the great extinction that never happened the demise of the dinosaurs considered the concept of a sudden extinction of the dinosaurs consequent upon the impact of some extraterrestrial object is so dramatic that it has taken hold upon the imaginations of many scientists as w

trace fossils after the k t boundary event from the agost section se spain palaeogene trace fossils penetrate the uppermost cretaceous sediments in the agost section betic cordillera se spain chondrites targionii zoophycos isp planolites isp a planolites isp b thalassinoides isp a thalassinoides isp b thalassinoides isp c alcyonidiopsis longobardiae and diplocraterion parallelum have been identified a well developed endobenthic tiering pattern is interpreted the uppermost tier a represents major benthic activity in the shallowest sediments at or just below the seafloor recorded as bioturbated background only discrete rare planolites the next upper tier b displays the highest trace fossil diversity with planolites in the shallow levels and thalassinoides and alcyonidiopsis at slightly deeper ones the intermediate tier c contains randomly distributed thalassinoides and alcyonidiopsis cross cut by zoophycos and large and medium sized chondrites the deepest tier d contains zoophycos cross cut by medium and mainly small sized chondrites two interpretations are proposed 1 vertical partitioning of a singled multi tiered community under steady stable conditions in well oxygenated water bottom reflecting gradual changes deep into the sediment with decreasing oxygen pore water and benthic food and increasing substrate consistency and 2 sequential colonization and community replacement reflecting the work of two successive communities the first community mainly represented by planolites alcyonidiopsis and thalassinoides was produced in a shallow oxygenated soft substrate probably related to decreasing oxygen content and benthic food availability this community was replaced by deeply burrowing organisms that produced zoophycos and chondrites this sequential colonization can be determined by changes in environmental parameters related to the cretaceous palaeogene k t event or may have resulted from normal ecological and early diagenetic processes

significant changes in land vegetation and oceanic redox across the cretaceous paleogene boundary abstract the impact of an extraterrestrial body 65 5 ma caused the so called cretaceous paleogene k pg event that resulted in a mass extinction and rapid changes in the surface environment on earth here we report changes in land vegetation and oceanic redox across the k pg boundary at caravaca southeastern spain using biomarkers the results reveal that the basal 3 mm thick layer of the k pg boundary clay is marked by a rapid increase in the concentration of terrestrial long chain n alkanes and dibenzofuran indicating the destruction of land vegetation and an increase in the supply of terrestrial organic matter into the marine environment during the deposition of the k pg boundary clay this layer also records a rapid increase in the concentration of dibenzothiophenes which indicates a change in redox conditions from oxic to anoxic euxinic conditions in the intermediate water over the seafloor the low oxygen conditions could have been caused by an increase in the influx of terrestrial organic matter into the ocean a rapid increase in the concentration of retene and retene cadalene occurred during the deposition of the upper part of the boundary clay 10 kyr after the mass extinction indicating the recovery of conifers which greatly decreased at the k pg boundary

the cretaceous tertiary boundary stratotype section at el kef tunisia how catastrophic was the mass extinction abstract the cretaceous tertiary k t boundary stratotype section at el kef tunisia represents the most complete and expanded sedimentary record across this important mass extinction horizon presently known high resolution analysis of planktic foraminifera in two outcrops el kef i stratotype and el kef ii along with comparisons between planktic and benthic foraminifera calcareous nannofossils ostracods pollen and spores and dinoflagellates indicate that major changes across the k t boundary are registered only in benthic and planktic foraminifera and calcareous nannofossils biotic changes in benthic foraminifera are unique to el kef and similarly shallow continental shelf sections and appear to be the result of a sea level regression in the latest maastrichtian followed by a sea level rise across the k t boundary that was accompanied by expansion of the local oxygen minimum zone omz biotic changes in planktic foraminifera appear partly related to these conditions also but in general reflect more global oceanographic changes for instance species extinctions are gradual and selective as observed in k t sections worldwide rather than random and abrupt although there is a 69 decline in species richness between 25 cm below and 10 cm above the k t boundary only rare species disappeared their combined relative abundance constitute less than 20 of the total population about 52 of these extinct taxa 8 of the population are large ornate morphologically complex tropical subtropical forms that lived at or below the thermocline no planktic foraminifera from this depth range survived the k t boundary event all survivor taxa were surface dwellers living within the photic zone their relative abundance 80 dominates both cretaceous and early tertiary populations these data indicate that the k t biotic record in the shallow continental shelf section at el kef was significantly influenced by local conditions which combined with the latest maastrichtian sea level regression and subsequent sea level rise resulted in shallowing of the local omz relative to the sea surface shallowing of the local omz lead to the selective disappearance of benthic faunas and may have adversely affected the surviving photic zone dwellers the selective nature of species extinctions however appear to be related partly to long term global oceanographic changes which were accelerated at the k t boundary possibly by a bolide impact

oceanic primary productivity and dissolved oxygen levels at the cretaceous tertiary boundary their decrease subsequent warming and recovery thirty six different geochemical and foraminiferal analyses were conducted on samples collected at closely spaced intervals across the cretaceous tertiary k t boundary exposed at caravaca spain a rapid reduction in the gradient between 13c values in fine fraction carbonate and benthic foraminiferal calcite and a decrease in the abundance of phosphorus a proxy for organic carbon and calcium were recorded in sediments 0 0 5 cm above the k t boundary these trends imply that an abrupt mass mortality occurred among pelagic organisms leading to a significant reduction in the flux of organic carbon to the seafloor in addition variations in sulfur isotope ratios the hydrocarbon generating potential of kerogen measured as the hydrogen index and foraminiferal indices of dissolved oxygen level all imply that a rapid decrease in dissolved oxygen was coincident with the 13c event evidence of the low oxygen event has also been recognized in japan and new zealand suggesting that intermediate water oxygen minima were widely developed during earliest danian time a threefold increase in the kaolinite illite ratio and a 1 2 decrease in 18o carbonate fine fraction were recorded in the basal 0 1 2 cm of danian age sediments these trends suggest that atmospheric warming and an increase in surface water temperature occurred 0 3 kyr after the 13c event recovery in the difference between 13c values in the carbonate fine fraction and in benthic foraminiferal calcite as well as increases in phosphorus and calcium contents occur at the base of planktonic foraminiferal zone pla implying that an increase in primary productivity commenced some 13 kyr after the k t boundary tables a1 a3 are available on diskette or via anonymous ftp from kosmos agu org directory apeno username anonymous password guest diskette may be ordered from american geophysical union 2000 florida avenue n w washington dc 20009 or by phone at 800 966 2481 15 00 payment must accompany order

deep water agglutinated foraminiferal changes and stable isotope profiles across the cretaceous paleogene boundary in the rotwandgraben section eastern alps austria abstract the studied interval extends from 2 5 m below to 1 m above the cretaceous paleogene k p boundary and encompasses the uppermost abathomphalus mayaroensis po subzones poa guembelitria cretacea and pob globoconusa conusa p or parvularugoglobigerina eugubina and lowermost p1 subzone p1a or subbotina pseudobulloides planktonic foraminiferal zones the agglutinated benthic foraminiferal assemblages of the uppermost abathomphalus mayaroensis zone are moderately diversified and composed of mixed epifaunal and infaunal morphogroups in the lower part of the guembelitria cretacea subzone benthic foraminifers are extremely rare and represented only by a few epifaunal species in the upper part of this subzone they are still not abundant but assemblages are again moderately diversified in the globoconusa conusa subzone deep water agglutinated foraminifers are abundant highly diversified and represented by mixed epifaunal and infaunal morphogroups bulk rock stable isotope analysis shows a significant drop of both 13 c and 18 o values at the k p boundary it appears that a drastic decrease in abundance and diversity of deep water agglutinated foraminifers as well as a change of the community structure from mixed epifaunal and infaunal to one dominated by epifaunal morphogroups are related to a reduction in marine primary productivity the instantaneous environmental stress and the collapse of primary productivity are compatible with a large bolide impact

