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Sample records for cretaceous-tertiary k-t boundary

  1. Astronomical age of the Cretaceous-Tertiary (K-T) Boundary

    NASA Astrophysics Data System (ADS)

    Runnegar, B.; Varadi, F.; Jgi, P.; Ghil, M.

    2007-12-01

    Recent refinements of models for the motions of the planets, including the Earth-Moon system, have led to the realization that the calculated cyclical changes in Earth's orbital eccentricity may be approximately correct for the whole of the Cenozoic. This raises the possibility of an astronomically-tuned geological timescale that extends to, and perhaps beyond, the Cretaceous-Tertiary (K-T) boundary. In order to test the validity of these long numerical integrations, we compare calculations of Earth's orbital eccentricity 62-67 million years (Ma) ago with a well-documented succession of basinal limestones and marlstones at Zumaia in the Basque region of Spain. Previous work has shown that each limestone-marlstone couplet records one axial precession cycle (~21 ka). An obvious bundling of couplets defines 36 "short" (~100-ka) eccentricity cycles between a carbonate-rich interval, used previously to tie the Zumaia section to our calculations, and the K-T boundary. If we assume an uninterrupted succession of couplets, each 20.8 ka in duration, and step the amplitudes of the time series according to the color (white, pink, or red) of the carbonates, we retrieve a strong 102-ka eccentricity signal with spectral analysis. This permits other ties to be made between prominent features of the calculated time series and the observed rock record. On this basis, the K-T boundary is >65.83 or >65.84 Ma using the ~100 ka cycles, >65.88 Ma using the 20.8-ka precessional cycles, and ?65.95 Ma using the metronomic 406-ka eccentricity cycle line frequency, all significantly older than the current consensus age of 65.5 Ma.

  2. An extended Cretaceous-Tertiary (K/T) stable isotope record. Implications for paleoclimate and the nature of the K/T boundary event

    NASA Technical Reports Server (NTRS)

    Dhondt, Steven

    1988-01-01

    In order to obtain a detailed single site record of marine productivity and temperature across the Cretaceous-Tertiary (K/T) boundary, both delta C-13 and delta O-18 values were measured in paired surface and deep water microfossil and nannofossil samples of mid-latitude South Atlantic Deep Sea Drilling Project (DSDP) Site 528. Additionally, the percent sedimentary carbonate content of the rock samples from which the analyzed fossil samples were taken, were determined. The analyzed interval spanned the last approximately 1 million years of the Cretaceous (the Abathomphalus mayaroensis foraminiferal zone) and the first approximately 9 million years of the Tertiary (the Paleocene). Paired samples were analyzed every 150 cm of the entire 165 m sampled interval (1 sample per recovered DSDP section), every 20 cm for 2.0 m below and 2.5 m above the K/T boundary, and every 0.25 cm immediately below, at, and above the K/T boundary clay. The Cretaceous-Tertiary boundary and earliest Paleocene record of DSDP Site 528 is marked by at least two strong decreases in the surface-to-deep delta C-13 gradient (one at the K/T boundary (66.4 mybp1) and one approximately 150,000 to 200,000 years later). Both of these decreases co-occur with radical decreases in percent carbonate content and appear to indicate not one, but two, strong decreases in marine primary productivity during the analyzed interval.

  3. Impact and extinction signatures in complete Cretaceous-Tertiary (K-T) boundary sections

    NASA Technical Reports Server (NTRS)

    Smit, J.; Groot, H.; Dejonge, R.; Smit, P.

    1988-01-01

    The Zumaya, Caravaca and Agost sections in Spain, the El Kef section in Tunisia and the Negev (Nahal Avdat) sections in Israel are among the most continuous, expanded and complete K-T boundary sections. The distribution patterns of the planktic faunas were quantitatively analyzed in closely spaced samples across the K-T boundary in these sections, in conjuction with the geochemistry, stable isotopes, mineralogy and magnetostratigraphy. Three hundred foraminiferal specimens were randomly selected and determined. Reliable estimates for the foraminiferal productivity changes across the K-T boundary and for the 1 to 2 Ma interval preceding the K-T boundary were made from the numbers of individuals/gram of sediment corrected for the sedimentation rates (calculated from magnetic reversals and lithology). No gradual or stepwise extinction is seen below the K-T boundary nor any productivity decrease. Stable isotope analyses show a warming just after deposition of the ejecta layer, not cooling as predicted by nuclear winter scenarios, although the duration of such cooling may be too short to be observed even in these complete sections. Low REE values and cpx spherules with quench textures idential to quench-textures in diagenetically altered spherules, strongly indicate an oceanic site of (one of) the impactor(s).

  4. The Cretaceous/Tertiary (K/T) boundary: 25 Years of controversial discussion

    NASA Astrophysics Data System (ADS)

    Harting, M.; Wittler, F. A.

    2006-05-01

    The K/T transition is under geoscientific focus since many years. Ever since the discovery of the Chicxulub- Impact theory in the early 1980s, its ctrater and its subsurface structure in the late 1990s many scientists and media, Hollywood, and the general public have become convinced that a large meteorite caused the K/T boundary and killed the dinosaurs and other organisms in the late Maastrichtian. However, today a much more comprehensive and detailed scientific background is present. Many scientist today believe that there is doubt that the Chicxulub impact is the "smoking gun". Moreover, there is increasing evidence that the Chicxulub impact predates the K/T mass extinction by about 300.000 years and did not cause the end of the dinosaures or of other marine and terrestrial organisms. On the other hand, some scientist still fixed to the general theory of a catastropic event. Due to recent field work on highly important sites and drillings inside the Chicxulub Impact structure itself, major new results are present today. In general, these new evidence, such as multiple ejecta layer, in locations in the Gulf of Mexico, the Caribbean, the Tethys and beyond, could not be interpreted by secondary (e.g. sedimentological-) features (slumping, reworking). Unfortunately, due to the highly emotional and controversal discussion - sometimes more like a religious than a scientific fight - many scientist feel uncomfortable to join the K/T problem. In fact, in between only a couple of major groups in various Universities are focussed - and leading - the discussion. A more open interaction between various geoscientific disciplines and researcher may the key to solve the mystery of the Chicxulub Impact and its relation to the K/T boundary.

  5. Carbon isotopic compositions of organic matter across continental Cretaceous-Tertiary (K-T) boundary sections: Implications for paleoenvironment after the K-T impact event

    USGS Publications Warehouse

    Maruoka, T.; Koeberl, C.; Bohor, B.F.

    2007-01-01

    To assess the environmental perturbation induced by the impact event that marks the Cretaceous-Tertiary (K-T) boundary, concentrations and isotopic compositions of bulk organic carbon were determined in sedimentary rocks that span the terrestrial K-T boundary at Dogie Creek, Montana, and Brownie Butte, Wyoming in the Western Interior of the United States. The boundary clays at both sites are not bounded by coals. Although coals consist mainly of organic matter derived from plant tissue, siliceous sedimentary rocks, such as shale and clay, may contain organic matter derived from microbiota as well as plants. Coals record ??13C values of plant-derived organic matter, reflecting the ??13C value of atmospheric CO2, whereas siliceous sedimentary rocks record the ??13C values of organic matter derived from plants and microbiota. The microbiota ??13C value reflects not only the ??13C value of atmospheric CO2, but also biological productivity. Therefore, the siliceous rocks from these sites yields information that differs from that obtained previously from coal beds. Across the freshwater K-T boundary at Brownie Butte, the ??13C values decrease by 2.6??? (from - 26.15??? below the boundary clay to - 28.78??? above the boundary clay), similar to the trend in carbonate at marine K-T sites. This means that the organic ??13C values reflect the variation of ??13C of atmospheric CO2, which is in equilibrium with carbon isotopes at the ocean surface. Although a decrease in ??13C values is observed across the K-T boundary at Dogie Creek (from - 25.32??? below the boundary clay to - 26.11??? above the boundary clay), the degree of ??13C-decrease at Dogie Creek is smaller than that at Brownie Butte and that for marine carbonate. About 2??? decrease in ??13C of atmospheric CO2 was expected from the ??13C variation of marine carbonate at the K-T boundary. This ??13C-decrease of atmospheric CO2 should affect the ??13C values of organic matter derived from plant tissue. As such a decrease in ??13C value was not observed at Dogie Creek, a process that compensates the ??13C-decrease of atmospheric CO2 should be involved. For example, the enhanced contribution of 13C-enriched organic matter derived from algae in a high-productivity environment could be responsible. The ??13C values of algal organic matter become higher than, and thus distinguishable from, those of plant organic matter in situations with high productivity, where dissolved HCO3- becomes an important carbon source, as well as dissolved CO2. As the ??13C-decrease of atmospheric CO2 reflected a reduction of marine productivity, the compensation of the ??13C decrease by the enhanced activity of the terrestrial microbiota means that the microbiota at freshwater environment recovered more rapidly than those in the marine environment. A distinct positive ??13C excursion of 2??? in the K-T boundary clays is superimposed on the overall decreasing trend at Dogie Creek; this coincides with an increase in the content of organic carbon. We conclude that the K-T boundary clays include 13C-enriched organic matter derived from highly productive algae. Such a high biological productivity was induced by phenomena resulting from the K-T impact, such as nitrogen fertilization and/or eutrophication induced by enhanced sulfide formation. The high productivity recorded in the K-T boundary clays means that the freshwater environments (in contrast to marine environments) recovered rapidly enough to almost immediately (within 10??yr) respond to the impact-related environmental perturbations. ?? 2006 Elsevier B.V. All rights reserved.

  6. The Manson impact structure, a possible site for a Cretaceous-Tertiary (K-T) boundary impact

    NASA Technical Reports Server (NTRS)

    Hartung, J. B.; Kunk, M. J.; Anderson, R. R.

    1988-01-01

    The Manson impact structure, about 35 km in diameter, is the largest impact crater recognized in the United States. Its center is located near the town of Manson, 29 km west of Fort Dodge, Iowa. The structure is not well known geologically because it is covered by tens of meters of glacial deposits. What is known about the structure was learned mostly from the study of water well cuttings. At Manson the normal Phanerozoic and Proterozoic sedimentary rocks were replaced by centrally uplifted Proterozoic crystalline rocks that are representative of the normal basement: This central uplift is surrounded by completely disrupted rocks which are roughly encircled by peripherally faulted and slumped sequences of normal sedimentary strata. Radially outward normal sedimentary strata are uplifted slightly. Manson, once interpreted as a cryptovolcanic structure, is now considered an impact structure based on its circular shape, its central uplift and the presence of multiple intersecting sets of shock lamellae in quartz grains from the central uplift. The Ar-40/Ar-39 age spectrum dating results for a microcline separate from the Manson 2-A core in the central uplift is shown. This spectrum is interpreted to indicate a nearly complete degassing of the microcline at the time of the Manson impact. The remainder of the gas released climbs in age with increasing temperature of release. This pattern of the age spectrum is interpreted to represent diffusional loss due to reheating at the time of the impact and during subsequent cooling. Shocked quartz grains, present in the iridium-bearing layer at the K-T boundary throughout the world, have a significantly larger size and are more abundant in the western interior of North America than elsewhere in the world. Furthermore, shocked feldspar and granitic fragments are found at the K-T boundary in North America. These observations indicate the K-T boundary impact must have penetrated continental crust in North America.

  7. The Cretaceous-Tertiary (K/T) impact: One or more source craters?

    NASA Technical Reports Server (NTRS)

    Koeberl, Christian

    1992-01-01

    The Cretaceous-Tertiary (K/T) boundary is marked by signs of a worldwide catastrophe, marking the demise of more than 50 percent of all living species. Ever since Alvarez et al. found an enrichment of IR and other siderophile elements in rocks marking the K/T boundary and interpreted it as the mark of a giant asteroid (or comet) impact, scientists have tried to understand the complexities of the K/T boundary event. The impact theory received a critical boost by the discovery of shocked minerals that have so far been found only in association with impact craters. One of the problems of the K/T impact theory was, and still is, the lack of an adequate large crater that is close to the maximum abundance of shocked grains in K/T boundary sections, which was found to occur in sections in Northern America. The recent discovery of impact glasses from a K/T section in Haiti has been crucial in establishing a connection with documented impact processes. The location of the impact-glass findings and the continental nature of detritus found in all K/T sections supports at least one impact site near the North American continent. The Manson Impact Structure is the largest recognized in the United States, 35 km in diameter, and has a radiometric age indistinguishable from that of the Cretaceous-Tertiary (K/T) boundary. Although the Manson structure may be too small, it may be considered at least one element of the events that led to the catastrophic loss of life and extinction of many species at that time. A second candidate for the K/T boundary crater is the Chicxulub structure, which was first suggested to be an impact crater more than a decade ago. Only recently, geophysical studies and petrological (as well as limited chemical) analyses have indicated that this buried structure may in fact be of impact origin. At present we can conclude that the Manson crater is the only confirmed crater of K/T age, but Chicxulub is becoming a strong contender; however, detailed geochemical, geochronological, and isotopic data are necessary to provide definitive evidence.

  8. The Western North American Cretaceous-Tertiary (K-T) boundary interval and its content of shock-metamorphosed minerals: Implications concerning the K-T boundary impact-extinction theory

    NASA Technical Reports Server (NTRS)

    Izett, G. A.

    1988-01-01

    At 20 sites in the Raton Basin of Colorado and New Mexico, and at several other sites in Wyoming, Montana, and Canada, a pair of claystone units, an Ir abundance anomaly, and a concentration of shock-metamorphosed minerals mark the palynological K-T boundary. The K-T boundary claystone, which is composed of kaolinite and small amounts of illite/smectite mixed-layer clay, is similar in most respects to kaolinite tonstein layers in coal beds. At some, but not all, K-T boundary localities, the boundary claystone contains solid kaolinite and hollow and solid goyazite spherules, 0.05 to 1.2 mm in diameter. The upper unit, the K-T boundary impact layer, consists chiefly of kaolinite and various amounts of illite/smectite mixed-layer clay. The impact layer and boundary claystone are similar chemically, except that the former has slightly more Fe, K, Ba, Cr, Cu, Li, V, and Zn than the latter. The facts that the boundary claystone and impact layer contain anomalous amounts of Ir, comprise a stratigraphic couplet at Western North American sites, and form thin, discrete layers, similar to air-fall units (volcanic or impact), suggest that the claystone units are of impact origin. Significantly, the impact layer contains as much as 2 percent clastic mineral grains, about 30 percent of which contain multiple sets of shock lamellae. Only one such concentration of shocked minerals has been found near the K-T boundary. The type of K-T boundary shock-metamorphosed materials (quartzite and metaquartzite) in the impact layer and the lack of shock lamellae in quartz and feldspar of pumice lapilli and granitic xenoliths in air-fall pumice units of silicic tuffs, such as the Bishop Tuff, eliminate the possibility that the shock-metamorphosed minerals in the K-T impact layer are of volcanic origin. The global size distribution and abundance of shock-metamorphosed mineral grains suggest that the K-T impact occurred in North America.

  9. Fullerenes in the cretaceous-tertiary boundary layer

    SciTech Connect

    Heymann, D.; Chibante, L.P.F.; Smalley, R.E. ); Brooks, R.R. ); Wolbach, W.S. )

    1994-07-29

    High-pressure liquid chromatography with ultraviolet-visible spectral analysis of toluene extracts of samples from two Cretaceous-Tertiary (K-T) boundary sites in New Zealand has revealed the presence of C[sub 60] at concentrations of 0.1 to 0.2 parts per million of the associated soot. This technique verified also that fullerenes are produced in similar amounts in the soots of common flames under ambient atmospheric conditions. Therefore, the C[sub 60] in the K-T boundary layer may have originated in the extensive wildfires that were associated with the cataclysmic impact event that terminated the Mezozoic era about 65 million years ago.

  10. Seawater strontium isotopes at the Cretaceous-Tertiary boundary

    NASA Technical Reports Server (NTRS)

    Macdougall, J. D.; Martin, E.

    1988-01-01

    Anomalously high values of Seawater Sr-87/Sr-86 near the Cretaceous-Tertiary (K-T) boundary have been reported. However, few of the data from the literature are from a single continuous section, and perhaps the most complete study of the boundary region, from a shallow marine limestone sequence in Alabama, showed elevated Sr-87/Sr-86 but no pronounced spike. Thus, in order to investigate the cause of the change in strontium isotopic composition, it is important to determine the exact nature and magnitude of the increase by studying in detail continuous sections through the boundary. If there is indeed a Sr isotope spike at the K-T boundary, it requires the addition of a large amount of radiogenic Sr to the oceans over a short time period, a phenomenon that may be linked to other large-scale environmental disturbances which occurred at that time. In order to address this question, a high-resolution strontium isotope study of foraminifera from three Deep Sea Drilling Project (DSDP) cores which recovered the K-T boundary section: Site 356 in the South Atlantic, Site 384 in the North Atlantic and Site 577 from the Shatsky Rise in the Pacific was initiated. The isotope measurements are being made on either single or small numbers of forams carefully picked and identified and in most cases examined by SEM before analysis. Because this work is not yet complete, conclusions drawn here must be viewed as tentative. They are briefly discussed.

  11. Proximal cretaceous-tertiary boundary impact deposits in the Caribbean.

    PubMed

    Hildebrand, A R; Boynton, W V

    1990-05-18

    Trace element, isotopic, and mineralogic studies indicate that the proposed impact at the Cretaceous-Tertiary (K-T) boundary occurred in an ocean basin, although a minor component of continental material is required. The size and abundance of shocked minerals and the restricted geographic occurrence of the ejecta layer and impact-wave deposits suggest an impact between the Americas. Coarse boundary sediments at sites 151 and 153 in the Colombian Basin and 5- to 450-meter-thick boundary sediments in Cuba may be deposits of a giant wave produced by a nearby oceanic impact. On the southern peninsula of Haiti, a approximately 50-centimeter-thick ejecta layer occurs at the K-T boundary. This ejecta layer is approximately 25 times as thick as that at any known K-T site and suggests an impact site within approximately 1000 kilometers. Seismic reflection profiles suggest that a buried approximately 300-km-diameter candidate structure occurs in the Colombian Basin. PMID:17811835

  12. The debate over the Cretaceous-Tertiary boundary

    NASA Astrophysics Data System (ADS)

    Alvarez, W.; Asaro, F.; Alvarez, L. W.; Michel, H. V.

    Large-body impact on the Earth is a rare but indisputable geologic process. The impact rate is approximately known from objects discovered in Earth-crossing orbits and from the statistics of craters on the Earth's surface. Tektite and microtektite strewn fields constitute unmistakable ejecta deposits that can be due only to large-body impacts. The Cretaceous-Tertiary (K-T) boundary coincides with an unusually severe biological trauma, and this stratigraphic horizon is marked on a worldwide basis by anomalous concentrations of noble metals in chondritic proportions, mineral spherules with relict quench-crystallization textures, and mineral and rock grains showing shock deformation. These features are precisely compatible with an impact origin. Although only impact explains all the types of K-T boundary evidence, the story may not be as simple as once thought. The original hypothesis envisioned one large impact, triggering one great extinction. Newer evidence hints at various complications. Different challenges are faced by the occupants of each apex of a three-cornered argument over the K-T event. Proponents of a non-impact explanation must show that the evidence fits their preferred model better than it fits the impact scenario. Proponents of the single impact-single extinction view must explain away the complications. Proponents of a more complex impact crisis must develop a reasonable scenario which honors the new evidence.

  13. Cathodoluminescence of shocked quartz at the Cretaceous-Tertiary boundary

    NASA Technical Reports Server (NTRS)

    Owen, Michael R.; Anders, Mark H.

    1988-01-01

    Empirical studies have documented an association between rock type and the cathodoluminescence color of constituent quartz grains. Quartz from extrusive igneous sources luminesces uniform pale blue. Quartz from intrusive igneous and high-grade metamorphic rocks generally luminesces darker purple-blue, whereas quartz recrystallized under low-grade metamorphic conditions luminesces reddish-brown. Quartz grains in most sandstones luminesce a heterogeneous mixture of these colors because the grains were derived from a variety of ultimate source rocks. If shocked quartz found at the Cretaceous-Tertiary (K-T) boundary is volcanic in origin, its cathodoluminescence should be predominantly pale blue. Alternatively, quartz grains derived from bolide impact upon, and ejection of, mixed igneous, metamorphic, and sedimentary rocks should luminesce a variety of colors. Grain mounts of sand collected at the K-T boundary horizon from the Clear Creek North site in the Raton Basin, Colorado were examined. Shocked quartz luminesced a variety of colors and very few grains luminesced the pale blue color that is typical of volcanic quartz. It was concluded that the shocked quartz was derived from a petrologically diverse source region without substantial volcanic contribution. Most shocked grains apparently were derived from low-grade metamorphic rocks, with a slightly smaller contribution from high-grade metamorphic and intrusive igneous rocks. Rare quartz grains with brown-luminescing rims reflect a minor addition from detrital sedimentary sources. The apparent relative abundances of intrusive (and rare extrusive) igneous, metamorphic, and sedimentary ultimate source rocks suggested by CL colors of shock-deformed quartz at the K-T boundary is consistent with a crustal/supracrustal origin for the grains.

  14. Magnesioferrite from the Cretaceous-Tertiary boundary, Caravaca, Spain

    USGS Publications Warehouse

    Bohor, B.F.; Foord, E.E.; Ganapathy, R.

    1986-01-01

    Magnesioferrite grading toward magnetite has been identified as a very small but meaningful constituent of the basal iron-rich portion of the Cretaceous-Tertiary (K-T) boundary clay at the Barranco del Gredero section, Caravaca, Spain. This spinel-type phase and others of the spinel group, found in K-T boundary clays at many widely separated sites, have been proposed as representing unaltered remnants of ejecta deposited from an earth-girdling dust cloud formed from the impact of an asteroid or other large bolide at the end of the Cretaceous period. The magnesioferrite occurs as euhedral, frequently skeletal, micron-sized octahedral crystals. The magnesioferrite contains 29 ?? 11 ppb Ir, which accounts for only part of the Ir anomaly at this K-T boundary layer (52 ?? 1 ppb Ir). Major element analyses of the magnesioferrite show variable compositions. Some minor solid solution exists toward hercynite-spinel and chromite-magnesiochromite. A trevorite-nichromite (NiFe2O4NiCr2O4) component is also present. The analyses are very similar to those reported for sites at Furlo and Petriccio, Umbria, Italy. On the basis of the morphology and general composition of the magnesioferrite grains, rapid crystallization at high temperature is indicated, most likely directly from a vapor phase and in an environment of moderate oxygen fugacity. Elemental similarity with metallic alloy injected into rocks beneath two known impact craters suggests that part of the magnesioferrite may be derived from the vaporized chondritic bolide itself, or from the mantle; there is no supporting evidence for its derivation from crustal target rocks. ?? 1986.

  15. 40Ar/39Ar age of Cretaceous-Tertiary boundary tektites from Haiti

    USGS Publications Warehouse

    Izett, G.A.; Dalrymple, G.B.; Snee, L.W.

    1991-01-01

    40Ar/39Ar dating of tektites discovered recently in Cretaceous-Tertiary (K-T) boundary marine sedimentary rocks on Haiti indicates that the K-T boundary and impact event are coeval at 64.5 ?? 0.1 million years ago. Sanidine from a bentonite that lies directly above the K-T boundary in continental, coal-bearing, sedimentary rocks of Montana was also dated and has a 40Ar/39Ar age of 64.6 ?? 0.2 million years ago, which is indistinguishable statistically from the age of the tektites.

  16. Extraterrestrial amino acids at the Cretaceous-Tertiary boundary

    SciTech Connect

    Lee, N.C.; Bada, J.L.

    1985-01-01

    The Earth has apparently been impacted by numerous large asteroids (>10 km diameter) or comets throughout its history. The rate of these collisions is roughly 2-4 x 10/sup -8/ events yr/sup -1/. The collision of a large asteroid or comet with the Earth could result in the addition of extra-terrestrial organic compounds. Certain types of meteorites (C2-carbonaceous chondrites) contain a vast assortment of organics, including amino acids, aliphatic and aromatic hydrocarbons, carboxylic acids, heterocycles, and various low molecular weight compounds. Molecules important in abiotic organic syntheses are present in comets, and thus these objects are also likely rich inorganics. The authors have investigated whether the amino acid ..cap alpha..-amino isobutyric acid (AIBA) can be used to ascertain whether extraterrestrial amino acids (ETAA) were added to the Earth's surface at the proposed asteroid or comet impact event associated with the Cretaceous-Tertiary (K-T) boundary. AIBA was utilized in these studies since it is a dominant amino acid in C2-carbonaceous meteorites and only rarely occurs in terrestrial organisms. Detection of AIBA was performed using OPA pre-column derivatization-HPLC methodology. Since the AIBA fluorescent yield is increased relative to non ..cap alpha..-methyl substituted amino acids at elevated temperatures, derivatization was carried out at both room temperature and 90/sup 0/C. Ocean sediments of various geological ages were analyzed. The results indicate that only in DSDP Leg 43 K-T boundary samples are detectable levels of AIBA present.

  17. Major wildfires at the Cretaceous-Tertiary boundary

    NASA Technical Reports Server (NTRS)

    Anders, Edward; Wolbach, Wendy S.; Gilmour, Iain

    1991-01-01

    The current status of the reconstruction of major biomass fire events at the Cretaceous-Tertiary boundary is discussed. Attention is given to the sources of charcoal and soot, the identification of biomass and fossil carbon, and such ignition-related problems as delated fires, high atmospheric O2 content, ignition mechanisms, and the greenhouse-effect consequences of fire on the scale envisioned. Consequences of these factors for species extinction patterns are noted.

  18. Biostratigraphy of the Cretaceous/Tertiary boundary in the Sirwan Valley (Sulaimani Region, Kurdistan, NE Iraq)

    NASA Astrophysics Data System (ADS)

    Sharbazheri, Khalid Mahmood; Ghafor, Imad Mahmood; Muhammed, Qahtan Ahmad

    2009-10-01

    The Cretaceous/Tertiary (K/T) boundary sequence, which crops out in the studied area is located within the High Folded Zone, in the Sirwan Valley, northeastern Iraq. These units mainly consist of flysch and flysch-type successions of thick clastic beds of Tanjero/Kolosh Formations. A detailed lithostratigraphic study is achieved on the outcropping uppermost part of the Upper Cretaceous successions (upper part of Tanjero Formation) and the lowermost part of the Kolosh Formation. On the basis of the identified planktonic foraminiferal assemblages, five biozones are recorded from the uppermost part of Tanjero Formation and four biozones from the lower part of the Kolosh Formation (Lower Paleocene) in the Sirwan section. The biostratigraphic correlations based on planktonic foraminiferal zonations showed a comparison between the biostratigraphic zones established in this study and other equivalents of the commonly used planktonic zonal scheme around the Cretaceous/Tertiary boundary in and outside Iraq.

  19. Proximal Cretaceous-Tertiary boundary impact deposits in the Caribbean

    NASA Technical Reports Server (NTRS)

    Hildebrand, Alan R.; Boynton, Willam V.

    1990-01-01

    Trace element, isotopic, and mineralogic studies indicate that the proposed impact at the Cretaceous-Tertiary boundary occurred in an ocean basin, although a minor component of continental material is required. The size and abundance of shocked minerals and the restricted geographic occurrence of the ejecta layer and impact-wave deposits suggest an impact between the Americas. Coarse boundary sediments at sites 151 and 153 in the Colombian Basin and 5- to 450-meter-thick boundary sediments in Cuba may be deposits of a giant wave produced by a nearby oceanic impact.

  20. Proximal Cretaceous-Tertiary boundary impact deposits in the Caribbean

    NASA Astrophysics Data System (ADS)

    Hildebrand, Alan R.; Boynton, Willam V.

    1990-05-01

    Trace element, isotopic, and mineralogic studies indicate that the proposed impact at the Cretaceous-Tertiary boundary occurred in an ocean basin, although a minor component of continental material is required. The size and abundance of shocked minerals and the restricted geographic occurrence of the ejecta layer and impact-wave deposits suggest an impact between the Americas. Coarse boundary sediments at sites 151 and 153 in the Colombian Basin and 5- to 450-meter-thick boundary sediments in Cuba may be deposits of a giant wave produced by a nearby oceanic impact.

  1. Ignition of global wildfires at the Cretaceous/Tertiary boundary

    NASA Technical Reports Server (NTRS)

    Melosh, H. J.; Schneider, N. M.; Zahnle, K. J.; Latham, D.

    1990-01-01

    The recent discovery of an apparently global soot layer at the Cretaceous/Tertiary boundary indicates that global wildfires were somehow ignited by the impact of a comet or asteroid. It is shown here that the thermal radiation produced by the ballistic reentry of ejecta condensed from the vapor plume of the impact could have increased the global radiation flux by factors of 50 to 150 times the solar input for periods ranging from one to several hours. This great increase in thermal radiation may have been responsible for the ignition of global wildfires, as well as having deleterious effects on unprotected animal life.

  2. Ignition of global wildfires at the Cretaceous/Tertiary boundary.

    PubMed

    Melosh, H J; Schneider, N M; Zahnle, K J; Latham, D

    1990-01-18

    An impressive amount of evidence supports the proposal of Alvarez et al. that the Cretaceous era was ended abruptly by the impact of a comet or asteroid. The recent discovery of an apparently global soot layer at the Cretaceous/Tertiary boundary indicates that global wildfires were somehow ignited by the impact. Here we show that the thermal radiation produced by the ballistic re-entry of ejecta condensed from the vapour plume of the impact could have increased the global radiation flux by factors of 50 to 150 times the solar input for periods ranging from one to several hours. This great increase in thermal radiation may have been responsible for the ignition of global wildfires, as well as having deleterious effects on unprotected animal life. PMID:11536461

  3. Stishovite at the cretaceous-tertiary boundary, raton, new Mexico.

    PubMed

    McHone, J F; Nieman, R A; Lewis, C F; Yates, A M

    1989-03-01

    Stishovite, a dense phase of silica, has become widely accepted as an indicator of terrestrial impact events. Stishovite occurs at several impact structures but has not been found at volcanic sites. Solid-state silicon-29 magic-angle spinning nuclear magnetic resonance (silicon-29 MAS NMR) and X-ray diffraction of samples from the Cretaceous-Tertiary boundary layer at Raton, New Mexico, indicate that stishovite occurs in crystalline mineral grains. Stishovite was indicated by a single, sharp resonance with a chemical shift value of -191.3 ppm, characteristic of silicon in octahedral coordination, that disappeared after heating the sample at 850 degrees Celsius for 30 minutes. An X-ray diffraction pattern of HF residuals from the unheated sample displayed more than 120 peaks, most of which correspond to quartz, zircon, rutile, and anatase. Eight unambiguous weak to moderate reflections could be ascribed to d-spacings characteristic of stishovite. PMID:17799900

  4. Sanidine spherules at the Cretaceous-Tertiary boundary indicate a large impact event

    NASA Astrophysics Data System (ADS)

    Smit, J.; Klaver, G.

    1981-07-01

    The hypothesis that a catastrophic impact of an extraterrestrial body caused the terminal Cretaceous mass extinctions of dinosaurs, planktonic foraminfera and other species is now accepted as respectable following the discovery of a worldwide iridium enrichment in the Cretaceous-Tertiary (K-T) boundary clay1-5. In the basal lamina of the K-T boundary clay of Caravaca (Spain)7 numerous spherules were discovered composed of finely crystallized, almost pure K-feldspar in the structural state of high sanidine. It is concluded here that these spherules solidified from a melt and were probably derived from the impacting body. This poses problems as high K-values are not reported from bulk analyses of meteorites6. The K-feldspar phenocrysts reported in some iron meteorites23 suggest the body may have been a metal-sulphide-silicate planetesimal. A cometary body is suggested as an alternative.

  5. A short duration of the Cretaceous-Tertiary boundary event: evidence from extraterrestrial helium-3.

    PubMed

    Mukhopadhyay, S; Farley, K A; Montanari, A

    2001-03-01

    Analyses of marine carbonates through the interval 63.9 to 65.4 million years ago indicate a near-constant flux of extraterrestrial helium-3, a tracer of the accretion rate of interplanetary dust to Earth. This observation indicates that the bolide associated with the Cretaceous-Tertiary (K-T) extinction event was not accompanied by enhanced solar system dustiness and so could not have been a member of a comet shower. The use of helium-3 as a constant-flux proxy of sedimentation rate implies deposition of the K-T boundary clay in (10 +/- 2) x 10(3) years, precluding the possibility of a long hiatus at the boundary and requiring extremely rapid faunal turnover. PMID:11239153

  6. Palynologically calibrated vertebrate record from North Dakota consistent with abrupt dinosaur extinction at the Cretaceous-Tertiary boundary

    USGS Publications Warehouse

    Pearson, D.A.; Schaefer, T.; Johnson, K.R.; Nichols, D.J.

    2001-01-01

    New data from 17 Cretaceous-Tertiary (K-T) boundary sections and 53 vertebrate sites in the Hell Creek and Fort Union Formations in southwestern North Dakota document a 1.76 m barren interval between the highest Cretaceous vertebrate fossils and the palynologically recognized K-T boundary. The boundary is above the formational contact at 15 localities and coincident with it at two, demonstrating that the formational contact is diachronous. Dinosaurs are common in the highest Cretaceous vertebrate samples and a partial dinosaur skeleton in the Fort Union Formation is the highest recorded Cretaceous vertebrate fossil in this area.

  7. Orbital Cyclicities Above and Below the Cretaceous-Tertiary Boundary, Umbria-Marche Region, Italy

    NASA Technical Reports Server (NTRS)

    King, D. T., Jr.; Petruny, L. W.; Rampino, M. R.; Prokoph, A.; Pope, K.; Fischer, A. G.; Montanari, A.; Ocampo, A. C.

    2000-01-01

    In the Umbria-Marche region of central Italy, the deep basinal carbonate Scaglia Rossa Formation contains an important sequence of Cretaceous-Tertiary strata including a detailed paleomagnetic record and the distal impactoclastic Cretaceous-Tertiary boundary clay layer. In addition to this significant paleomagnetic and impactoclastic record, the Scaglia Rossa also contains potentially important stratigraphic evidence of relatively long-term oceanic and atmospheric consequences of the Cretaceous-Tertiary bolide catastrophe, which we will describe for the first time herein. Additional information is contained in the original extended abstract.

  8. Seawater Sr isotopes at the Cretaceous/Tertiary boundary

    NASA Astrophysics Data System (ADS)

    Martin, E. E.; Macdougall, J. D.

    1991-06-01

    Seawater 87Sr/ 86Sr 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].

  9. Wildfires and animal extinctions at the Cretaceous/Tertiary boundary

    NASA Astrophysics Data System (ADS)

    Adair, Robert K.

    2010-06-01

    Persuasive models of the ejection of material at high velocities from the Chicxulub asteroid impact marking the Cretaceous/Tertiary boundary have led to the conclusion that upon return, that material, heated in passage through the upper atmosphere, generated a high level of infrared energy density over the Earth's surface. That radiant energy has been considered to be a direct source of universal wildfires, which were presumed to be a major cause of plant and animal species extinctions. The extinction of many animal species, especially the dinosaurs, has also been attributed to the immediate lethal effects of the radiation. I find that the absorption of the radiation by the atmosphere, by cloud formations, and by ejecta drifting in the lower atmosphere reduced the radiation at the surface to a level that cannot be expected to have generated universal fires. Although the reduced radiation will have likely caused severe injuries to many animals, such insults alone seem unlikely to have generated the overall species extinctions that have been deduced.

  10. Calcareous nannofossils and clastic sediments at the Cretaceous-Tertiary boundary, northeastern Mexico

    NASA Astrophysics Data System (ADS)

    Pospichal, James J.

    1996-03-01

    A quantitative analysis of calcareous nannofossil assemblages on the Cretaceous-Tertiary (K-T) boundary of the Mimbral and Mulato outcrops of northeast Mexico indicates that the sections are biostratigraphically complete across the boundary and that there is a prominent spherule-bearing clastic unit located precisely at the K-T boundary. The sections consist of uppermost Maastrichtian (Micula prinsii Zone) marly limestones of the Mendez Formation and marlstones of the lower Paleocene (Zone NP1) Velasco Formation separated by a distinct, 1 3-m-thick sandstone unit that has a basal spherule-bearing layer. The origin of this clastic unit and the time of deposition relative to the K-T mass extinctions have been the subjects of much controversy. Some workers attribute this unit to rapid tsunami-induced deposition triggered by the nearby Chicxulub impact, and others consider it a turbidite deposited at some time prior to the K-T mass extinctions. Cretaceous nannofossils abruptly decrease in abundance at the base of the spherule bed and only rare to few reworked specimens are present in the clastic unit and in the basal Velasco Formation. Survivors and Tertiary species are common above the clastic unit. Cretaceous nannoplankton show no evidence of recovery after deposition of the clastic unit, which indicates that extinctions probably occurred correlative with the deposition of the clastic unit and in association with the Chicxulub impact.

  11. Field guide to the continental Cretaceous-Tertiary boundary in the Raton basin, Colorado and New Mexico

    USGS Publications Warehouse

    Pillmore, C.L.; Nichols, D.J.; Fleming

    1999-01-01

    This guide consists of three general sections: an introduction that includes discussions of Raton basin stratigraphy and the Cretaceous Tertiary (K-T) boundary; descriptions of the geology along the route from Denver, Colorado, to Raton, New Mexico; and descriptions of several K-T sites in the Raton basin. Much of the information is from previous articles and field guides by the authors together with R. M. Flores and from road logs co-authored with Glenn R. Scott, both of the U.S.Geological Survey.

  12. Extraterrestrial amino acids in Cretaceous/Tertiary boundary sediments at Stevns Klint, Denmark.

    PubMed

    Zhao, M; Bada, J L

    1989-06-01

    Since the discovery nearly a decade ago that Cretaceous/Tertiary (K/T) boundary layers are greatly enriched in iridium, a rare element in the Earth's crust, there has been intense controversy on the relationship between this Ir anomaly and the massive extinction of organisms ranging from dinosaurs to marine plankton that characterizes the K/T boundary. Convincing evidence suggests that both the Ir spike and the extinction event were caused by the collision of a large bolide (greater than 10 km in diameter) with the Earth. Alternative explanations claim that extensive, violent volcanism can account for the Ir, and that other independent causes were responsible for the mass extinctions. We surmise that the collision of a massive extraterrestrial object with the Earth may have produced a unique organic chemical signature because certain meteorites, and probably comets, contain organic compounds which are either rare or non-existent on the Earth. In contrast, no organic compounds would be expected to be associated with volcanic processes. Here we find that K/T boundary sediments at Stevns Klint, Denmark, contain both alpha-amino-isobutyric acid [AIB,(CH3)2CNH2COOH] and racemic isovaline [ISOVAL, CH3CH2(CH3)CNH2COOH], two amino acids that are exceedingly rare on the Earth but which are major amino acids in carbonaceous chondrites. An extraterrestrial source is the most reasonable explanation for the presence of these amino acids. PMID:2725679

  13. Selective extinction and survival across the Cretaceous/Tertiary boundary in the northern Atlantic Coastal Plain

    SciTech Connect

    Gallagher, W.B. )

    1991-10-01

    The inner Atlantic Coastal Plain in New Jersey and the Delmarva Peninsula is underlain by an Upper Cretaceous-lower Tertiary sequence of marine and paralic sand, clay, and glauconitic beds. Campanian, Maastrichtian, Danian, and Thanetian deposits are especially fossiliferous and yield a succession of marine faunas that reveal a pattern of selective extinction and survival across the Cretaceous/Tertiary (K/T) boundary in this area. Cretaceous benthic invertebrate communities are dominated by oysters and other semi-infaunal and infaunal molluscs with planktotrophic larval stages. These are replaced in the Danian by brachiopod-dominated communities that are composed of epifaunal benthos with a variety of nonplanktotrophic reproductive strategies. A similar pattern is observable in the nektonic cephalopod populations in this sequence; the typical ammonites of the Cretaceous became extinct at the K/T boundary, whereas the nautilids survived. Ammonites are thought to have had a planktotrophic larval stage, whereas nautilids are known to lay large lecithotrophic eggs. This pattern of differential survival is attributed to the planktonic population crash at the K/T boundary which placed planktotrophically reproducing species at a disadvantage while favoring the varied groups that practiced alternative reproductive strategies.

  14. High-resolution leaf-fossil record spanning the Cretaceous/Tertiary boundary

    USGS Publications Warehouse

    Johnson, K.R.; Nichols, D.J.; Attrep, M., Jr.; Orth, C.J.

    1989-01-01

    THEORIES that explain the extinctions characterizing the Cretaceous/Tertiary (K/T) boundary1-3 need to be tested by analyses of thoroughly sampled biotas. Palynological studies are the primary means for stratigraphic placement of the terrestrial boundary and for estimates of plant extinction4-12, but have not been combined with quantitative analyses of fossil leaves (megaflora). Megafloral studies complement palynology by representing local floras with assemblages capable of high taxonomic resolution13, but have previously lacked the sample size and stratigraphic spacing needed to resolve latest Cretaceous floral history5,14-18. We have now combined megafloral data from a 100-m-thick composite K/T boundary section in North Dakota with detailed palynological analysis. Here the boundary is marked by a 30% palynofloral extinction coincident with iridium and shocked-mineral anomalies and lies ???2 m above the highest dinosaur remains. The megaflora undergoes a 79% turnover across the boundary, and smaller changes 17- and 25-m below it. This pattern is consistent with latest Cretaceous climatic warming preceding a bolide impact. ?? 1989 Nature Publishing Group.

  15. The Cretaceous/Tertiary Boundary Carbon and Oxygen Isotope Stratigraphy, Diagenesis, and Paleoceanography at Zumaya, Spain

    NASA Astrophysics Data System (ADS)

    Margolis, Stanley V.; Mount, Jeffrey F.; Doehne, Eric; Showers, William; Ward, Peter

    1987-08-01

    Carbon and oxygen isotope analysis of 240 m of Upper Cretaceous and Lower Tertiary limestones and marlstones from Zumaya, Spain, has revealed three distinct, negative carbon isotope excursions of up to 2 per mil, occurring both before and during the Cretaceous/Tertiary (K/T) transition. Although diagenesis has affected these rocks to varying degrees during burial and lithification, we believe that these excursions may reflect paleoceanographic changes. Sr/Ca, electron microscopic, and petrographic analysis have been used to assess the type and magnitude of diagenesis, allowing us to distinguish samples with significantly altered isotopic values. Carbon isotopes of rocks at Zumaya exhibit absolute values and ranges similar to semiconsolidated sediments of the same age. Oxygen isotopes of these rocks, however, exhibit a 1-2 per mil or more depletion, defined here as a diagenetic overprint, in comparison with values from semi-consolidated sediments of the same age. Ammonite and inoceramid macrofossils disappear in this section 12.5 and 120 m below the K/T boundary, coincident with two distinct episodes of negative ?13C values. These may reflect localized paleoceanographic or ecological changes. The last and largest of the isotope excursions corresponds with the K/T boundary marl and mass extinctions of calcareous plankton. The K/T boundary carbon isotope excursion is one of three that took place during the last 1 million years of the Cretaceous, each one possibly being associated with biotic changes in the oceanic realm. The K/T boundary excursion coincides with iridium concentration and spherules of unidentified origin, perhaps indicating that paleoceanographic change coincided with either extraterrestrial impacts or volcanic events that amplified their effects and accelerated biotic changes during times of stressed oceanic ecosystems.

  16. Magnetostratigraphy of the Cretaceous/Tertiary boundary section at La Ceiba, central-Eastern Mexico

    NASA Astrophysics Data System (ADS)

    Martinez-Lopez, M.; Urrutia-Fucugauchi, J.; Rebolledo-Vieyra, M.

    2003-04-01

    We report initial paleomagnetic and magnetostratigraphic results for one of the Cretaceous/Tertiary (K/T) boundary sections from northeastern Mexico. La Ceiba section is located in the Tampico-Mizantla carbonate basin, northeastern Puebla State. The section is characterized by three sedimentary clastic units, which have been described in detail in previous studies of K/T sections of northern Mexico. Its basal unit is formed by an alternation of calcareous reddish-greenish to gray shales, with calcareous clay layers. Unit II is 1.10-m thick and includes a shperulitic layer at the base and four sandstone layers. The top of the K/T sediments is marked by a clay layer and is covered by the Paleocene Velasco Formation. The Palaeocene is represented by 0.7-m dark brown-gray calcarenites with interbedded greenish-gray fine-grained material. Twenty-eight oriented cores were drilled from several beds in the K/T clastic units and the Paleocene sediments. All samples were measured in the laboratory (low-field magnetic susceptibility, NRM intensity and direction). Alternating field and thermal demagnetizations were used to investigate on the vectorial composition and stability of remanences. The magnetic mineralogy was further studied by imparting samples an isothermal remanent magnetization (IRM) and measuring magnetic hysteresis parameters using the MicroMag system. Well-defined characteristic magnetizations were isolated and used to construct a polarity stratigraphy for the K/T section. The clastic unit II and Paleocene sediments present a reverse polarity magnetization, which correlates with the expected polarity within 29r chron that includes the K/T boundary.

  17. Dinoflagellate and calcareous nannofossil response to sea-level change in Cretaceous-Tertiary boundary sections

    SciTech Connect

    Habib, D. ); Moshkovitz, S. ); Kramer, C. )

    1992-02-01

    Stratigraphic sections in south-central Alabama were studied to test palynological evidence of sea-level change across the Cretaceous-Tertiary boundary. New evidence from both calcareous nannofossils and dinoflagellate cysts places the regional disconformity in Alabama (Type 1 sequence boundary) virtually at the K-T boundary. This suggests that sea-level fall may have contributed to mass-extinction event. Dinoflagellate diversity varies between systems tract components of coastal onlap. This parameter is useful for interpreting sea-level change in this part of the section, because dinoflagellates did not participate in the mass extinction. The iridium spikes in the roadcut near Braggs are of earliest Danian age and correlate in relative magnitude with the lower values reported from directly above the K-T boundary in the Gubbio stratotype section. Iridium was concentrated in marine flooding surfaces in episodes of higher productivity of algal organic matter at the time when the iridium-enriched ocean encroached on the shelf during the first Cenozoic episode of sea-level rise.

  18. Deccan volcanism at the Cretaceous-Tertiary boundary

    NASA Technical Reports Server (NTRS)

    Courtillot, V.; Vandamme, D.; Besse, J.

    1988-01-01

    The accuracy with which one can claim that Deccan trap volcanism occurred at the Cretaceous-Tertiary boundary (KTB) over a very short time interval is of key importance in deciding whether a volcanic origin of the KTB events should be taken seriously. In the two years since paleomagnetic, paleontological and geodynamic evidence was published, further data have become available and the case now appears to be well constrained. The Ar-40/Ar-39 results from six labs have yielded some 24 reliable plateau ages that narrow the age range to 65 to 69 Ma. Moreover, it appears that a significant part of this range results from inter-lab spread and possible minor alteration. Paleontology demonstrates that volcanism started in the Maestrichtian, more precisely in the A. mayaroensis zone. Paleomagnetism shows that volcanism spanned only 3 chrons and only one correlation remains possible, that of the main central reversed chron with 29R. Therefore, whereas Ar-40/Ar-39 is able only to restrict the duration of volcanism to some 4 Ma, paleomagnetism restricts it to 0.5 Ma. Using some geochemical indicators such as C-13 as proxy, it is suggested that volcanism actually consists of a few shorter events of unequal magnitude. Extrusion rates may be as high as 100 cu km/yr and fissure lengths as long as several 100 km. Such a scenario appears to be at least as successful as others in accounting for most anomalies observed at the KTB. Particularly important are Iridium and other platinum group elements (PGE) profiles, Sr-87/Sr-86, C-13, 0-18, other exotic geochemical signatures, spherules, soot, shocked minerals, selective and stepwise extinctions. The environmental impact of CO2 possibly released during explosive phases of volcanism, and SO2 released during effusive phases, and the ability of volcanism to ensure worldwide distribution of KTB products are now all addressed. In conclusion, the case for a causal link between internal hotspot activity, birth of the Reunion hotspot itself as the Deccan and KTB events appears to rest on an increasingly stronger basis.

  19. The origin of the White Beds below the Cretaceous-Tertiary boundary in the Gubbio section, Italy

    NASA Technical Reports Server (NTRS)

    Lowrie, W.; Alvarez, W.; Asaro, F.

    1990-01-01

    This paper examines the origin of the 20-50-cm-thick set of whitish limestone beds found immediately underlying the Cretaceous-Tertiary (K-T) boundary in Umbrian sections. On the basis of isothermal remanent magnetization (IRM) acquisitions and thermal demagnetization experiments, it is argued that the white beds were deposited under the same conditions as the underlying pink beds and that the anomalously low IRM intensities found in the white beds resulted from the reduction of hematite in the originally pink beds followed by the removal of the Fe(2+) ions. The whitening of the beds is ascribed to the consequence of downward infiltration of reducing waters resulting from the large quantity of organic matter produced by the extinctions at the K-T boundary. The white interval below the K-T boundary is thus compatible with the hypothesis of impact-triggered mass extinction.

  20. 40Ar-39Ar dating of the Manson impact structure: A cretaceous-tertiary boundary crater candidate

    USGS Publications Warehouse

    Kunk, M.J.; Izett, G.A.; Haugerud, R.A.; Sutter, J.F.

    1989-01-01

    The mineralogy of shocked mineral and lithic grains in the Cretaceous-Tertiary (K-T) boundary claystone worldwide is most consistent with a bolide impact on a continent. Both the concentrations and sizes of these shocked grains are greatest in the western interior of North America. These data suggest that the Manson impact structure in north-central Iowa is a viable candidate for the K-T boundary impact event. Argon-40-argon-39 age spectrum dating of shocked microcline from the crystalline central uplift of the Manson impact structure indicates that there was severe argon-40 loss at 65.7 ?? 1.0 million years ago, an age that is indistinguishable from that of the K-T boundary, within the limits of analytical precision.

  1. Clay mineralogy of the Cretaceous-Tertiary boundary clay. [in search for asteroid ejecta

    NASA Technical Reports Server (NTRS)

    Rampino, M. R.; Reynolds, R. C.

    1983-01-01

    Cretaceous-Tertiary boundary layer clay samples from four localities were subjected to analyses which imply that they are neither mineralogically exotic nor distinct from locally derived clays above and below the boundary. The anomalous iridium-rich ejecta component predicted by the asteroid impact scenario of Alvarez et al (1980) was not detected. It is proposed that volcanic material be considered as an explanation of the geochemical anomalies of the Cretaceous-Tertiary boundary. A model which involves a period of intense volcanism at the end of the Cretaceous would generate a variety of climatic and biological effects consonant with the geologic history of that period.

  2. Mineralogy of Cretaceous/Tertiary boundary clays in the Chicxulub structure in northern Yucatan

    NASA Technical Reports Server (NTRS)

    Ming, D. W.; Sharpton, Virgil L.; Schuraytz, B. C.

