide further support of presence of a monsoon climate over south america sasm is compared and contrasted to the classic east asian summer monsoon easm many similar features including evolution characteristics between the two systems have been identified contrasting aspects of the sasm from the easm are also discussed it is pointed out that a number of monsoonal characteristics of the climate of south america such as the seasonal reversal of the low level wind become apparent only when the strong annual mean wind is removed based on the characteristic features and their evolution the authors conclude that a monsoon climate does exist over south america

small scale variations of 87 sr 86 sr isotope composition of barite in the madjarovo low sulphidation epithermal system se bulgaria implications for sources of sr fluid fluxes and pathways of the ore forming fluids the madjarovo ore district is located in the volcanic rocks of the oligocene madjarovo shield volcano and underlying precambrian and palaeozoic high grade metamorphic rocks of the rhodope massif bulgaria it is situated in the eastern part of a large tertiary magmatic metallogenic belt which resulted from the cretaceous collision of serbo macedonian and rhodope massifs with the pelagonian microplate the low sulphidation base and precious metal mineralisation at madjarovo 32 1 ma formed shortly after the cessation of the shoshonitic and high k calc alkaline volcanic and intrusive activity 32 6 32 2 ma and is spatially and temporally related to late monzonite trachyte intrusions the strontium isotope composition of five barite samples hosted in the volcanic sequence is used to characterise the source s of sr in associated base and precious metal mineralisation and to infer fluid fluxes and pathways of the ore forming fluids the 87sr 86sr compositions for barite samples from ore veins fall in the range 0 70854 0 70955 with the lowest and highest values found in the smaller brecciated veins barite from a thin vein in the basal latite lava flow has the most radiogenic 87sr 86sr isotope composition likely reflecting the involvement of more radiogenic metamorphic basement rocks the least radiogenic composition was determined for barite from a similar vein high in the volcanic pile 500 600 m above the metamorphic basement barites from large veins taken from different stratigraphic positions in the host lavas have almost identical isotopic compositions in the range 0 70883 0 70899 the 87sr 86sr values for barite within the deposit are higher than those for host magmatic rocks 0 70775 0 70863 but lower than those of the metamorphic basement 0 7110 0 7278 it is concluded that strontium in the fluids is a mixture of predominantly magmatic strontium and a variable amount of more radiogenic sr from the metamorphic basement rocks the ore bearing fluid may have been derived from a shallow 1 4 km silicic pluton with an initial 87sr 86sr value 0 7080 because of the short distance to the site of deposition the fault focused ore fluids maintained homogeneous strontium predominantly magmatic strontium isotope ratios with slight contribution s of more radiogenic strontium from the metamorphic basement rocks larger variations in the small brecciated veins can be explained by more extensive fluid rock interaction with local host metamorphic or volcanic rocks

regolith modeling and its relation to earthquake induced building damage a remote sensing approach regolith thickness is known as a major factor in influencing the intensity of earthquake induced ground shaking and consequently building damages it is however often simplified or ignored due to its variable and complex nature to evaluate the role of regolith thickness on earthquake induced building damage a remote sensing based methodology is developed to model the spatial variation of regolith thickness based on dem derived topographic attributes and geology regolith thickness samples were evenly collected in geological formations at representative sites of topographic attributes topographic attributes elevation slope twi distance from stream computed from the aster derived dem and a geology map were used to explore their role in spatial variation of regolith thickness stepwise regression was used to model the spatial variation of regolith thickness in erosional landscape of the study area topographic attributes and geology explain 60 of regolith thickness variation in the study area to test if the modeled regolith can be used for prediction of seismic induced building damages it is compared with the 2005 kashmir earthquake induced building damages derived from high resolution remote sensing images and field data the comparison shows that the structural damages increase with increasing regolith thickness the predicted regolith thickness can be used for demarcating site prone to amplified seismic response

major changes in glacial and holocene terrestrial temperatures and sources of organic carbon recorded in the amazon fan by tetraether lipids the amazon basin is a major component of the global carbon and hydrological cycles a significant natural source of methane and home to remarkable biodiversity and endemism reconstructing past climate changes in the amazon basin is important for a better understanding of the effect of such changes on these critical functions of the basin using a novel biomarker proxy based on the membrane lipids of soil bacteria with a new regional calibration we present a reconstruction of changes in mean annual air temperatures for the amazon catchment during the last 37 kyr b p biomarkers were extracted from ocean drilling program sediment core odp942 recovered from the amazon fan the amazon fan is a major depository for terrestrial sediments with the advantage that the terrestrial material captured reflects a regional integration of the whole river catchment the reconstructed tropical amazonian temperatures were similar to 5 degrees c cooler at the last glacial maximum similar to 21 degrees c compared to modern values similar to 26 degrees c this is in agreement with previous estimates of tropical continental temperatures in the tropical amazon basin and tropical africa during the last glacial maximum moreover we also illustrate how the soil bacterial membrane lipid record reveals major changes in basin dynamics and sediment provenance during the glacial holocene transition impacting the biomarker reconstructions from similar to 11 kyr onward

the last glacial maximum stability and change in a western amazonian cloud forest the climatic and vegetation history of a western amazonian cloud forest is documen ted in a continuous pollen record spanning the full last glacial period between 43 5 and 22k cal yr bp the chronology for this record is based on eight radiocarbon dates yielding a low resolu tion pollen analysis for the region a bioclimatic envelope model was generated on the basis of mod ern altitudinal distributions and the pollen data which produced a glacial palaeotemperature estimate of ca 5 c relative to present palaeoecological evidence of continuous moist cloud forest cover in the basin indicates that western amazonian forests were not fragmented during the lgm this evidence supports wet conditions in western amazonia at the lgm and further refutes hypotheses of amazonian aridity during the last ca 44k cal yr bp copyright 2005 john wiley sons ltd

reply to discussion by kalkan and gulkan on attenuation relationship based on turkish strong motion data and iso acceleration map of turkey by ulusay et al eng geol 74 265 291 2004

palaeofires in amazon interplay between land use change and palaeoclimatic events interpreting the geological record of amazon biomass combustion requires comparing charcoal accumulation rates in various biomes at different time scales charcoal accumulation rates a proxy for palaeofire records were obtained in sediment cores from amazon lakes surrounded by several vegetation types and from a reservoirs in an intense land use change region the records presented in this study were obtained in the following areas i a reservoirs in alta floresta region northern mato grosso state ii lago do saci southern para state a lake close to alta floresta and located at the southern border of para state iii a bog in an ecotone area in the humaita region southern amazonas state iv lakes in lateritic iron crust of the carajas hills southeastern para state v lago comprido a floodplain lake close to the amazon river and surrounded by tropical rain forest monte alegre para state vi lagoa da pata in the morro dos seis lagos alkaline complex sao gabriel da cachoeira amazonas state and vii lago caracarana a secluded lake in the northern amazon cerrado roraima state the highest charcoal accumulation rates were observed for modern records related to an intense change in land use at alta floresta which had no precedent during the holocene history of the amazon high charcoal accumulation rates that were observed in the carajas region during low lake level phases in the amazon in the mid holocene were comparable to those at the onset of the human settlement in alta floresta region an increase in charcoal accumulation rate was observed in the late holocene when the lake level was high suggesting an interaction between climates and human presence low charcoal accumulation rates are typical of modern high rainfall environments as observed in lagoa da pata where the environment is not susceptible to occurrences of wildfires even during relatively drier climatic phases low charcoal accumulation rates also exist in the relatively dry cerrado savanna type biome even during relatively dry phases in the caracarana region where the savanna type vegetation biomass is lower and thus generates less charcoal particles than forest ecosystems

