magnetic fingerprinting of hydrodynamic variations and channel erosion across the turbidity maximum zone of the yangtze estuary china abstract magnetic measurements were conducted on surface sediments and suspended particles collected across the turbidity maximum zone of the yangtze estuary in order to examine the spatial distribution of magnetic mineral assemblages and the factors responsible for this distribution the results indicate that magnetic properties are dominated by ferrimagnetic grains bulk magnetic susceptibility and saturation isothermal remanent magnetization sirm values show positive correlations with the proportion of the 63 m fraction in the north channel while anhysteretic remanent magnetization arm is significantly correlated with the proportion of the arm sirm ratios which is consistent with the coarsest particle size due to strong hydrodynamics i e currents within each channel and sirm values are higher in sediments from shallower water depth due to energetic conditions resulting from waves compared with surface sediments suspended particles have lower and sirm values but higher arm sirm ratios due to lower sand fractions the increasing trend of arm sirm of suspended particles along the pathway of sediment transport indicates weakening hydrodynamics from the inner estuary to the outer estuary diagenesis is another factor influencing magnetic properties in addition to particle size channel erosion leads to local exposure of buried sediments on the channel bed as a result of a stronger diagenetic imprint they show magnetic properties different from the recently deposited sediments our results indicate that magnetic properties cannot only indicate spatial variations in hydrodynamics but also provide insight into sediment erosion deposition processes combined granulometric and magnetic methods can therefore be used to interpret hydrodynamics and track changes in estuary morphology

a 4 ma record of thermal evolution in the tropical western pacific and its implications on climate change article i nfo orbital resolution thermal histories over the last 4 ma at odp site 1143 in the tropical western pacific are reconstructed using alkenone paleothermometry the temperature profile is characterized by a steady state of 29 c with fluctuations b1 c before 2 7 ma and by a strong oscillating state from 2 7 ma largely due to cooling by up to 4 c from 29 c in interglacial to 26 c in glacial intervals this implies a relative warm and stable surface hydrography during the early and mid pliocene in this region influenced by the warm pool before temperature decreases in responding to global cooling and the formation of the distinct glacial stages since the late pliocene therefore the smaller sst gradient between tropical eastern and western pacific and between southern and northern south china sea before the late pliocene indicates a super sized pliocene pacific warm pool while the larger sst gradient since then marks progressively intensification of the zonal walker circulation and meridional hadley circulation representing the monsoon circulations in the region the intensification of the walker and hadley circulations over the tropical pacific may also have helped on the onset of glaciations and subsequent deglaciations during the late pliocene and pleistocene 2011 published by elsevier b v

deep pacific caco 3 compensation and glacial interglacial atmospheric co 2 abstract benthic foraminiferal 13c suggests that there was a net shift of isotopically light metabolic co2 from the upper ocean into the deep ocean during the last glacial period according to the caco3 compensation hypothesis this should have caused a transient drop in deep ocean co32 that was eventually reversed by seafloor dissolution of caco3 the resulting increase in whole ocean ph may have had a significant impact on atmospheric co2 compounding any decrease that was due to the initial vertical co2 shift the opposite hypothetically occurred during deglaciation when co2 was returned to the upper ocean and atmosphere and deep ocean co32 temporarily increased followed by excess burial of caco3 and a drop in whole ocean ph the deep sea record of caco3 preservation appears to reflect these processes with the largest excursion during deglaciation as expected but various factors make quantification of deep sea paleo co32 difficult here we reconstruct deep equatorial pacific co32 over the last glacial interglacial cycle using benthic foraminiferal zn ca which is strongly affected by saturation state during calcite precipitation our data are in agreement with the caco3 compensation theory including glacial co32 concentrations similar to or slightly lower than today and a termination i co32 peak of 25 30 mol kg 1 the deglacial co32 rise precedes ice sheet melting consistent with the timing of the atmospheric co2 rise a later portion of the peak could reflect removal of co2 from the atmosphere ocean system due to boreal forest regrowth caco3 compensation alone may explain more than one third of the atmospheric co2 lowering during glacial times