    1991-01-01

    The Cretaceous/Tertiary (K/T) boundary clay layer is thought to be derived from ejecta material from meteorite impact, based on the anomalous concentrations of noble metals in the layer. Because of recent findings of a half-meter thick ejecta deposit at the K/T boundary in Haiti, efforts have focused on locating a large impact feature in the Caribbean and the Gulf of Mexico. One of the leading candidates for the site of a large impact is the Chicxulub structure located on the northern Yucatan Peninsula in Mexico. The Chicxulub structure is a subsurface zone of upper Cretaceous igneous rocks, carbonates, and breccias. The structure has been interpreted to be a 200 km diameter; however, there is some question to the size of the structure or to the fact that it even is an impact feature. Little is known about the mineralogy of this structure; the objective of this study was to determine the clay mineralogy of core samples from within the Chicxulub structure.

  3. Cretaceous-Tertiary boundary in the Antarctic: Climatic cooling precedes biotic crisis

    NASA Technical Reports Server (NTRS)

    Stott, Lowell D.; Kennett, James P.

    1988-01-01

    Stable isotopic investigations were conducted on calcareous microfossils across two deep sea Cretaceous-Tertiary boundary sequences on Maud Rise, Weddell Sea, Antarctica. The boundary is taken at the level of massive extinctions in calcareous planktonic microfossils, and coincides with a sharp lithologic change from pure calcareous ooze to calcareous ooze with a large volcanic clay component. The uppermost Maestrichtian is marked by a long-term decrease in delta value of 0 to 18 which spans most of the lower and middle A. mayaroensis Zone and represents a warming trend which culminated in surface water temperatures of about 16 C. At approximately 3 meters below the K-T boundary this warming trend terminates abruptly and benthic and planktonic isotopic records exhibit a rapid increase in delta value of 0 to 18 that continues up to the K-T boundary. The trend towards cooler surface water temperatures stops abruptly at the K-T boundary and delta value of 0 to 18 values remain relatively stable through the Paleocene. Comparison of the Antarctic sequence with the previously documented deep sea records in the South Atlantic reveal shifts of similar magnitude in the latest Maestrichtian. It is indicated that the Southern Ocean underwent the most significant, and apparently permanent, climatic change. The latest Cretaceous oxygen isotopic shift recorded at Maud Rise and other deep sea sites is similar in magnitude to large positive delta valve of 0 to 18 shifts in the middle Eocene, at the Eocene/Oligocene boundary and in the middle Miocene that marked large scale climatic transitions which ultimately lead to cryospheric development of the Antarctic. The climatic shift at the end of the Cretaceous represents one of the most significant climatic transitions recorded in the latest Phanerozoic and had a profound effect on global climate as well as oceanic circulation.

  4. High-resolution late Maastrichtian early Danian oceanic 87Sr/86Sr record: Implications for Cretaceous-Tertiary boundary events

    NASA Astrophysics Data System (ADS)

    Vonhof, H. B.; Smit, J.

    1997-04-01

    A high-resolution late Maastrichtian early Danian seawater 87Sr/86Sr reference curve is constructed from two Cretaceous-Tertiary boundary (K-T boundary) sections: Bidart (France) and El Kef (Tunisia). The 87Sr/86Sr curve shows maxima at 0.3 0.4 Ma before the K-T boundary and at the K-T boundary. The first maximum could mark the onset of a major outflow of the Deccan Traps. The second maximum, a rapid 0.000 06 87Sr/86Sr, shift, extends from 3 4 m below to 1 m above the K-T boundary. This profile probably results from diagenetic smoothing of an originally sharp K-T boundary 87Sr/86Sr anomaly, rather than from a gradual process. The sharp shift could result from (1) the vaporization of the Chicxulub target rocks, (2) global wildfires, and (3) acid-rain leaching of soils and sialic surface rocks. Of these three possibilities, only Sr release by soil leaching combined with increased rainfall associated with the K-T event appears to be sufficiently large to produce the observed K-T 87Sr/86Sr anomaly.

  5. Geologic framework of nonmarine cretaceous-tertiary boundary sites, raton basin, new mexico and colorado

    USGS Publications Warehouse

    Pillmore, C.L.; Tschudy, R.H.; Orth, C.J.; Gilmore, J.S.; Knight, J.D.

    1984-01-01

    Indium 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.

  6. Trace element patterns at a non-marine cretaceous-tertiary boundary

    USGS Publications Warehouse

    Gilmore, J.S.; Knight, J.D.; Orth, C.J.; Pillmore, C.L.; Tschudy, R.H.

    1984-01-01

    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. ?? 1984 Nature Publishing Group.

  7. Nanometre-size diamonds in the Cretaceous/Tertiary boundary clay of Alberta

    NASA Astrophysics Data System (ADS)

    Carlisle, David B.; Braman, Dennis R.

    1991-08-01

    Evidence is presented that the Cretaceous/Tertiary boundary clay of the Red Deer Valley of Alberta contains diamonds, which strengthens the case for an extraterrestrial impact at the end of the Cretaceous. The diamond/iridium ratio is close to the value found in type C2 chondritic meteorites.

  8. The Cretaceous-Tertiary boundary biotic crisis in the Basque country

    NASA Technical Reports Server (NTRS)

    Lamolda, M. A.

    1988-01-01

    The Zumaya section has been selected as a classic locality for the study of the Cretaceous-Tertiary (K-T) boundary due to its richness in microfaune, macrofaune, and nannoflora. The sections present similar good conditions for the study of the K-T boundary. The sedimentary rocks of the Uppermost Maastrichtian from the Basque Country are purple or pink marls and marls-tones. Above it is found a clayed bed, 40 to 29 cm thick, grey or dark grey in its basal part, of Lowermost Danian age. Above there is alternation of micritic grey-pink limestones and thin clay beds of Dano-Montian age. The average sedimentation is 7 to 8 times higher during the Upper Maastrichtian than in the Dano-Montian. The macrofauna underwent a decrease since the Campanian and was not found in the last 11 m of the Zumaya section; it was associated with changes in paleoceanographic conditions and primary productivity of the oceans. The microfossil assemblages in the K-T transition allows the recognition of several phases of a complex crisis between two well established planktonic ecosystems. In the Mayaroensis Zone there is a stable ecosystem with 45 to 47 planktonic foraminifera species. The disappearance of A. mayaroensis starts a degradation of the ecosystem. The number of planktonic foraminiera species decreases between 20 and 45 percent. The next phase of the crisis was the result of main extinction events in the planktonic calcareous ecosystem. There are several cretaceous planktonic foraminifera species, probably reworked, whose numbers decrease upward. The next and last phase of the biotic crisis shows a diversification of the ecosystem; the number of planktonic foraminifera is 2 to 3 times higher than before and it is noted the first appearance of Tertiary nannoflora species, while Cretaceous species decrease and persisting species are still the main ones.

  9. Major wildfires at the Cretaceous-Tertiary boundary

    NASA Technical Reports Server (NTRS)

    Gilmour, Iain; Wolbach, Wendy S.; Anders, Edward

    1989-01-01

    K-T boundary (KTB) clays from five sites are enriched in soot and charcoal by factors of 100-1000 over Cretaceous levels, apparently due to a global fire. The soot profile nearly coincides with the Ir profile, implying that the fire was triggered by the impact. Much or all of the fuel was biomass, as indicated by the presence of retene and by the C isotopic composition. The amount of elemental C at the KTB (0.012 g/sq cm) is very large, and requires either that most of the Cretaceous biomass burned down or that the soot yield was higher than in small fires. At undisturbed sites, soot correlates tightly with Ir, As, Sb, and Zn. Apparently soot and Ir-bearing ejecta particles coagulated in the stratosphere and then scavenged additional chalcophiles from the hydrosphere. In view of this coagulation, the K-T fire would only slightly prolong the period of darkness and cold caused by impact ejecta.

  10. A new Cretaceous-Tertiary boundary locality in the western powder River basin, Wyoming: biological and geological implications

    USGS Publications Warehouse

    Nichols, D.J.; Brown, J.L.; Attrep, M., Jr.; Orth, C.J.

    1992-01-01

    A newly discovered Cretaceous-Tertiary (K-T) boundary locality in the western Powder River basin, Wyoming, is characterized by a palynologically defined extinction horizon, a fern-spore abundance anomaly, a strong iridium anomaly, and shock-metamorphosed quartz grains. Detailed microstratigraphic analyses show that about one third of the palynoflora (mostly angiosperm pollen) disappeared abruptly, placing the K-T boundary within a distinctive, 1- to 2-cm-thick claystone layer. Shocked quartz grains are concentrated at the top of this layer, and although fern-spore and iridium concentrations are high in this layer, they reach their maximum concentrations in a 2-cm-thick carbonaceous claystone that overlies the boundary claystone layer. The evidence supports the theory that the K-T boundary event was associated with the impact of an extraterrestrial body or bodies. Palynological analyses of samples from the K-T boundary interval document extensive changes in the flora that resulted from the boundary event. The palynologically and geochemically defined K-T boundary provides a unique time-line of use in regional basin analysis. ?? 1992.

  11. Multiple impacts across the Cretaceous-Tertiary boundary

    NASA Astrophysics Data System (ADS)

    Keller, G.; Stinnesbeck, W.; Adatte, T.; Stben, D.

    2003-09-01

    The stratigraphy and age of altered impact glass (microtektites, microkrystites) ejecta layers from the Chicxulub crater are documented in Late Maastrichtian and Early Danian sediments in Mexico, Guatemala, Belize and Haiti. In northeastern Mexico, two to four ejecta layers are present in zone CF1, which spans the last 300 ky of the Maastrichtian. The oldest ejecta layer is dated at 65.270.03 Ma based on sediment accumulation rates and extrapolated magnetostratigraphy. All younger ejecta layers from the Maastrichtian and Early Danian Parvularugoglobigerina eugubina zone Pla(l) may represent repeated episodes of reworking of the oldest layer at times of sea level changes and tectonic activity. The K/T boundary impact event (65.0 Ma) is not well represented in this area due to widespread erosion. An Early Danian Pla(l) Ir anomaly is present in five localities (Bochil, Actela, Coxquihui, Trinitaria and Haiti) and is tentatively identified as a third impact event at about 64.9 Ma. A multiimpact scenario is most consistent with the impact ejecta evidence. The first impact is associated with major Deccan volcanism and likely contributed to the rapid global warming of 3-4 C in intermediate waters between 65.4 and 65.2 Ma, decrease in primary productivity and onset of terminal decline in planktic foraminiferal populations. The K/T boundary impact marks a major drop in primary productivity and the extinction of all tropical and subtropical species. The Early Danian impact may have contributed to the delayed recovery in productivity and evolutionary diversity.

  12. The Origin of White Beds below the Cretaceous-Tertiary Boundary Revisited

    NASA Astrophysics Data System (ADS)

    Abrajevitch, A.; Font, E.; Florindo, F.; Roberts, A. P.

    2014-12-01

    The respective roles of an asteroid impact and Deccan Traps eruptions in biotic changes at the Cretaceous-Tertiary (K-T) boundary are still debated. In many shallow marine sections around the world, the K-T boundary is marked by a distinct impact clay layer that is often underlain by a several decimeter-thick "white" low susceptibility zone. A previous study of the Gubbio section, Italy [Lowrie et al., 1990; EPSL, 98, 302-312], attributed the loss of coloration and low magnetization intensity in the white beds to post-depositional dissolution of ferrimagnetic minerals. Dissolution is thought to be a consequence of downward infiltration of reducing waters that resulted from rapid accumulation of organic matter produced by mass extinctions after the impact. We compared rock magnetic characteristics of the Gubbio section with those of the Bidart section in France. The two sections are similar in their carbonate lithology, presence of a boundary clay and low susceptibility zone. When compared to background Cretaceous sediments, the white zone in both sections is marked by an absence of biogenic magnetite, a decrease in total ferrimagnetic mineral content, and preferential loss of magnetite with respect to hematite - features that are consistent with reductive dissolution. However, unlike the Gubbio section, where the white zone starts immediately below the impact clay, at Bidart the low susceptibility zone and the clay layer are separated by a ~2 cm carbonate interval that contains abundant biogenic magnetite. Such separation casts doubt on a causal link between the impact and sediment bleaching. The white layer, thus, is more likely to record an episode of unusual bottom water chemistry that preceded the asteroid impact. A change in sea-water acidity associated with Deccan Traps volcanism may explain the magnetic mineral dissolution in the white beds.

  13. Step-wise extinctions at the Cretaceous-Tertiary boundary and their climatic implications

    NASA Technical Reports Server (NTRS)

    Maurrasse, Florentin J-M. R.

    1988-01-01

    A comparative study of planktonic foraminifera and radiolarian assemblages from the Cretaceous-Tertiary (K-T) boundary section of the Beloc Formation in the southern Peninsula of Haiti, and the lowermost Danian sequence of the Micara Formation in southern Cuba reveals a remarkable pattern of step-wise extinctions. This pattern is consistent in both places despite the widely different lithologies of the two formations. Because of a step-wise extinction and the delayed disappearance of taxa known to be more representative of cooler water realms, it is inferred that a cooling trend which characterized the close of the Maastrichtian and the onset of the Tertiary had the major adverse effect on the existing biota. Although repetitive lithologic and faunal fluctuations throughout the Maastrichtian sediments found at Deep Sea Drilling Project (DSDP) site 146/149 in the Caribbean Sea indicate variations reminiscent of known climatically induced cycles in the Cenozoic, rapid biotic succession appears to have taken place during a crisis period of a duration greater than 2 mission years. Widespread and abundant volcanic activities recorded in the Caribbean area during the crisis period gives further credence to earlier contention that intense volcanism may have played a major role in exhacerbating pre-existing climatic conditions during that time.

  14. Ocean alkalinity and the Cretaceous/Tertiary boundary

    NASA Technical Reports Server (NTRS)

    Caldeira, K. G.; Rampino, Michael R.

    1988-01-01

    A biogeochemical cycle model resolving ocean carbon and alkalinity content is applied to the Maestrichtian and Danian. The model computes oceanic concentrations and distributions of Ca(2+), Mg(2+), and Sigma-CO2. From these values an atmospheric pCO2 value is calculated, which is used to estimate rates of terrestrial weathering of calcite, dolomite, and calcium and magnesium silicates. Metamorphism of carbonate rocks and the subsequent outgassing of CO2 to the atmosphere are parameterized in terms of carbonate rock reservoir sizes, total land area, and a measure of overall tectonic activity, the sea-floor generation rate. The ocean carbon reservoir computed by the model is used with Deep Sea Drilling Project (DSDP) C-13 data to estimate organic detrital fluxes under a variety of ocean mixing rate assumptions. Using Redfield ratios, the biogenic detrital flux estimate is used to partition the ocean carbon and alkalinity reservoirs between the mixed layer and deep ocean. The calcite flux estimate and carbonate ion concentrations are used to determine the rate of biologically mediated CaCO3 titration. Oceanic productivity was severely limited for approximately 500 kyr following the K/T boundary resulting in significant increases in total ocean alkalinity. As productivity returned to the ocean, excess carbon and alkalinity was removed from the ocean as CaCO3. Model runs indicate that this resulted in a transient imbalance in the other direction. Ocean chemistry returned to near-equilibrium by about 64 mybp.

  15. Spherules from the Cretaceous/Tertiary boundary clay at Gubbio, Italy: the problem of outcrop contamination

    SciTech Connect

    Montanari, A.

    1986-12-01

    Surficial outcrop contamination has occurred in some well-known stratigraphic sections of carbonate rocks in the northern Apennines. A critical case involves several contaminated clay partings, including the Cretaceous/Tertiary boundary clay in the classic Bottaccione section near Gubbio, Italy. These clay layers contain shiny spherules which, in several recent studies, have been said to consist of volcanic glass and have been used to support the hypothesis that the terminal Cretaceous mass extinction was caused by widespread volcanism. Laboratory tests, however, indicate that these shiny spherules are made of HF-insoluble and combustible material and are therefore of recent biological origin. These objects were introduced into the Cretaceous/Tertiary boundary clay and other clay layers from the surrounding soil along with abundant detrital contaminants derived from erosion of the middle Miocene flysch exposed at the head of the Bottaccione Gorge. They are completely different from the altered and flattened microtektitelike spheroids that are found only in the iridium-rich Cretaceous/Tertiary boundary clay and that provide strong evidence for a large impact.

  16. Marine and continental K-T boundary clays compared

    NASA Astrophysics Data System (ADS)

    Schmitz, B.

    Detailed geochemical and mineralogical studies (1 to 5) of sediments across the Cretaceous-Tertiary (K-T) boundary at Stevns Klint, Karlstrup, Nye Klov, Dania, and Kjolby Gaard in Denmark, at Limhamn in Sweden, at Caravaca in Spain, at Waipara and Woodside Creek in New Zealand, at Trinidad in Colorado, and at various sites in Montana, have induced conclusions and reflections which are given and briefly discussed.

  17. Marine and continental K-T boundary clays compared

    NASA Technical Reports Server (NTRS)

    Schmitz, B.

    1988-01-01

    Detailed geochemical and mineralogical studies (1 to 5) of sediments across the Cretaceous-Tertiary (K-T) boundary at Stevns Klint, Karlstrup, Nye Klov, Dania, and Kjolby Gaard in Denmark, at Limhamn in Sweden, at Caravaca in Spain, at Waipara and Woodside Creek in New Zealand, at Trinidad in Colorado, and at various sites in Montana, have induced conclusions and reflections which are given and briefly discussed.

  18. Palynological and iridium anomalies at Cretaceous-Tertiary boundary, south-central Saskatchewan

    USGS Publications Warehouse

    Nichols, D.J.; Jarzen, D.M.; Orth, C.J.; Oliver, P.Q.

    1986-01-01

    The Cretaceous-Tertiary boundary in south-central Saskatchewan is marked by coincident anomalies in abundance of iridium and fern spores at the extinction level of a suite of Cretaceous pollen taxa. Evidence of disruption of the terrestrial flora includes the fern-spore abundance anomaly and local extinction of as much as 30 percent of angiosperm species. The reorganized earliest Tertiary flora is made up largely of surviving species that assumed new roles of dominance. Persistence of climatically sensitive taxa across the boundary indicates that if paleoclimate was altered by the terminal Cretaceous event, it returned quickly to the pre-event condition.

  19. Disruption of the terrestrial plant ecosystem at the Cretaceous-Tertiary boundary, western interior

    USGS Publications Warehouse

    Tschudy, R.H.; Pillmore, C.L.; Orth, C.J.; Gilmore, J.S.; Knight, J.D.

    1984-01-01

    The palynologically defined Cretaceous-Tertiary boundary in the western interior of North America occurs at the top of an iridium-rich clay layer. The boundary is characterized by the abrupt disappearance of certain pollen species, immediately followed by a pronounced, geologically brief change in the ratio of fern spores to angiosperm pollen. The occurrence of these changes at two widely separated sites implies continentwide disruption of the terrestrial ecosystem, probably caused by a major catastrophic event at the end of the period.

  20. Disruption of the terrestrial plant ecosystem at the Cretaceous-Tertiary boundary, western interior

    SciTech Connect

    Tschudy, R.H.; Pillmore, C.L.; Orth, C.J.; Gilmore, J.S.; Knight, J.D.

    1984-09-07

    The palynologically defined Cretaceous-Tertiary boundary in the western interior of North America occurs at the top of an iridium-rich clay layer. The boundary is characterized by the abrupt disappearance of certain pollen species, immediately followed by a pronounced, geologically brief change in the ratio of fern spores to angiosperm pollen. The occurrence of these changes at two widely separated sites implies continent-wide disruption of the terrestrial ecosystem, probably caused by a major catastrophic event at the end of the period. 15 references, 2 figures.

  1. Biospheric effects of a large extraterrestrial impact: Case study of the cretaceous/tertiary boundary crater

    NASA Technical Reports Server (NTRS)

    Pope, Kevin O.

    1995-01-01

    The Chicxulub impact crater, buried in the Yucatan carbonate platform in Mexico, is the site of the impact purported to have caused mass extinctions at the Cretaceous/Tertiary (K/T) boundary. A recently discovered Chicxulub ejecta deposit in Belize contains evidence of carbonate vaporization and precipitation from the vapor plume. Sulfate clasts are almost absent in the Belize ejecta, but are abundant in the coarse ejecta near the crater rim, hwich may reflect the greater abundance of sulfates deep in the target section. The absence of sulfate precipitates in Belize may indicate that most of the vaporized sulfur was deposited in the upper atmosphere. Hydrocode modeling of the impact indicates that between 0.4 to 7.0 x 10(exp 17) g of sulfur were vaporized by the impact in sulfates. Laser experiments indicate that SO2, SO3, and SO4 are produced, and that complex chemical reactions between plume constituents occur during condensation. The sulfur released as SO3 or SO4 converted rapidly into H2HO4 aerosol. A radiative transfer model coupled with a model of coagulation predicts that the aerosol prolonged the initial blackout period caused by impact dust only if it contained impurities. The sulfur released as SO2 converted to aerosol slowly due to the rate limiting oxidation of SO2. Radiative transfer calculations combined with rates of acid production, coagulation, and diffusion indicate that solar transmission was reduced to 10-20 percent of normal for a period of 8-13 years. This reduction produced a climate forcing (cooling) of -300 Wm(exp -2), which far exceeded the +8 Wm(exp -2) greenhouse warming caused by the CO2 released through the vaporization of carbonates, and therefore produced a decade of freezing and near-freezing temperatures. Several decades of moderate warming followed the decade of severe cooling due to the long residence time of CO2. The prolonged impact winter may have been a major cause of the K/T extinctions.

  2. Biospheric effects of a large extraterrestrial impact: Case study of the Cretaceous/Tertiary boundary crater

    NASA Technical Reports Server (NTRS)

    Pope, Kevin O.

    1994-01-01

    The Chicxulub Crater in Yucatan, Mexico, is the primary candidate for the impact that caused mass extinctions at the Cretaceous/Tertiary boundary. The target rocks at Chicxulub contain 750 to 1500 m of anhydrite (CaSO4), which was vaporized upon impact, creating a large sulfuric acid aerosol cloud. In this study we apply a hydrocode model of asteroid impact to calculate the amount of sulfuric acid produced. We then apply a radiative transfer model to determine the atmospheric effects. Results include 6 to 9 month period of darkness followed by 12 to 26 years of cooling.

  3. Trace element and isotope geochemistry of Cretaceous-Tertiary boundary sediments: identification of extra-terrestrial and volcanic components

    NASA Technical Reports Server (NTRS)

    Margolis, S. V.; Doehne, E. F.

    1988-01-01

    Trace element and stable isotope analyses were performed on a series of sediment samples crossing the Cretaceous-Tertiary (K-T) boundary from critical sections at Aumaya and Sopelano, Spain. The aim is to possibly distinguish extraterrestrial vs. volcanic or authigenic concentration of platinum group and other elements in K-T boundary transitional sediments. These sediments also have been shown to contain evidence for step-wise extinction of several groups of marine invertebrates, associated with negative oxygen and carbon isotope excursions occurring during the last million years of the Cretaceous. These isotope excursions have been interpreted to indicate major changes in ocean thermal regime, circulation, and ecosystems that may be related to multiple events during latest Cretaceous time. Results to date on the petrographic and geochemical analyses of the Late Cretaceous and Early Paleocene sediments indicate that diagenesis has obviously affected the trace element geochemistry and stable isotope compositions at Zumaya. Mineralogical and geochemical analysis of K-T boundary sediments at Zumaya suggest that a substantial fraction of anomalous trace elements in the boundary marl are present in specific mineral phases. Platinum and nickel grains perhaps represent the first direct evidence of siderophile-rich minerals at the boundary. The presence of spinels and Ni-rich particles as inclusions in aluminosilicate spherules from Zumaya suggests an original, non-diagenetic origin for the spherules. Similar spherules from southern Spain (Caravaca), show a strong marine authigenic overprint. This research represents a new approach in trying to directly identify the sedimentary mineral components that are responsible for the trace element concentrations associated with the K-T boundary.

  4. Surface-water acidification and extinction at the Cretaceous-Tertiary boundary

    NASA Astrophysics Data System (ADS)

    D'Hondt, Steven; Pilson, Michael E. Q.; Sigurdsson, Haraldur; Hanson, Alfred K., Jr.; Carey, Steven

    1994-11-01

    If published estimates of SO2 volatilization and NOx generation by the Cretaceous-Tertiary (K-T) impact were atmospherically converted to sulfuric and nitric acid, globally dispersed, and rapidly rained out, the resulting acid concentrations would bracket a critical threshold in surface-ocean chemistry. Rapid and globally uniform deposition of masses corresponding to the lowest estimates would have had no major effect on sea-surface chemistry. However, similar deposition of masses corresponding to the highest estimates would have provided enough acid to destroy the carbonate-buffering capacity of the upper 100 m of the world ocean and catastrophically reduce surface-ocean pH. Despite the possible effect of the highest estimated acid yields, scenarios that rely on acid rain as the primary explanation of global K-T extinctions are not readily compatible with K-T records of terrestrial and marine survival or culturing studies of modern marine plankton. The possibility that acid rain was a primary cause of K-T extinctions can be tested further by analysis of geographic variation in extinction intensity, because such variation was a likely consequence if the impact resulted in global dispersal and rapid globally uniform deposition of more than 6 x 1016 mol of H2SO4 or 1.2 x 1017 mol of HNO3.

  5. The Precursor of the Cretaceous-Tertiary Boundary Clays at Stevns Klint, Denmark, and DSDP Hole 465A.

    PubMed

    Kastner, M; Asaro, F; Michel, H V; Alvarez, W; Alvarez, L W

    1984-10-12

    Results of detailed mineralogical, chemical, and oxygen isotope analyses of the clay minerals and zeolites from two Cretaceous-Tertiary (K/T) boundary regions, Stevns Klint, Denmark, and Deep Sea Drilling Project (DSDP) Hole 465A in the north central Pacific Ocean, are presented. In the central part of the Stevns Klint K/T boundary layer, the only clay mineral detected by x-ray diffraction is a pure smectite with > 95 percent expandable layers. No detrital clay minerals or quartz were observed in the clay size fraction in these beds, whereas the clay minerals above and below the boundary layer are illite and mixed-layer smectite-illite of detrital origin as well as quartz. The mineralogical purity of the clay fraction, the presence of smectite only at the boundary, and the delta(18)O value of the smectite (27.2 +/- 0.2 per mil) suggest that it formed in situ by alteration of glass. Formation from impact rather than from volcanic glass is supported by its major element chemistry. The high content of iridium and other siderophile elements is not due to the cessation of calcium carbonate deposition and resulting slow sedimentation rates. At DSDP Hole 465A, the principal clay mineral in the boundary zone (80 to 143 centimeters) is a mixed-layer smectite-illite with >/=90 percent expandable layers, accompanied by some detrital quartz and small amounts of a euhedral authigenic zeolite (clinoptilolite). The mixed-layer smectite-illite from the interval 118 to 120 centimeters in the zone of high iridium abundance has a very low rare earth element content; the negative cerium anomaly indicates formation in the marine environment. This conclusion is corroborated by the delta(18)O value of this clay mineral (27.1 +/- 0.2 per mil). Thus, this mixed-layer smectite-illite formed possibly from the same glass as the K/T boundary smectite at Stevns Klint, Denmark. PMID:17814325

  6. Chicxulub impact predates the K-T boundary mass extinction.

    PubMed

    Keller, Gerta; Adatte, Thierry; Stinnesbeck, Wolfgang; Rebolledo-Vieyra, Mario; Fucugauchi, Jaime Urrutia; Kramar, Utz; Stben, Doris

    2004-03-16

    Since the early l990s the Chicxulub crater on Yucatan, Mexico, has been hailed as the smoking gun that proves the hypothesis that an asteroid killed the dinosaurs and caused the mass extinction of many other organisms at the Cretaceous-Tertiary (K-T) boundary 65 million years ago. Here, we report evidence from a previously uninvestigated core, Yaxcopoil-1, drilled within the Chicxulub crater, indicating that this impact predated the K-T boundary by approximately 300,000 years and thus did not cause the end-Cretaceous mass extinction as commonly believed. The evidence supporting a pre-K-T age was obtained from Yaxcopoil-1 based on five independent proxies, each with characteristic signals across the K-T transition: sedimentology, biostratigraphy, magnetostratigraphy, stable isotopes, and iridium. These data are consistent with earlier evidence for a late Maastrichtian age of the microtektite deposits in northeastern Mexico. PMID:15004276

  7. Multiple factors in the origin of the Cretaceous/Tertiary boundary: the role of environmental stress and Deccan Trap volcanism.

    PubMed

    Glasby, G P; Kunzendorf, H

    1996-06-01

    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 global, role in the K/T extinction. PMID:11543126

  8. Local Structure of Sb in Cretaceous-Tertiary Boundary Clays from Stevns Klint By the XAFS Method

    NASA Astrophysics Data System (ADS)

    Hongu, H.; Yoshiasa, A.; Tobase, T.; Hiratoko, T.; Isobe, H.; Arima, H.; Sugiyama, K.; Okube, M.

    2014-12-01

    The Cretaceous-Tertiary (K-T) mass extinctions has been thought to be due to the asteroid impact since Ir anomalies was found by Alvarez et al. (1980) . The boundary clay is also enriched in Cr, Co, Ni, Cu, Zn, As and Sb. Especially concentrations of Sb and As are unusually large. However, the origins and concentration processes of Sb are unknown. In this study, local structure around antimony atoms in K-T boundary clay from Stevns Klint, Denmark, was determined by Sb K-edge XAFS spectroscopy. The XAFS analyses give the information about the chemical state and coordination environment around Sb atoms and help identify of the concentration phase, and also may provide various kinds of information about the asteroid impact and mass extinction. The XAFS measurements were performed at the BL-NW10A beamline at the Photon Factory in KEK, Tsukuba, Japan. The XANES spectra and radial structure function (RSF) showed that Sb in K-T boundary clays is high oxidation state Sb5+ and occupies a SbO6 octahedral site. The Sb-O interatomic distance in K-T clay sample is 2.08(1) A. It is known that Sb5+ is stable form in soil and soil water under an equilibrium situation within the Earth's surface environment. Antimony belongs to group 15 in the periodic table below arsenic, and the chemical behavior of Sb5+ is similar to that of As5+. Because there is a close correlation on co-precipitation between As and Fe (Ebihara and Miura, 1996; Sakai et al., 2007) , it is considered that Sb also correlates closely with Fe compounds (e.g., ferric hydroxides). Abundant ferric hydroxides occur in K-T boundary clays. It is considered that one of the reasons of abnormal high concentrations of Sb and As in K-T boundary clays is a lot of dust from impact ejecta falls with iron ions and deposits on surface of the Earth for a short period of time after the asteroid impact. ReferencesL. W. Alvarez, Science, 208, 1095-1108 (1980) M. Ebihara and T. Miura, Geochimica et Cosmochimica Acta, 60, 5133-5144 (1996) S. Sakai et al., The American Institute of Physics, Conference Proceeding, 882, 274-276 (2007)

  9. Tektite-bearing, deep-water clastic unit at the Cretaceous-Tertiary boundary in northeastern Mexico

    NASA Technical Reports Server (NTRS)

    Smit, J.; Montanari, A.; Swinburne, N. H.; Alvarez, W.; Hildebrand, A. R.; Margolis, S. V.; Claeys, P.; Lowrie, W.; Asaro, F.

    1992-01-01

    The hypothesis of Cretaceous-Tertiary (K-T) boundary impact on Yucatan, Mexico, predicts that nearby sites should show evidence of proximal impact ejecta and disturbance by giant waves. An outcrop along the Arroyo el Mimbral in northeastern Mexico contains a layered clastic unit up to 3 m thick that interrupts a biostratigraphically complete pelagic-marl sequence deposited at more than 400 m water depth. The marls were found to be unsuitable for determining magnetostratigraphy, but foraminiferal biostratigraphy places the clastic unit precisely at the K-T boundary. We interpret this clastic unit as the deposit of a megawave or tsunami produced by an extraterrestrial impact. The clastic unit comprises three main subunits. (1) The basal "spherule bed" contains glass in the form of tektites and microtektites, glass spherules replaced by chlorite-smectite and calcite, and quartz grains showing probable shock features. This bed is interpreted as a channelized deposit of proximal ejecta. (2) A set of lenticular, massive, graded "laminated beds" contains intraclasts and abundant plant debris, and may be the result of megawave backwash that carried coarse debris from shallow parts of the continental margin into deeper water. (3) At the top, several thin "ripple beds" composed of fine sand are separated by clay drapes; they are interpreted as deposits of oscillating currents, perhaps a seiche. An iridium anomaly (921 +/- 23 pg/g) is observed at the top of the ripple beds. Our observations at the Mimbral locality support the hypothesis of a K-T impact on nearby Yucatan.

  10. Tektite-bearing, deep-water clastic unit at the Cretaceous-Tertiary boundary in northeastern Mexico

    SciTech Connect

    Smit, J. ); Montanari, A.; Swinburne, N.H.M.; Alvarez, W. ); Hildebrand, A.R. ); Margolis, S.V.; Claeys, P. ); Lowrie, W. ); Asaro, F. )

    1992-02-01

    The hypothesis of Cretaceous-Tertiary (K-T) boundary impact on Yucatan, Mexico, predicts that nearby sites should show evidence of proximal impact ejecta and disturbance by giant waves. An outcrop along the Arroyo el Mimbral in northeastern Mexico contains a layered clastic unit up to 3 m thick that interrupts a biostratigraphically complete pelagic-marl sequence deposited at more than 400 m water depth. The marls were found to be unsuitable for determining magnetostratigraphy, but foraminiferal biostratigraphy places the clastic unit precisely at the K-T boundary. The authors interpret this clastic unit as the deposit of a megawave or tsunami produced by an extraterrestrial impact. The clastic unit comprises three main subunits. (1) The basal 'spherule bed' contains glass in the form of tektites and microtektites, glass spherules replaced by chlorite-smectite and calcite, and quartz grains showing probable shock features. This bed is interpreted as a channelized deposit of proximal ejecta. (2) A set of lenticular, massive, graded 'laminated beds' contains intraclasts can abundant plant debris, and may the result of megawave backwash that carried coarse debris from shallow parts of the continental margin into deeper water. (3) At the top, several thin 'ripple beds' composed of fine sand are separated by clay drapes; they are interpreted as deposits of oscillating currents, perhaps a seiche. An iridium anomaly (921 {plus minus} 23 pg/g) is observed at the top of the ripple beds. Their observations at the Mimbral locality support the hypothesis of a K-T impact on nearby Yucatan.

  11. Tektite-bearing, deep-water clastic unit at the Cretaceous-Tertiary boundary in northeastern Mexico.

    PubMed

    Smit, J; Montanari, A; Swinburne, N H; Alvarez, W; Hildebrand, A R; Margolis, S V; Claeys, P; Lowrie, W; Asaro, F

    1992-02-01

    The hypothesis of Cretaceous-Tertiary (K-T) boundary impact on Yucatn, Mexico, predicts that nearby sites should show evidence of proximal impact ejecta and disturbance by giant waves. An outcrop along the Arroyo el Mimbral in northeastern Mexico contains a layered clastic unit up to 3 m thick that interrupts a biostratigraphically complete pelagic-marl sequence deposited at more than 400 m water depth. The marls were found to be unsuitable for determining magnetostratigraphy, but foraminiferal biostratigraphy places the clastic unit precisely at the K-T boundary. We interpret this clastic unit as the deposit of a megawave or tsunami produced by an extraterrestrial impact. The clastic unit comprises three main subunits. (1) The basal "spherule bed" contains glass in the form of tektites and microtektites, glass spherules replaced by chlorite-smectite and calcite, and quartz grains showing probable shock features. This bed is interpreted as a channelized deposit of proximal ejecta. (2) A set of lenticular, massive, graded "laminated beds" contains intraclasts and abundant plant debris, and may be the result of megawave backwash that carried coarse debris from shallow parts of the continental margin into deeper water. (3) At the top, several thin "ripple beds" composed of fine sand are separated by clay drapes; they are interpreted as deposits of oscillating currents, perhaps a seiche. An iridium anomaly (921 +/- 23 pg/g) is observed at the top of the ripple beds. Our observations at the Mimbral locality support the hypothesis of a K-T impact on nearby Yucatn. PMID:11537752

  12. Surface alteration and physical properties of glass from the Cretaceous-Tertiary boundary

    USGS Publications Warehouse

    Barkatt, A.; Sang, J.C.; Thorpe, A.N.; Senftle, F.E.; Talmy, I.G.; Norr, M.K.; Mazer, J.J.; Izett, G.; Sigurdsson, Haraldur

    1994-01-01

    The scalloped surface feature on Cretaceous-Tertiary boundary glass is often explained as being due to terrestrial aqueous leaching. Leaching of man-made glass results in a reduction in density of the glass. Also, Fe, because of its relative insolubility, is concentrated by the leaching process. Thus, the Haitian glass specimens which have been heavily altered should have a thin rim of less dense glass in which the Fe is concentrated compared to the core glass. The higher Fe concentration in the rim glass should cause it to have an enhanced Curie constant and a lower density compared to the unaltered glass. The magnetic Curie constant, density, and scanning electron microscopic studies were made on altered specimens of Haitian glass and also on specimens showing a minimum of alteration. The results show that the less altered samples have the highest density and the lowest Curie constant. The data substantiate the terrestrial hypothesis. ?? 1994.

  13. Oxygen isotope constraints on the origin of impact glasses from the cretaceous-tertiary boundary

    SciTech Connect

    Blum, J.D.; Chamberlain, C.P. )

    1992-08-21

    Laser-extraction oxygen isotope and major element analyses of individual glass spherules from Haitian Cretaceous-Tertiary boundary sediments demonstrate that the glasses fall on a mixing line between an isotopically heavy ({delta}{sup 18}O = 14 per mil) high-calcium composition and an isotopically light ({delta}{sup 18}O = 6 per mil) high-silicon composition. This trend can be explained by melting of heterogeneous source rocks during the impact of an asteroid (or comet) {approximately}65 million years ago. The data indicate that the glasses are a mixture of carbonate and silicate rocks and exclude derivation of the glasses either by volcanic processes or as mixtures of sulfate-high evaporate and silicate rocks.

  14. Oxygen isotope constraints on the origin of impact glasses from the cretaceous-tertiary boundary.

    PubMed

    Blum, J D; Chamberlain, C P

    1992-08-21

    Laser-extraction oxygen isotope and major element analyses of individual glass spherules from Haitian Cretaceous-Tertiary boundary sediments demonstrate that the glasses fall on a mixing line between an isotopically heavy (delta(18)O = 14 per mil) high-calcium composition and an isotopically light (delta(18)O = 6 per mil) high-silicon composition. This trend can be explained by melting of heterogeneous source rocks during the impact of an asteroid (or comet) approximately 65 million years ago. The data indicate that the glasses are a mixture of carbonate and silicate rocks and exclude derivation of the glasses either by volcanic processes or as mixtures of sulfate-rich evaporate and silicate rocks. PMID:17840280

  15. Maastrichtian molluscan biostratigraphy and extinction patterns in a Cretaceous/Tertiary boundary section exposed at Zumaya, Spain

    NASA Astrophysics Data System (ADS)

    Ward, Peter; Wiedmann, Jost; Mount, Jeffrey F.

    1986-11-01

    Ammonites and inoceramid bivalves were stratigraphically collected from lower and upper Maastrichtian units in continuous exposure along the seacoast near Zumaya, Spain. Three ammonite teilzones can be recognized: (1) a lower zone correlative with parts of the Globotruncana ganserri planktonic foram zone and characterized by numerous inoceramids among three different species as well as Pachydiscus neubergicus, a noded Baculites, Polyptychoceras sipho, and Hauericeras renbda; (2) a middle zone that has no inoceramids but that has Pachydiscus fresvillensis and P. neubergicus and is correlative with the lower parts of the Abathomphalus mayaroensis Zone (planktonic foram); and (3) an upper zone that has P. colligatus and is correlative with the upper parts of the A. mayaroensis Zone. These three teilzones may be the basis for a Tethyan, facies-wide ammonite zonation of the Maastrichtian. The four main components of the fossil record at the Zumaya section show differing range characteristics with respect to the Cretaceous/Tertiary (K/T) boundary exposed in this section. The inoceramids disappear at the top of the lower Maastrichtian, except for the small enigmatic form Tenuipteria, which has a restricted range in the uppermost levels of the Cretaceous. Ammonites range upward to levels approximately 10 m below the boundary. Most larger planktonic forams and many nannofossil species disappear within several centimetres of the boundary. Echinoid fossils range up to, and possibly across, the K/T boundary. The Zumaya section is thus characterized by apparently nonsynchronous or graded extinctions of most of its fossil content.

  16. Iridium and trace element measurements from the Cretaceous-Tertiary boundary, site 752, Broken Ridge, Indian Ocean

    NASA Technical Reports Server (NTRS)

    Schuraytz, B. C.; O'Connell, S.; Sharpton, V. L.

    1991-01-01

    Fourteen samples spanning a 2.5 m interval that includes the Cretaceous-Tertiary (K/T) boundary from Hole 752B near the crest of Broken Ridge in the eastern Indian Ocean were studied in order to search for anomalous enrichments of iridium (Ir) and shock-metamorphosed quartz grains. No allogenic quartz grains larger than 10 microns were observed, hence the presence of quartz containing diagnostic evidence of shock-metamorphism could not be confirmed. Two Ir anomalies of 2.2 +/- 0.6 and 2.0 +/- 0.4 parts per billion (ppb) were measured in samples of dark green ash-bearing chalk at depths of 357.93 and 358.80 m below seafloor, respectively. These samples containing anomalous enrichments of Ir were taken from approximately 82 cm above and 5 cm below the extinction level of Globotruncanids. Our results are consistent with those of Michel et al., who observe elevated concentrations of Ir at these depths in addition to a larger Ir anomaly associated with the extinction level of Globotruncanids.

  17. Biotic, geochemical, and paleomagnetic changes across the Cretaceous/Tertiary boundary at Braggs, Alabama

    NASA Astrophysics Data System (ADS)

    Jones, Douglas S.; Mueller, Paul A.; Bryan, Jonathan R.; Dobson, Jon P.; Channell, James E. T.; Zachos, James C.; Arthur, Michael A.

    1987-04-01

    Exposed near Braggs, Alabama, is one of the few well-studied, nearly continuous shallow-marine Cretaceous/Tertiary boundary sections; it allows a glimpse of the biotic and environmental changes that occurred in the latest Cretaceous to earliest Paleocene. Paleomagnetic, strontium isotopic, and biostratigraphic data closely constrain the age of a series of lithologic, geochemical, and biotic variations and suggest that no more than 100 200 ka could be missing at the boundary. A major reduction in macrofaunal diversity associated with lithofacies changes occurs prior to but within 300 ka of the nannofossil-defined boundary. Approximately 40% of the apparent faunal reduction is attributed to the Lazarus effect. Faunal and floral assemblages, trends in carbon isotopic composition of benthic invertebrates, and lithologic characteristics indicate that a latest Maestrichtian regression culminated near the boundary (Chron C29R; Micula murus zone), significantly later than recent estimates. Water depths at this site remained shallow during the subsequent early Paleocene (zone NP1) transgression and did not reach depths equivalent to those of the late Maestrichtian until zone NP2. Relatively minor climatic changes across the boundary are suggested by a ?4 C cooling trend seen in the oxygen-isotope paleotemperatures. A high-resolution 87Sr/86Sr record from well-preserved macrofossil calcite shows a pattern of smooth variation and elevated values near the boundary; however, the early Paleocene spike of other workers was not found.

  18. Iridium profile for 10 million years across the Cretaceous-Tertiary boundary at Gubbio (Italy)

    NASA Technical Reports Server (NTRS)

    Alvarez, Walter; Asaro, Frank; Montanari, Alessandro

    1990-01-01

    The iridium anomaly at the Cretaceous-Tertiary (KT) boundary was discovered in the pelagic limestone sequence at Gubbio on the basis of 12 samples analyzed by neutron activation analysis (NAA) and was interpreted as indicating impact of a large extraterrestrial object at exactly the time of the KT mass extinction. Continuing controversy over the shape of the Ir profile at the Gubbio KT boundary and its interpretation called for a more detailed follow-up study. Analysis of a 57-meter-thick, 10-million-year-old part of the Gubbio sequence using improved NAA techniques revealed that there is only one Ir anomaly at the KT boundary, but this anomaly shows an intricate fine structure, the origin of which cannot yet be entirely explained. The KT Ir anomaly peaks in a 1-centimeter-thick clay layer, where the average Ir concentration is 3000 parts per trillion (ppt); this peak is flanked by tails with Ir concentrations of 20 to 80 ppt that rise above a background of 12 to 13 ppt. The fine structure of the tails is probably due in part to lateral reworking, diffusion, burrowing, and perhaps Milankovitch cyclicity.

  19. Iridium profile for 10 million years across the Cretaceous-Tertiary boundary at Gubbio (Italy).

    PubMed

    Alvarez, W; Asaro, F; Montanari, A

    1990-12-21

    The iridium anomaly at the Cretaceous-Tertiary (KT) boundary was discovered in the pelagic limestone sequence at Gubbio on the basis of 12 samples analyzed by neutron activation analysis (NAA) and was interpreted as indicating impact of a large extraterrestrial object at exactly the time of the KT mass extinction. Continuing controversy over the shape of the Ir profile at the Gubbio KT boundary and its interpretation called for a more detailed follow-up study. Analysis of a 57-meter-thick, 10-million-year-old part of the Gubbio sequence using improved NAA techniques revealed that there is only one Ir anomaly at the KT boundary, but this anomaly shows an intricate fine structure, the origin of which cannot yet be entirely explained. The KT Ir anomaly peaks in a 1-centimeter-thick clay layer, where average Ir concentration is 3000 parts per trillion (ppt); this peak is flanked by tails with Ir concentrations of 20 to 80 ppt that rise above a background of 12 to 13 ppt. The fine structure of the tails is probably due in part to lateral reworking, diffusion, burrowing, and perhaps Milankovitch cyclicity. PMID:11538083

  20. Geochemical Markers of the Cretaceous-Tertiary Boundary Event at Brazos River, Texas, USA

    NASA Astrophysics Data System (ADS)

    Heymann, D.; Yancey, T. E.; Wolbach, W. S.; Thiemens, M. H.; Johnson, E. A.; Roach, D.; Moecker, S.

    1998-01-01

    The Cretaceous-Tertiary boundary sites around the Gulf of Mexico are close to the Chixculub impact site and are relatively well studied, yet much remains to be learned about them. Therefore, the first integrated study of carbon, soot, and fullerenes in a Cretaceous-Tertiary boundary section was undertaken at the Brazos-1 site on the Brazos River in Texas at the most complete section of end Cretaceous and basal Paleocene deposits on the Texas segment of the Gulf Coast area. Up to 409 ppm of native sulfur (S o) were serendipitously discovered in a spherule-bearing unit of the BR-1 section, and lesser amounts were found in spherule-bearing units of nearby Brazos riverbed sections in a section on Darting Minnow Creek. The isotopic composition, ? 33S = -12.97, ? 34S = -24.89, and ? 36S = -46.4, implies that this S o cannot have come to Earth by the impactor that formed the Chicxulub crater, but, most likely, was produced by sulfate-reducing bacteria during a local, transient bacterial bloom for which the sulfate was provided by CaSO 4-bearing spherules. Carbon and soot were determined in twelve samples representing all units of BR-1 from the Cretaceous Corsicana/Kemp Formation to the Tertiary Kincaid Formation. A significant increase of C and soot contents, up to 2.210 4 ppm and 1.410 4 ppm, respectively, occurs in a sandy bed at the top of the KT complex. Fullerenes were determined in fifty-four samples from all units of the same BR-1 section. Less than 1 ppb was reliably detected at the same sandy bed where the strongest Ir anomaly of the section is known to occur. It is suggested here that the Chicxulub impact 65 Ma ago ignited local wildfires that produced C, soot, and fullerene, which settled onshore, or near-shore, whence they were transported to the Brazos site by coastal flooding and associated sediment-laden water plumes moving offshore.

  1. Octopods: Nude ammonoids that survived the Cretaceous-Tertiary boundary mass extinction

    NASA Astrophysics Data System (ADS)

    Lewy, Z.

    1996-07-01

    Certain ammonoids changed the mode of coiling or the growth angle of their last body chamber, constricted the terminal aperture, or developed apertural processes, which restricted all life functions. The modified terminal body chamber of macroconchs apparently functioned as a floating egg case for a single breeding phase. The young that hatched from tiny eggs fed on the enclosed female corpse. This same breeding strategy is executed by the extant octopod Argonauta. As a nude cephalopod, the sexually mature female secretes an egg case, which resembles Cretaceous ammonites, for the tiny eggs. The remarkable similarity in mode of breeding between Argonauta and ammonoids with modified terminal body chambers suggests that the ancestral argonautid was a nude ammonoid. Other octopods, which lay large, yolk-rich eggs attached onto substrates, likewise originate from ancestral nude ammonoids, which, however, did not breed in a floating egg case. Nude ammonoids crossed the Cretaceous-Tertiary boundary, as did the genuine coleoids comprising rudimentary endoskeletons.

  2. Modelling of dispersal and deposition of impact glass spherules from the Cretaceous-Tertiary boundary deposit

    NASA Technical Reports Server (NTRS)

    Espindola, J. M.; Carey, S.; Sigurdsson, H.

    1993-01-01

    The dispersal of glass spherules or tektites from a bolide impact with the Earth is modelled as ballistic trajectories in standard atmosphere. Ballistic dispersal of Cretaceous-Tertiary boundary impact glass spherules found in Haiti and Mimbral, Mexico requires a fireball radius in excess of 50 km but less than 100 km to account for the observed distribution. Glass spherules from 1 and up to 8 mm in diameter have been found at the KT boundary at Beloc in Haiti, at Mimbral, Mexico, and at DSDP Sites 536 and 540 in the Gulf of Mexico corresponding to paleodistances of 600 to 1000 km from the Chicxulub crater. In Haiti the basal and major glass-bearing unit at the KT boundary is attributed to fallout on basis of sedimentologic features. When compared with theoretical and observed dispersal of volcanic ejecta, the grain size versus distance relationship of the KT boundary tektite fallout is extreme, and rules out a volcanic fallout origin. At a comparable distance from source, the KT impact glass spherules are more than an order of mangitude coarser than ejecta of the largest known volcanic events. We model the dispersal of KT boundary impact glass spherules as ballistic ejecta from a fireball generated by the impact of a 10 km diameter bolide. Mass of ejecta in the fireball is taken as twice the bolide mass. Melt droplets are accelerated by gas flow in the fireball cloud, and leave the fireball on ballistic trajectories within the atmosphere, subject to drag, depending on angle of ejection and altitude. The model for ballistic dispersal is based on equations of motion, drag and ablation for silicate spheres in standard atmosphere.

  3. Proximal impact deposits at the Cretaceous-Tertiary boundary in the Gulf of Mexico: a restudy of DSDP Leg 77 Sites 536 and 540

    NASA Technical Reports Server (NTRS)

    Alvarez, W.; Smit, J.; Lowrie, W.; Asaro, F.; Margolis, S. V.; Claeys, P.; Kastner, M.; Hildebrand, A. R.

