tourmaline b isotopes fingerprint marine evaporites as the source of high salinity ore fluids in iron oxide copper gold deposits carajas mineral province brazil the carajas mineral province in northern brazil contains a variety of world class 100 mt ore iron oxide copper gold iocg deposits including the only archean examples of this deposit class e g the igarape bahia alemao and salobo deposits tourmaline of schorldravite composition a common gangue mineral in these deposits precipitated shortly prior to and after the ore assemblage a boron isotope study of texturally different tourmaline from three iocg deposits igarape bahia salobo and sossego using secondary ion mass spectrometry sims provides new evidence in the long standing debate of magmatic versus non magmatic sources for the high salinity up to 50 wt nacl equiv of ore fl uids in these deposits values of 11 b from 14 to 26 5 for the igarape bahia and salobo deposits confi rm marine evaporite derived brines in the ore fl uids whereas lower 11 b values for the igarape bahia deposit 5 8 to 8 8 suggest that these fl uids may have mixed with an isotopically different hydrothermal fl uid or one that had a mixed boron source more variable and isotopically lighter boron in tourmaline from the sossego deposit 8 to 11 is attributed to mixed sources including light boron leached from felsic intrusive and volcanic host rocks and heavy boron derived from marine evaporites the boron isotope data indicate that the characteristic high salinity of the ore fl uids in the carajas mineral province was acquired by the interaction of hydrothermal fl uids with marine evaporites for iocg deposits that contain tourmaline as a common gangue mineral boron isotopes offer a valuable tool to constrain the high salinity source problem which is a critical issue in metallogenesis of iocg deposits worldwide

large scale sediment underplating in the makran accretionary prism southwest pakistan field relations in the emergent part of the makran accretionary prism show that a mid miocene to early pliocene slope and shelf sedimentary sequence was deposited directly on abyssal plain turbidites without any detectable stratigraphic or structural discordance sedimentological evidence for rapid shoaling however indicates that the underlying sediment column was tectonically thickened by a factor of between two and three during this period this can be explained by large scale underthrusting and underplating of sediment a mode of accretion that is also favored by mass balance considerations the visible deformation in the coastal makran occurred when the region was 70 100 km north of the contemporary prism front

makran continental margin sedimentation during the late holocene sedimentation in the makran active margin is governed by a complex interaction of atmospheric tectonics and hydrodynamic setting of the northern flank of the gulf of oman the mixed clastic carbo

sedimentology of seismo turbidites off the cascadia and northern california active tectonic continental margins northwest pacific ocean abstract holocene turbidites from turbidite channel systems along the active tectonic continental margins of the cascadia subduction zone offshore vancouver island to mendocino triple junction and the northern san andreas transform fault the triple junction to san francisco bay have been analyzed for sedimentologic features related to their seismic origin centimeter thick silt sand beds turbidite base capped by mud layers turbidite tail and interbedded with hemipelagic silty clay intervals with high biogenic content have been characterized by visual core descriptions grain size analysis x ray radiographs and physical properties along the northern california margin in upstream single tributary canyons and channels most turbidites are uni pulsed classic fining up whereas downstream below multiple tributary canyon and channel confluences most deposits are stacked turbidites because each set of stacked turbidites has no hemipelagic sediment between each turbidite unit and each unit has a distinct mineralogy from a different tributary canyon we interpret that a stacked turbidite is deposited by several coeval turbidity currents fed by multiple tributary canyons and channels with synchronous triggering from a single san andreas fault earthquake the cascadia margin is characterized by individual multi pulsed turbidites that contain multiple coarse grained sub units without hemipelagic sediment between pulses because the number and character of multiple coarse grained pulses for each correlative multi pulsed turbidite is almost always constant both upstream and downstream in different channel systems for 600 km along the margin we interpret that the earthquake shaking or aftershock signature is usually preserved for the much stronger cascadia 9 mw compared to weaker california 8 mw earthquakes which result in upstream uni pulsed turbidites and downstream stacked turbidites consequently both the strongest 9 mw great earthquakes and downstream confluences cause multi pulsed and stacked turbidites that are typical for seismo turbidites generated by a single great earthquake along both margins earthquake triggering and multi pulsed or stacked turbidites become an alternative explanation for amalgamated turbidite beds in active tectonic margins and show that multiple grain size pulses and reverse grading are not unique criteria for hyperpycnites thalweg levee turbidites or mini basin margin turbidites the analyses of the turbidites along the cascadia and northern california margins reveal common sedimentologic characteristics of turbidites triggered by great earthquakes that can be used to distinguish seismo turbidites in other active tectonic margins around the world