the cretaceous paleogene transition at galanderud northern alborz iran a multidisciplinary approach abstract we investigated the cretaceous paleogene k pg transition at the galanderud section northern alborz iran to identify the pattern of mass extinction of planktic foraminifera and to unravel the associated paleoenvironmental changes in a little studied area of the eastern tethys we applied a high resolution quantitative and multidisciplinary study based upon benthic and planktic foraminiferal assemblages clay mineralogy rock magnetic properties stable isotopes and geochemistry in this section the k pg boundary is marked by an abrupt change in lithology from marl to a clay boundary layer a marked decrease in magnetic susceptibility a negative 2 2 13c excursion and a peak in iridium in the uppermost maastrichtian foraminifera are well preserved and diversified suggesting a stable mesotrophic environment by contrast the k pg boundary and basal danian is marked by high values of epifaunal benthic morphogroups low planktic diversity and high percentages of opportunistic species guembelitria cretacea and cervisiella operculata suggesting highly stressed and variable conditions partly due to the dramatic collapse of calcareous primary producers benthic foraminiferal assemblages indicate outer neritic uppermost bathyal depths with slight bathymetric variations the most peculiar and unique aspect of the galanderud section is the occurrence of the three thin chalk layers interbedded within clays above the k pg boundary each marked by positive shifts in 13c and 18o values and consisting of 80 carbonate we propose that the chalk clay deposits in the basal danian reflect changes in seawater chemistry and dynamic changes in circulation upwelling alternating with episodes of enhanced weathering and runoff this section on the northern margin of eastern tethys provides new clues about the pattern of the k pg mass extinction and the paleoenvironmental changes occurring during the biotic recovery phase

dual frequency interferometric sar observations of a tropical rain forest repeat pass interferometric radar observations of tropical rain forest collected by the shuttle imaging radar c sir c in the state of rondonia brazil reveal signal coherence is destroyed at c band 5 6 cm in the forest whereas l band 24 cm radar signals remain strongly coherent over the entire landscape at l band the rms difference in inferred topographic height between the forest and adjacent clearings is 5 m equivalent to the height noise atmospheric delays are large however forming kilometer sized anomalies with a 1 2 cm rms one way radar interferometric studies of the humid tropics must therefore be conducted at long radar wavelengths with kilometric baselines or with two antennas operating simultaneously

benthic foraminiferal ecomarker species of the terminal cretaceous late maastrichtian deep sea tethys abstract benthic foraminiferal distribution patterns throughout the late maastrichtian tethyan deep sea are analyzed many species are ubiquitously distributed throughout this region and therefore it is hard to assess their ecological preferences however five species show distribution patterns which suggest that they may have distinctive paleoenvironmental preferences these preferences are interpreted from hypothesized surface circulation and upwelling patterns additional information comes from recent benthic foraminiferal ecology and from responses to the cretaceous paleogene k pg boundary event this enables us to assess the ecological preferences of these late maastrichtian taxa and establish them as ecological marker ecomarker species for paleoenvironmental interpretation of the late maastrichtian bathyal abyssal tethyan realm 1 eouvigerina subsculptura is suggested to be indicative of reasonably oxygenated upper middle bathyal environments though with high abundance of utilizable organic matter 2 sliteria varsoviensis is linked to areas of late maastrichtian upwelling and seems to have been an epibenthic species with an opportunistic life mode 3 gavelinella beccariiformis and 4 nuttallides truempyi are considered to be indicative of oligotrophic conditions unless they occur with a large proportion of endobenthic morphotypes 5 gavelinella pertusa is proposed to indicate neritic middle bathyal environments of the boreal realm which might be influenced by more seasonal food fluxes and by higher oxygen levels than similar settings in the sub tropics finally the anomalous high abundances of the buliminid species sitella cf plana in deep open ocean environments is discussed in terms of possible mechanisms permitting such a morphologically opportunistic species to thrive in such an assumedly oligotrophic environment

cretaceous paleogene boundary bathyal paleo environments in the central north pacific dsdp site 465 the northwestern atlantic odp site 1049 the gulf of mexico and the tethys the benthic foraminiferal record uppermost maastrichtian benthic foraminiferal assemblages n63 am are diverse indicating mesotrophic conditions in lower bathyal dsdp hole 465a hess rise central north pacific in 4 lower bathyal land sections in central east and northeastern mexico and in the upper to middle bathyal agost section tethys area southeastern spain they indicate more eutrophic conditions in lower bathyal odp hole 1049c blake nose northwestern atlantic benthic foraminifers did not suffer significant extinction at the k pg boundary but diversity and heterogeneity of the assemblages and the percentage of infaunal morphogroups decreased drastically in all sections with the exception of dsdp hole 465a where the percentage of infaunal taxa increased these faunal changes probably reflect the effect on the benthic faunas of a widespread decrease in the food supply to the sea floor as a result of the collapse of primary productivity at the k pg boundary the decrease in food supply apparently affected the benthic faunas least at more eutrophic nwatlantic odp site 1049 and at pacific dsdp site 465 which is distal from the impact site of the k pg bolide on the yucatan peninsula at these sites the faunas recovered within the parvulorugoglobigerina eugubina biozone 100 ky although diversity and heterogeneity remained low through the early danian possibly indicating environmental stress this stress might be related to a high or fluctuating food supply by primary producers that could not easily be used by the benthos such as various bloom species of dinoflagellates benthic assemblages recovered more slowly 300 ky in the mexican and spanish sections low oxygen conditions after the k pg boundary could be inferred from the benthic assemblages at agost southeastern spain only a short episode of hypoxia however may be obscured at pacific dsdp hole 465a by drilling disturbance and in the mexican sections and hole 1049c by incomplete sections due to downslope transport benthic foraminiferal assemblages thus appear to have been affected by the collapse of

the cretaceous palaeogene boundary succession at stevns klint denmark foraminifers and stable isotope stratigraphy the cretaceous palaeogene boundary exposed at stevns klint denmark provides an important location for the investigation of the end cretaceous event in this work we have used a number of sections across the boundary including the little described expanded stratigraphic sequence at kulstirenden which is located 7 km north of hojerup where most published work is derived using stratigraphical micropalaeontological and stable isotope 18o and 13c data we have shown that there is clear evidence of shallowing in the latest maastrichtian prior to and across the cretaceous palaeogene boundary there are significant changes in sea water temperature including an important cooling event in the very latest maastrichtian the 13c record in the expanded boundary clay fish clay sequence at kulstirenden indicates a number of significant excursions of decreasing magnitude up section the evidence from the distribution of the foraminifers has been incorporated with previous work to develop a sequence stratigraphical interpretation for the succession that can be compared to other cretaceous palaeogene boundary successions in europe

magma sources for mesozoic anorogenic granites of the white mountain magma series new england usa the magma sources for granitic intrusions related to the mesozoic white mountain magma series in northern new england usa are addressed relying principally upon nd isotopes many of these anorogenic complexes lack significant volumes of exposed mafic lithologies and have been suspected of representing crustal melts sm nd and rb sr isotope systematics are used to evaluate magma sources for 18 felsic plutons with ages ranging from about 120 to 230 ma the possibility of crustal sources is further examined with analyses of representative older crust including paleozoic granitoids which serve as probes of the lower crust in the region multiple samples from two representative intrusions are used to address intrapluton initial isotopic heterogeneities and document significant yet restricted variations 1 in end overall mesozoic granite plutons range in end t from 4 2 to 2 3 with most 2 to 0 and in initial 87sr 86sr from 0 7031 to 0 709 the isotopic variations are roughly inversely correlated but are not obviously related to geologic geographic or age differences older igneous and metamorphic crust of the region has much lower nd isotope ratios with the most radiogenic paleozoic granitoid at end 180 ma of 2 8 these data suggest mid proterozoic separation of the crust in central northern new england moreover the bulk of the mesozoic granites cannot be explained as crustal melts but must have large mantle components the ranges of nd and sr isotopes are attributed to incorporation of crust by magmas derived from midly depleted mantle sources crustal input may reflect either magma mixing of crustal and mantle melts or crustal assimilation which is the favored interpretation the results indicate production of anorogenic granites from mantle derived mafic magmas