patterns of deglacial warming in the pacific ocean a review with emphasis on the time interval of heinrich event 1 abstract based on a compilation of currently available records of past sea surface temperature sst variability estimated from a variety of different proxies the regional scale deglacial sst development in the pacific ocean is tentatively classified into four endmember types the subtropical and tropical pacific is characterized by a continuous deglacial warming without marked interruption during the time interval of heinrich event 1 h1 whereas the subarctic north pacific exhibits centennial scale warm cold oscillations during this time interval sst records from marginal seas of the pacific show a deglacial warming interrupted by a cooling event coeval with h1 followed by a marked bolling sst increase a single sst record from the southwestern subantarctic pacific displays a continuous deglacial warming across h1 followed by an antarctic cold reversal type cooling during the allerod thus in contrast to the deglacial sst development in the atlantic which has been inferred to be overwhelmingly driven by the redistribution of heat through changes in the meridional overturning circulation moc none of the open oceanic pacific sst records reviewed here displays any obvious and or dominant response to the reduction of the moc and or the reorganization of atmospheric circulation during h1 within the limits of absolute chronologies all tropical and subtropical pacific sst records show an onset of deglacial warming at 19 1 ka coeval with the onset of the deglacial rise in sea level

sedimentary facies and sequence stratigraphy of the asmari formation at chaman bolbol zagros basin iran abstract the oligocene miocene asmari formation of the zagros basin is a thick sequence of shallow water carbonate in the study area it is subdivided into 14 microfacies that are distinguished on the basis of their depositional textures petrographic analysis and fauna based on the paleoecology and lithology four distinct depositional settings can be recognized tidal flat lagoon barrier and open marine the asmari formation represents sedimentation on a carbonate ramp in the inner ramp the most abundant lithofacies are medium grained wackestone packstone with imperforated foraminifera the middle ramp is represented by packstone grainstone to floatstone with a diverse assemblage of larger foraminifera with perforate wall red algae bryozoa and echinoids the outer ramp is dominated by argillaceous wackestone characterized by planktonic foraminifera and large and flat nummulitidae and lepidocyclinidae three third order depositional sequences are recognized from deepening and shallowing trends in the depositional facies changes in cycle stacking patterns and sequence boundary features

sequence biostratigraphy and paleoenvironmental reconstruction in the early eocene figols group of the tremp graus basin south central pyrenees spain the dinoflagellate cyst palynofacies and foraminiferal records from the early eocene figols group of the spanish pyrenees exhibit major changes associated with relative sea level fluctuations and variations in efficiency of the fluvial systems the mixed siliciclastic carbonate marine succession exposed in the merli esdolomada area was deposited on the shelf in a tectonically active basin under oxic conditions in shallow to moderately deep marine waters close to the lower boundary of the photic zone influenced by river discharge from adjacent emerged lands sedimentary cycles are mainly recorded by fine grained deposits the paleoenvironmental interpretation of palynological and calcareous microfaunal records allows the definition of depositional sequences and enables to trace basinward surfaces identified in more proximal settings by means of sedimentological facies analysis at the same time the solid regional stratigraphic framework already available for the figols group allows new insights on the paleoecology of extinct taxa the merli esdolomada section me spans two 3rd order sequences the upper sequence reflects more marginal marine conditions than the lower one thus pointing to an overall shallowing trend with time in the lower sequence the maximum flooding interval is characterised by a rich and diverse microfauna highest relative abundances of marine phytoplankton and typically neritic dinoflagellate cyst dinocyst assemblages dominated by spiniferites and cordosphaeridium the final phase of the highstand systems tract in proximity of the main sequence boundary is characterised by a decrease in abundance and diversity of dinocysts with the dominance of the lagoonal genus polysphaeridium and by decreased microfaunal diversity discorbids miliolids larger foraminifers palynological records permit the reconstruction of activation and deactivation phases of the fluvial systems variations in runoff from the hinterland nutrient delivery to the sea and productivity in surface waters of the tremp graus basin the overall abundance of spiniferites and the scarcity of peridinioid cysts lingulodinium pediastrum and botryococcus algae are interpreted to indicate oligotrophic conditions during the deposition of the investigated succession recurrent intervals where the temporary disappearance of spiniferites corresponds to highest relative abundances of operculodinium and herbaceous debris are the main evidence for river plumes and denote periods of enhanced fluvial discharge reflecting a milankovitch type cyclicity the rotalia group which shows abundance peaks of cuvillierina spp in the shallower intervals is often associated with these episodes thus suggesting for this taxon more tolerance to turbidity than larger foraminifera within the maximum flooding zone a thalassiphora patula acme corresponding to the local disappearance of homotryblium is deemed to record the distal expression of a fluvial activation which triggered water salinity stratification despite broad morphological similarities homotryblium exhibits more cosmopolitan preferences than polysphaeridium which is instead confirmed as a lagoonal euryhaline taxon the increase of spinizonocolpites pollen toward the top of the figols group records the northwestward migration of nypa mangrove palms from southern europe during the mid early eocene