new views of tropical paleoclimates from corals abstract corals offer a rich archive of past climate variability in tropical ocean regions where instrumental data are limited and where our knowledge of multi decadal climate sensitivity is incomplete in the eastern equatorial pacific coral isotopic records track variations in enso related changes in sea surface temperature further west corals record variability in sea surface temperature and rainfall that accompanies zonal displacement of the indonesian low during enso events these multi century records reveal previously unrecognised enso variability on time scales of decades to centuries outside the enso sensitive equatorial pacific long term trends towards recent warmer wetter conditions suggest the tropics respond to global forcings new coral paleothermometers indicate that surface ocean temperatures in the tropical southwestern pacific were depressed by 4 6 c during the younger dryas climatic event and rose episodically during the next 4000 yr high temporal resolution measurements of sr ca and 18 o in corals provide information about the surface ocean hydrologic balance and can resolve the seasonal balance between precipitation and evaporation radiocarbon measurements in corals coupled with ocean circulation models may be used to reconstruct near surface ocean circulation past mixing rates and the distribution of fossil fuel co2 in the upper ocean most recently seasonal to interannual variations in the radiocarbon of corals from the equatorial pacific have been linked to the redistribution of surface waters associated with the enso

absence of last glacial maximum records in lowland tropical forests abstract environmental conditions of the lowland tropical forests during the last glacial maximum lgm between ca 20 000 and 18 00014c yr b p are reevaluated in terms of dating control and lithology analyzed in seven pollen records from south america the reevaluation shows that probably in none of the published records are lgm sediments present or abundant this conclusion is based on the occurrence of abrupt lithologic changes coupled with changes in sedimentation rate interpolated from radiocarbon dates these findings suggest that the lgm was represented probably by a hiatus of several thousand years indicative of drier climates than before or after

annual cycle of upper air circulation and convective activity over the tropical americas a combination of novel data sets including satellite derived outgoing longwave radiation and highly reflective clouds rain gauge records and upper air analyses of the european centre for medium range weather forecasts have been evaluated in context to reappraise the multiyear mean convective activity and circulation and their annual cycle variations over the tropical americas in austral summer a maximum of 200 mbar geopotential height anticyclonic vortex in the wind field and extremum of stream function are located over the western part of the amazon basin well to the west of the extremum of the velocity potential to the north of that and the nucleus of the most intense convection and rainfall the major upper tropospheric divergence is found over northern south america from this outflow is directed primarily northward into an area of strongest convergence situated over the equatorward side of the north atlantic surface high in the evolution from austral to boreal summer the high over western amazonia vanishes and the centers of strongest convection upper tropospheric velocity potential and divergence establish themselves in the realm of the intertropical convergence zone over the eastern equatorial pacific with outflow directed mainly into a broad zone of upper tropospheric convergence in the southern hemisphere after the height of the boreal summer the centers of convection and velocity potential develop again over southeastern amazonia and the upper tropospheric high and weak anticyclone separately form again over the western portion of the amazon basin

site response in victoria british columbia from spectral ratios and 1d modeling this article examines site response in victoria british columbia using weak ground motion recordings 3 5 g of the 2001 m w 6 8 nisqually earthquake in washington state 150 km distant significant variations are observed in acceleration spectra across the city that can be largely attributed to local site conditions thin soil sites 3 m generally have flat amplitude spectra at frequencies less than 10 hz whereas thicker soil sites 5 11 m show peak amplitudes at 2 5 hz standard spectral ratios bedrock reference and horizontal to vertical spectral ratios are computed for sites with varying geology thin soil sites show flat site response like bedrock at frequencies 10 hz whereas the thicker soil sites show peak amplification of up to six times that of bedrock at frequencies of 2 5 hz there is good agreement between these standard spectral ratio site response estimates with the horizontal to vertical spectral ratios at each site and spectral ratios from four other earthquakes between 1996 and 2002 ground motion spectra obtained from numerical 1d modeling indicate that 3 m of soft soil national earthquake hazard reduction program nehrp class e generates a flat response at 10 hz whereas thick layers of either grey victoria clay nehrp class e or pleistocene till nehrp class c produce peak amplitudes at 2 5 hz the correlation of near surface soft soil conditions on crystalline bedrock with observed weak ground motions provides an important baseline toward future seismic hazard studies in the victoria area

estimation of non linear site response in a deep alpine valley summary we simulate non linear behaviour of soils during strong ground motion in the rh one valley in southern switzerland previous studies of the site response using weak ground motion ambient noise and linear 3 d fd simulations suggest that the 2 d structure of the basin will lead to amplification factors of up to 12 in the frequency band between 0 5 and 10 hz to estimate the importance of non linear soil behaviour during strong ground motion in the rh one valley we simulate the response of a superficial soft layer with a fully nonlinear 1 d finite difference code the non linear wave propagator is based on an effective stress constitutive soil model capable of predicting pore pressure evolution due to shear we determine the required dilatancy parameters from laboratory analysis of soil samples using cyclic triaxial tests in order to include the effect of the strong 2 d structure in our non linear analysis synthetic seismograms are convolved with the transfer function of the basin and then propagated through a 1 d non linear layer we find that reduced amplification due to soil non linearity can be expected at rock accelerations above 0 5 ms 2 and that de amplification occurs at ground motion levels of approximately 2 ms 2 nevertheless the spectral accelerations simulated for the valley centre are still exceeding the design spectra at about 0 5 hz for magnitudes above 6 0 which reflects the strong amplification of ground motion by the deep 2 d resonance of the basin for frequencies above 1 hz the design spectra are generally in agreement with the strongest simulated accelerations we evaluate the occurrence of soil failure using the 5 per cent strain criterion as a function of hypocentral distance and magnitude results confirm observations of liquefaction reported after the 1855 mw 6 4 earthquake of visp and they suggest that soil liquefaction may occur at distances beyond those predicted by empirical relations in the valley near the basin edge however the simulated liquefaction occurrence agrees with the empirical relations these results suggest that the response of the whole structure needs to be simulated in order to

