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 sediments of lake logurinn a unique proxy record of holocene glacial meltwater variability in eastern iceland the full holocene development of the large 8100 km 2 vatnajokull ice cap in iceland with its many outlet glaciers is poorly known the idea of an early deglaciation leading to a glacier free period in mid holocene followed by the neoglaciation is still the main concept for the glacial history in the north atlantic region including iceland we have examined a continuous sediment record from the glacier fed lake logurinn in eastern iceland to infer holocene meltwater variability of eyjabakkajokull which is a surge type outlet glacier of the vatnajokull ice cap we focus on the early and mid holocene and our data show that eyjabakkajokull receded rapidly during the final phase of the last deglaciation and did not deliver glacial meltwater to lake logurinn by 9000 years bp suggesting that eyjabakkajokull was significantly smaller than today at that time the return of glacial meltwater transport to lake logurinn and thus a return of eyjabakkajokull is dated to ca 4400 years bp suggesting an almost 5000 years long glacier free period during early and mid holocene during this time period we infer that the 8 2 ka cold event did not cause a significant expansion of eyjabakkajokull however we note a marked decrease in the aquatic productivity in lake logurinn which is suggested to be the result of shorter ice free seasons of lake logurinn the holocene thermal maximum is inferred by a period of maximum holocene aquatic productivity and dated to ca 7900 7000 years bp following the re formation of eyjabakkajokull ca 4400 years bp we suggest that the glacier reached stable conditions ca 1700 years bp and remained fairly stable until the later part of the little ice age when eyjabakkajokull reached its maximum holocene extent c 2012 elsevier ltd all rights reserved less

mass mortality and its environmental and evolutionary consequences the latest mesozoic and earliest tertiary sediments at deep sea drilling project site 524 provide an amplified record of environmental and biostratographic changes at the end of cretaceous closely spaced samples representing time intervals as short as 102 or 103 years were analyzed for their bulk carbonate and trace metal compositions and for oxygen and carbon isotopic compositions the data indicate that at the end of cretaceous when a high proportion of the ocean9s planktic organisms were eliminated an associated reduction in productivity led to a partial transfer of dissolved carbon dioxide from the oceans to the atmosphere this resulted in a large increase of the atmospheric carbon dioxide during the next 50 000 years which is believed to have caused a temperature rise revealed by the oxygen isotope data the lowermost tertiary sediments at site 524 include fossils with cretaceous affinities which may include both reworked individuals and some forms that survived for a while after the catastrophe our data indicate that many of the cretaceous pelagic organisms became extinct over a period of a few tens of thousands of years and do not contradict the scenario of cometary impact as a cause of mass mortality in the oceans as suggested by an iridium anomaly at the cretaceous tertiary boundary

siderophile interelement variations in the cretaceous tertiary boundary sediments from caravaca spain a detailed profile of the siderophiles fe co ni pd re os ir pt and au from the cretaceous tertiary boundary at caravaca spain indicates that the major fractionation mechanisms are local redistribution reworking and diagenetic mobilization large fractions of the fe co and re and perhaps a small amount of pd and au appear to be terrestrially derived but nearly all of the ni os ir and pt must be derived from an extraterrestrial source only the basal layers at caravaca and stevns klint denmark are representative of the initial fallout and integrated ir fluences across entire sections can be misleading these suggest a concentration oft 120mg g projectile in the fallout and a global fluence of chondritic matter oft 140mg cm 2

a sequence of events across the cretaceous tertiary boundary the lithological and biological sequence of events across the cretaceous tertiary k t as developed in thick and complete landbased sections and termed the standard k t event sequence is also found in many i sdp cores from all over the globe microtektite like spherules have been found in almost every core or outcrop with an iridium anomaly forming a worldwide strewnfield these microtektites are an excellent indicator of the k t boundary level the basal paleocene globigerina eugubma zone is nov established in all major ocean basins the difference in faunas between the pacific and tethys atlantic oceans may point to different recovery of the oldest paleocene planktonic foraminiferal assemblages in different ocean basins planktonic foraminifera and nannoplankton apparently show a different extinction recovery pattern at the k t boundary which suggests that the nannoplankton underwent final extinction later and recover later than planktonic foraminifera these patterns may be important for the evaluation of the type and range of environmental stress resulting from the hypothesized impact s at the k t boundary blocking of sunlight by the dust cloud still can account for the clear mass mortality at the k t boundary but seems less likely as explanation for the final nannoplankton extinction as photosynthetic nannoplankton appear to survive 1000 10 000 years into the tertiary