coastal boulders as evidence for high energy waves on the iranian coast of makran abstract coastal boulder deposits attesting to large waves are found along the rocky coast of makran iran from chabahar to lipar boulders are either scattered on the rocky coastal platform or accumulated in imbricated clusters the boulders are mostly rectangular and composed of biogenic calcarenite deriving from the present coastal platform significant morphological features observed on the boulders include supratidal karstic pools sharp broken edges and fractures some boulders contain boreholes and shells of marine bivalves suggesting detachment and transportation from the subtidal zone the dimensions elevation and distance from the coastline of 58 representative boulders are documented to estimate their volume weight and inland displacement the boulders weighing up to 18 t are found up to 6 m above present mean sea level and up to 40 m from the present shoreline we applied hydrological models to estimate and compare the wave height and inundation distance required to transport the boulders inland our results demonstrate that no known or probable storm event on the makran coast is capable of detaching and transporting the boulders in contrast tsunami wave height of 4 m is enough to detach all the boulders from the rocky coast and transport them inland we conclude that a tsunamigenic origin for boulder deposits is most plausible our results imply that the western part of the makran coast has archived evidence of paleotsunami events probably generated by large earthquakes at the makran subduction zone

controls on terrigenous sediment supply to the arabian sea during the late quaternary the makran continental slope the input of terrigenous sediment along the tectonically active makran continental margin off south western pakistan gulf of oman northern arabian sea is studied on the basis of sediment cores distributed along a transect from the upper slope to the abyssal plain spatial and temporal variations in sediment composition sedimentation rate and turbidite frequency in late pleistocene holocene time last 20 14c ka will be discussed and related to changes in sea level and climate and tectonic activity end member modelling of the grain size distributions of the hemipelagic and turbiditic sediments indicate that the sediments are adequately described as mixtures of three end members which represent turbidite sand turbidite silt or eolian dust and fluvial mud the geochemical and mineralogical compositions of the hemipelagic sediments indicate that the eolian dust was dominantly supplied from the northern arabian peninsula and the persian gulf region and that the fluvial input is from the makran margin the ratio of contributions of eolian and fluvial sediment in the hemipelagic intervals is used as an indicator of continental aridity i e summer monsoon intensity highest holocene turbidite frequencies and sedimentation rates are recorded at the deepest coring sites they are related to the proximity of the deformation front of the accretionary prism turbidite sedimentation on the upper continental slope was most frequent during the last glacial period of sea level lowstand and continued during the entire deglaciation and sea level rise infrequent turbidite sedimentation occurred during the holocene highstand of sea level turbidite sedimentation during the period of late sea level rise and the holocene sea level highstand is inferred to be due to the strong impact of episodic events i e flash floods and earthquakes and because of the narrow shelf of the active makran continental margin

cyclone gonu storm surge in oman super cyclone gonu is the strongest tropical cyclone on record in the arabian sea gonu caused coastal damage due to storm surge and storm wave impact as well as wadi flooding high water marks overland flow depths and inundation distances were measured in the coastal flood zones along the gulf of oman from 1 to 4 august 2007 the high water marks peaked at ras al hadd at the eastern tip of oman exceeding 5 m the storm surge of gonu is modeled using the advanced circulation model adcirc the multi hazard aspect is analyzed by comparing observations from cyclone gonu with the 2004 indian ocean tsunami

the sawqirah contourite drift system in the arabian sea nw indian ocean a case study of interactions between margin reactivation and contouritic processes the relationships between oceanic circulation in the arabian sea and late cenozoic climate changes including variations in monsoon intensity at the million year time scale remain poorly investigated using multibeam and seismic data we provide the first description of a contourite drift in the arabian sea along the south eastern oman margin this contourite drift is referred as the sawqirah contourite drift system late miocene reactivation of the south eastern oman margin resulted in the formation of a complex anticline system which shaped the seafloor topography above which the sawqirah drift subsequently developed the drift resulted from the circulation of bottom currents within the north intermediate indian water major seismic unconformities identified within the sawqirah drift were tied to ocean drilling program odp drill holes and allowed defining distinct episodes of drift construction at least two of these unconformities record reorganizations of the oceanic circulation at 4 5 4 8 ma and 2 4 ma the 4 5 4 8 ma old unconformity is coeval with the onset of upwelling of deep and cold waters in the owen basin the 2 4 ma old unconformity records a major episode of indian monsoon intensification at the million year time scale over the arabian sea indicating strong coupling between oceanic and atmospheric circulation processes