    1992-01-01

    Restudy of Deep Sea Drilling Project Sites 536 and 540 in the southeast Gulf of Mexico gives evidence for a giant wave at Cretaceous-Tertiary boundary time. Five units are recognized: (1) Cenomanian limestone underlies a hiatus in which the five highest Cretaceous stages are missing, possibly because of catastrophic K-T erosion. (2) Pebbly mudstone, 45 m thick, represents a submarine landslide possibly of K-T age. (3) Current-bedded sandstone, more than 2.5 m thick, contains anomalous iridium, tektite glass, and shocked quartz; it is interpreted as ejecta from a nearby impact crater, reworked on the deep-sea floor by the resulting tsunami. (4) A 50-cm interval of calcareous mudstone containing small Cretaceous planktic foraminifera and the Ir peak is interpreted as the silt-size fraction of the Cretaceous material suspended by the impact-generated wave. (5) Calcareous mudstone with basal Tertiary forams and the uppermost tail of the Ir anomaly overlies the disturbed interval, dating the impact and wave event as K-T boundary age. Like Beloc in Haiti and Mimbral in Mexico, Sites 536 and 540 are consistent with a large K-T age impact at the nearby Chicxulub crater.

  4. Proximal impact deposits at the Cretaceous-Tertiary boundary in the Gulf of Mexico: a restudy of DSDP Leg 77 Sites 536 and 540.

    PubMed

    Alvarez, W; Smit, J; Lowrie, W; Asaro, F; Margolis, S V; Claeys, P; Kastner, M; Hildebrand, A R

    1992-08-01

    Restudy of Deep Sea Drilling Project Sites 536 and 540 in the southeast Gulf of Mexico gives evidence for a giant wave at Cretaceous-Tertiary boundary time. Five units are recognized: (1) Cenomanian limestone underlies a hiatus in which the five highest Cretaceous stages are missing, possibly because of catastrophic K-T erosion. (2) Pebbly mudstone, 45 m thick, represents a submarine landslide possibly of K-T age. (3) Current-bedded sandstone, more than 2.5 m thick, contains anomalous iridium, tektite glass, and shocked quartz; it is interpreted as ejecta from a nearby impact crater, reworked on the deep-sea floor by the resulting tsunami. (4) A 50-cm interval of calcareous mudstone containing small Cretaceous planktic foraminifera and the Ir peak is interpreted as the silt-size fraction of the Cretaceous material suspended by the impact-generated wave. (5) Calcareous mudstone with basal Tertiary forams and the uppermost tail of the Ir anomaly overlies the disturbed interval, dating the impact and wave event as K-T boundary age. Like Beloc in Haiti and Mimbral in Mexico, Sites 536 and 540 are consistent with a large K-T age impact at the nearby Chicxulub crater. PMID:11538163

  5. Proximal impact deposits at the Cretaceous-Tertiary boundary in the Gulf of Mexico: A restudy of DSDP Leg 77 Sites 536 and 540

    SciTech Connect

    Alvarez, W.; Asaro, F. ); Smit, J. ); Lowrie, W. ); Asaro, F. ); Margolis, S.V.; Claeys, P. ); Kastner, M. ); Hildebrand, A.R. )

    1992-08-01

    Restudy of Deep Sea Drilling Project Sites 536 and 540 in the southeast Gulf of Mexico gives evidence for a giant wave at Cretaceous-Tertiary boundary time. Five units are recognized: (1) Cenomanian limestone underlies a hiatus in which the five highest Cretaceous stages are missing, possibly because of catastrophic K-T erosion. (2) Pebbly mudstone, 45 m thick, represents a submarine landslide possibly of K-T age. (3) Current-bedded sandstone, more than 2.5 m thick, contains anomalous iridium, tektite glass, and shocked quartz; it is interpreted as ejecta from a nearby impact crater, reworked on the deep-sea floor by the resulting tsunami. (4) A 50-cm interval of calcareous mudstone containing small Cretaceous planktic foraminifera and the Ir peak is interpreted as the silt-size fraction of the Cretaceous material suspended by the impact-generated wave. (5) Calcareous mudstone with basal Tertiary forams and the uppermost tail of the Ir anomaly overlies the disturbed interval, dating the impact and wave event as K-T boundary age. Like Beloc in Haiti and Mimbral in Mexico, Sites 536 and 540 are consistent with a large K-T age impact at the nearby Chicxulub crater.

  6. Cretaceous-tertiary boundary spherules and Cenozoic microtektites: Similarities and differences

    NASA Technical Reports Server (NTRS)

    Glass, B. P.; Bohor, Bruce F.; Betterton, William J.

    1993-01-01

    Bohor and Betterton pointed out that the K-T spherules can be divided into three groups. Their Type 1 spherules appear to be found in or adjacent to North America, particularly the Western Interior and in Haiti and Mexico. The Type 1 spherules occur in the lower part of the K-T boundary clay below an Ir anomaly. It is the Type 1 spherules which are most similar to microtektites. The discovery of K-T boundary spherules in Beloc, Haiti, and Mimbral, Mexico, with residual tektite-like glass cores supports the hypothesis that the Type 1 spherules are diagenetically altered microtektites. The similarities and differences of the Type 1 K-T boundary spherules to previously described Cenozoic microtektites are discussed.

  7. An atmospheric pCO2 reconstruction across the Cretaceous-Tertiary boundary from leaf megafossils

    PubMed Central

    Beerling, D. J.; Lomax, B. H.; Royer, D. L.; Upchurch, G. R.; Kump, L. R.

    2002-01-01

    The end-Cretaceous mass extinctions, 65 million years ago, profoundly influenced the course of biotic evolution. These extinctions coincided with a major extraterrestrial impact event and massive volcanism in India. Determining the relative importance of each event as a driver of environmental and biotic change across the Cretaceous-Tertiary boundary (KTB) crucially depends on constraining the mass of CO2 injected into the atmospheric carbon reservoir. Using the inverse relationship between atmospheric CO2 and the stomatal index of land plant leaves, we reconstruct Late Cretaceous-Early Tertiary atmospheric CO2 concentration (pCO2) levels with special emphasis on providing a pCO2 estimate directly above the KTB. Our record shows stable Late Cretaceous/Early Tertiary background pCO2 levels of 350500 ppm by volume, but with a marked increase to at least 2,300 ppm by volume within 10,000 years of the KTB. Numerical simulations with a global biogeochemical carbon cycle model indicate that CO2 outgassing during the eruption of the Deccan Trap basalts fails to fully account for the inferred pCO2 increase. Instead, we calculate that the postboundary pCO2 rise is most consistent with the instantaneous transfer of ?4,600 Gt C from the lithic to the atmospheric reservoir by a large extraterrestrial bolide impact. A resultant climatic forcing of +12 W?m?2 would have been sufficient to warm the Earth's surface by ?7.5C, in the absence of counter forcing by sulfate aerosols. This finding reinforces previous evidence for major climatic warming after the KTB impact and implies that severe and abrupt global warming during the earliest Paleocene was an important factor in biotic extinction at the KTB. PMID:12060729

  8. The Cretaceous/Tertiary Extinction Controversy Reconsidered.

    ERIC Educational Resources Information Center

    McCartney, Kevin; Nienstedt, Jeffrey

    1986-01-01

    Reviews varying positions taken in the Cretaceous/Tertiary (K/Y) extinction controversy. Analyzes and contests the meteoritic impact theory known as the Alvarez Model. Presents an alternative working hypothesis explaining the K/T transition. (ML)

  9. The Manson impact structure - Its contribution to impact materials observed at the Cretaceous/Tertiary boundary

    NASA Technical Reports Server (NTRS)

    Anderson, Raymond R.; Hartung, Jack B.

    1992-01-01

    The Manson impact structure (MIS) in Iowa is an excellently preserved complex crater that formed 65.7 Ma ago at the K/T boundary. Drill and seismic data have been used to identify three primary terranes within the 35-km diameter crater: (1) an outermost ring graben composed of listric normal fault blocks that structurally preserve Paleozoic and Cretaceous strata, impact ejecta, and possibly earliest Tertiary lake sediments; (2) a crater moat region of slumped and fallback materials overlain by Tertiary lake sediments in most areas; and (3) a central peak of uplifted basement rock capped in many areas by impact breccia. It is argued that concentrations of Ir at a K/T boundary exposure near Gubbio, Italy and clasts of glass reported from the K/T boundary in Haiti are consistent with possible production in the MIS.

  10. The Unique Significance and Origin of the Cretaceous-Tertiary Boundary: Historical Context and Burdens of Proof

    NASA Technical Reports Server (NTRS)

    Ryder, Graham

    1996-01-01

    The abruptness and intensity of the Cretaceous-Tertiary boundary have been deemphasized by some authors over recent years, mainly by those skeptical of an impact origin for the boundary. However, it was recognized at the birth of stratigraphy as both abrupt and of major importance. It was used to define the change from the Mesozoic to the Cenozoic; the boundary has become continually more precisely defined and its global sequences more correlatable. It is now unique in being an event boundary marked by an iridium-bearing layer of global extent, rather than an arbitrary boundary in a sequence of little change. The Permian-Triassic boundary, in contrast, is arbitrary and the transition is not yet proven to be abrupt, the extinctions that define it perhaps having taken place in pulses over several millions of years. Some of those who have denied the importance (and in some cases even the existence) of an impact in the Cretaceous-Tertiary extinctions have placed burdens of proof on the impact hypothesis that they do not place on strictly terrestrial mechanisms. Terrestrial mechanisms have always been unsatisfactory (or at least unconvincing for global, massive, multienvironment faunal change) and are now even more so. Some authors have required of the impact hypothesis attributes that are not inherent in it, including particular patterns of extinction selectivity and timing.

  11. The Origin of Fullerenes in the 65 Myr Old Cretaceous/Tertiary Boundary

    NASA Technical Reports Server (NTRS)

    Becker, L.; Poreda, R. J.; Bunch, T. E.

    2000-01-01

    In this work we have searched for extraterrestrial (ET) helium (He) in fullerenes isolated from several K/T boundary (KTB) sediments. Measurements of He in these KTB fullerene residues revealed He-3/He-4 ratios that can only be explained as ET in origin.

  12. New Evidence links Deccan Traps to the Cretaceous-Tertiary Boundary Mass Extinction

    NASA Astrophysics Data System (ADS)

    Adatte, T.; Keller, G.

    2012-04-01

    Recent studies indicate that Deccan Trap volcanism began with a relatively minor eruption phase (~6% of total volume) during the late Maastrichtian magnetic polarity C30n. The main eruption phase (~80%) occurred over a short period in C29r just below the Cretaceous-Tertiary boundary (KTB) and the last Deccan phase (~14%) erupted in the early Danian C29n. Multiproxy studies from sections in Meghalaya (NE India), Jhilmili in central India (Madhya Pradesh), 6 quarry outcrops from Rajahmundry (SE India), 10 deep wells from the Krishna-Godavari Basin (K-G) (Andhra Pradesh) place the KTB mass extinction near the end of the main Deccan phase coincident with the mass extinction. These studies show that the second and third phase of eruptions each produced the world's largest and longest lava megaflows ~1500 km across India through the K-G Basin into the Bay of Bengal. These megaflows are separated by sand, silt and shale which record the mass extinction across an interval that spans zones CF1-CF2 and most of the nannofossil Micula prinsii zone and is correlative with the rapid global warming and subsequent cooling near the end of the Maastrichtian. The mass extinction began preceding the first of the four mega-flows in C29r. Planktic foraminifera suffered a 50% drop in species richness. Survivors suffered another 50% drop after the first mega-flow, leaving just 7 to 8 survivor species. No recovery occurred between the next three mega-flows and the mass extinction was complete with the last phase-2 megaflow at the KTB. The last phase of Deccan volcanism and its 3 to 4 megaflows in the early Danian C29n (zone P1b) delayed biotic recovery of marine plankton. Correlative with these intense volcanic phases, climate changed from humid/tropical to arid conditions and returned to normal tropical humidity after the last phase of volcanism. Similar environmental conditions, mass extinction and delayed recovery patterns are observed in Meghalaya, NE India.The mass extinction was likely the consequence of rapid and massive volcanic CO2 and SO2 gas emissions, leading to high continental weathering rates, global warming, cooling, acid rains, ocean acidification and a carbonate crisis in the marine environment.

  13. Comet dust as a source of amino acids at the Cretaceous/Tertiary boundary

    NASA Technical Reports Server (NTRS)

    Zahnle, Kevin; Grinspoon, David

    1990-01-01

    It is suggested here that the large amounts of apparently extraterrestrial amino acids detected recently in rocks at the K/T boundary at Stevns Klint, Denmark were actually deposited with the dust from a giant comet trapped in the inner solar system, a fragment of which comprised the K/T impactor. Amino acids or their precursors in the comet dust would have been swept up by the earth both before and after the impact, but any conveyed by the impactor itself would have been destroyed. The observed amino acid layers would thus have been deposited without an impact.

  14. Ar-40 to Ar-39 ages of the large impact structures Kara and Manicouagan and their relevance to the Cretaceous-Tertiary and the Triassic-Jurassic boundary

    NASA Technical Reports Server (NTRS)

    Trieloff, M.; Jessberger, E. K.

    1992-01-01

    Since the discovery of the Ir enrichment in Cretaceous-Tertiary boundary clays in 1980, the effects of a 10-km asteroid impacting on the Earth 65 Ma ago have been discussed as the possible reason for the mass extinction--including the extinction of the dinosaurs--at the end of the Cretaceous. But up to now no crater of this age that is large enough (ca. 200 km in diameter) has been found. One candidate is the Kara Crater in northern Siberia. Kolesnikov et al. determined a K-Ar isochron of 65.6 +/- 0.5 Ma, indistinguishable from the age of the K-T boundary and interpreted this as confirmation of earlier proposals that the Kara bolide would have been at least one of the K-T impactors. Koeberl et al. determined Ar-40 to Ar-39 ages ranging from 70 to 82 Ma and suggested an association to the Campanian-Maastrichtian boundary, another important extinction horizon 73 Ma ago. We dated four impact melts, KA2-306, KA2-305, SA1-302, and AN9-182. Results from the investigation are discussed.

  15. Evidence for a single impact at the Cretaceous-Tertiary boundary from trace elements

    NASA Technical Reports Server (NTRS)

    Gilmour, Iain; Anders, Edward

    1988-01-01

    Not only meteoritic elements (Ir, Ni, Au, Pt metals), but also some patently non-meteoritic elements (As, Sb) are enriched at the K-T boundary. Eight enriched elements at 7 K-T sites were compared and it was found that: All have fairly constant proportions to Ir and Kilauea (invoked as an example of a volcanic source of Ir by opponents of the impact theory) has too little of 7 of these 8 elements to account for the boundary enrichments. The distribution of trace elements at the K-T boundary was reexamined using data from 11 sites for which comprehensive are available. The meteoritic component can be assessed by first normalizing the data to Ir, the most obviously extraterrestrial element, and then to Cl chondrites. The double normalization reduces the concentration range from 11 decades to 5 and also facilitates the identification of meteoritic elements. At sites where trace elements were analyzed in sub-divided samples of boundary clay, namely, Caravaca (SP), Stevns Klint (DK), Flaxbourne River (NZ) and Woodside Creek (NZ), Sb, As and Zn are well correlated with Ir across the boundary implying a common deposition mechanism. Elemental carbon is also enriched by up to 10,000 x in boundary clay from 5 K-T sides and is correlated with Ir across the boundary at Woodside Creek. While biomass would appear to be the primary fuel source for this carbon a contribution from a fossil fuel source may be necessary in order to account for the observed C abundance.

  16. Macrofossil extinction patterns at Bay of Biscay Cretaceous-Tertiary boundary sections

    NASA Technical Reports Server (NTRS)

    Ward, Peter D.; Macleod, Kenneth

    1988-01-01

    Researchers examined several K-T boundary cores at Deep Sea Drilling Project (DSDP) core repositories to document biostratigraphic ranges of inoceramid shell fragments and prisms. As in land-based sections, prisms in the deep sea cores disappear well before the K-T boundary. Ammonites show a very different extinction pattern than do the inoceramids. A minimum of seven ammonite species have been collected from the last meter of Cretaceous strata in the Bay of Biscay basin. In three of the sections there is no marked drop in either species numbers or abundance prior to the K-T boundary Cretaceous strata; at the Zumaya section, however, both species richness and abundance drop in the last 20 m of the Cretaceous, with only a single ammonite specimen recovered to date from the uppermost 12 m of Cretaceous strata in this section. Researchers conclude that inoceramid bivalves and ammonites showed two different times and patterns of extinction, at least in the Bay of Biscay region. The inoceramids disappeared gradually during the Early Maestrichtian, and survived only into the earliest Late Maestrichtian. Ammonites, on the other hand, maintained relatively high species richness throughout the Maestrichtian, and then disappeared suddenly, either coincident with, or immediately before the microfossil extinction event marking the very end of the Cretaceous.

  17. Iridium, shocked minerals, and trace elements across the Cretaceous/Tertiary boundary at Maud Rise, Wedell Sea, and Walvis Ridge, South Atlantic Ocean

    NASA Technical Reports Server (NTRS)

    Huffman, Alan R.; Crocket, James H.; Carter, Neville L.

    1988-01-01

    Sediments spanning a 5 meter section across the Cretaceous-Tertiary boundary at ODP holes 689B and 690D, Maud Rise, Wedell Sea and hole 527, Walvis Ridge, are being analyzed for shock deformation, PGE's and other trace elements (including REE's). Mineral separates from each sample were studied with optical microscopy to determine the distribution and microstructural state of quartz and feldspar present in the sediments. Samples from Maud Rise were taken of the K/T transition and at about 50 cm intervals above and below it. These samples consist of carbonate-rich sediments, with the K/T transition marked by a change from white Maastrichtian oozes to a greenish ooze with higher concentrations of altered volcanic clay and vitric ash. The Walvis Ridge site is characterized by more clay-rich sediments with average carbonate content about 60 to 70 percent. Initial results from RNAA studies indicate that iridium is present in all the Maud Rise samples in concentrations equal to or greater than 0.01 ppb (whole-rock basis). Preliminary results from optical microscopy indicate the occurrence of shock mosaicism in quartz and feldspar in all of the samples studied. The pervasiveness of shock mosaicism and presence of planar features to 2 meters from the K/T boundary indicates that a single impact or volcanic explosion 66 ma may be ruled out as responsible for the K/T event. A similar conclusion may be drawn independently from the distribution of iridium and other trace elements. Regardless of the source of the shock waves and sediment contamination, multiple events are required over a ca.0.5 my timespan; currently we favor endogenous sources.

  18. Extinction and survival of plant life following the Cretaceous/Tertiary boundary event, Western Interior, North America ( USA).

    USGS Publications Warehouse

    Tschudy, R.H.; Tschudy, B.D.

    1986-01-01

    The palynological Cretaceous/Tertiary boundary is recognized in the northern part of the Western Interior by the abrupt disappearance of a few characteristic Cretaceous pollen genera. In the southern part, the boundary is recognized by the disappearance of a somewhat different group of pollen. The abrupt change in both regions takes place precisely at the stratigraphic horizon at which boundary clay layers containing anomalously high concentrations of iridium are found. All the principal Cretaceous pollen genera that disappear regionally have been reported from Tertiary rocks in other parts of North America. Differential apparent extinction and/or survival reflects a pronounced temporary disruption of plant life immediately after the impact event. Some Cretaceous plants must have persisted in refugia to have provided the propagules for the rapid recovery of the flora. No massive total extinction of plant genera at the end of the Cretaceous can be seen from the palynologic record. -from Authors

  19. Ammonite and inoceramid bivalve extinction patterns in Cretaceous/Tertiary boundary sections of the Biscay region (southwestern France, northern Spain)

    NASA Astrophysics Data System (ADS)

    Ward, P. D.; Kennedy, W. J.; MacLeod, K. G.; Mount, J. F.

    1991-12-01

    Cretaceous/Tertiary boundary sections located in the Biscay region of southwestern France and northern Spain are among the most complete of all known land-based sequences across this boundary. New collections of ammonites and inoceramid bivalves from five localities show quite distinct extinction patterns for these two groups of characteristic Cretaceous molluscs: from eight to ten ammonite species extend into the latest Cretaceous, and possibly to the boundary. In contrast, inoceramid bivalve diversity gradually diminished from a minimum of six species in the early Maastrichtian to zero at the beginning of the late Maastrichtian, when they were replaced by the cryptic pteriomorph Tenuipteria. Extinction of typical inoceramids well before the end of the Maastrichtian is supported by data from other regions, indicating that it was a global rather than local phenomenon.

  20. Faunal, geochemical and paleomagnetic change across the Cretaceous-Tertiary boundary at Braggs, Alabama

    SciTech Connect

    Jones, D.S.; Mueller, P.A.; Channell, J.E.T.; Dobson, J.P.; Bryan, J.R.

    1985-01-01

    Near Braggs, Alabama the Upper Cretaceous Prairie Bluff Chalk underlies the Paleocene Pine barren Member of the Clayton Formation in a well-exposed, continuous K/T boundary section composed of interbedded sands, shales, and limestones of shallow marine origin. As determined from foraminiferal and calcareous nannofossil biostratigraphies, and the Maastrichtian/Danian contact at Braggs lies below a marine hardground in a zone associated with slow sedimentation and a deepening paleoenvironment. The K/T boundary occurs within a well-defined reversed magnetozone which we correlate to the reversed interval between marine magnetic anomalies 29 and 30. This magnetozone is approx.3.2 m thick, suggesting a sedimentation rate of only 6.8 m/m.y. across the boundary. The boundary occurs in the lower part of the magnetozone, about 1 m above its base, unlike the Italian sections where the boundary occurs toward the top of the reversed magnetozone. Marine macrofossils occur abundantly throughout the sequence had have been analyzed on a bed by bed basis to document the pattern of extinction and paleoenvironmental change. To help calibrate the rate of faunal change and refine the bio- and magnetostratigraphies, the Rb-Sr systematics of glauconites from the section are being investigated and the change of /sup 87/Sr//sup 86/Sr in seawater is being investigated by analysis of CaCO/sub 3/ from molluscan shells and foraminiferal tests. Initial Rb-Sr measurements of glauconites from a bed above the contact suggest an age of 60 Ma with an initial /sup 87/Sr//sup 86/Sr compatible with /sup 87/Sr//sup 86/Sr measured in shell carbonate at this site. Values for shell carbonate range from .707713 to .707826 and appear to show a maximum near the boundary.

  1. The Cretaceous-Tertiary boundary interval in Badlands National Park, South Dakota

    USGS Publications Warehouse

    Stoffer, Philip W.; Messina, Paula; Chamberlain, John A., Jr.; Terry, Dennis O., Jr.

    2001-01-01

    A marine K-T boundary interval has been identified throughout the Badlands National Park region of South Dakota. Data from marine sediments suggest that deposits from two asteroid impacts (one close, one far away) may be preserved in the Badlands. These impact-generated deposits may represent late Maestrichtian events or possibly the terminal K-T event. Interpretation is supported by paleontological correlation, sequence stratigraphy, magnetostratigraphy, and strontium isotope geochronology. This research is founded on nearly a decade of NPS approved field work in Badlands National Park and a foundation of previously published data and interpretations. The K-T boundary occurs within or near the base of a stratigraphic interval referred to as the "Interior Zone." We interpret the stratigraphy of the Interior Zone as a series of distinct, recognizable lithologic members and units from oldest to youngest, an upper weathered interval of the Elk Butte Member of the Pierre Shale (early late Maestrichtian), a complete (albeit condensed) interval of Fox Hill Formation, a pedogenically altered K-T Boundary "Disturbed Zone," and a generally unresolved sequence of marine to marginal marine units ranging in age from possibly latest Maestrichtian to late Paleocene (the "Yellow Mounds"), that underlie a basal red clay unit (the late Eocene overbank channel facies of the Chamberlain Pass Formation at the base of the White River Group). Within this sequence is a series of unconformities that all display some degree of subaerial weathering and erosion. The dating of marine fossils above and below these unconformities are in line with generally accepted global sea-level changes recognized for the late Campanian through early Eocene. Within the greater framework of regional geology, these findings support that the Western Interior Seaway and subsequent Cannonball Seaway were dependently linked to the changing base-level controlled by sea-level of the global ocean through the Gulf of Mexico and possibly the Arctic Ocean. The variation of facies preserved in Late Cretaceous strata in the Badlands National Park area were in part controlled by local or regional tectonic blocks that were either rising or sinking contemporaneous with deposition.

  2. The Cretaceous-Tertiary boundary marine extinction and global primary productivity collapse

    NASA Technical Reports Server (NTRS)

    Zachos, J. C.; Arthus, M. A.; Dean, W. E.

    1988-01-01

    The extinction of marine phyto-and zoo-plankton across the K-T boundary has been well documented. Such an event may have resulted in decreased photosynthetic fixation of carbon in surface waters and a collapse of the food chain in the marine biosphere. Because the vertical and horizontal distribution of the carbon isotopic composition of total dissolved carton (TDC) in the modern ocean is controlled by the transfer of organic carbon from the surface to deep reservoirs, it follows that a major disruption of the marine biosphere would have had a major effect on the distribution of carbon isotopes in the ocean. Negative carbon isotope excursions have been identified at many marine K-T boundary sequences worldwide and are interpreted as a signal of decreased oceanic primary productivity. However, the magnitude, duration and consequences of this productivity crisis have been poorly constrained. On the basis of planktonic and benthic calcareous microfossil carbon isotope and other geochemical data from DSDP Site 577 located on the Shatsky Rise in the north-central Pacific, as well as other sites, researchers have been able to provide a reasonable estimate of the duration and magnitude of this event.

  3. Ruthenium/iridium ratios in the Cretaceous-Tertiary boundary clay: Implications for global dispersal and fractionation within the ejecta cloud

    NASA Technical Reports Server (NTRS)

    Evans, Noreen Joyce; Goodfellow, W. D.; Gregoire, D. C.; Veizer, J.

    1992-01-01

    Ruthenium (Ru) and iridium (Ir) are the least mobile platinum group elements (PGE's) within the Cretaceous-Tertiary (K-T) boundary clay (BC). The Ru/Ir ratio is, therefore, the most useful PGE interelement ratio for distinguishing terrestrial and extraterrestrial contributions to the BC. The Ru/Ir ratio of marine K-T sections (1.77 +/- 0.53) is statistically different from that of the continental sections (0.93 +/- 0.28). The marine Ru/Ir ratios are chondritic (C1 = 1.48 +/- 0.09), but the continental ratios are not. We discovered an inverse correlation of shocked quartz size (or distance from the impact site) and Ru/Ir ratio. This correlation may arise from the difference in Ru and Ir vaporization temperature and/or fractionation during condensation from the ejecta cloud. Postsedimentary alteration, remobilization, or terrestrial PGE input may be responsible for the Ru/Ir ratio variations within the groups of marine and continental sites studied. The marine ratios could also be attained if approximately 15 percent of the boundary metals were contributed by Deccan Trap emissions. However, volcanic emissions could not have been the principal source of the PGE's in the BC because mantle PGE ratios and abundances are inconsistent with those measured in the clay. The Ru/Ir values for pristine Tertiary mantle xenoliths (2.6 +/- 0.48), picrites (4.1 +/- 1.8), and Deccan Trap basalt (3.42 +/- 1.96) are all statistically distinct from those measured in the K-T BC.

  4. Dynamic deformation of volcanic ejecta from the Toba caldera: possible relevance to Cretaceous/Tertiary boundary phenomena

    SciTech Connect

    Carter, N.L.; Officer, C.B.; Chesner, C.A.; Rose, W.I.

    1986-05-01

    Plagioclase and biotite phenocrysts in ignimbrites erupted from the Toba caldera, Sumatra, show microstructures and textures indicative of shock stress levels higher than 10 GPa. Strong dynamic deformation has resulted in intense kinking in biotite and, with increasing shock intensity, the development of plagioclase of planar features, shock mosaicism, incipient recrystallization, and possible partial melting. Microstructures in quartz indicative of strong shock deformation are rare, however, and many shock lamellae, if formed, may have healed during post-shock residence in the hot ignimbrite; they might be preserved in ash falls. Peak shock stresses from explosive silicic volcanism and other endogenous processes may be high and if so would obviate the need for extraterrestrial impacts to produce all dynamically deformed structures, possibly including shock features observed near the Cretaceous/Tertiary boundary. 38 references, 3 figures.

  5. Extended period of K/T boundary mass extinction in the marine realm

    NASA Technical Reports Server (NTRS)

    Keller, G.

    1988-01-01

    The Cretaceous/Tertiary (K/T) boundary mass extinction has been widely recognized as a nearly instantaneous catastrophy among marine plankton such as foraminifera. However, the suddenness of this extinction event may have been overemphasized because most pelagic K/T boundary sequences are stratigraphically incomplete and generally lack the earliest Tertiary (Zones P0 and P1a) either due to carbonate dissolution and/or non-deposition. Stratigraphically complete sections appear to be restricted to continental shelf regions with high sedimentation rates and deposition well above the CCD. Such sections have been recovered from El Kef, Tunisia (1) and Brazos River, Texas. Quantitative foraminiferal analysis of these sections indicate an extinction pattern beginning below the K/T boundary and ending above the boundary. These data imply that the mass extinction event was not geologically instantaneous, but occurred over an extended period of time. Evidence supporting this conclusion is discussed.

  6. Nitrogen geochemistry of a Cretaceous-Tertiary boundary site in New Zealand

    NASA Technical Reports Server (NTRS)

    Gilmour, Iain; Boyd, Stuart R.

    1988-01-01

    Nitrogen in the basal layer of the K-T boundary clay at Woodside Creek, New Zealand, has an abundance of 1100 ppm, a 20-fold enrichment over Cretaceous and Tertiary values. The enrichment parallels that for Ir and elemental carbon (soot); all decrease over the next 6 mm of the boundary clay. The C/N ratio, assuming the nitrogen to be associated with organic rather than elemental carbon, is approximately 5 for the basal layer compared to 20 to 30 for the remainder of the boundary clay. The correlation between N and Ir abundances appears to persist above the boundary, implying that the N is intimately associated with the primary fallout and remained with it during the secondary redeposition processes that kept the Ir abundance relatively high into the lowermost Tertiary. Apparently the basal layer of the boundary clay represents the accumulation of a substantial quantity of N with an isotopic composition approximately 10 percent heavier than background delta value of N-15 values. If the boundary clay represents an altered impact glass from a meteorite impact than it probably denotes a time period of less than 1 year. Therefore, the changes in nitrogen geochemistry apparently occurred over a very short period of time. The high abundance of N and the correspondingly low C/N ratio may reflect enhanced preservation of organic material as a result of the rapid sweepout and burial of plankton by impact ejecta, with little or no bacterial degradation. It is conceivable that the shift in delta value of N-15 may represent an influx of nitrogen from a different source deposited contemporaneously with the impact ejecta. An interesting possibility is that it may be derived from nitrate, produced from the combustion of atmospheric nitrogen.

  7. Impact mineralogy and chemistry of the cretaceous-tertiary boundary at DSDP site 576

    NASA Technical Reports Server (NTRS)

    Bostwick, Jennifer A.; Kyte, Frank T.

    1993-01-01

    We have identified the K/T boundary in pelagic clay sediments from cores at DSDP Site 576 in the western North Pacific. Detailed geochemical and trace mineralogical analyses of this boundary section are in progress and initial results indicate similarities and differences relative to the only other clay core investigated in detail; DSDP Site 596, a locality in the western South Pacific. Peak Ir concentrations of 13 ng/g in DSDP Hole 576B are virtually identical with those observed in the South Pacific, but in the North Pacific this peak is much narrower and the integrated Ir fluence of 85 ng cm(exp -2) is 4 times lower (320 in Hole 596). Of the 34 elements measured, only Ir and Cr were found to have anomalous concentrations in K/T boundary samples. Trace mineral residues were obtained by washing away clays and sequential chemical leaches (including HF) to remove typical hydrogenous and biogenous sediment components (e.g., zeolites and radiolarian opal). We attempted to quantitatively recover the entire trace mineral assemblage for grains greater than 30 micrometers in diameter. Our mineral residues were dominated by two phases: quartz and magnesioferrite spinel. Other non-opaque mineral grains we have positively identified were trace K-feldspar, plagioclase, corundum, and muscovite. Of these only K-feldspar exhibited planar deformation features (PDF). We have not found abundant plagioclase, as in the South Pacific suggesting that this phase was either not preserved in the North Pacific, or that in the south, it has a non-impact (i.e., volcanic) source. PDF in quartz were commonly obscured by secondary overgrowths on the surfaces of quartz grains, presumably from diagenetic reprecipitation of silica dissolved from opaline radiolarian tests that are common in these sediments. However, careful examination revealed that most grains had multiple sets of PDF. Of the 133 quartz grains greater than 30 micrometers analyzed, 62 percent showed evidence of shock. The largest shocked grain recovered to date had a maximum diameter of 160 micrometers, consistent with other sites in the Pacific.

  8. Tektites in Cretaceous-Tertiary boundary rocks on Haiti and their bearing on the Alvarez impact extinction hypothesis

    USGS Publications Warehouse

    Izett, G.A.

    1991-01-01

    Relic tektites are associated with a Pt-group metal abundance anomaly and shocked minerals in a thin marl bed that marks the K-T boundary on Haiti. The presence of these three impact-produced materials at the precise K-T boundary enormously strengthens the Alvarez impact extinction hypothesis. The Haitian tektites are the first datable impact products in K-T boundary rocks, and 40Ar-39Ar ages of the glass show that the K-T boundary and impact event are coeval at 64.5 ?? 0.1 Ma. -from Author

  9. Chicxulub's Cretaceous-Tertiary Boundary Twin Crater. Was There a Double Impact in the Yucatan Peninsula?

    NASA Astrophysics Data System (ADS)

    Camargo, A. Z.; Juarez, J. S.

    2004-05-01

    In 1980, Alvarez and co-authors proposed that the K/T extinctions were caused by the effects of a celestial body falling on Earth. After a long search for the impact site, the 1981 work by Penfield and Camargo on a 170 km structure in the Yucatan Peninsula got the attention of the specialists, and it was later proved that it was the crater created by the impact of that celestial body. New data suggests the existence of a second impact crater close to Chicxulub, both being of the same age and created by two fragments of the same celestial boby. A new magnetic map plotted as a color-coded shaded relief surface, reveals a feature not evident before: two interlaced ringed anomalies of about 100 and 50 km diameters, the larger one related to the magnetic signature of the Chicxulub Crater, and the second located at its E-SE edge. The 50 km anomaly, with morphology similar to Chicxulub's, is interpreted as also corresponding to an impact crater, centered at about 89 Deg. Long. W and 21 Deg. Lat. N, close to the city of Izamal. The anomaly size indicates that the diameter of the IZAMAL CRATER is about 85 km. The Chicxulub Crater, being buried under several hundred meters of Tertiary carbonate rocks, is not visible from the surface or from space; although some surface expression of its morphology has been reported. The best known is the ring of cenotes (sink holes) at the crater's rim, visible on satellite images and photographs. The JPL/NASA image PIA03379, is a color-coded shaded relief image of terrain elevation in which the topography was exagerated to highlight the Chicxulub Crater rim. On this image, a semi circular arc of dark spots is also visible immediately to the E-SE of the Chicxulub Crater rim. These spots are interpreted as large irregular karstic depressions, similar to the ones along the cenote ring of Chicxulub. On the evidence of the spatial relationship of the magnetic anomalies and the satellite image features, we tested how well the proposed Izamal Crater would fit the karstic depressions E-SE of the Chicxulub crater. We found that an 82 km diameter circle fits well the semi circle of dark spots, and interpret it as a portion of the rim of the IZAMAL impact crater. The interpreted relationships and origin of the Chicxulub and Izamal craters are: The Chicxulub crater was created after Izamal. They were created by two different impact bodies. The craters are of the same age. They were formed by two parts of the same celestial body, the MAYA BOLIDE. The diameter of the fragment impacted in Izamal is estimated to be about 4 km. This finding has implications on studies related to the K/T extinction event. Some scientists argue that the Chicxulub crater is somewhat small to account for the global K/T extinction all by itself. The double impact may account for the observed effects. Also, multiple impacts at sea may have put into the atmosphere much more sea water salts capable of dissociating into damaging chlorine compounds. Furthermore, the impact sequence may help explain the origin of the K/T boundary glasses from Haiti and better define the ballistic trajectories of the impacts ejecta and its effects on the extinctions. And the Maya Bolide orbit can be investigated to define its origin and characteristics as a comet or asteroid.

  10. Provenance of mineral phases in the Cretaceous-Tertiary boundary sediments exposed on the southern peninsula of Haiti

    NASA Technical Reports Server (NTRS)

    Kring, David A.; Hildebrand, Alan R.; Boynton, William V.

    1994-01-01

    Acid-insoluble mineral residua of tektite-bearing Cretaceous-Tertiary boundary sediments in the Beloc Formation of Haiti contain abundant shocked quartz and lesser amounts of shocked plagioclase. The shocked quartz grains typically have 2 or 3 sets of planar deformation features, although grains with up to 15 sets were observed. The proportion of shocked quartz in the boundary sediments increases with stratigraphic height; at least 70 +/- 11% of the proportion of the quartz grains are shocked in the uppermost stratigraphic interval. The proportion of shocked quartz throughout the boundary sediments indicates that these grains were excavated primarily from crystalline silicate units, which may have been covered with a small amount of porous quartz-bearing sediments. Polyhedral and moderately sutured margins in shocked polycrystalline quartz grains, the size of the crystal units in these grains and the presence of shocked plagioclase, indicate these ejecta components were excavated from a target with continental affinites, containing quartzites or metaquartzites and a sialic metamorphic and/or igneous component. Other evidence suggests the target may also have contained a significant amount of calcium carbonate and/or sulfate. The large size and amount of shocked quartz grains deposited in Haiti indicate the crater from which they were excavated was produced in the proto-Caribbean region.

  11. Field guide to Cretaceous-tertiary boundary sections in northeastern Mexico

    NASA Technical Reports Server (NTRS)

    Keller, Gerta; Stinnesbeck, Wolfgang; Adatte, Thierry; Macleod, Norman; Lowe, Donald R.

    1994-01-01

    This guide was prepared for the field trip to the KT elastic sequence of northeastern Mexico, 5-8 February 1994, in conjunction with the Conference on New Developments Regarding the KT Event and Other Catastrophes in Earth History, held in Houston, Texas. The four-day excursion offers an invaluable opportunity to visit three key outcrops: Arroyo El Mimbral, La Lajilla, and El Pinon. These and other outcrops of this sequence have recently been interpreted as tsunami deposits produced by the meteorite impact event that produced the 200 to 300-km Chicxulub basin in Yucatan, and distributed ejecta around the world approximately 65 m.y. ago that today is recorded as a thin clay layer found at the K/T boundary. The impact tsunami interpretation for these rocks has not gone unchallenged, and others examining the outcrops arrive at quite different conclusions: not tsunami deposits but turbidites; not KT at all but 'upper Cretaceous.' Indeed, it is in hopes of resolving this debate through field discussion, outcrop evaluation, and sampling that led the organizers of the conference to sanction this field trip. This field guide provides participants with background information on the KT clastic sequence outcrops and is divided into two sections. The first section provides regional and logistical context for the outcrops and a description of the clastic sequence. The second section presents three representative interpretations of the outcrops by their advocates. There is clearly no way that these models can be reconciled and so two, if not all three, must be fundamentally wrong. Readers of this guide should keep in mind that many basic outcrop observations that these models are based upon remain unresolved. While great measures were taken to ensure that the information in the description section was as objective as possible, many observations are rooted in interpretations and the emphasis placed on certain observations depends to some degree upon the perspective of the author.

  12. New method for the measurement of osmium isotopes applied to a New Zealand Cretaceous/Tertiary boundary shale

    USGS Publications Warehouse

    Lichte, F.E.; Wilson, S.M.; Brooks, R.R.; Reeves, R.D.; Holzbecher, J.; Ryan, D.E.

    1986-01-01

    The determination of osmium content and isotopic abundances in geological materials has received increasing attention in recent years following the proposal of Alvarez et al.1 that mass extinctions at the end of the Cretaceous period were caused by the impact of a large (???10km) meteorite which left anomalously high iridium levels as a geochemical signature in the boundary shales. Here we report a new and simple method for measuring osmium in geological materials, involving fusion of the sample with sodium peroxide, distillation of the osmium as the tetroxide using perchloric acid, extraction into chloroform, and absorption of the chloroform extract onto graphite powder before instrumental neutron activation analysis. In a variant of this technique, the chloroform extract is back-extracted into an aqueous phase and the osmium isotopes are determined by plasma-source mass spectrometry (ICPMS). We have used this method on the Woodside Creek (New Zealand) Cretaceous/Tertiary boundary clay and have obtained the first osmium content (6g ng g-1) for this material. The 187Os/186Os ratio is 1.12??0.16, showing a typical non-crustal signature. This combined distillation-extraction- ICPMS method will prove to be useful for measuring osmium isotopes in other geological materials. ?? 1986 Nature Publishing Group.

  13. Micropaleontology and sedimentology across the Cretaceous/Tertiary boundary at La Ceiba (Mexico): impact-generated sediment gravity flows

    NASA Astrophysics Data System (ADS)

    Arz, J. A.; Arenillas, I.; Soria, A. R.; Alegret, L.; Grajales-Nishimura, J. M.; Liesa, C. L.; Melndez, A.; Molina, E.; Rosales, M. C.

    2001-10-01

    A micropaleontological and sedimentological study across the Cretaceous/Tertiary boundary-officially Cretaceous/Paleogene (K/P) boundary from the La Ceiba section (Mexico) was performed to examine the K/P planktic foraminiferal biostratigraphy, the sedimentology of a controversial K/P clastic unit, and the benthic and planktic foraminiferal assemblages turnover across this boundary. The clastic unit is stratigraphically placed between two pelagic marly units (Mndez and Velasco Formations) and displays a fining-upward gradation similar to a turbidite sequence. This K/P clastic unit contains a basal subunit consisting of calcareous marls rich in millimeter-sized spherules (microtektites) altered to clay minerals, abundant detrital quartz, mica minerals, and shocked quartz. According to the K/P stratotype definition from El Kef (Tunisia), the K/P boundary at La Ceiba must be placed at the base of the clastic (microspherules) unit since it is equivalent to the base of the boundary clay at El Kef. A short hiatus affects the lower part of the Danian, including the Guembelitria cretacea and Parvularugoglobigerina eugubina biozones and the lower part of the Parasubbotina pseudobulloides biozone. Nearly all commonly recorded Maastrichtian planktic foraminiferal species were found in the uppermost Maastrichtian interval, and there was no support for a gradual mass extinction pattern in the terminal Cretaceous. Benthic foraminiferal assemblages suggest that the La Ceiba section was deposited at lower bathyal depths. Oscillating megatsunami waves and/or a sea-level lowstand cannot explain the nature of the clastic deposits because of the observed deposition paleodepth (more than 1000 m). There is also evidence that the clastic unit was deposited under a high-sedimentation rate in upper flow regimes and that was emplaced as a single-pulse event as turbidites. This datum and other sedimentological features support a sediment gravity flow genesis for the clastic unit. All these results are consistent with the K/P impact theory and the asteroid impact on the Yucatan Peninsula.

  14. Kara and Ust-Kara impact structures (USSR) and their relevance to the K/T boundary event

    NASA Technical Reports Server (NTRS)

    Koeberl, Christian; Sharpton, Virgil; Murali, A. V.; Burke, Kevin

    1990-01-01

    Ample evidence exists for at least one major meteorite impact event at the time of the Cretaceous/Tertiary (K/T) boundary, and it is therefore important to establish if any recognized terrestrial impact craters are K/T in age. The Kara, USSR, impact structure consists of two adjacent large impact craters (a rare and interesting geologic phenomenon), and it has been suggested that this twin impact structure might be related to the K/T boundary event. However, newly determined (Ar-40)/(Ar-39) and K-Ar ages presented here suggest that these structures are slightly older than 70 Ma, and may thus be too old for a 66 Ma K/T boundary event. Still, these two craters represent a substantial impact event that could have initiated regional, if not global, degradation of the biosphere. Their age suggests a possible relation with the Campanian/Maastrichtian boundary.

  15. Faunal and erosional events in the Eastern Tethyan Sea across the K/T boundary

    NASA Technical Reports Server (NTRS)

    Keller, G.; Benjamini, C.

    1988-01-01

    A regional pattern of three closely spaced erosional events at and above the K/T boundary was determined from six Cretaceous/Tertiary boundary sections in the Negev of Israel. The sections were collected from locations throughout the central and northern Negev. All sections are lithologically similar. The Maastrichtian consists of a sequence of limestone beds intercalated with thin marly beds. In some sections, the last limestone bed is followed by 1 to 2 m of calcareous marls grading upwards into several meters of grey shale. In other sections the limestone bed is followed directly by grey shale with the contact containing particles of limestone and marl. A 5 to 20 cm thick dark grey organic-rich clay layer is present about 1.5 to 2.5 m above the base of the grey shale. The grey shale grades upwards into increasingly carbonate rich marls. No unconformities are apparent in field outcrops. During field collection the dark grey clay layer was believed to represent the K/T boundary clay. Microfossil analysis however identified the boundary at the base of the grey shale. The black shale represents a low productivity anoxic event similar to, but younger than, the K/T boundary clay in other K/T boundary sections. High resolution planktic foraminiferal and carbonate analysis of these sections (at 5 to 10 cm intervals) yield surprising results. The K/T boundary is marked by an erosional event which removed part or all of the uppermost Maastrichtian marls above the last limestone bed. Percent carbonate data for four Negev sections are illustrated and show the regional similarities in carbonate sedimentation. Faunal and carbonate data from the Negev sections thus show three closely spaced short erosional events at the K/T boundary and within the first 50,000 to 100,000 years of the Danian. These K/T boundary erosional events may represent global climatic or paleoceanographic events.

  16. Quenched magnetite in cretaceous-tertiary boundary microtekite-like spheroid

    NASA Technical Reports Server (NTRS)

    Smit, J.; Kyte, F. T.; Wasson, J. T.

    1984-01-01

    The magnetite containing spheres collected from a kt boundary localities in Italy were analyzed. It was found that these spheres contain relatively high concentrations of Ir. The spheres were analyzed for siderophile elements Ir, Pt, Au, Pd, Os, and Re. Elements Ir, Pt, Pd, and Au were found in high concentrations in magnetic spheres and their concentrations are similar to those in most meteorites. It is suggested that the magnetite spheres do not contain a meteorite component which may be a relic of the kt event.

  17. A Search for Soot from Global Wildfires in Central Pacific Cretaceous-Tertiary Boundary and Other Extinction and Impact Horizon Sediments

    NASA Technical Reports Server (NTRS)

    Wolbach, Wendy S.; Widicus, Susanna; Kyte, Frank T.

    2003-01-01

    Hypotheses of global wildfires following the Cretaceous-Tertiary (KT) boundary impact are supported by high concentrations of elemental carbon (3.6 mg cm-3) and soot (1.8 mg cm-2) in DSDP Site 465, which was located several thousand kilometers from potential continental sources at 65 Ma. Soot is not preserved at four other central Pacific KT localities, but this is attributed to loss during oxic diagenesis. We find no evidence for wildfires related to major impacts in the late Eocene or to Ir anomalies and extinctions in the late Cenomanian.

  18. Detritus in K/T boundary clays of western North America - Evidence against a single oceanic impact

    NASA Technical Reports Server (NTRS)

    Sharpton, V. L.; Schuraytz, B. C.; Burke, K.; Murali, A. V.; Ryder, G.

    1990-01-01

    Understanding the crustal signature of impact ejecta contained in the Cretaceous/Tertiary (K/T) boundary layer is crucial to constraining the possible site(s) of the postulated K/T impact event. The relatively unaltered clastic constituents of the boundary layer at widely separated outcrops within the western interior of North America are not compatible with a single oceanic impact but require instead an impact site on a continent or continental margin. On the other hand, chemical compositions of highly altered K/T boundary layer components in some marine sections have suggested to others an impact into oceanic crust. We suspect that post-depositional alteration within the marine setting accounts for this apparent oceanic affinity. If, however, this is not the case, multiple simultaneous impacts, striking continent as well as ocean floor, would seem to be required.

  19. Shocked quartz and more: Impact signatures in K-T boundary clays and claystones

    NASA Technical Reports Server (NTRS)

    Bohor, Bruce F.

    1988-01-01

    Quartz grains displaying multiple sets of planar features are described from numerous Cretaceous-Tertiary (K-T) boundary clays and claystones at both marine and nonmarine depositional sites around the world. All these sites also show anomalously high amounts of iridium and enrichments of other siderophile elements in cosmic ratios within these boundary units. This combination of mineralogical and geochemical features are used in support of an impact hypothesis for the end-Cretaceous event. Recently, it was suggested that some combination of explosive and nonexplosive volcanism associated with the formation of the Deccan traps in India could be responsible for the mineralogy and geochemistry seen in the K-T boundary units. Besides the obvious contradition of simultaneous explosive and nonexplosive volcanism from one locality during an instant of geologic time, there remains the difficulty of spreading both iridium (and trace elements in cosmic proportions) and quartz grains around the world by volcanic (atmospheric) transport. In addition, the ability of volcanism to produce the type of shock metamorphism seen in minerals at the K-T boundary was not demonstrated. Multiple sets of shock lamellae in quartz are considered characteristic of shock metamorphism in rocks at the sites of known impact craters and are the type of deformation seen in quartz from K-T boundary clays and claystones. Single sets of poorly defined lamellae described from rare quartz grains in certain volcanic deposits are characteristic of tectonic deformation and do not correspond to the shock lamellae in quartz from K-T sediments and impact structures. So-called shock mosaicism in quartz and feldspar grains described from volcanic deposits can result from many processes other than shock metamorphism, and therefore is not considered to be an effect characteristic solely of shock. The mineralogy of shock-metamorphosed grains at the K-T boundary also argues against a volcanic origin.

  20. Deccan volcanism and K-T boundary signatures

    NASA Technical Reports Server (NTRS)

    Murali, A. V.; Schuraytz, B. C.; Parekh, P. P.

    1988-01-01

    The Deccan Traps in the Indian subcontinent represent one of the most extensive flood basalt provinces in the world. These basalts occur mainly as flat-lying, subaerially erupted tholeiitic lava flows, some of which are traceable for distances of more than 100 km. Offshore drilling and geophysical surveys indicate that a part of the Deccan subsided or was downfaulted to the west beneath the Arabian Sea. The presence of 1 to 5 m thick intertrappean sediments deposited by lakes and rivers indicates periods of quiescence between eruptions. The occurrence of numerous red bole beds among the flows suggests intense weathering of flow tops between eruptive intervals. Although the causative relationship of the Cretaceous-Tertiary (K-T) biotic extinctions to Deccan volcanism is debatable, the fact that the main Deccan eruptions straddle the K-T event appears beyond doubt from the recent Ar-40/Ar-39 ages of various Deccan flows. This temporal relationship of the K-T event with Deccan volcanism makes the petrochemical signatures of the entire Deccan sequence (basalt flows, intercalated intertrappean sediments, infratrappean Lameta beds (with dinosaur fossils), and the bole beds) pertinent to studies of the K-T event. The results of ongoing study is presented.