the cretaceous tertiary boundary problem an assessment from lead isotope systematics abstract the presence of high concentrations of siderophile elements particularly of ir in clay rich layers corresponding to the end of the cretaceous and thus correlated with many mass extinctions has given rise to various studies and theories to provide new isotopic arguments we have used u pb systematics in four famous ir rich locations where the cretaceous tertiary k t boundary is exposed three were marine sites stevns klint denmark caravaca spain and a site just near woodside creek new zealand and one was a continental site raton basin colorado new mexico u s a in all sites the pb isotopic ratio is characteristic of local conditions without any change at the k t boundary these pb isotopic ratios are different from those of carbonaceous chondrites iron meteorites and deccan basalts in stevns klint as in caravaca the amount of pb increases very suddenly at the k t boundary because this pb enrichment occurred only in two boundary beds which contain pyrites or iron hydroxides we suggest that pb and ir might have been concentrated in the clay level by precipitation of sulfides produced by anaerobic bacterial activity the enrichment remained even after alteration processes destroyed the sulfides leaving iron hydroxides in the boundary levels these pb data imply also a possible terrestrial explanation for other volatile element enrichments in k t boundary layers

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

iridium sulfur isotopes and rare earth elements in the cretaceous tertiary boundary clay at stevns klint denmark microbial activity and redox controlled precipitation have been of major importance in the process of metal accumulation in the strongly ir enriched cretaceous tertiary k t boundary clay the fish clay at stevns klint in denmark two important findings support this view 1 1 kerogen recovered by leaching the fish clay in hcl and hf shows an ir concentration of 1100 ppb this represents about 50 of the ir present in the bulk sample fish clay strong organometallic complexes is the most probable carrier phase for this fraction of ir kerogen separated from the k t boundary clay at caravaca spain similarly exhibits enhanced ir concentrations 2 2 sulfur isotope analyses of metal rich pyrite spherules which occur in extreme abundance about 10 by weight in the basal fish clay give a 34s value of 32 this very low value shows that sulfide formation by anaerobic bacteria was intensive in the fish clay during early diagenesis since the pyrite spherules are major carriers of elements such as ni co as sb and zn microbial activity may have played an important role for concentrating these elements in the fish clay large amounts of rare earth elements have precipitated from sea water on fish scales analyses reveal that compared with sea water the fish clay is only about four times less enriched in sea water derived lanthanides than in ir this shows that a sea water origin is plausible for elements that are strongly enriched in the clay but whose origin cannot be accounted for by a lithogenic precursor

origin of drumlins on the floor of lake ontario and in upper new york state abstract upper new york state usa contains one of the largest drumlin fields 12 000 km2 on the north america continent consisting of some 10 000 drumlins located between lake ontario in the north and the finger lakes drumlin like bedforms have also recently been discovered in deep water 200 m on the nearby floor of the rochester basin in lake ontario the new york state drumlin field was produced under the laurentide ice sheet 18 000 years ago when it extended southwards to terminate against the allegheny plateau outcrops of drumlin cores exposed by erosion along the lake ontario shoreline provide windows into the stratigraphy and sedimentology of the northern part of the field sedimentological description of 10 coastal drumlin cores combined with quantitative morphometric analysis of 1487 drumlins shows that they are the product of subglacial erosion of till sheets separated by glaciolacustrine deposits a two phase subglacial model for drumlin formation is suggested consisting of initial aggradation of extensive till deposits during ice advance followed by erosion and streamlining possibly accompanying stillstand of the ice margin and building of moraines systematic changes in drumlin morphometry and spacing are evident ranging from small numbers 60 closely spaced ovoid drumlins l w ratios between 1 and 3 drumlin shape appears to be systematically related to sediment thickness available for erosional streamlining elongate spindle forms occur on the crests and lee sides of bedrock escarpments where sediment cover is thin larger ovoid drumlins occur in topographic depressions where sediment thickness is greater offshore streamlined forms on the floor of the deep water rochester basin in lake ontario have long axes at right angles to the trend of onshore drumlins these are composed of rock rock drumlins and have an orientation structurally controlled by a newly identified inlier of proterozoic grenville province metasediments