productivity changes in the bering sea during the late quaternary changes in biological productivity of the bering sea have been evaluated for the late quaternary based on biogenic opal calcium carbonate and microfossils in two piston cores biological productivity increased during marine isotope stage mis 1 after the last glaciation during the last deglaciation two pronounced peaks of calcium carbonate content were observed at ca 2400 m water depth which can be explained by the caco3 compensation hypothesis and coccolithophore blooms simultaneous with the caco3 peaks oxygen poor deep water was apparently distributed in the aleutian basin based on benthic foraminiferal assemblages the low o2 events seem to be related to deep water circulation and or elevated productivity in the northwest pacific after the caco3 peak events biogenic opal contents and diatoms increased gradually associated with enhanced vertical mixing with an inflow of the alaskan stream through the eastern aleutian arc passes r 2005 elsevier ltd all rights reserved

facies analysis and palaeoenvironmental interpretation of the late oligocene attard member lower coralline limestone formation malta the oligocene represents a key interval during which coralline algae became dominant on carbonate ramps and luxuriant coral reefs emerged on a global scale so far few studies have considered the impact that these early reefs had on ramp development consequently this study aimed at presenting a high resolution analysis of the attard member of the lower coralline limestone formation late oligocene malta in order to decipher the internal and external factors controlling the architecture of a typical late oligocene platform excellent exposures of the lower coralline limestone formation occurring along continuous outcrops adjacent to the victoria lines fault reveal in detail the three dimensional distribution of the reef associated facies a total of four sedimentary facies have been recognized and are grouped into two depositional environments that correspond to the inner and middle carbonate ramp the inner ramp was characterized by a very high energy shallow water setting influenced by tide and wave processes this setting passed downslope into an inner ramp depositional environment which was colonized by seagrass and interfingered with adjacent areas containing scattered corals the middle ramp lithofacies were deposited in the oligophotic zone the sediments being generated from combined in situ production and sediments swept from the shallower inner ramp by currents compositional characteristics and facies distributions of the attard ramp are more similar to the miocene ramps than to those of the eocene an important factor controlling this similarity may be the expansion of the seagrass colonization within the euphotic zone this expansion may have commenced in the late oligocene and was associated with a concomitant reduction in the aerial extent of the larger benthonic foraminifera facies stacking pattern analysis shows that the depositional units parasequences at the study section are arranged into transgressive regressive facies cycles this cyclicity is superimposed on the overall regressive phase recorded by the attard succession furthermore a minor highstand correlated with the ru4 ch1 sequence and subsequent minor lowstand ch2 sequence have been recognized the biota assemblages of the attard member suggest that carbonate sedimentation took place in subtropical waters and oligotrophic to slightly mesotrophic conditions the apparent low capacity of corals to form wave resistant reef structures is considered to have been a significant factor affecting substrate stability at this time the resulting lack of resistant mid ramp reef frameworks left this zone exposed to wave and storm activity thereby encouraging the widespread development of coralline algal associations dominated by rhodoliths

habitats of larger foraminifera on the upper reef slope of sesoko island okinawa japan larger foraminifera living in the upper 50 m in front of the fringing coral reef northwest off sesoko island japan show strong habitat differences this study closely examines the distributions of larger foraminifers and relates these to a number of key environmental factors using rigorous statistical methods since all larger foraminifera house symbiotic algae light attenuation by the water column is the most important limiting factor that must be dealt with wall structures water energy is also countered by test structure the local topography is responsible for different intensities of hydrodynamic forces which are expressed in various substrates mostly coral rubble and coarse grained sand the genus peneroplis very common on the reef flat clearly prefers hardgrounds of the shallowest slope parts down to 30 m while dendritina is restricted to sandy bottoms and avoids the uppermost meters of the slope it can be found down to 50 m at least alveolinella shows a similar depth distribution to dendritina but is common on hard bottom the distribution of parasorites which is restricted to sandy substrates starts at 20 m and extends to 80 m sorites on the other hand was found only on firm substrates between the reef edge and 50 m the same depth distribution was recorded for amphisorus but this genus is not correlated with specific substrates most of the amphistegina species prefer hardgrounds while amphistegina radiata is also common on sand the calcarinids capable of withstanding high water energy are abundant on firm substrates close to the reef edge only baculogypsinoides inhabits deeper parts of the slope on sandy bottom and avoids the shallowest parts sections with hard substrates are settled by heterostegina even down to 80 m although this genus was occasionally found on sandy bottoms nummulites in contrast is restricted to sands between 20 and 70 m operculina starting at 20 m also prefers sandy substrates but rare individuals were detected on coral rubble and macroids

