a new cretaceous tertiary boundary site at flaxbourne river new zealand biostratigraphy and geochemistry abstract an exceptionally complete rock sequence across the cretaceous tertiary k t boundary has been discovered near the flaxboume river marlborough province south island new zealand the boundary is marked by a large ir anomaly 21 ng g on a decalcified basis with an integrated abundance of 134 ng cm2 after correction for background above the boundary there is a 30 cm transition zone in which a few cretaceous foraminiferal taxa such as hedbergella monmouthensis and guembelitria cretacea survived though with reduced abundance and size only ca 1 2 to 1 4 of normal apparently reflecting environmental stresses inaa and icp analyses show that in addition to ir the boundary clay is also enriched in cr and ni mainly from meteoritic material and as co cu sb and zn from terrestrial sources volcanic sources even when scaled to the 10 7 km 3 volume of the deccan basalts fail by three orders of magnitude to account for the ir and as at the k t boundary and by even larger factors for sb zn cu etc comparison of our data with those from six other k t boundary sites shows that the zn sb as sb and zn as ratios generally fall between crustal and oceanic values suggesting contributions from both sources mass balance calculations show that as and sb could be derived from only 300 500 m of ocean water or also from modest amounts 20 36 g cm 2 of average crustal rock copper and zn on the other hand can only be derived from crustal or mantle rock 5 15 g cm 2 presumably impact ejecta such an amount of ejecta is fairly close to the global fallout of boundary clay 2 5 g cm 2

the stratigraphic distribution of ni rich spinels in cretaceous tertiary boundary rocks at el kef tunisia caravaca spain and hole 761c leg 122 abstract ni rich spinels have been found throughhout the world at the cretaceous tertiary boundary these minerals have no counterparts in terrestrial rocks but have been observed in meteoroid ablation material and impact debris suggesting that the cretaceous tertiary boundary spinels result from an extraterrestrial event their stratigraphic distribution which has been observed at the cretaceous tertiary boundary sites of el kef tunisia caravaca spain and hole 761c odp leg 122 indian ocean are markedly different from site to site and are all much less extended than the ir anomalies regional differences in ni rich spinel distibution are entirely explained by a brief event recorded under different bioturbation conditions the wider stratigraphic dispersion of ir is attributed to postdepositional chemical processes at el kef the site which appears to be the least affected by bioturbation and which has the highest sedimentation rate the 1 2 mm thick ni rich spinel spike indicates that the deposition time did not exceed an upper limit of 100 years this upper limit is consistent only with the collision of an asteroid or a comet at the close of the cretaceous

pt group metal anomalies in the lower mississippian of southern oklahoma four iridium pt group elements abundance anomalies have been found within a stratigraphic span of 3 m in the lower mississippian of oklahoma in ascending order the first anomalies occur at the top of the woodford shale ir 0 25 ppb pt 48 ppb os 7 5 ppb and au 18 ppb the anomalies occur just below a redox boundary and we suspect that the enriched elements were precipitated from sea water that contacted the organic and sulfide rick black shale two more anomalies occur in the welden limestone the lower one weak and the upper one strong ir 0 42 ppb pt 50 ppb os 0 075 ppb and au 0 14 ppb the excess ir and pt also co as and ni might have been enriched from sea water by bacteria at these two horizons a 70 cm thick interval of excess heavy siderophiles occurs in the overlying caney shale the interval contains the following peak concentrations ir 0 56 ppb pt 150 ppb os 0 51 ppb co 725 ppm and ni 1450 ppm these elements vary in proportion to the al clay content and we suspect that they were carried in with detrital material from erosion of ultramafic source rocks we found no evidence of microspherules or shocked mineral grains in any of these anomaly zones

preliminary evidence for the involvement of budding bacteria in the origin of alaskan placer gold lacelike networks of micrometre size filiform gold associated with alaskan placer gold particles are interpreted as low temperature pseudomorphs of a pedomicrobium like budding bacterium submicron reproductive structures hyphae and other morphological features similar to those of pedomicrobium manganicum occur as detailed three dimensional facsimiles in high purity gold in and on placer gold particles from lillian creek alaska in a scanning electron microscope survey the majority of gold particles at nine alaskan placer deposits appear to include gold that has accumulated chemically at low temperatures in and on the cells of p manganicum similar bacterioform gold from a paleozoic deposit in china and from the precambrian witwatersrand deposit in south africa may indicate that bacterioform gold is widespread