submarginal drumlin formation and late holocene history of flaajokull southeast iceland this study was funded by the university of iceland research fund and the icelandic research fund rannis as part of our drumlin studies in iceland

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

recent drumlins flutes and lineations at vestari hagafellsjokull iceland in the foreland of the vestari hagafellsjokull glacier langajokull central iceland three scales of subglacial bed forms are found drumlins flutes and lineations the smaller bed forms are superimposed upon the larger these three bed forms probably formed as a result of the presence of a rigid subglacial core producing a lee side low pressure area into which sediment flowed and collected the cores of the drumlins are tumuli lava blisters whilst the cores of the flutes and lineations were large clasts differences between the three scales of bed forms are that a the flutes and lineations are far more mobile features as their cores could move within the deforming layer whilst the drumlin bedrock cores were fixed b the lineations formed in association with a clast pavement the change in scale of the bed forms may be related to changes in thickness of the deforming layer and size of the core at this site smaller bed forms were superimposed upon larger bed forms and these may have formed as the deforming layer progressively thinned in association with glacial retreat

the nature of the kt impactor a 54cr reappraisal according to the variations observed in the various meteorite classes 54cr represents an isotopic tool for planetary body discrimination in the search for the nature of the cretaceous tertiary kt impactor cr isotopic measurements were already performed at kt boundary the current work is aimed to modernize cr isotopic data with high precision measurements to confirm a carbonaceous chondrite type infall the contribution of which is also estimated isotopic signatures of two marine clays caravaca stevens klint exhibit an isotopic ratio which would represent a mixing of a carbonaceous chondrite of cm2 type with terrestrial material in a ratio 6 to 19 a single impactor may account for both marine and continental cr isotopic signatures

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

what causes till thickness to change over distance answers from mýrdalsjokull iceland abstract many explanations have been provided for variations of the spatial distribution and thickness of till sheets this paper gives new insight into the architecture of a stratigraphically distinct till sheet as a function of the type of substratum and preadvance topography at a scale of 10 km this emphasises the sensitivity of the subglacial system to changes in the basal drainage conditions the study area is the forefield of slettjokull at the northern margin of the m rdalsjokull ice cap central south iceland here detailed lithostratigraphical and sedimentological investigations including mapping of the thickness for two till units sediment logging clast fabric and geotechnical measurements provide a basis for interpretations the results show that the thickness of a stratigraphically distinct till sheet is directly correlated to the type of substratum where the substratum consists of sorted sediments the till is thin conversely the till is thick where the substratum consists of till overlying sorted sediments a sedimentological model is presented in which till thickness is tied to the variable hydraulic conditions experienced in a deforming subglacial bed

isotopic evidence for the cretaceous tertiary impactor and its type high precision mass spectrometric analysis of chromium in sediment samples from the cretaceous tertiary k t boundary coincident with the extinction of numerous organisms on earth confirms the cosmic origin of the k t phenomenon the isotopic composition of chromium in k t boundary samples from stevns klint denmark and caravaca spain is different from that of earth and indicates its extraterrestrial source the chromium isotopic signature is consistent with a carbonaceous chondrite type impactor the observed differences in the chromium isotopic composition among various meteorite classes can serve as a diagnostic tool for deciphering the nature of impactors that have collided with earth during its history