an overview of local site effects and the associated building damage in adapazari during the 17 august 1999 izmit earthquake two major earthquakes occurred in turkey along the north anatolian fault in 1999 the first one which occurred on 17 august 1999 had a moment magnitude of 7 4 and ruptured the 140 km segment of the fault in the marmara region adapazari a city with a population of 190 000 which is mostly located on a deep alluvial basin in the near field of the ruptured fault was among the worst affected urban areas in the earthquake affected region the distribution of damage over the city was highly nonuniform indicating the variability of the ground response to the strong motion five to six story buildings located over deep alluvial soils were most adversely affected by the earthquake geotechnical characteristics of the alluvial basin of adapazari are evaluated using the deep and shallow borehole logs and the measured parameters from the field and laboratory this data is used for developing representative one dimensional site response models for various depths of alluvium and for liquefaction assessment in saturated surface soils recorded data from several aftershocks are utilized for model calibration the results of soil response studies are found to be highly correlated with the general trends in the intensity and distribution of building damage based on in situ tests soil liquefaction is determined to have occurred extensively in adapazari which is in conformity with the postearthquake observations of widespread liquefaction induced foundation displacements evidently liquefied soil layers served as passive isolation mechanism for numerous buildings some of which were subjected to excessive foundation displacements of various forms without signs of significant structural damage manuscript received 30 august 2000

sm nd direct dating of the collins bay hydrothermal uranium deposit saskatchewan primary pitchblende mineralization from the collins bay unconformity type uranium deposit in northern saskatchewan has been dated using the sm nd method the mineral isochron age of 1281 80 ma is in good agreement with other geologic and geochronological data and demonstrates the potential of the sm nd technique for the direct dating of hydrothermal mineral deposits 23 references 5 figures 7 tables

critical parameters affecting bias and variability in site response analyses using kik net downhole array data because of the limited number of strong motion records that have measured ground response at large strains any statistical analyses of seismic site response models subject to strong ground motions are severely limited by a small number of observations recent earthquakes in japan including the m w 9 0 tohoku earthquake of march 2011 have substantially increased the observations of strong motion records that can be used to compare alternative site response models at large strains and can subsequently provide insight into the accuracy and precision of site response models using the kiban kyoshin network kik net downhole array data in japan we analyze the accuracy bias and variability precision resulting from common site response modeling assumptions and we identify critical parameters that significantly contribute to the uncertainty in site response analyses we perform linear and equivalent linear site response analyses at 100 kik net sites using 3720 ground motions ranging in amplitude from weak to strong 204 of these records have peak ground accelerations greater than graphic 1 at the ground surface we find that the maximum shear strain in the soil profile the observed peak ground acceleration at the ground surface and the predominant spectral period of the surface ground motion are the best predictors of where the evaluated models become inaccurate and or imprecise the peak shear strains beyond which linear analyses become inaccurate in predicting surface pseudospectral accelerations psa presumably as a result of nonlinear soil behavior are a function of vibration period and are between 0 01 and 0 1 for periods 0 5 s do not display noticeable effects of nonlinear soil behavior online material site specific information and model residuals at 100 kik net stations 1 embed inline graphic 1 gif

forest changes in the amazon basin during the last glacial maximum we report here the discovery of forest beds in the amazon basin radiocarbon dated to the wisconsin wurm glaciation these are the first dates from the last glaciation determined on amazonian samples the locality is in ecuador at 1 100 m elevation near the upper limit of the present amazonian rainforest both pollen spectra and podocarpus wood in the deposits suggest that vegetation comparable to the present andean forest grew at least 700 m lower than it does now suggesting a temperature depression of at least 4 5 c for the amazon lowlands

astronomical forcing of contrasting rainfall changes in tropical south america between 12 400 and 8800 cal yr b p abstract today precipitation over tropical south america is largely controlled by the seasonal movements of the inter tropical convergence zone itcz during the summer the itcz is shifted southward due to the warming of the continent paleoclimate data from southeastern amazonia and the central andes indicate that these two areas evolved similarly during the last 30 000 yr however between 12 400 and 8800 cal yr b p eastern amazonia received substantial moisture whereas the bolivian altiplano was arid this suggests that the itcz during summer was then farther north than it is today

the relative importance of enso and tropical atlantic sea surface temperature anomalies for seasonal precipitation over south america a numerical study the role of tropical atlantic sea surface temperature sst anomalies during enso episodes over northeast brazil nordeste is investigated using the cptec cola atmospheric general circulation model agcm four sets of integrations are performed using sst in el nino and la nina enso episodes changing the sst of the atlantic ocean a positive dipole sst higher than normal in the tropical north atlantic and below normal in the tropical south atlantic and a negative dipole opposite conditions are set as the boundary conditions of sst in the atlantic ocean the four experiments are performed using el nino or la nina sst in all oceans except in the tropical atlantic where the two phases of the sst dipole are applied five initial conditions were integrated in each case in order to obtain four ensemble results the positive sst dipole over the tropical atlantic ocean and el nino conditions over the pacific ocean resulted in dry conditions over the nordeste when the negative dipole and el nino conditions over the pacific ocean were applied the results showed precipitation above normal over the north of nordeste when la nina conditions over pacific ocean were tested together with a negative dipole positive precipitation anomalies occurred over the whole nordeste using the positive dipole over the tropical atlantic the precipitation over nordeste was below average during la nina episodes the atlantic ocean conditions have a larger effect on the precipitation of nordeste than the pacific ocean in el nino conditions only the north region of nordeste is affected by the atlantic sst other tropical areas of south america show a change only in the intensity of anomalies central and southeast regions of south america are affected by the atlantic conditions only during la nina conditions whereas during el nino these regions are influenced only by conditions in the pacific ocean

the history of south american tropical precipitation for the past 25 000 years long sediment cores recovered from the deep portions of lake titicaca are used to reconstruct the precipitation history of tropical south america for the past 25 000 years lake titicaca was a deep fresh and continuously overflowing lake during the last glacial stage from before 25 000 to 15 000 calibrated years before the present cal yr b p signifying that during the last glacial maximum lgm the altiplano of bolivia and peru and much of the amazon basin were wetter than today the lgm in this part of the andes is dated at 21 000 cal yr b p approximately coincident with the global lgm maximum aridity and lowest lake level occurred in the early and middle holocene 8000 to 5500 cal yr b p during a time of low summer insolation today rising levels of lake titicaca and wet conditions in amazonia are correlated with anomalously cold sea surface temperatures in the northern equatorial atlantic likewise during the deglacial and holocene periods there were several millennial scale wet phases on the altiplano and in amazonia that coincided with anomalously cold periods in the equatorial and high latitude north atlantic such as the younger dryas