  1. Bio-, Magneto- and event-stratigraphy across the K-T boundary

    NASA Technical Reports Server (NTRS)

    Preisinger, A.; Stradner, H.; Mauritsch, H. J.

    1988-01-01

    Determining the time and the time structure of rare events in geology can be accomplished by applying three different and independent stratigraphic methods: Biostratigraphy, magneto-stratigraphy and event-stratigraphy. The optimal time resolution of the two former methods is about 1000 years, while by means of event-stratigraphy a resolution of approximately one year can be achieved. For biostratigraphy across the Cretaceous-Tertiary (K-T) boundary micro- and nannofossils have been found best suited. The qualitative and quantitative analyses of minerals and trace elements across the K-T boundary show anomalies on a millimeter scale and permit conclusions regarding the time structure of the K-T event itself. The results of the analyses find a most consistent explanation by the assumption of an extraterrestrial impact. The main portion of the material rain from the atmosphere evidently was deposited within a short time. The long-time components consist of the finest portion of the material rain from the atmosphere and the transported and redeposited fall-out.

  2. Impact wave deposits provide new constraints on the location of the K/T boundary impact

    NASA Technical Reports Server (NTRS)

    Hildebrand, A. R.; Boynton, W. V.

    1988-01-01

    All available evidence is consistent with an impact into oceanic crust terminating the Cretaceous Period. Although much of this evidence is incompatible with an endogenic origin, some investigators still feel that a volcanic origin is possible for the Cretaceous/Tertiary (K/T) boundary clay layers. The commonly cited evidence for a large impact stems from delicate clay layers and their components and the impact site has not yet been found. Impact sites have been suggested all over the globe. The impact is felt to have occurred near North America by: the occurrence of a 2 cm thick ejecta layer only at North American locales, the global variation of shocked quartz grain sizes peaking in North America, the global variation of spinel compositions with most refractory compositions occurring in samples from the Pacific region and possibly uniquely severe plant extinctions in the North American region. The K/T boundary interval was investigated as preserved on the banks of the Brazos River, Texas. The K/T fireball and ejecta layers with associated geochemical anomalies were found interbedded with this sequence which apparently allows a temporal resolution 4 orders of magnitude greater than typical K/T boundary sections. A literature search reveals that such coarse deposits are widely preserved at the K/T boundary. Impact wave deposits have not been found elsewhere on the globe, suggesting the impact occurred between North and South America. The coarse deposits preserved in Deep Sea Drilling Project (DSDP) holes 151-3 suggest the impact occurred nearby. Subsequent tectonism has complicated the picture.

  3. Constraints on the Nature and Distribution of Iridium Host Phases at the Cretaceous-Tertiary Boundary: Implications for Projectile Identity and dispersal on impact

    NASA Technical Reports Server (NTRS)

    Schuraytz, B. C.; Lindstrom, D. J.; Sharpton, V. L.

    1997-01-01

    Among Cretaceous-Tertiary boundary sites worldwide, variations in the concentrations and ratios of elements commonly enriched in meteorites complicate traditional geochemical attempts at impactor identification. Yet they may provide constraints on the physical and chemical processes associated with large-body disruption and dispersal, as well as with diagenesis of projectile components. To this end, we continue our efforts to identify the mineral host-phases of projectile-derived elements, particularly for Ir, and to document their partitioning between crater deposits and ejecta resulting from the Chicxulub basin-forming impact. Building on earlier work, we used INAA to measure Ir concentrations in successively smaller splits of finely powdered impact melt breccia from the Chicxulub Crater in Mexico (sample Y6Nl9-R(b)), and K/T boundary fish clay from Stevns Klint, Denmark (sample FC-1, split from 40 kg of homogenized material intended as an analytical standard). Results for the Chicxulub sample show a heterogeneous Ir distribution and document that at least five discrete Ir-bearing host phases were isolated in subsequent splits, having Ir masses equivalent to pure Ir spheres from about 0.8 to about 3.5 mm in diameter. Three of these are within a sufficiently reduced mass of powder to warrant searching for them using backscattered electron microscopy. In contrast, successively smaller splits of the Stevns Klint fish clay show no statistically significant deviation from the reported value of 32 +/- 2 ng/g Ir, suggesting a uniform Ir host-phase distribution. For the smallest split obtained thus far (100 +/- 40 ng/g Ir), a pure Ir sphere of equivalent Ir mass would be <0.05 min in diameter. (n.b. Although homogenizing and sieving of FC-1 to <75 min obviously obscured variations in stratigraphic distribution, it is unlikely to have affected the size-frequency distribution of Ir host phases.) We previously identified micrometer-scale Ir host phases by electron microscopy in melt-rock samples from two widely separated drill holes at the Chicxulub Basin, including a replicate split of Y6-NI9-R. One is an aggregate of subhedral Ir metal grains enclosed in silicate, in which no other Pt group elements (PGE) were detected. A second particle with twice the mass as the first, concentrated predominantly in a single grain, is associated with minor concentrations of Os, Ru, and Pt, and with adhering particles of corundum and perovskite. A third Ir-rich particle, with a greater apparent Os concentration, was identified before being lost as a result of charging under the electron beam. In addition to demonstrating the preservation of projectile components within the Chicxulub Crater, analogous phase associations in Ca- and Al-rich inclusions (CAI) from C2 and C3 chondrites suggest to us that these melt-rock Ir host phases are relics from a carbonaceous chondrite K/T boundary impactor Although the obviously low Ru/Ir ratios of the Chicxulub Ir host phases are qualitatively consistent with suggested PGE fractionation with distance during condensation in an ejecta cloud, it seems difficult to explain the accumulation of the about 3 x 10(exp 11) Ir atoms required to form a about 10(exp -10) g nugget of pure Ir metal within a jet of vaporized projectile expanding at 1-4 km/s, or to effectively exclude or remove commonly alloyed PGE and siderophile elements by fractionation processes resulting from condensation, oxidation, sulfidization, exsolution, or autometamorphism during cooling of the melt. We do not dismiss the importance of these processes entirely; on the contrary, other geochemical and mineralogical aspects of the melt rocks require them, and condensation from the expanding ejecta cloud appears to best explain the primary Ir host-phase distribution in the fish clay, as well as the high Ir concentrations associated with spinel-bearing spheroids at the K/T boundary in the Pacific Ocean . If the "relict" hypothesis is correct, micronuggets of other PGEs and alloys, not detected by our INAA screening, should also occur in the melt rocks. Possibly, the discrete host phases with lesser Ir masses are such alloys with subordinate Ir, rather than simply smaller, predominantly Ir-bearing particles. A CAI source for the relics would be consistent with either a comet or an asteroid K/T impact at Chicxulub. (Additional information contained in the original.)

  4. Platinum-group elements (PGE) and Rhenium in Marine Sediments across the Cretaceous-Tertiary Boundary: Constraints on Re-PGE Transport in the Marine Environment

    NASA Technical Reports Server (NTRS)

    Lee, Cin-Ty Aeolus; Wasserburg, Gerald J.; Kyte, Frank T.

    2003-01-01

    The nature of Re-platinum-group element (PGE; Pt, Pd, Ir, Os, Ru) transport in the marine environment was investigated by means of marine sediments at and across the Cretaceous-Tertiary boundary (KTB) at two hemipelagic sites in Europe and two pelagic sites in the North and South Pacific. A traverse across the KTB in the South Pacific pelagic clay core found elevated levels of Re, Pt, Ir, Os, and Ru, each of which is approximately symmetrically distributed over a distance of approx. 1.8 m across the KTB. The Re-PGE abundance patterns are fractionated from chondritic relative abundances: Ru, Pt, Pd, and Re contents are slightly subchondritic relative to Ir, and Os is depleted by approx. 95% relative to chondritic Ir proportions. A similar depletion in Os (approx. 90%) was found in a sample of the pelagic KTB in the North Pacific, but it is enriched in Ru, Pt, Pd, and Re relative to Ir. The two hemipelagic KTB clays have near-chondritic abundance patterns. The approx. 1.8-m-wide Re-PGE peak in the pelagic South Pacific section cannot be reconciled with the fallout of a single impactor, indicating that postdepositional redistribution has occurred. The elemental profiles appear to fit diffusion profiles, although bioturbation could have also played a role. If diffusion had occurred over approx. 65 Ma, the effective diffusivities are approx. 10(exp -13)sq cm/s, much smaller than that of soluble cations in pore waters (approx. 10(exp -5) sq cm/s). The coupling of Re and the PGEs during redistribution indicates that postdepositional processes did not significantly fractionate their relative abundances. If redistribution was caused by diffusion, then the effective diffusivities are the same. Fractionation of Os from Ir during the KTB interval must therefore have occurred during aqueous transport in the marine environment. Distinctly subchondritic Os/Ir ratios throughout the Cenozoic in the South Pacific core further suggest that fractionation of Os from Ir in the marine environment is a general process throughout geologic time because most of the inputs of Os and Ir into the ocean have OsAr ratios greater than or = 1. Mass balance calculations show that Os and Re burial fluxes in pelagic sediments account for only a small fraction of the riverine Os (less than 10%) and Re (less than 0.1%) inputs into the oceans. In contrast, burial of Ir in pelagic sediments is similar to the riverine Ir input, indicating that pelagic sediments are a much larger repository for Ir than for Os and Re. If all of the missing Os and Re is assumed to reside in anoxic sediments in oceanic margins, the calculated burial fluxes in anoxic sediments are similar to observed burial fluxes. However, putting all of the missing Os and Re into estuarine sediments would require high concentrations to balance the riverine input and would also fail to explain the depletion of Os at pelagic KTB sites, where at most approx. 25% of the K-T impactor's Os could have passed through estuaries. If Os is preferentially sequestered in anoxic marine environments, it follows that the OsAr ratio of pelagic sediments should be sensitive to changes in the rates of anoxic sediment deposition. There is thus a clear fractionation of Os and Re from Ir in precipitation out of sea water in pelagic sections. Accordingly, it is inferred here that Re and Os are removed from sea water in anoxic marine depositional regimes.

  5. Constraints on the Nature and Distribution of Iridium Host Phases at the Cretaceous-Tertiary Boundary: Implications for Projectile Identity and dispersal on impact

    NASA Technical Reports Server (NTRS)

    Schuraytz, B. C.; Lindstrom, D. J.; Sharpton, V. L.

    1997-01-01

    Among Cretaceous-Tertiary boundary sites worldwide, variations in the concentrations and ratios of elements commonly enriched in meteorites complicate traditional geochemical attempts at impactor identification. Yet they may provide constraints on the physical and chemical processes associated with large-body disruption and dispersal, as well as with diagenesis of projectile components. To this end, we continue our efforts to identify the mineral host-phases of projectile-derived elements, particularly for Ir, and to document their partitioning between crater deposits and ejecta resulting from the Chicxulub basin-forming impact. Building on earlier work, we used INAA to measure Ir concentrations in successively smaller splits of finely powdered impact melt breccia from the Chicxulub Crater in Mexico (sample Y6Nl9-R(b)), and K/T boundary fish clay from Stevns Klint, Denmark (sample FC-1, split from 40 kg of homogenized material intended as an analytical standard). Results for the Chicxulub sample show a heterogeneous Ir distribution and document that at least five discrete Ir-bearing host phases were isolated in subsequent splits, having Ir masses equivalent to pure Ir spheres from about 0.8 to about 3.5 mm in diameter. Three of these are within a sufficiently reduced mass of powder to warrant searching for them using backscattered electron microscopy. In contrast, successively smaller splits of the Stevns Klint fish clay show no statistically significant deviation from the reported value of 32 +/- 2 ng/g Ir, suggesting a uniform Ir host-phase distribution. For the smallest split obtained thus far (100 +/- 40 ng/g Ir), a pure Ir sphere of equivalent Ir mass would be <0.05 min in diameter. (n.b. Although homogenizing and sieving of FC-1 to <75 min obviously obscured variations in stratigraphic distribution, it is unlikely to have affected the size-frequency distribution of Ir host phases.) We previously identified micrometer-scale Ir host phases by electron microscopy in melt-rock samples from two widely separated drill holes at the Chicxulub Basin, including a replicate split of Y6-NI9-R. One is an aggregate of subhedral Ir metal grains enclosed in silicate, in which no other Pt group elements (PGE) were detected. A second particle with twice the mass as the first, concentrated predominantly in a single grain, is associated with minor concentrations of Os, Ru, and Pt, and with adhering particles of corundum and perovskite. A third Ir-rich particle, with a greater apparent Os concentration, was identified before being lost as a result of charging under the electron beam. In addition to demonstrating the preservation of projectile components within the Chicxulub Crater, analogous phase associations in Ca- and Al-rich inclusions (CAI) from C2 and C3 chondrites suggest to us that these melt-rock Ir host phases are relics from a carbonaceous chondrite K/T boundary impactor Although the obviously low Ru/Ir ratios of the Chicxulub Ir host phases are qualitatively consistent with suggested PGE fractionation with distance during condensation in an ejecta cloud, it seems difficult to explain the accumulation of the about 3 x 10(exp 11) Ir atoms required to form a about 10(exp -10) g nugget of pure Ir metal within a jet of vaporized projectile expanding at 1-4 km/s, or to effectively exclude or remove commonly alloyed PGE and siderophile elements by fractionation processes resulting from condensation, oxidation, sulfidization, exsolution, or autometamorphism during cooling of the melt. We do not dismiss the importance of these processes entirely; on the contrary, other geochemical and mineralogical aspects of the melt rocks require them, and condensation from the expanding ejecta cloud appears to best explain the primary Ir host-phase distribution in the fish clay, as well as the high Ir concentrations associated with spinel-bearing spheroids at the K/T boundary in the Pacific Ocean . If the "relict" hypothesis is correct, micronuggets of other PGEs and alloys, not detected by our INAA screening, should also occur in

  6. Isotopic signatures of black tektites from the K-T boundary on Haiti - Implications for the age and type of source material

    NASA Technical Reports Server (NTRS)

    Premo, W. R.; Izett, G. A.

    1992-01-01

    An isotopic study was carried out to characterize the type of black tektites from the Cretaceous-Tertiary (K-T) boundary on Haiti (the first reasonably well-preserved impact-derived material recovered from the K-T boundary), in order to help characterize the tektite source material (i.e., the type of rocks that were melted and ejected during the impact event(s) at around 64.5 Ma). Results show that the isotopic data and all of the element concentration data obtained are consistent with an andesitic-dacitic composition for the tektites and their source material. The Nd isotopic data suggest that the source rocks were not older than Silurian (T(chur) = 400 Ma) in age, and were composed largely of young (less than 1080 Ma) crustal material. Of the suspected K-T boundary impact sites, both the Manson (Iowa) and Chicxulub (Yucatan) structures occur in suitable lithologies to yield the Haitian black tektites.

  7. Rb-Sr, Sm-Nd, K-Ca, O, and H isotopic study of Cretaceous-Tertiary boundary sediments, Caravaca, Spain Evidence for an oceanic impact site

    NASA Technical Reports Server (NTRS)

    Depaolo, D. J.; Kyte, F. T.; Marshall, B. D.; Oneil, J. R.; Smit, J.

    1983-01-01

    The results of isotopic and trace-element-abundance analyses of Ir-enriched Cretaceous-Tertiary-boundary clay sediments from Caravaca, Spain, and of adjacent carbonate and marl layers, are presented. Acetic-acid and HCl leachates and residues were analyzed by isotope dilution to determine K, Rb, Sr, Sm, and Nd concentrations and Sr-87/Sr-86 and Nd-143/Nd-144 ratios. The stable isotope ratios delta-D, delta-(C-13), and delta-(0-18) were also determined. The results are presented in tables and graphs and compared with published data on the Caravaca sediments and on samples from other locations. The boundary clay is found to be distinguished from the adjacent layers by its isotopic ratios and to be of mainly terrestrial, lithospheric (deeper than 3-km) origin. Although submarine-weathering effects are evident and difficult to quantify, the degree of variation in Ni, Ir, Sr, and REE concentrations is considered too large to be attributed to postdepositional processes alone. These findings are seen as evidence for the ocean impact of a large single asteroid producing a worldwide blanket of ejecta, a large injection of water vapor into the atmosphere, and perhaps a gigantic tsunami, at the end of the Cretaceous period.

  8. Shocked quartz found at the K/T boundary

    NASA Astrophysics Data System (ADS)

    Loper, David E.; McCartney, Kevin

    What killed the dinosaurs? This is the most popular question of the “Cretaceous/Tertiary (K/T) controversy,” which is concerned with the extinction some 65 m.y. ago of more than 75% of the world's existing floral and faunal species [Surlyk, 1980]. A popular hypothesis of their untimely demise is the impact of a meteorite [Alvarez et al., 1980]. However, despite the claim [Alvarez, 1983] that this has been proven, some serious doubts remain [Hallam, 1987; Officer et al., 1987]. A rival claim, that the dinosaurs were done in by a catastrophic volcanic eruption, has attracted some proponents and has some evidence in its favor, but that case is far from proven. However, it does have the advantage of having a definite event to point to the Deccan Traps in India. These are the largest continental flood basalts known from the Phanerozoic. According to recent studies [Courtillot et al., 1986; Feraud et al., 1988], the Deccan Traps were emplaced close to 65 m.y. ago. Is this timing a coincidence or are the two events (the mass extinction and the Deccan volcanism) related?

  9. Coeval Ar-40/Ar-39 ages of 65.0 million years ago from Chicxulub crater melt rock and Cretaceous-Tertiary boundary tektites

    NASA Technical Reports Server (NTRS)

    Swisher, Carl C., III; Grajales-Nishimura, Jose M.; Montanari, Alessandro; Margolis, Stanley V.; Claeys, Philippe; Alvarez, Walter; Renne, Paul; Cedillo-Pardo, Esteban; Maurrasse, Florentin J.-M. R.; Curtis, Garniss H.

    1992-01-01

    Ar-40/Ar-39 dating of drill-core samples of a glassy melt rock recovered from beneath a massive impact breccia contained with the 180-kilometer subsurface Chicxulub crater yields well-behaved incremental heating spectra with a mean plateau age of 64.98 +/- 0.05 million years ago (Ma). The glassy melt rock of andesitic composition was obtained from core 9 (1390 to 1393 meters) in the Chicxulub 1 well. The age of the melt rock is virtually indistinguishable from Ar-40/Ar-39 ages obtained on tektite glass from Beloc, Haiti, and Arroyo el Mimbral, northeastern Mexico, of 65.01 +/- 0.08 Ma (mean plateau age for Beloc) and 65.07 +/- 0.10 Ma (mean total fusion age for both sites). The Ar-40/Ar-39 ages, in conjunction with geochemical and petrological similarities, strengthen the suggestion that the Chicxulub structure is the source for the Haitian and Mexican tektites and is a viable candidate for the Cretaceous-Tertiary boundary impact site.

  10. Coeval 40Ar/39Ar Ages of 65.0 Million Years Ago from Chicxulub Crater Melt Rock and Cretaceous-Tertiary Boundary Tektites.

    PubMed

    Swisher, C C; Grajales-Nishimura, J M; Montanari, A; Margolis, S V; Claeys, P; Alvarez, W; Renne, P; Cedillo-Pardoa, E; Maurrasse, F J; Curtis, G H; Smit, J; McWilliams, M O

    1992-08-14

    (40)Ar/(39)Ar dating of drill core samples of a glassy melt rock recovered from beneath a massive impact breccia contained within the 180-kilometer subsurface Chicxulub crater in Yucatn, Mexico, has yielded well-behaved incremental heating spectra with a mean plateau age of 64.98 +/- 0.05 million years ago (Ma). The glassy melt rock of andesitic composition was obtained from core 9 (1390 to 1393 meters) in the Chicxulub 1 well. The age of the melt rock is virtually indistinguishable from (40)Ar/(39)Ar ages obtained on tektite glass from Beloc, Haiti, and Arroyo el Mimbral, northeastern Mexico, of 65.01 +/- 0.08 Ma (mean plateau age for Beloc) and 65.07 +/- 0.10 Ma (mean total fusion age for both sites). The (40)Ar/(39)Ar ages, in conjunction with geochemical and petrological similarities, strengthen the recent suggestion that the Chicxulub structure is the source for the Haitian and Mexican tektites and is a viable candidate for the Cretaceous-Tertiary boundary impact site. PMID:17789640

  11. Rb-Sr, Sm-Nd, K-Ca, O, and H isotopic study of Cretaceous-Tertiary boundary sediments, Caravaca, Spain: evidence for an oceanic impact site

    USGS Publications Warehouse

    DePaolo, D.J.; Kyte, F.T.; Marshall, B.D.; O'Neil, J.R.; Smit, J.

    1983-01-01

    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 low 87Sr/86Sr and high 143Nd/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. ?? 1983.

  12. Climatic changes resulting from mass extinctions at the K-T boundary (and other bio-events)

    NASA Technical Reports Server (NTRS)

    Rampino, Michael R.; Volk, Tyler

    1988-01-01

    The mass extinctions at the Cretaceous-Tertiary (K-T) boundary include about 90 percent of marine calcareous nannoplankton (coccoliths), and carbon-isotope data show that marine primary productivity was drastically reduced for about 500,000 years after the boundary event, the so-called Strangelove Ocean effect. One result of the elimination of most marine phytoplankton would have been a severe reduction in production of dimethyl sulfide (DMS), a biogenic gas that is believed to be the major precursor of cloud condensation nuclei (CCN) over the oceans. A drastic reduction in marine CCN should lead to a cloud canopy with significantly lower reflectivity, and hence cause a significant warming at the earth's surface. Calculations suggest that, all other things being held constant, a reduction in CCN of more than 80 percent (a reasonable value for the K-T extinctions) could have produced a rapid global warming of 6 C or more. Oxygen-isotope analyses of marine sediments, and other kinds of paleoclimatic data, have provided for a marked warming, and a general instability of climate coincident with the killoff of marine plankton at the K-T boundary. Similar reductions in phytoplankton abundance at other boundaries, as indicated by marked shifts in carbon-isotope curves, suggest that severe temperature changes may have accompanied other mass extinctions, and raises the intriguing possibility that the extinction events themselves could have contributed to the climatic instabilities at critical bio-events in the geologic record.

  13. Collapse of florisitic diversity coincident with a fungal spike and iridium anomaly at the Cretaceous-Tertiary boundary in New Zealand

    NASA Astrophysics Data System (ADS)

    Vajda, V.; Raine, J. I.

    2003-04-01

    Analysis of pollen and spore assemblages from both terrestrial and near-shore marine sediments in New Zealand had revealed an instant, extensive destruction of land plants directly associated with the Cretaceous-Tertiary boundary (KTB) event, (Vajda et al., 2001). A recent palynological investigation, based on millimeter resolution sampling of the terrestrial KTB sediments at Moody Creek Mine, Greymouth coalfield, New Zealand has been carried out. The sediments were deposited in a terrestrial wetland environment and the KTB is defined within a coal seam. Preliminary results of the high-resolution investigation reveal a diverse vascular plant spore/pollen flora (>80 species) that was replaced by an assemblage impoverished in vascular plant pollen and spores, but rich in fungal spores. The "barren" layer is coincident with the extinction of several miospore taxa and contains an iridium abundance of 3ppb. The fungal spike covers 5 mm, and is followed by a 40-cm interval with abundant fern spores. The relative abundance of fern spores, increases from 25% below the boundary to 98% in the sediment following the KTB. We argue that the abrupt palynofloristic changes at this high southern palaeolatitude site are evidence of massive disruptions to terrestrial plant communities as a consequence of the Chicxulub impact. Palynofloristic evidence indicates that the complex mire and forest vegetation was totally devastated at the time of impact. Global cooling and several months with extremely low light levels following the impact, perhaps in combination with extensive wildfires would explain the devastation of the vegetation. The "barren" layer at the KTB corresponds to immediate post-impact conditions with low light levels and dust-related cooling unfavorable to forest growth but favoring saprophytic fungi. The recovery succession is initiated by opportunistic species of ground ferns, the plants best adapted to low light, lowered temperatures and high acidity. Vajda, V., Raine, I. &Hollis, C. (2001). Science, Vol. 294, p. 1700-1702.

  14. Is there evidence for Cretaceous-Tertiary boundary-age deep-water deposits in the Caribbean and Gulf of Mexico?

    NASA Astrophysics Data System (ADS)

    Keller, G.; MacLeod, N.; Lyons, J. B.; Officer, C. B.

    1993-09-01

    Over most of the Gulf of Mexico and Caribbean a hiatus is present between the lower upper Maastrichtian and lowermost Tertiary deposits; sedimentation resumed 200 ka (upper zone Pla) after the K-T boundary. Current-bedded volcaniclastic sedimentary rocks at Deep Sea Drilling Project (DSDP) Sites 536 and 540, which were previously interpreted as impact-generated megawave deposits of K-T boundary age, are biostratigraphically of pre-K-T boundary age and probably represent turbidite or gravity-How deposits. The top 10 to 20 cm of this deposit at Site 536 contains very rare Micula prinsii, the uppermost Maastrichtian index taxon, as well as low values of Ir (0.6 pbb) and rare Ni-rich spinels. These indicate possible reworking of sediments of K-T boundary age at the hiatus. Absence of continuous sediment accumulation across the K-T boundary in the 16 Gulf of Mexico and Caribbean sections examined prevents their providing evidence of impact-generated megawave deposits in this region. Our study indicates that the most complete trans-K-T stratigraphic records may be found in onshore marine sections of Mexico, Cuba, and Haiti. The stratigraphic records of these areas should be investigated further for evidence of impact deposits.

  15. A Cretaceous-Tertiary mass extinction? Were most of Earth's species killed off?

    NASA Technical Reports Server (NTRS)

    Briggs, J. C.

    1991-01-01

    For the past decade, the scientific and popular press have carried frequent articles about a catastrophic mass extinction that supposedly destroyed the majority of the earth's species, including the dinosaurs, approximately 65 million years ago. Since 1980, more than 2000 papers and books have dealt with some aspect of a mass extinction at the Cretaceous-Tertiary (K/T) boundary. One authoritative estimate of the severity of the extinctions is that 60-80% of all the living species became extinct at this boundary (Raup 1988). There appears to be a general acceptance of the fact that such a great catastrophe did occur. Most of the argument among scientists now is devoted to the determination of the cause. In this article, I argue that the species changes at the K/T boundary were neither sudden nor catastrophic. They were most likely caused by a regression of sea level that led to a decrease in primary production.

  16. Mineralogy and petrology of the Cretaceous- Tertiary boundary clay bed and adjacent clay-rich rocks, Raton Basin, New Mexico and Colorado.

    USGS Publications Warehouse

    Pollastro, R.M.; Pillmore, C.L.

    1987-01-01

    The K-T boundary occurs at the top of a kaolinitic claystone layer, commonly referred to as the 'boundary clay layer', in an interval of coal and carbonaceous shale. The boundary is defined by the disappearance of certain fossil-pollen taxa. The boundary clay layer also contains shocked quartz grains and abundance anomalies of iridium, chromium, and other elements. Each of these characteristics support the hypothesis of an asteroid impact at the end of the Cretaceous. -from Authors

  17. Biospheric Effects of the Chicxulub Impact and Their Role in the Cretaceous/Tertiary Mass Extinction

    NASA Technical Reports Server (NTRS)

    Pope, Kevin O.

    1997-01-01

    A comprehensive analysis of volatiles in the Chicxulub impact strongly supports the hypothesis that impact-generated sulfate aerosols caused over a decade of global cooling, acid rain, and disruption of ocean circulation, which contributed to the mass extinction at the Cretaceous/Tertiary (K/T) boundary. The crater size, meteoritic content of the K/T boundary clay, and impact models indicate that the Chicxulub crater was formed by a short period comet or an asteroid impact that released 0.7-3.4 x 10(exp 31) ergs of energy. Impact models and experiments combined with estimates of volatiles in the projectile and target rocks predict that over 200 gigatons (Gt) each of SO2 and water vapor, and over 500 Gt of CO2, were globally distributed in the stratosphere by the impact.

  18. The Cretaceous-Tertiary extinction: A lethal mechanism involving anhydrite target rocks

    USGS Publications Warehouse

    Brett, R.

    1992-01-01

    The Chicxulub Crater, Yucatan, Mexico, is a leading contender as the site for the impact event that caused the Cretaceous-Tertiary (K-T) extinctions. A considerable thickness of anhydrite (CaSO4) forms part of the target rock. High temperatures resulting from impact would drive SO2 off from the anhydrite. Hundreds of billions of tonnes of sulfuric acid aerosol would thus enter the stratosphere and cause considerable cooling of the Earth's surface, decrease photosynthesis by orders of magnitude, deplete the ozone layer, and permit increased UV radiation to reach the Earth's surface. Finally, the aerosol would fall back to Earth as acid rain and devastate land and some lacustrine biota and near-surface marine creatures. The presence of anhydrite in the Chicxulub target rock may thus help explain the many extinctions observed at the K-T boundary. ?? 1992.

  19. Dinosaurs, spherules, and the “magic” layer: A new K-T boundary clay site in Wyoming

    NASA Astrophysics Data System (ADS)

    Bohor, Bruce F.; Triplehorn, Don M.; Nichols, Douglas J.; Millard, Hugh T., Jr.

    1987-10-01

    A new Cretaceous-Tertiary (K-T) boundary clay site has been found along Dogie Creek in Wyoming in the drainage of Lance Creek—the type area of the Lance Formation of latest Cretaceous age. The boundary clay was discovered in the uppermost part of the Lance Formation, 4 7 cm beneath the lowest lignite in the Paleocene Fort Union Formation and approximately 1 m above a fragmented dinosaur bone. The boundary clay consists of a basal kaolinitic claystone layer as much as 3 cm thick containing hollow goyazite spherules, overlain by a 2 3 mm smectitic layer (the “magic” layer) containing both shock-metamorphosed minerals and an iridium anomaly of 21 ppb. A palynological break coincides with the base of the claystone layer; numerous Late Cretaceous palynomorph species terminate at this boundary. The paleontological significance of this new boundary site lies in its close association with the well-studied assemblage of dinosaurs and other vertebrates and flora within the type area of the Lance Formation. The spherules at the Dogie Creek site are extremely well preserved by virtue of their replacement by the mineral goyazite. This preservation should facilitate the resolution of the origin of the spherules and of their host layer.

  20. Rocks, resolution, and the record at the terrestrial K/T boundary, eastern Montana and western North Dakota

    NASA Technical Reports Server (NTRS)

    Fastovsky, D. E.

    1988-01-01

    Reconstructions of mass extinction events are based upon faunal patterns, reconstructed from numerical and diversity data ultimately derived from rocks. It follows that geological complexity must not be subsumed in the desire to establish patterns. This is exemplified at the Terrestrial Cretaceous-Tertiary (K/T) boundary in eastern Montana and western North Dakota, where there are represented all of the major indicators of the terrestrial K/T transition: dinosaurian and non-dinosaurian vertebrate faunas, pollen, a megaflora, iridium, and shocked quartz. It is the patterns of these indicators that shape ideas about the terrestrial K/T transition. In eastern Montana and western North Dakota, the K/T transition is represented lithostratigraphically by the Cretaceous Hell Creek Formation, and the Tertiary Tullock Formation. Both of these are the result of aggrading, meandering, fluvial systems, a fact that has important consequences for interpretations of fossils they contain. Direct consequences of the fluvial depositional environments are: facies are lenticular, interfingering, and laterally discontinuous; the occurrence of fossils in the Hell Creek and Tullock formations is facies-dependent; and the K/T sequence in eastern Montana and western North Dakota is incomplete, as indicated by repetitive erosional contacts and soil successions. The significance for faunal patterns of lenticular facies, facies-dependent preservation, and incompleteness is discussed. A project attempting to reconstruct vertebrate evolution in a reproducible manner in Hell Creek-type sediments must be based upon a reliable scale of correlations, given the lenticular nature of the deposits, and a recognition of the fact that disparate facies are not comparable in terms of either numbers of preserved vertebrates or depositional rates.

  1. Explosive volcanism, shock metamorphism and the K-T boundary

    NASA Technical Reports Server (NTRS)

    Desilva, S. L.; Sharpton, V. L.

    1988-01-01

    The issue of whether shocked quartz can be produced by explosive volcanic events is important in understanding the origin of the K-T boundary constituents. Proponents of a volcanic origin for the shocked quartz at the K-T boundary cite the suggestion of Rice, that peak overpressures of 1000 kbars can be generated during explosive volcanic eruptions, and may have occurred during the May, 1980 eruption of Mt. St. Helens. Attention was previously drawn to the fact that peak overpressures during explosive eruptions are limited by the strength of the rock confining the magma chamber to less than 8 kbars even under ideal conditions. The proposed volcanic mechanisms for generating pressures sufficient to shock quartz are further examined. Theoretical arguments, field evidence and petrographic data are presented showing that explosive volcanic eruptions cannot generate shock metamorphic features of the kind seen in minerals at the K-T boundary.

  2. Terrestrial ecosystem destabilization at the K/T boundary in southwestern North Dakota, USA.

    NASA Astrophysics Data System (ADS)

    Bercovici, Antoine; Pearson, Dean; Villanueva-Amadoz, Uxue

    2010-05-01

    Much of the debate regarding mass extinction events tend to discuss the relationship between such events relative to the moment and timing of internal or external factors (such as volcanism, impact(s), climate, sea-level changes and so on). However, the details of the extinction process itself is still poorly understood, and most of the analysis are based on biodiversity patterns without integrating the biogeographic and environmental context. Another way of approaching the problem would be to propose precise paleoenvironment reconstructions and analyzing their evolution through time, which allows for the understanding of such processes. The badlands of southwestern North Dakota provides some of the most prolific exposures of the continental Cretaceous/Tertiary (K/T) boundary in the world. The stratigraphical context indicates that the K/T boundary is coincident or lies in close proximity to the contact between the Hell Creek and the Fort Union Formations. In this area, a series of eight stratigraphical sections across a 40 km north-south transect were studied. These sections bracket the formational contact on a 10 m stratigraphical interval. Reconstruction of the depositional environment was undertaken at a centimeter scale by using sedimentological data, as well as palynological, paleobotanical and palaeontological content of the strata, using the K/T boundary as a precise chronological datum of correlation between the sections. Results shows a consistent evolution of pattern across the entire study area : 1) The uppermost 10 to 20 cm of the Hell Creek Formation always corresponds to a sequence of dark rooted mudstone. Pollen content is consistent with a Cretaceous age and displays a diversity of terrestrial taxa. 2) Immediately above, the formation contact lies at the lower part of the first laterally traceable lignite horizon. The K/T boundary indicators (iridium anomaly, shocked quartz, fern spike and boundary claystone) are located at or adjacent to this stratigraphical interval, when preserved. 3) Within or just above the formation contact coal, the relative abundance of palynological taxa indicative of the Cretaceous (K-taxa) drop significantly without significant subsequent recovery. 4) Above the formation contact lignite, lithology systematically the lithology consistently appears as a 1-2 m thick dark mudstone sequence. The palynological record of this interval is dominated by freshwater taxa (Pediastrum sp. and Penetetrapites sp.) indicating general flooding in the study area. 5) Change in the sedimentation style in comparison of the Hell Creek is reflected by the preservation of variegated beds, multiple lignite seams and small scale meandering river systems. The palynological content attest for reworking and erosion. Conclusions shows that both palaeoenviroments and biodiversity patterns stay consistent throughout the Hell Creek Formation, with the exception of its uppermost part. The vertebrate and plant communities underwent a significant change at this time coincident with the evidence for a impact scenario or catastrophic event of massive scale. Beginning at the very end of the Cretaceous and continuing up into the overlying Fort Union Formation, the area was experiencing the onset of a transgression cycle which contributed to widespread ponding. Following the impact, modifications in the environment caused by land denudation, changes in sea level and drainage patterns promoted run-off and reworking. The destabilization of terrestrial ecosystems in southwestern North Dakota is coincident with markers of the K/T boundary that supports a catastrophic event taking place over a very short duration.

  3. Osmium, tungsten, and chromium isotopes in sediments and in Ni-rich spinel at the K-T boundary: Signature of a chondritic impactor

    NASA Astrophysics Data System (ADS)

    Quitt, Ghylaine; Robin, Eric; Levasseur, Sylvain; Capmas, Franoise; Rocchia, Robert; Birck, Jean-Louis; Allgre, Claude Jean

    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.

  4. The global Cretaceous-Tertiary fire: Biomass or fossil carbon

    NASA Technical Reports Server (NTRS)

    Gilmour, Iain; Guenther, Frank

    1988-01-01

    The global soot layer at the K-T boundary indicates a major fire triggered by meteorite impact. However, it is not clear whether the principal fuel was biomass or fossil carbon. Forests are favored by delta value of C-13, which is close to the average for trees, but the total amount of elemental C is approximately 10 percent of the present living carbon, and thus requires very efficient conversion to soot. The PAH was analyzed at Woodside Creek, in the hope of finding a diagnostic molecular marker. A promising candidate is 1-methyl-7-isopropyl phenanthrene (retene,), which is probably derived by low temperature degradation of abietic acid. Unlike other PAH that form by pyrosynthesis at higher temperatures, retene has retained the characteristic side chains of its parent molecule. A total of 11 PAH compounds were identified in the boundary clay. Retene is present in substantial abundance. The identification was confirmed by analysis of a retene standard. Retene is characteristic of the combustion of resinous higher plants. Its formation depends on both temperature and oxygen access, and is apparently highest in oxygen-poor fires. Such fires would also produce soot more efficiently which may explain the high soot abundance. The relatively high level of coronene is not typical of a wood combustion source, however, though it can be produced during high temperature pyrolysis of methane, and presumably other H, C-containing materials. This would require large, hot, low O2 zones, which may occur only in very large fires. The presence of retene indicates that biomass was a significant fuel source for the soot at the Cretaceous-Tertiary boundary. The total amount of elemental C produced requires a greater than 3 percent soot yield, which is higher than typically observed for wildfires. However, retene and presumably coronene imply limited access of O2 and hence high soot yield.

  5. Catastrophic volcanism as a cause of shocked features found at the K/T boundary and in cryptoexplosion structures

    NASA Astrophysics Data System (ADS)

    Loper, D. E.; McCartney, K.

    The presence of quartz grains containing shock lamellae at the Cretaceous/Tertiary (K/T) boundary is viewed by many as the single most compelling evidence of meteoritic or cometary impact because there is no known endogenous mechanism for producing these features. Similarly the presence of shocked quartz, shatter cones, coesite and stishovite at cryptoexplosion structures is comonly taken as conclusive evidence of impact. However, several recent studies have cast doubt on this interpretation. It is argued that basaltic volcanism, although not normally explosive, can under exceptional circumstances produce overpressures sufficiently high to produce shock features. The exceptional circumstances include a high content of volatiles, usually CO2, and no preestablished pathway to the surface. Rapid cooling of the saturated basaltic magma can occur if it underlies a cooler more evolved magma in a chamber. Initial slow cooling and partial exsolution of the volatiles will cause the density of the basaltic magma to become less than that of the overlying magma, leading to overturning and mixing. Gas will escape the magma chamber along planar cracks once the pressure becomes sufficiently high. In the vicinity of the crack tip there is a smallscale deviatoric stress pattern which is thought to be sufficiently high to produce transient cracks along secondary axes in the quartz crystals, causing the planar features. The CO2-rich fluid inclusions which have been found along planar elements of quartz in basement rocks of the Vredefort Dome were likely to have been emplaced by such a process. If the mechanism described is capable of producing shocked features as above, it would require a reassessment of the origin of many cryptoexplosion structures as well as seriously weakening the case for an impact origin of the K/T event.

  6. Catastrophic volcanism as a cause of shocked features found at the K/T boundary and in cryptoexplosion structures

    NASA Technical Reports Server (NTRS)

    Loper, D. E.; Mccartney, K.

    1988-01-01

    The presence of quartz grains containing shock lamellae at the Cretaceous/Tertiary (K/T) boundary is viewed by many as the single most compelling evidence of meteoritic or cometary impact because there is no known endogenous mechanism for producing these features. Similarly the presence of shocked quartz, shatter cones, coesite and stishovite at cryptoexplosion structures is comonly taken as conclusive evidence of impact. However, several recent studies have cast doubt on this interpretation. It is argued that basaltic volcanism, although not normally explosive, can under exceptional circumstances produce overpressures sufficiently high to produce shock features. The exceptional circumstances include a high content of volatiles, usually CO2, and no preestablished pathway to the surface. Rapid cooling of the saturated basaltic magma can occur if it underlies a cooler more evolved magma in a chamber. Initial slow cooling and partial exsolution of the volatiles will cause the density of the basaltic magma to become less than that of the overlying magma, leading to overturning and mixing. Gas will escape the magma chamber along planar cracks once the pressure becomes sufficiently high. In the vicinity of the crack tip there is a smallscale deviatoric stress pattern which is thought to be sufficiently high to produce transient cracks along secondary axes in the quartz crystals, causing the planar features. The CO2-rich fluid inclusions which have been found along planar elements of quartz in basement rocks of the Vredefort Dome were likely to have been emplaced by such a process. If the mechanism described is capable of producing shocked features as above, it would require a reassessment of the origin of many cryptoexplosion structures as well as seriously weakening the case for an impact origin of the K/T event.

  7. A regional perspective on the palynofloral response to K-T boundary event(s) with emphasis on variations imposed by the effects of sedimentary facies and latitude

    NASA Technical Reports Server (NTRS)

    Sweet, A. R.

    1988-01-01

    Palynological studies deal with fossil reproductive bodies that were produced by fully functioning plants, whereas most faunal studies are based on death assemblages. Therefore, changes in pollen and spore assemblages cannot be used directly as evidence of catastrophic mass killings but only to indicate changes in ecological conditions. The impact of the Cretaceous-Tertiary boundary event on terrestrial plant communities is illustrated by the degree, rate and selectivity of change. As in most classical palynological studies, the degree of change is expressed in terms of relative abundance and changes in species diversity. It is recognized that sampling interval and continuity of the rock record within individual sections can affect the percieved rate of change. Even taking these factors into account, a gradual change in relative abundance and multiple levels of apparent extinctions, associated with the interval bounding the K-T boundary, can be demonstrated. Climatic change, which locally exceeds the tolerance of individual species, and the possible loss of a group of pollinating agents are examined as possible explanations for the selectivity of apparent extinctions and/or locally truncated occurrences. The aspects of change are demonstrated with data from four different K-T boundary localities in Western Canada between paleolatitudes 60 and 75 deg north. Together, the four localities discussed allow changes imposed by latitude and differences in the depositional environment be isolated from the boundary event itself which is reflected by the truncated ranges of several species throughout the region of study. What must be recognized is that variations in the response of vegetation to the K-T boundary event(s) occurred throughout the Western Interior basin.

  8. The record of impact on earth - Implications for a major Cretaceous/Tertiary impact event

    NASA Technical Reports Server (NTRS)

    Grieve, R. A. F.

    1982-01-01

    Cratering mechanics suggests that if the proposed Cretaceous-Tertiary impact event occurred in the ocean, it may have been able to locally excavate the oceanic crust and bring upper mantle material to the surface, thereby creating a geophysical anomaly that has yet to be detected. If the siderophile enrichments in the Cretaceous-Tertiary boundary layer denote projectile-contaminated ejecta from a major impact, the source of this material will probably be ejecta which had been accelerated upwards as the projectile penetrated the target rocks. The difficulties in defining projectile types from the siderophile anomalies in the relatively well known environment of impact melt rocks suggest that more detailed geochemistry and mineralogy will be needed before the siderophile enrichments at the Cretaceous-Tertiary boundary can be linked to a specific meteoritic compositional class.

  9. Evidence for the recovery of terrestrial ecosystems ahead of marine primary production following a biotic crisis at the Cretaceous-Tertiary boundary

    USGS Publications Warehouse

    Beerling, D.J.; Lomax, B.H.; Upchurch, G.R., Jr.; Nichols, D.J.; Pillmore, C.L.; Handley, L.L.; Scrimgeour, C.M.

    2001-01-01

    The fossil record demonstrates that mass extinction across the Cretaceous–Tertiary (K–T) boundary is more severe in the marine than the terrestrial realm. We hypothesize that terrestrial ecosystems were able to recover faster than their marine counterparts. To test this hypothesis, we measured sedimentary δ13C as a tracer for global carbon cycle changes and compared it with palaeovegetational changes reconstructed from palynomorphs and cuticles across the K–T boundary at Sugarite, New Mexico, USA. Different patterns of perturbation and timescales of recovery of isotopic and palaeobotanical records indicate that the δ13C excursion reflects the longer recovery time of marine versus terrestrial ecosystems.

  10. Large meteorite impacts: The K/T model

    NASA Technical Reports Server (NTRS)

    Bohor, B. F.

    1992-01-01

    The Cretaceous/Tertiary (K/T) boundary event represents probably the largest meteorite impact known on Earth. It is the only impact event conclusively linked to a worldwide mass extinction, a reflection of its gigantic scale and global influence. Until recently, the impact crater was not definitively located and only the distal ejecta of this impact was available for study. However, detailed investigations of this ejecta's mineralogy, geochemistry, microstratigraphy, and textures have allowed its modes of ejection and dispersal to be modeled without benefit of a source crater of known size and location.

  11. Extraterrestrial cause for the Cretaceous-Tertiary extinction

    NASA Technical Reports Server (NTRS)

    Alvarez, L. W.; Alvarez, W.; Asaro, F.; Michel, H. V.

    1980-01-01

    Direct physical evidence is presented for an unusual event at exactly the time of extinctions in the planktonic realm. Deep-sea limestones exposed in Italy, Denmark, and New Zealand indicate iridium increases of about 30, 160, and 20 times, respectively, above the background level at precisely the time of the Cretaceous-Tertiary extinctions, 65 million years ago. Reasons are given that this iridium is of extraterrestrial origin, but did not come from a nearby supernova. A hypothesis is set forth which accounts for the extinctions and the iridium observations. One prediction of this hypothesis is verified, that the chemical composition of the boundary clay, which is thought to come from the stratospheric dust, is markedly different from that of clay mixed with the chemically similar Cretaceous and Tertiary limestones.

  12. Reverse Polarity Magnetized Melt Rocks from the Cretaceous/Tertiary Chicxulub Structure, Yucatan Peninsula, Mexico

    NASA Technical Reports Server (NTRS)

    Urrutia-Fucugauchi, J.; Marin, Luis; Sharpton, Virgil L.

    1994-01-01

    We report paleomagnetic results for core samples of the breccia and andesitic rocks recovered from the Yucatan-6 Petrolcos Mexicanos exploratory well within the Chicxulub structure (about 60 km SSW from its center), northern Yucatan, Mexico. A previous study has shown that the rocks studied contain high iridium levels and shocked breccia clasts and an Ar/Ar date of 65.2 +/- 0.4 Ma. Andesitic rocks are characterized by stable single-component magnetizations with a mean inclination of -42.6 deg +/- 2.4 deg. Breccias present a complex paleomagnetic record characterized by multivectorial magnetizations with widely different initial NRM inclinations. However, after alternating field demagnetization, well defined characteristic components with upward inclinations are defined. IRM acquisition experiments, comparison of IRM and NRM coercivity spectra and the single component magnetization of the andesitic rocks indicate the occurrence of iron-rich titanomagnetites of single or pseudo-single domain states as the dominant magnetic carriers. Mean inclinations from the andesitic rocks and most of the breccia samples give a mean inclination of about -40 deg to -45 deg, indicating a reverse polarity for the characteristic magnetization that is consistent with geomagnetic chron 29R, which spans the Cretaceous/Tertiary (K/T) boundary. The inclination is also consistent with the expected value (and corresponding paleolatitude) for the site estimated from the reference polar wander curve for North America. We suggest that the characteristic magnetizations for the andesitic and breccia rocks are the result of shock heating at the time of formation of the impact structure and that the age, polarity and pateolatitude are consistent with a time at the K/T boundary.

  13. Impact winter and the Cretaceous/Tertiary extinctions: Results of a Chicxulub asteroid impact model

    NASA Technical Reports Server (NTRS)

    Pope, Kevin O.; Baines, Kevin H.; Ocampo, Adriana C.; Ivanov, Boris A.

    1994-01-01

    The Chicxulub impact crater in Mexico is the site of the impact purported to have caused mass extinctions at the Cretaceous/Tertiary (K/T) boundary. 2-D hydrocode modeling of the impact, coupled with studies of the impact site geology, indiate that between 0.4 and 7.0 x 10(exp 17) g of sulfur were vaporized by the impact into anhydrite target rocks. A small portion of the sulfur was released as SO3 or SO4, which converted rapidly into H2SO4 aerosol and fell as acid rain. A radiative transfer model, coupled with a model of coagulation indicates that the aerosol prolonged the initial blackout period caused by impact dust only if the aerosol contained impurities. A larger portion of sulfur was released as SO2, which converted to aerosol slowly, due to the rate-limiting oxidation of SO2. Our radiative transfer calculations, combined with rates of acid production, coagulation, and diffusion indicate that solar transmission was reduced to 10-20% of normal for a period of 8-13 yr. This reduction produced a climate forcing (cooling) of -300 W/sq.m, which far exceeded the +8 W/sq.m greenhouse warming, caused by the CO2 released through the vaporization of carbonates, and therefore produced a decade of freezing and near-freezing temperatures. Several decades of moderate warming followed the decade of severe cooling due to the long residence time of CO2. The prolonged impact winter may have been a major cause of the K/T extinctions.

  14. Cretaceous-Tertiary findings, paradigms and problems

    NASA Technical Reports Server (NTRS)

    Officer, C. B.; Drake, C. L.

    1988-01-01

    The asteroid hypothesis has stimulated numerous studies of the paleontological record at Cretaceous/Tertiary time as well as of geological indicators of environmental crisis preserved in the rock record. Both extinctions and geological anomalies often occur at times that do not appear to be synchronous or instantaneous. The record includes paleontological indicators of dinosaurs, terrestrial flora, marine planktonic organisms, and shallow water marine macrofauna and geological phenomena include occurrences of iridium and other platinum metals, trace elements, clay mineralogy, shocked minerals, soot, microspherules, and isotopes of osmium, strontium and carbon. These findings are reviewed in the context of the alternate hypotheses of an exogenic cause, involving either a single asteroid impact or multiple commentary impacts, and an endogenic cause, involving intense global volcanism and major sea level regression.

  15. TEM study of meteorite impact glass at New Zealand Cretaceous-Tertiary sites: evidence for multiple impacts or differentiation during global circulation?

    NASA Astrophysics Data System (ADS)

    Bauluz, Blanca; Peacor, Donald R.; Hollis, Christopher J.