ice stream sticky spots a review of their identification and influence beneath contemporary and palaeo ice streams rapidly flowing ice streams are the arterial drainage routes in continental ice sheets and exert a major influence on ice sheet mass balance recent observations have revealed that ice stream flow exhibits considerable variability with relatively rapid changes taking place in speed and direction this spatial and temporal variability is intimately linked to the conditions at the base of the ice streams and the distribution of localised patches of basal friction known as sticky spots in this paper we provide a detailed review of sticky spot observations from both contemporary and palaeo ice stream beds in order to better understand their nature and influence observations and theoretical considerations reveal four primary causes of stickiness i bedrock bumps ii till free areas iii areas of strong well drained till and iv freeze on of subglacial meltwater these may act together in one location or in isolation and a progressive increase in their distribution could lead to ice stream shut down bedrock bumps are influential under active ice streams where they provide form drag and can create thinner ice which increases the likelihood of basal freeze on increased bed roughness may prevent the lateral migration of some ice streams but bedrock bumps are unlikely to cause ice stream shut down because over long time scales ice stream erosion might be expected to reduce their amplitude the influence of till free areas beneath an ice stream will depend critically on the amount of water that might be drawn out of the surrounding till to lubricate such areas they are likely to be most important in ice stream onset zones but their identification has proved difficult beneath active ice streams if an ice stream operates solely by till deformation it is conceivable that a progressive increase in the exposure of till free areas could lead to shut down through a process of sediment exhaustion areas of strong well drained till have been identified beneath both active and ancient ice streams and are most likely to result from the reorganisation of subglacial meltwater the collapse of an inefficient cannalised system to a more efficient channelised system can occur rapidly and this mechanism has been hypothesised as a candidate for ice stream shut down in both contemporary and palaeo settings basal freeze on has also been observed and inferred from beneath modern and palaeo ice streams and a reduction in basal meltwater supply coupled with ice stream drawdown and the advection of cold ice increases the likelihood of switching off an ice stream a paucity of data from ice stream sticky spots limits a better understanding of their nature distribution and evolution beneath ice streams future technological advances are likely to improve the resolution of the data collected from the beds of modern ice streams but well preserved palaeo ice stream beds also hold potential for investigating their influence on ice stream flow and we present simple landsystems models to aid their identification such data will considerably enhance the basal boundary condition in ice stream models which will ultimately refine our predictions of the response of contemporary ice sheets to future changes in climate

the cretaceous tertiary transition the fossil sequences from cores across the cretaceous tertiary boundary show a range of transition times and transition time intervals depending on the fossil indicators and the location of the site these variations together with the pattern of iridium distribution with depth at some sites differences in total amounts of iridium variations in noble metal abundances normalized to extraterrestrial concentrations the depositional effects that might be expected in a reducing environment and the clay mineralogy of the boundary layer clays put into question the interpretation that an extraterrestrial event was the cause of the faunal changes and the iridium anomaly in the vicinity of the cretaceous tertiary transition it seems more likely that an explanation for the changes during the transition will come from continued examination of the great variety of terrestrial events that took place at that time including extensive volcanism major regression of the sea from the land geochemical changes and paleoclimatic and paleoceanographic changes

physical environment of drumlin formation review of published descriptions of drumlin fields suggests that the following conditions are important to drumlin growth 1 compressive longitudinal and possibly extending transverse strain rates in the ice 2 thin ice such as occurs near the glacier margin and 3 high pore water pressure in the subglacial sediments most drumlin fields display all of these and no fields of well developed drumlins were found that did not on the oilier hand the lithology of drumlin forming sediment appears not to be important in promoting drumlin growth since it varied widely nor are the lithology and large scale topography of the bed