hydrology and circulation in the strait of hormuz and the gulf of oman results from the gogp99 experiment 1 strait of hormuz in october and early november 1999 the gogp99 experiment collected hydrological currentmeter tide recorder thermistor and drifting buoy data near the strait of hormuz data analysis provides the water mass structure in the strait persian gulf water pgw core is banked against the omani coast while indian ocean surface water iosw lies near the iranian coast these water masses are most often covered by a homogeneous surface layer thermohaline characteristics of the pgw core decrease substantially downstream from the persian arabian gulf to the gulf of oman pgw and iosw thermohaline characteristics and distribution also exhibit notable changes at periods shorter than a month as shown by repeated hydrological sections the tidal signal measured south of the strait by moored adcp and thermistor chains has predominant semi diurnal m2 and s2 and diurnal k1 components and possesses a complex vertical structure tidal intensification near the surface pycnocline is associated with noticeable internal waves at subtidal timescale mooring recordings confirm the water mass variability observed in the repeated hydrological sections the mixed layer also deepens substantially during the 1 month period finally trajectories of surface buoys drogued at 15 m exhibit reversals over periods characteristic of changes in wind direction

holocene strengthening of the oxygen minimum zone in the northwestern arabian sea linked to changes in intermediate water circulation or indian monsoon intensity abstract a high resolution 14 000 year old record of benthic foraminifera from odp hole 723a was produced to understand changing intensity of the nw arabian sea oxygen minimum zone omz and its links with intermediate water circulation and indian monsoon intensity during the latest pleistocene the omz was very weak marked by the abundance of oxic species from early to mid holocene period up to 6500 years bp intense sw monsoon related high surface productivity led to the development of an omz in the arabian sea however presence of oxic and suboxic species indicate that omz intensification was minimized by cyclic incursions of oxygen rich intermediate waters from the south the middle holocene was a transitional period to intense omz conditions the intensification of the omz could be due to replacement of oxygen rich southern source sub antarctic mode and antarctic intermediate waters samw aaiw with oxygen poor red sea water rsw from the north during the middle holocene as the intensity of the summer monsoon weakened during the late holocene 4200 years bp onwards the arabian sea omz intensified suggesting total cut off from the oxygenated samw aaiw spectral analysis of information function h benthic foraminifer bolivina spp and oxic species of benthic foraminifera indicate that the intensity of the omz and deep water conditions respond closely to solar cycles

character and dynamics of the red sea and persian gulf outflows historical hydrographic data and a numerical plume model are used to investigate the initial transformation dynamics and spreading pathways of red sea and persian gulf outflow waters where they enter the indian ocean the annual mean transport of these outflows is relatively small 0 4 sv but they have a major impact on the hydrographic properties of the indian ocean at the thermocline level because of their high salinity they are different from other outflows in that they flow over very shallow sills depth 200 m into a highly stratified upper ocean environment and they are located at relatively low latitudes 12 n and 26 n furthermore the red sea outflow exhibits strong seasonal variability in transport the four main results of this study are as follows first on the basis of observed temperature salinity t s characteristics of the outflow source and product waters we estimate that the red sea and persian gulf outflows are diluted by factors of 2 5 and 4 respectively as they descend from sill depth to their depth of neutral buoyancy the high dilution factor for the persian gulf outflow results from the combined effects of large initial density difference between the outflow source water and oceanic water and low outflow transport second the combination of low latitude and low outflow transport and associated low outflow thickness results in ekman numbers for both outflows that are o 1 this indicates that they should be thought of as frictional density currents modified by rotation rather than geostrophic density currents modified by friction third different mixing histories along the two channels that direct red sea outflow water into the open ocean result in product waters with significantly different densities which probably contributes to the multilayered structure of the red sea product waters in both outflows seasonal variations in source water and oceanic properties have some effect on the t s of the product waters but they have only a minor impact on equilibrium depth fourth product waters from both outflows are advected away from the sill region in narrow boundary currents at least during part of the year at other times the product water appears more in isolated patches