an iridium anomaly in the middle lower jurassic of the venetian region northern italy a significant iridium enrichment has been found in a jurassic marine sequence about 180 million years old outcropping in the alps of the venetian region the maximum iridium concentration of 3 2 0 2 ng g 1 occurs in a brown crust 2 3 mm thick containing essentially iron hydroxide this crust characterized by a nearly total absence of detritic components lies on top of upper lias limestones and is overlaid with bajocian bathonian limestones the origin of the ir anomaly is not clearly understood yet but could be explained by either a drop in the sedimentation rate resulting in the concentration within a thin sediment layer of the normally infalling cosmic dust and or by an increase of cosmic material infall following an asteroid or comet impact s

iridium emissions from kilauea volcano during may 1983 gas and particulate samples were collected at the cooling vents of kilauea volcano in hawaii three vents on the southeast rift zone were sampled using base treated filter packs to absorb acidic gases and teflon filters for particles the samples were analyzed for 40 elements by nondestructive neutron activation analysis as with other volcanoes the chalcophilic and volatile elements were enriched by up to seven orders of magnitude relative to the erupted basalt unlike the case of other volcanoes iridium was observed to be highly enriched 105 fold at the two higher temperature vents and the degree of enrichment appears to be related to both high temperatures and high fluorine content of the gases estimates of the emission rates of ir during eruptions of kilauea based on the measurements reported here and those of the hawaiian volcano observatory yield an emission rate of about 3 g ir per 106 m3 of magma this rate amounts to only about 0 3 of the ir present in the magma that is being released by the volcano this previously unidentified ir source to the atmosphere and ocean may have a significant influence on the geochemical cycle of ir on the earth the uniqueness of kilauea in its emissions of ir is probably related to the deep source of magma which contains significant levels of ir 0 32 ppb and high levels of the halogens f and cl

evidence for multiple ground rupturing earthquakes in the past 4 000 years along the pasuruan fault east java indonesia documentation of active normal faulting in the javan backarc

trace element patterns at a non marine cretaceous tertiary boundary at the fossil pollen defined cretaceous tertiary boundary in the raton basin of new mexico and colorado an iridium abundance anomaly and excess scandium titanium and chromium are associated with a thin ash or dust fallout bed now kaolinitic clay that was preserved in freshwater coal swamps

magnetostratigraphy late devonian iridium anomaly and impact hypotheses paleomagnetism sedimentology and fine scale stratigraphy have been integrated to explain the origin of an iridium anomaly in the late devonian of western australia thermal demagnetization experiments were carried out on 93 specimens of marginal slope limestone form the northern canning basin samples are from a condensed sequence of deep water 100 m frutexites microstromatolites frutexites is a shrublike cyanobacterial organism that probably precipitated hematite or a metastable precursor from sea water when plotted within the microstratigraphic framework for the study area the observed characteristic directions from the sampled interval 14 5 cm thick are in five discrete layer parallel normal and reversed polarity zones the measured northeast southwest declinations and shallow inclinations probably record late devonian magnetostratigraphy on a centimetre scale the frutexites bed studied there occurs close to the frasnian famennian late devonian boundary a time of mass extinction of a wide variety of marine organisms throughout the world anomalously high iridium concentrations observed in the frutexites bed have suggested to some authors that the mass extinction was caused by meteorite impact this study concludes that iridium which is present over the span of five layer parallel magnetic reversals was concentrated over a long period of time by biologic processes thus the canning basin iridium anomalymore may be unrelated to meteorite impact less

post depositional mobility of platinum iridium and rhenium in marine sediments the discovery of high concentrations of iridium in cretaceous tertiary boundary sediments engendered the hypothesis1 that a meteorite collided with the earth 65 million years ago coincident with the mass extinction that occurred at that time iridium spikes of various magnitudes have subsequently been reported at more than 10 other extinction horizons2 11 it has been suggested on the other hand that geochemical processes might create or modify many of these spikes5 11 4 but a critical evaluation of these suggestions has been hindered by incomplete understanding of low temperature iridium geochemistry other platinum group elements ru rh pd re os pt au are often found to be associated with ir spikes and inter element ratios have been used to assess the cosmic or terrestrial nature of the enrichments5 7 9 28 29 but the geochemical influences on these relative abundances are also poorly constrained here we describe analyses of recent abyssal marine sediments which allow us to characterize the behaviour of pt re and ir during early diagenesis these elements are redistributed by changes in sedimentary redox conditions such changes can probably account for many of the small platinum group element spikes found in the geological record and may render ambiguous attempts to interpret inter element ratios