evolution of geochemistry and depositional settings of early palaeozoic siliciclastics of the barrandian tepla barrandian unit bohemian massif czech republic cambrian and ordovician middle devonian sequences of two successive early palaeozoic basins of the barrandian unconformably overlie cadomian basement in the bohemian massif nw interior tepla barrandian unit which is the easternmost peri gondwanan remnant within the variscides correlation of stratigraphy and geochemistry of the early palaeozoic siliciclastic rocks elucidated sediment provenances sandstones of the middle cambrian p ibram jince basin were derived from a cadomian neoproterozoic island arc the source area of the ordovician shallow marine siliciclastics of the successor prague basin is a dissected cadomian orogen late cambrian acid volcanics of the barrandian and cambrian meta granitoids emplaced in the w part of the tepla barrandian cadomian basement are also discernible in these sediments old sedimentary component increased during the ordovician early llandovery siliciclastic rocks show characteristics of an abruptly weakened supply of terrigenous material and an elevated proportion of synsedimentary basic volcanics as a result of silurian transgression emsian siliciclastics intercalated in the late silurian to early devonian limestone suite presumably comprise an addition of coeval basic ultrabasic volcaniclastics middle devonian flysch like siliciclastics indicate reappearance of cadomian source near the barrandian during early variscan convergences of armorican microplates that preceeded accretion of the tepla barrandian unit within the bohemian massif terrane mosaic

isotopic systematics of the early mauna kea shield phase and insight into the deep mantle beneath the pacific ocean 1 the 3500 m deep hawai i scientific drilling project core provides a 680 kyr record of the magmatic history and source components of mauna kea volcano we report high precision pb sr nd isotopic compositions of 40 basalts from the last 408 m of the final drilling phase hsdp2 b and hsdp2 c and show that these lowermost basalts represent the early shield stage of mauna kea s growth history two sample groups are distinguished based on their isotopic variability compared to the rest of the core over a depth interval of 210 m 3098 2 3308 2 mbsl the basalts show very restricted isotopic variation and represent sampling of a relatively homogeneous source samples from the bottom 192 m record the largest range of 206pb 204pb and 208pb 204pb in the core reflecting the greater isotopic variability of the earlier stages of volcanism compared to subsequent stages the heterogeneity of mauna kea lavas is explained by mixing variable proportions of four distinct components intrinsic to the hawaiian mantle plume one of these components kea is a prevalent and long lived composition within the hawaiian plume whereas the other three components are involved at different stages of the volcano s history and contribute to the short term isotopic variability of mauna kea the compositional similarity of the kea component to c and to the super chondritic bulk silicate earth suggests that kea may be part of the primitive mantle of a non chondritic earth other pacific oceanic island basalts share kea like compositions indicating that the kea component is a common widespread composition within the pacific deep mantle

insights into crustal assimilation by icelandic basalts from boron isotopes in melt inclusions from the 1783 1784 lakagigar eruption abstract the boron isotope system has great potential for tracing alteration and assimilation in basaltic systems due to the very low concentrations of b in mantle derived melts and the strong isotopic contrast between the mantle and surface materials however variability in b concentrations and isotope ratios in basalts can also be interpreted to reflect inputs from enriched regions of the mantle as the extent of mantle heterogeneity with respect to boron remains poorly delineated we have determined boron concentrations and isotope ratios in fresh glassy plagioclase hosted melt inclusions and unaltered scoriaceous matrix glasses from four localities associated with the 1783 1784 lakagigar laki fissure eruption iceland boron concentrations range from 0 59 to 1 25 ppm in the melt inclusions and from 1 25 to 1 65 ppm in the matrix glasses while 11 b nbs 951 ranges from 7 8 to 16 5 in the melt inclusions and 10 5 to 16 9 in the matrix glasses in contrast to previous studies of boron in basaltic melt inclusions from other fissure swarms in iceland gurenko and chaussidon 1997 chem geol 135 21 34 the lakagigar melt inclusions display a significant range of boron concentrations and isotope ratios at constant k 2 o wt which is more consistent with b addition by assimilation of altered basalt than it is with mixing between depleted and enriched mantle sources assimilation of freshwater altered crustal materials at depth may impart a light 11 b signature such as that observed in the lakagigar melt inclusions and tephra host glasses considering boron concentrations and isotope ratios in the lakagigar glasses and previously studied altered icelandic basalts together with volatile equilibration depths of the lakagigar melt inclusions we propose that a mantle derived magmas formed beneath lakagigar assimilated 5 20 altered crust at a depth of 3 4 km or more probably during magma accumulation in sills formed at the boundaries of low density hyaloclastite layers and b the magma subsequently underwent extensive mixing and homogenization prior to eruption quite possibly within the magma chamber beneath the grimsvotn central volcano assimilating an additional 10 of altered crust at that time for a total of up to 30 crustal assimilation we hypothesize that volatiles including h 2 o co 2 s f and cl which were responsible for the majority of the considerable casualties attributed to the lakagigar eruption were added together with isotopically light b by assimilation of hydrothermally altered crustal materials