the kupferschiefer cu ag ore deposits in poland a re appraisal of the evidence of their origin and presentation of a new genetic model the kupferschiefer stratiform copper deposits in central europe have long been considered a classic example of syngenetic mineralization however metal zoning and host rock relationships determined during exploration around the recently discovered lubin district orebodies in southwest poland suggest that the ore may instead be late diagenetic the mineralization occurs as thin extensive blankets of sulphides in the pyritic organic rich basal units of the late permian zechstein restricted marine sequence and in the eolian weissliegendes sandstone at the top of the early permian rotliegendes continental rift sequence of bimodal volcanic rocks and redbeds it is directly underlain and controlled by irregular oval zones of rote faule rf a barren oxidized and reddened portion of the normally dark grey pyritic basal zechstein rocks in plan view the metals occur as successive belts enriched in copper silver lead and zinc which developed laterally from and encircle the rf zones the ore transgres

organic matter preservation on the pakistan continental margin as revealed by biomarker geochemistry in order to assess whether the oxygen minimum zone omz in the arabian sea has an eaect on the preservation and composition of organic matter in surface sediments we investigated samples from three diaerent transects on the pakistan continental margin across the omz in addition to determining the total amount of organic carbon toc we analyzed the extractable lipids by gas chromatography combined gas chromatography mass spectrometry and compound specific stable carbon isotope measurements the extractable lipids are dominated by marine organic matter as indicated by the abundance of lipids typical of marine biota and by the bulk and molecular isotopic composition sediments from within the omz are enriched in organic carbon and in several extractable lipids i e phytol n alcohols total sterols n c35 alkane relative to stations above and below this zone other lipid concentrations such as those of total n fatty acids and total n alkanes fail to show any relation to the omz only a weak correlation of toc with mineral surface area was found in sediments deposited within the omz in contrast sediments from outside the omz do not show any relationship between toc and surface area among the extractable lipids only the n alkane concentration is highly correlated with surface area in sediments from the hab and makran transects in sediments from outside the omz the phytol and sterol concentrations are also weakly correlated with mineral surface area the depositional environment of the indus fan oaers the best conditions for an enhanced preservation of organic matter the omz together with the undisturbed sedimentation at moderate rates seems to be mainly responsible for the high toc values in this area overall the type of organic matter and its lability toward oxic degradation the mineral surface area the mineral composition and possibly the secondary productivity by sedimentary bacteria also appear to have an influence on organic matter accumulation and composition 2000 elsevier science ltd all rights reserved

comparison of laser grain size analysis with pipette and sieve analysis a solution for the underestimation of the clay fraction classically the grain size of soil and sediment samples is determined by the sieve method for the coarse fractions and by the pipette method based on the stokes sedimentation rates for the fine fractions results from the two methods are compared with results from laser diffraction size analysis which is based on the forward scattering of monochromatic coherent light from a point of view of laboratory efficiency the laser sizing technique is far superior accuracy and reproducibility are shown by measurements on certified materials it appears that laser grain size measurements of certified materials correspond very well with the certificated measurements tests were also done on a set of randomly selected sediments of fluvial aeolian and lacustrine origin except for the 2 m clay fraction there is a coarsening of the mean diameter of one to two size classes 0 25 caused by the non sphericity of the particles the platy form of the clay particles induces considerable differences eight size classes between pipette and laser measurements the 2 m grain size defined by the pipette method corresponds with a grain size of 8 m defined by the laser particle sizer for the studied sediments using a higher grain size level for the clay fraction when laser analysis is applied enables workers in the geological and environmental field to compare classical pipette analysis with a laser sizing technique