    2004-03-01

    Study by transmission electron microscopy of samples from the Cretaceous-Tertiary (K-T) boundary clay at Flaxbourne River and Woodside Creek, New Zealand, has revealed the occurrence of nanometer-sized meteorite impact-derived glass. The average glass composition is exceptionally Ca-rich and is distinct from other glass found on Earth, apart from glass inferred to be of impact origin at Mexican and Haitian K-T sites. The glass shards are partially altered to montmorillonite-like smectite, with the dominant interlayer cation, Ca, reflecting the composition of the parent glass. The data imply a heterogeneous global distribution in composition of K-T boundary impact glass: Si-rich and Ca-rich in Mexico and Haiti, Si-rich in Denmark, and Ca-rich in New Zealand. This heterogeneous distribution may relate to dispersal processes similar to those used to account for the asymmetric distribution of clastic debris from the Chicxulub impact site. However, recent discovery of an impact crater of K-T boundary age in Ukraine raises the possibility of impact clusters which produce material of heterogeneous composition.

  16. Strontium isotope profiles across K/T boundary sequences in Denmark and Antarctica

    NASA Astrophysics Data System (ADS)

    McArthur, J. M.; Thirlwall, M. F.; Engkilde, M.; Zinsmeister, W. J.; Howarth, R. J.

    1998-07-01

    Strontium isotope profiles, derived from minimally altered samples, across marine K/T boundary sequences exposed at Kjlby Gaard and Nye Klv, Denmark, and on Seymour Island, Antarctica, show neither the boundary excursions, nor the boundary spikes, in 87Sr/ 86Sr that have been reported for K/T boundary sequences from elsewhere. Nor do our data conform to modelled predictions of the Sr isotopic response of the oceans to a positive spike in 87Sr/ 86Sr at the terminal Cretaceous. Boundary values for 87Sr/ 86Sr (with 95% confidence intervals) are 0.7078283 in Denmark and 0.7078327 in Antarctica. Our data suggest that 87Sr/ 86Sr stopped increasing and started decreasing at least 90 ka before the K/T boundary.

  17. Provenance of the K/T boundary layers

    NASA Technical Reports Server (NTRS)

    Hildebrand, A. R.; Boynton, W. V.

    1988-01-01

    An array of chemical, physical and isotopic evidence indicates that an impact into oceanic crust terminated the Cretaceous Period. Approximately 1500 cu km of debris, dispersed by the impact fireball, fell out globally in marine and nonmarine environments producing a 2 to 4 mm thick layer (fireball layer). In North American locales, the fireball layer overlies a 15 to 25 mm thick layer of similar but distinct composition. This 15 to 25 mm layer (ejecta layer) may represent approximately 1000 cu km of lower energy ejecta from a nearby impact site. Isotopic and chemical evidence supports a mantle provenance for the bulk of the layers. The extraordinary REE pattern of the boundary clays was modelled as a mixture of oceanic crust, mantle, and approximately 10 percent continental material. The results are presented. If the siderophiles of the ejecta layer were derived solely from the mantle, a test may be available to see if the siderophile element anomaly of the fireball layer had an extraterrestrial origin. Radiogenic Os-187 is depleted in the mantle relative to an undifferentiated chondritic source. Os-187/Os-186 ratios of 1.049 and 1.108 were calculated for the ejecta and fireball layers, respectively.

  18. Energy, volatile production, and climatic effects of the Chicxulub Cretaceous/Tertiary impact

    NASA Technical Reports Server (NTRS)

    Pope, K. O.; Baines, K. H.; Ocampo, A. C.; Ivanov, B. A.

    1997-01-01

    A comprehensive analysis of volatiles in the Chicxulub impact strongly supports the hypothesis that impact-generated sulfate aerosols caused over a decade of global cooling, acid rain, and disruption of ocean circulation, which contributed to the mass extinction at the Cretaceous/Tertiary (K/T) boundary. The crater size, meteoritic content of the K/T boundary clay, and impact models indicate that the Chicxulub crater was formed by a short period comet or an asteroid impact that released 0.7-3.4 x 10(31) ergs of energy. Impact models and experiments combined with estimates of volatiles in the projectile and target rocks predict that over 200 gigatons (Gt) each of SO2 and water vapor, and over 500 Gt of CO2, were globally distributed in the stratosphere by the impact. Additional volatiles may have been produced on a global or regional scale that formed sulfate aerosols rapidly in cooler parts of the vapor plume, causing an early, intense pulse of sulfuric acid rain. Estimates of the conversion rate of stratospheric SO2 and water vapor to sulfate aerosol, based on volcanic production of sulfate aerosols, coupled with calculations of diffusion, coagulation, and sedimentation, demonstrate that the 200 Gt stratospheric SO2 and water vapor reservoir would produce sulfate aerosols for 12 years. These sulfate aerosols caused a second pulse of acid rain that was global. Radiative transfer modeling of the aerosol clouds demonstrates (1) that if the initial rapid pulse of sulfate aerosols was global, photosynthesis may have been shut down for 6 months and (2) that for the second prolonged aerosol cloud, solar transmission dropped 80% by the end of first year and remained 50% below normal for 9 years. As a result, global average surface temperatures probably dropped between 5 degrees and 31 degrees K, suggesting that global near-freezing conditions may have been reached. Impact-generated CO2 caused less than 1 degree K greenhouse warming and therefore was insignificant compare to the sulfate cooling. The magnitude of sulfate cooling depends largely upon the rate of ocean mixing as surface waters cool, sink, and are replaced by upwelling of deep ocean water. This upwelling apparently drastically altered ocean stratification and circulation, which may explain the global collapse of the delta 13C gradient between surface and deep ocean waters at the K/T boundary.

  19. Energy, volatile production, and climatic effects of the Chicxulub Cretaceous/Tertiary impact.

    PubMed

    Pope, K O; Baines, K H; Ocampo, A C; Ivanov, B A

    1997-09-25

    A comprehensive analysis of volatiles in the Chicxulub impact strongly supports the hypothesis that impact-generated sulfate aerosols caused over a decade of global cooling, acid rain, and disruption of ocean circulation, which contributed to the mass extinction at the Cretaceous/Tertiary (K/T) boundary. The crater size, meteoritic content of the K/T boundary clay, and impact models indicate that the Chicxulub crater was formed by a short period comet or an asteroid impact that released 0.7-3.4 x 10(31) ergs of energy. Impact models and experiments combined with estimates of volatiles in the projectile and target rocks predict that over 200 gigatons (Gt) each of SO2 and water vapor, and over 500 Gt of CO2, were globally distributed in the stratosphere by the impact. Additional volatiles may have been produced on a global or regional scale that formed sulfate aerosols rapidly in cooler parts of the vapor plume, causing an early, intense pulse of sulfuric acid rain. Estimates of the conversion rate of stratospheric SO2 and water vapor to sulfate aerosol, based on volcanic production of sulfate aerosols, coupled with calculations of diffusion, coagulation, and sedimentation, demonstrate that the 200 Gt stratospheric SO2 and water vapor reservoir would produce sulfate aerosols for 12 years. These sulfate aerosols caused a second pulse of acid rain that was global. Radiative transfer modeling of the aerosol clouds demonstrates (1) that if the initial rapid pulse of sulfate aerosols was global, photosynthesis may have been shut down for 6 months and (2) that for the second prolonged aerosol cloud, solar transmission dropped 80% by the end of first year and remained 50% below normal for 9 years. As a result, global average surface temperatures probably dropped between 5 degrees and 31 degrees K, suggesting that global near-freezing conditions may have been reached. Impact-generated CO2 caused less than 1 degree K greenhouse warming and therefore was insignificant compare to the sulfate cooling. The magnitude of sulfate cooling depends largely upon the rate of ocean mixing as surface waters cool, sink, and are replaced by upwelling of deep ocean water. This upwelling apparently drastically altered ocean stratification and circulation, which may explain the global collapse of the delta 13C gradient between surface and deep ocean waters at the K/T boundary. PMID:11541145

  20. Stratigraphy and sedimentology of the K/T boundary deposit in Haiti

    NASA Technical Reports Server (NTRS)

    Carey, S.; Sigurdsson, H.; Dhondt, S.; Espindola, J. M.

    1993-01-01

    The K/T boundary sequence is exposed in uplifted carbonate sediments of the southwest peninsula of Haiti. It is found at 15 localities within the Beloc formation, a sequence of limestone and marls interpreted as a monoclinal nappe structure thrust to the north. This tectonic deformation has affected the K/T boundary deposit to varying degrees. In some cases the less competent K/T deposit has acted as a slip plane leading to extensive shearing of the boundary layer, as well as duplication of the section. The presence of glassy tektites, shocked quartz, and an Ir anomaly directly link the deposit to a bolide impact. Stratigraphic and sedimentological features of the tripartite sequence indicate that it was formed by deposition from ballistic fallout of coarse tektites, emplacement of particle gravity flows and fine grained fallout of widely dispersed impact ejecta.

  1. The Cretaceous-Tertiary impact crater and the cosmic projectile that produced it.

    PubMed

    Sharpton, V L; Marin, L E

    1997-05-30

    Evidence gathered to date from topographic data, geophysical data, well logs, and drill-core samples indicates that the buried Chicxulub basin, the source crater for the approximately 65 Ma Cretaceous-Tertiary (K/T) boundary deposits, is approximately 300 km in diameter. A prominent topographic ridge and a ring of gravity anomalies mark the position of the basin rim at approximately 150 km from the center. Wells in this region recovered thick sequences of impact-generated breccias at 200-300 m below present sea level. Inside the rim, which has been severely modified by erosion following impact, the subsurface basin continues to deepen until near the center it is approximately 1 km deep. The best planetary analog for this crater appears to be the 270 km-diameter Mead basin on Venus. Seismic reflection data indicate that the central zone of downward displacement and excavation (the transient crater is approximately 130 km in diameter, consistent with previous studies of gravity anomaly data). Our analysis of projectile characteristics utilizes this information, coupled with conventional scaling relationships, and geochemical constraints on the mass of extraterrestrial material deposited within the K/T boundary layer. Results indicate that the Chicxulub crater would most likely be formed by a long-period comet composed primarily of nonsilicate materials (ice, hydrocarbons, etc.) and subordinate amounts (< or = 50%) primitive chondritic material. This collision would have released the energy equivalent to between 4 x 10(8) and 4 x 10(9) megatons of TNT. Studies of terrestrial impact rates suggest that such an event would have a mean production rate of approximately 1.25 x 10(-9) y-1. This rate is considerably lower than that of the major mass extinctions over the last 250 million years (approximately 5 x 10(-7) y-1). Consequently, while there is substantial circumstantial evidence establishing the cause-effect link between the Chicxulub basin forming event and the K/T biological extinctions, the results of our analysis do not support models of impact as a common or singular causative agent of mass extinctions on Earth. PMID:11543120

  2. The Cretaceous-Tertiary Impact Crater and the Cosmic Projectile that Produced it

    NASA Technical Reports Server (NTRS)

    Sharpton, Virgil L.; Marin, Luis E.

    1997-01-01

    Evidence gathered to date from topographic data, geophysical data, well logs, and drill-core samples indicates that the buried Chicxulub basin, the source crater for the approximately 65 Ma Cretaceous-Tertiary (K/T) boundary deposits, is approximately 300 km in diameter. A prominent topographic ridge and a ring of gravity anomalies mark the position of the basin rim at approximately 150 km from the center. Wells in this region recovered thick sequences of impact-generated breccias at 200-300 m below present sea level. Inside the rim, which has been severely modified by erosion following impact, the subsurface basin continues to deepen until near the center it is approximately 1 km deep. The best planetary analog for this crater appears to be the 270 km-diameter Mead basin on Venus. Seismic reflection data indicate that the central zone of downward displacement and excavation (the transient crater is approximately 130 km in diameter, consistent with previous studies of gravity anomaly data). Our analysis of projectile characteristics utilizes this information, coupled with conventional scaling relationships, and geochemical constraints on the mass of extraterrestrial material deposited within the K/T boundary layer. Results indicate that the Chicxulub crater would most likely be formed by a long-period comet composed primarily of nonsilicate materials (ice, hydrocarbons, etc.) and subordinate amounts (less than or equal to 50 percent) primitive chondritic material. This collision would have released the energy equivalent to between 4 x 10(exp 8) and 4 x 10(exp 9) megatons of TNT. Studies of terrestrial impact rates suggest that such an event would have a mean production rate of approximately 1.25 x 10(exp -9) y(exp -1). This rate is considerably lower than that of the major mass extinctions over the last 250 million years (approximately 5 x 10(exp -7) y(exp -1). Consequently, while there is substantial circumstantial evidence establishing the cause-effect link between the Chicxulub basin forming event and the K/T biological extinctions, the results of our analysis do not support models of impact as a common or singular causative agent of mass extinctions on Earth.

  3. Water content of glasses from the K/T boundary, Haiti - An indication of impact origin

    NASA Astrophysics Data System (ADS)

    Koeberl, Christian

    1992-12-01

    The water content in seven glass samples from the K/T boundary on Haiti was determined by micro-infrared spectrometry. These glasses are thought to result from impact melting associated with the K/T boundary impact, although this interpretation is not unanimous. The results of the water determinations, 0.013-0.021 wt pct H2O2, show that the Haiti glasses are water-poor. This is a common characteristic of impact glasses and tektites, which usually have water contents below 0.05 wt pct, and is not in agreement with interpretations that the Haitian glasses are of volcanic origin.

  4. Origin and diagenesis of K/T impact spherules - from Haiti to Wyoming and beyond

    USGS Publications Warehouse

    Bohor, B.F.; Glass, B.P.

    1995-01-01

    Impact spherules in Cretaceous/Tertiary (K/T) boundary clays and claystones consist of two types; each type is confined to its own separate layer of the boundary couplet in the Western Hemisphere. The form and composition of each of the spherule types result from its own unique mode of origin during the K/T event. Type 1 splash-form spherules occur only in the melt-ejecta (basal) layer of the K/T couplet. This layer was deposited from a ballistic ejecta curtain composed of melt-glass droplets transported mostly within the atmosphere. In contrast, Type 2 spherules are accreted, partially crystalline, spheroidal bodies that formed by condensation of vaporized bolide and target-rock materials in an expanding fireball cloud, from which they settled out of buoyant suspension to form the fireball layer. Dendritic and skeletal Ni-rich spinel crystals are unique to these Type 2 spherules in the fireball layer. -from Authors

  5. K/T boundary stratigraphy: Evidence for multiple impacts and a possible comet stream

    NASA Technical Reports Server (NTRS)

    Shoemaker, E. M.; Izett, G. A.

    1992-01-01

    A critical set of observations bearing on the K/T boundary events were obtained from several dozen sites in western North America. Thin strata at and adjacent to the K/T boundary are locally preserved in association with coal beds at these sites. The strata were laid down in local shallow basins that were either intermittently flooded or occupied by very shallow ponds. Detailed examination of the stratigraphy at numerous sites led to the recognition of two distinct strata at the boundary. From the time that the two strata were first recognized, E.M. Shoemaker has maintained that they record two impact events. We report some of the evidence that supports this conclusion.

  6. Chicxulub Impact Predates K-T Boundary in Texas and Caused no Mass Extinction

    NASA Astrophysics Data System (ADS)

    Fucugauchi, J. U.; Soler-Arechalde, A. M.; Rebolledo-Vieyra, M.; Keller, G.; Adatte, T.; Berner, Z.; Baum, G.; Stueben, D.

    2005-05-01

    In the Chicxulub crater and throughout NE Mexico the impact breccia and spherule ejecta layer, respectively, predate the K-T boundary by about 300,000 years (Keller et al., 2003, 2004). The stratigraphic separation between the K-T boundary and the Chicxulub impact ejecta varies from 50 cm in the Chicxulub crater, to over 14 m in NE Mexico, with the variation due to erosion, non-deposition and paloetopography. New studies from drilling and exposures along the Brazos River, Texas, confirm these findings based on biostratigraphy, paleomagnetic stratigraphy, geochemistry, stable isotopes, and faunal assemblages. In this area, the spherule ejecta is reworked near the base of a series of `event beds' representing variable storm deposits separated by repeated colonization of the ocean floor by invertebrates. The base of these storm beds overlies an undulating erosion surface of latest Maastrichtian claystone. The original spherule ejecta layer appears to be within the underlying claystone, in the lower part of chron 29R and near the base of biozone CF1, which marks the last 300,000 years of the Cretaceous. Above the `event beds' latest Maastrichtian claystone sedimentation continues up to the K-T boundary, which is characterized by a sharp (1.4 ng/g) iridium anomaly that marks the K-T as a second major impact. The distance between the top of the `event beds' and the K-T boundary varies from 20 cm to 1.6 m depending on local tectonics and erosion. Evaluation of the biotic effects of the Chicxulub and K-T impacts upon planktic foraminifera, which suffered most severely of all marine organisms, reveals no species extinctions associated with the Chicxulub impact and no significant species population changes, except for species dwarfing as a result of increased biotic stress. These Brazos results confirm the 65.3 Ma age for the Chicxulub impact determined from NE Mexico and the crater core Yaxcopoil-1. They also show that the Chicxulub impact did not cause a mass extinction, but the 65.0 Ma K-T impact did.

  7. Resistance of spiders to Cretaceous-Tertiary extinction events.

    PubMed

    Penney, David; Wheater, C Philip; Selden, Paul A

    2003-11-01

    Throughout Earth history a small number of global catastrophic events leading to biotic crises have caused mass extinctions. Here, using a technique that combines taxonomic and numerical data, we consider the effects of the Cenomanian-Turonian and Cretaceous-Tertiary mass extinctions on the terrestrial spider fauna in the light of new fossil data. We provide the first evidence that spiders suffered no decline at the family level during these mass extinction events. On the contrary, we show that they increased in relative numbers through the Cretaceous and beyond the Cretaceous-Tertiary extinction event. PMID:14686534

  8. The Chicxulub Impact - Connection to K/T Boundary Event Based on Petrophysical and Paleomagnetic Investigations

    NASA Astrophysics Data System (ADS)

    Elbra, T.; Pesonen, L. J.

    2004-12-01

    Establishing relationships between the Chicxulub impact crater and the K/T boundary event has been one of the main reasons for Chicxulub Scientific Drilling what was carried out in framework of the International Continental Drilling Program (ICDP). Drilling-site (Hacienda Yaxcopoil) was chosen on the basis of previous work achieved by drillings of the oil exploratory program by Petrleos Mexicanos and more recently by the National University of Mexico (UNAM). The Yaxcopoil-1 borehole is 1511 m deep, and sampling started from 404 m. Drillcore runs through 3 intervals: the post-impact layer, the impact layer and the pre-impact target rock. Samples of this study were gathered in collaboration of many institutions (Helsinki University, UNAM, Vrije University of Amsterdam and Humboldt University of Berlin) and cover all these intervals. Standard petrophysical and paleomagnetic measurements (including magnetostratigraphy) were carried out in order to clarify some of the dating issues. Results show that paleomagnetic measurements of the drillcore, coupled with petrophysical data provide a good tool of isolating various units including the impact layer, the K/T boundary- and the post-impact sequences. NRM and susceptibility values of samples from pre- and post-impact layers show that most samples are very weakly magnetized, with exception of the interval from 790 m to 900 m that includes the K/T boundary layer. Also our data show that magnetostratigraphy of the impact layer is quite complex due to possible hydrothermal remagnetization process. Additionally these data reveal that the Chicxulub impact event took probably place within the magnetic chron 29R and therefore can be related to K/T boundary event.

  9. Geochemical comparison of K-T boundaries from the Northern and Southern Hemispheres

    NASA Technical Reports Server (NTRS)

    Tredous, M.; Verhagen, B. TH.; Hart, R. J.; Dewit, C. B.; Smith, C. B.; Perch-Nielsen, K.; Sellschop, J. P. F.

    1988-01-01

    Closely spaced (cm-scale) traverses through the K-T boundary at Stevns Klint (Denmark), Woodside Creek (New Zealand) and a new Southern Hemisphere site at Richards Bay (South Africa) were subjected to trace element and isotopic (C, O, Sr) investigation. Intercomparison between these data-sets, and correlation with the broad K-T database available in the literature, indicate that the chemistry of the boundary clays is not globally constant. Variations are more common than similarities, both of absolute concentrations, and interelement ratios. For example, the chondrite normalized platinum-group elements (PGE) patterns of Stevns Klint are not like those of Woodside Creek, with the Pt/Os ratios showing the biggest variation. These differences in PGE patterns are difficult to explain by secondary alteration of a layer that was originally chemically homogeneous, especially for elements of such dubious crustal mobility as Os and Ir. The data also show that enhanced PGE concentrations, with similar trends to those of the boundary layers, occur in the Cretaceous sediments below the actual boundary at Stevns Klint and all three the New Zealand localities. This confirms the observations of others that the geochemistry of the boundary layers apparently does not record a unique component. It is suggested that terrestrial processes, eg. an extended period of Late Cretaceous volcanism can offer a satisfactory explanation for the features of the K-T geochemical anomaly. Such models would probably be more consistent with the observed stepwise, or gradual, palaeontological changes across this boundary, than the instant catastrophe predicated by the impact theory.

  10. Preliminary Ar-40/Ar-39 age spectrum and laser probe dating of the M1 core of the Manson Impact Structure, Iowa: A K-T boundary crater candidate

    NASA Technical Reports Server (NTRS)

    Kunk, M. J.; Snee, L. W.; French, B. M.; Harlan, S. S.; Mcgee, J. J.

    1993-01-01

    Preliminary Ar-40/Ar-39 age spectrum and laser probe dating results from new drill core from the 35-km-diameter Manson Impact Structure (MIS), Iowa indicates a reasonable possibility that the MIS is a Cretaceous-Tertiary (K-T) boundary impact event. Several different types of samples from a melt-matrix breccia, a unit of apparent crater fill intersected by the M1 core, were analyzed. Ar-40/Ar-39 results from these samples indicate a maximum age for the MIS of about 65.4 plus or minus 0.4(2 sigma) Ma. Petrographic analyses of the samples indicate a high probability that all the dated samples from the melt-matrix breccia contain relict grains that were not entirely melted or degassed at the time of impact, suggesting that the actual age of the MIS could be somewhat younger than our preliminary results indicate. The results are consistent with a previously published age estimate of shocked microcline from the MIS central uplift of 65.7 plus or minus 1.0 Ma.

  11. Formation of spinels in the mesosphere after K/T impact

    NASA Astrophysics Data System (ADS)

    Preisinger, A.; Aslanian, S.; Brandstaetter, F.; Grass, F.

    1997-03-01

    Continuous Cretaceous/Tertiary (K/T) boundary sections were studied in the eastern Balkan Mountains at the Black Sea coast near Bjala, Bulgaria, in the Scaglia Rossa of the Apennines, 25 km north of Gubbio at Cerrara, Italy, and in the Betic Zone in the Barranco del Gredero near Caravaca, Spain. Spinels were extracted with a strong magnet from water suspensions of clays sampled stepwise at intervals of a few millimeters from the K/T boundaries and were investigated by X-ray powder diffraction, SEM, EDS, and instrumental neutron activation analysis. Spinels from the east-west range of the Mediterranean area of 3000 km (Bjala-Caravaca) have structural and chemical compositions which are characteristic of the KT-spinels of the boundary clay sites. The majority of these KT-spinels are single crystals of Ni-rich magnesioferrite spinels of octahedral shape of 1-20 micron in sizes.

  12. Mass extinctions, atmospheric sulphur and climatic warming at the K/T boundary

    NASA Technical Reports Server (NTRS)

    Rampino, Michael R.; Volk, Tyler

    1988-01-01

    The possible climatic effects of a drastic decrease in cloud condensation nuclei (CCN) associated with a severe reduction in the global marine phytoplankton abundance are investigated. Calculations suggest that a reduction in CCN of more than 80 percent and the resulting decrease in marine cloud albedo could have produced a rapid global warming of 6 C or more. Oxygen isotope analyses of marine sediments from many parts of the world have been interpreted as indicating a marked warming coincident with the demise of calcareous nannoplankton at the K/T boundary. Decreased marine cloud albedo and resulting high sea surface temperatures could have been a factor in the maintenance of low productivity in the 'Strangelove Ocean' period following the K/T extinctions.

  13. Distinguishing between sudden and gradual extinctions in the fossil record: Predicting the position of the Cretaceous-Tertiary iridium anomaly using the ammonite fossil record on Seymour Island, Antarctica

    NASA Astrophysics Data System (ADS)

    Marshall, Charles R.

    1995-08-01

    A simple method, employing 50% confidence intervals, may be used to distinguish sudden from gradual extinctions. In cases where the fossil record is consistent with a sudden disappearance, the expected position of the extinction horizon may als o be determined. Analysis of the fossil ammonites on Seymour Island shows that their pattern of disappearances is consistent with a sudden mass extinction at the Cretaceous-Tertiary (K-T) boundary, even though a literal reading of the fossil record shows they disappeared gradually over a stratigraphic interval 10 50 m below the boundary. It is striking that the iridium anomaly on Seymour Island falls within the stratigraphic interval determined by the 50% confidence intervals to be the most likely place for the K-T boundary (assuming there was a sudden disappearance of ammonites at the boundary). However, a computer simulation of the Seymour Island ammonite fossil record indicates a wide range of other extinction scenarios, including gradual extinctions ranging over as much as 20 m (? = 0.05), that are consistent with the ammonite fossil record; without saturation collecting near the K-T boundary it will be impossible to distinguish between gradual and sudden extinction scenarios for the Seymour Island ammonites based on the ammonite fossil record alone.

  14. Magnetic properties and Moessbauer analyses of glass from the K-T boundary, Beloc, Haiti

    NASA Technical Reports Server (NTRS)

    Senftle, F. E.; Thorpe, A. N.; May, L.; Barkatt, A.; Adel-Hadadi, M. A.; Marbury, G. S.; Izett, G.; Sigurdsson, H.; Maurasse, F. J.-M. R.

    1993-01-01

    The experimental magnetic susceptibility, the temperature-independent component of the magnetic susceptibility, the magnetization, and the Curie constant have been measured for a number of specimens of glass from the K-T boundary found at Beloc, Haiti, and the results are compared with those of similar measurements of tektites. Because the Fe(3+)/Fe(2+) ratio is needed to calculate the magnetic parameters, Moessbauer spectroscopic measurements were also made. The data were consistent with the classification of the Beloc glasses as tektites.

  15. The Koshak section: Evidence for element fractionation and an oxidation event at the K/T boundary

    NASA Technical Reports Server (NTRS)

    Nazarov, M. A.; Badjukov, D. D.; Barsukova, L. D.; Kolesov, G. M.; Naidin, D. P.

    1993-01-01

    The Koshak site is a new K/T section located about 125 km EEN of the Fort Shevchenko city, Mangyshlak, Kazakhstan. In this paper, we report results of geochemical and mineralogical studies of this section which indicate a deep element fractionation and an oxidation event at the K/T boundary.

  16. Micropaleontological and Paleomagnetic Characterization of La Ceiba K/T Boundary Section, Central Mexico

    NASA Astrophysics Data System (ADS)

    Martnez-Lpez, M.; Urrutia-Fucugauchi, J.

    2007-05-01

    We report results of a micropaleontological and magnetostratigraphic study of the La Ceiba section that spans the K/T boundary. La Ceiba is located in central Mexico (20o 19.8' N, 97o 41.0' W) within the Tampico-Mizantla basin. The K/T boundary is marked by a clastic unit of about one-meter thickness intercalated between the carbonate hemipelagic marls of the Cretaceous Mendez Formation and the Paleocene Velasco Formation. The clastic unit can be divided into four sub-units, according to their texture and architectural characteristics following Arenillas et al. (2002). The basal sub-unit is formed by calcareous marls and is rich in shocked quartz and millimeter size spherules with microtektites and bioclasts of shallow water origin. The second sub-unit is formed by medium-grained sandstones, with clasts and quartz fragments, feldspars, metamorphic and calcareous fragments and re-worked benthic and planktic foraminifera. The third sub-unit is composed by a single body of medium- to fine-grained sandstones with tabular geometry. In this sub-unit, cross- and parallel-lamination trough cross-stratification, current ripples and climbing ripples have been observed. The top sub-unit is a tabular body of fine-grained sandstones, showing parallel-lamination and low-angle cross-lamination, with asymmetric ripples and burrow traces to the top. For the paleontologic and paleomagnetic study we collected twenty-five oriented samples across the section. We measured the low-field susceptibility, intensity and direction of the NRM. The vectorial composition and stability of NRM were analyzed by progressive thermal and alternating field demagnetization. Vectorial orthogonal diagrams and vector subtraction and principal component analysis were used to determine the characteristic magnetization and secondary components for each sample. The characteristic NRM negative inclination and southward declination in the K/T clastic sediments indicate a reverse polarity, which is correlated to reverse chron 29r that spans the K/T boundary. Micropaleontology analyses permit identification of six biozones. Two biozones (biozone of Rugoglobigerina scootti and Abathomphalus mayaroensis) correspond to the Maastrichtian. Four biozones (Guembelitria cretcea, Parvularogoglobigerina eugubina, Parasubotina pseudobulloides and Acarina trinidadensis) correspond to the Danian.

  17. First evidence for a massive extinction event affecting bees close to the K-T boundary.

    PubMed

    Rehan, Sandra M; Leys, Remko; Schwarz, Michael P

    2013-01-01

    Bees and eudicot plants both arose in the mid-late Cretaceous, and their co-evolutionary relationships have often been assumed as an important element in the rise of flowering plants. Given the near-complete dependence of bees on eudicots we would expect that major extinction events affecting the latter would have also impacted bees. However, given the very patchy distribution of bees in the fossil record, identifying any such extinctions using fossils is very problematic. Here we use molecular phylogenetic analyses to show that one bee group, the Xylocopinae, originated in the mid-Cretaceous, coinciding with the early radiation of the eudicots. Lineage through time analyses for this bee subfamily show very early diversification, followed by a long period of seemingly no radiation and then followed by rapid diversification in each of the four constituent tribes. These patterns are consistent with both a long-fuse model of radiation and a massive extinction event close to the K-T boundary. We argue that massive extinction is much more plausible than a long fuse, given the historical biogeography of these bees and the diversity of ecological niches that they occupy. Our results suggest that events near the K-T boundary would have disrupted many plant-bee relationships, with major consequences for the subsequent evolution of eudicots and their pollinators. PMID:24194843

  18. Geochemical evidence for combustion of hydrocarbons during the K-T impact event.

    PubMed

    Belcher, Claire M; Finch, Paul; Collinson, Margaret E; Scott, Andrew C; Grassineau, Nathalie V

    2009-03-17

    It has been proposed that extensive wildfires occurred after the Cretaceous-Tertiary (K-T) impact event. An abundance of soot and pyrosynthetic polycyclic aromatic hydrocarbons (pPAHs) in marine K-T boundary impact rocks (BIRs) have been considered support for this hypothesis. However, nonmarine K-T BIRs, from across North America, contain only rare occurrences of charcoal yet abundant noncharred plant remains. pPAHs and soot can be formed from a variety of sources, including partial combustion of vegetation and hydrocarbons whereby modern pPAH signatures are traceable to their source. We present results from multiple nonmarine K-T boundary sites from North America and reveal that the K-T BIRs have a pPAH signature consistent with the combustion of hydrocarbons and not living plant biomass, providing further evidence against K-T wildfires and compelling evidence that a significant volume of hydrocarbons was combusted during the K-T impact event. PMID:19251660

  19. Twelve-year trail of clues leads to impact crater from the K-T boundary

    SciTech Connect

    Levi, B.G.

    1992-12-01

    In 1980, scientists at the University of California, Berkeley proposed that a massive comet or asteroid might have struck the earth about 65 million years ago, changing the earth's climate so drastically that dinosaurs and other creatures could no longer survive. This article describes the evidence for the elusive crater required to support this theory. The structure in question is 180 km in diameter and is submeged beneath the Yucatan peninsula and centered on the Mexican village of Chicxulub. Material drilled from this crater has been linked chemically and geologically to pellets found in Northeast Mexico and Haiti. The link between this ejecta material and the crater was confirmed by a report that the Chicxulub melt rock and pellets are coeval, all having ages consistent with 65 million years. This puts the possible impact at the K-T boundary -- the dividing line between the Cretaceous period of the dinosaurs and the Tertiary period of the mammals. 13 refs.

  20. Late cretaceous and paroxysmal cretaceous/tertiary extinctions

    NASA Astrophysics Data System (ADS)

    Officer, Charles B.; Drake, Charles L.; Hallam, Anthony; Devine, Joseph D.

    1987-03-01

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

  1. Environmental effects of an impact-generated dust cloud - Implications for the Cretaceous-Tertiary extinctions

    NASA Technical Reports Server (NTRS)

    Pollack, J. B.; Toon, O. B.; Ackerman, T. P.; Mckay, C. P.; Turco, R. P.

    1983-01-01

    A model of the evolution and radiative effects of a debris cloud from a hypothesized impact event at the Cretaceous-Tertiary boundary suggests that the cloud could have reduced the amount of light at the earth's surface below that required for photosynthesis for several months and, for a somewhat shorter interval, even below that needed for many animals to see. For 6 months to 1 year, the surface would cool; the oceans could cool only a few degrees Celsius at most, but the continents might cool a maximum of 40 Kelvin. Extinctions in the ocean may have been caused primarily by the temporary cessation of photosynthesis, but those on land may have been primarily induced by a combination of lowered temperatures and reduced light.

  2. Meteorite impact, cryptoexplosion, and shock metamorphism - A perspective on the evidence at the K/T boundary

    NASA Technical Reports Server (NTRS)

    Sharpton, V. L.; Grieve, R. A. F.

    1990-01-01

    A perspective on the evidence of a major impact event at the K/T boundary is proposed using field and laboratory studies of terrestrial impact craters. Recent assertions that diagnostic indications of shock metamorphism are also produced in volcanic environments are challenged. A general geological framework of impact structures is developed and the issue of volcanically induced shock metamorphism is examined. Cryptoexplosion is addressed by assessing the geology of two structures: the Slate Islands and Manson, which are often cited by advocates of an internal origin for shock metamorphism as volcanic structures. It is concluded that the link between shock metamorphism and meteorite impact is now established beyond reasonable doubt. The occurrence and worldwide distribution of shocked minerals at the K/T boundary is considered to be the conclusive evidence for a major impact event.

  3. Geochemical evidences for two chondritic-like cometary or asteroidal impacts before and at the K/T boundary

    NASA Technical Reports Server (NTRS)

    Liu, Y.-G.; Schmitt, R. A.

    1993-01-01

    A number of geological and palaeontological evidences support multiple impacts of cometary showers within a short time (approximately 1-3 Ma) and their connection with mass extinctions. Observations include clustered crater ages, stratigraphic horizons of impact ejecta closely spaced in time, and evidence for stepwise mass extinctions spanning intervals of 1-3 Ma. For the K/T boundary, three candidates, Popigai, Manson, and Yucatan, have been proposed as impact craters. Two distinct strata at the K/T boundary in western North America have been interpreted as evidence for two sequential impacts. If multiple impacts occurred within a time span of about 1 Ma then multiple Ir enrichments should be observed. DSDP Hole 577B on the Shatsky Plateau in the northern Pacific at K/T time is the first site. Samples contain approximately greater than 97 percent CaCO3, which exhibit clear chemical signals associated with asteroidal/cometary impact. Ir, Fe, and Cr data are presented. From the Th-normalized data, two satellite peaks below the major peak at 78 cm and 81 cm of 577B-1-4 are clearly shown. The major Ir peak (K/T boundary) is at 72 cm. Fe and Cr, from C1-like impactor ejecta fallout, also show two peaks at the same positions. For hole 738C on the southern Kerguelen Plateau, Ir values reach a peak concentration of 18 ppb in the clay layer at 96.0-96.2 cm in section 20R-5, and gradually tail off. In the sample 115 cm above the boundary, Ir concentrations have still not reached background levels. From the Ir peak downward to the lowermost sample analyzed at 102 cm, the Ir concentration is still as high as 1.7 ppb. From the Th-normalized data, we observe a small Ir/Th peak at 100-101 cm. Though this peak is within the error margin, the trend is clear. Fe and Cr exhibit the same pattern. The third case is Hole 690C on the Queen Maud Ridge. Again, the Ir/Th plot indicates the strong possibility of satellite peaks at approximately 52 cm. The main peak is at 39-40 cm. For the Stevns Klint K/T boundary layers, the stratification of trace elements appears threefold with peak concentrations in sublayers A1, A3, and B2 for different element groups, including Ir. C1 ratios for many siderophile elements found in combined layers III and IV, corresponding to layers A, B, C, and D, strongly support the impact hypothesis. Also, multiple Ir anomalies in the K/T section at Lattengebirge, Bavarian Alps are reported. Recent works on Ni-rich spinels and Ir at the K/T boundaries clearly establish cometary/asteroidal impacts at the K/T boundary. Lastly, cometary showers can explain the enhanced Ir contents over approximately a 1 Ma interval in Gubbio shales.

  4. The Disposition of Pt, Pd, Ir, Os, and Ru in Marine Sediments and the K/T Boundary

    NASA Technical Reports Server (NTRS)

    Lee, Cin-Ty; Wasserburg, Gerald; Kyte, Frank

    2003-01-01

    The marine record of platinum group elements (PGEs) and Os isotopic compositions provides information on different inputs of PGEs into the oceans. Some studies based on a smaller subset of the PGEs suggest that the PGEs may suffer post-depositional mobility during diagenesis. In some K/T boundary clays, Kyte and others showed that the relative abundances of Pt, Pd, Ir, and Os can differ significantly from chondritic, which is the signature expected from fallout of the meteorite impact. In some K/T boundary sections, elevated Ir concentrations are observed as far as 1 meter from the cm-thick boundary clay containing the meteoritic ejecta. The purpose of this study was to characterize Pt, Pd, Ir, Os, and Ru abundances in zones including the K/T boundary. We determined PGE abundances of boundary clays at two hemipelagic sites (Stevns Klint, Denmark and Caravaca, Spain) in which previous studies by Kyte and others showed that the Ir anomaly is confined to within a few cm. We also analyzed two pelagic Pacific sites: a boundary clay from the north Pacific (Hole 465A) characterized by a 0.5 m thick Ir anomaly and a transect across the K/T boundary from the south Pacific (Hole 596) where the Ir anomaly spans 2 m. The Stevns Klint, Caravaca, and north Pacific sites are characterized by abundant marls and limestones in the section, whereas the south Pacific site is dominated by clays. Samples were spiked with isotopic tracers, mixed with a flux, S and Ni, and equilibrated by fusion. PGEs were extracted from the Ni and analyzed on a Finnigan Element ICP-MS. We find that the narrow Caravaca and Stevns Klint boundary clays have relative PGE abundance patterns indistinguishable from chondritic values. The two Pacific sites were found to have nearly identical PGE patterns but have ratios at the peak, which differ from chondritic values as found earlier by Evans et al. The Pacific sites were found to have nearly identical PGE patterns but are extremely depleted in OS (Os/Ir = 0.07-0.15) and slightly enriched in Pd and Pt relative to Ir.

  5. Environments and extinctions at the K-T boundary in eastern Montana are compatible with an asteroid impact

    SciTech Connect

    Fastovsky, D.E. ); Sheehan, P.M. )

    1992-01-01

    In the terrestrial latest Cretaceous Hell Creek (HC) Formation, both non-biotic events and patterns of extinction and survivorship are consistent with an asteroid impact causing the extinctions. Environments through the last 2--3 million-year interval represented by the HC remained relatively constant: an aggrading coastal lowland dissected by meandering rivers. The K-T boundary occurred during an abrupt change to impeded drainage represented by coals and pond deposits formed under low-energy conditions. Because of the close temporal proximity of the sediments of the Paleocene Cannonball Sea to the K-T boundary in South Dakota, impeded drainage in the earliest Paleocene in eastern Montana may be attributable to riverine base-level changes associated with a renewed transgression of the western interior sea during the K-T transition. Patterns within the biota mirror those of the paleoenvironments. The ecological diversity of HC dinosaurs remains statistically unchanged through HC time. Analyses of vertebrates at the species level indicate a differential extinction in which the terrestrial biota underwent far more extinction than its aquatic counterpart. There is no evidence for changing environments in the upper HC, and there is circumstantial evidence that the latest Cretaceous was a time of renewed transgression rather than regression. Likewise, biotic patterns do not accord with gradual, environmentally driven extinctions. While the paleoenvironmental change that marks the K-T transition in eastern Montana accounts for some of the extinctions, the pattern of differential extinction is concordant with an asteroid impact. In this scenario, aquatic ecosystems and some land-based food chains would be buffered by detritus-based feeding. Terrestrial systems, dependent upon primary productivity, would undergo a short-term loss of resources causing extinctions.

  6. Diamonds from the iridium-rich K-T boundary layer at Arroyo el Mimbral, Tamaulipas, Mexico

    NASA Astrophysics Data System (ADS)

    Hough, R. M.; Gilmour, I.; Pillinger, C. T.; Langenhorst, F.; Montanari, A.

    1997-11-01

    Diamonds, up to 30 ?m in size, were found in the iridium-rich layer from the K-T boundary site at Arroyo El Mimbral and the spherule bed from Arroyo El Peon, northeastern Mexico. Stepped heating experiments indicate two or more isotopically distinct diamond components with carbon isotopic compositions characteristic of a mixture of carbon sources. The diamonds' crystal form is cubicnot the hexagonal polymorph of diamond, lonsdaleite, which has been used previously to infer formation due to shock transformation of graphite. The size, crystallography, and mineralogic associations of K-T diamonds are similar to those of impact-produced diamonds from the Ries crater in Germany where both shock transformation of graphite and a mode of formation by condensation from a vapor plume have been inferred. The discovery of impact-produced diamonds in association with high Ir contents for these sediments supports their impact origin, K-T age, and the inference that their source was from the buried impact crater of Chicxulub on the Yucatan peninsula, Mexico.

  7. Iridium enrichment in volcanic dust from blue ice fields, Antarctica, and possible relevance to the K/T boundary event

    NASA Technical Reports Server (NTRS)

    Koeberl, Christian

    1989-01-01

    The analysis of samples of volcanic ash dust layers from the Lewis Cliff/Beardmore Glacier in Antarctica shows that some of the samples contain Ir concentrations up to 7.5 ppb. It is shown that the Ir is positively correlated with Se, As, Sb, and other volcanogenic elements. The results show that Ir may be present in some volcanic ash deposits, suggesting that the Ir in the K/T boundary clays is not necessarily of cosmic origin, but may have originated from mantle reservoirs tapped during extensive volcanic eruptions possibly triggered by impact events.

  8. U-Pb provenance ages of shocked zircons from the K-T boundary, Raton Basin, Colorado

    NASA Technical Reports Server (NTRS)

    Premo, W. R.; Izett, G. A.

    1993-01-01

    U-Pb isotopic systematics from analyses of single zircons identify at least two provenance ages, approximately 575 Ma and approximately 330 Ma, for zircons from the impact layer of the K-T boundary, Raton Basin, Colorado. These data are a preliminary confirmation of results reported from the same layer. The zircon provenance ages provide a unique signature for identification of the source crater since igneous rocks of these ages (or sedimentary rocks derived from them) must characterize part of the impact stratigraphy.

  9. Altered spherules of impact melt and associated relic glass from the K/T boundary sediments in Haiti

    SciTech Connect

    Kring, D.A.; Boynton, W.V. )

    1991-06-01

    Partially to wholly altered glass spherules produced by impact-induced shock melting have been found in the K/T boundary sediments of Haiti which also contain grains of shocked quartz. The relic glass has an approximately dacitic composition, and although grossly similar in composition to most previously described tektite glasses, it is slightly enriched in Ca and slightly depleted in Si, suggesting the Haitian glass was produced either from a target with a greater fraction of carbonate and anhydrite lithologies and fewer silicate units than the targets from which most other tektites were produced, and/or from one with a significant mafic component. The composition of the glass can best be reconciled with a continental margin terrane, consistent with studies of shocked mineral phases reported elsewhere. The thickness of the deposit in which the impact spherules occur indicates the source of the ejecta was in the proto-Caribbean region.

  10. Cosmic Genes in the Cretaceous-Tertiary transition

    NASA Astrophysics Data System (ADS)

    Wallis, M. K.

    2003-07-01

    It is proposed that genes coding for Aib-polypeptides arose early on in the K/T transition, presumed from the Earth's accretion of interplanetary (comet) dust. Aib-fungi flourished because of the evolutionary advantage of novel antibiotics. The stress on Cretaceous biology led directly and indirectly to mass species extinctions, including many dinosaur species, in the epoch preceding the Chicxulub impact.

  11. Strontium and oxygen isotope study of M-1, M-3 and M-4 drill core samples from the Manson impact structure, Iowa: Comparison with Haitian K-T impact glasses

    NASA Technical Reports Server (NTRS)

    Blum, Joel D.; Chamberlain, C. Page; Hingston, Michael P.; Koeberl, Christian

    1993-01-01

    Strontium and oxygen isotope analyses were performed on 8 samples from the M-1, M-3, and M-4 cores recently drilled at the Manson impact structure. The samples were three elastic sedimentary rocks (of probable Cretaceous age) which occurred as clasts within the sedimentary clast breccia, two samples of crystalline rock breccia matrix, and three samples of dolomite and limestone. The Sr-87/Sr-86 (corrected to 65 Ma) ratios were much higher than those in impact glasses from the Haitian Cretaceous-Tertiary (K-T) boundary. Isotope mixing calculations demonstrate that neither the silicate or carbonate rocks analyzed from the Manson crater, or mixtures of these rocks are appropriate source materials for the Haitian impact glasses. However, the Sr-87/Sr-86 (65Ma) ratio and delta O-18 value of the Ca-rich Haitian glasses are well reproduced by mixtures of Si-rich Haitian glass with platform carbonate of K-T age.

  12. Trace-element composition of Chicxulub crater melt rock, K/T tektites and Yucatan basement

    NASA Technical Reports Server (NTRS)

    Hildebrand, A. R.; Gregoire, D. C.; Attrep, M., Jr.; Claeys, P.; Thompson, C. M.; Boynton, W. V.

    1993-01-01

    The Cretaceous/Tertiary (K/T) boundary Chicxulub impact is the best preserved large impact in the geologic record. The Chicxulub crater has been buried with no apparent erosion of its intracrater deposits, and its ejecta blanket is known and is well preserved at hundreds of localities globally. Although most of the molten material ejected from the crater has been largely altered, a few localities still preserve tektite glass. Availability of intra- and extracrater impact products as well as plausible matches to the targeted rocks allows the comparison of compositions of the different classes of impact products to those of the impacted lithologies. Determination of trace-element compositions of the K/T tektites, Chicxulub melt rock, and the targeted Yucatan silicate basement and carbonate/evaporite lithologies have been made using instrumental neutron activation analysis (INAA) and inductively coupled plasma mass spectrometry (ICP-MS). Some sample splits were studied with both techniques to ensure that inter-laboratory variation was not significant or could be corrected. The concentration of a few major and minor elements was also checked against microprobe results. Radiochemical neutron activation analysis (RNAA) was used to determine Ir abundances in some samples.

  13. Spatial and Temporal Variations of the K/T Boundary Record: Implications Concerning Possible Megaseiche in the Reworking Processes

    NASA Astrophysics Data System (ADS)

    Maurrasse, F. J.; Lamolda, M. A.

    2004-05-01

    Major physical disruptions characterize the sedimentary record of the K/T boundary (KTB) layer from different sites in the Southern Peninsula of Haiti as well as in diverse areas of the world. These disturbances are most important within the vicinity of the crater at Chicxulub, Yucatan, Mexico, and 65 million years ago that can be chronologically correlated with the bolide impact postulated by Alvarez et al (1981). At all sites the KTB layer shows spatial and temporal differences even within short distances, and the complexity of its characteristic signals includes serious micropaleontological inconsistencies with mixed biotic assemblages that perpetuate divergence of interpretations, thereby they raise doubts on the timing and real causal mechanisms of the biotic turnover that characterizes the boundary. Indeed, often the biostratigraphic signals are difficult to resolve because of hiatuses, or sediments are highly reworked, and distinct taxonomic successions are not clearly defined. Well defined as well as cryptic primary sedimentary structures within the boundary layer are constant at all outcrops, and they indicate complex, multiphase, subaqueous flow processes that affected sedimentation of the KTB layer at different times. The structures are known to characterize oscillatory wave processes that affect cohesionless sediments, and such water motion is only known to be associated with seiche as a modern analog that may have generated the amalgamation recorded at the KTB layer. We believe that "Megaseiche" associated with the KT impact event and its subsequent effects provides a plausible unifying mechanism to explain how various levels of the water column in different large basins can oscillate to develop the structures observed. Because of the magnitude of the bolide impact that generated initial tsunamis and large seismic waves worldwide, megaseiches of different frequencies and nodal modes must have developed in the oceans worldwide to leave different signatures in the mixing pattern. Most importantly, the heterogeneity must have been further intensified in subsequent times when more localized megaseiches developed in independent basins at different times during major crustal readjustment. These phenomena may explain the heterogeneity of patterns and apparent irreconcilable discrepancies observed at KTB sites worldwide, as the structures represent a record of water movement and resuspension of sediment of different intensities and at different timesat certain locations. As observed in smaller-scale modern seiche, various oscillatory modes controlled the duration and attenuation of the water movement, the magnitude of bottom traction and resuspension that led to complex sedimentary structures and reworking patterns of the sediments and microfossils.

  14. Avian evolution, Gondwana biogeography and the Cretaceous-Tertiary mass extinction event.

    PubMed Central

    Cracraft, J.

    2001-01-01

    The fossil record has been used to support the origin and radiation of modern birds (Neornithes) in Laurasia after the Cretaceous-Tertiary mass extinction event, whereas molecular clocks have suggested a Cretaceous origin for most avian orders. These alternative views of neornithine evolution are examined using an independent set of evidence, namely phylogenetic relationships and historical biogeography. Pylogenetic relationships of basal lineages of neornithines, including ratite birds and their allies (Palaleocognathae), galliforms and anseriforms (Galloanserae), as well as lineages of the more advanced Neoves (Gruiformes, (Capimulgiformes, Passeriformes and others) demonstrate pervasive trans-Antarctic distribution patterns. The temporal history of the neornithines can be inferred from fossil taxa and the ages of vicariance events, and along with their biogeographical patterns, leads to the conclusion that neornithines arose in Gondwana prior to the Cretaceous Tertiary extinction event. PMID:11296857

  15. Cretaceous - Tertiary Hoploparia species: Occurrence, paleobiogeography and predation context

    NASA Astrophysics Data System (ADS)

    El-Shazly, Soheir

    2015-12-01

    The study of Hoploparia species in 25 localities in Northern and Southern Hemispheres from Early Cretaceous to Early Miocene reveals the appearance of 51 species in Early Cretaceous, mostly in Northern Hemisphere, 46 species from Late Cretaceous (42 and 4 carryover from the Early Cretaceous), 7 species from Danian (4 plus 3 carryover from the Late Cretaceous), 7 species from Eocene (6 plus one from the Early Cretaceous), 2 species from Lower Oligocene and the last recorded species Hoploparia persisted in the Early Miocene of Antarctica. The oldest Hoploparia was recorded from Europe and distributed through the Northern and Southern Hemispheres with the facilitation of the Indo-Madagascar sea-way and Hispanic corridor. The tolerance for temperature and water depth as well as the morphological changes in genus Hoploparia in the Late Cretaceous and Tertiary periods, helped some species to survive the K/T event. Drill-hole predation in Hoploparia longimana (Sowerby, 1826) was recorded for the first time from the Lower Cretaceous (Albian) of Egypt.