metal precipitation in the cretaceous tertiary boundary clay at stevns klint denmark abstract alvarez et al 1980 explained anomalous ir concentrations in the cretaceous tertiary k t boundary informal type sediment the fish clay in denmark in terms of a global fall out of extraterrestrial matter however geochemical and mineralogical analyses of the various sublayers in the clay reveal that not only ir but also elements such as ni co zn mo as se and sb are substantially enriched in the clay the enrichments may be due to precipitation of elements as sulfides at a redoxcline the facts supporting this view are 1 1 the over all chalcophile element abundance pattern in the clay 2 2 the occurrence of a redoxcline deduced from the distribution of organic matter and oxidized iron in the clay 3 3 the large amounts of small pyrite spheroids present at this redoxcline 4 4 the high concentration of trace elements in these spheroids also ni co and ir elements that have previously been presumed to have a meteoritic origin are substantially enriched in the spheroids a model is suggested in which metal bearing pore solutions lose their metals by precipitation upon passing the boundary between the oxic cretaceous chalk and the overlying anoxic and hydrogen sulnde rich fish clay the great similarity in geochemistry and lithological appearance between several strongly ir enriched clays suggest that the model may also be applied to other k t boundary clays

multiple factors in the origin of the cretaceous tertiary boundary the role of environmental stress and deccan trap volcanism a review of the scenarios for the cretaceous tertiary k t boundary event is presented and a coherent hypothesis for the origin of the event is formulated many scientists now accept that the event was caused by a meteorite impact at chicxulub in the yucatan peninsula mexico our investigations show that the oceans were already stressed by the end of the late cretaceous as a result of the long term drop in atmospheric co2 the long term drop in sea level and the frequent development of oceanic anoxia extinction of some marine species was already occurring several million years prior to the k t boundary the biota were therefore susceptible to change the eruption of the deccan traps which began at 66 2 ma coincides with the k t boundary events it erupted huge quantities of h2so4 hcl co2 dust and soot into the atmosphere and led to a significant drop in sea level and marked changes in ocean temperature the result was a major reduction in oceanic productivity and the creation of an almost dead ocean the volcanism lasted almost 0 7 m y extinction of biological species was graded and appeared to correlate with the main eruptive events elements such as ir were incorporated into the volcanic ash possibly on soot particles this horizon accumulated under anoxic conditions in local depressions and became the marker horizon for the k t boundary an oxidation front penetrated this horizon leading to the redistribution of elements the eruption of the deccan traps is the largest volcanic event since the permian triassic event at 245 ma it followed a period of 36 m y in which the earth s magnetic field failed to reverse instabilities in the mantle are thought to be responsible for this eruption and therefore for the k t event we therefore believe that the k t event can be explained in terms of the effects of the deccan volcanism on an already stressed biosphere the meteorite impact at chicxulub took place after the onset of deccan volcanism it probably played a regional rather than a global role in the k t extinctions

intense acidic volcanism at the cretaceous tertiary boundary abstract a 87 sr 86 sr spike in seawater strontium with amplitude 2 10 4 and duration of order 2 ma is superimposed on longer term variations at the cretaceous tertiary boundary the anomaly has been attributed to increased continental runoff due either to meteorite impact related acid rain or sea level regression we speculate here that the spike could have resulted from intense explosive acid volcanism preceding the development of the deccan traps a good model both in tectonic position and geochemical characteristics for these as yet elusive acidic products is provided by granites in the seychelles islands and particularly mahe

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

hydrothermal nickel deposits secular variation and diversity abstract hydrothermal nickel systems are one of the most puzzling mineral systems that involve trace element mobility in the earth s crust nickel is an abundant element in the crust however the processes that are involved in its mobility and accumulation at ore scale are challenging a new empirical stochastic model is required to gain a deeper insight into these systems this special issue presents several studies on hydrothermal nickel accumulations world wide aiming to stimulate the debate on this intriguing deposit type

osmium tungsten and chromium isotopes in sediments and in ni rich spinel at the k t boundary signature of a chondritic impactor it is now established that a large extraterrestrial object hit the earth at the end of the cretaceous period about 65 ma ago we have investigated re os hf w and mn cr isotope systems in sediments from the cretaceous and the paleogene in order to characterize the type of impactor within the cretaceous tertiary k t boundary layer extraterrestrial material is mixed with terrestrial material causing a dilution of the extraterrestrial isotope signature that is difficult to quantify a phase essentially composed of ni rich spinel formed in the atmosphere mainly from melted projectile material is likely to contain the extraterrestrial isotopic signature of the impactor we show that the analysis of spinel is indeed the best approach to determine the initial isotope composition of the impactor and that w and cr isotopes confirm that the projectile was a carbonaceous chondrite