benthic foraminiferal turnover across the cretaceous paleogene boundary at agost southeastern spain paleoenvironmental inferences abstract we studied upper cretaceous and lower paleogene benthic foraminifera from the agost section southeastern spain to infer paleobathymetrical changes and paleoenvironmental turnover across the cretaceous paleogene k p transition benthic foraminifera indicate uppermost bathyal depths at agost during the abathomphalus mayaroensis biochron from about 400 kyr before the k p boundary through the early plummerita hantkeninoides biochron about 120 150 kyr before that boundary the depth increased to middle bathyal for the remainder of the cretaceous and remained so for the danian part of the studied section parasubbotina pseudobulloides biochron at least 200 kyr after the k p boundary there were no perceivable bathymetrical changes at the k p boundary where 5 of the species became extinct and the species composition of the benthic foraminiferal fauna changed considerably below the boundary infaunal morphogroups constitute up to 65 73 of the faunas directly above the boundary in the black clays of the lower guembelitria cretacea biozone benthic foraminifera are rare several opportunistic taxa e g the agglutinant haplophragmoides sp have short peaks in relative abundance possibly reflecting low oxygen conditions as well as environmental instability with benthos receiving food from short lived local blooms of primary producers above the clays through the end of the studied interval epifaunal morphogroups dominate up to 70 of the assemblages or there is an even mixture or epifaunal and infaunal morphogroups infaunal groups do not recover to pre extinction relative abundances indicating that the food supply to the benthos did not recover fully over the studied interval about 200 kyr after the k p boundary the benthic foraminiferal faunal changes are compatible with the direct and indirect effects of an asteroid impact which severely destabilized primary producers and the oceanic food web that was dependent upon them

paleoenvironments of the latest cretaceous oil shale sequence southern tethys israel as an integral part of the prevailing upwelling system abstract the late cretaceous succession in israel is part of an extensive high productivity upwelling regime that persisted over 20 m y in the southern margins of tethys the deposition of a 40 m thick organic rich carbonate oil shale sequence in the negev israel indicates a major change in the evolution of this high productivity regime and reorganization of the marine ecosystem during the latest campanian early maastrichtian time the main objective of this study was to reconstruct changes in surface water productivity and seafloor oxygenation during the deposition of the oil shale member osm and transitions with the underlying phosphate and overlying marl members using high resolution records of planktic and benthic foraminifera and total organic carbon toc content the updated age of the osm determined by integrating planktic foraminifera calcareous nannofossils and inoceramids suggests that this sequence spans a maximum of 1 85 m y from 71 6 to 69 85 ma with a sedimentation rate of at least 2 4 cm kyr five distinct planktic p types and benthic b type foraminiferal assemblages were distinguished in the studied sequence the change from p type 5 to p type 1 along the sequence correlates with a distinct decrease in toc content 18 0 0 1 wt and signifies an upward decline in surface productivity based on this relationship it was inferred that species of globigerinelloide s principally globigerinelloides asper are the best tracers for extreme eutrophic surface water whereas heterohelicids are associated with more mesotrophic conditions the transition in time from assemblages b types 5 to 1 mainly reflects a change from the predominance of praebuliminids and neobuliminids to a more diversified rotaliid dominated assemblage indicating an increase in bottom water aeration the appearances of planktic foraminifera coincident with the establishment of benthic rotaliid fauna at the phosphate oil shale member transition mark the most prominent change in the upwelling sequence this change probably reflects moderate weakening of the eutrophic surface water productivity and a regional sea level rise resulting in seafloor deepening and improved seafloor aeration a further step in the decrease in toc content to 5 5 8 wt occurs in the uppermost part of the osm latest campanian and corresponds to the transitions to assemblages p type 1 and b type 1 this change suggests a shift to mesotrophic conditions additional increase in bottom and pore water aeration and thus the demise of the upwelling activity in the southern tethys

did the european dinosaurs disappear before the k t event magnetostratigraphic evidence abstract debate on the non catastrophic or catastrophic extinction of the dinosaurs by an asteroid impact k t event remains a controversy and is mainly based on the interpretation of the sedimentary continental sequences in the north american western interior the global aspect of this event needs to be tested in sedimentary record from all continents where continuous terrestrial deposits through the cretaceous paleogene are well preserved in the western mediterranean realm recognition of the cretaceous paleogene boundary is limited by the lack of biostratigraphic data in the upper cretaceous lower tertiary continental sedimentary sequences new magnetostratigraphic results were obtained from the analysis of two sections in southern france and compared to previous results in northern spain the last occurrence of in situ dinosaurs eggshells the only dinosaur remains found is located in chron 30n southeast france or 31n southwest france and northern spain this last occurrence could demonstrate that the extinction of the european dinosaurs occurred prior to the cretaceous paleogene boundary and would therefore support the idea of a gradual or stepwise extinction unlinked to the k t event

the response of benthic foraminifera to the k pg boundary biotic crisis at elles northwestern tunisia abstract the high resolution quantitative study of benthic foraminifera from the elles section nw tunisia that contains one of the most complete cretaceous paleogene k pg boundary transition and spans about 357 kyr provides detailed data on the palaeoenvironmental turnover across the k pg boundary benthic foraminifera indicate outer neritic uppermost bathyal depths without perceivable bathymetrical changes throughout uppermost maastrichtian assemblages are well preserved and highly diversified indicating stable environment and mesotrophic to weakly eutrophic conditions during the latest cretaceous benthic foraminifera underwent a major faunal turnover in coincidence with the k pg boundary where a dramatic and sudden decrease in the percentage of both infaunal morphogroups and buliminids as well as in diversity heterogeneity and genus and species richness of the assemblages are recorded indicating overall oligotrophic conditions benthic foraminifera do not show significant extinction at the end of the cretaceous with only about 3 of the species clearly becoming extinct together with the temporary disappearance of some taxa a stepped pattern of faunal recovery and restructuring is recognizable during the lowermost danian reflecting the gradual restabilization of the environmental conditions after the k pg boundary event the nature and the abundance of food supply to the sea floor conditioned the faunal turnover in the earliest paleogene which reflects not only a sudden collapse of the food web due to the extinction of calcareous primary producers but also a major rapid change in composition and abundance of food supply just after the k pg boundary short term blooms of some opportunistic species within the g cretacea zone and the lowermost part of the ps pseudobulloides zone would reflect instability in the benthic assemblages that might be related to the transfer to the sea floor of food supply not easily used by the benthos through short term large blooms or changes in abundance of opportunistic various phytoplankton groups the major environmental instability at the sea floor that just follows the k pg boundary event may have been thus related to changes in the phytoplankton composition and abundance and would have taken place over a period of about 25 kyr benthic foraminiferal assemblages appear to stabilize in the lowermost part of zone ps pseudobulloides 65 kyr after the k pg boundary event the sea floor ecosystem at least at outer neritic uppermost bathyal depths may have recovered over a considerably shorter period than commonly suggested even if the food delivery to the sea floor had not fully recovered the pre k pg levels as indicated by the lower percentages of infaunal morphogroups and buliminids this would be also in agreement with the rapid recovery of terrestrial ecosystems following the biotic crisis at the k pg boundary the drastic change of benthic foraminiferal assemblages coincident with the k pg boundary at elles and their staggered reorganization during the lowermost paleogene are largely compatible with the catastrophic effects of a huge asteroid impact on earth at the k pg boundary that severely destabilized the oceanic phytoplankton based food web

biochemical vs detrital mechanism of remanence acquisition in marine carbonates a lesson from the k t boundary interval abstract an apparently complete carbonate rich cretaceous tertiary boundary interval in odp section 119 738c 20r 5 from the southern kerguelen plateau provides a unique insight into processes of magnetization acquisition in marine carbonates the boundary interval is characterized by a 1 m thick clay rich zone distinct depositional lamina are preserved within the basal 15 cm of this zone the upper part is bioturbated previous studies have demonstrated that the bulk of the detrital fraction in the laminated and bioturbated carbonates has the same local source and hence the two intervals likely had similar initial detrital assemblages magnetic properties of these rocks however differ significantly the laminated sediments have a higher content of non silicate bound iron yet approximately an order of magnitude lower intensity of the natural remanent magnetization compared to the bioturbated rocks our detailed rock magnetic study indicates that in the bioturbated interval the dominant iron bearing phase is single domain magnetite likely of biogenic origin in the laminated interval apart from a small ferromagnetic fraction with multi domain like behavior non silicate bound iron is mainly sequestered in paramagnetic phases likely poorly crystalline oxyhydroxides it appears that a shut down of biological productivity after the k t event allowed preservation of the initial detrital early authigenic iron phases that are dominated by reactive iron oxyhydroxides with recovery of the normal biological activity as evidenced by resumption of bioturbation the oxyhydroxides had been replaced with biogenic magnetite thus produced biochemical magnetization led to a several fold increase in the remanence our results suggest that in areas where bioavailable iron constitutes a significant part of the detrital input such as in pelagic marine environments distant from clastic sources the biochemical remanent magnetization may be the dominant process of magnetization acquisition