a long history of cloud and forest migration from lake consuelo peru abstract the complete paleoecological history from lake consuelo forest yields a record of ground level cloud formation and changes in its lower altitudinal limit over the last 46 300 cal yr bp the timing of early lake level fluctuations prior to 37 000 cal yr bp appears sensitive to north atlantic temperature oscillations corresponding to dansgaard oeschger interstadials 11 10 and 8 recorded in gisp2 after the lgm the first hint of warming is recorded in lake consuelo at 22 000 cal yr bp and agrees with other estimates for the region the mid holocene 7400 5000 cal yr bp was the period of highest rates of change and most significant reorganizations in the consuelo forest these community changes resulted from a regionally widespread dry period results from lake consuelo indicate that moisture availability mediated through cloud cover played the most significant role in ecological change in this system rates of past climate fluctuations never exceeded the forest capacity to accommodate change unfortunately this might not be the case under predicted scenarios for the end of the current century

the hill of six lakes revisited new data and re evaluation of a key pleistocene amazon site the new analyses of a sedimentary record of lake pata in the hill of six lakes in nw amazon and its correlation with other quaternary proxy records in the region provide new insights regarding the vegetation and climate of the lowland forest during the last glacial despite what has been reported previously in the literature the sedimentary and pollen records are not continuous the hill remained forested however clear signals of structural change are seen in the record which indicate that the area experienced a significantly drier climate during the last glacial maximum lgm the herbs and taxa that are known to be more dominant in seasonally dry forests were all more abundant during the glacial part of the record and the cool adapted elements were mixed with warm lowland elements which indicates a temperature depression a comparison of the palaeoecological data with other regional geoenvironmental records of the upper negro river basin and other areas of the amazon provides additional support for a cooler and more seasonal environment during the middle pleniglacial which then became drier during the lgm a wet lgm is strongly refuted therefore the palaeoclimatic and ecological models that used the previous proxy data from six lakes to sustain wet conditions and a continuous forest record during the lgm to reconstruct the palaeoenvironmental conditions in the amazon should be reviewed

paleolimnological record of the pampean plains argentina as a natural archive of south american hydroclimatic variability since the lgm to the current warm period abstract laguna mar chiquita lmc 30 54 s 62 51 w is a highly variable and shallow saline lake located in the pampean plains of argentina the paleolimnological record of lmc contains information on the environmental variability that occurred in a large area of southern south america since the last glacial maximum lgm until the present as inferred from the diatom assemblages sedimentary features and geochemical proxies prolonged intervals of high and lowstands have caused variations in water salinity trophic state and sedimentary processes this is the first paleolimnological reconstruction covering the hydroclimatic variability that occurred over the last 25 000 cal yr bp in the argentinean pampean region results are in accordance with well known global climatic phases the late pleistocene record is characterized by a scenario dominated by lowstands hypersaline and oligotrophic lake conditions radiocarbon ages 25 000 19 000 cal yr bp indicate that the onset of the record is coeval with the lgm later a progressive lake water level increase was registered at 17 000 cal yr bp which can be assigned to the heinrich stadial 1 a shift toward comparatively drier conditions identified in the record between 14 700 and 13 000 cal yr bp can be chronologically related to the antarctic cold reversal the transition from the late pleistocene to the holocene 13 500 10 500 cal yr bp is recorded by highstand phases while the early holocene record is characterized by high to intermediate water levels the hydrological reconstruction corresponding to the mid holocene is characterized by alternating phases of high lowstands the onset of the late holocene record is marked by the development of dry conditions and thus lowstand phases while around 1300 cal yr bp a distinct water lake level increase is recognized this humid phase ascribed to the medieval climatic anomaly is followed by the record of lowstands between 500 and 1000 cal yr bp being coeval with the little ice age the uppermost part of the record of lmc encompasses the current warm period showing a marked shift towards high lake water level conditions the hydrological variability registered in the paleolimnological record highlights the importance of laguna mar chiquita as an outstanding paleoclimate sensor of hydroclimatic variations for a large area of south eastern south america

contrasting platinum group element concentration patterns in cumulates of the bushveld complex chromite rich lithologies in both the lower and the critical zones of the bushveld complex in the potgietersrus area display flat chondrite normalized platinum group element pge concentration patterns whereas those of associated sulphide bearing but chromite poor rocks are considerably steeper the low pt pd os ir ru ratio in the chromite bearing rocks is maintained irrespective of the amount of sulphide or chromite in the rock this feature suggests that the partitioning of the individual pge into pge bearing phases during conditions in the magma under which crystallization of chromite in excess of the normal cotectic amounts was favoured differed from conditions under which an immiscible sulphide liquid separated from the same magma in the absence of enhanced chromite crystallization these changes in the partitioning coefficients of the individual pge are considered to reflect changes in the solubility of these elements in response to variations in the intensive parameters in the magma necessary to bring about the enhanced crystallization of chromite

discussion of subsurface characterization at ground failure sites in adapazari turkey by jonathan d bray rodolfo b sancio turan durgunoglu akin onalp t leslie youd jonathan p stewart raymond b seed onder k cetin ertan bol m b baturay c christensen and t karadayilar a discussion of an article with the aforementioned title published in this journal in july 2004 is presented the discussers question the authors reasoning concerning soil liquefaction without consideration of the bearing capacity failure of the foundations and the likelihood of liquefaction of the surface deposits encountered in adapazari during the 1999 earthquake while there were boils observed at several of the case sites in adapazari there is a concern that the samples might not be representative of the soil that actually liquefied it also appears that the peak ground accelerations exceeded the ultimate capacity of the foundations

hydrology and climatology at laguna la gaiba lowland bolivia complex responses to climatic forcings over the last 25 000 years diatom geochemical and isotopic data provide a record of environmental change in laguna la gaiba lowland bolivia 17 45 s 57 35 w over the last ca 25 000 years high resolution diatom analysis around the last glacial interglacial transition provides new insights into this period of change the full and late glacial lake was generally quite shallow but with evidence of periodic flooding at about 13 100 cal a bp just before the start of the younger dryas chronozone the diatoms indicate shallower water conditions but there is a marked change at about 12 200 cal a bp indicating the onset of a period of high variability with rising water levels punctuated by periodic drying from ca 11 800 to 10 000 cal a bp stable deeper water conditions persisted there is evidence for drying in the early to middle holocene but not as pronounced as that reported from elsewhere in the southern hemisphere tropics of south america this was followed by the onset of wetter conditions in the late holocene consistent with insolation forcing conditions very similar to present were established about 2100 cal a bp a complex response to both insolation forcing and millennial scale events originating in the north atlantic is noted