rb sr sm nd k ca o and h isotopic study of cretaceous tertiary boundary sediments caravaca spain evidence for an oceanic impact site isotopic ratios and trace element abundances were measured on samples of ir enriched clay at the cretaceous tertiary boundary and in carbonate and marl from 5 cm below and 3 cm above the boundary samples were leached with acetic acid to remove carbonate and with hydrochloric acid leachates and residues were measured the sr nd o and h isotopic compositions of the boundary clay residues are distinct from those of the stratigraphically neighboring materials the data indicate that most of the clay material was derived from a terrestrial source with relatively low87sr 86sr and high143nd 144nd ratios the 18o data suggest that the detritus has been modified by submarine weathering k ca and rb sr systematics as well as o isotope ratios of k feldspar spherules within the boundary clay suggest that they are predominantly authigenic and may have formed after the time of deposition however sm nd and rb sr isotopic data indicate that the spherules contain relict material that provides information on the nature of the original detritus the isotopic evidence for foreign terrestrial detritus in the boundary clay the low rare earth element concentrations and high ni concentration support the hypothesis of a terminal cretaceous asteroidal impact that produced a global layer of fallout the data are most easily explained if the impact site was on oceanic crust rather than continental crust and if a substantial fraction of the fallout was derived from relatively deep within the lithosphere 3 km this would probably require a single large impactor

a multi isotopic and trace element investigation of the cretaceous tertiary boundary layer at stevns klint denmark inferences for the origin and nature of siderophile and lithophile element geochemical anomalies abstract os sr nd and pb isotope data were collected from a profile across the cretaceous tertiary k t boundary layer at stevns klint denmark nd t 65 ma values from within the boundary layer fish clay are lower by 1 unit than those of the underlying maastrichtian limestone and the overlying danian chalk sequences systematic profile upward changes of pb sr and os isotopic compositions and concentrations in the boundary layer cannot be accounted for by in situ growth of daughter products since the sedimentation of the fish clay while os nd and pb isotopes indicate the admixing of less radiogenic components to the fish clay sr isotopes show elevated radiogenic values in the boundary layer relative to the carbonate sequences beneath and above it the sudden change in lithophile e g sr pb and nd isotope compositions at the base of the fish clay and profile upward trends of 87sr 86sr and 206pb 204pb ratios towards those of the overlying danian chalk are interpreted to reflect recovery from enhanced acid rain induced continental local weathering input to the seawater however a continental crustal source is invalid for the siderophile element os in the light of evidence from chromium isotopes for a cosmic origin of the platinum group elements pges and certain moderately siderophile elements cr ni co v in k t boundary sediments including stevns klint shukolyukov and lugmair science 282 1998 927 929 and supported by the finding of projectile debris bauluz et al earth planet sci lett 182 2000 127 136 and the occurrence of abundant ni rich spinel at many k t sites robin et al nature 363 1993 615 617 kyte nature 396 1998 237 239 we favor to explain the sudden drop of 187os 188os ratios from 0 210 to 0 160 at the k t boundary to derive from global fall out of extraterrestrial matter the present 186os 188os ratio of 0 119836 0 000004 measured in the basal layer of the fish clay is within the uncertainty a chondritic value we therefore exclude the possibility of a major contribution of pges to the sediment from iron meteorites chondrite normalized ru ir n ratios of 0 95 0 14 and os ir n ratios of 0 93 0 14 in the fish clay cannot distinguish between abundance ratios of different types of chondrites and strongly sub chondritic pt ir n ratios of 0 62 0 09 2 suggest differential pge remobilization through the sedimentary column and consequently the alteration of inter element ratios pges and the moderately siderophile elements cr ni v and co form an elemental association with systematically upward decreasing concentrations in the fish clay low co ni ratios of 0 12 in the fish clay relative to values of 0 35 in the over and underlying carbonate sequences support mixing of meteorite derived co ni 0 05 and terrestrial upper mantle crustal co ni 0 3 sources while lithophile element isotope data indicate an increased continental crustal input to the fish clay at the k t transition the uncertainty with respect to possible post depositional alteration of abundance patterns of siderophile and moderately siderophile elements though not affecting the chondritic isotopic composition of os does not allow confirmation of indications from chromium isotopes for a carbonaceous cv type meteorite as the preferred k t impactor type by shukolyukov and lugmair science 282 1998 927 929