deep sea environments across the cretaceous paleogene boundary in the eastern south atlantic ocean odp leg 208 walvis ridge sediments recovered at odp site 1262 on walvis ridge eastern south atlantic ocean paleodepth 2500 3000 m offer an opportunity to look into the nature and cause s of the benthic foraminiferal turnover across the cretaceous paleogene k pg boundary at abyssal depths at a location relatively remote from the location of the asteroid impact on the yucatan peninsula late maastrichtian assemblages were diverse and heterogeneous reflecting oligo to mesotrophic conditions at the sea floor as at other locations there was no significant extinction of benthic foraminiferal species at the k pg boundary but the diversity and heterogeneity of the assemblages decreased precipitously the percentage of infaunal buliminid taxa decreased rapidly but the total percentage of infaunal taxa remained essentially unchanged benthic foraminiferal accumulation rates bfar dropped at the boundary itself and fluctuated strongly later in the danian after the k pg boundary opportunistic taxa increased in relative abundance and diversity and heterogeneity strongly fluctuated there thus is no clear agreement between three proxies which have been used to indicate a high food supply to the sea floor percentage buliminids percentage infaunal taxa and bfar this discrepancy might indicate that the food supply changed in character e g type of food temporal variability in flux but did not show a long term large net change in total amount the strong fluctuations in bfar heterogeneity and diversity indicate that environmental instability started at the k pg boundary and persisted through planktic foraminiferal zones p and p1a in lower planktic foraminiferal zone p1b agglutinated species of the genera spiroplectammina and clavulinoides thought to be infaunal and indicative of increasing levels of food supply increased in relative abundance while the relative abundance of buliminids remained low possibly agglutinated taxa took over at least part of the infaunal niche in the paleocene as a result of the rise in the calcium carbonate compensation depth towards the upper part of the studied interval lower planktic foraminiferal subzone 1c benthic foraminiferal assemblages stabilized with heterogeneity almost back to maastrichtian values although diversity and bfar did not fully recover

deep sea benthic foraminiferal recolonization of the 1991 mt pinatubo ash layer in the south china sea a census count of rose bengal stained benthic foraminifera from the surface area on top of a 2 to 6 cm thick ashfall layer at three deep water stations along the western margin of the philippines exhibits a unique assemblage composition of benthic foraminifera the total number of benthic foraminifera is low and the ratio of living individuals to empty tests is high specific diversity is low with a significant dominance of infaunal morphotypes including species of the genus reophax r scorpiurus r bilocularis and r dentaliniformis which are regarded as successful recolonizers assemblages below the ash layers are diverse and contain many epifaunal suspension feeding agglutinated and calcareous foraminifera the 1991 mt pinatubo eruption caused mass mortality of benthic foraminifera in a vast area of the eastern south china sea followed by step wise recolonization of the ash substrate three years after the eruption the benthic foraminiferal community structure is still far from recovery to background levels

precise determination of phanerozoic zircon pb pb age by multicollector sims without external standardization 1 zircon has long been recognized as the best geochronometer and the most important timekeeper in geosciences modern microbeam techniques such as sims and la icpms have been successfully applied to in situ u pb zircon age determinations at spatial resolutions of 20 30 m or less matrix matched calibration by external standardization of well characterized natural zircon references is a principal requirement for precise microbeam u pb zircon age determination due to fractionation effects between pb and u which usually result in an external age error exceeding 1 alternatively zircons with a closed u pb system can be directly dated by measurement of 207pb 206pb isotopic ratio without external standardization which has been a common practice for zircons older than 1 0 ga but not for relatively young 1 0 ga and particularly phanerozoic ones because of limitations of analytical precision we describe in this paper a method of 207pb 206pb measurement on phanerozoic zircons using a new generation of large radius magnetic sector multicollector cameca ims 1280 sims in combination with multicollector mode a nuclear magnetic resonance nmr magnet controller and oxygen flooding techniques we achieve precisions of 207pb 206pb ratio of 0 1 and 0 1 0 2 propagating to pb pb age errors 0 4 and 1 3 excluding u decay constant uncertainties for zircons of latest neoproterozoic and late paleozoic to mesozoic age respectively therefore the multicollector sims is capable of direct determination of zircon pb pb ages as young as mesozoic age with uncertainties of geological significance this technique is useful for direct dating of zircons in thin sections moreover it has significance for dating of some other u rich minerals i e baddeleyite and zirconolite that are not suitable for sims u pb dating by external standardization

k t boundary extinction geologically instantaneous or gradual event evidence from deep sea benthic foraminifera a stepped pattern of benthic foraminiferal decimation survival and recovery identified across the cretaceous tertiary k t boundary at caravaca southeast spain suggests that an exceptionally large influx of nutrients reached the sea floor suddenly at the time of the k t extinction event rapid reestablishment of pre k t boundary environmental conditions followed our data demonstrate a close coupling between the collapse of the ecologic system in the upper water column at caravaca and a correspondent decimation of bottom dwellers on the sea floor the dramatic environmental collapse of deep water benthic foraminiferal communities at the end of the cretaceous at caravaca suggests that the k t boundary event was geologically instantaneous and catastrophic

benthic foraminifera and environmental turnover across the cretaceous paleogene boundary at blake nose odp hole 1049c northwestern atlantic sediments recovered at lower bathyal odp site 1049 on blake nose northwestern atlantic offer an opportunity to study environmental changes at the cretaceous paleogene k p boundary relatively close to the chicxulub impact structure on the yucatan peninsula mexico in hole 1049c the boundary is located at the base of a 9 cm thick layer with abundant spherules considered to be impact ejecta uppermost maastrichtian oozes below and lowermost danian pelagic oozes above the spherulebed contain well preserved bathyal benthic foraminifera the spherule bed itself in contrast contains a mixture of shallow neritic and deeper bathyal species and specimens vary strongly in preservation this assemblage was probably formed by reworking and down slope transport triggered by the k p impact across the spherule bed i e the k p boundary only f7 of benthic foraminiferal species became extinct similar to the low extinction rates of benthic foraminifera worldwide quantitative analysis of benthic foraminiferal assemblages and morphogroups in the 63 am size fraction indicates a relatively eutrophic stable environment during the latest maastrichtian interrupted by a sudden decrease in the food supply to the benthos at the k p boundary and a decrease in diversity of the faunas followed by a stepped recovery during the earliest danian the recovery was probably linked to the gradual recovery of surface dwelling primary producers d 2004 elsevier b v all rights reserved

evidence and causes of the main extinction events in the paleogene based on extinction and survival patterns of foraminifera abstract we review the four main extinction events in the paleogene from the cretaceous paleogene boundary to the eocene oligocene boundary integrating the results obtained from a study of foraminiferal assemblages with other paleontological and geological data different survival strategies followed by the species are described and the duration of the phases of extinction survival and recovery is estimated the models and patterns of extinction of the foraminifera are highlighted we present a range of evidence and paleo environmental factors and analyze the possible causes of extinction a new terminology for mass extinction events is proposed sudden mass extinction would have happened virtually instantaneously and the process would have taken a few years or decades cretaceous paleogene boundary rapid mass extinction is defined as that which occurred in relatively short events around 100 kyr paleocene eocene and eocene oligocene boundaries slow mass extinctions are suggested to have lasted around 1 myr bartonian priabonian transition and may even have lasted for several million years