bayesian inversion of microtremor array dispersion data in southwestern british columbia summary this paper applies bayesian inversion with evaluation of data errors and model parametrization to produce the most probable shear wave velocity profile together with quantitative uncertainty estimates from microtremor array dispersion data generally the most important property for characterizing earthquake site response is the shear wave velocity vs profile the microtremor array method determines phase velocity dispersion of rayleigh surface waves from multi instrument recordings of urban noise inversion of dispersion curves for vs structure is a non unique and non linear problem such that meaningful evaluation of confidence intervals is required quantitative uncertainty estimation requires not only a non linear inversion approach that samples models proportional to their probability but also rigorous estimation of the data error statistics and an appropriate model parametrization this paper applies a bayesian formulation that represents the solution of the inverse problem in terms of the posterior probability density ppd of the geophysical model parameters markov chain monte carlo methods are used with an efficient implementation of metropolis hastings sampling to provide an unbiased sample from the ppd to compute parameter uncertainties and inter relationships nonparametric estimation of a data error covariance matrix from residual analysis is applied with rigorous a posteriori statistical tests to validate the covariance estimate and the assumption of a gaussian error distribution the most appropriate model parametrization is determined using the bayesian information criterion which provides the simplest model consistent with the resolving power of the data parametrizations considered vary in the number of layers and include layers with uniform linear and power law gradients parameter uncertainties are found to be underestimated when data error correlations are neglected and when compressional wave velocity and or density nuisance parameters are fixed in the inversion bayesian inversion of microtremor array data is applied at two sites in british columbia the area of highest seismic risk in canada to study the ability to recover an accurate vs profile in relatively deep and shallow geological settings on the fraser river delta in greater vancouver and in victoria respectively a well resolved vs profile to at least 110 m depth is determined at the fraser river delta site for a power law gradient parametrization at the victoria site a layer with low vs and a weak linear gradient is indicated to 15 18 m depth above much higher velocity material invasive vs measurements from seismic cone penetration testing and or surface to downhole methods are used to assess the reliability of the bayesian microtremor inversion results with excellent agreement obtained at both sites

temporal evolution of arc magmatism and hydrothermal activity including epithermal gold veins borovitsa caldera southern bulgaria plutonic volcanic and hydrothermal activity in magmatic arcs is commonly focused spatially leaving behind complex records of multiple ore forming processes that can be appreciated in detail only if the timing of igneous and hydrothermal systems is ascertained the spahievo ore district bulgaria is adjacent to the oligocene borovitsa caldera one of the largest in europe juxtaposition of porphyry mineralization barren advanced argillic alteration and low sulfidation epithermal alteration and mineralization zones along the caldera margin provides an uncommon opportunity to examine the temporal development of an evolved magmatic hydrothermal system 40 ar 39 ar ages determined using a co 2 laser to fuse or incrementally heat minerals from fresh igneous and altered rocks indicate a rapid succession of 1 pre caldera intermediate magmatism including monzonitic intrusion and coeval porphyry style mineralization and advanced argillic alteration between 32 9 and 32 3 ma 2 rhyolitic ash flow tuffs dikes and domes with adularia sericite alteration accompanied by epithermal precious metal mineralization at 32 1 ma and 3 nearly synchronous collapse of a nested caldera and intrusion of a ring fault rhyolite dome and intracaldera dikes at 31 8 ma these ages link monzonitic intrusion cu mo mineralization and advanced argillic alteration and indicate that rhyolitic magmatism and adularia sericite alteration with associated base metal plus au mineralization is slightly younger about 100 to 500 k y deposition of au ore ca 300 k y prior to caldera collapse distinguishes this ore district from many well known deposits in which ore formation accompanied andesitic or rhyolitic intrusions along ring fractures that postdate the collapse

metamorphism and cooling of the ne dalradian the buchan area of dalradian rocks represents a distinct tectonothermal domain within the scottish highlands and the portsoy duchray hill lineament on the western margin of this block is one of the best examples of a long lived domain boundary rb sr mica cooling ages from metamorphic rocks from across the trace of this lineament document a prolonged ordovician cooling history delayed but then relatively rapid cooling to the west of the portsoy duchray hill lineament is recognized whereas to the east the age data point to a high heat flow regime lasting more than 50 ma the isotopic ages suggest that c 460 ma was a time of active tectonism resulting in final cooling of the low grade rocks and differential uplift and rapid cooling of deeper structural levels to the west the radiometric ages do not support previous tectonic models for the region that have invoked thrust thickening along the line of the portsoy duchray hill lineament and a new model for the metamorphism is proposed the overprinting of andalusite bearing assemblages by kyanite to the west of the portsoy duchray hill lineament is linked to pressure increases associated with the intrusion of the newer gabbros and represents a magmatic loading related to the same tectonothermal event that generated the low pressure metamorphism rather than a separate tectonic episode

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

correlation between earthquake damage and seismic site effects the study case of lentini and carlentini italy abstract on december 13th 1990 a magnitude 5 6 seismic event felt throughout sicily and having maximum seismic intensity vii viii occurred although it is classified as moderate magnitude it caused causalities and the collapse of a few buildings two of the most struck cities were carlentini and lentini located in south eastern sicily at about 20 km from the instrumental epicenter in order to evaluate the influence of ground features on the damage distribution both vulnerability and damage maps were drawn using information collected in about 6000 forms coming from official ascertainments significant damage observed in some portions of the investigated areas appears related to the modest quality of the buildings that were classified as medium to high vulnerability to evaluate the role played by the geologic setting two sites were instrumented to measure shear wave velocity of the main lithotypes sixty three ambient vibrations measurements were also performed both in free field and inside some buildings moreover using information coming from geological and geophysical surveys 1d numerical modelling were done to achieve information about the main ground motion parameters the results highlight the occurrence of significant site effects and the potential presence of resonance phenomena between site and structure during the occurrence of a seismic event seismic site amplifications together with the buildings vulnerability observed through damage surveys contributed to enhance the inherent seismic risk of the investigated area

tertiary granitoids of rhodope northern greece magmatism related to extensional collapse of the hellenic orogen abstract many granites that occur in orogenic belts such as the himalaya the hercynides or caledonides are thought to result from anatexis of the lower parts of over thickened thrust stacked crustal units just preceding termination of the orogenic cycle numerous tertiary granitoids occur in the rhodope zone of northern greece and adjacent regions of bulgaria a belt regarded as an eastern extension of the alpine system these granites could also be regarded as syn or late tectonic crustal melts in that some have been emplaced as sheet like bodies along major alpine thrust planes and show a strong marginal foliation parallel to the pervasive alpine compressional fabrics in detail however the geochemistry of the granitoids their timing and relationships with country rocks suggest they have been emplaced in an extensional regime that is related to the collapse of the hellenic orogen and more particularly to the crustal thinning that the aegean region has suffered since the mid tertiary rather than being products of crustal thickening it is suggested that their petrogenesis is related to the elevation of thermal gradients during the extensional phase which initiated thermal breakdown of hydrous minerals in the lithosphere and lower crust that had existed metastably during compression and the subduction of cool ocean lithosphere beneath the region in the late mesozoic early tertiary

modeling of 3d subsurface structure and numerical simulation of strong ground motion in the adapazari basin during the 1999 kocaeli earthquake turkey the 1999 kocaeli izmit earthquake seriously damaged the downtown area of adapazari turkey the wavefield of the strong ground motions is considered to have been affected by the deep ground structure a refraction and reflection seismic survey was made to obtain the velocity structure of the profile in the north south direction across the basin a 3d subsurface model is presented based on results of the refraction and reflection survey on data obtained from a gravity survey and on observations of microseisms and aftershocks the proposed model shows deep sediment with a steep slope beneath downtown adapazari strong ground motions in the frequency range of 0 1 1 0 hz propagating in the subsurface model during the kocaeli earthquake also were simulated numerically by the 3d finite difference method the simulated results show that ground motions in downtown adapazari were larger than those in the area between downtown and the source fault because the former were significantly amplified by the basin edge effect