iridium bearing sublimates at a hot spot volcano piton de la fournaise indian ocean sublimates and incrustations derived upon the cooling of volcanic gases have been collected on various sites piton de la fournaise poas momotombo etna ardoukoba and erta ale they have been analysed for ir and other volatile elements se as cu au ag pb tl by means of instrumental neutron activation analysis inaa and proton induced x ray emission pixe among the investigated volcanoes only piton de la fournaise is found to release detectable amounts of iridium ir in piton de la fournaise sublimates is associated with f minerals this confirms its gaseous transport as a volatile fluoride compound iridium seems to be preferentialy released by hot spot type volcanoes and its detection in piton de la fournaise sublimates provides a positive argument in favour of a volcanic hypothesis to explain the ktb events

active diagenetic formation of metal rich layers in n e atlantic sediments sediment cores from the porcupine abyssal plain exhibit an indurated layer 0 5 3 cm thick at depths of approximately 50 cm this is some 15 20 cm below the glacial holocene transition as interpreted by radiocarbon dating and the palaeontological criteria of ruddiman and mcintyre 1981 the layer is forming currently at the oxic post oxic boundary in the sediments as revealed by pore water data o2 and no 3 are present in solution above the layer while fe2 mn2 po3 4 and nh 4 are present in solution below and all these species show concentration gradients indicating fluxes into the layer these data are consistent with the hypothesis for the initiation and sustained formation of such layers proposed by wilsonet al 1986a b the elements mn ni co fe p v cu zn and u are all enriched to varying degrees in the vicinity of the layer some differential stratification of these elements in the vertical consistent with a redox control is observed at one site with a 0 5 cm layer with mn ni and co above fe p v and cu in the layer and u below at another site the metal rich layer has higher fe and p concentrations and is more indurated here all enrichments except co are contained within a single layer sample 3 cm thick

mineralogy and phase chemistry of an ir enriched pre k t layer from the lattengebirge bavarian alps and significance for the ktb problem abstract three distinct iridium anomalies are exposed in the cretaceous tertiary boundary ktb section of the lattengebirge bavarian alps comprising a pelagic calcareous sequence from below a continental slope multiple ir anomalies are in contrast to most reported k t sections which are characterized by a single ir peak two of these ir spikes are contained in the 20 cm thick actual ktb termed clayey interval with the main peak of 4 4 ppb precisely at the boundary and the second peak of 2 8 ppb 10 cm above a third peak of 3 6 ppb was detected at 16 cm below the ktb in a thin turbiditic and coal bearing sandstone layer of upper maastrichtian age the distribution of ir anomalies provides evidence of episodic ir delivering events over an extended period of time whereas the worldwide distributed single spiked ktb layers are composed entirely of diagenetically altered materials various phases are discernible in the well preserved ir bearing pre k t layer 1 sandstone clastic minerals in a carbonate matrix 2 coal which is partly burned 3 sulfides chalcopyrite included in coal and 4 silicate melt glasses the glasses represent the first ones reported from a k t section and were formed by combustion metamorphism from sedimentary parent rocks of the coal as indicated by their major element chemistry and ree patterns phase chemistry of the layer components reveals ir concentrations of up to 110 ppb indicating that ir and chalcophile trace elements tre are primarily contained in the sulfides this carrier phase points to ir enrichment by processes unrelated to impact and its stratigraphic position demonstrates availability of ir for incorporation into sediments before the ktb the uptake of ir and chalcophile tre into the coal and subsequent combustion metamorphism occurred on the continent during a time interval of 14 000 9000 yr prior to the ktb as constrained by radiometric age determinations stratigraphy and sedimentation rates in the lattengebirge k t sediments no indications of shock are found the results suggest a volcanic origin for the multiple ir bearing horizons like the worldwide ktb layers they are concomitantly enriched in ir and chalcophile tre and hence have a common source the lattengebirge k t profile is largely continuous and was recently reexamined by micropaleontological methods contribution by d herm and k f weidich the preservation of multiple ir anomalies is attributed to high sedimentation rates of 1 75 cm kyr and the absence of carbonate dissolution and condensation of sediments usually encountered in the worldwide ktb layers