  16. The liming of the Earth after the Chicxulub large meteorite impact at the K/T boundary

    NASA Astrophysics Data System (ADS)

    Agrinier, P.; Michard, G.; Martinez, I.; Scharer, U.; Deutsch, A.

    2005-05-01

    Shock metamorphism induced by large meteorite impacts on Earth decomposes sediments (carbonates: CaCO3, CaMg(CO3)2 and sulfates: CaSO4) into CaO, MgO, CO2 and SO2. For the Chicxulub case at the K/T boundary, up to 2850 Gt of CO2 and up to 550 Gt of SO2 were liberated into the atmosphere (Ivanov et al., 1996; Pierazzo et al., 1998; Gupta et al., 2002). Though numerous works have depicted the resulting environmental consequences of dispersing CO2, SO2, dust into the atmosphere (greenhouse warming, aerosol cooling, acid rains,...), no study has described the fate of the corresponding liberated CaO and MgO (up to 3718 Gt of CaO) in the atmosphere. Considering the high reactivity and the caustic nature of CaO (lime), we argue that spreading lime on the Earth surface increases the pH of natural waters up to 12.5. It would produce harmful environmental effects (carbonate and metal depletion in natural waters, oxydation of organic matter) and symptomatic isotopic 13C- and 18O-depleted, metal-enriched carbonates would form. Neutralization by the natural carbonate acid-base system (H2CO3/HCO3-/CO32-) of waters, by acid rains (H2CO3, H2SO4, HNO3) produced by the impact generated-CO2 and SO2, NOx and atmospheric CO2 pumping control the duration of this high pH effect on lands, while at the surface of the oceans, dilution and mixing with normal pH (? 8) seawater further reduce the duration of this high pH effect. The timescale of this high pH severe effects would be as short as a few months. As a conclusion, due to its high reactivity, lime rapidly neutralizes a significant part of the acidic atmospheric perturbation produced by the impact-liberated CO2, SO2, NOx. Ivanov et al., 1996 ; Geol. Soc. Amer. Spec. Pap., 307, 125-142. Pierazzo et al., 1998; J. Geophys. Res., Planet 103(E12), 28607-28625. Gupta et al., 2002; Earth Planet. Sci. Lett., 201, 1-12

  17. RESULTS OF A DATING ATTEMPT -CHEMICAL AND PHYSICAL MEASUREMENTS RELEVANT TO THE CASE OF THE CRETACEOUS TERTIARY EXTINCTIONS

    SciTech Connect

    Asaro, Frank; Michel, Helen V.; Alvarez, Luis W.; Alvarez, Walter

    1980-09-01

    In Gubbio, Italy, a l em layer of clay between extensive limestone formations marks the boundary between the Cretaceous and Tertiary Periods. This clay layer was known to have been deposited about 65 million years ago when many life forms became extinct, but the length of time associated with the deposition was not known. In an attempt to measure this time with normally deposited meteoritic material as a clock, extensive measurements of iridium abundances (and those of many other elements) were made on the Gubbio rocks. Neutron activation analysis was the principal tool used in these studies. About 50 elements are searched for in materials like the earth's crust, about 40 are detected and about 30 are measured with useful precision. We were not able to determine exactly how long the clay deposition took. Instead the laboratory studies on the chemical and physical nature of the Cretaceous-Tertiary boundary led to the theory that an asteroid collision with the earth was responsible for the extinction of many forms of life including the dinosaurs.

  18. Plants with double genomes might have had a better chance to survive the CretaceousTertiary extinction event

    PubMed Central

    Fawcett, Jeffrey A.; Maere, Steven; Van de Peer, Yves

    2009-01-01

    Most flowering plants have been shown to be ancient polyploids that have undergone one or more whole genome duplications early in their evolution. Furthermore, many different plant lineages seem to have experienced an additional, more recent genome duplication. Starting from paralogous genes lying in duplicated segments or identified in large expressed sequence tag collections, we dated these youngest duplication events through penalized likelihood phylogenetic tree inference. We show that a majority of these independent genome duplications are clustered in time and seem to coincide with the CretaceousTertiary (KT) boundary. The KT extinction event is the most recent mass extinction caused by one or more catastrophic events such as a massive asteroid impact and/or increased volcanic activity. These events are believed to have generated global wildfires and dust clouds that cut off sunlight during long periods of time resulting in the extinction of ?60% of plant species, as well as a majority of animals, including dinosaurs. Recent studies suggest that polyploid species can have a higher adaptability and increased tolerance to different environmental conditions. We propose that polyploidization may have contributed to the survival and propagation of several plant lineages during or following the KT extinction event. Due to advantages such as altered gene expression leading to hybrid vigor and an increased set of genes and alleles available for selection, polyploid plants might have been better able to adapt to the drastically changed environment 65 million years ago. PMID:19325131

  19. Dynamics of exploding magma chambers: Implications for K-T volcanism and mass extinctions

    NASA Technical Reports Server (NTRS)

    Rice, A. R.

    1988-01-01

    Although it is well known that unconfined chemical explosives may yield pressures to several megabars on detonation in air, the explosive literature has yet to be accessed by some contributors to the volcanological literature who've indicated that pressures in excess of the overburden and/or tensile cannot be obtained. Idealized ballistic assessments of pressures internal to volcanoes yield pressures in the hundreds of kilobar range upon correction by addition of friction, etc. Previous assessments of exploding magma chamber pressure have been made from the characteristics of the Mt. St. Helens explosion. A variety of methods yield pressures of similar value: at least hundreds of kilobars. Such results are consistent with free energy requirements for quench supersaturation explosion, a process occurring in solidifying industrial melts. Several reviews of geochemical literature emphasize the carbon event at the Cretaceous-Tertiary (K-T) boundary as being an indicator of a massive dump of CO2 derived from the mantle and entering the atmosphere by extensive global volcanism. Oxygen isotope data indicates extreme warming at the end of the Cretaceous which is consistent with a greenhouse effect attending the CO2 event. Reaction rate equations for the quench supersaturation explosion mechanism indicated, are consistent with the rise in pressure to 30 kbar on solidification of magmatic melts, these pressures limited by the strength of the experimental apparatus.

  20. Cretaceous Tertiary phenomena in the context of seafloor rearrangements and P(CO 2) fluctuations over the past 100 m.y.

    NASA Astrophysics Data System (ADS)

    Liu, Y.-G.; Schmitt, R. A.

    1996-03-01

    Both the bolide impact hypothesis and the volcanism hypothesis suggest, as one of the major environmental consequences, the release of large amounts of SO 2 and CO 2 into the atmosphere, with consequent lowering of the pH of ocean water. In the study of rare earth elements (REEs) in seawater and in carbonate sediments, we found that the Ce in seawater is depleted relative to other REEs due to the partial oxidation of Ce 3+ to Ce 4+ by dissolved oxygen. This oxidation is enhanced by the formation of highly insoluble Ce(OH) 4 and its removal from seawater. The relative Ce depletion is expressed as the Ce anomaly, Ce A*. A quantitative expression for relating Ce A* with pH and PO 2 has been derived. Owing to the involvement of OH - in this process, Ce A* is essentially controlled by the pH of seawater. The REE pattern in seawater is preserved in carbonate sediments. Therefore, the Ce anomalies in marine carbonate sediments provide a unique tool for recording pH changes in paleo-ocean water. Furthermore, the pH of ocean water is controlled by the partial pressure of CO 2, PCO 2, in the atmosphere; therefore, the corresponding PCO 2 changes are derived. About 340 Pacific carbonate sediment samples have been studied by INAA (Instrumental Neutron Activation Analysis). Three major Ce A* peaks at ~17, ~53, and ~63 Ma, as well as two minor peaks at 64.6 and 65.2 Ma, were found. The correspondence between observed Ce A* major peaks and the enhanced hydrothermal activity associated with tectonic seafloor rearrangements at these times suggests that the pH of the deep (>600 m) Pacific water was lowered by CO 2 generated by enhanced hydrothermal activity. Manganese and Co, which are highly enriched in hydrothermal solutions, closely follow the Ce A* pattern. This is strong evidence that the Ce A* peaks are related to the elevated levels of hydrothermal activity. The absence of Ce A* changes at the K/T (Cretaceous/Tertiary)-Ir boundary (≡65.0 Ma) suggests that the proposed release of SO 2 and CO 2 by cratering has not significantly lowered the pH of deep ocean water. Our analysis supports only ≲5× increase of atmospheric CO 2 by the putative K/T bolide impact into a ~3 km thick carbonate terrane. We did not observe the pH changes of deep ocean water which could be unambiguously attributed to the volcanic release of SO 2 and CO 2 from the Deccan Trap flows. The ~5 ka (FWHM, Full Width Half Maximum) Ce A* peak ~0.2 m.y. before the K/T-Ir boundary is too short to account for the Deccan Trap eruptions. Of course, our results do not rule out surface water pH changes due to either the Urey-comet or Alvarezasteroid impact or volcanism. The elevated PCO 2 of ~1.9× PCO 20 ( PCO 20 ≡ present pressure) which started ~0.75 Ma after the K/T-Ir event and lasted for ~2.3 m.y., may be one of the factors responsible for the extended period of extinctions across the K/T boundary for some species. If any species of dinosaurs lived beyond the K/T-Ir event, we predict that they would not have survived the greenhouse effect that very likely occurred between 64.25-62.0 Ma. Our PCO 2 absolute values are in general much lower than the theoretical values suggested by Berner (1990, 1993) during the Phanerozoic except for the Carboniferous and very late Cenozoic where our estimates of ~1.0× PCO 20 agree with Berner's. Also, our PCO 2 values are lower than CO 2 estimates derived from paleosol carbonate studies (e.g., Cerling, 1992; Mora et al., 1991).

  1. The K-T Transition in Meghalaya, NE India

    NASA Astrophysics Data System (ADS)

    Gertsch, B.; Keller, G.; Adatte, T.; Garg, R.; Prasad, V.; Berner, Z.; Ateequzzaman, K.; Stueben, D.

    2008-12-01

    The TEX86 paleotemperature proxy, based on tetraether membrane lipids derived from aquatic Crenarchaeota has been applied in a variety of marine and lacustrine systems. A recent study analyzing a suite of 50 globally distributed lakes for TEX86 discovered that this proxy does not appear to work in all lake systems and that the TEX86 correlates well with both annual and winter lake surface water temperature in those systems where it does appear to work. Besides this observed empirical relationship between TEX86 values and lake surface temperatures, very little is known about the ecology of the crenarchaeota in lakes. We combined both biogeochemical and molecular techniques in a multiyear study of Lake Superior using both sediment trap collection of settling particulate matter over the annual cycle and filtration of suspended particulate matter from lake water to create vertical profiles of crenarchaeotal cell numbers and lipid concentrations to investigate the spatial and temporal ecology of the lacustrine Crenarchaeota. Initial results show that the flux of the tetraether lipids is highly seasonal and mainly occurs during two time periods in winter and spring. The flux-weighted TEX86-derived temperatures from the sediment trap material agrees with the TEX86 temperature from a sediment core top from the sampling site and mixed water temperatures during the two periods of highest flux within the error of the method. Spatially, lipids used in TEX86 are found throughout the water column when the Lake Superior is isothermal, but mainly in the hypolimnion when the lake is stratified. During stratification tetraether lipids in the eplimnion appear to reflect a surface water temperature, while the more abundant tetraether lipids in the hypolimnion reflect a deep water temperature. These data suggest that the TEX86 in sediments of Lake Superior mainly reflect the water temperatures of times of highest lipid flux, mixed with a smaller portion of lipids that are mainly produced in the hypolimnion. Sedimentological, mineralogical, geochemical, biostratigraphic and paleoecological studies of the Um Sohryngkew Cretaceous-Tertiary (K-T) transition in the Khasi Hills of Meghalaya, India, reveal biotic and environmental changes about 800 km from the Deccan volcanic province (DVP). Upper Cretaceous sediments consist mainly of conglomerates, glauconitic sandstone, sandy shale, calcareous shale with a few shell beds and rare coal pockets, all of which indicate deposition in a shallow marine environment with high detrital influx from nearby continental terrains. High kaolinite and illite indicate high humidity and high runoff. The K-T transition is in calcareous silty shale and marked by a 1 cm thin "rust colored" layer with high anomalies in Ir (11.8 ppb), Ru (108 ppb), Rh (93 ppb) and Pd (75 pbb). In the Danian, kaolinite remains the dominant clay mineral, suggesting humid climatic conditions. In contrast, semi-arid climate conditions prevailed in the contemporaneous Deccan Traps province, which appears to be linked to "mock aridity" (Harris and Van Couvering, 1995, Khadkikar et al., 1999). Microfossil assemblages define the K-T boundary. Nannofossils are common throughout the Upper Maastrichtian interval. Assemblages dominated by Micula decussata and Watzenueria barnesae along with common Ceratolithioides kampteneri and Lithraphidites quadratus are typical of the low latitude Tethys and Micula prinsii attests to the presence of the terminal Maastrichtian. Dinoflagellate cysts are common to abundant with increased frequencies of peridiniods, terrestrial organic matter and framboidal pyrite in the uppermost Maastrichtian. This suggests high nutrient loading possibly leading to stressful eutrophic conditions. Dinogymnium and Alisogymnium species have their last occurrences at the K-T boundary. The first appearence of Danian nannofossil species Neobiscutum romeinii and Biantholithus sparsus appear at 5 cm and 15 cm above the K-T boundary, respectively. Dinocysts Damassadinium californicum, Carpatella cornuta, Kenleyia loph

  2. Paleosols and the Cretaceous/Tertiary transition in the Big Bend region of Texas

    SciTech Connect

    Lehman, T.M. )

    1990-04-01

    A marked change in paleosols coincides with Cretaceous/Tertiary transition in fluvial sediments of the Big Bend region in Texas. Early Paleocene paleosols exhibit thick, black epipedons and a greater depth to the argillic and petrocalcic horizons compared to Late Cretaceous paleosols. These features and comparison with modern soils suggest that early Paleocene soils developed under conditions of higher rainfall and cooler temperatures than did Late Cretaceous soils. The change in paleosols occurs abruptly at the highest occurrence of dinosaur bones in the section.

  3. Did Deccan Volcanism or the Chicxulub Impact Cause the K-T Mass Extinction?

    NASA Astrophysics Data System (ADS)

    Keller, G.; Reddy, A. N.; Jaiprakash, B. C.; Gertsch, B.; Adatte, T.; Upadhyay, H.; Bhowmick, P. K.; Pande, D. K.

    2008-12-01

    It is generally believed that the Chicxulub impact caused the Cretaceous-Tertiary (K-T) mass extinction. However, strong evidence from Mexico and Texas shows that this impact predates the K-T boundary and caused no species extinctions or any other significant environmental effects (Keller et al., 2003, 2007). The Chicxulub impact and K-T mass extinction are thus two separate and unrelated events and the biotic effects of this impact have been vastly overestimated. The real cause for the K-T mass extinction may now have been discovered in the Deccan volcanic eruptions of India. Recent discoveries reveal Deccan volcanism as the most likely cause for the K-T mass extinction for several reasons detailed in Chenet et al. (2007), Keller et al. (2008) and Self et al. (2008): (1) The main phase of Deccan Trap eruptions may have occurred over as little as 10,000 to 100,000 years. (2) The K-T mass extinction coincides with the end of this main phase of volcanism. (3) The longest lava flows (megaflows), spanning 1000 km across India and out to the Gulf of Bengal, mark this phase of Deccan volcanism and the mass extinction. (4) SO2 emissions associated with just one of these major volcanic pulses, or megaflows, are on the order of SO2 emissions estimated from the Chicxulub impact. (5) The total SO2 emissions during the main phase of Deccan volcanism are estimated at 30 to 100 times that of the Chicxulub impact. Thus, the short duration of volcanism and the repeated massive SO2 injections may have caused a deadly runaway effect that lead to the K-T mass extinction. Critical new data on the K-T mass extinction comes from investigations of Deccan Traps outcrops at Jhilmili, Madhya Pradesh, central India, quarry outcrops in Rajahmundry and subsurface cores drilled in the Krishna-Godavari Basin, eastern India, by the Oil and Natural Gas Corporation of India (ONGC). In eight subsurface cores examined, a total of 9 volcanic megaflows have been identified as occurring in very rapid succession. The biotic effects of these megaflows can be evaluated based on planktic foraminifera, which suffered the most severe mass extinction of all organisms. After the first megaflow up to 50% of the species disappeared and with each new megaflow more species died out culminating in near total mass extinction coincident with the last megaflow at the K-T boundary. After the mass extinction, no megaflows reached the Krishna-Godavari Basin for about 250-280 ky during which a low diversity early Danian assemblage of small new species evolved. The last major Deccan volcanic pulses began at the C29R/C29N boundary and appear to have been the cause for the long delay in the full biotic recovery. Deccan volcanism can thus explain both the K-T mass extinction and the long delayed biotic recovery that has been an enigma for so long. Chenet, A-L. et al. (2007) EPSL 263, 1-15; Keller, G. et al. (2003) ESR 62, 327-363; Keller, G., et al. (2007) EPSL 255, 339- 356; Keller, G. et al. (2008) EPSL 268, 293-311. Self, S. et al. (2008) Science, 319, 54-57.

  4. Assessment of Undiscovered Oil and Gas Resources in Cretaceous-Tertiary Coal Beds of the Gulf Coast Region, 2007

    USGS Publications Warehouse

    Warwick, Peter D.

    2007-01-01

    Using a geology-based assessment methodology, the U.S. Geological Survey estimated a mean of 4.06 trillion cubic feet of undiscovered, technically recoverable natural gas in Cretaceous-Tertiary coal beds of the onshore lands and State waters of the Gulf Coast.

  5. Evidence of volcanic ash at a K-T boundary section: Ocean drilling program hole 690 C, Maud Rise, Weddell Sea off East Antarctica

    NASA Technical Reports Server (NTRS)

    Wise, S. W.; Hamilton, N.; Pospichal, J.; Barker, P. F.; Kennett, James P.; Oconnell, S.; Bryant, W. R.; Burckle, L. H.; Egeberg, P. K.; Futterer, D. K.

    1988-01-01

    Rare vitric volcanogenic ash but more abundant clay minerals considered volcanogenic in origin are associated with an expanded and essentially complete K-T boundary sequence from Ocean Drilling Project (ODP) Hole 690 C on Maud Rise in the Weddell Sea off East Antarctica. Results at this writing are preliminary and are still based to some extent on shipboard descriptions. Further shore-based studies are in progress. It would appear, however, that the presence of volcanic ash and altered ash in the Danian section beginning at the biostratigraphically and paleomagnetically determined K-T boundary on Maud Rise can be cited as evidence of significant volcanic activity within the South Atlantic-Indian Ocean sector of the Southern Ocean coincident with the time of biotic crises at the end of the Maestrichtian. This is a postulated time of tectonic and volcanic activity within this Southern Hemisphere region, including possible initiation of the Reunion hot spot and a peak in explosive volcanism on Walvis Ridge (1) among other events. A causal relationship with the biotic crisis is possible and volcanism should be given serious consideration as a testable working hypothesis to explain these extinctions.

  6. Mass Wasting during the Cretaceous/Tertiary Transition in the North Atlantic: Relationship to the Chicxulub Impact?

    NASA Astrophysics Data System (ADS)

    Mateo, Paula; Keller, Gerta; Adatte, Thierry; Spangenberg, Jorge

    2015-04-01

    Deep-sea sections in the North Atlantic are claimed to contain the most complete sedimentary records and ultimate proof that the Chicxulub impact is Cretaceous-Tertiary boundary (KTB) in age and caused the mass extinction. A multi-disciplinary study of North Atlantic DSDP Sites 384, 386 and 398, based on high-resolution planktonic foraminiferal biostratigraphy, carbon and oxygen stable isotopes, clay and whole-rock mineralogy and granulometry, reveals the age, stratigraphic completeness and nature of sedimentary disturbances. Results show a major KTB hiatus at Site 384 with zones CF1, P0 and P1a missing, spanning at least ~540 ky, similar to other North Atlantic and Caribbean localities associated with tectonic activity and Gulf Stream erosion. At Sites 386 and 398, discrete intervals of disturbed sediments with mm-to-cm-thick spherule layers have previously been interpreted as KTB age impact-generated earthquakes destabilizing continental margins prior to settling of impact spherules. However, improved age control based on planktonic foraminifera indicates deposition in the early Danian zone P1a(2) (upper Parvularugoglobigerina eugubina zone) more than 100 ky after the KTB. At Site 386, two intervals of white chalk contain very small (<63 μm) early Danian zone P1a(2) (65%) and common reworked Cretaceous (35%) species, in contrast to the in situ red-brown and green abyssal clays that are devoid of carbonate. In addition, high calcite, mica and kaolinite and upward-fining are observed in the chalks, indicating downslope transport from shallow waters and sediment winnowing via distal turbidites. At Site 398, convoluted red to tan sediments with early Danian and reworked Cretaceous species represent slumping of shallow water sediments as suggested by dominance of mica and low smectite compared to in situ deposition. We conclude that mass wasting was likely the result of earthquakes associated with increased tectonic activity in the Caribbean and the Iberian Peninsula during the early Danian well after the Chicxulub impact.

  7. The Cretaceous-Tertiary transition in Guatemala: limestone breccia deposits from the South Petn basin

    NASA Astrophysics Data System (ADS)

    Stinnesbeck, W.; Keller, G.; de la Cruz, J.; de Len, C.; MacLeod, N.; Whittaker, J. E.

    Limestone breccia deposits in southern Mexico, Guatemala and Belize have recently been interpreted as proximal to distal ballistic fallout deposits, generated by a bolide impact that struck Yucatan at K/T boundary time. We review the age, lithology and the depositional environment of five K/T boundary sections in the South Petn area of Guatemala (Caribe, Aserradero, Chisec, Actela, Chemal) in order to evaluate the nature and origin of K/T limestone breccia deposition. The sections are located 500 km south of the proposed impact site at Chicxulub and trend in an east-west direction from the Guatemala/Mexico border to southern Belize. In four of the five sections examined, a breccia unit up to 50 m thick overlies reef-bearing shallow-water limestones of late Cretaceous (Campanian-Maastrichtian) age. Rhythmically bedded limestones, marls and siltstones of early Danian age overlie the breccia and were deposited under middle-to outer-neritic conditions. The breccia consists of differently coloured layers of shallow-water limestones. Clast size generally decreases upsection to thin layers of predominantly rounded clasts, and these fine-grained rudstones grade into grainstones at the top. In at least one section (EI Caribe) diagenetically altered glass spherules are present in the uppermost layers of the grainstone. These glass spherules are of stratigraphic position and chemical composition similar to black and yellow glass from Beloc, Haiti and Mimbral, Mexico, which some workers have chemically linked to melt glass within the breccia of the Chicxulub cores. We suggest that breccia deposition in Guatemala may have been multi-event, over an extended time period, and related to the collision of the Yucatan and Chortis plates as well as related to a major impact or volcanic event at the end of the Cretaceous.

  8. Hexagonal Diamonds (Lonsdaleite) Discovered in the K/T Impact Layer in Spain and New Zealand

    NASA Astrophysics Data System (ADS)

    Bunch, T. E.; Wittke, J. H.; West, A.; Kennett, J. P.; Kennett, D. J.; Que Hee, S. S.; Wolbach, W. S.; Stich, A.; Mercer, C.; Weaver, J. C.

    2008-12-01

    We present the first evidence from Cretaceous-Tertiary (K/T) boundary clay and rock for shocked hexagonal nanodiamonds (lonsdaleite), these being found in concentrations greater than 50 ppm at Needles Point, New Zealand, and Caravaca, Spain. This is also the first evidence for K/T diamonds of any kind outside of North America. No diamonds were detected immediately above or below the impact layer. Cubic diamonds have been reported earlier from North American K/T sediments by Carlisle and Braman (1991; 45 ppm) and Hough et al. (1997; 18 ppm), but lonsdaleite was not detected. Carlisle and Braman suggested that the cubic diamonds arrived already formed within the impactor, but Hough argued that they were shock-produced by the impact with Earth. Hence, it is not yet clear that K/T cubic diamonds were formed through shock. Lonsdaleite does not co-occur with terrestrial diamonds but is found with cubic diamonds in ET impact craters (e.g., Popigai, Sudbury). Both also have been reported in the impact layer of the proposed Younger Dryas impact event at 12.9 ka. Lonsdaleite is formed by shocking carbonaceous material, e. g., graphite, under extreme conditions of pressure and temperature (more than 15 GPa at more than 1000 C), thus making this mineral an excellent impact-shock indicator (DeCarli, 2002). Although lonsdaleite is also contained in meteorites, such as ureilites, there appears to be a consensus of opinion that crater-related lonsdaleite formed during ET impact. K/T sediment samples were acquired from the boundary layer, as well as above and below. To extract the diamonds from the sediments, we utilized the protocol from Amari (1994) and Huss and Lewis (1995), but modified their methodology after determining that phosphoric and perchloric acids oxidize metastable lonsdaleite. We extracted the diamonds successfully after eliminating those acids, which may explain why lonsdaleite was not apparent in extractions by others. The extracted lonsdaleite was analyzed by transmission electron microscopy (TEM) and by selected area diffraction (SAED), which displayed characteristic reflections corresponding to lattice planar spacings of 2.18, 1.26, 1.09, and 0.82 A. A scanning electron microscope (SEM) with energy dispersive X-ray spectroscopy (EDS) confirmed their carbon composition. With exposure to long-wave ultraviolet (365 nm) radiation, clusters of lonsdaleite crystals exhibited a blue fluorescence that is characteristic of many diamonds. Individual crystals were angular to sub-rounded in shape and ranged in size from 20 to 1000 nm, with a mean size of about 50 nm. This discovery represents (1) the strongest available evidence for K/T diamond formation during the impact; (2) the first discovery of K/T diamonds outside North America; and (3) the first occurrence of any form of K/T diamonds in the Southern Hemisphere, about 12,000 km from the Chicxulub Crater in Mexico.

  9. The high oxygen atmosphere toward the end-Cretaceous; a possible contributing factor to the K/T boundary extinctions and to the emergence of C(4) species.

    PubMed

    Gale, J; Rachmilevitch, S; Reuveni, J; Volokita, M

    2001-04-01

    Angiosperm plants were grown under either the present day 21 kPa O(2) atmosphere or 28 kPa, as estimated for the end-Cretaceous (100-65 MyBP). CO(2) was held at different levels, within the 24-60 Pa range, as also estimated for the same period. In C(3) Xanthium strumarium and Atriplex prostrata, leaf area and net photosynthesis per unit leaf area, were reduced by the high O(2), while the whole-plant respiration/photosynthesis ratio increased. The high O(2) effects were strongest under 24 Pa, but still significant under 60 Pa CO(2). Growth was reduced by high O(2) in these C(3) species, but not in Flaveria sp., whether C(3), C(4), or intermediary grown under light intensities <350 micromol m(-2) s(-1) PPF. Photosynthesis of C(3) Flaveria sp. was reduced by high O(2), but only at light intensities >350 micromol m(-2) s(-1) PPF. It is concluded that the high O(2) atmosphere at the end-Cretaceous would have reduced growth of at least some of the vegetation, thus adversely affecting dependent fauna. The weakened biota would have been predisposed to the consequences of volcanism and the K/T boundary bolide impact. Conversely, photosynthesis and growth of C(4) Zea mays and Atriplex halimus were little affected by high, 28 kPa, O(2). This suggests an environmental driver for the evolution of C(4) physiology. PMID:11413216

  10. Sea water strontium isotopes, acid rain, and the cretaceous-tertiary boundary

    SciTech Connect

    MacDougall, J.D.

    1988-01-29

    A large bolide impact at the end of the Cretaceous would have produced significant amounts of nitrogen oxides by shock heating of the atmosphere. The resulting acid precipitation would have increased continental weathering greatly and could be an explanation for the observed high ratio of strontium-87 to strontium-86 in sea water at about this time, due to the dissolution of large amounts of strontium from the continental crust. Spikes to high values in the sea water strontium isotope record at other times may reflect similar episodes. 17 references, 1 figure, 1 table.

  11. Seawater strontium isotopes, Acid rain, and the cretaceous-tertiary boundary.

    PubMed

    Macdougall, J D

    1988-01-29

    A large bolide impact at the end of the Cretaceous would have produced significant amounts of nitrogen oxides by shock heating of the atmosphere. The resulting acid precipitation would have increased continental weathering greatly and could be an explanation for the observed high ratio of strontium-87 to strontium-86 in seawater at about this time, due to the dissolution of large amounts of strontium from the continental crust. Spikes to high values in the seawater strontium isotope record at other times may reflect similar episodes. PMID:17838885

  12. Bolide impacts, acid rain, and biospheric traumas at the Cretaceous-Tertiary boundary

    NASA Technical Reports Server (NTRS)

    Prinn, Ronald G.; Fegley, Bruce, Jr.

    1987-01-01

    Two plausible projectiles are considered: an ice-rich long-period comet and a much smaller rock-metal asteroid. In the framework of a proposal addressed by Lewis et al. (1982), it is shown that, while the impact projectiles themselves do not shock-heat the atmosphere very extensively, the supersonic plume of water vapor and rock produced on impact does shock the atmosphere up to global scales and the shock is of sufficient intensity to produce abundant nitric oxide. For example, an ice-rich long-period comet with a mass of 1.25 x 10 to the 16th kg and a velocity of 65 km/s striking the earth would produce about 7 x 10 to the 40th molecules NO through shock-heating of the atmosphere by the high-velocity ejecta plume fragments. Specific attention is given to the fraction of the atmosphere shock-heated, the global circulation of the nitrogen oxides, the effects of the ejecta plume water on acid rain (AR) predictions, the effects of AR on continental soils, the relationship between AR production rates and the total amount of acid needed to acidify the surface oceans, and the longevity of the oceanic acidity event and the exhaled CO2 event and their implications for the environment in the first millenia or so after the impact.

  13. Seawater strontium isotopes, acid rain, and the Cretaceous-Tertiary boundary

    NASA Technical Reports Server (NTRS)

    Macdougall, J. D.

    1988-01-01

    A large bolide impact at the end of the Cretaceous would have produced significant amounts of nitrogen oxides by shock heating of the atmosphere. The resulting acid precipitation would have increased continental weathering greatly and could be an explanation for the observed high ratio of strontium-87 to strontium-86 in seawater at about this time, due to the dissolution of large amounts of strontium from the continental crust. Spikes to high values in the seawater strontium isotope record at other times may reflect similar episodes.

  14. An iridium abundance anomaly at the palynological Cretaceous-Tertiary boundary in northern New Mexico

    USGS Publications Warehouse

    Orth, C.J.; Gilmore, J.S.; Knight, J.D.; Pillmore, C.L.; Tschudy, R.H.; Fassett, J.E.

    1981-01-01

    An iridium abundance anomaly, with concentrations up to 5000 parts per trillion over a background level of 4 to 20 parts per trillion, has been located in sedimentary rocks laid down under freshwater swamp conditions in the Raton Basin of northeastern New Mexico. The anomaly occurs at the base of a coal bed, at the same stratigraphic position at which several well-known species of Cretaceous-age pollen became extinct. Copyright ?? 1981 AAAS.

  15. Nature and timing of extinctions in Cretaceous-Tertiary planktic foraminifera preserved in Deccan intertrappean sediments of the Krishna-Godavari Basin, India

    NASA Astrophysics Data System (ADS)

    Keller, G.; Adatte, T.; Bhowmick, P. K.; Upadhyay, H.; Dave, A.; Reddy, A. N.; Jaiprakash, B. C.

    2012-08-01

    In C29r below the Cretaceous-Tertiary boundary (KTB) massive Deccan Trap eruptions in India covered an area the size of France or Texas and produced the worlds largest and longest lava megaflows 1500 km across India through the Krishna-Godavari (K-G) Basin into the Bay of Bengal. Investigation of ten deep wells from the K-G Basin revealed four lava megaflows separated by sand, silt and shale with the last megaflow ending at or near the KTB. The biologic response in India was swift and devastating. During Deccan eruptions prior to the first megaflow, planktic foraminifera suffered 50% species extinctions. Survivors suffered another 50% extinctions after the first megaflow leaving just 7-8 species. No recovery occurred between the next three megaflows and the mass extinction was complete with the last mega-flow at or near the KTB. The last phase of Deccan volcanism occurred in the early Danian C29n with deposition of another four megaflows accompanied by delayed biotic recovery of marine plankton. Correlative with these intense volcanic phases, climate changed from humid/tropical to arid conditions and returned to normal tropical humidity after the last phase of volcanism. The global climatic and biotic effects attributable to Deccan volcanism have yet to be fully investigated. However, preliminary studies from India to Texas reveal extreme climate changes associated with high-stress environmental conditions among planktic foraminifera leading to blooms of the disaster opportunist Guembelitria cretacea during the late Maastrichtian.

  16. Clasts of Bladed Serpentine in a K/T Boundary Layer From the Central North Pacific: Implications for Catastrophic Impact by a Chondritic Projectile

    NASA Astrophysics Data System (ADS)

    Leung, I. S.; Hagstrum, J. T.

    2007-12-01

    A 24-m long piston core (LL44-GPC3) retrieved marine sediments from the central North Pacific. At a depth of 2055-2056 cm downcore, a thin layer having an Ir anomaly of 10 ng/g was identified as the 65 m.y. old K/T boundary layer by Kyte et al.,1995. We studied 6 samples of clay selected from 2042-2060 cm by Jim Broda (Woods Hole Oceanographic Institution), and found that only the 1 cm-thick Ir layer contains many microtektites (impact glass), 4 crystals of silicon carbide (SiC), about 20 clasts of serpentine, usually associated with several grains of magnetite. We believe that this sharply defined Ir layer might have been deposited by a catastrophic event of relatively short duration, perhaps triggered by an impactor. Serpentine crystals in the clasts are blade-like, but may also be foliated or granular. Bladed crystals are reminiscent of barred textures, or excentroradial groups of olivine and/or pyroxene, commonly found in chondrules. We also found a fine-grained, white substance which forms veins between serpentine crystals, resembling "Saponite" reported in an interplanetary dust particle (IDP) which was also composed of serpentine, by Keller et al., 1992, who believed that the IDP had links to hydrated CI chondrites. Thus, the precursor of serpentine clasts found in the GPC3 core, might have been a CI, or a carbonaceous chondrite (carrier of SiC) whose collision with Earth might have set off a fireball capable of transporting serpentinized chondritic particles and grains of SiC to our core site in the North Pacific.

  17. K-T magmatism of western Rajasthan, India: Manifestation of Reunion plume activity or extensional lithospheric tectonics?

    NASA Astrophysics Data System (ADS)

    Sharma, K.

    2004-12-01

    A number of alkaline plutons have been recorded at the K-T (Cretaceous-Tertiary) boundary in western Rajasthan, India. Significant magmatism occurred at Mundwara, Barmer, Sarnu-Dandali and Tavider. The evolution of the Cambay-Sanchor-Barmer rift during the K-T period resulted in these alkaline complexes at the rift margins. Sedimentary basins are developed in the Barmer and Jaiselmer regions. The magmatism of Mundwara and Sarnu-Dandali is dated at 68.50 Ma and considered as an early pulse of Deccan volcanism. Several workers correlated K-T sedimentary basin evolution, magmatism and other tectonic features of western Rajasthan with the Reunion plume-interaction in the northwestern Indian shield. Alkaline igneous complexes along the rift from the southern part are reported from Phenai Mata, Amba Dongar and Seychelles. The Seychelles was part of the northwestern Indian shield prior to Deccan volcanism. The Mundwara igneous complex represents three distinct circular plutonic bodies - Toa, Mer and Mushala, which are situated in the periphery of an area three kilometers in radius. Besides these, there are numerous concentric and radial dykes of lamprophyre, carbonatite, dolerite and amphibolite. All these three bodies represent different phases of intrusion and are not similar to each other. The alkaline rocks of Sarnu-Dandali occur as dykes and isolated plugs in the desert sand. Carbonatite dykes are also reported from southeast of Barmer. The Tavider outcrop is devoid of any plutonic rock and consists of rhyolite, andesite and basalt. These rocks occur along the Precambrian Malani magmatic lineaments. The development of the Cambay-Sanchor-Barmer rift caused reactivation of Precambrian fractures and resulted in magmatism at the basin margin. The Gondwanaland fragmentation during the Mesozoic era caused extensional tectonics in the northwestern Indian shield. This led to the development of rift basins in Gujarat and western Rajasthan. Deccan volcanism, separation of the Seychelles microcontinent from India, sedimentary basin development in western Rajasthan and the alkaline magmatism of Mundwara, Sarnu-Dandali and elsewhere are considered to be the products of Reunion plume activity in western India. However, basin development began in western Rajasthan in the Jurassic period and no plume has been suggested for this. The continual extensional tectonic regime caused deep fractures in the continental and oceanic lithosphere. The Cambay-Sanchor-Barmer rift developed in continental lithosphere. The Mundwara, Sarnu-Dandali and Barmer magmatism with nephelinite-carbonatite affinity at the basin margin represents a typical rift-tectonic setting. The tectonic setting and crustal development during the K-T period in western Rajasthan represents an extensional tectonic regime rather than the manifestation of Reunion plume activity.

  18. The Talara Basin province of northwestern Peru: cretaceous-tertiary total petroleum system

    USGS Publications Warehouse

    Higley, Debra K.

    2004-01-01

    More than 1.68 billion barrels of oil (BBO) and 340 billion cubic feet of gas (BCFG) have been produced from the Cretaceous-Tertiary Total Petroleum System in the Talara Basin province, northwestern Peru. Oil and minor gas fields are concentrated in the onshore northern third of the province. Current production is primarily oil, but there is excellent potential for offshore gas resources, which is a mostly untapped resource because of the limited local market for gas and because there are few pipelines. Estimated mean recoverable resources from undiscovered fields in the basin are 1.71 billion barrels of oil (BBO), 4.79 trillion cubic feet of gas (TCFG), and 255 million barrels of natural gas liquids (NGL). Of this total resource, 15 percent has been allocated to onshore and 85 percent to offshore; volumes are 0.26 BBO and 0.72 TCFG onshore, and 1.45 BBO and 4.08 TCFG offshore. The mean estimate of numbers of undiscovered oil and gas fields is 83 and 27, respectively. Minimum size of fields that were used in this analysis is 1 million barrels of oil equivalent and (or) 6 BCFG. The Paleocene Talara forearc basin is superimposed on a larger, Mesozoic and pre-Mesozoic basin. Producing formations, ranging in age from Pennsylvanian to Oligocene, are mainly Upper Cretaceous through Oligocene sandstones of fluvial, deltaic, and nearshore to deep-marine depositional origins. The primary reservoirs and greatest potential for future development are Eocene sandstones that include turbidites of the Talara and Salinas Groups. Additional production and undiscovered resources exist within Upper Cretaceous, Paleocene, and Oligocene formations. Pennsylvanian Amotape quartzites may be productive where fractured. Trap types in this block-faulted basin are mainly structural or a combination of structure and stratigraphy. Primary reservoir seals are interbedded and overlying marine shales. Most fields produce from multiple reservoirs, and production is reported commingled. For this reason, and also because geochemical data on oils and source rocks is very limited, Tertiary and Cretaceous production is grouped into one total petroleum system. The most likely source rocks are Tertiary marine shales, but some of the Cretaceous marine shales are also probable source rocks, and these would represent separate total petroleum systems. Geochemical data on one oil sample from Pennsylvanian rock indicates that it was probably also sourced from Tertiary shales.

  19. Strangelove ocean at era boundaries, terrestrial or extraterrestrial cause

    NASA Technical Reports Server (NTRS)

    Hsue, Kenneth J.

    1988-01-01

    Negative perturbations in carbon-isotope value of calcite in pelagic sediments were found at times of biotic crisis, marking horizons which are, or were proposed as era boundaries: Cretaceous/Tertiary (K/T), Permian/Triassic (P/T), and Precambrian/Cambrian (PreC/C). The anomaly was also found at several other mass-extinction horizons, such as terminal Ordovician, Frasnian-Famenian, etc. Studies of K/T boundary indicate that only the planktic fraction of the sediments has the negative isotope anomaly, whereas the benthic fraction has the same value across the boundary. This geochemical signal is thus considered a record of strangelove ocean, or an ocean where isotope fractionation of dissolved carbonate ions in surface waters (by biotic function of planktic organisms) has been significantly reduced because of the drastic reduction of the biomass in the oceans. The reduction of marine biomass at each of the era boundaries was related to chemical pollution of the oceans as a consequence of a catastrophic event; a pH decrease of 0.5 could inhibit the fertility of planktons. Studies of earthquakes, volcanic eruptions, and meteorite-impact occurrences have indicated a linearly inverse log/log relationship between the magnitude and frequency of events. The frequency of era boundaries in geologic history supports the postulate that the rare events causing those biotic crises were large bolide-impacts.

  20. Multielement geochemical investigations by SRXRF microprobe studies on tectite material: Evidence from the NE-Mexican Cretaceous/Tertiary record

    NASA Astrophysics Data System (ADS)

    Harting, M.; Rickers, K.; Kramar, U.; Simon, R.; Staub, S.; Schulte, P.

    2002-12-01

    The K/T boundary is long known as one of a few mass extinctions in earth history. The impact of a big meteorite at the Chicxulub on the northern Yucatan peninsula in Mexico is discussed to have triggered the faunal mass extinction and the rapid change of the palaeoenvironmental conditions near the K/T boundary. Tectite material, especially spherules are explained from many of the sections in correlation to the K/T-boundary event. This rare, glassy or alterated material is extremely variable in its major element chemistry, morphology and stratigraphic position in K/T transitions worldwide. For the first time, we perfom trace element analysis on tectites from the K/T boundary using synchrotron radiation XRF (SRXRF). Measurements were performed at the Hamburger Strahlungssynchrotronlabor HASYLAB at DESY (Hamburg, Germany) and at the ANKA (Karlsruhe, Germany) with polychromatic and monochromatic excitation, respectively collimating the beam to 15 m by capillary optics. Based on results from SRXRF microprobe determinations, these structures are to be interpreted as mixing of several melts with different chemical composition. The different components may represent melts from different sediment layers and possibly of basement material excavated by the Chicxulub impact. Igneous rocks with andesitic composition in cores at Chicxulub are considered to be impact melt rocks and are correlated mainly by the composition of major elements with the glass spherules found in the surrounding. Our investigations show that it is possible to trace elements with high sensitivity and a high spatial resolution. Some of the samples show clearly zonation and alteration parts, as well as carbonate inclusions, triggered by the Chicxulub impact event. In general, the results from the SRXRF show that the tectite material have different trace element patterns, formed by mixing of melts with different chemical composition derived from different sediment layers and possibly of basement material excavated by the Chicxulub impact. There is no evidence at the moment that there is a homogeneous origin in the sample material or distribution in the investigated sections. The enrichment of Ce in spherules from the Mesa-Juan Perez section indicates a possible origin from the Yucatan carbonate platform generated by the Chicxulub impact event near the K/T-boundary. Area scans from tektite material of the Bochil section show a clearly zonation in the inner part, dominated by Ba and Sr as well as a alteration margin dominated by secondary CaCO3. Glassy material of the Beloc (Haiti) section is characterised by a homogeneous trace element distribution but shows characteristic differences between Ca-rich and Ca-poor glass. Moreover there is no similarity to material from other sections investigated. A clear differentiation between alteration rims, non-alterated material and mixing of different source materials can be shown by space resolved trace element determination in m scale of schlieren structures and inclusions.(see also Schulte et al. this volume)

  1. Formation of the Shelf-edge Cretaceous-Tertiary contact off the southeastern U.S. Coast

    USGS Publications Warehouse

    Poppe, L.J.; Hathaway, J.C.; Hall, R.E.; Commeau, R.F.

    1986-01-01

    Submarine erosion, associated with changes in position of the proto-Gulf Stream, was the dominant mechanism controlling the formation of the Cretaceous-Tertiary unconformity in AMCOR borehole 6004. Paleontologic evidence indicates that this unconformity, which is marked by a gravelly-sand enriched in glauconitic and phosphoritic concretions, represents a hiatus of about 7 m.y. Both Cretaceous and Paleocene sediments contain middle-outer neritic foraminiferal assemblages that become more diverse with distance from the contact. Of the elemental abundances measured, Al, Ba, Co, Fe, Ga, K, Mg/Ca, Mo, Ni, P, Sr/Ca, V, Y, and Zn show a strong positive correlation with proximity to the contact, probably as a result of the concentration of authigenic and heavy minerals present as lag sediments on the erosion surface. ?? 1986.

  2. An asteroid breakup 160 Myr ago as the probable source of the K/T impactor.

    PubMed

    Bottke, William F; Vokrouhlick, David; Nesvorn, David

    2007-09-01

    The terrestrial and lunar cratering rate is often assumed to have been nearly constant over the past 3 Gyr. Different lines of evidence, however, suggest that the impact flux from kilometre-sized bodies increased by at least a factor of two over the long-term average during the past approximately 100 Myr. Here we argue that this apparent surge was triggered by the catastrophic disruption of the parent body of the asteroid Baptistina, which we infer was a approximately 170-km-diameter body (carbonaceous-chondrite-like) that broke up 160(-20)+30Myr ago in the inner main asteroid belt. Fragments produced by the collision were slowly delivered by dynamical processes to orbits where they could strike the terrestrial planets. We find that this asteroid shower is the most likely source (>90 per cent probability) of the Chicxulub impactor that produced the Cretaceous/Tertiary (K/T) mass extinction event 65 Myr ago. PMID:17805288

  3. Biogeochemical modeling at mass extinction boundaries

    NASA Technical Reports Server (NTRS)

    Rampino, M. R.; Caldeira, K. G.

    1991-01-01

    The causes of major mass extinctions is a subject of considerable interest to those concerned with the history and evolution of life on earth. The primary objectives of the proposed plan of research are: (1) to develop quantitative time-dependent biogeochemical cycle models, coupled with an ocean atmosphere in order to improve the understanding of global scale physical, chemical, and biological processes that control the distribution of elements important for life at times of mass extinctions; and (2) to develop a comprehensive data base of the best available geochemical, isotopic, and other relevant geologic data from sections across mass extinction boundaries. These data will be used to constrain and test the biogeochemical model. These modeling experiments should prove useful in: (1) determining the possible cause(s) of the environmental changes seen at bio-event boundaries; (2) identifying and quantifying little-known feedbacks among the oceans, atmosphere, and biosphere; and (3) providing additional insights into the possible responses of the earth system to perturbations of various timescales. One of the best known mass extinction events marks the Cretaceous/Tertiary (K/T) boundary (66 Myr ago). Data from the K/T boundary are used here to constrain a newly developed time-dependent biogeochemical cycle model that is designed to study transient behavior of the earth system. Model results predict significant fluctuations in ocean alkalinity, atmospheric CO2, and global temperatures caused by extinction of calcareous plankton and reduction in the sedimentation rates of pelagic carbonates and organic carbon. Oxygen-isotome and other paleoclimatic data from K/T time provide some evidence that such climatic fluctuations may have occurred, but stabilizing feedbacks may have acted to reduce the ocean alkalinity and carbon dioxide fluctuations.

  4. Assessment of undiscovered oil and gas resources of the Cretaceous-Tertiary Composite Total Petroleum System, Taranaki Basin Assessment Unit, New Zealand

    USGS Publications Warehouse

    Wandrey, Craig J.; Schenk, Christopher J.; Klett, Timothy R.; Brownfield, Michael E.; Charpentier, Ronald R.; Cook, Troy A.; Pollastro, Richard M.; Tennyson, Marilyn E.

    2013-01-01

    The Cretaceous-Tertiary Composite Total Petroleum System coincident Taranaki Basin Assessment Unit was recently assessed for undiscovered technically recoverable oil, natural gas, and natural gas liquids resources as part of the U.S. Geological Survey (USGS) World Energy Resources Project, World Oil and Gas Assessment. Using a geology-based assessment methodology, the USGS estimated mean volumes of 487 million barrels of oil, 9.8 trillion cubic feet of gas, and 408 million barrels of natural gas liquids.

  5. A Detailed Study of the Drastic Worldwide Climatic Change by the Cretaceous/Paleogene (K/T)-Impact of Chicxulub

    NASA Astrophysics Data System (ADS)

    Preisinger, Anton; Aslanian, Selma; Grass, Fritz; Beigelbeck, Roman; Wernisch, Johann

    2010-05-01

    The impact of Chicxulub (Yucatan, Mexico) was a global event exhibiting a short-time (fallout) and a long-time (boundary clay) sedimentation of the K/T-boundary [1]. The fallout is mainly characterized by iridium, Ni-Cr-rich magnesia-ferrite spinels (K/T-spinels), spherules, as well as shocked quartzes. The amount of the sediments and their distribution depend on the distance from the impact crater. The Cretaceous/Paleogene (K/T) boundaries at three different locations namely Caravaca (Spain), Cerbara (Italy), and Bjala (Bulgaria) have been well analyzed. About 65 million years ago, they were located at the distances from the impact crater ~6000 km, ~7500 km, and ~8800 km, respectively. The boundary clay is characterized by transported minerals like quartzes and feldspars, authigenically formed minerals, as well as biominerals like Mg-calcites and greigites (Fe3S4). The samples were analyzed by scanning X-ray diffractometry (Bruker Analytical X-ray System), scanning electronic microscopy (XL30, ESEM-Philips), neutron activation analyses, Delta13C and Delta18O analyses, and the determination of nannofossils and foraminifera. Owing to the Earth's rotation, the analyzed samples lie along a great circle (crossing the equator under an angle of ~23° ) which covers Chicxulub, Caravaca, Cerbara, and Bjala indicating the existence of only a single impact. The study of this K/T-boundary by means of high resolution scanning X-ray diffractometry in combination with the scanning electron microscopy and neutron activation analyzes revealed the time dependency of the K/T-event in the fallout as well as in the boundary clay. The biomineralization of sulfate-reducing bacteria by greigites provided the duration of the sulfuric acid rain. The reoccurrence of algae is indicated by the appearance of Mg-calcite at the end of the boundary clay. The K/T-spinels were formed on the nucleus of metallic iridium [2]. They were built in the mesosphere (in a height of about 100 km) and grew during the fall to the Earth's surface by forming ferrimagnetic twins, which were etched by the H2SO4 content of the atmosphere. We developed an extensive mathematical model incorporating all relevant physical effects (particle growth, pressure dependence of the atmosphere, fluid resistance, centrifugal and coriolis forces, etc.) in order to study the development of the particles during the fall. For Caravaca, the shortest flight time for the Iridium fallout is approximately 6.5 days, while the shortest flight time for the ejecta near Chicxulub last only a few hours. The K/T-impact took place about 65 million years ago in a sea depth of more than 2000 m. Consequently, the impact heated up the sea water and the water molecules reacted with the CaCO3, CaSO4, and the silicates down to a depth of 28 km. This hydrothermal reaction reduced the melt temperature significantly, especially those of silicates. Therefore, the pyroxenes and plagioclases changed to clay minerals. The sedimentation rate of Chron 29RK is about twice than that of Chron 29RT, which equals to Chron 29N in Caravaca, Cerbara, and Bjala. The precession cycles of Chron 29R and Chron 29N are 22.5 kyears. The time span of the K/T-boundaries between Chron 29RK and Chron 29RT is worldwide about 1 kyear. Concluding all our results, only one big impact took place at Chicxulub (Yucatan, Mexico) about 65 million years ago and caused, during the formation of the K/T-boundary, a worldwide climatic change. References: [1] Eder, G. and Preisinger, A.: Zeitstruktur globaler Ereignisse veranschaulicht an der Kreide/Terziär-Grenze. Naturwissenschaften, Band 74, 35-37, 1987. [2] Preisinger, A., Aslanian, S., Brandstätter, F., Grass, F., Stradner, H., and Summesberger, H.: Cretaceous-Tertiary profile, rhythmic deposition, and geomagnetic polarity reversals of marine sediments near Bjala, Bulgaria. Geo. Soc. Amer. special paper 356, 229-312, 2002.