glacial and postglacial pollen records from the ecuadorian andes and amazon abstract a long pollen record is derived from sediments of a lake dammed behind a low moraine of the last glaciation at 3 s latitude in the ecuadorian andes and is compared with a glacial age pollen record from the amazon rainforest immediately below lake surucucho llaviucu lies at 3180 m on the amazonian flank of the andes and above the glacial age pollen record from san juan bosco at 970 m the surucucho pollen record is interpreted as showing treeless vegetation in glacial times advance of treeline in late glacial time and holocene development of modern andean forests combining the surucucho and san juan bosco records shows that andean vegetation was affected by glacial cooling at all elevations vegetation did not move up and down slope as belts rather plant associations were reformed as temperature sensitive species found different centers of distribution with changing temperature

principles of mobilization dissolution of metals in mafic and ultramafic rocks the role of immiscible magmatic sulphides in the generation of hydrothermal gold and volcanogenic massive sulphide deposits abstract immiscible magmatic sulphides exert a major control over both the absolute precious and base metal contents of magmas and on the availability of these metals from rocks during ore formation it is concluded that only those mafic magmas that attained s saturation at a late stage are not depleted in the chalcophile elements and are hence suitable source rocks for metals in hydrothermal ore deposits immiscible magmatic sulphides are not only strongly enriched in the ore forming metals but they are also much more reactive than silicates the ore forming metals may be liberated from the sulphides at the sea floor alteration stage and deposited in interflow chemical sediments au deposits or volcanogenic massive sulphide deposits subsequent mobilization remobilization of au from the interflow sediments may concentrate au within the interflow sediments to form economic au deposits the mobilized remobilized au may also be transported to form epigenetic style gold deposits in archaean greenstone belts and in palaeozoic slate belts

hydrothermal alteration associated with gold mineralization in the southern apuseni mountains romania preliminary sr isotopic data precious metal mineralization in the southern apuseni mountains of western romania is hosted by mid miocene 14 ma andesitic stocks and lava flows the mineralized veins are surrounded by aureoles of hydrothermal alteration consisting of quartz sericite k feldspar pyrite and calcite the alteration process caused a total homogenization of initial 87sr 86sr in the rocks ages determined for the hydrothermal alteration are 13 7 15 7 ma indicating that hydrothermal alteration immediately followed igneous activity furthermore a large influx of radiogenic sr took place during alteration this sr probably being derived from the hydrothermal leaching of continental meta sedimentary rocks in the basement

late pleistocene temperature depression and vegetation change in ecuadorian amazonia abstract paleoecological pollen phytolith and wood analyses of sediments radiocarbon dated 33 000 to 26 000 yr b p from two sites in ecuadorian amazonia provide data that suggest a cooling of ca 7 5 c below present in equatorial lowlands from 33 000 to 30 000 yr b p a period of warning followed in which novel species assemblages a blend of montane and lowland floral components persisted for at least 4000 years these data of forest community change from sites lying within the postulated glacial rain forest napo refugium provide the strongest paleoecological refutation of the refugial hypothesis yet obtained the large temperature depression at ca 30 000 yr b p allows the possibility that if maximum cooling at the equator was synchronous with the last glacial maximum lgm of the northern hemisphere freezing temperatures would have been experienced in parts of lowland amazonia between 25 000 and 18 000 b p

late quaternary environmental and climatic changes in central brazil paleoenvironmental changes dating back to 30 000 yr b p documented in a pollen record from central brazil lat 19 s permit the reconstruction of climatic changes related to shifts of the antarctic polar fronts the paleoclimatic inferences were obtained by a study of modern vegetation and pollen distribution taking into account present day climatic parameters at 30 000 yr b p the climate must have been warmer and moister than today judging from the high amount of tree pollen taxa characteristic of floodplain forest from 17 000 to 14 000 yr b p the climate was drier although tree pollen percentages were relatively high after 12 000 yr b p araucaria forest elements increased suggesting a moister and cooler climate the araucaria forest disappeared during a short interval between 11 000 and 10 000 yr b p this could be related to the younger dryas event at the beginning of the holocene the climate became cool and moist again as indicated by the reexpansion of the araucaria forest the latter was progressively replaced by a mesophytic semideciduous forest indicating warmer and drier climate after 8500 yr b p at 5000 yr b p an arid interval was followed by the expansion of mesophytic semideciduous forest elements

tropical climate changes at millennial and orbital timescales on the bolivian altiplano tropical south america is one of the three main centres of the global zonal overturning circulation of the equatorial atmosphere generally termed the walker circulation1 although this area plays a key role in global climate cycles little is known about south american climate history here we describe sediment cores and down hole logging results of deep drilling in the salar de uyuni on the bolivian altiplano located in the tropical andes we demonstrate that during the past 50 000 years the altiplano underwent important changes in effective moisture at both orbital 20 000 year and millennial timescales long duration wet periods such as the last glacial maximum marked in the drill core by continuous deposition of lacustrine sediments appear to have occurred in phase with summer insolation maxima produced by the earth s precessional cycle short duration millennial events correlate well with north atlantic cold events including heinrich events 1 and 2 as well as the younger dryas episode at both millennial and orbital timescales cold sea surface temperatures in the high latitude north atlantic were coeval with wet conditions in tropical south america suggesting a common forcing

neogene and quaternary development of the neotropical rain forest the forest refugia hypothesis and a literature overview abstract the upheaval of the northern andes in miocene and pliocene time changed the drainage system in northern south america significantly and caused the present day rain forest areas of choco and the lower magdalena valley became separated from amazonas plant diversity may have reached the highest level in the miocene or pliocene and excessive present day phytodiversity may be regarded as a legacy of the tertiary rather than an evolutionary product of the quaternary in the quaternary strong temperature oscillations related to the series of ice ages were superposed on the late tertiary forest dynamics which included river displacement and latitudinal migrations of the equatorial rain belt caloric equator with the rhythm of the precession cycle of orbital climate forcing the hypothesis that claims a permanent rain forest cover all over the amazon basin during the last glacial is in contrast with the forest refugia hypothesis which accepts replacement of rain forest by savanna or savanna forest during dry climatic intervals both scenarios have been evidenced by pollen records in this paper it is suggested that both hypotheses are not necessarily conflicting and apparently did occur in different parts of the amazon basin and in different periods depending on the climatological constraints a compilation of the most important literature concerning the vegetational climatic and environmental history of the rain forest areas of amazonas and choco and surrounding dry ecosystems has been included