a 5000 yr record of climate change in varved sediments from the oxygen minimum zone off pakistan northeastern arabian sea the upper holocene marine section from a kasten core taken from the oxygen minimum zone off karachi pakistan at water depth 700 m contains continuously laminated sediments with a sedimentation rate of 1 2 mm yr and a unique record of monsoonal climatic variability covering the past 5000 years our chronostratigraphy is based on varve counts verified by conventional and ams 14 c dating individual hemipelagic varve couplets are about 0 8 1 5 mm thick with light colored terrigenous laminae a deposited mainly during the winter monsoon alternating with dark colored laminae b rich in marine organic matter coccoliths and fish debris that reflect deposition during the high productivity season of the late summer monsoon august october precipitation and river runoff appear to control varve thickness and turbidite frequency we infer that precipitation decreased in the river watershed indicated by thinning varves after 3500 4000 yr b p this is about the time of increasing aridification in the near east and middle east as documented by decreasing nile river runoff data and lake level lowstands between turkey and northwestern india this precipitation pattern continued until today with precipitation minima about 2200 1900 yr b p 1000 yr b p and in the late middle ages 700 400 yr b p and precipitation maxima in the intervening periods as documented by spectral analysis the thickness of varve couplets responds to the average length of a 250 yr cycle a 125 yr cycle the gleissberg cycle of solar activity 95 yr and a 56 yr cycle of unknown origin higher frequency cycles are also present at 45 39 29 31 and 14 yr the sedimentary gray value also shows strong variability in the 55 yr band plus a 31 yr cycle because high frequency cyclicity in the enso band ca 3 5 and 5 yr is only weakly expressed our data do not support a straightforward interaction of the pacific enso with the monsoon driven climate system of the arabian sea

meta evaporite in the carajas mineral province northern brazil evidence for connecting evaporite sourced high salinity fluids with iron oxide copper gold iocg deposits in the carajas mineral province has solely been based on boron isotope compositions of tourmaline presence of meta evaporitic rocks remains unrecognised here we report laminated albitite tourmalinite and banded albite phlogopite rock intercepted by exploratory drilling in a clastic metasedimentary sequence these rocks represent evaporite precursors their location in the copper gold prospects acai and angelica in the westernmost part of the carajas mineral province indicates that i evaporite sourced fluids were regional and ii evaporite bearing metasedimentary sequences may have been an important source of high salinity fluids and or sulfur for the iocg deposits of the carajas mineral province

paleoethologic interpretation of complex thalassinoides in shallow marine limestones lower ordovician southern sweden abstract lower ordovician thalassinoides t bacae isp nov from oland sweden is characterized by irregularly anastomosing horizontal tunnel mazes with highly variable branching angles accompanied by numerous closely spaced short vertical shafts that must have provided a large number of burrow openings to the sea floor these complex trace fossils appear to be agrichnial burrow systems that represent chemosymbiotic feeding behavior by infaunal animals they occur profusely in thin bedded fossiliferous lime mudstone and wackestone that were deposited on a shallow marine carbonate platform

palynology a tool to identify abrupt events an example from chabahar bay southern iran tsunami storm and flood events are destructive agents that have the potential to cause much damage and cost lives the coastal regions around the north western arabian sea are prone to these natural disasters with recent events including the storm and flood of ad 1842 the makran tsunami of 1945 and cyclone gonu in 2007 despite their severity the paucity of reliable historical records does not allow us to answer pertinent questions concerning their frequency intensity and impact palaeo event analysis from the geological record allows us to extend and test the historical record here we have dated and examined a 92 cm long sediment core from the tectonically active cyclone and storm prone chabahar bay area southern iran our appraisal directly tests conventional proxies for identifying abrupt events e g grain size geochemical data which we supplement with a novel palynological pollen and dinocyst approach both sedimentological and palynological approaches suggest a large event which was dated at ad 1808 41 whereas geochemical approaches remain inconclusive the increase of continentally derived pollen pinaceae salix betula and typha sparganium increases in brigantedinium sp and s ramosus as well as decreases in lingulodinium machaerophorum suggest enhanced fluvial delivery in association with a flood this investigation provides evidence of a major flash flood affecting the chabahar bay region at ad 1808 41 which we infer is the geological expression of the storm and associated flash flood of ad 1842 moreover our study demonstrates the utility of palynology in identifying and understanding the causes of abrupt events to complement more widely applied techniques