deep sea benthic foraminiferal recolonisation following a volcaniclastic event in the lower campanian of the scaglia rossa formation umbria marche basin central italy we studied the distribution of deep water agglutinated foraminiferal dwaf assemblages across a 15 cm thick volcaniclastic layer in the lower campanian scaglia rossa limestones of the umbria marche basin above the volcaniclastic layer which is devoid of foraminifera a remarkable pattern of recovery among dwaf has been observed the complete recovery of dwaf in terms of trophic groups and complexity of assemblages is observed in the first 5 cm above the volcaniclastic layer representing 4 8 kyr based upon the mean sedimentation rate of the campanian scaglia rossa formation in its initial stage the recovery pattern is remarkably similar to that observed following the 15 june 1991 mount pinatubo ashfall in the abyssal south china sea where various species of reophax a small organically cemented species of textularia and the calcareous species quinqueloculina seminula and bolivina difformis are the earliest recolonisers on top of the tephra layer such similarities between modern and fossil analogues strengthens the reliability of environmental reconstructions based on dwaf fl 2002 elsevier science b v all rights reserved

perturbation at the sea floor during the paleocene eocene thermal maximum evidence from benthic foraminifera at contessa road italy abstract detailed analyses of the benthic foraminiferal assemblages extracted with the cold acetolyse method together with high resolution geochemical and mineralogical investigations across the paleocene eocene p e boundary of the classical succession at contessa road western tethys allowed to recognize and document the paleocene eocene thermal maximum petm interval the position of the benthic extinction event bee and the early recovery of benthic faunas in the aftermath of benthic foraminiferal extinction the stratigraphical interval spanning the p e boundary consists of dominantly pelagic limestones and two prominent marly beds benthic foraminifera indicate that these sediments were deposited at lower bathyal depth not deeper than 1000 1500 m the carbon isotope excursion cie interval is characterized by high barite abundance with a peak at the base of the same stratigraphic interval indicating a complete although condensed record of the early cie a succession of events and changes in the taxonomic structure of benthic foraminifera has been recognized that may be of use for supra regional stratigraphic correlation across the p e boundary interval the composition of the benthic foraminiferal assemblages dominated by infaunal taxa indicates mesotrophic and changing conditions on the sea floor during the last 45 kyr of the paleocene the bee occurs at the base of the cie within the lower marly bed and it is recorded by the extinction of several deep water cosmopolitan taxa then the lysocline ccd rose and severe carbonate dissolution occurred preservation deteriorated the faunal density and simple diversity dropped to minimum values and a peak of glomospira spp has been observed stress tolerant and opportunistic groups represented mainly by bi and triserial taxa dominate the low diversity post extinction assemblages indicating a benthic foraminiferal recovery under environmental unstable conditions probably within a context of sustained food transfer to the bottom a three phase pattern of faunal recovery is recognizable at first the lysocline ccd started to descend and then recovered small sized bulimina oridorsalis umbonatus and tappanina selmensis rapidly repopulated the severely stressed environment later on siphogenerinoides brevispinosa massively returns dominating the assemblage together with other buliminids nuttallides truempyi and anomalinoides sp 1 finally a marked drop in abundance of s brevispinosa is followed by a bloom of the opportunistic and recolonizer agglutinated pseudobolivina that for the first time is recorded within the main cie a second interval of dissolution but less severe than the previous one has been recognized within the upper marly bed uppermost part of the main cie interval and it is interpreted as a renewed less pronounced shoaling of the lysocline ccd that interrupted the recovery of benthic faunas this further rise likely represents a response to persistent instability of ocean geochemistry in this sector of the tethys before the end of the cie in the cie recovery and post cie intervals the composition of the benthic foraminiferal assemblages suggests mesotrophic and unstable conditions at the sea floor according to the geochemical proxy for redox conditions the deposition of the petm sediments at contessa road occurred in well oxygenated waters leading out a widespread oxygen depletion as major cause of the bee changing oceanic productivity carbonate corrosivity and global warming appear to have played a much more important role in the major benthic foraminiferal extinction at the p e boundary

carbon isotope evidence for the timing of the cretaceous palaeogene macrobenthic colonisation at the agost section southeast spain abstract the cretaceous palaeogene k t boundary section of agost southeast spain one of the most complete sections existing contains a well developed trace fossil assemblage composed of dark and light filled trace fossils registered in the uppermost cretaceous maastrichtian plummerita hantkeninoides biozone sediments the trace fossil assemblage reveals that significant macrobenthic colonisation occurred around the k t boundary interval however difficulties in recognising trace fossils affecting the k t boundary layer as well as in biostratigraphically characterising these trace fossils hindered a conclusive interpretation on the timing of this macrobenthic colonisation with the aim of this characterisation we determined the 13c of the carbonate fraction of dark and light filling materials from the trace fossils since the carbon isotope compositions of uppermost cretaceous and lowermost palaeogene materials are clearly different the data compiled provide evidence for a significant distinction between light filled trace fossils with 13c values higher than 1 6 peedee belemnite pdb and dark filled trace fossils with 13c values between 0 21 and 1 2 pdb most of these being lower than 0 7 pdb the comparison of these values with those from the uppermost maastrichtian to the lowermost danian sediments reveals that the macrobenthic colonisation occurred in different phases across the k t boundary interval

a spike of woody plant biomarkers in the deep sea iridium layer at the cretaceous paleogene boundary abstract at the cretaceous paleogene k pg boundary 66 million years ago the chixulub impact resulted in significant environmental changes and a mass extinction of dinosaurs and marine invertebrates such as ammonites here we report that accumulation of woody plant biomarkers in the deep water occurred in the iridium anomaly at 700 km from the impact crater the results reveal that the concentration of terrestrial organic molecules derived from woody plants namely biphenyl and dibenzofuran shows synchronized changes and increases abruptly in the red layer fine ejecta which has an iridium spike above tsunami like coarse deposits indicating a significant increase in the influx of woody plant fragments into the ocean a few years after the impact long chain n alkanes and cadalene derived from land vegetation in the tsunami like coarse deposits prior to the transportation of trees were also transported to the deep sea this implies that transportation of grass to the deep sea started within a few days of the bolide impact transportation of trees then began a few years later a rapid increase in the concentration of dibenzothiophenes also occurs in the red layer indicating that low dissolved oxygen conditions had expanded in the bathypelagic zone over the seafloor an increase in the influx of terrestrial organic matter into the deep ocean could have resulted in the low dissolved oxygen conditions furthermore the stratigraphic distribution of planktonic foraminifera at beloc shows that cretaceous planktonic foraminifera became extinct as the result of an asteroid impact

benthic foraminiferal faunal turnover across the cretaceous tertiary boundary at agost southeastern spain paleoenvironmental inferences we studied upper cretaceous and lower paleogene benthic foraminifera from the agost section southeastern spain to infer paleobathymetrical changes and paleoenvironmental turnover across the cretaceous paleogene k p transition benthic foraminifera indicate uppermost bathyal depths at agost during the abathomphalus mayaroensis biochron from about 400 kyr before the k p boundary through the early plummerita hantkeninoides biochron about 120 150 kyr before that boundary the depth increased to middle bathyal for the remainder of the cretaceous and remained so for the danian part of the studied section parasubbotina pseudobulloides biochron at least 200 kyr after the k p boundary there were no perceivable bathymetrical changes at the k p boundary where v5 of the species became extinct and the species composition of the benthic foraminiferal fauna changed considerably below the boundary infaunal morphogroups constitute up to 65 73 of the faunas directly above the boundary in the black clays of the lower guembelitria cretacea biozone benthic foraminifera are rare several opportunistic taxa e g the agglutinant haplophragmoides sp have short peaks in relative abundance possibly reflecting low oxygen conditions as well as environmental instability with benthos receiving food from short lived local blooms of primary producers above the clays through the end of the studied interval epifaunal morphogroups dominate up to 70 of the assemblages or there is an even mixture or epifaunal and infaunal morphogroups infaunal groups do not recover to pre extinction relative abundances indicating that the food supply to the benthos did not recover fully over the studied interval about 200 kyr after the k p boundary the benthic foraminiferal faunal changes are compatible with the direct and indirect effects of an asteroid impact which severely destabilized primary producers and the oceanic food web that was dependent upon them 2003 elsevier science b v all rights reserved