fe iii reducing bacteria in deeply buried sediments of the atlantic coastal plain the possibility that microorganisms are catalyzing the ongoing reduction of fe iii in the sediments of deep 20 250 m aquifers was investigated acetate oxidizing fe iii reducing bacteria were recovered from deep subsurface sediments but only from sediments in which it appeared that fe iii reduction was the terminal electron accepting process for oxidation of organic matter the fe iii reducing microorganisms were capable of reducing ferric oxides present in deep subsurface sediments although fe iii reduction in subsurface sediments is frequently regarded as an abiological reaction the enzymatic reduction of fe iii by microorganisms reported here is the first mechanism of any kind actually shown to have the potential to couple the oxidation of organic matter to carbon dioxide with the reduction of fe iii under the environmental conditions typically found in deep aquifers we propose that microbially catalyzed fe iii reduction is responsible for such late postdepositional phenomena as the formation of variegated red beds and the release of high concentrations of dissolved iron into anaerobic ground waters

terminal cretaceous environmental events the geologic record of terminal cretaceous environmental events indicates that iridium and other associated elements were not deposited instantaneously but during a time interval spanning some 10 000 to 100 000 years the available geologic evidence favors a mantle rather than meteoritic origin for these elements these results are in accord with the scenario of a series of intense eruptive volcanic events occurring during a relatively short geologic time interval and not with the scenario of a single large asteroid impact event

cretaceous tertiary boundary of dsdp site 596 south pacific sediments from the cretaceous tertiary k t boundary at deep sea drilling project site 596 record accumulation of pelagic clays at about lat 45 s in the center of the ancestral south pacific the k t boundary in this region is characterized by oxidized thoroughly bioturbated sediments containing large amounts of ir and relict high pressure and high temperature mineral phases the net ir fluence 320 ng cm 2 is among the largest on earth and the number of shocked quartz grains 30 m in size 1800 cm 2 exceeds that in all localities outside of north america

chemostratigraphy across the cretaceous tertiary boundary and a critical assessment of the iridium anomaly the elevated concentration of iridium one of the platinum group elements pge at the cretaceous tertiary boundary is still the most generally accepted evidence that a large bolide struck the earth at the time of the end cretaceous mass extinctions new chemostratigraphic data for cross boundary sections from both hemispheres are not easily explained in terms of such an impact event for example the observation that the pge patterns show marked differences between the hemispheres the new constraints indicate that models of mantle derived pge should be seriously considered and that pge anomalies might not be as useful as previously thought as unambiguous identifiers of large impact events in the earth s history

proximal impact deposits at the cretaceous tertiary boundary in the gulf of mexico a restudy of dsdp leg 77 sites 536 and 540 restudy of deep sea drilling project sites 536 and 540 in the southeast gulf of mexico gives evidence for a giant wave at cretaceous tertiary boundary time five units are recognized 1 cenomanian limestone underlies a hiatus in which the five highest cretaceous stages are missing possibly because of catastrophic k t erosion 2 pebbly mudstone 45 m thick represents a submarine landslide possibly of k t age 3 current bedded sandstone more than 2 5 m thick contains anomalous iridium tektite glass and shocked quartz it is interpreted as ejecta from a nearby impact crater reworked on the deep sea floor by the resulting tsunami 4 a 50 cm interval of calcareous mudstone containing small cretaceous planktic foraminifera and the ir peak is interpreted as the silt size fraction of the cretaceous material suspended by the impact generated wave 5 calcareous mudstone with basal tertiary forams and the uppermost tail of the ir anomaly overlies the disturbed interval dating the impact and wave event as k t boundary age like beloc in haiti and mimbral in mexico sites 536 and 540 are consistent with a large k t age impact at the nearby chicxulub crater

accretion rate of extraterrestrial particles determined from osmium isotope systematics of pacific pelagic clay and manganese nodules abstract pelagic clay and mn nodules from domes sites in the north pacific and a varved glacial lake deposit from connecticut were analysed for os concentration and isotopic composition by isotope dilution secondary ion mass spectrometry after treatment by nis fusion or oxalic acid leaching bulk pelagic clay from domes site c has 187 os 186 os 6 5 and os 0 14 ng g oxalic acid leaches of this same sediment and of mn nodules from domes sites a and c have more radiogenic 187 os 186 os ratios which average 8 3 bulk glacial lake hitchcock sediment has 187 os 186 os 12 5 and os 0 06 ng g the total os flux to north pacific pelagic clay is 7 to 10 ng os cm2 106 y lake hitchcock sediment provides an integrated value for the local crustal 187 os 186 os ratio the oxalic acid leaches are assumed to attack hydrogenous phases selectively a simple model in which the only sources of os to the ocean are continental crust with the isotopic composition of lake hitchcock 187 os 186 os 12 5 and extraterrestrial particles with 187 os 186 os 1 1 results in a cosmic flux of osmium to the sediment of 4 9 ngos cm2 106 y of which 20 is hydrogenous a model in which the sources of os to the ocean are continental crust with an 187os 186os ratio of 30 from the model of palmer and turekian 1986 oceanic mantle or crust with 187 os 186 os 1 04 and extraterrestrial particles with 187 os 186 os 1 1 results in a cosmic flux of os to the sediment of 5 7 ngos cm2 106 y of which none is hydrogenous these extraterrestrial os fluxes correspond to maximum c 1 chondrite accretion rates of between 4 9 104 and 5 6 104 tonnes y