bryozoan beds in northern italy as a shallow water expression of environmental changes during the oligocene isotope event 1 abstract shifts in carbonate producing biotic communities in the geological record provide evidence of past environmental changes in the neritic realm the shallow marine calcare di nago formation exposed in the san valentino section northern italy covers the late eocene and earliest oligocene the succession is characterized by the occurrence of light dependent biota such as coralline algae and larger benthic foraminifera in the uppermost part of the section however the fossil association is dominated by bryozoans which are filter feeder organisms this ca 12 m thick interval locally contains up to 86 bryozoans while coralline algae as well as larger benthic foraminifera are absent coralline algae and nummulitid foraminifera recover in the upper part of the bryozoan beds whereas orthophragminids do not recover the gradual disappearance of larger foraminifera and coralline algae within the bryozoan dominated deposits is coeval with a pronounced positive shift in 13c based on its biostratigraphic position this positive shift is interpreted to be linked to the positive shift in 13c recognized in deep sea records shortly above the eocene oligocene boundary which in turn is associated to the positive shift in 18o leading to the oi 1 oligocene isotope event 1 cooling phase total phosphorus content increases in the bryozoan beds suggesting enhanced nutrient supply to the neritic ecosystem this phosphorous peak is coeval with the globally recognized increment in ocean productivity around the oi 1 and 13c positive shift thus disappearance of light dependent biota and the dominance of bryozoans in the platform carbonates studied are interpreted to result not necessarily from a deepening of the depositional environment but from the combination of lower sea surface temperatures and the deterioration of underwater light conditions on account of elevated turbidity in surface waters resulting from enhanced primary productivity as bryozoan beds occur in several italian localities around the eocene oligocene boundary they are interpreted to represent the regional expression of neritic carbonate depositional systems to global environmental changes occurring at the dawn of an ice house earth

fine scale segmentation of volcanic hydrothermal systems along fast spreading ridge crests abstract fine scale 3rd and 4th order segments of the mid ocean ridge mor are morphologically defined units of crustal accretion with enigmatic origins at fast spreading centers 3rd order segments are bounded by discontinuities in the structure of the axial high most 3rd order segments are 20 10 km long and terminate at ridge axis discontinuities rads exhibiting 0 2 3 km lateral offsets and or 20 m axial depth increases nested within 3rd order segments are shorter 4th order segments bounded by smaller rads along the fast spreading east pacific rise epr at 10 02 9 08 n and 17 11 42 s spatial distributions of active high temperature hydrothermal vents biological communities and lava flow morphology are known accurately from extensive near bottom surveys and submersible dives along a total of seven 3rd order segments and twenty four 4th order segments the cumulative northern and southern epr data show that 3rd order segments but not 4th order segments consistently exhibit apparently higher rates of lava effusion near segment middles in comparison to segment ends supporting the hypothesis that each 3rd order segment is a discrete centrally fed volcanic system or volcanic segment spatial analyses of the cumulative hydrothermal data reveal a striking increase in abundance of hydrothermal features within the middle portions of 3rd order segments approximately 60 of ongoing high temperature focused flow is concentrated within the middle 40 of 3rd order segments and twice as many biological communities are found at mid segment in comparison to segment ends the two independent data sets volcanic and hydrothermal both indicate that magmatic heat sources are focused beneath the central portions of 3rd order segments and that magmatic hydrothermal systems are spatially and temporally segmented at 3rd order length and time scales we propose that 3rd order segmentation arises from processes controlling melt supply to the middle to lower crust and that 4th order segmentation largely arises from more rapid frequent upper crust processes of crack formation and dike intrusion future work is needed to test the applicability of our results along portions of the fast spreading epr notched by fault bounded axial troughs and in areas farther south where spreading rate reaches a maximum