  6. End of the Cretaceous: sharp boundary or gradual transition

    SciTech Connect

    Alvarez, W.; Alvarez, L.W.; Asaro, F.; Michel, H.V.

    1984-03-16

    Evidence indicates that the Cretaceous-Tertiary boundary is very sharp, and, within the limits of resolution, it is apparently synchronous at the various boundary localities. Arguments to the contrary, particularly those of Officer and Drake, are shown to be invalid. 35 references, 2 figures.

  7. Iridium abundance patterns across extinction boundaries

    SciTech Connect

    Orth, C.J.; Gilmore, J.S.; Oliver, P.Q.; Quintana, L.R.

    1985-01-01

    The authors are measuring elemental abundances, with emphasis on high sensitivity Ir assay, across biological crisis zones in the fossil record. Samples are measured in an automated neutron activation analysis system, with radiochemical separations for the heavy Pt-group elements and Au. They are collaborating with paleontologic and stratigraphic experts to home-in on the boundaries, and to date they have performed at least one set of measurements across the following transition and extinction boundaries: Precambrian/Cambrian(Pc/C); 2 U. Cambrian biomere boundaries; the basal Ordovician; Ordovician;/Silurian; U. Devonian Frasnian/Famennian (F/F); Devonian/Miss.; Miss./Penn.; Permian/Triassic (P/Tr); Triassic/Jurassic; L. Jurassic Toarcian; Cretaceous/Tertiary (K/T); and the U. Eocene. The authors work on K/T sequences that were deposited under freshwater conditions in the western interior of North America supports the Alvarez asteroid impact hypothesis. The Earth has been struck many times in the Phanerozoic by large impactors that probably have done tremendous damage to the local environment. However, to day scientists have not found any firm chemical evidence for the association of impacts with global extinctions older than the massive terminal Cretaceous event, which might have been unique in the Phanerozoic. Although they have measured a moderate Ir and Pt anomaly in the F/F boundary zone in NW Australia, their evidence indicates that these and several other elements were enriched from seawater by bacteria. Although the authors data, except for the U. Eocene, do not support the periodic comet swarm-global extinction arguments, much more work is needed to resolve this issue.

  8. Comparison of the magnetic properties and Mossbauer analysis of glass from the Cretaceous-Tertiary boundary, Beloc, Haiti, with tektites

    NASA Technical Reports Server (NTRS)

    Thorpe, A. N.; Senftle, F. E.; May, L.; Barkatt, A.; Adel-Hadadi, M. A.; Marbury, G. S.; Izett, G. A.; Maurrasse, F. R.

    1994-01-01

    The magnetic properties of black Beloc glass have been measured. The Curie constant, the magnetization, and the magnetic susceptibility of the Beloc glass fall within the known ranges observed for tektites. However, the temperature-independent component of the magnetic susceptibility is slightly higher than that found for tektites. Moreover, it is not possible to match the experimental magnetic data for the Beloc glass with the calculated values using the previously reported Fe(3+)/Fe(2+) ratio of 0.7. The oxidation state of Fe was therefore redetermined by Mossbauer measurements, and the Fe(3+)/Fe(2+) ratio was found to be 0.024 plus or minus 0.015. Using the redetermined value of the ratio, the magnetic parameters were again calculated using formulas that are applicable to tektites, and good agreement was found between the calculated and experimental values. The experimental magnetic measurements and the redetermined Fe(3+)/Fe(2+) ratio of the Beloc glass specimens are essentially the same as those found for tektite glass.

  9. Patterns of megafloral change across the Cretaceous-Tertiary boundary in the Northern Great Plains and Rocky Mountains

    NASA Technical Reports Server (NTRS)

    Johnson, Kirk R.; Hickey, Leo J.

    1988-01-01

    The spatial and temporal distribution of vegetation in the terminal Cretaceous of Western Interior North America was a complex mosaic resulting from the interaction of factors including a shifting coastline, tectonic activity, a mild, possibly deteriorating climate, dinosaur herbivory, local facies effects, and a hypothesized bolide impact. In order to achieve sufficient resolution to analyze this vegetational pattern, over 100 megafloral collecting sites were established, yielding approximately 15,000 specimens, in Upper Cretaceous and lower Paleocene strata in the Williston, Powder River, and Bighorn basins in North Dakota, Montana, and Wyoming. These localities were integrated into a lithostratigraphic framework that is based on detailed local reference sections and constrained by vertebrate and palynomorph biostratigraphy, magnetostratigraphy, and sedimentary facies analysis. A regional biostratigraphy based on well located and identified plant megafossils that can be used to address patterns of floral evolution, ecology, and extinction is the goal of this research. Results of the analyses are discussed.

  10. The K/T-boundary carbonate breccia succession at the Cantarell Field, Campeche Bay area: a representative example of the influence of the Chicxulub meteorite-impact event on the formation of extraordinary petroleum reservoirs

    NASA Astrophysics Data System (ADS)

    Murillo-Mueton, G.; Grajales-Nishimura, J. M.; Velasquillo-Martnez, L. G.; Garca-Hernndez, J.

    2013-05-01

    Over the last decade, intense petroleum exploration and exploitation activities have been conducted in the Campeche Bay area. Detailed stratigraphic studies in this region based on seismic, well logs, and core data have allowed the documentation of numerous deep-water carbonate breccia deposits throughout the Cretaceous stratigraphic column. However, the uppermost carbonate breccia succession is very distinctive in terms of its sedimentological properties compared to the underlying and older calcareous breccia layers. The unique characteristics of this deposit include: its unusual thickness, stratigraphic position, distribution, and content of impact-metamorphic constituents. At the Cantarell field, this carbonate breccia sedimentary package is a representative example of how the Chuxulub meteorite-impact event influenced the formation of a remarkable carbonate reservoir. This deposit was the most important oil-producing stratigraphic horizon for long time in that field. Nevertheless, this reservoir is still important not only in that field but also in other fields in offshore Campeche. The K/T boundary carbonate breccia succession is a typical fining-upward deposit made up, from base to top, of three units. The 50 to 300-m thick, basal Unit 1 consists of a coarse-grained carbonate breccia. Unit 2 is a 10 to 20 m-thick, fine-grained carbonate breccia. The 25 to 30 m-thick, uppermost Unit 3 is a greenish interval of friable sand, silt and clay-sized constituents with abundant ejecta material. In some wells, a 10 to 20 m-thick, non-oil producing fine-grained calcareous breccia occurs interbedded within Unit 3. The K/T boundary carbonate sedimentary package is underlain and overlain by deep-water shaly calcareous facies of Upper Maastrichtian and Lower Paleocene age, respectively. Studies of cronostratigraphic-equivalent outcrop analogs of this K/T boundary carbonate reservoir carried out by the authors in the Sierra de Chiapas (El Guayal, Tabasco and Bochil, Chiapas) support the stratigraphic architecture documented at the Cantarell Field. Lithoclasts of the calcareous breccias were derived dominantly from platform-interior and platform-margin environments and a few from deep-water settings. Ejecta material includes: shocked quartz, quartz with ballen structure, shocked plagioclase, altered melt rock, and rare fragments of the crystalline basement. Its paleogeographic distribution, stratigraphic position, and abundance of impact-metamorphic constituents in this carbonate breccia deposit are the most striking evidences of a genetic relation to the Chicxulub meteorite-impact event. Hence, this carbonate breccia succession, deposited by gravity-driven processes under deep-water conditions, represents the collapse of the western paleomargin of the Yucatan Peninsula, ballistic transport and tsunami-related current reworking as a consequence of the Chicxulub meteorite-impact incident.

  11. K-T impact(s): Continental, oceanic or both

    NASA Technical Reports Server (NTRS)

    Sharpton, V. L.; Schuraytz, B. C.; Murali, A. V.; Ryder, G.; Burke, K.

    1988-01-01

    Although geochemical and mineralogical evidence indicate that a major accretionary event occurred at the K-T boundary, no impact crater of suitable size and age was recognized. The 35 km Manson Structure, Iowa, was suggested recently as a possibility and Ar-40/Ar-39 determinations indicate that its formation age is indistinguishable from that of the K-T boundary. In order to test a possible association between Manson and the K-T boundary clay, the geochemistry and mineralogy of the K-T boundary clays at the Scollard Canyon section, Alberta and the Starkville South section, Colorado are compared with three dominant lithologies affected by the Manson impact: Proterozoic red clastics, underlying late-state granites, and gneisses. The chemical and mineralogical makeup of the Scollard Canyon boundary clay and its clastic constituents are presented, commenting on the implications for impact models. An impact into crystalline material of continental affinity appears to be required to explain the mineralogy and chemistry of the Scollard Canyon (and other Western N. American K-T sections). The low REE abundances of some K-T boundary layers are unusual but perhaps attempts should be made to understand the contributions of individual crustal components (e.g., carbonates, arkoses) as well as the potential for alteration involving these and other elements during and after impact-induced vaporization, before mantle excavation is invoked. If further studies confirm the results of published studies of marine boundary clays that indicate an oceanic target, attention must be paid to the possibility that multiple impacts occurred at the K-T boundary - one or more on the continents and one or more in the ocean.

  12. The role of Deccan volcanism during the K-T mass extinction

    NASA Astrophysics Data System (ADS)

    Adatte, T.; Keller, G.; Gertsch, B.

    2012-12-01

    The potential role of major volcanic provinces has long been neglected as potential cause for major mass extinctions in Earth's history. This is despite the fact that volcanic activity is implicated in four of the five Phanerozoic mass extinctions, whereas a large asteroid impact is only associated with the K-T mass extinction. After 28 years of nearly unchallenged perception that a large impact (Chicxulub) on Yucatan caused the end-Cretaceous mass extinction, this theory is facing its most serious challenge from Deccan volcanism in India. Recent advances in Deccan volcanic studies show that Deccan Trap volcanism began with a relatively minor eruption phase (~6% of total volume) during the late Maastrichtian magnetic polarity C30n. The main eruption phase (~80%) occurred over a short period in C29r just below the Cretaceous-Tertiary boundary (KTB) and the last Deccan phase (~14%) erupted in the early Danian C29n. Multiproxy studies from sections in Meghalaya (NE India), Jhilmili in central India (Madhya Pradesh), 6 quarry outcrops from Rajahmundry (SE India), 10 deep wells from the Krishna-Godavari Basin (K-G) (Andhra Pradesh) place the KTB mass extinction near the end of the main Deccan phase coincident with the mass extinction. These studies show that the second and third phase of eruptions each produced the world's largest and longest lava megaflows ~1500 km across India through the K-G Basin into the Bay of Bengal. These megaflows are separated by sand, silt and shale which record the mass extinction across an interval that spans zones CF1-CF2 and most of the nannofossil Micula prinsii zone and is correlative with the rapid global warming and subsequent cooling near the end of the Maastrichtian. The mass extinction began preceding the first of the four mega-flows in C29r. Planktic foraminifera suffered a 50% drop in species richness. Survivors suffered another 50% drop after the first mega-flow, leaving just 7 to 8 survivor species. No recovery occurred between the next three mega-flows and the mass extinction was complete with the last phase-2 megaflow at the KTB. The last phase of Deccan volcanism and its 3 to 4 megaflows in the early Danian C29n (zone P1b) delayed biotic recovery of marine plankton. Correlative with these intense volcanic phases, climate changed from humid/tropical to arid conditions and returned to normal tropical humidity after the last phase of volcanism. Similar environmental conditions, mass extinction and delayed recovery patterns are observed in Meghalaya, NE India. The mass extinction was likely the consequence of rapid and massive volcanic CO2 and SO2 gas emissions, leading to high continental weathering rates, global warming, cooling, acid rains, ocean acidification and a carbonate crisis in the marine environment. Combined with an impact, Deccan volcanism can thus explain both the KTB mass extinction and the long delayed biotic recovery that has been an enigma for so long. But added to impact catastrophe, a cascade of rapid massive volcanic eruptions and their complex destructive interactions with Earth's equilibrium may have done the deed. The observed climate, faunal and floral changes may have been triggered by Deccan volcanism as a result of massive CO2 and SO2 emissions.

  13. Shock-induced devolatilization of calcium sulfate and implications for K-T extinctions

    NASA Technical Reports Server (NTRS)

    Chen, Guangqing; Tyburczy, James A.; Ahrens, Thomas J.

    1994-01-01

    The devolatilization of calcium sulfate, which is present in the target rock of the Chicxulub, Mexico impact structure, and dispersal in the stratosphere of the resultant sulfuric acid aerosol have been suggested as a possible mechanism for the Cretaceous-Tertiary extinctions. We measured the amount of SO2 produced from two shock-induced devolatilization reactions of calcium sulfate up to 42 GPa in the laboratory. We found both to proceed to a much lower extent than calculated by equilibrium thermodynamic calculations. Reaction products are found to be approx. 10(exp -2) times those calculated for equilibrium. Upon modeling the quantity of sulfur oxides degassed into the atmosphere from shock devolatilization of CaSO4 in the Chicxulub lithographic section, the resulting 9 x 10(exp 16) to 6 x 10(exp 17) g (in sulfur mass) is lower by a factor of 10-100 than previous upper limit estimates, the related environmental stress arising from the resultant global cooling and fallout of acid rain is insufficient to explain the widespread K-T extinctions.

  14. Shock-induced devolatization of calcium sulfate and implications for K-T extinctions

    NASA Technical Reports Server (NTRS)

    Chen, Guangqing; Tyburczy, James A.; Ahrens, Thomas J.

    1993-01-01

    Calcium sulfate devolatization during the impact at Chicxulub, Mexico and dispersal in the stratosphere of the resultant sulfuric acid aerosol have been suggested as a possible mechanism for the Cretaceous-Tertiary extinctions. In this paper, we investigated two shock-induced devolatization reactions of calcium sulfate up to 42 GPa in the laboratory: CaSO4 + SiO2 yields CaSiO3 + SO3(degassed) and CaSO4 yields CaO + SO2(degassed) + 1/2 O2(degassed). We found both to proceed to a much less extent than calculated by equilibrium thermodynamic calculations. Reaction products are found to be 10(exp -2) times those calculated for equilibrium. Consequently our estimate of the amount of sulfur oxides degassed into the atmosphere from shock devolatization of CaS04 in the Chicxulub lithographic section (6x10(exp 15)-2x10(exp 16)g in sulfur mass) is lower by a factor of 70 to 400 than previous estimates; the related environmental stress arising from the resultant global cooling of approximately 4 K and fallout of acid rain does not appear to suffice to explain the widespread K-T extinctions.

  15. Causal Link Between Flood Basalts and Large Impacts: Were The K-t and P-tr Impactors `verneshots' Fired From Terrestrial Plume-fed Co2-guns?

    NASA Astrophysics Data System (ADS)

    Phipps Morgan, J.; Reston, T.; Ranero, C.

    Both bolide impacts (Alvarez et al., 1980) and Continental Flood Basalt (CFB) events (Courtillot, 1996; Courtillot et al., 1994; Morgan, 1986) have been proposed to be the cause of the three largest Phanerozoic mass-extinctions. The Cretaceous-Tertiary (K-T) boundary is the age of both one of the largest known terrestrial impact struc- tures (the Chixculub site on the Yucatan peninsula) and a very large continental flood basalt (the Deccan Traps event, the first well-documented trace of the Reunion plume- hotspot). In the past year, two papers (Becker et al., 2001; Kaiho et al., 2001) have suggested that the Permian-Triassic (P-Tr) boundary, the age of the largest well- documented CFB (the Siberian Traps), is also marked, in some marine sediments, by the geochemical signature of a large bolide impact. If correct, this would require that both a bolide impact and a CFB occurred at the P-Tr boundary. Finally, the Frasnian- Famennian (Late Devonian) event appears to be contemporaneous with an impact or impacts (e.g. Siljan Ring - Grieve and Robertson, 1987), the eruption of both a Siberian Kimberlite field (Agashev et al., 2001), and the Dniepr-Donets CFB (Wilson et al., 1996). Both large bolide impacts (K-T anomaly appears to occur well within the flood-basalt stratigraphy (Bhandari et al., 1994). Therefore, here we examine whether terrestrial processes can produce the `signal' of an extraterrestrial impact event. We explore a physical model where sub-cratonic plume activity leads to massive C- and S-volatile build-up at 80-100km depths within cold cratonic lithosphere, consis- tent with recent E-M soundings (Jones et al., 2001) beneath the Slave Craton (Canada). If this gas-rich phase can build up to a 1% fraction, than its catastrophic release may be large enough to be the environmental shock that leads to a mass extinction event. 1 Furthermore, its release would supply large amounts of plume mantle rare-gases (and possibly core-entrained iridium?) to the surface environment. Such super-kimberlite- precurser gas-release events appear capable of providing a terrestrial source for the recently found geochemical signals of `extraterrestrial' P-Tr bolide impacts, while also better explaining the massive mantle-linked geochemical anomalies (in particular S-isotope excursions) that take place at this time. Furthermore, the energy release from sudden cratonic CO2 escape is large enough, that if released at one time, it could eject a suborbital mass-jet that causes a secondary impact event itself. Was even the Chix- culub impactor such a `Verneshot', fired from a Deccan-Reunion plume CO2-gun? 2

  16. Relative contribution of Precambrian metamorphic rocks and Cretaceous-Tertiary igneous rocks to Oligocene and Holocene fluvial sands and the unroofing of a magmatic arc

    SciTech Connect

    Molinaroli, E.; Basu, A. )

    1991-03-01

    Oligocene and Holocene fluvial sands were deposited in small extensional basins in a magmatic arc in southwestern Montana under relatively humid and semi-arid conditions, respectively. The source rocks are roof-pendants and thrust-slices of Precambrian metamorphic rocks (PCM) and Cretaceous-Tertiary igneous rocks (KTI) that make up the arc. The authors have surveyed 143,607 heavy mineral grains (HMGs) in polished thin sections of 55 samples collected from adjacent but discrete geomorphologic units. In the Holocene sands, of 5440 HMGs 519 are garnets and of 97,667 HMGs 395 are zircons. In the Oligocene sandstones, of 6397 HMGs 998 are garnets, and of 45,940 HMGs 331 are zircons. Garnets are absent in the igneous rocks and zircons are extremely rare in the metamorphic rocks. Garnets ar estimated to be about 100 times as abundant in the metamorphic rocks as the zircons are in the igneous rocks. Mass balance calculations show that the proportion of PCM/(PCM+KTI) ranges from 0 to 21% in Oligocene sandstones, and from 3 to 76% in Holocene sands in different local units. However, the overall PCM/(PCM+KTI) proportions in the Holocene and the Oligocene sands in southwestern Montana are 19% and 18%, respectively. This suggests that the roof pendants, thrust slices, and magmatic arc rocks have been unroofed in constant proportions since the Oligocene although locally the proportions have been different.

  17. An Asteroid Breakup 160 My Ago as the Probable Source of the K-T Impactor

    NASA Astrophysics Data System (ADS)

    Bottke, William; Vokrouhlicky, D.; Nesvorny, D.

    2007-10-01

    The terrestrial and lunar cratering rate is often assumed to have been nearly constant over the last 3 Gy. Different lines of evidence, however, suggest the impact flux from kilometer-sized bodies increased by at least a factor of 2 over the last 100 My. Here we report that this apparent surge was triggered by the catastrophic disruption of the Baptistina parent body, a 170 km diameter carbonaceous chondrite-like asteroid that broke up 160 ± 20 My ago in the inner main belt. According to our numerical simulations, this family's age, location near Jupiter's 7:2 and Mars' 5:9 mean motion resonances, and its steep fragment size distribution are remarkably well suited to generate a prolonged surge in the multi-kilometer NEO population and explain the above observations. Numerous fragments produced by the collision were slowly delivered by dynamical processes (Yarkovsky effect, resonances) to orbits where they could strike the terrestrial planets. The number of D > 1 km, D > 5 km, and D > 10 km impacts produced on Earth by Baptistina fragments are 200 ± 60, 6 ± 2, and 1 ± 1, respectively, while those from the background are 260 ± 20, 3 ± 2, and 0.5 ± 0.7, respectively. Using numerical modeling this asteroid shower and combining our results with meteoritic constraints, we find it is the most likely source (> 90% probability) of the Chicxulub impactor that produced the Cretaceous-Tertiary (K/T) mass extinction event 65 My ago. This shower may have also produced the conspicuous lunar crater Tycho that formed 109 My ago (> 70% probability). Among all km-sized NEOs, Baptistina fragments may currently be responsible for 40% of all C/X-types and 20% of the entire population. These bodies should predominantly have compositions that mimic CM meteorites.

  18. Geochemical anomalies near the Eocene-Oligocene and Permian-Triassic boundaries

    SciTech Connect

    Asaro, F.; Alvarez, L.W.; Alvarez, W.; Michel, H.V.

    1981-10-01

    Evidence is presented to support the theory that several mass extinctions, i.e., those that define the Permian-Triassic boundary, the Cretaceous-Tertiary boundary, and the Eocene-1 Oligocene boundary, were caused by impact on the earth of extraterrestrial objects having the composition of carbonaceous chondrites and diameters of about 10 km. The evidence consists of anomalously high concentrations of iridium and other siderophile elements at the stratigraphic levels defining the extinctions. (ACR)

  19. Darkness after the K-T impact: Effects of soot

    NASA Technical Reports Server (NTRS)

    Wolbach, Wendy S.; Anders, Edward; Orth, Charles J.

    1988-01-01

    Dust from the K-T impact apparently settled from the atmosphere in less than 6 months, restoring sunlight to minimum photosynthesis levels in about 4 months. However, the discovery of a global soot component in the boundary clay makes it necessary to reconsider the problem, as soot particles not only are smaller (0.1 vs. about 0.5 micrometer) and thus settle more slowly, but also are better light absorbers (optical depth of 13 mg soot cm(-2) about 1800; and are more resistant to rainout. Still, the darkness cannot have lasted very much longer than 6 months, else no larger animals would have survived. Perhaps the soot coagulated with the rock dust and fell out with it. Evidence on this point may be sought at a relatively undisturbed K-T boundary site, such as Woodside Creek, N.Z. There the boundary clay and lowermost Tertiary strata are finely laminated and show large chemical and isotopic differences on a millimeter scale, apparently representing a detailed time sequence. Researchers studied a 3 m section across the boundary at this site, analyzing the principal forms of carbon (soot, elemental C, kerogen, and carbonate) as well as 33 elements. Correlations among the elements were sought. Apparently soot came early and coagulated with the ejecta, staying with them for the primary fallout and in the next 5 cm, but then parting company, perhaps due to size sorting.

  20. Search for extractable fullerenes in clays from the cretaceous/tertiary boundary of the Woodsite Creek and Flaxbourne River sites, New Zealand

    SciTech Connect

    Heymann, D.; Chibante, L.P.F.; Smalley, R.E. ); Wolbach, W.S. ); Brooks, R.R. )

    1994-08-01

    When fullerenes were first discovered to form spontaneously in condensing carbon vapors, it was suggested that they might be widely distributed in the Universe. Searchers for fullerenes in meteorites were unsuccessful, but C[sub 60] and C[sub 70] were reported to occur on Earth in samples of shungite, a meta-anthracite from a deposit near Shunga, Russia, and in [open quotes]fulgurite[close quotes], a substance formed when lightning strikes certain soils or rocks. The occurrence of fullerenes in shungite is particularly surprising since fullerene synthesis in the laboratory has always involved gas phase chemistry at temperatures over 1000[degrees]C. Such conditions may be attained during lightning strikes, but shungite is believed to have formed from carbonaceous material creeping into fissures of a Precambrian rock which metamorphosed under extreme pressures. If the original carbonaceous material did not already contain fullerenes perhaps from wildfires, they must have formed during the metamorphism by as yet unknown solid- or liquid-phase mechanisms.

  1. Determination of rapid Deccan eruptions across the Cretaceous-Tertiary boundary using paleomagnetic secular variation: Results from a 1200-m-thick section in the Mahabaleshwar escarpment

    NASA Astrophysics Data System (ADS)

    Chenet, Anne-Lise; Fluteau, FrDRic; Courtillot, Vincent; GRard, Martine; Subbarao, K. V.

    2008-04-01

    Flow-by-flow reanalysis of paleomagnetic directions in two sections of the Mahabaleshwar escarpment, coupled with analysis of intertrappean alteration levels shows that volcanism spanned a much shorter time than previously realized. The sections comprise the upper part of magnetic chron C29r, transitional directions and the lowermost part of C29n. Lack of paleosecular variation allows identification of four directional groups, implying very large (40 to 180 m thick) single eruptive events (SEEs) having occurred in a few decades. Paleomagnetism allows temporal constraints upon the formation of 9 out of 23 thin red bole levels found in the sections to no more than a few decades; the two thickest altered layers could have formed in 1 to 50 ka. The typical volumes of SEEs (corresponding to magnetic directional groups) are estimated at 3000 to 20,000 km3, with flux rates 100 km3 a-1, having lasted for decades. Flood basalt emission can be translated into SO2 injection rates of several Gt a-1, which could have been the main agent of environmental change. The total volume of SO2 emitted by the larger SEEs could be on the order of that released by the Chicxulub impact. Moreover, each SEE may have injected 10 to 100 times more SO2 in the atmosphere than the deleterious 1783 Laki eruption. The detailed time sequence of SEEs appears to be the key feature having controlled the extent of climate change. If several SEEs erupted in a short sequence (compared to the equilibration time of the ocean), they could have generated a runaway effect leading to mass extinction.

  2. Shock-synthesized hexagonal diamonds in Younger Dryas boundary sediments

    PubMed Central

    Kennett, Douglas J.; Kennett, James P.; West, Allen; West, G. James; Bunch, Ted E.; Culleton, Brendan J.; Erlandson, Jon M.; Que Hee, Shane S.; Johnson, John R.; Mercer, Chris; Shen, Feng; Sellers, Marilee; Stafford, Thomas W.; Stich, Adrienne; Weaver, James C.; Wittke, James H.; Wolbach, Wendy S.

    2009-01-01

    The long-standing controversy regarding the late Pleistocene megafaunal extinctions in North America has been invigorated by a hypothesis implicating a cosmic impact at the Ållerød-Younger Dryas boundary or YDB (≈12,900 ± 100 cal BP or 10,900 ± 100 14C years). Abrupt ecosystem disruption caused by this event may have triggered the megafaunal extinctions, along with reductions in other animal populations, including humans. The hypothesis remains controversial due to absence of shocked minerals, tektites, and impact craters. Here, we report the presence of shock-synthesized hexagonal nanodiamonds (lonsdaleite) in YDB sediments dating to ≈12,950 ± 50 cal BP at Arlington Canyon, Santa Rosa Island, California. Lonsdaleite is known on Earth only in meteorites and impact craters, and its presence strongly supports a cosmic impact event, further strengthened by its co-occurrence with other nanometer-sized diamond polymorphs (n-diamonds and cubics). These shock-synthesized diamonds are also associated with proxies indicating major biomass burning (charcoal, carbon spherules, and soot). This biomass burning at the Younger Dryas (YD) onset is regional in extent, based on evidence from adjacent Santa Barbara Basin and coeval with broader continent-wide biomass burning. Biomass burning also coincides with abrupt sediment mass wasting and ecological disruption and the last known occurrence of pygmy mammoths (Mammuthus exilis) on the Channel Islands, correlating with broader animal extinctions throughout North America. The only previously known co-occurrence of nanodiamonds, soot, and extinction is the Cretaceous-Tertiary (K/T) impact layer. These data are consistent with abrupt ecosystem change and megafaunal extinction possibly triggered by a cosmic impact over North America at ≈12,900 ± 100 cal BP. PMID:19620728

  3. Geochemical evidence for combustion of hydrocarbons during the K-T impact event

    PubMed Central

    Belcher, Claire M.; Finch, Paul; Collinson, Margaret E.; Scott, Andrew C.; Grassineau, Nathalie V.

    2009-01-01

    It has been proposed that extensive wildfires occurred after the Cretaceous–Tertiary (K-T) impact event. An abundance of soot and pyrosynthetic polycyclic aromatic hydrocarbons (pPAHs) in marine K-T boundary impact rocks (BIRs) have been considered support for this hypothesis. However, nonmarine K-T BIRs, from across North America, contain only rare occurrences of charcoal yet abundant noncharred plant remains. pPAHs and soot can be formed from a variety of sources, including partial combustion of vegetation and hydrocarbons whereby modern pPAH signatures are traceable to their source. We present results from multiple nonmarine K-T boundary sites from North America and reveal that the K-T BIRs have a pPAH signature consistent with the combustion of hydrocarbons and not living plant biomass, providing further evidence against K-T wildfires and compelling evidence that a significant volume of hydrocarbons was combusted during the K-T impact event. PMID:19251660

  4. Magnetic microspherules associated with the K/T and upper Eocene extinction events

    NASA Technical Reports Server (NTRS)

    Cisowski, Stanley M.

    1988-01-01

    Magnetic microspherules were identified in over 20 K/T boundary sites, and in numerous Deep Sea Drilling Project (DSDP) cores from the Caribbean and Pacific, synchronous with the extinction of several radiolarian species near the end of the Eocene. The K/T magnetic spherules are of particular interest as carriers of Ir and other siderophiles generally found in abundance in K/T boundary clay. Furthermore the textures and unusual chemistry of their component magnetic phases indicate an origin at high temperature, possibly related to (an) unusual event(s) marking the end of the Cretaceous and Eocene periods. Their origin, along with the non-magnetic (sanidine) spheules, is generally ascribed directly to megaimpact events hypothesized to have periodically disrupted life on Earth. A survey of microspherical forms associated with known meteorite and impact derived materials reveals fundamental differences from the extinction related spherules. Low temperature magnetic experiments on the K/T and Upper Eocene spheroids indicate that, unlike tektites, extremely small superparamagnetic carriers are not present in abundance. The extensive subaerial exposure of Cretaceous combustible black shale during sea level regression in the latest Cretaceous represents a potential source for the magnetic spheroids found in certain K/T boundary clays. The recent discovery of high Ir abundances distributed above and below the K/T boundary within shallow water sediments in Israel, which also contain the most extensive known zones of combustion metamorphism, the so called Mottled Zone, adds a further dramatic footnote to the proposed association between the magnetic spheroids and combustion of organic shales. Interestingly, the Mottled Zone also contains the rare mineral magnesioferrite, which was identified both within the K/T magnetic spheroids and as discrete crystals in boundary clay from marine and continental sites.

  5. KT boundary impact glasses from the Gulf of Mexico region

    NASA Technical Reports Server (NTRS)

    Claeys, Philippe; Alvarez, Walter; Smit, Jan; Hildebrand, A. R.; Montanari, Alessandro

    1993-01-01

    Cretaceous-Tertiary boundary (KTB) tektite glasses occur at several sites around the Gulf of Mexico. Contrary to rumor among KTB workers, glass fragments have been found by several researchers in the base of the spherule bed at Arroyo el Mimbral in NE Mexico. The presence of green, red, and transparent glass fragments at Mimbral only, demonstrates that the Mimbral glass is not a laboratory contamination by Beloc glass. The chemistry and ages of the glass are consistent with an origin from the Chixculub impact crater in Yucatan. No evidence supports a volcanic origin for the KTB glasses. A discussion of tektite glass from the KT boundary is presented.

  6. Mass extinction of birds at the Cretaceous-Paleogene (K-Pg) boundary.

    PubMed

    Longrich, Nicholas R; Tokaryk, Tim; Field, Daniel J

    2011-09-13

    The effect of the Cretaceous-Paleogene (K-Pg) (formerly Cretaceous-Tertiary, K-T) mass extinction on avian evolution is debated, primarily because of the poor fossil record of Late Cretaceous birds. In particular, it remains unclear whether archaic birds became extinct gradually over the course of the Cretaceous or whether they remained diverse up to the end of the Cretaceous and perished in the K-Pg mass extinction. Here, we describe a diverse avifauna from the latest Maastrichtian of western North America, which provides definitive evidence for the persistence of a range of archaic birds to within 300,000 y of the K-Pg boundary. A total of 17 species are identified, including 7 species of archaic bird, representing Enantiornithes, Ichthyornithes, Hesperornithes, and an Apsaravis-like bird. None of these groups are known to survive into the Paleogene, and their persistence into the latest Maastrichtian therefore provides strong evidence for a mass extinction of archaic birds coinciding with the Chicxulub asteroid impact. Most of the birds described here represent advanced ornithurines, showing that a major radiation of Ornithurae preceded the end of the Cretaceous, but none can be definitively referred to the Neornithes. This avifauna is the most diverse known from the Late Cretaceous, and although size disparity is lower than in modern birds, the assemblage includes both smaller forms and some of the largest volant birds known from the Mesozoic, emphasizing the degree to which avian diversification had proceeded by the end of the age of dinosaurs. PMID:21914849

  7. A search for iridium abundance anomalies at two late cambrian biomere boundaries in Western utah.

    PubMed

    Orth, C J; Knight, J D; Quintana, L R; Gilmore, J S; Palmer, A R

    1984-01-13

    Iridium concentrations have been measured in samples taken across two Late Cambrian biomere boundaries (crisis zones) in search of evidence for possible elemental abundance anomalies similar to the one observed at the Cretaceous-Tertiary boundary. Sampling was performed in uplifted marine limestone deposits in the House Range of western Utah. Although the two trilobite-brachiopod extinction boundaries could be assigned to +/-4 millimeters of vertical section by laboratory examination of the rocks, only background amounts of iridium (2 x 10(-12) to 17 x 10(-12) gram per gram of whole rock) were observed. PMID:17733805

  8. Synchroneity of the K-T oceanic mass extinction and meteorite impact: Blake Nose, western North Atlantic

    USGS Publications Warehouse

    Norris, R.D.; Huber, B.T.; Self-Trail, J.

    1999-01-01

    A 10-cm-thick layer of green spherules occurs precisely at the biostratigraphic boundary between the Cretaceous and Paleogene (K-T boundary) at Ocean Drilling Program Site 1049 (lat 30??08???N, long 76??06???W). The spherulitic layer contains abundant rock fragments (chalk, limestone, dolomite, chert, mica books, and schist) as well as shocked quartz, abundant large Cretaceous planktic foraminifera, and rounded clasts of clay as long as 4 mm interpreted as altered tektite glass probably derived from the Chicxulub impact structure. Most of the Cretaceous foraminifera present above the spherule layer are not survivors since small specimens are conspicuously rare compared to large individuals. Instead, the Cretaceous taxa in Paleocene sediments are thought to be reworked. The first Paleocene planktic foraminifera and calcareous nannofossil species are recorded immediately above the spherule bed, the upper part of which contains an iridium anomaly. Hence, deposition of the impact ejecta exactly coincided with the biostratigraphic K-T boundary and demonstrates that the impact event was synchronous with the evolutionary turnover in the oceans. These results are consistent with a reanalysis of the biostratigraphy of the K-T boundary stratotype, which argues that shallow-marine K-T boundary sections are not biostratigraphically more complete than deep-sea K-T boundary sites.

  9. K/T spherules from Haiti and Wyoming: Origin, diagenesis, and similarity to some microtektites

    NASA Astrophysics Data System (ADS)

    Bohor, B. F.; Glass, B. P.; Betterton, W. J.

    1993-03-01

    Spherules with relict glass cores in the K/T boundary bed of Haiti allow for a comparison of these bodies with hollow goyazite shells in the K/T boundary claystone of Wyoming and with younger microtektites of the Ivory Coast strewn field. Samples of the Haitian beds from undisturbed sections at Beloc, as determined by Jehanno et al., contain both hollow shells and relict glass cores rimmed by palagonite that has been partially converted to smectite. These palagonite rims developed from hydration zones formed when hot, splash-form droplets of andesitic impact glass were deposited into water. Mutual collisions between these droplets in the ejecta curtain may have formed point-source stresses on their surfaces. Initiation of hydration would be facilitated at these surface stress points and propagated radially into the glass. The inner surface of these merged hemispherical fronts appears mammillary, which is reflected as scalloping in Haitian relict glass cores.

  10. K/T spherules from Haiti and Wyoming: Origin, diagenesis, and similarity to some microtektites

    NASA Technical Reports Server (NTRS)

    Bohor, B. F.; Glass, B. P.; Betterton, W. J.

    1993-01-01

    Spherules with relict glass cores in the K/T boundary bed of Haiti allow for a comparison of these bodies with hollow goyazite shells in the K/T boundary claystone of Wyoming and with younger microtektites of the Ivory Coast strewn field. Samples of the Haitian beds from undisturbed sections at Beloc, as determined by Jehanno et al., contain both hollow shells and relict glass cores rimmed by palagonite that has been partially converted to smectite. These palagonite rims developed from hydration zones formed when hot, splash-form droplets of andesitic impact glass were deposited into water. Mutual collisions between these droplets in the ejecta curtain may have formed point-source stresses on their surfaces. Initiation of hydration would be facilitated at these surface stress points and propagated radially into the glass. The inner surface of these merged hemispherical fronts appears mammillary, which is reflected as scalloping in Haitian relict glass cores.

  11. Dinosaur bone beds and mass mortality: Implications for the K-T extinction

    NASA Technical Reports Server (NTRS)

    Carpenter, Kenneth

    1988-01-01

    Mass accumulations of fossilized large terrestrial vertebrate skeletons (bone beds: BB) provide a test for K-T catastrophic extinction hypotheses. The two major factors contributing to BB formation are mode of death and sedimentation rate. Catastrophic mass mortality (CMM) is the sudden death of numerous individuals where species, age, health, gender, or social ranking offer no survivorship advantage. Noncatastrophic mass mortality (NCMM) occurs over time and is strongly influenced by species, age, or gender. In addition to cause of death, sedimentation rate is also important in BB formation. Models of BBs can be made. The CMM drops all individuals in their tracks, therefore, the BB should reflect the living population with respect to species, age, or gender. The NCMM results in monospecific BBs skewed in the direction of the less fit, usually the very young or very old, or towards a specific gender. The NCMM and AM BBs may become more similar the more spread out over time NCMM deaths occur because carcasses are widely scattered requiring hydraulic accumulation, and the greater time allows for more disarticulation and weathering. The CMM and NCMM BB appear to be dominated by social animals. Applying this and the characteristics of mortality patterns to the uppermost Cretaceous Hell Creek Formation indicates that only NCMM and AM BB occur. Furthermore, NCMM BB are rare in the upper third of the Hell Creek. Near the K-T boundary, only AM BB are known. The absence of CMM and NCMM BB appears to be real reflecting a decrease in population levels of some dinosaurs prior to the K-T event. The absence of CMM suggests that the K-T event did not lead to an instantaneous extinction of dinosaurs. Nor was there a protracted die-off due to an asteroid impact winter, because no NCMM BB are known at or near the K-T boundary.

  12. Origin and diagenesis of K/T impact spherules -- From Haiti to Wyoming and beyond

    NASA Astrophysics Data System (ADS)

    Bohor, B. F.; Glass, B. P.

    1995-03-01

    Impact spherules in Cretaceous/Tertiary (KIT) boundary clays and claystones consist of two types; each type is confined to its own separate layer of the boundary couplet in the Western Hemisphere. The form and composition of each of the spherule types result from its own unique mode of origin during the KIT event. Type 1 splash-form spherules occur only in the melt-ejecta (basal) layer of the KIT couplet. This layer was deposited from a ballistic ejecta curtain composed of melt-glass droplets transported mostly within the atmosphere. h contrast, Type 2 spherules are accreted, partially crystalline, spheroidal bodies that formed by condensation of vaporized bolide and target-rock materials in an expanding fireball cloud, from which they settled out of buoyant suspension to form the fireball layer. Dendritic and skeletal Ni-rich spinel crystals are unique to these Type 2 spherules in the fireball layer. Compositions of relict glasses found in Type 1 KIT spherules from Haiti indicate that they were derived from intermediate silicic target rocks. These melt-glass droplets were deposited into an aqueous environment at both continental and marine sites. We propose that the surfaces of the hot melt droplets hydrated rapidly in water and that these hydrated glass rims then altered to palagonite. Subsequent alteration of the palagonite rims to smectite, glauconite, chlorite, kaolinite, or goyazite occurred later during various modes of progressive diagenesis, accompanied by dissolution of some of the glass cores in spherules from continental sections and from marine sections that were subsequently raised above sea level. In many of the nonmarine sections in the Western Interior, the glass cores altered to kaolinite instead of dissolving. Directly comparable spherule morphologies (splash forms), textural features of the altered shells, and scalloping and grooving of relict glass cores or secondary casts demonstrate that the Haitian and Wyoming spherules are equivalent altered Type 1 melt-droplet bodies. The spherules at both locations were deposited in a melt-ejecta layer as part of the KIT impact event. Previously, two types of relict impact glasses had been identified in the Haitian spherule beds: black glass of andesitic composition and high-Ca yellow glass with an unusually high S content. Most workers agree that the latter probably formed by impact melting and mixing of surficial carbonate (and minor anhydrite) rocks with the more deeply-buried crystalline parent rocks of the black glasses. However, some workers have suggested that an intermediate compositional gap exists between the two groups of glasses, implying a different origin than simple mixing of end members during impact. We report glass compositional analyses with values extending throughout this intermediate range, lending support to the impact-mixing model. Inclusions of CaSO4 found by us in relict yellow glasses further support this model.

  13. Factors responsible for catastrophic extinction of marine organisms at the Mesozoic-Cenozoic boundary

    NASA Astrophysics Data System (ADS)

    Barash, M. S.

    2011-08-01

    The mass death of organisms at the Cretaceous-Tertiary boundary (KT boundary) resulted in the extinction of approximately half of marine genera. Some taxa had degraded by the end of the Cretaceous to become eventually extinct either before or precisely at the KT boundary. Most of them became extinct immediately at this boundary. The terminal Cretaceous was marked by changes in many environmental processes, which influenced the biota. These included tectonic events, powerful basalt eruptions, falls of large asteroids (impact events), anoxia, transgressions and regressions, cooling and warming episodes, and the chemistry of the atmosphere and seawater. All these factors, except for impact events, could stimulate degradation of some groups of organisms, not their extinction. The Cretaceous-Tertiary boundary was marked by major impact events, which are reflected in the occurrence of the Chicxulub, Shiva, Boltysh, Silverpit, and, probably some other impact craters. Some known craters were left by asteroids at that time or slightly earlier. At least as many asteroids undoubtedly fell into the ocean. The combination of many factors in the terminal Cretaceous harmful for organisms and seemingly unrelated to each other may be likely explained only by a single supreme cause beyond the Solar System.

  14. Chondritic ratios of Fe/Cr/Ir in Kerguelen Plateau (Hole 738C) K/T carbonate-rich sediments support asteroid-cometary impact at K/T time

    NASA Technical Reports Server (NTRS)

    Liu, Y. G.; Schmitt, R. A.

    1993-01-01

    In the study of marine carbonate sediments from Holes 577 and 577B, Shatsky Plateau (Rise), a net extraterrestrial Fe/Ir = C1 chondritic ratio at the K/T boundary was reported. Applying a similar procedure to Hole 738C (Kerguelen Plateau) data reported, Fe/Cr/Ir ratios similar to C1 or C2 chondritic ratios were obtained.

  15. Mexican site for K/T impact crater?

    NASA Astrophysics Data System (ADS)

    Pope, K. O.; Ocampo, A. C.; Duller, C. E.

    1991-05-01

    Research throughout the Caribbean suggests that the geophysical anomalies in the Yucatan first noted by Penfield and Camargo (1981) and called the Chicxulub crater could be the site of the impact purported to have caused the K/T extinctions. A semicircular ring of sink holes, known locally as cenotes, which correlates with the geophysical anomalies has been identified, and it is argued that the origin of the cenote ring is related to postimpact subsidence of the Chicxulub crater rim. If there is indeed a crater, the region within the cenote ring corresponds to its floor and the crater rim diameter is probably larger than 200 km. If confirmed as a site of impact, the Chicxulub crater would be the largest terrestrial impact crater known, which is consistent with the uniqueness of the K/T global catastrophe.

  16. Mexican site for K/T impact crater?

    NASA Technical Reports Server (NTRS)

    Pope, Kevin O.; Ocampo, Adriana C.; Duller, Charles E.

    1991-01-01

    Research throughout the Caribbean suggests that the geophysical anomalies in the Yucatan first noted by Penfield and Camargo (1981) and called the Chicxulub crater could be the site of the impact purported to have caused the K/T extinctions. A semicircular ring of sink holes, known locally as cenotes, which correlates with the geophysical anomalies has been identified, and it is argued that the origin of the cenote ring is related to postimpact subsidence of the Chicxulub crater rim. If there is indeed a crater, the region within the cenote ring corresponds to its floor and the crater rim diameter is probably larger than 200 km. If confirmed as a site of impact, the Chicxulub crater would be the largest terrestrial impact crater known, which is consistent with the uniqueness of the K/T global catastrophe.

  17. Multiproxy Approach of the K-T and Chicxulub Ejecta Layers Along the Brazos River, Texas, USA

    NASA Astrophysics Data System (ADS)

    Adatte, T.; Keller, G.

    2006-05-01

    We report the results of preliminary investigations of four K-T boundary sections, which are located in small tributaries (Cottonmouth and Darting Minnow creeks) of the Brazos River and the recently drilled Mullinax-1 core. The study is based on high-resolution sampling, sedimentological observations, biostratigraphy, bulk rock and clay mineralogy, major and trace elements geochemistry and granulometry. The Cottonmouth Creek exposure is characterized by Late Maastrichtian dark grey fossiliferous claystone, interrupted by laterally variable channel fill storm deposits, which previously have been erroneously interpreted as impact tsunami deposits. These deposits consist of a basal shell hash (10cm), followed by glauconitic sand with altered impact spherules (10cm), laminated sandstones, and 4 to 5 hummocky cross-bedded sandstone layers separated by burrowed erosion surfaces that mark repeated colonization of the ocean floor between storm events. Above and below these storm events are dark grey fossiliferous claystones of the late Maastrichtian zone CF1, which spans the last 300,000 years of the Cretaceous. The observed sedimentary succession correspond therefore to incised valley infillings linked to a sea-level drop with a possible emersion, followed by a transgression which culminates at the K-T boundary. More specifically, the storms beds overlying the sequence boundary would correspond to late LST sediments which infill the incised valley, the overlying Maastrichtian claystone corresponds to the Early TST with a maximum at KTB (MFS). The K-T boundary is 40 cm and 90 cm above the storm deposits in the outcrop and Mullinax-1 core respectively. In the Mullinax-1 core, high resolution granulometric analyses of this interval reveal the event bed as repeated thinning upwards sequences, from the spherule- and glauconite-rich sandstones with HCS to fine laminated carbonated sandstones and finally thick bedded mudstone. But the last thinning upwards sequence is separated from the K-T boundary by at least 20 to cm of normal hemipelagic claystone showing calcite, phyllosilicates, TOC, isotope and granulometric values similar to the pre-event sediments and reflect therefore normal sedimentary conditions. The Chicxulub spherule ejecta in the glauconitic sand near the base of the storm beds is reworked from an older original ejecta layer, as indicated by abundant reworked fossil shells. This is similar to the reworked spherule layers at the base of the siliciclastic deposits throughout NE Mexico, where the original layer is within marls up to 5 m below (base of CF1) and predating the K-T by 300,000 years. The original ejecta layer in Cottonmouth Creek lies 60 cm below the basal unconformity of the storm beds and within claystones near the base of zone CF1. This layer consists of a prominent 3-4 cm thick yellow clay of pure and well-crystallized smectite (Cheto Mg-smectite) that possibly represents the alteration product of Chicxulub impact glass. Glass altered smectite spherules are commonly present and present the same geochemical composition as glass and spherules weathered to smectite from Haiti and NE-Mexico. Similar Cheto smectite layers have been documented from ejecta spherule deposits in Central America and the Caribbean. The Brazos results confirm that the Chicxulub impact predates the K-T boundary by about 300,000 years, as earlier observed based on impact glass spherule layers in northeastern Mexico and the suevite breccia from the Yaxcopoil-1 core in Yucatan.

  18. Carbon dioxide emissions from Deccan volcanism and a K/T boundary greenhouse effect

    NASA Technical Reports Server (NTRS)

    Caldeira, Ken; Rampino, Michael R.

    1990-01-01

    A greenhouse warming caused by increased emissions of carbon dioxide from the Deccan Traps volcanism has been suggested as the cause of the terminal Cretaceous extinctions on land and in the sea. Total eruptive and noneruptive CO2 output by the Deccan eruptions (from 6 to 20 x 10 to the 16th moles) over a period of several hundred thousand years is estimated based on best estimates of the CO2 weight fraction of the original basalts and basaltic melts, the fraction of CO2 degassed, and the volume of the Deccan Traps eruptions. Results of a model designed to estimate the effects of increased CO2 on climate and ocean chemistry suggest that increases in atmospheric pCO2 due to Deccan Traps CO2 emissions would have been less than 75 ppm, leading to a predicted global warming of less than 1 C over several hundred thousand years. It is concluded that the direct climate effects of CO2 emissions from the Deccan eruptions would have been too weak to be an important factor in the end-Cretaceous mass extinctions.

  19. Carbon dioxide emissions from Deccan volcanism and at K/T boundary greenhouse effect

    SciTech Connect

    Caldeira, K. ); Rampino, M.R. NASA Goddard Space Flight Center, New York, NY )

    1990-08-01

    A greenhouse warming caused by increased emissions of carbon dioxide from the Deccan Traps volcanism has been suggested as the cause of the terminal Cretaceous extinctions on land and in the sea. The authors estimate total eruptive and noneruptive CO{sub 2} output by the Deccan eruptions (from 6 to 20 {times} 10{sup 16} moles) over a period of several hundred thousand years based on best estimates of the CO{sub 2} weight fraction of the original basalts and basaltic melts, the fraction of CO{sub 2} degassed, and the volume of the Deccan Traps eruptions. Results of a model designed to estimate the effects of increased CO{sub 2} on climate and ocean chemistry suggest that increases in atmospheric pCO{sub 2} due to Deccan Traps CO{sub 2} emissions would have been less than 75 ppm, leading to a predicted global warming of less than 1C over several hundred thousand years. They conclude that the direct climate effects of CO{sub 2} emissions from the Deccan eruptions would have been too weak to be an important factor in the end-Cretaceous mass extinctions.