mechanisms to explain the platinum concentration in ferromanganese seamount crusts abstract ferromanganese seamount crusts cover large areas of hard substrates of sea floor edifices in the central pacific they can be distinctly enriched in pt and show pt pd ratios which are several orders of magnitude greater than those orders of magnitude greater than those of seawater thirty four selected samples of the younger and the older crust generation were analyzed for mn fe ni co and pt the bulk pt concentration varies between 0 14 and 1 02 ppm and averages to 0 51 0 24 ppm the older generation is generally somewhat richer in pt 0 63 0 25 ppm than the younger one 0 39 0 15 ppm compared to the earth s upper continental crust the ferromanganese material contains about 100 times more pt in the studied depth range between 1100 and 3800 m the pt concentration is controlled by the water depth in addition to the bulk data the distribution of pt and pd is recorded through a complete ferromanganese crust profile the average pd value amounts to 16 2 8 ppb for the younger and 16 4 8 ppb for the older generation two immediate sources may be responsible for the pt concentration in the ferromanganese crusts seawater and cosmic spherules the presented thermodynamic approaches are based on the presumption that the pt tetrachlorocomplex is the prevailing species under seawater conditions precipitation of pt in seawater may take place if this complex is decomposed by reduction of pt 2 to the elemental state on the other hand the mno 2 precipitation is caused by oxidation of dissolved mn 2 ions which are supplied from the oxygen minimum zone a model reaction by combining the two half reactions is formulated assuming a coprecipitation of pt with mno 2 an alternative mechanism to explain pt enrichment in ferromanganese crusts might be surface adsorption of anionic pt tetrachloro complexes onto positively charged amorphous iron hydroxide particles cosmic spherules were discovered in samples of the older ferromanaganese crust generation the spherules are mostly concentrated in the upper part of this crust layer iron meteorites often have pt concentrations up to 20 ppm the relative quantity recovered in the grain size class 0 1 0 4 mm only amounts to 2 10 4 which is significantly too low to explain the pt content of the crust samples however smaller cosmic particles may exist and also contribute to the pt enrichment suggesting that rough crust surfaces are excellent collectors of denser detrital material the maximum pt values observed in the youngest part of the older crust generation may be explained by physical incorporation of cosmic particles

sedimentology and ichnology of the cretaceous tertiary boundary in denmark implications for the causes of the terminal cretaceous extinction abstract trace fossils and other sedimentologic evidence of bioturbation in latest cretaceous and earliest tertiary marine deposits in denmark provide important clues to understanding the ecology of the sea bottom immediately before during and after the terminal cretaceous boundary event trace fossil associations at all the onshore danish boundary sites indicate a general upward shoaling of the late maastrichtian chalk sea which was accompanied by an abrupt shift from a carbonate ooze sea floor to a marly clay rich unstable substrate at the boundary although the substrate condition may have become more stable in the early danian water depths never did return to their former deep level there is evidence of localized anoxia during the deposition of some boundary sediments in the fish clay in shallow parts of the danish maastrichtian sea but no clear evidence of anaerobic conditions occurring at the era boundary was observed in boundary strata deposited in deeper water near the center of the basin in fact earliest danian marl there is totally bioturbated a pulse of calcite dissolution in shallow water coincided precisely with the era boundary and this event played a major role in the formation of the fish clay in eastern denmark which is a condensed series of smectitic clay rich layers from which much calcite has dissolved the effects of this dissolution episode however were not so extreme in the marl that was deposited at the same time in slightly deeper water in northwestern denmark evidence from cretaceous tertiary boundary sequences in denmark and elsewhere suggests that no single catastrophe can account for the major biotic extinctions that occurred at the end of the cretaceous period the primary causal factors of the terminal cretaceous extinction event appear to be drastic global sea level regression occurring simultaneously with extensive volcanism on land and a strong pulse of calcite dissolution in ocean surface waters