zircon ages and nd isotopic and chemical compositions of orthogneisses from the black forest germany evidence for a cambrian magmatic arc single zircon u pb dating combined with 207pb 206pb ages obtained by the evaporation method constrains the emplacement of tonalitic trondhjemitic and granodioritic orthogneisses of the moldanubian zone in the black forest between 500 and 510 ma two detrital zircon populations of 1 9 and 1 6 ga indicate early middle proterozoic material in the former setting of the basement the initial end values range from 0 1 to 3 4 and mean crustal residence ages of 1 0 1 4 ga are consistent with involvement of early middle proterozoic crust and a subordinate juvenile component probably originating from subduction related melting of the mantle the orthogneisses have fractionated ree patterns and slightly higher k2o na2o ratios than typical low k tonalite trondhjemite granite suites the chemical data are interpreted as evidence for melting of amphibolite and contributions from evolved crust the emplacement of the orthogneisses was superceded by a high temperature metamorphic event at 480 ma which we interpret as a result of lithospheric thinning in a marginal basin behind a cambrian magmatic arc

the impact of the 1991 mt pinatubo eruption on deep sea foraminiferal communities a model for the cretaceous tertiary k t boundary the ash layer from the 1991 mt pinatubo eruption provided a natural laboratory to assess mass mortality and the rates of recovery of deep marine ecosystems after a catastrophic event and to draw a parallel with the environmental impact of the k t boundary event on deep sea foraminiferal communities the first recolonization assemblages of benthic foraminifers after the mt pinatubo ash fall exhibit surprising similarities with benthic foraminiferal communities established following the k t boundary event i e comparatively low abundance and diversity absence of suspension feeders dominance of mobile infaunal taxa and a high proportion of agglutinated foraminifers the first foraminifers to recolonize the deep sea after both catastrophic events were opportunistic forms with high capability for rapid dispersal however major differences are evident in the timing and duration of the faunal transitions post eruption assemblages with high proportions of epibenthic suspension feeders became established after a short initial recolonization phase of approx 6 7 years on the mt pinatubo ash layer in the k t sections comparatively stable new benthic foraminiferal assemblages including suspension feeders only became established several thousand years after the event delayed recovery of the pelagic ecosystem and poor deep water ventilation probably slowed down the recovery of the benthic community structure after the k t boundary c 2005 elsevier b v all rights reserved

the chesapeake bay bolide impact a convulsive event in atlantic coastal plain evolution abstract until recently cenozoic evolution of the atlantic coastal plain has been viewed as a subcyclical continuum of deposition and erosion marine transgressions alternated with regressions on a slowly subsiding passive continental margin their orderly succession modified mainly by isostatic adjustments occasional appalachian tectonism and paleoclimatic change this passive scenario was dramatically transformed in the late eocene however by a bolide impact on the inner continental shelf the resultant crater is now buried 400 500 m beneath lower chesapeake bay its surrounding peninsulas and the continental shelf east of delmarva peninsula this convulsive event and the giant tsunami it engendered fundamentally changed the regional geological framework and depositional regime of the virginia coastal plain and produced the following principal consequences 1 the impact excavated a roughly circular crater twice the size of rhode island 6400 km2 and nearly as deep as the grand canyon 1 3 km deep 2 the excavation truncated all existing ground water aquifers in the target area by gouging 4300 km3 of rock from the upper lithosphere including proterozoic and paleozoic crystalline basement rocks and middle jurassic to upper eocene sedimentary rocks 3 synimpact depositional processes including ejecta fallback massive crater wall failure water column collapse and tsunami backwash filled the crater with a porous breccia lens 600 1200 m thick at a phenomenal rate of 1200 m hr the breccia lens replaced the truncated ground water aquifers with a single 4300 km3 reservoir characterized by ground water 1 5 times saltier than normal sea water chlorinities as high as 25 700 mg l 4 a structural and topographic low created by differential subsidence of the compacting breccia persisted over the crater at least through the pleistocene in the depression are preserved postimpact marine lithofacies and biofacies upper eocene lower oligocene lower miocene not known elsewhere in the virginia coastal plain 5 long term differential compaction and subsidence of the breccia lens spawned extensive fault systems in the postimpact strata many of these faults appear to reach the bay floor and may be potential hazards for motion sensitive structures in population centers around chesapeake bay near surface fracturing and faulting generated by the impact shock may extend as far as 90 km from the crater rim 6 having never completely filled with postimpact sediments the sea floor depression over the crater appears to have predetermined the location of chesapeake bay 7 as large impact craters are principal sources for some of the world s precious metals it is reasonable to expect that metal enriched sills dikes and melt sheets are present in the inner basin of the crater in addition to these specific consequences the crater and the convulsive event that produced it have widespread implications for traditional interpretations of certain structural and depositional features of the atlantic coastal plain particularly in southeastern virginia

deep sea environments across the cretaceous paleogene boundary in the eastern south atlantic ocean sediments recovered at odp site 1262 on walvis ridge eastern south atlantic ocean paleodepth 2500 3000 m offer an opportunity to look into the nature and cause s of the benthic foraminiferal turnover across the cretaceous paleogene k pg boundary at abyssal depths at a location relatively remote from the location of the asteroid impact on the yucatan peninsula late maastrichtian assemblages were diverse and heterogeneous reflecting oligoto mesotrophic conditions at the sea floor as at other locations there was no significant extinction of benthic foraminiferal species at the k pg boundary but the diversity and heterogeneity of the assemblages decreased precipitously the percentage of infaunal buliminid taxa decreased rapidly but the total percentage of infaunal taxa remained essentially unchanged benthic foraminiferal accumulation rates bfar dropped at the boundary itself and fluctuated strongly later in the danian after the k pg boundary opportunistic taxa increased in relative abundance and diversity and heterogeneity strongly fluctuated there thus is no clear agreement between three proxies which have been used to indicate a high food supply to the sea floor percentage buliminids percentage infaunal taxa and bfar this discrepancy might indicate that the food supply changed in character e g type of food temporal variability in flux but did not show a long term large net change in total amount the strong fluctuations in bfar heterogeneity and diversity indicate that environmental instability started at the k pg boundary and persisted through planktic foraminiferal zones p and p1a in lower planktic foraminiferal zone p1b agglutinated species of the genera spiroplectammina and clavulinoides thought to be infaunal and indicative of increasing levels of food supply increased in relative abundance while the relative abundance of buliminids remained low possibly agglutinated taxa took over at least part of the infaunal niche in the paleocene as a result of the rise in the calcium carbonate compensation depth towards the upper part of the studied interval lower planktic foraminiferal subzone 1c benthic foraminiferal assemblages stabilized with heterogeneity almost back to maastrichtian values although diversity and bfar did not fully recover 2006 elsevier b v all rights reserved

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

shelf hypoxia in response to global warming after the cretaceous paleogene boundary impact the chicxulub asteroid impact at the cretaceous paleogene k pg boundary resulted in one of the most abrupt global warming events in the past 100 m y presenting an analogue to current global warming here we present high resolution geochemical micropaleontological and palynological records of the brazos 1 texas usa stevns klint denmark and caravaca spain k pg boundary sections to assess the rapid environmental changes during the global warming following the brief k pg boundary impact winter warming during the first millennia after the impact is associated with hypoxic bottom waters at the studied shelf sites as indicated by molybdenum enrichments causing major stress for benthic communities we attribute this decline in dissolved oxygen to a combination of decreased gas solubility and ocean ventilation resulting from the warming of the sea water and increased oxygen demand in shelf bottom waters due to increased nutrient inputs and associated high productivity