a 28 ka history of sea surface temperature primary productivity and planktonic community variability in the western arabian sea 1 uranium series radionuclides and organic biomarkers which represent major groups of planktonic organisms were measured in western arabian sea sediments that span the past 28 ka variability in the past strength of the southwest and northeast monsoons and its influence on primary productivity sea surface temperature sst and planktonic community structure were investigated the average alkenone derived sst for the last glacial period was 3 c lower than that measured for the holocene prior to the deglacial the lowest ssts coincide with the highest measured fluxes of organic biomarkers which represent primarily a planktonic suite of diatoms coccolithophorids dinoflagellates and zooplankton we propose that intensification of winter northeast monsoon winds during the last glacial period resulted in deep convective mixing cold ssts and enhanced primary productivity in contrast postdeglacial 17 ka ssts are warmer during times in which biomarker fluxes are high associated with this transition is a planktonic community structure change in which the ratio of the average cumulative flux of diatom biomarkers to the cumulative flux of coccolithophorid biomarkers is twice as high during the deglacial and holocene than the average ratio during the last glacial period we suggest that this temporal transition represents a shift from a winter northeast monsoon dominated pre 17 ka to a summer southwest monsoon dominated post 17 ka wind system

variations in productivity and eolian fluxes in the northeastern arabian sea during the past 110 ka abstract high resolution one to two samples ka radionuclide proxy records from core 93kl in the northeastern arabian sea provide evidence for millennial climate variability over the past 110 ka we interpret 230th normalized 232th fluxes as a proxy for eolian input and authigenic uranium concentrations as a proxy for past productivity we attribute orbital and suborbital variations in both proxies to changes in the intensity of the southwest indian ocean monsoon the highest 230th normalized 232th fluxes occur at times that are consistent with the timing of the younger dryas heinrich events 1 7 and cold dansgaard oeschger stadial events recorded in the gisp2 ice core such high dust fluxes may be due to a weakened southwest monsoon in conjunction with strengthened northwesterlies from the arabian peninsula and mesopotamia authigenic uranium concentrations on the other hand are highest during warm dansgaard oeschger interstadials when the southwest monsoon is intensified relative to the northwesterly winds our results also indicate that on orbital timescales maximum average eolian fluxes coincide with the timing of marine isotopic stage mis 2 and 4 while minimum fluxes occur during mis 1 3 and 5 although the forcing mechanism s controlling suborbital variabilities in monsoonal intensity is still debated our findings suggest an atmospheric teleconnection between the low latitude southwest monsoon and north atlantic climate

present day crustal deformation and plate kinematics in the middle east constrained by gps measurements in iran and northern oman summary a network of 27 gps sites was implemented in iran and northern oman to measure displacements in this part of the alpine himalayan mountain belt we present and interpret the results of two surveys performed in 1999 september and 2001 october gps sites in oman show northward motion of the arabian plate relative to eurasia slower than the nuvel 1a estimates e g 22 2m m yr 1 at n8 5 e instead of 30 5 mm yr 1 at n6 e at bahrain longitude we define a gps arabia eurasia euler vector of 27 9 0 5 n 19 5 1 4 e 0 41 0 1 myr 1 the arabia eurasia convergence is accommodated differently in eastern and western iran east of 58 e most of the shortening is accommodated by the makran subduction zone 19 5 2m m yr 1 and less by the kopet dag 6 5 2m m yr 1 west of 58 e the deformation is distributed in separate fold and thrust belts at the longitude of tehran the zagros and the alborz mountain ranges accommodate 6 5 2m m yr 1 and 8 2m m yr 1 respectively the right lateral displacement along the main recent fault in the northern zagros is about 3 2m m yr 1 smaller than what was generally expected by contrast large rightlateral displacement takes place in northwestern iran up to 8 mm yr 1 the central iranian block is characterized by coherent plate motion internal deformation 2m m yr 1 sites east of 61 e show very low displacements relative to eurasia the kinematic contrast between eastern and western iran is accommodated by strike slip motions along the lut block to the south the transition zone between zagros and makran is under transpression with right lateral displacements of 11 2m m yr 1