fires at the k t boundary carbon at the sumbar turkmenia site abstract we have measured carbon at the marine k t boundary site sm 4 at the sumbar river in turkmenia ussr which has an undisturbed ir profile and the largest known ir anomaly 580 ng cm 2 twenty samples ranging from 100 to 100 cm were analyzed to determine the concentration and 13 c of elemental carbon and kerogen using a cr 2 o 7 oxidation method wolbach and anders 1989 to resolve these components the samples were unusually complex containing 3 kerogen components of distinctive ir spectra and half lives in cr 2 o 7 200 100 and 60 h in addition to soot and charcoal from the k t fire the elemental c has 13 c 25 96 0 6 l o close to the mean for 11 k t sites 25 8 0 6 11 mg cm 2 the first of the 2 kerogen components 13 c 22 8 which dominates in the cretaceous appears to come from detrital carbonaceous shale the second 13 c 27 7 o occurs only in the boundary clay and may come from land plant material swept to sea or phytoplankton grown in the presence of excess light co 2 from fires on land the great thickness of the boundary clay 10 5 cm permits determination of the compositional profiles with unprecedented spatial resolution ir and shocked quartz both representing impact ejecta rise sharply at the boundary peak in the basal layer and then decline soot and total elemental c show a similar spike in the basal layer but then rise rather than fall peaking at 7 cm apparently fires started before the basal layer had settled implying that ignition and spreading of major fires became possible if not immediately then very soon after the impact there is no basis for claims by hansen et al 1987 that k t carbon black first occurs 3 5 m below the danish k t boundary and has 13 c of 27 4 to 27 8 o reexamination of a sample from nye klov shows that these authors confused kerogen with carbon black

geochemistry of eastern mediterranean sediments primary sediment composition and diagenetic alterations abstract two cores recovered in the eastern mediterranean were analysed for major minor and trace elements the primary chemical composition of the sediment is different at each location probably because the lithological sources and the relative biogenic contributions differ carbonates are important for the concentration of ca mg and sr whereas aluminosilicates determine the concentration of si al k li y and be and to a lesser extent that of fe cr ti mg zn and zr in sapropels organic carbon and sulphur seem to be closely related bromine mo p fe v cu zn co ni and cr are closely associated with organic and sulphidic compounds the concentration versus depth profile for organic carbon in two sapropels points to a rapid establishment of conditions that gave rise to sapropel formation followed by a gradual transition back to normal conditions the primary composition is overprinted by diagenetic processes sulphate reducing conditions occurred during and just after sapropel deposition a progressive oxidation front mechanism which became active after sapropel deposition is responsible for additional major geochemical changes this diagenetic phenomenon has strong implications for the chemistry of fe mn ni co zn cu cr v u as and sb

comet showers as a cause of mass extinctions if at least some mass extinctions are caused by impacts why do they extend over intervals of one to three million years and have a partly stepwise character the solution may be provided by multiple cometary impacts astronomical geological and palaeontological evidence is consistent with a causal connection between comet showers clusters of impact events and stepwise mass extinctions but it is too early to tell how pervasive this relationship may be

osmium in marine sediments osmium is enriched in ferromanganese minerals and its concentrations follow those of other pt group metals except pd oxidative capture during solid formation is the probable mechanism for uptake in some sediments forming under reducing conditions phosphorites and anoxic coastal deposits there is also an enrichment this may relate to reductive capture although deposits also formed under reducing conditions from hydrothermal areas are depleted in osmium

seawater sr isotopes at the cretaceous tertiary boundary abstract seawater 87 sr 86 sr values increase abruptly by 28 10 6 across the cretaceous tertiary boundary ktb this small but rapid shift is superimposed on the larger scale structure of the seawater sr isotope curve the time scale of radiogenic sr addition appears to be too rapid to reconcile with sources associated with volcanism and we show that the amount of sr required to produce even this small increase is too large to be derived from 1 a kt bolide of the size constrained by the ir anomaly 2 continental crust ejecta from the impact of such a bolide 3 soot from global wildfires initiated by an impact or 4 any combination of these sources the probable source of the radiogenic sr is enhanced continental weathering but the high rate of increase appears to rule out processes such as sea level regression glaciation or tectonism a plausible mechanism for rapid addition of radiogenic sr to the oceans is enhanced weathering associated with globally distributed acid rain ph 1 which is a proposed by product of a bolide impact 51 epsl vol 83

late cretaceous and paroxysmal cretaceous tertiary extinctions the various geological signatures at cretaceous tertiary time including iridium and other associated elements microspherules and shock deformation features are compatible with the suggestion that the transition is marked by a period of intense volcanism the volatile emissions from this volcanism would lead to acid rain reduction in the alkalinity and ph of the surface ocean global atmospheric temperature changes and ozone layer depletion these environmental effects coupled with those related to the major sea level regression of the late cretaceous provide the framework for an explanation of the selective nature of the observed extinction record