north pacific seasonality and the glaciation of north america 2 7 million years ago in the context of gradual cenozoic cooling the timing of the onset of significant northern hemisphere glaciation 2 7 million years ago is consistent with milankovitch s orbital theory which posited that ice sheets grow when polar summertime insolation and temperature are low however the role of moisture supply in the initiation of large northern hemisphere ice sheets has remained unclear the subarctic pacific ocean represents a significant source of water vapour to boreal north america but it has been largely overlooked in efforts to explain northern hemisphere glaciation here we present alkenone unsaturation ratios and diatom oxygen isotope ratios from a sediment core in the western subarctic pacific ocean indicating that 2 7 million years ago late summer sea surface temperatures in this ocean region rose in response to an increase in stratification at the same time winter sea surface temperatures cooled winter floating ice became more abundant and global climate descended into glacial conditions we suggest that the observed summer warming extended into the autumn providing water vapour to northern north america where it precipitated and accumulated as snow and thus allowed the initiation of northern hemisphere glaciation

mesophotic coral buildups in a prodelta setting late eocene southern pyrenees spain a mixed carbonate siliciclastic system lower priabonian coral bioherms and biostromes encased in prodelta marls clays occur in the ainsa jaca piggyback basin in the south central pyrenean zone detailed mapping of lithofacies and bounding surfaces onto photomosaics reveals the architecture of coral buildups coral lithosomes occur either isolated or amalgamated in larger buildups isolated lithosomes are 1 to 8 m thick and a few hundred metres wide clay content within coral colonies is significant stacked bioherms form low relief buildups commonly 20 to 30 m thick locally up to 50 m these bioherms are progressively younger to the west following progradation of the deltaic complex the lowermost skeletal rich beds consist of bryozoan floatstone with wackestone to packstone matrix in which planktonic foraminifera are abundant and light related organisms absent basal coral biostromes and the base of many bioherms consist of platy coral colonies floating in a fine grained matrix rich in branches of red algae corals with domal or massive shape locally mixed with branching corals and phaceloid coral colonies dominate buildup cores these corals are surrounded by matrix and lack organic framework the matrix consists of wackestone to packstone locally floatstone with conspicuous red algal and coral fragments along with bryozoans planktonic and benthonic foraminifera and locally sponges coral rudstone and skeletal packstone with wackestone to packstone matrix also occur as wedges abutting the buildup margins integrative analysis of rock textures skeletal components buildup anatomy and facies architecture clearly reveal that these coral buildups developed in a prodelta setting where shifting of delta lobes or rainfall cycles episodically resulted in water transparency that allowed zooxanthellate coral growth the bathymetric position of the buildups has been constrained from the light dependent communities and lithofacies distribution within the buildups the process product analysis used here reinforces the hypothesis that zooxanthellate corals thrived in mesophotic conditions at least during the late eocene and until the late miocene comparative analysis with some selected upper eocene coral buildups of the north mediterranean area show similarities in facies components and textures and suggest that they also grew in relatively low light mesophotic and low hydrodynamic conditions

an ordinary chondrite impactor for the popigai crater siberia with a diameter of 100 km popigai in northern siberia is the largest crater known in the cenozoic the concentrations in platinum group elements pge were analyzed in twenty samples of homogeneous impact melt collected in the northwestern flank of the crater to identify the composition of the projectile the method selected was preconcentration by nis fire assay followed by inductively coupled plasma mass spectrometry icp ms this technique measures all the pge except os and by using aliquots 10g the results are highly reproducible the major and trace element composition of the impact melt resembles that of gneissic lithologies of the anabar shield which are representative of the target rock the pge are enriched in the melt by factors of 3 to 14 compared to the main target lithology but the meteoritic contamination is only around 0 2 wt using plots of elemental ratios such as ru rh vs pt pd or ru rh vs pd ir the popigai impactor is clearly identified as an ordinary chondrite and most likely l chondrite this study indicates that pge elemental ratios allow discrimination of the type of impactor even in the case of low meteoritic contamination this study confirms that a significant fraction of the crater forming projectiles presently documented could have an ordinary chondrite composition their probable source the s type asteroids appears to form the majority of the bodies in the main asteroid belt and among near earth objects neos the ordinary chondrite origin of the popigai projectile supports an asteroidal origin for the late eocene impacts as a plausible alternative to the comet shower scenario proposed by farley et al 1998 copyright 2005 elsevier ltd