an 85 ka record of climate change in lowland central america drill cores obtained from lake peten itza peten guatemala contain a 85 kyr record of terrestrial climate from lowland central america that was used to reconstruct hydrologic changes in the northern neotropics during the last glaciation sediments are composed of alternating clay and gypsum reflecting relatively wet and dry climate conditions respectively from 85 to 48 ka sediments were dominated by carbonate clay indicating moist conditions during marine isotope stages mis 5a 4 and early 3 the first gypsum layer was deposited at 48 ka signifying a shift toward drier hydrologic conditions and the onset of wet dry oscillations during the latter part of mis 3 peten climate varied between wetter conditions during interstadials and drier states during stadials the pattern of clay gypsum wet dry oscillations during the latter part of mis 3 48 23 ka closely resembles the temperature records from greenland ice cores and north atlantic marine sediment cores and precipitation proxies from the cariaco basin the most arid periods coincided with heinrich events when cold sea surface temperatures prevailed in the north atlantic meridional overturning circulation was reduced and the intertropical convergence zone itcz was displaced southward a thick clay unit was deposited from 23 to 18 ka suggesting deposition in a deep lake and pollen accumulated during the same period indicates vegetation consisted of a temperate pine oak forest this finding contradicts previous inferences that climate was arid during the last glacial maximum lgm chronozone 21 2 ka at 18 ka peten climate switched from moist to arid conditions and remained dry from 18 to 14 7 ka during the early deglaciation moister conditions prevailed during the warmer bolling allerod 14 7 12 8 ka with the exception of a brief return to dry conditions at 13 8 ka that coincides with the older dryas and meltwater pulse 1a the onset of the younger dryas at 12 8 ka marked the return of gypsum and hence dry conditions the lake continued to precipitate gypsum until 10 3 ka when rainfall increased markedly in the early holocene

biogeochemical indicators of environmental changes from 50 ka to 10 ka in a humid region of the brazilian amazon abstract we present a geochemical record of a 113 6 cm sediment core lpt v from lagoa da pata which is located in the forested upper rio negro basin the record reveals significant changes in the environmental history of amazonia during the late quaternary the results of biogeochemical analyses revealed three hydrological and climatic regimes from 50 000 to 10 000 cal yr bp the first phase between 50 000 and 26 300 cal yr bp was characterized by a relatively wet climate as suggested by relatively high total organic carbon toc and chlorophyll derivate concentrations indicating high productivity linked to a high lake level a decrease of the toc and chlorophyll derivate accumulation rates between 43 100 cal yr bp and 26 300 cal yr bp marks a decrease in the productivity linked to a reduced lake level indicating a decrease in moisture at the end of this phase the second phase between 26 300 and 15 300 cal yr bp was characterized by a decrease in productivity reaching a minimum at 21 950 cal yr bp as indicated by a minima in sedimentary chlorophyll and toc accumulation rates values of 13 c increased by 5 in relation to the preceding phase indicating an influence of the c 4 organic matter high iron concentrations and accumulation rates related to intense erosion of the lateritic crust in the watershed were observed all of the observations indicate a dry phase during this period a third phase from approximately 15 300 to 10 000 cal yr bp was characterized by an increase in lacustrine productivity as shown by an increased in toc and chlorophyll derivate concentrations and accumulation rates these increases likely correspond to a lake level rise due to a wetter climate

investigation of surface geology and intensity variability in the palermo italy urban area after the 6 september 2002 earthquake this work was funded by the miur legge 488 92 delibera cipe 08 08 96 r catalano 60 2000 2001

experimental study of the solubility of platinum and iridium in basic silicate melts implications for the differentiation of platinum group elements during magmatic processes this study presents evidence for the dissolution of two platinum group elements pge s pt and ir in silicate melts of basic composition in the absence of any associated fluid phase the dissolution of these pge s is attributed to the formation of a complex ion in which the noble metal is uncharged an increase in oxygen fugacity in equilibrium with the melt brings about a considerable decrease in ir solubility in this way we can explain the early enrichment in ir group pge s ipge s ir ru os observed during the crystallization of ultrabasic cumulates by contrast however pt remains soluble in the melt an increase in the fs2 results in a pronounced increase in the solubility of pt in the silicate melt the sulfur saturation which leads to the precipitation of the base metal sulfides bms s also brings about the fixation of pt group pge s ppge s pt pd rh which are dissolved in bms s this accounts for the presence of ppge s in the nickel sulfide horizons of stratiform deposits the occurrence of platiniferous fe crystallizing with chromite in alaskan type complexes at oxygen fugacities of 10 6 bar can be explained by the low activity of fe in fe pt alloys such alloys have been formed in our laboratory at such fo2

2 hydrothermal ore deposits related to post orogenic extensional magmatism and core complex formation the rhodope massif of bulgaria and greece abstract the rhodope massif in southern bulgaria and northern greece hosts a range of pb zn ag cu mo and au ag deposits in high grade metamorphic continental sedimentary and igneous rocks following a protracted thrusting history as part of the alpine himalayan collision major late orogenic extension led to the formation of metamorphic core complexes block faulting sedimentary basin formation acid to basic magmatism and hydrothermal activity within a relatively short period of time during the early tertiary large vein and carbonate replacement pb zn deposits hosted by high grade metamorphic rocks in the central rhodopean dome e g the madan ore field are spatially associated with low angle detachment faults as well as local silicic dyke swarms and or ignimbrites ore formation is essentially synchronous with post extensional dome uplift and magmatism which has a dominant crustal magma component according to pb and sr isotope data intermediate and high sulphidation pb zn ag au deposits and minor porphyry cu mo mineralization in the eastern rhodopes are predominantly hosted by veins in shoshonitic to high k calc alkaline volcanic rocks of closely similar age base metal poor high grade gold deposits of low sulphidation character occurring in continental sedimentary rocks of synextensional basins e g ada tepe show a close spatial and temporal relation to detachment faulting prior and during metamorphic core complex formation their formation predates local magmatism but may involve fluids from deep mantle magmas the change in geochemical signatures of palaeogene magmatic rocks from predominantly silicic types in the central rhodopes to strongly fractionated shoshonitic bulgaria to calc alkaline and high k calc alkaline greece magmas in the eastern rhodopes coincides with the enrichment in cu and au relative to pb and zn of the associated ore deposits this trend also correlates with a decrease in the radiogenic pb and sr isotope components of the magmatic rocks from west to east reflecting a reduced crustal contamination of mantle magmas which in turn correlates with a decreasing crustal thickness that can be observed today hydrogen and oxygen isotopic compositions of the related hydrothermal systems show a concomitant increase of magmatic relative to meteoric fluids from the pb zn ag deposits of the central rhodopes to the magmatic rock hosted polymetallic gold deposits of the eastern rhodopes