geochemistry and petrogenesis of 270 ma ni cu pge sulfide bearing mafic intrusions in the huangshan district eastern xinjiang northwest china implications for the tectonic evolution of the central asian orogenic belt abstract the central asian orogenic belt caob is composed of remnants of microcontinents island arcs and ophiolites the presence of voluminous phanerozoic a type granites suggest that continental growth occurred through addition of juvenile crust and the presence of mafic ultramafic intrusions provides direct evidence for a mantle contribution the origin of the mafic ultramafic intrusions in the huangshan area eastern xinjiang has been debated because of the lack of precise age data or trace element and isotopic analyses we have studied the geology petrology geochemistry and geochronology of two of the intrusions the huangshanxi and huangshandong intrusions both are typical layered mafic ultramafic intrusions composed of diorite troctolite norite gabbronorite gabbro wehrlite websterite and lherzolite with systematic geochemical variations that are consistent with the following crystallization sequence ol chr ol pyx chr cpx pl and hbl bt igneous zircons separated from a diorite in the huangshanxi intrusion yield a 269 2 ma shrimp u pb age the rocks are enriched in rb ba u k sr relative to th and lree depleted in nb ta relative to th and exhibit positive end values 6 7 to 9 3 ni cu pge sulfide mineralization occurs in the lower parts of the intrusions primarily strata bound within wehrlite or lherzolite and locally stratiform along the margins of the intrusions the parental magmas appear to have been derived from a mantle source that was previously contaminated by subduction of oceanic crust and to have been variably contaminated by upper continental crustal components the intrusions appear to have formed by plume related activity within a continental setting likely related to post orogenic extension following carboniferous amalgamation of arc related terranes in the caob this plume activity was most likely also responsible for providing heat sources to generate large amounts of a type granites across the caob

food supply to the seafloor in the pacific ocean after the cretaceous paleogene boundary event article i nfo deep sea benthic foraminifera show important but transient assemblage changes at the cretaceous paleogene k pg boundary when many biota suffered severe extinction we quantitatively analyzed benthic foraminiferal assemblages from lower bathyal upper abyssal 1500 2000 m northwest pacific odp site 1210 shatsky rise and compared the results with published data on assemblages at lower bathyal 1500 m pacific dsdp site 465 hess rise to gain insight in paleoecological and paleoenvironmental changes at that time at both sites diversity and heterogeneity rapidly decreased across the k pg boundary then recovered species assemblages at both sites show a similar pattern of turnover from the uppermost maastrichtian into the lowermost danian 1 the relative abundance of buliminids indicative of a generally high food supply increases towards the uppermost cretaceous and peaks rapidly just above the k pg boundary coeval with a peak in benthic foraminiferal accumulation rate bfar a proxy for food supply 2 a peak in relative abundance of stensioeina beccariiformis a cosmopolitan form generally more common at the middle than at the lower bathyal sites occurs just above the buliminid peak 3 the relative abundance of nuttallides truempyi a more oligotrophic form decreases at the boundary then increases above the peak in stensioeina beccariiformis the food supply to the deep sea in the pacific ocean thus apparently increased rather than decreased in the earliest danian the low benthic diversity during a time of high food supply indicates a stressed environment this stress might have been caused by reorganization of the planktic ecosystem primary producer niches vacated by the mass extinction of calcifying nannoplankton may have been rapidly b10 kyr filled by other possibly opportunistic primary producers leading to delivery of another type of food and or irregular food delivery through a succession of opportunistic blooms the deep sea benthic foraminiferal data thus are in strong disagreement with the widely accepted hypothesis that the global deep sea floor became severely food depleted following the k pg extinction due to the mass extinction of primary producers strangelove ocean model or to the collapse of the biotic pump living ocean model

ichnological analysis of the cretaceous palaeogene boundary interval at the caravaca section se spain abstract ichnological analysis of the cretaceous palaeogene k pg boundary at caravaca betic cordillera southeast spain reveals significant data for the interpretation of the k pg boundary event the uppermost maastrichtian marls below the cretaceous palaeogene k pg boundary at caravaca contains the dark coloured trace fossils chondrites targionii planolites thalassinoides zoophycos and alcyonidiopsis the composition of trace fossil associations in the upper maastrichtian and lower danian marls is generally the same yet much more poorly preserved in the latter showing in general no ichnological evidence of a severe macroinfaunal crisis at the k pg boundary the dark coloured trace fossils penetrate from two bioturbated horizons in the dark boundary layer separated by two horizons with primary lamination the ichnofauna rapidly recovered after the k pg event following deposition of the lower parallel laminated bed 14 mm thick that occurs in the dark boundary layer above the k pg boundary zoophycos is the deepest trace fossil penetrating as far as 90 cm below the k pg boundary probably in stiff or partly firm substrate which was dewatered to some extent during the slow accumulation of the danian dark boundary layer the firmness probably prevented the chondrites trace maker from deeper burrowing the maastrichtian sediments may be contaminated with danian microfossils due to bioturbation

the cretaceous tertiary biotic transition mass extinctions are recognized through the study of fossil groups across event horizons and from analyses of long term trends in taxonomic richness and diversity both approaches have inherent flaws and data that once seemed reliable can be readily superseded by the discovery of new fossils and or the application of new analytical techniques herein the current state of the cretaceous tertiary k t biostratigraphical record is reviewed for most major fossil clades including calcareous nannoplankton dinoflagellates diatoms radiolaria foraminifera ostracodes scleractinian corals bryozoans brachio pods molluscs echinoderms fish amphibians reptiles and terrestrial plants macrofossils and palynomorphs these reviews take account of possible biasing factors in the fossil record in order to extract the most comprehensive picture of the k t biotic crisis available results suggest that many faunal and floral groups ostracodes bryozoa ammonite cephalopods bivalves archosaurs were in decline throughout the latest maastrichtian while others diatoms radiolaria benthic foraminifera brachiopods gastropods fish amphibians lepidosaurs terrestrial plants passed through the k t event horizon with only minor taxonomic richness and or diversity changes a few microfossil groups calcareous nannoplankton dinoflagellates planktonic foraminifera did experience a turnover of varying magnitudes in the latest maastrichtian earliest danian however many of these turnovers along with changes in ecological dominance patterns among benthic foraminifera began in the latest maastrichtian improved taxonomic estimates of the overall pattern and magnitude of the k t extinction event must await the development of more reliable systematic and phylogenetic data for all upper cretaceous clades

the cretaceous palaeogene k p boundary at ain settara tunisia restructuring of benthic foraminiferal assemblages benthic foraminiferal assemblages in contrast to planktic foraminifera generally did not suffer mass extinctions at the cretaceous palaeogene k p boundary extinctions were fewer in deeper water however the outer shelf upper bathyal section at ain settara tunisia records a dramatic change in the structure of benthic foraminiferal assemblages across the k p boundary at the level of extinction of planktic assemblages and enrichment in ir and other geochemical anomalies highly diversified low dominance upper maastrichtian assemblages with infaunal and epifaunal morphogroups were suddenly replaced by taxonomically impoverished assemblages strongly dominated by epifaunal morphogroups this extinction or temporary emigration of most infaunal morphogroups is interpreted to be the result of a sudden breakdown in food supply this in turn is the consequence of a sudden collapse in primary productivity probably resulting from the impact of the k p asteroid

genesis of post collisional granitoids and basement nature of the junggar terrane nw china nd sr isotope and trace element evidence the post collisional magmatism of the junggar terrane is characterized by intrusion of large amounts of granitoids and minor basic ultrabasic rocks the granitoids comprise two magmatic suites calc alkaline and alkaline which were emplaced contemporaneously at about 294 ma the calc alkaline rocks are typically sodium rich na2o k2o 1 1 3 5 and metaluminous a nk 1 0 a cnk 0 78 1 04 they show mildly fractionated ree patterns la yb n 15 and spidergrams with strong depletion of nb ti and to a lesser extent sr the alkaline granites have high contents of sio2 75 78 alkalis nb hree y sn f and high feo mgo ratios and huge sr and eu depletion in the spidergrams moreover they display characteristic tetrad ree patterns and non charac trace element behaviour the two rock suites have similar initial nd and sr isotopic compositions with end t in the range 5 2 to 7 1 and isr mostly in the range 0 7031 0 7041 this points to a predominance of juvenile components in their sources the calc alkaline rocks are most probably derived by dehydration melting of a basic lower crust leaving behind a granulite residue the process was probably triggered by underplating of mantle derived basic magmas in an extensional regime the alkaline granites are considered to have formed by differentiation of the calc alkaline granitoids our study argues for a juvenile continental crust for the basement of the junggar terrane which is likely dominated by early paleozoic oceanic crust and arc complex that were deeply buried during the late paleozoic subduction and accretion