reef building and carbonate production modes in the west central tethys during the cenozoic abstract changing components rock textures lithofacies platform types and architecture throughout time are unique characteristics of carbonate rocks characterizing these attributes has been approached by 1 building reference models for specific phanerozoic intervals 2 recognizing the climatic impact in modulating carbonate production and 3 analyzing the influence of changing bio geochemical conditions the reference model approach is mostly based on biological evolution the climatic impact approach emphasizes temperature and the bio geochemical approach considers the changes in mg ca ratios and ca concentrations in the oceans to date however an analysis integrating all of these factors is still missing the analysis presented here includes all these factors but also co 2 which is fundamental for both photosynthesis and caco 3 precipitation here we analyze the waxing and waning of cenozoic reef limestones from the central tethys region through several steps 1 on the basis of rock volume rock textures associated sediments and light dependent skeletal components as records of light penetration and wave energy depth 2 on global environmental conditions 13 c 18 o p co 2 temperature and 3 on the basis of functionality nutritional requirements and available resources through the cenozoic water motion whether induced by surface or internal waves or by currents increased as the thermal gradients strengthened both with depth and with latitude active water motion is essential for plankton catchers such as corals but less so for many larger benthic foraminifers lbf pycnoclines in the meso oligophotic zone would then favor the benthic plankton catchers such as corals but would be detrimental for many lbf warm temperatures favored lbf the eocene lbf families predominated during lowering of atmospheric p co 2 by using respiratory co 2 to enhance the symbiont production of photosynthates under oligotrophic conditions and limited turbulence whereas the miocene families had to adapt to a progressive increase in turbulence the eurythermal coralline red algae however became preponderant producers in the mesophotic zone during times when the 13 c was relatively high this explains two apparent paradoxes 1 corals thrive best when the earth s high latitudes cool and 2 the dominance of corals and lbf is inversely correlated despite they both require tropical conditions and have similar trophic strategies mixotrophy

mechanisms for millennial scale global synchronization during the last glacial period global climate during the last glacial period was punctuated by abrupt warmings and occasional pulses of freshwater into the north atlantic that disrupted deepwater production these massive freshwater pulses known as heinrich events arose in part from instabilities within the laurentide ice sheet paleoevidence from the north atlantic suggests that these events altered the production of deep water and changed downstream climate throughout the northern hemisphere in the tropical western pacific sea surface temperatures and salinity varied together with ocean and climate changes at high latitudes here we present results from coupled modeling experiments that shed light on a possible dynamical link between the north atlantic ocean and the western tropical pacific this link involves a global oceanic standing wave pattern brought about by millennial scale glacial density variations in the north atlantic atmospheric teleconnections triggered by meridional sea surface temperature gradients and local air sea interactions furthermore our modeling results are compared with hydrological records from the cariaco basin the indian ocean the sulu sea and northern australia

a model for the palaeoenvironmental distribution of larger foraminifera based on late middle eocene deposits on the margin of the south pyrenean basin ne spain abstract on the margin of the south pyrenean basin the late middle eocene sediments represent a well preserved regressive system permitting determination of the distribution of larger foraminifera along the depth gradient eocene deposits are compared with distribution patterns of recent larger foraminifera based on taxa occupying comparable positions along similar ecological gradients eocene taxa reveal by their test morphology a similar response to specific ecological conditions to that recorded for recent foraminifera four assemblages characterise an open marine shelf they range from the lower limit of the photic zone to the lower part of the upper photic zone two assemblages characterise the upper part of the upper photic zone and indicate respectively two different substrates firm or soft below the photic zone no larger foraminifera exist and the foraminiferal assemblages are dominated by smaller benthic foraminifera