late holocene vegetation and ocean variability in the gulf of oman fossil pollen and dinocyst records in marine sequences are frequently combined to reveal the response of vegetation and ocean conditions to changes in both regional and global climate in this study we analysed pollen and dinocysts within a clearly laminated sediment core off the iranian coast in the gulf of oman an extremely data poor area to reconstruct climatic change during the late holocene last 1900 years the vegetation record from southern iran indicates a replacement of savannah by desert formations at c 910 ce shortly after the islamic invasion and the subsequent collapse of the sassanid empire from c 910 to 1145 ce during the medieval climate anomaly mca the vegetation was heavily dominated by desert formations such as amaranthaceae caryophyllaceae asteraceae centaurea and calligonum in parallel in the gulf of oman the presence of impagidinium paradoxum indicates a lack of freshwater discharge into the ocean around this time the desert taxa of the mca were subsequently replaced by savannah formations at c 1145 ce comprised mainly of poaceae and cyperaceae corresponding to the little ice age lia indicating generally wetter climatic conditions a sudden increase in spiniferites ramosus 1 63 at c 1440 ce suggests an increase in the strength of the sw summer monsoon with increased freshwater discharge into the ocean at this time our data indicate that over the past two millennia the nw arabian sea region has alternated between contrasting climatic conditions with firstly a humid phase equivalent to the cultural period of the sassanid empire a significantly drier climate during the mca and a relatively wetter climate during the lia the mechanisms resulting in dry conditions during the mca in the middle east associated with the northward shift of the itcz and the intensification of the indian summer monsoon may be similar to those causing the dry conditions which dominated the early holocene in the near east our palaeoenvironmental proxy data support current observations that a globally anthropogenically induced warmer climate is likely to lead to increased drought severity in the middle east putting additional stress on governments already struggling with poverty and social tensions

hydrology and circulation in the strait of hormuz and the gulf of oman results from the gogp99 experiment 2 gulf of oman art no c12038 hydrological adcp and drifting buoy data obtained during the gogp99 experiment in october and early november 1999 are analyzed to describe the persian gulf water pgw core and the regional circulation in the gulf of oman the warm and salty pgw core flows out of the strait of hormuz heading southeastward unto 25degrees20 n 57degreese approximately from there it cascades down the continental slope veers southwestward and joins the omani coast near 24degrees50 n 56degrees50 e to form a slope current this pgw current has then thermohaline maxima on isopycnal sigma 0 26 5 near 220 m depth its thermohaline characteristics decrease along its progression to ra s al hadd and then offshore into the arabian sea but maintain a sharp contrast with surrounding waters outflow variability at the strait of hormuz can be related to downstream fluctuations of the thermohaline maxima in the pgw core at gulf scale and over a 2 to 3 week period moreover several mechanisms baroclinic instability flow intermittency cape effects are examined to explain the widening of this pgw core upstream and downstream of ra s al hamra in the eastern part of the gulf of oman the regional circulation is a cyclonic gyre the circulation in the western part of the gulf is more complex with the outflow of pgw and southeastward currents in the upper 250 m near the omani coast and a recirculation of upwelled waters near ra s jagin on the iranian coast the large cyclonic gyre occupies at least the upper 300 m of the water column and undergoes little variation over a month the pgw outflow in the northern arabian sea is southward and located 50 100 km from the coast it borders a shallower northward current located offshore

superposition of burial and hydrothermal events post variscan thermal evolution of the erzgebirge germany the post variscan thermal history of the erzgebirge germany is the result of periods of sedimentary burial exhumation and superimposed hydrothermal activity the timing and degree of thermal overprint have been analysed by zircon and apatite u th he and apatite fission track thermochronology the present day surface of the erzgebirge was exhumed to a near surface position after the variscan orogeny thermal modelling reveals permo mesozoic burial to temperatures of up to 80 100 c although the sedimentary cover thins out towards the north resulting in maximum burial temperatures of less than 40 c this thermal pattern was locally modified by cretaceous hydrothermal activity that reset the zircon u th he thermochronometer along ore veins the thermal models show no significant regional exhumation during cenozoic times indicating that the peneplain like morphology of the basement is a late cretaceous feature

late cretaceous bonanza style metal enrichment in the serra pelada au pd pt deposit para brazil a 40 ar 39 ar age of 75 6 ma 2 was obtained for aggregates of mn ba oxide intergrown with palladiferous gold and pd pt minerals representative of near surface bonanza au pd pt mineralization that triggered the gold rush to serra pelada in northern brazil the mineralization occurs in goethite rich tectonic breccia and records recurrent fault displacement in the still active cinzento strike slip fault system the goethite rich tectonic breccia is truncated by the bonanza style au pd pt mn ba enrichment with which tabular hematite is spatially associated on a micrometric scale the tabular hematite is coarsely crystalline 5 m in grain size and lines cavity walls in the goethite rich breccia the presence of coarsely crystalline tabular hematite constrains the metalliferous overprint to temperatures in excess of about 100 c we suggest that the bonanza mineralization is a late cretaceous epithermal like fault breccia system that overprinted paleoproterozoic intrusion related au pd pt mineralization preserved at depth