rare earth element mobility in alteration pipes below massive cuzn sulfide deposits abstract a convincing demonstration of trace element mobility should satisfy two criteria 1 the range of trace element concentrations in the rock before and after alteration must be known with confidence and 2 the absolute abundances and the ratios of the mobile trace elements should vary between altered and unaltered rocks these criteria have been applied to the host felsic volcanics and alteration pipes associated with several canadian massive cu zn sulfide deposits although there is no evidence of rare earth element ree mobility in the pervasive low grade alteration envelopes adjacent to the deposits the light and middle ree lree and mree plus y have been systematically mobilized relative to the heavy ree hree and other trace elements in the alteration pipes beneath the ore zones there is evidence of minor lree and mree depletion in the most altered rocks at the south bay mine uchi lake and of significant lree depletion in the alteration pipe beneath the mattabi mine sturgeon lake however the strongest mobility is found at the kidd creek mine where the lree were leached from the rocks in the footwall stringer zone and redeposited in a metasomatic chlorite zone directly beneath the massive ore horizon and the mree and y were preferentially lost from the system producing distinctive chondrite normalized ree patterns with tb yb n ratios less than unity eu2 was found to be more mobile than the trivalent ree especially at kidd creek where there is a marked increase in the magnitude of the eu anomaly in the most altered samples high field strength elements such as u th hf and zr have not decoupled and apparently remained relatively immobile during all but the most intense alteration i e kidd creek preliminary data suggest that the degree of ree mobility increases with the size of the deposit thus ree mobility is a potentially useful method of distinguishing between small and large massive sulfide deposits at an early stage in exploration however this hypothesis requires further testing

foraminiferal faunal estimates of paleotemperature circumventing the no analog problem yields cool ice age tropics the sensitivity of the tropics to climate change particularly the amplitude of glacial to interglacial changes in sea surface temperature sst is one of the great controversies in paleoclimatology here we reassess faunal estimates of ice age ssts focusing on the problem of no analog planktonic foraminiferal assemblages in the equatorial oceans that confounds both classical transfer function and modern analog methods a new calibration strategy developed here which uses past variability of species to define robust faunal assemblages solves the no analog problem and reveals ice age cooling of 5 o to 6oc in the equatorial current systems of the atlantic and eastern pacific oceans classical transfer functions underestimated temperature changes in some areas of the tropical oceans because core top assemblages misrepresented the ice age faunal assemblages our finding is consistent with some geochemical estimates and model predictions of greater ice age cooling in the tropics than was inferred by climate long range investigation mapping and prediction climap 1981 and thus may help to resolve a long standing controversy our new foraminiferal transfer function suggests that such cooling was limited to the equatorial current systems however and supports climap s inference of stability of the subtropical gyre centers

contrasting pollen histories of mis 5e and the holocene from lake titicaca bolivia peru two long sediment records cores lto1 2b and lt01 3b from lake titicaca bolivia peru are compared with a previously analysed holocene record from this lake core ne98 1pc the holocene records of lt01 2b and ne98 1pc are similar there are striking differences however between the mis 5e sections of the long cores and the holocene records in these records tempera ture is probably the dominant parameter that determines the total fossil pollen concentration and is used to time the onset and termination of deglaciation in contrast the relative and absolute abun dance of specific taxa e g polylepis acaena chenopodiaceae are indicators of relative moisture availability although the holocene contains a period of aridity between ca 8000 cal yr bp and 4300 cal yr bp it is a minor event compared with the more extreme aridity of mis 5e core lt01 3b showed similar trends during mis 5e when compared to lt01 2b as did ne98 1pc when com paring holocene records mis 5e and the holocene are markedly different interglacials depicted by shifts in pollen concentration and taxa representation over time copyright 2005 john wiley sons ltd

a 24 700 yr paleolimnological history from the peruvian andes abstract a new paleolimnological dataset from lake pacucha 13 s 3095 m elevation in the peruvian andes provides evidence of changes in lake level over the past 24 700 yr a late glacial highstand in lake level gave way to an early holocene lowstand this transition appears to have paralleled precessional changes that would have reduced insolation during the wet season the occurrence of benthic salt tolerant diatoms and caco3 deposition suggest that the lake had lost much of its volume by c 10 000 cal yr bp pronounced holocene oscillations in lake level included a second phase of low lake level and heightened volatility lasting from c 8300 to 5000 cal yr bp while a polymictic lake formed at c 5000 cal yr bp these relatively wet conditions were interrupted by a series of drier events the most pronounced of which occurred at c 750 cal yr bp paleolimnological changes in the holocene were more rapid than those of either the last glacial maximum or the deglacial period

rb sr k ar and stable isotope evidence for the ages and sources of fluid components of gold bearing quartz veins in the northern sierra nevada foothills metamorphic belt california gold bearing quartz veins occur in and near major fault zones in deformed oceanic and island arc rocks west of the main outcrop of the sierra nevada composite batholith veins typically occupy minor reverse faults that crosscut blueschist to amphibolite grade metamorphic rocks whose metamorphic ages range from early paleozoic to jurassic vein micas and carbonate quartz mica assemblages that formed by hydrothermal metasomatism of ultramafic wall rocks in the alleghany grass valley washington and mother lode districts yield concordant k ar and rb sr ages the dated veins are significantly younger than prograde metamorphism penetrative deformation and accretion of their host rocks to the continental margin new and previously published mineralization ages from 13 localities in the sierra foothills range from about 140 to 110 m y ago with mean and median between 120 and 115 m y the age relations suggest that mineralizing fluids were set in motion by deep magmatic activity related to the resumption of east dipping subduction along the western margin of north america following the late jurassic nevadan collision event co 2 bearing fluids responsible for metasomatism and much of the vein mica carbonate albite and quartz deposition in several northern mines were isotopically heavy delta 18 o asymp 8 14ppm delta d between about 10 and 50ppm and do not resemble seawater magmatic or meteoric waters metasomatic and vein filling mica dolomite magnesite and quartz in altered ultramafic rocks generally formed from fluids with similar sr and o isotope ratios at a given locality consistent quartz mica delta 18 o fractionations delta 18 o sub q m 4 5 4 9ppm from various localities imply uniform equilibration temperatures probably between 300 degrees and 350 degrees c on a local mine scale fluids responsible for both carbonate alteration of mafic and ultramafic wall rocks and albitic alteration of felsic and pelitic rocks had similar sr isotope ratios samples from three veins in the central alleghany district fit a 115 7 or 3 m y rb sr isochron with a 87 sr 86 sr i value of approximately 0 7119 inferred 87 sr 86 sr ratios of metasomatic fluids from mines in different parts of the foothills region vary considerably 0 704 0 718 suggesting that sr was derived from sources ranging from western assemblage mesozoic ophiolitic or arc volcanic rocks to early paleozoic continent derived clastic rocks of the shoo fly complex systematic geographic variations in both sr and o isotopes can be rationalized by assuming extensive fluid interaction with rocks similar to the ones that are exposed within a few kilometers of the veins but the ultimate sources of the fluids and of au and other constituents may be independent of these isotopically lighter meteoric fluids deposited some late quartz overgrowths and occupied secondary fluid inclusions in earlier vein quartz