distribution of diatoms coccolithophores and planktic foraminifers along a trophic gradient during sw monsoon in the arabian sea the distribution of diatoms coccolithophores and planktic foraminifers mirrored the hydrographic and trophic conditions of the surface ocean 0 100 m across the upwelling area off the oman coast to the central arabian sea during may june 1997 and july august 1995 the number of diatoms was increased in waters with local temperature minimum and enhanced nutrient concentration nitrate phosphate silicate caused by upwelling vegetative cells of chaetoceros dominated the diatom assemblage in the coastal upwelling area towards the more nutrient depleted and stratified surface waters to the southeast the number of diatoms decreased coccolithophore and planktic foraminiferal numbers increased and floral and faunal composition changed in particular the transition between the eutrophic upwelling region off oman and the oligotrophic central arabian sea was marked by moderate nutrient concentration and high coccolithophore and foraminifer numbers florisphaera profunda previously often referred as a lower photic zone species was frequent in water depths as shallow as 20 m and at high nutrient concentration up to 14 mol no3 l 1 and 1 2 mol po4 l 1 to the oligotrophic southeast of the divergence cell densities of coccolithophores declined and umbellosphaera irregularis prevailed throughout the water column down to 100 m depth in general total coccolithophore numbers were limited by nutrient threshold concentration with low numbers 70 103 cells l 1 at low no3 and po4 the components of the complex microplankton succession diatoms coccoliths and planktic foraminifers and possibly others should ideally be used as a combined paleoceanographic proxy consequently models on plankton ecology should be resolved at least for the seasonality to account for the bias of paleoceanographic transfer calculations

synthesis and thermal decomposition of tetragonal rbclo4 and volume of fluid o2 from 2 to 9 gpa 1 orthorhombic o rbclo4 transforms to a new tetragonal t form at pressures above 20 kbar thermal decomposition proceeds through the reversible equilibrium reaction t rbclo4 b2 rbcl 2o2 at modestly increasing temperatures centered 550 c over the pressure range investigated from 20 to 90 kbar cell volumes for t rbclo4 and b2 rbcl were determined by high pressure high temperature in situ x ray diffraction on station 16 4 of the daresbury synchrotron radiation source from which the partial molar volume of o2 along the decomposition curve was determined this volume 10 cm3 mol is in close agreement with volumes determined from studies of the thermal decomposition of kclo3 and kclo4 but is difficult to reconcile with fluid o2 volumes determined using shock wave techniques if these new o2 partial molar volumes are relevant to molten iron solutions then storage of substantial amounts of o2 in the core becomes feasible

o2 volumes at high pressure from kclo4 decomposition d as a siderophile element pump instead of a lid on the core 1 new measurements of the high pressure volume of oxygen make plausible old controversial diamond anvil cell dac observations of a high pressure reaction between liquid fe and fe bearing silicate in which feo dissolved into liquid fe if the earth s d layer between core and mantle is the waste product of this reaction proceeding forward with oxygen transfer to the core then d would form an effective lid preventing escape of siderophile elements from the core on the other hand it is at least as plausible that the core is now oxygen saturated and that core cooling and internal crystallization drive this reaction backward with transfer of fe and o rich material out of the core into d the 186os anomalies in some plume basalts are more consistent with this d as a siderophile element pump scenario than the d as lid scenario contributions of siderophile elements to the mantle from the core could assist in balancing the persistently enigmatic budget of these elements

re os depositional age for black shales from the kaimur group upper vindhyan india abstract proterozoic sedimentary deposits from the vindhyan supergroup central india are excellent archives of paleo environmental conditions meaningful interpretation of these geological signatures and their global correlation requires depositional age information for the sediments data on which are limited for the upper vindhyan sediments in this work re os isotopic study of the bijaigarh shale kaimur group from the upper vindhyan has been carried out to infer their depositional age and paleo hydrological conditions the re os isochron for the bijaigarh shale a lagoonal deposit with an open ocean connection provides a depositional age of 1210 52 ma model 3 mswd 69 n 15 2 this age for the kaimur group is younger by 400 ma than the underlying semri group age 1600 ma confirming existence of a long sedimentary hiatus between the two groups the isochron derived initial 187os 188os osi ratio for these shales 0 6 is higher than those reported for mesoproterozoic marine shales 0 3 from other global margins osi ratios of shales could be regulated by regional paleo hydrological conditions osmium mass balance calculations for the restricted basin of the bijaigarh shale show that a minor increase in freshwater influx as low as 2 4 i e salinity change by 0 8 psu to the euxinic deep water of the basin is sufficient to elevate osi ratio from 0 3 marine value to 0 6 osi ratio of the lagoonal shale in contrast to lagoonal shales the osi ratios of marine shales seem to mimic the seawater 187os 188os during their deposition period compilation of marine osi ratios shows coarse synchrony between temporal changes in osi during the proterozoic eon and the atmospheric oxygen level pointing to the dominant role of oxidative continental weathering on paleo seawater 187os 188os ratio