critical assessment of geochronological data from the carajas mineral province brazil implications for metallogeny and tectonic evolution abstract the carajas domain in the amazonian craton brazil displays remarkable metallogenetic diversity containing iron oxide copper gold iocg cu au mn fe ni co pge cr and au pge mineral systems it consists of mesoarchean 2 83 3 08 ga basement granitoids and gneisses overlain by the ca 2 73 2 76 ga rift related meta volcanosedimentary units of the neoarchean carajas basin coeval ca 2 76 mafic ultramafic complexes host nickel cobalt laterite vermelho puma onca and magmatic pge cr luanga deposits unconformably overlying this is the aguas claras formation a package of fluvial to shallow marine sedimentary rocks of controversial but probable archean age based on 2 6 2 7 ga cross cutting mafic dikes this hosts manganese deposits azul small polymetallic cu au deposits breves and the serra pelada au pt pd deposit iocg deposits are located along wnw regional shear zones hosted within the itacaiunas supergroup mesoarchean basement and bimodal 2 76 2 73 ga neoarchean granitoids and gabbro geochronology supports the existence of multiple superimposed and episodic hydrothermal and mineral systems multiple mineralization ages are common within single deposits and establishing the age of primary mineralization as opposed to overprinting hydrothermal events is challenging copper mineralization formed as early as ca 2 76 ga coeval with basin formation while structurally controlled iocg deposits formed or were substantially modified during multiple hydrothermal episodes ca 2 72 2 68 ga 2 6 2 45 ga and 1 88 ga for the northern iocg deposits e g salobo and igarape bahia alemao a temporal overlap between 2 57 ga mineralization and the 2 57 ga alkaline old salobo granite is commonly used to infer a genetic link yet this geochronology s reliability is debatable younger ages exist for the old salobo granite 2 55 2 53 ga zircons are metamict and older mineralization ages have been reported suggesting a more complex history the occurrence of ages ca 2 60 2 45 ga is spatially restricted to the north and coincides with an important yet poorly understood tectono thermal event involving reactivation of the northern cinzento shear zone and amphibolite facies metamorphism whether iocg deposits formed during this tectonic event or represent substantially modified or metamorphosed older mineralization or both is contentious older mineralization ca 2 71 ga at the igarape cinzento iocg deposit in the north is coeval with the southern iocg deposits formed ca 2 72 2 68 ga sequeirinho bacaba and bacuri this does not convincingly overlap with the intrusion of widespread 2 76 2 73 ga syntectonic granitoids so a genetic link with magmatic fluids is speculative and basinal brines may play a role due to controversy regarding the timing of compression and basin closure the tectonic setting is debated mineralization either formed during rifting or synchronous with basin inversion but the latter is more supported by geochronology and ore textures in the south paleoproterozoic ca 1 88 ga iocgs the sossego curral orebodies of the sossego deposit and alvo 118 or alternatively overprinting cu au systems formed coeval with craton wide a type 1 88 ga granite magmatism this magmatic hydrothermal system is responsible for a large part of the metallogenetic diversity of carajas domain small generally

climate change and the collapse of the akkadian empire evidence from the deep sea the akkadian empire ruled mesopotamia from the headwaters of the tigris euphrates rivers to the persian gulf during the late third millennium b c archeological evidence has shown that this highly developed civilization collapsed abruptly near 4170 150 calendar yr b p perhaps related to a shift to more arid conditions detailed paleoclimate records to test this assertion from mesopotamia are rare but changes in regional aridity are preserved in adjacent ocean basins we document holocene changes in regional aridity using mineralogic and geochemical analyses of a marine sediment core from the gulf of oman which is directly downwind of mesopotamian dust source areas and archeological sites our results document a very abrupt increase in eolian dust and mesopotamian aridity accelerator mass spectrometer radiocarbon dated to 4025 125 calendar yr b p which persisted for 300 yr radiogenic nd and sr isotope analyses confirm that the observed increase in mineral dust was derived from mesopotamian source areas geochemical correlation of volcanic ash shards between the archeological site and marine sediment record establishes a direct temporal link between mesopotamian aridification and social collapse implicating a sudden shift to more arid conditions as a key factor contributing to the collapse of the akkadian empire