trace element anomalies at the mississippian pennsylvanian boundary in oklahoma and texas trace element abundance anomalies have been found at the mississippian pennsylvania boundary at sites in oklahoma and texas where the boundary has been precisely located on the basis of an abrupt change in conodont diversity and species composition enriched elements include osmium indium platinum chromium most chalcophiles rare earths and uranium the anomalies are more intense e g os 4 ppb ir 0 38 ppb pt 6 ppb cr 12000 ppm u 380 ppm and peisist through a thicker interval at the south central texas locality than in oklahoma and in bolh locations the anomalies are associated with an increase in phosphate content of the rocks there is no tangible evidence of an asteroid or comet impact source for the excess pt group elements and fauna crisis the cause of the elemental enrichments and the biological disturbance may possibly be related to a change in the ocean chemistry of the paleozoic seaway such as increased upwelling stagnation or nearby submarine volcanism

the extraterrestrial component in marine sediments description and interpretation the influx of extraterrestrial matter to the earth is dominated by two size fractions sub millimeter interplanetary dust and impacting asteroids and comets over geologic time the major contribution of extraterrestrial matter is from the largest impactors interplanetary dust is largely vaporized by atmospheric entry but some surviving material is found in sediments as cosmic spherules impacting asteroids and comets can produce fallout layers either regionally or globally which may contain a significant fraction of meteoritic material as well as shock metamorphosed and shock melted terrestrial material iridium is a sensitive tracer of extraterrestrial matter although high concentrations of ir in marine sediments probably have an extraterrestrial origin they do not necessarily indicate the presence of a major impact event of the thousands of impact horizons which must be resolvable in the sedimentary record to date only seven probable impact horizons have been identified in the entire phanerozoic the marine geochemistry and occurrence of ir is still poorly understood but the thousands of ir analyses performed in the last several years have demonstrated that the global occurrence high ir 10 ng g concentrations in cretaceous tertiary boundary sediments is a truly anomalous phenomenon

the geochemistry of au and pt in peat and algal mats a case study from sri lanka abstract the geochemistry of au and pt in the muthurajawela peat deposit the largest in sri lanka has been studied together with the au and pt contents of algal mats from the tidal flats of mannar nw of sri lanka both peat and algal mats are enriched in au and pt the source material presumably being a laterite known to contain large amounts of au and pt au appears to be enriched in the clay and fe and mn in the colloid phase whereas pt does not correlate with any particular element in the tidal flat environment of the algal mats au shows a greater tendency to migrate seawards whereas pt is enriched in the clastic rich landward side as well as in the seaward algal mats possibly being mobilized as the chloride complex

iridium and other platinum group elements as geochemical markers in sedimentary environments iridium anomalies are commonly used as indicators of extraterrestrial processes which caused global extinctions however platinum group element pge anomalies may result from several different processes both syn and postdepositional acting separately or jointly the sources and processes of enrichment involved are extraterrestrial asteroid comet cosmic dust impact ejecta volcanogenic pge rich condensates precipitation from seawater low sedimentation rate anoxic conditions microbial concentration dissolution reprecipitation exhalative hydrothermal leaching transport and precipitation at a redox boundary geochemical characteristics of pge and accompanying elements in sediments can be used to identify the contributions of some specific sources and processes 1 extraterrestrial chondritic ru ir and os ir ratios low 187os 186os ratio high ir compared to pt pd and au 2 volcanogenic high iridium and se as sb and in contents 3 exhalative hydrothermal high au pd and pt relatively low ir contents 4 precipitation from seawater high pt and low pd contents also high cd and ag contents under anoxic conditions and 5 reduction from intermediate and low temperature solutions high pge and cu or mo u ni contents

some comparative marine chemistries of platinum and iridium abstract iridium has seawater concentrations about one hundred times less than those of platinum as a consequence of its weaker complexing abilities with halides and of a stronger tendency to hydrolyze iridium like platinum is enriched in some ferromanganese minerals compared to palladium platinum and iridium are probably oxidized during mineral formation from the divalent and trivalent states respectively to the tetravalent ones the pelagic sediment contents of irridium as well as those of platinum are related to the manganese contents for higher platinum contents of the authigenic ferromanganese minerals the pt ir ratios approach the seawater ratio suggesting little dilution by platinum and iridium in detrital minerals the marked enrichments of platinum and iridium in the ferromanganese concretions enhance their value as potential ores for heavy metals