abrupt and massive influx of terrestrial biomarkers into the marine environment at the cretaceous tertiary boundary caravaca spain the mass extinction at the cretaceous tertiary k t boundary ca 65 million years ago caused a major change in the nature and abundance of global life in earth history we present the first vertical high resolution records of molecular distributions of n fatty acids across the k t boundary at caravaca spain the results reveal that the first basal thin horizon 0 to 0 5 cm 0 k t boundary of the k t boundary clay layer showed as much as a 35 fold increase in concentrations of terrestrial longchain n fatty acids zc20 representative of an eight fold increase in mass accumulation rate compared with the subjacent cretaceous layers thereafter concentrations rapidly declined back to almost pre boundary values within 3 cm above the k t boundary the abrupt increase in supply of terrestrial organic matter into the marine environment at the k t boundary could have been caused by an enhanced riverine flux probably due to heavy rains associated with global warming combined with enhanced fragments of terrestrial higher plants withered by acid rain and or by temporal darkness and cooling d 2005 elsevier b v all rights reserved

geochronology geochemistry and petrogenesis of early permian alkaline magmatism in the eastern tianshan implications for tectonics of the southern altaids abstract in the early permian large volumes of volcanic rocks developed in the eastern tianshan of the southern altaids the shaerhu alkaline complex which occurs along a nw trending transcurrent fault in the dananhu arc is composed of alkaline gabbro intrusions granites and rhyolites the gabbros and rhyolites have similar zircon crystallization ages of 286 5 2 1 ma and 286 7 2 1 ma respectively the granitic and rhyolitic rocks have typical a type granite geochemical signatures i e high oxide ratios in wt k2o na2o k2o na2o cao k2o mgo and sio2 high trace element values zr nb ga ce y and ree and high zr ce y and 10 000 ga al ratios however spidergrams and ree patterns indicate major depletions in ba sr p ti and eu the presence of positive end t values of 7 0 to 11 2 and low 87sr 86sr i 0 70148 0 70416 indicates that these alkaline rocks were derived from a depleted mantle and not from old continental crust the geochemical characters indicate that the rocks of the complex have the same source and that fractionation was important in their generation a type granitic rocks are the most highly fractionated of alkaline basic rocks in summary the shaerhu complex is a product of mantle derived alkaline magma fractionation which is one of the main mechanisms of a type granite genesis the felsic rocks of the shaerhu complex have the geochemical signature of an a2 type granite and thus were not derived from a rift or mantle plume in the early permian oblique subduction in the southern altaids gave rise to strike slip extensional faults which controlled the emplacement of large volumes of mantle derived melts

benthic foraminifera at the cretaceous tertiary boundary around the gulf of mexico cretaceous tertiary k t boundary sections in northeastern mexico contain marly formations separated by a controversial clastic unit benthic foraminifera in seven sections indicate middle and lower bathyal depths of deposition for the marls with the exception of the upper bathyal northernmost section mixed neritic bathyal faunas were present in the clastic unit indicating redeposition in the deep basin by mass wasting processes resulting from the k t bolide impact in the gulf of mexico benthic foraminifera in the mexican sections and at other deep sea locations were not subject to major extinction at the time of impact but there were temporary changes in assemblage composition benthic faunas indicate welloxygenated bottom waters and mesotrophic conditions during the late maastrichtian and increased food supply during the latest maastrichtian the food supply decreased drastically just after the k t boundary possibly because of the collapse of surface productivity cretaceous and early paleogene benthic foraminifera however did not exhibit the benthic pelagic coupling of present day faunas as documented by the lack of significant extinction at the k t collapse of surface productivity much of the food supplied to the benthic faunas along this continental margin might have been refractory material transported from land or shallow coastal regions the decrease in food supply at the k t boundary might be associated with the processes of mass wasting which removed surface food rich sediment benthic faunas show a staggered pattern of faunal recovery in the lowermost paleogene consistent with a staged recovery of the vertical organic flux but also with a gradual buildup of organic matter in the sediment

paleozoic accretion and cenozoic redeformation of the chinese tien shan range central asia the tien shan range in central asia contains two late paleozoic sutures the older southern suture marks the collision of a passive margin at the north of the tarim block and an active continental margin subduction under the latter was to the north the younger northern suture separates a northern carboniferous island arc from an active continental margin developed over a south dipping subduction zone the subduction direction under the island arc is unknown mesozoic elastics were deposited over the doubly sutured orogen rate and energy of sedimentation waned until deposition of oligocene conglomerates above a regional unconformity interpreted as marking the onset of deformation induced by the india asia collision molasse deposition accelerated in pliocene and quaternary time and deposition continues today as active thrusts generate relief paleozoic structures control the gross divergence of cenozoic thrusts across the orogen

recovery of the deep sea floor after the cretaceous paleogene boundary event the benthic foraminiferal record in the basque cantabrian basin and in south eastern spain abstract a detailed analysis of the upper cretaceous and lower paleogene benthic foraminiferal assemblages 63 m from the middle bathyal loya section basque cantabrian basin southwestern france has been carried out the benthic foraminiferal and palaeoenvironmental turnover across the k pg boundary at loya has been compared to that observed in the nearby bidart section both sections exhibit mesotrophic conditions in the uppermost maastrichtian and a drastic decrease in the nutrient supply to the sea floor in coincidence with the k pg boundary moreover a faunal recovery of the assemblages is observed through the lowermost danian the pattern of faunal and palaeoenvironmental recovery in the basque cantabrian basin has been compared to that observed in the middle bathyal agost and caravaca sections south eastern spain where a similar decrease in the food supply to the sea floor is observed in coincidence with the k pg boundary however whereas low oxygen conditions have been recorded in the lowermost danian in these two sections no evidence for oxygen deficiency has been found in the basque cantabrian basin thus pointing to the regional and not global nature of low oxygen conditions following the k pg boundary event benthic foraminifera from the g cretacea biozone suggest environmental instability in the basque cantabrian basin and in southeastern spain such environmental stress has been related not only to the collapse of the food web due to the extinction of calcareous primary producers but also to a rapidly changing food supply driven by phytoplankton blooms although stabilization of the ecosystems in surface waters probably occurred towards the upper part of the g cretacea biozone data available from the ps pseudobulloides biozone at bidart and agost indicate that food supply to the benthos had not completely recovered at least 200 kyr after the k pg boundary

a type granites in northeastern china age and geochemical constraints on their petrogenesis abstract a type granites are widely distributed in northeastern china ne china they were emplaced during three major episodes the permian late triassic to early jurassic and early cretaceous and evolved in different tectonic regimes according to their mineralogical and geochemical characteristics two subgroups of a type granites aluminous and peralkaline can be recognized the peralkaline subgroup contains alkali mafic minerals such as riebeckite arfvedsonite and sodic pyroxene while the aluminous subgroup contains annite and fe rich calcic or sodic calcic amphibole with respect to the aluminous subgroup the peralkaline granites contain higher rb ga and total rare earth elements ree but lower mgo cao al 2 o 3 ba and sr based on the discrimination criteria of eby geology 20 1992 641 the permian and late triassic to early jurassic a type granites belong to the a 2 post orogenic type whereas the early cretaceous granites are of the a 1 anorogenic type nd isotopic compositions of these a type granites indicate their derivation from a dominantly juvenile crustal source their origin is thought to have involved partial melting of an underplated lower crustal source because the generation of a type granites requires high melting temperature we propose models involving slab break off lithospheric delamination and extension the permian a type granites have the same age range as those in eastern junggar southern mongolia and central inner mongolia they occur along a major suture and form a narrow belt between the north china and siberian cratons we suggest that their formation was associated with post collisional slab break off the late triassic to early jurassic a type granites are likely to be the product of lithospheric delamination after the final collision of the major crustal blocks in the late paleozoic to early triassic the early cretaceous a type granites have an anorogenic affinity and were possibly associated with rifting in eastern china at this time associated with the onset of paleo pacific subduction consequently we conclude that the a type granites in ne china were generated at three different times involving multiple processes operative in different tectonic environments