pb isotopic tracers of the cretaceous tertiary extinction event the global excess of ir in sediments at the cretaceous tertiary k t boundary has been attributed to either a meteorite impact or enhanced volcanism e g deccan traps the isotopic composition of pb associated with this ir provides a test of these hypotheses because meteoritic pb is isotopically quite distinct from pb of volcanic or continental origin pb abundances and isotopic compositions of pelagic oozes from dsdp site 577a shatsky rise nw pacific measured in this study show little change over the deposition interval of ir rich sediment 10 cm however a pb enriched layer with a more radiogenic isotopic composition is found in the basal 0 5 cm of the tertiary these observations appear to preclude the ir excess in these sediments originating as impact fallout from a stony meteorite although an iron meteorite impactor cannot be excluded any pb flux accompanying ir in volcanogenic aerosols from the deccan traps should be considerable however the boundary pb spike does not isotopically resemble known deccan trap lavas there is isotopic overlap with coal ash although the lack of correlation between soot and pb abundance precludes any simple relationship between the two overall any wind pattern changes following the k t event were apparently short lived as neither airborne sources of pb nor their magnitude to the then central pacific were affected while the ir enriched sediments were being laid down

holocene and latest pleistocene climate and glacier fluctuations in iceland abstract multiproxy climate records from iceland document complex changes in terrestrial climate and glacier fluctuations through the holocene revealing some coherent patterns of change as well as significant spatial variability most studies on the last glacial maximum and subsequent deglaciation reveal a dynamic iceland ice sheet iis that responded abruptly to changes in ocean currents and sea level the iis broke up catastrophically around 15 ka as the polar front migrated northward and sea level rose indications of regional advance or halt of the glaciers are seen in late allerod early younger dryas time and again in preboreal time due to the apparent rise of relative sea level in iceland during this time most sites contain evidence for fluctuating tidewater glacier termini occupying paleo fjords and bays the time between the end of the younger dryas and the preboreal was characterized by repeated jokulhlaups that eroded glacial deposits by 10 3 ka the main ice sheet was in rapid retreat across the highlands of iceland the holocene thermal maximum htm was reached after 8 ka with land temperatures estimated to be 3 c higher than the 1961 1990 reference and net precipitation similar to modern such temperatures imply largely ice free conditions across iceland in the early to mid holocene several marine and lacustrine sediment climate proxies record substantial summer temperature depression between 8 5 and 8 ka but no moraines have been detected from that time termination of the htm and onset of neoglacial cooling took place sometime after 6 ka with increased glacier activity between 4 5 and 4 0 ka intensifying between 3 0 and 2 5 ka although a distinct warming during the medieval warm period is not dramatically apparent in icelandic records the interval from ca ad 0 to 1200 is commonly characterized by relative stability with slow rates of change the literature most commonly describes little ice age moraines ca ad 1250 1900 as representing the most extensive ice margins since early holocene deglaciation with temperature depressions of 1 2 c compared to the ad 1961 1990 average steep north south and west east temperature gradients are reconstructed in the holocene records of iceland suggesting a strong maritime influence on the terrestrial climate of iceland

geologic framework of nonmarine cretaceous tertiary boundary sites raton basin new mexico and colorado iridium concentrations are anomalously high at the palynological cretaceous tertiary boundary in fluvial sedimentary rocks of the lower part of the raton formation at several localities in the raton basin of new mexico and colorado the iridium anomaly is associated with a thin bed of kaolinitic claystone in a discontinuous carbonaceous shale and coal sequence