role for microorganisms in the formation of iridium anomalies we propose a microbial role in the enhancement erasure dispersal and creation of certain sedimentary iridium anomalies such as those of the cretaceous tertiary boundary the proposal is based on laboratory experiments that have demonstrated the ability of some bacteria and fungi to concentrate iridium from solution and to dissolve iridium from source igneous and meteoritic rocks

weathered spheroids in a cretaceous tertiary boundary shale at woodside creek new zealand three types of spheroids are found in the iridium rich shale layer at the cretaceous tertiary boundary at woodside creek south island new zealand two of the types a and b consist mainly of microcrystalline goethite whereas the third type f contains an appreciable quantity of hematite there is a strong correlation between the iridium content of the spheroids and their matrices and the concentrations of other siderophiles such as chromium cobalt iron and nickel a similar pattern was observed for the chalcophiles arsenic copper and zinc it is suggested that spheroids of types a and b are weathering products derived from diagenetic pyrite clumps and that type f which contains hematite represents a further stage in the weathering process and was derived from goethite the original pyritic material could have readily scavenged arsenic and other siderophiles from the sea water column under organic rich reducing conditions at the end of the cretaceous and the siderophiles including iridium could have been incorporated into the original meteoritic material it was concluded therefore that types a b and f spheroids are weathering products and do not represent original meteoritic material

unmelted meteoritic debris in the late pliocene iridium anomaly evidence for the ocean impact of a nonchondritic asteroid ir bearing particles have been recovered from 2 piston cores in the antarctic basin in the southeastern pacific in core e13 3 the particles closely correspond to the late pliocene ir anomaly and have a fluence of 100 mg cm 2 in core e13 4 120 km to the southwest the particle fluence is 4 mg cm 2 particles with diameters from 0 5 to 4 mm contain at least 35 of the ir in this horizon three types of particles have been identified 1 vesicular 2 basaltic and 3 metal the vesicular particles appear to be shock melted debris derived from the oceanic impact of a howarditic asteroid containing a minor metal component these particles have recrystallized from a melt and impact into the ocean has resulted in the incorporation of na k cl and radiogenic sr from the ocean water target the basaltic clasts appear to be unmelted fragments of the original asteroid which may have separated from the main body prior to impact combined vesicular and basaltic particles are believed to have formed by collisions in the debris cloud estimates of the diameter of the projectile range from 100 to 500 m by many orders of magnitude this is the most massive achondrite sampled by a single meteorite fall

extraterrestrial spherules in glacial sediment from the transantarctic mountains antarctica structure mineralogy and chemical composition silicate and glassy spherules of probably extraterrestrial origin have been discovered in glacial till from localities in the beardmore glacier region transantarctic mountains antarctica these spherules are similar in structure appearance and composition to spherules found in deep sea sediments and in greenland most spherules have a shiny and smooth dark surface while some show a characteristic brickwork pattern composed of intergrown olivine crystals and magnetite dendrites several spherules have been sectioned after trace element analysis by inaa the interiors of the spherules contain olivine crystals of varying size predominantly of forsteritic composition set in a glassy fe rich and mg poor matrix the matrix contains very fine grained dendritic magnetite crystals and rare accessory wustite sem and microprobe studies show that most of the spherules have not experienced significant weathering trace element analyses for individual particles confirm the extraterrestrial nature of the spherules they have undifferentiated chondritic rare earth element ree patterns and are enriched in ir and other siderophile elements with ir contents between 10 and 1 000 ppb some spherules have experienced loss of volatile elements and some differentiation of siderophile elements e g ni the antarctic spherules which might be micrometeorites that melted during passage through the atmosphere or ablation spherules are amore significant addition to the collection of extraterrestrial microparticles of key importance is their high abundance in the sediment and the fact that they have been concentrated by glacial action less

187os 186os in marine manganese nodules and the constraints on the crustal geochemistries of rhenium and osmium during their formation marine manganese or more properly ferromanganese oxide nodules include and commonly concentrate elements dissolved in seawater this attribute makes them especially valuable recorders of the isotopic composition of elements supplied to the oceans having radiogenic isotopes for these can be used in exploring crustal composition and evolution1 5 from measurements of 187os 186os ratios in marine manganese nodules and comparison with the 143nd 144nd ratios of the same nodules we have calculated the os isotopic composition and the osmium and rhenium concentrations of the weatherable portion of the continental crust together with the proportions of ultra mafic and granitic rock that constitute this crustal mass