  20. Investigating a 65-Ma-Old Smoking Gun: Deep Drilling of the Chicxulub Impact Structure

    NASA Technical Reports Server (NTRS)

    Dressler, B.; Sharpton, V. L.; Morgan, J.; Buffler, R.; Moran, D.; Smit, J.; Stoeffler, D.; Urrutia, J.

    2003-01-01

    The Phanerozoic paleontological record is marked by several biological extinction events. One of them,at the Cretaceous/Tertiary (K/T) boundary was responsible for the demise of about 50% of genera and 75% of species, including the dinosaurs.These drastic and abrupt changes in the development of life on Earth puzzled paleontologists in the past. Many a cause was put forward to account for them, amongst them climate changes, disease, or overspecialization.

  1. In-situ Ir concentration measurements in KT-boundary sediments by accelerator secondary ion mass spectrometry

    NASA Astrophysics Data System (ADS)

    Maden, C.; Dbeli, M.; Hofmann, B.; Suter, M.

    2004-06-01

    Accelerator SIMS is the extension of secondary ion mass spectrometry (SIMS) with accelerator mass spectrometry (AMS) by which molecular interferences in the SIMS spectrum are removed. The potential of the PSI/ETH accelerator SIMS facility with respect to concentration analysis is demonstrated by presenting in-situ iridium concentration measurements in sedimentary layers around the Cretaceous-Tertiary transition (KT-boundary) from the Starkville South section, Raton basin, Colorado. In these sediments an iridium concentration anomaly is believed to originate from the impact of a meteorite 65 million years ago. By accelerator SIMS iridium concentrations in the range of 0.1 ng/g could be measured with a lateral resolution of 100 ?m reproducing neutron activation analysis data. The characteristics of accelerator SIMS together with boundary conditions influencing measurements are discussed.

  2. The Cometary Hypothesis of the K/t Mass Extinctions

    NASA Astrophysics Data System (ADS)

    Wickramasinghe, N. C.; Wallis, M. K.

    1994-09-01

    The correlation of the extended period of biological mass extinctions around the KIT boundary with extraterrestrial amino acids in the sediment record constitutes strong evidence of a cometary cause. While the fact that the dinosaurs' extinction coincided with the Chixculub cratering event and iridium-rich sediments suggests a chance asteroidal or cometary impact, the enhanced input of extraterrestrial matter over 1 0 yr supports the hypothesis of a Jupiter-associated giant comet, fragmented into a multitude of pieces, as demonstrated by comet Shoemaker-Levy 9, and perturbed into Earth-crossing orbits. Copious amounts of dust were released also, enhancing the dust abundance in the Solar system by several orders of magnitude. By studying the radiative properties of the submicron dust fraction of organic composition, we find that it is retained in the inner Solar system and is available for planetary accretion, uniike the IR-containing metallic and mineral dust. The shroud of dust accreted in the Earth's upper atmosphere can be sufficient to impose climatic stresses and cause extinctions of species over a protracted period of 10 yr. Dynamical arguments imply that the impacting comet most probably came directly from Jupiter's family. Details of the iridium record are compatible with re-accretion of some of the material ejected into space from the Chixculub impact. Key words: gravitation - comets: general - Earth - interplanetary medium - planets and satellites: individual: Jupiter - Solar system: general.

  3. Sudden and Gradual Molluscan Extinctions in the Latest Cretaceous of Western European Tethys

    PubMed

    Marshall; Ward

    1996-11-22

    Incompleteness of the fossil record has confounded attempts to establish the role of the end-Cretaceous bolide impact in the Late Cretaceous mass extinctions. Statistical analysis of latest Cretaceous outer-shelf macrofossils from western European Tethys reveals (i) a major extinction at or near the Cretaceous-Tertiary (K-T) boundary, probably caused by the impact, (ii) either a faunal abundance change or an extinction of up to nine ammonite species associated with a regression event shortly before the boundary, (iii) gradual extinction of most inoceramid bivalves well before the K-T boundary, and (iv) background extinction of approximately six ammonites throughout the latest Cretaceous. PMID:8910273

  4. A high resolution, one million year record of extraterrestrial 3Helium from the Shatsky Rise (site 1209) following the K/T impact

    NASA Astrophysics Data System (ADS)

    Bhattacharya, A.; Mukhopadhyay, S.; Hull, P. M.; Norris, R. D.

    2010-12-01

    Located in the North Pacific Ocean, site 1209 on the Shatsky rise offers one of the best-preserved sections for studying biological, oceanographic and climatic events in the aftermath of the K-T impact at ~65 Ma. At this site, the first 450 kyrs after the boundary is represented by an extended carbonate section [1]. The expanded section, also known as the strange interval [1] is in direct contrast to sites in the Atlantic and Indian Ocean that have low carbonate deposition during this interval. The strange interval is important for evaluating the immediate changes in climate, ocean circulation, and evolutionary dynamics that accompanied K-T impact in the Pacific Ocean. Here we present measurements of extraterrestrial 3He at site 1209 for the first one million year following the K-T impact event at a resolution of 2.5 cm. Our goal is to better constrain the timescale of climatic and biotic events during this interval of time. Accumulation rates of interplanetary dust particles (IDPs), as traced by extraterrestrial 3He [2], provide a tool with which to investigate sedimentation rates at high resolution. Prior work has shown that the accretion rate of IDPs across the K-T boundary is constant [2], allowing us to invert the extraterrestrial 3He flux for instantaneous sedimentation rates. Sedimentation rates derived from extraterrestrial 3He for the first 1.91 meters i.e. 261.60-259.72 revised composite meters depth (rmcd) following the K-T impact are on an average 0.48 cm/kyr- a factor of 1.6 lower than previously suggested [1]. For a brief period, between 259.69-259.44 rmcd after the K/T boundary, 3He-based sedimentation rates increase sharply to 2.88cm/kyra factor of 4.23 higher than has been reported for the same time interval [1]. The short lived increase in sedimentation rate may be explained by higher productivity and/or better carbonate preservation through a deepening lysocline. The 3He based sedimentation rates indicate that the duration of the strange interval is 721 kyrs and not 450 kyrs as previously suggested based on astronomical tuning [1]. Hence, our results indicate that there are significant differences between the astronomically tuned timescale [1] and the 3He-derived timescale over the first million years following the K-T impact event. [1] Westerhold et al. Paleogeography, paleoclimatology,paleoecology vol 257. pp373. 2008. [2] Mukhopadhyay et al. Geochimica Cosmochimica Acta. Vol 65. pp 653. 2001.

  5. Analysis of exclusive kT jet algorithms in electron-positron annihilation

    NASA Astrophysics Data System (ADS)

    Chay, Junegone; Kim, Chul; Kim, Inchol

    2015-10-01

    We study the factorization of the dijet cross section in e+e- annihilation using the generalized exclusive jet algorithm which includes the cone-type, the JADE, the kT, the anti-kT and the Cambridge/Aachen jet algorithms as special cases. In order to probe the characteristics of the jet algorithms in a unified way, we consider the generalized kT jet algorithm with an arbitrary weight of the energies, in which various types of the kT-type algorithms are included for specific values of the parameter. We show that the jet algorithm respects the factorization property for the parameter ? <2 . The factorized jet function and the soft function are well defined and infrared safe for all the jet algorithms except the kT algorithm. The kT algorithm (? =2 ) breaks the factorization since the jet and the soft functions are infrared divergent and are not defined for ? =2 , though the dijet cross section is infrared finite. In the jet algorithms which enable factorization, we give a phenomenological analysis using the resummed and the fixed-order results.

  6. A detailed taxonomy of Upper Cretaceous and lower Tertiary Crassatellidae in the Eastern United States; an example of the nature of extinction at the boundary

    USGS Publications Warehouse

    Wingard, G. Lynn

    1993-01-01

    Current theories on the causes of extinction at the CretaceousTertiary boundary have been based on previously published data; however, few workers have stopped to ask the question, 'How good is the basic data set?' To test the accuracy of the published record, a quantitative and qualitative analysis of the Crassatellidae (Mollusca, Bivalvia) of the Gulf and Mid-Atlantic Coastal Plains of the United States for the Upper Cretaceous and lower Tertiary was conducted. Thirty-eight species names and four generic names are used in publications for the Crassatellidae within the geographic and stratigraphic constraints of this analysis. Fourteen of the 38 species names are represented by statistically valid numbers of specimens and were tested by using canonical discriminant analysis. All 38 names, with the exception of 1 invalid name and 4 names for which no representative specimen could be located, were evaluated qualitatively. The results show that the published fossil record is highly inaccurate. Only 8 valid, recognizable species exist in the Crassatellidae within the limits of this study, 14 names are synonymized, and 11 names are represented by indeterminate molds or poorly preserved specimens. Three of the four genera are well founded; the fourth is based on the juvenile of another genus and therefore synonymized. This detailed taxonomic analysis of the Crassatellidae illustrates that the published fossil record is not reliable. Calculations of evolutionary and paleobiologic significance based on poorly defined, overly split fossil groups, such as the Crassatellidae, are biased in the following ways: Rates of evolution and extinction are higher, Faunal turnover at mass extinctions appears more catastrophic, Species diversity is high, Average species durations are shortened, and Geographic ranges are restricted. The data on the taxonomically standardized Crassatellidae show evolutionary rates one-quarter to one-half that of the published fossil record; faunal change at the Cretaceous-Tertiary boundary that was not catastrophic; a constant number of species on each side of the Cretaceous-Tertiary boundary; a decrease in abundance in the Tertiary; and lower species diversity, longer average species durations, and expanded geographic ranges. Similar detailed taxonomic studies need to be conducted on other groups of organisms to test the patterns illustrated for the Crassatellidae and to determine the extent and direction of the bias in the published fossil record. Answers to our questions about evolutionary change cannot be found in the literature but rather with the fossils themselves. Evolution and extinction occur within small populations of species groups, and it is only through detailed analysis of these groups that we can achieve an understanding of the causes and effects of evolution and extinction.

  7. Accelerating free breathing myocardial perfusion MRI using multi coil radial k - t SLR

    NASA Astrophysics Data System (ADS)

    Goud Lingala, Sajan; DiBella, Edward; Adluru, Ganesh; McGann, Christopher; Jacob, Mathews

    2013-10-01

    The clinical utility of myocardial perfusion MR imaging (MPI) is often restricted by the inability of current acquisition schemes to simultaneously achieve high spatio-temporal resolution, good volume coverage, and high signal to noise ratio. Moreover, many subjects often find it difficult to hold their breath for sufficiently long durations making it difficult to obtain reliable MPI data. Accelerated acquisition of free breathing MPI data can overcome some of these challenges. Recently, an algorithm termed as k - t SLR has been proposed to accelerate dynamic MRI by exploiting sparsity and low rank properties of dynamic MRI data. The main focus of this paper is to further improve k - t SLR and demonstrate its utility in considerably accelerating free breathing MPI. We extend its previous implementation to account for multi-coil radial MPI acquisitions. We perform k - t sampling experiments to compare different radial trajectories and determine the best sampling pattern. We also introduce a novel augmented Lagrangian framework to considerably improve the algorithms convergence rate. The proposed algorithm is validated using free breathing rest and stress radial perfusion data sets from two normal subjects and one patient with ischemia. k - t SLR was observed to provide faithful reconstructions at high acceleration levels with minimal artifacts compared to existing MPI acceleration schemes such as spatio-temporal constrained reconstruction and k - t SPARSE/SENSE.

  8. Fullerenes and interplanetary dust at the Permian-Triassic boundary.

    PubMed

    Poreda, Robert J; Becker, Luann

    2003-01-01

    We recently presented new evidence that an impact occurred approximately 250 million years ago at the Permian-Triassic boundary (PTB), triggering the most severe mass extinction in the history of life on Earth. We used a new extraterrestrial tracer, fullerene, a third carbon carrier of noble gases besides diamond and graphite. By exploiting the unique properties of this molecule to trap noble gases inside of its caged structure (helium, neon, argon), the origin of the fullerenes can be determined. Here, we present new evidence for fullerenes with extraterrestrial noble gases in the PTB at Graphite Peak, Antarctica, similar to PTB fullerenes from Meishan, China and Sasayama, Japan. In addition, we isolated a (3)He-rich magnetic carrier phase in three fractions from the Graphite Peak section. The noble gases in this magnetic fraction were similar to zero-age deep-sea interplanetary dust particles (IDPs) and some magnetic grains isolated from the Cretaceous-Tertiary boundary. The helium and neon isotopic compositions for both the bulk Graphite Peak sediments and an isolated magnetic fraction from the bulk material are consistent with solar-type gases measured in zero-age deep-sea sediments and point to a common source, namely, the flux of IDPs to the Earth's surface. In this instance, the IDP noble gas signature for the bulk sediment can be uniquely decoupled from fullerene, demonstrating that two separate tracers are present (direct flux of IDPs for (3)He vs. giant impact for fullerene). PMID:12804366

  9. k-t FASTER: Acceleration of functional MRI data acquisition using low rank constraints

    PubMed Central

    Chiew, Mark; Smith, Stephen M; Koopmans, Peter J; Graedel, Nadine N; Blumensath, Thomas; Miller, Karla L

    2015-01-01

    Purpose In functional MRI (fMRI), faster sampling of data can provide richer temporal information and increase temporal degrees of freedom. However, acceleration is generally performed on a volume-by-volume basis, without consideration of the intrinsic spatio-temporal data structure. We present a novel method for accelerating fMRI data acquisition, k-t FASTER (FMRI Accelerated in Space-time via Truncation of Effective Rank), which exploits the low-rank structure of fMRI data. Theory and Methods Using matrix completion, 4.27 retrospectively and prospectively under-sampled data were reconstructed (coil-independently) using an iterative nonlinear algorithm, and compared with several different reconstruction strategies. Matrix reconstruction error was evaluated; a dual regression analysis was performed to determine fidelity of recovered fMRI resting state networks (RSNs). Results The retrospective sampling data showed that k-t FASTER produced the lowest error, approximately 34%, and the highest quality RSNs. These results were validated in prospectively under-sampled experiments, with k-t FASTER producing better identification of RSNs than fully sampled acquisitions of the same duration. Conclusion With k-t FASTER, incoherently under-sampled fMRI data can be robustly recovered using only rank constraints. This technique can be used to improve the speed of fMRI sampling, particularly for multivariate analyses such as temporal independent component analysis. Magn Reson Med 74:353364, 2015. 2014 Wiley Periodicals, Inc. PMID:25168207

  10. Late Paleocene to Early Eocene marine vertebrates from the Uppermost Aruma Formation (northern Saudi Arabia): implications for the K-T transition

    NASA Astrophysics Data System (ADS)

    Thomas, Herbert; Roger, Jack; Halawani, Mohammed; Memesh, Abdallah; Lebret, Patrick; Bourdillon, Chantal; Buffetaut, Eric; Cappetta, Henri; Cavelier, Claude; Dutheil, Didier; Tonge, Haiyan; Vaslet, Denis

    1999-12-01

    A new assemblage of marine vertebrates from northern Saudi Arabia, east of the Nafud, leads us to reconsider the age of the top unit of the Aruma Formation, the Lina Member, hitherto referred to the Maastrichtian. This assemblage contains the remains of a dozen selachian and actinopterygian fishes, as well as those of a giant sea turtle representing a new dermochelyid taxon. It suggests a Late Paleocene to Early Eocene age for this unit. This new dating and a revision of the stratigraphic position of the Lina Member demonstrate the existence, on a regional scale, of an important hiatus at the K-T boundary.

  11. Cartesian SENSE and k-t SENSE reconstruction using commodity graphics hardware.

    PubMed

    Hansen, Michael S; Atkinson, David; Sorensen, Thomas S

    2008-03-01

    This study demonstrates that modern commodity graphics cards (GPUs) can be used to perform fast Cartesian SENSE and k-t SENSE reconstruction. Specifically, the SENSE inversion is accelerated by up to two orders of magnitude and is no longer the time-limiting step. The achieved reconstruction times are now well below the acquisition times, thus enabling real-time, interactive SENSE imaging, even with a large number of receive coils. The fast GPU reconstruction is also beneficial for datasets that are not acquired in real time. We demonstrate that it can be used for interactive adjustment of regularization parameters for k-t SENSE in the same way that one would adjust window and level settings. This enables a new way of performing imaging reconstruction, where the user chooses the setting of tunable reconstruction parameters, in real time, depending on the context in which the images are interpreted. PMID:18306398

  12. Monitoring oil displacement processes with k-t accelerated spin echo SPI.

    PubMed

    Li, Ming; Xiao, Dan; Romero-Zern, Laura; Balcom, Bruce J

    2016-03-01

    Magnetic resonance imaging (MRI) is a robust tool to monitor oil displacement processes in porous media. Conventional MRI measurement times can be lengthy, which hinders monitoring time-dependent displacements. Knowledge of the oil and water microscopic distribution is important because their pore scale behavior reflects the oil trapping mechanisms. The oil and water pore scale distribution is reflected in the magnetic resonance T2 signal lifetime distribution. In this work, a pure phase-encoding MRI technique, spin echo SPI (SE-SPI), was employed to monitor oil displacement during water flooding and polymer flooding. A k-t acceleration method, with low-rank matrix completion, was employed to improve the temporal resolution of the SE-SPI MRI measurements. Comparison to conventional SE-SPI T2 mapping measurements revealed that the k-t accelerated measurement was more sensitive and provided higher-quality results. It was demonstrated that the k-t acceleration decreased the average measurement time from 66.7 to 20.3?min in this work. A perfluorinated oil, containing no (1) H, and H2 O brine were employed to distinguish oil and water phases in model flooding experiments. High-quality 1D water saturation profiles were acquired from the k-t accelerated SE-SPI measurements. Spatially and temporally resolved T2 distributions were extracted from the profile data. The shift in the (1) H T2 distribution of water in the pore space to longer lifetimes during water flooding and polymer flooding is consistent with increased water content in the pore space. Copyright 2015 John Wiley & Sons, Ltd. PMID:26626141

  13. Monitoring Oil Displacement Processes with k-t Accelerated Spin Echo SPI.

    PubMed

    Li, Ming; Xiao, Dan; Romero-Zern, Laura; Balcom, Bruce J

    2016-03-01

    Magnetic Resonance Imaging is a robust tool to monitor oil displacement processes in porous media. Conventional MRI measurement times can be lengthy which hinders monitoring time dependent displacements. Knowledge of the oil and water microscopic distribution is important because their pore scale behavior reflects the oil trapping mechanisms. The oil and water pore scale distribution is reflected in the magnetic resonance T2 signal lifetime distribution. In this feature article, the authors employed a pure phase encoding MRI technique, Spin Echo SPI, to monitor oil displacement during water flooding and polymer flooding. A k-t acceleration method, with low rank matrix completion, was employed to improve the temporal resolution of the SE-SPI MRI measurements. The authors demonstrate the k-t accelerated SE-SPI MRI method improves measurement efficiency and SNR compared to conventional T2 mapping SE-SPI measurement. High-quality 1D water saturation profiles were acquired from the k-t SE-SPI measurements. Spatially and temporally resolved T2 distributions were extracted from the profile data. The shift in the (1) H T2 distribution of water in the pore space to longer lifetimes during water flooding and polymer flooding is consistent with increased water content in the pore space. PMID:26849391

  14. Carbon-isotope events across the Precambrian/Cambrian boundary on the Siberian Platform

    NASA Astrophysics Data System (ADS)

    Magaritz, Mordeckai; Holser, William T.; Kirschvink, Joseph L.

    1986-03-01

    Variations of marine isotopes with time have been observed through the Phanerozoic1,2, in association with some period boundaries: Pleistocene/Holocene3, Cretaceous/Tertiary4, Permo-Triassic5,6 and Frasnian/Fammenian7. Most of these changes are associated with extinction events, reflecting changes in life on Earth. One of the major biological changes in Earth's history occurred near the end of Proterozoic time, with widespread increase of bio-mineralization and the appearance of shelly fauna8-10. We present here an initial survey of carbon isotope ratios in a section on the Siberian Platform that spans the Proterozoic/Palaeozoic boundary. After a high of ?13C = + 3.4, 15 m below the boundary, ?13C drops sharply in two cycles across the boundary, to ?13C = -2, near the end of the Tommotian Stage. These variations suggest an initial bloom of biomass in late Vendian time corresponding to the dramatic diversification that must have preceeded the widespread appearance of new taxa in the Cambrian fossil record.

  15. Arroyo el Mimbral, Mexico, K/T unit: Origin as debris flow/turbidite, not a tsunami deposit

    NASA Technical Reports Server (NTRS)

    Bohor, Bruce F.; Betterton, William J.

    1993-01-01

    Coarse, spherule-bearing, elastic units have been discovered at 10 marine sites that span the K/T boundary in northeastern Mexico. We examined one of the best exposed sites in Arroyo el Mimbral, northwest of Tampico. The Mimbral outcrop displays a layered elastic unit up to 3 m thick enclosed by marly limestones of the Mendez (Latest Maastrichian) and Velasco (Earliest Danian) Formations. At its thickest point, this channelized elastic unit is comprised of 3 subunits: (1) a basal, poorly-sorted, ungraded calcareous spherule bed 1 m thick containing relict impact glass and shocked mineral grains, (2) a massive set of laminated calcite-cemented sandstones up to 2 m thick with plant debris at its base, (3) capped by a thin (up to 20 cm) set of rippled sandstone layers separated by silty mudstone drapes containing a small (921 pg/g) iridium anomaly. This tripartite elastic unit is conformably overlain by marls of the Velasco Formation. We also visited the La Lajilla site east of Ciudad Victoria; its stratigraphy is similar to Mimbral's, but its elastic beds are thinner and less extensive laterally. The Mimbral elastic unit has been interpreted previously as being deposited by a megawave or tsunami produced by an asteroid impact on nearby Yucatan (Chicxulub crater). However, a presumed 400-m paleodepth of water at the Mimbral site, channeling of the spherule subunit into the underlying Mendez Formation marls, and the overtopping of the basal, spherule-bearing subunit by the laminated sandstone subunit, all suggest a combined debris flow/turbidite origin for this elastic unit similar to that proposed for Upper Pleistocene sand/silt beds occurring elsewhere in the Gulf of Mexico. In this latter model, the sediment source region for the elastic unit is the lower continental shelf and slope escarpment. For the K/T unit at Mimbral, we propose that thick ejecta blanket deposits composed mostly of spherules were rapidly loaded onto the lower shelf and slope from an impact-generated ejecta curtain.

  16. Arroyo el Mimbral, Mexico, K/T unit: Origin as debris flow/turbidite, not a tsunami deposit

    NASA Astrophysics Data System (ADS)

    Bohor, Bruce F.; Betterton, William J.

    1993-03-01

    Coarse, spherule-bearing, elastic units have been discovered at 10 marine sites that span the K/T boundary in northeastern Mexico. We examined one of the best exposed sites in Arroyo el Mimbral, northwest of Tampico. The Mimbral outcrop displays a layered elastic unit up to 3 m thick enclosed by marly limestones of the Mendez (Latest Maastrichian) and Velasco (Earliest Danian) Formations. At its thickest point, this channelized elastic unit is comprised of 3 subunits: (1) a basal, poorly-sorted, ungraded calcareous spherule bed 1 m thick containing relict impact glass and shocked mineral grains, (2) a massive set of laminated calcite-cemented sandstones up to 2 m thick with plant debris at its base, (3) capped by a thin (up to 20 cm) set of rippled sandstone layers separated by silty mudstone drapes containing a small (921 pg/g) iridium anomaly. This tripartite elastic unit is conformably overlain by marls of the Velasco Formation. We also visited the La Lajilla site east of Ciudad Victoria; its stratigraphy is similar to Mimbral's, but its elastic beds are thinner and less extensive laterally. The Mimbral elastic unit has been interpreted previously as being deposited by a megawave or tsunami produced by an asteroid impact on nearby Yucatan (Chicxulub crater). However, a presumed 400-m paleodepth of water at the Mimbral site, channeling of the spherule subunit into the underlying Mendez Formation marls, and the overtopping of the basal, spherule-bearing subunit by the laminated sandstone subunit, all suggest a combined debris flow/turbidite origin for this elastic unit similar to that proposed for Upper Pleistocene sand/silt beds occurring elsewhere in the Gulf of Mexico. In this latter model, the sediment source region for the elastic unit is the lower continental shelf and slope escarpment. For the K/T unit at Mimbral, we propose that thick ejecta blanket deposits composed mostly of spherules were rapidly loaded onto the lower shelf and slope from an impact-generated ejecta curtain.

  17. Geochemical and climatic effects of increased marine organic carbon burial at the Cenomanian/Turonian boundary

    USGS Publications Warehouse

    Arthur, M.A.; Dean, W.E.; Pratt, L.M.

    1988-01-01

    Perhaps the most significant event in the Cretaceous record of the carbon isotope composition of carbonate1,2, other than the 1-2.5??? negative shift in the carbon isotope composition of calcareous plankton at the Cretaceous/Tertiary boundary3, is the rapid global positive excursion of ???2??? (13C enrichment) which took place between ???91.5 Myr and 90.3 Myr (late Cenomanian to earliest Turonian (C/T boundary event))1,4,5. This excursion has been attributed to a change in the isotope composition of the marine total dissolved carbon (TDC) reservoir resulting from an increase in rate of burial of 13C-depleted organic carbon, which coincided with a major global rise in sea level5 during the so-called C/T oceanic anoxic event (OAE)6. Here we present new data, from nine localities, which demonstrate that a positive excursion in the carbon isotope composition of organic carbon at or near the C/T boundary7,8 is nearly synchronous with that for carbonate and is widespread throughout the Tethys and Atlantic basins (Fig. 1), as well as in more high-latitude epicontinental seas. The postulated increase in the rate of burial of organic carbon may have had a significant effect on CO2 and O2 concentrations in the oceans and atmosphere, and consequent effects on global climate and sedimentary facies. ?? 1988 Nature Publishing Group.

  18. The Kara and Ust-Kara impact structures (USSR) and their relevance to the K/T boundary event

    NASA Technical Reports Server (NTRS)

    Koeberl, Christian; Nazarov, M. A.; Harrison, T. M.; Sharpton, V. L.; Murali, A. V.; Burke, K.

    1988-01-01

    The Kara and Ust-Kara craters are twin impact structures situated at about 69 deg 10 min N; 65 deg 00 min E at the Kara Sea. For Kara a diameter of about 55 km would be a very conservative estimate, and field observations indicate a maximum current diameter of about 60 km. The diameter of Ust-Kara has to be larger than 16 km. A better estimate might be 25 km but in all likelihood it is even larger. Suevites and impactites from the Kara area have been known since the beginning of the century, but had been misidentified as glacial deposits. Only about 15 years ago the impact origin of the two structures was demonstrated, following the recognition of shock metamorphism in the area. The composition of the target rocks is mirrored by the composition of the clasts within the suevites. In the southern part of Kara, Permian shales and limestones are sometimes accompanied by diabasic dykes, similar to in the central uplift. Due to the high degree of shock metamorphism the shocked magmatic rocks are not easily identified, although most of them seem to be of diabasic or dioritic composition. The impact melts (tagamites) are grey to dark grey fine grained crystallized rocks showing very fine mineral components and are the product of shock-melting with later recrystallization. The impact glasses show a layered structure, inclusions, and vesicles, and have colors ranging from translucent white over brown and grey to black. A complete geochemical characterization of the Kara and Ust-Kara impact craters was attempted by analyzing more than 40 samples of target rocks, shocked rocks, suevites, impact melts, and impact glasses for major and trace elements.

  19. A new measure of molecular attractions between nanoparticles near kT adhesion energy

    NASA Astrophysics Data System (ADS)

    Kendall, Kevin; Dhir, Aman; Du, Shangfeng

    2009-07-01

    The weak molecular attractions of nanoparticles are important because they drive self-assembly mechanisms, allow processing in dispersions e.g. of pigments, catalysts or device structures, influence disease through the attraction of viruses to cells and also cause potential toxic effects through nanoparticle interference with biomolecules and organs. The problem is to understand these small forces which pull nanoparticles into intimate contact; forces which are comparable with 3kT/2z the thermal impact force experienced by an average Brownian particle hitting a linear repulsive potential of range z. Here we describe a new method for measuring the atomic attractions of nanoparticles based on the observation of aggregates produced by these small forces. The method is based on the tracking of individual monosize nanoparticles whose diameter can be calculated from the Stokes-Einstein analysis of the tracks in aqueous suspensions. Then the doublet aggregates are distinguished because they move slower and are also very much brighter than the dispersed nanoparticles. By finding the ratio of doublets to singlets, the adhesive energy between the particles can be calculated from known statistical thermodynamic theory using assumptions about the shape of the interaction potential. In this way, very small adhesion energies of 2kT have been measured, smaller than those seen previously by atomic force microscopy (AFM) and scanning tunneling microscopy (STM).

  20. Prompt photon and associated heavy quark production at hadron colliders with k T -factorization

    NASA Astrophysics Data System (ADS)

    Lipatov, A. V.; Malyshev, M. A.; Zotov, N. P.

    2012-05-01

    In the framework of the k T -factorization approach, the production of prompt photons in association with a heavy (charm or beauty) quarks at high energies is studied. The consideration is based on the {O}( {α α_s^2} ) off-shell amplitudes of gluon-gluon fusion and quark-(anti)quark interaction subprocesses. The unintegrated parton densities in a proton are determined using the Kimber-Martin-Ryskin prescription. The analysis covers the total and differential cross sections and extends to specific angular correlations between the produced prompt photons and muons originating from the semileptonic decays of associated heavy quarks. Theoretical uncertainties of our evaluations are studied and comparison with the results of standard NLO pQCD calculations is performed. Our numerical predictions are compared with the recent experimental data taken by the D∅ and CDF collaborations at the Tevatron. Finally, we extend our results to LHC energies.

  1. Modeling study of infrasonic detection of 1 kT atmospheric blast

    SciTech Connect

    Dighe, K.A.; Whitaker, R.W.; Armstrong, W.T.

    1998-12-31

    A modified version of the ``Pierce code``, which provides a theoretical prediction of acoustic-gravity pressure waveforms generated by explosions in the atmosphere, has been used to simulate detectable signal amplitudes from a 1 kT atmospheric detonation at high latitudes upton distances of about 1,000 kilometers from the source. Realistic prevailing winds and temperature profiles have been included in these simulations and propagation results for with wind and counter wind conditions are presented. En route, the code has been successfully ported from a CRAY/UNICOS platform to a more general UNIX/workstation environment in FORTRAN90. The effects of seasonal variations of winds and temperature at high latitudes will be presented at the symposium.

  2. Extended study of prompt photon photoproduction at HERA with kT-factorization

    NASA Astrophysics Data System (ADS)

    Lipatov, A. V.; Malyshev, M. A.; Zotov, N. P.

    2013-10-01

    We reconsider prompt photon photoproduction at HERA in the framework of the kT-factorization QCD approach. The proposed method is based on the O(?2?s) amplitudes for ?q??gq and ?g*??qq partonic subprocesses. Additionally, we take into account the O(?2?s2) box contributions ?g??g to the production cross sections. The unintegrated (or transverse momentum dependent) parton densities in the proton are determined using the Kimber-Martin-Ryskin prescription. Our consideration covers both inclusive and jet associated prompt photon photoproduction rates. We find that our numerical predictions agree well with the recent data taken by H1 and ZEUS Collaborations at HERA. We demonstrate that the box contributions are sizable and amount to up to 15% of the calculated total cross section.

  3. The post: pre dialysis plasma urea nitrogen ratio to estimate K.t/V and NPCR: validation.

    PubMed

    Daugirdas, J T

    1989-07-01

    The ability of empirical formulae to predict K.t/V based on the ratio (R) of the postdialysis (Ct) to predialysis (Co) plasma urea nitrogen levels was tested. In 256 patients, 336 three-point modeling sessions were performed. The K.t/V and NPCR were derived by interative solution of equations for V and G according to the variable volume single-pool model. The modeled K.t/V values were compared to K.t/V predicted from the formula: K.t/V = -ln (R - 0.008.t-UF/W), where R is the Ct/Co ratio, t the session length (h), UF the ultrafiltrate volume (liters) and W the postdialysis weight (kg). Further, the ratio-derived K.t/V was used in conjunction with the Gotch nomogram for 3/week dialysis to estimate NPCR (NPCR-R/N); the latter value was compared to the NPCR from standard 3-point modeling (NPCR-MOD). The two K.t/V values were quite similar, although statistically separable: modeled K.t/V, 0.97 +/- 0.22 (SD), ratio-derived K.t/V 0.96 +/- 0.23, p less than 0.001. The mean percent error was -0.73% +/- 2.5 (range - 11 to + 4.8), and the correlation coefficient was 0.994, slope 1.01, int -0.016. Modifications of the prediction formula which incorporated UF/V instead of UF/W, and/or which weighted the UF/V term according to the expected K.t/V, produced only slight improvement in accuracy. The two values of NPCR were less similar, but still highly correlated: NPCR-MOD, 1.04 +/- 0.26 g/kg/day, NPCR-R/N, 0.94 +/- 0.23, p less than 0.001; mean percent error, - 8.2 +/- 16; r = 0.78, slope = 0.68, int = 0.23.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:2486234

  4. Chicxulub multiring impact basin: size and other characteristics derived from gravity analysis.

    PubMed

    Sharpton, V L; Burke, K; Camargo-Zanoguera, A; Hall, S A; Lee, D S; Marn, L E; Suarez-Reynoso, G; Quezada-Mueton, J M; Spudis, P D; Urrutia-Fucugauchi, J

    1993-09-17

    The buried Chicxulub impact structure in Mexico, which is linked to the Cretaceous- Tertiary (K-T) boundary layer, may be significantly larger than previously suspected. Reprocessed gravity data over Northern Yucatan reveal three major rings and parts of a fourth ring, spaced similarly to those observed at multiring impact basins on other planets. The outer ring, probably corresponding to the basin's topographic rim, is almost 300 kilometers in diameter, indicating that Chicxulub may be one of the largest impact structures produced in the inner solar system since the period of early bombardment ended nearly 4 billion years ago. PMID:17798115

  5. Chicxulub multiring impact basin - Size and other characteristics derived from gravity analysis

    NASA Technical Reports Server (NTRS)

    Sharpton, Virgil L.; Burke, Kevin; Camargo-Zanoguera, Antonio; Hall, Stuart A.; Lee, D. S.; Marin, Luis E.; Suarez-Reynoso, Gerardo; Quezada-Muneton, Juan M.; Spudis, Paul D.; Urrutia-Fucugauchi, Jaime

    1993-01-01

    The buried Chicxulub impact structure in Mexico, which is linked to the Cretaceous-Tertiary (K-T) boundary layer, may be significantly larger than previously suspected. Reprocessed gravity data over Northern Yucatan reveal three major rings and parts of a fourth ring, spaced similarly to those observed at multiring impact basins on other planets. The outer ring, probably corresponding to the basin's topographic rim, is almost 300 kilometers in diameter, indicating that Chicxulub may be one of the largest impact structures produced in the inner solar system since the period of early bombardment ended nearly 4 billion years ago.

  6. Dating of Impact Events

    NASA Astrophysics Data System (ADS)

    Schrer, U.

    Introduction Some Numbers amd Definitions Geological Dating Methods Crater Counting Bio-magnetostratigraphy and Paleomagnetism Nuclear Dating Methods General Aspects Thermoluminescence Cosmogenic Nuclides Fission Track Dating Radioactive Decay Shock Wave Metamorphism General Aspects Coherent Impacts Melt Layers The Crater Basement Allochthonous Breccia Deposits Distant Ejecta Implications from Experiments Dating and Sample Selection Geological Frame Coherent Impact Melt Layers Allochthonous Breccia Deposits Crater Basement Distant Ejecta Deposits Examples Impactites of the Crater Area Distant Ejecta, and the Cretaceous/Tertiary (K/T) Boundary Crater Basement References

  7. Highly undersampled phase-contrast flow measurements using compartment-based k-t principal component analysis.

    PubMed

    Giese, Daniel; Schaeffter, Tobias; Kozerke, Sebastian

    2013-02-01

    The applicability of cine blood flow measurements in a clinical setting is often compromised by the long scan times associated with phase-contrast imaging. In this work, we propose an extension to the k-t principal component analysis method and demonstrate that by definition of spatial compartment-dependent temporal basis functions, significant improvements in reconstruction accuracy can be achieved relative to the original k-t principal component analysis and k-t SENSE formulations. Using this method, it is shown that prospective nominal undersampling of up to 16 corresponding to a net acceleration factor of 8 including training data acquisition can be realized while keeping the error in stroke volume below 5%. As a practical application, the acquisition of cine flow data in the aorta is demonstrated permitting assessment of two-dimensional velocity images and pulse wave velocities at 100 frames per second in a single breathhold per slice. PMID:22528878

  8. Mechanics performance test and feasibility analysis to replace the rigid sucker rod for 6K T300

    NASA Astrophysics Data System (ADS)

    Tong, Changhong

    2015-07-01

    A experiment plan was designed according to the working conditions of sucker rod and the requirements for pump depth in 3000 m in the oil field, the tensile strength for 6K T300 under a normal temperature and high temperature was measured by using universal testing machine, and then, the resistance to corrosion for a crude oil was verified by measuring the tensile strength for 6K T300 after crude oil immersion at a certain time, and the conclusions are that the material is sensitive relatively to corrosion of crude oil and that the tensile strength of the 6K T300 compared with similar products is lower, a proposal to the GH company that to meet the need of oil field production instead of the rigid rod the tensile strength and corrosion resistant for a crude of the T300 6 k materials have to do further efforts was pointed out.

  9. Measurement of the MACS of 159Tb(n, ?) at kT = 30 keV by Activation

    NASA Astrophysics Data System (ADS)

    Praena, J.; Mastinu, P. F.; Pignatari, M.; Quesada, J. M.; Capote, R.; Morilla, Y.

    2014-06-01

    The measurement of the Maxwellian-Averaged Cross-Section (MACS) of the 159Tb(n, ?) reaction at kT = 30 keV by the activation technique is presented. An innovative method for the generation of Maxwellian neutron spectra at kT = 30 keV is used. An experimental value of 2166 181 mb agrees well with the MACS value derived from the ENDF/B-VII.1 evaluation, but is higher than KADoNiS recommended value of 1580 150 mb. Astrophysical implications are studied.

  10. Measurement of the MACS of {sup 159}Tb(n, ?) at kT=30 keV by Activation

    SciTech Connect

    Praena, J.; Mastinu, P.F.; Pignatari, M.; Quesada, J.M.; Capote, R.; Morilla, Y.

    2014-06-15

    The measurement of the Maxwellian-Averaged Cross-Section (MACS) of the {sup 159}Tb(n, ?) reaction at kT=30 keV by the activation technique is presented. An innovative method for the generation of Maxwellian neutron spectra at kT=30 keV is used. An experimental value of 2166181 mb agrees well with the MACS value derived from the ENDF/B-VII.1 evaluation, but is higher than KADoNiS recommended value of 1580150 mb. Astrophysical implications are studied.

  11. Response of marine and freshwater algae to nitric acid and elevated carbon dioxide levels simulating environmental effects of bolide impact

    NASA Technical Reports Server (NTRS)

    Boston, P. J.

    1988-01-01

    One of the intriguing facets of the Cretaceous-Tertiary extinction is the apparently selective pattern of mortality amongst taxa. Some groups of organisms were severely affected and some remained relatively unscathed as they went through the K/T boundary. While there is argument concerning the exact interpretation of the fossil record, one of the best documented extinctions at the Cretaceous-Tertiary boundary is that of the calcareous nannoplankton. These organisms include coccolithic algae and foraminiferans. Attempts to explain their decline at the K/T boundary center around chemistry which could affect their calcium carbonate shells while leaving their silica-shelled cousins less affected or unaffected. Two environmental consequences of an extraterrestrial body impact which were suggested are the production of large quantities of nitrogen oxides generated by the shock heating of the atmosphere and the possible rise in CO2 from the dissolution of CaCO3 shells. Both of these phenomena would acidify the upper layers of the oceans and bodies of freshwater not otherwise buffered. The effects of nitric acid, carbon dioxide, or both factors on the growth and reproduction of calcareous marine coccoliths and non-calcareous marine and freshwater species of algae were considered. These experiments demonstrate that nitric acid and carbon dioxide have significant effects on important aspects of the physiology and reproduction of modern algae representative of extinct taxa thought to have suffered significant declines at the Cretaceous-Tertiary boundary. Furthermore, calcareous species showed more marked effects than siliceous species and marine species tested were more sensitive than freshwater species.

  12. Search for impact remains at the Frasnian-Famennian boundary in the stratotype area, southern France.

    PubMed

    Girard, C; Robin, E; Rocchia, R; Froget, L; Feist, R

    1997-08-01

    In order to detect whether the end-Frasnian worldwide biotic crisis is related to an extraterrestrial impact, the global stratotype section of the Frasnian-Famennian boundary and auxiliary sections within the stratotype area have been examined for impact indicators: iridium. Ni-rich spinel bearing spherules and glassy microtektites. This area is particularly well suited to the search for discrete events because it exhibits biostratigraphically continuous sections of sedimentologically homogenous off-shore deposits. Different environmental settings on oxygenated deep-water seamounts, such as the stratotype section at Coumiac, and in oxygen-depleted depressions (La Serre section) are available. The latter is investigated in more detail because it is the least condensed across the boundary, which is determined by the first occurrence of the typical morphotype of Palmatolepis triangularis, the indicator of the first Famennian conodont biozone. Samples from the biostratigraphically defined boundary and adjacent levels failed to provide significantly high Ir values and no Ni-rich spinel or microtektite has been recovered. This is in contradiction with the results of earlier investigations carried out by H. Geldsetzer on the same section. In contrast, the values of Ir concentrations that we measured are always very low or not detectable. The small overabundances observed in some samples, which are about two orders of magnitude lower than what is currently observed at the Cretaceous-Tertiary boundary, are probably due to the accumulation of the normal flux of cosmic dust during periods of relatively low depositional rates or to a terrestrial origin. At present, we have no evidence that an extraterrestrial impact occurred at the F-F transition. PMID:11541727

  13. What killed the dinosaurs?

    USGS Publications Warehouse

    Glen, W.

    1990-01-01

    Out of a number of earlier attempts to explain mass extinctions, only the volcanism alternative to the impact hypothesis remains under serious consideration. The evidence for an impact is reviewed, and the mechanisms which might have brought about the apocalyptic series of extinctions at the Cretaceous-Tertiary (K-T) boundary are reviewed, referring to Alvarez's and other research teams working on the problem. As suggested by the patterns of extinctions and the periodicity of this and other mass extinctions, the "volcanist alternative' is introduced. This would produce a series of selective extinctions spread over a considerable length of time, and which is similar to what the fossil record shows, and could account for the iridium anomaly at the K-T boundary. More support for this theory comes from models put forward by volcanist exponents, but it is concluded that the debate is far from ended. -J.W.Cooper

  14. Sub-kT/q subthreshold slope p-metal-oxide-semiconductor field-effect transistors with single-grained Pb(Zr,Ti)O3 featuring a highly reliable negative capacitance

    NASA Astrophysics Data System (ADS)

    Park, Jae Hyo; Joo, Seung Ki

    2016-03-01

    A reliable on/off switching with an sub-kT/q subthreshold slope (38 mV/dec at room temperature) is experimentally demonstrated with using selectively nucleated laterally crystallized single-grain Pb(Zr,Ti)O3 (PZT) ferroelectric and ZrTiO4 paraelectric thin-film. The combination of ferroelectric and paraelectric thin-film is enabled to form a negative capacitance (NC) at the weak inversion region. However, the PZT grain-boundary easily degrades the NC properties after switching the on/off more than 108 times. It is found that the polarization of PZT is diminished from the path of grain-boundary. Here, we effectively suppress the degradation of NC MOS-FET which did not showed any fatigue even after 108 on/off switching.

  15. Chicxulub impact: The origin of reservoir and seal facies in the southeastern Mexico oil fields

    NASA Astrophysics Data System (ADS)

    Grajales-Nishimura, Jos M.; Cedillo-Pardo, Esteban; Rosales-Domnguez, Carmen; Morn-Zenteno, Dante J.; Alvarez, Walter; Claeys, Philippe; Ruz-Morales, Jos; Garca-Hernndez, Jess; Padilla-Avila, Patricia; Snchez-Ros, Antonieta

    2000-04-01

    Stratigraphic and mineralogic studies of Cretaceous-Tertiary (K-T) boundary sections demonstrate that the offshore oil-producing breccias and seals from oil fields in the Campeche marine platform are of K-T boundary age and that their mode of formation is probably related to the K-T impact event at Chicxulub. The oil-producing carbonate breccia and the overlying dolomitized ejecta layer (seal) found in several wells on the Campeche marine platform contain typical Chicxulub impact products, such as shocked quartz and plagioclase, and altered glass. These offshore units are correlated with thick (50 300 m) onshore breccia and impact ejecta layers found at the K-T boundary in the Guayal (Tabasco) and Bochil (Chiapas) sections. Regionally the characteristic sequence is composed of, from base to top, coarse-grained carbonate breccia covered by an ejecta bed and typical K-T boundary clay. The onshore and offshore breccia sequences are likely to have resulted from major slumping of the carbonate platform margin triggered by the Chicxulub impact. Successive arrival times in this area, 350 600 km from the crater, of seismic shaking, ballistic ejecta, and tsunami waves fit the observed stratigraphic sequence. The K-T breccia reservoir and seal ejecta layer of the Cantarell oil field, with a current daily production of 1.3 million barrels of oil, are probably the most important known oil-producing units related to an impact event.

  16. k-t acceleration in pure phase encode MRI to monitor dynamic flooding processes in rock core plugs.

    PubMed

    Xiao, Dan; Balcom, Bruce J

    2014-06-01

    Monitoring the pore system in sedimentary rocks with MRI when fluids are introduced is very important in the study of petroleum reservoirs and enhanced oil recovery. However, the lengthy acquisition time of each image, with pure phase encode MRI, limits the temporal resolution. Spatiotemporal correlations can be exploited to undersample the k-t space data. The stacked frames/profiles can be well approximated by an image matrix with rank deficiency, which can be recovered by nonlinear nuclear norm minimization. Sparsity of the x-t image can also be exploited for nonlinear reconstruction. In this work the results of a low rank matrix completion technique were compared with k-t sparse compressed sensing. These methods are demonstrated with one dimensional SPRITE imaging of a Bentheimer rock core plug and SESPI imaging of a Berea rock core plug, but can be easily extended to higher dimensionality and/or other pure phase encode measurements. These ideas will enable higher dimensionality pure phase encode MRI studies of dynamic flooding processes in low magnetic field systems. PMID:24809307

  17. k-t Acceleration in pure phase encode MRI to monitor dynamic flooding processes in rock core plugs

    NASA Astrophysics Data System (ADS)

    Xiao, Dan; Balcom, Bruce J.

    2014-06-01

    Monitoring the pore system in sedimentary rocks with MRI when fluids are introduced is very important in the study of petroleum reservoirs and enhanced oil recovery. However, the lengthy acquisition time of each image, with pure phase encode MRI, limits the temporal resolution. Spatiotemporal correlations can be exploited to undersample the k-t space data. The stacked frames/profiles can be well approximated by an image matrix with rank deficiency, which can be recovered by nonlinear nuclear norm minimization. Sparsity of the x-t image can also be exploited for nonlinear reconstruction. In this work the results of a low rank matrix completion technique were compared with k-t sparse compressed sensing. These methods are demonstrated with one dimensional SPRITE imaging of a Bentheimer rock core plug and SESPI imaging of a Berea rock core plug, but can be easily extended to higher dimensionality and/or other pure phase encode measurements. These ideas will enable higher dimensionality pure phase encode MRI studies of dynamic flooding processes in low magnetic field systems.

  18. Post to predialysis plasma urea nitrogen ratio, ultrafiltration and weight to estimate K.t/V. Use in auditing the amount of dialysis being administered.

    PubMed

    Manahan, F J; Ramanujam, L; Ajam, M; Ing, T S; Gandhi, V C; Daugirdas, J T

    1989-01-01

    The formula -In (R - 0.03 - UF/W), where R is the ratio of the postdialysis to predialysis plasma urea nitrogen level, UF the ultrafiltrate volume per session, and W the postdialysis weight, has been shown by us to estimate K.t/V accurately. We audited the amount of dialysis being administered in a moderate size outpatient unit in which urea kinetic modeling was not being done and in which 4 hr dialysis at a 250 or 300 ml/min blood flow rate was routinely prescribed. R was determined once per month on each of six successive months, and standard three point urea kinetic modeling was done on all patients once. R was quite reproducible in each patient, with a coefficient of variation of 6.6% +/- 3.2 standard deviation (SD). The R:UF:W-derived K.t/V averaged 0.91 +/- 0.19; the R:UF:W-derived K.t/V correlated with the modeled K.t/V (r = 0.98), with a mean percent error of only 0.12% +/- 3.6. A negative correlation (r = -0.56) was present between the R:UF:W-derived K.t/V and postdialysis weight; 9 of 40 patients had K.t/V values below 0.8 and 7 of these 9 weighed more than 85 kg. In 13 other patients, K.t/V was between 0.8 and 0.9. After inclusion of residual renal function (Kru) to calculate KT, KT was still below 0.9 in 19 patients. The main cause of underdialysis was inadequate prescription. The results suggest that monthly monitoring of R, with inclusion of UF and W to estimate K.t/V, is one useful quality assurance tool to assess the amount of dialysis being administered. PMID:2597521

  19. Associated production of Higgs bosons and heavy quarks at the LHC: Predictions with the kT-factorization approach

    NASA Astrophysics Data System (ADS)

    Lipatov, A. V.; Zotov, N. P.

    2009-07-01

    In the framework of the kT-factorization approach, we study the production of Higgs bosons associated with a heavy (beauty or top) quark pair at the CERN LHC collider conditions. Our consideration is based mainly on the off-shell gluon-gluon fusion subprocess g*g*→Q Qmacr H. The corresponding matrix element squared has been calculated for the first time. We investigate the total and differential cross sections of b bmacr H and t tmacr H production taking into account also the non-negligible contribution from the q qmacr →Q Qmacr H mechanism. In the numerical calculations we use the unintegrated gluon distributions obtained from the Ciafaloni-Catani-Fiorani-Marchesini evolution equation. Our results are compared with the leading predictions of the collinear factorization of QCD.

  20. Investigating a 65-Ma-Old Smoking Gun: Deep Drilling of the Chicxulub Impact Structure

    NASA Astrophysics Data System (ADS)

    Dressler, B. O.; Sharpton, V. L.; Morgan, J.; Buffler, R.; Moran, D.; Smit, J.; Stöffler, D.; Urrutia, J.

    The Phanerozoic paleontological record is marked by several biological extinction events. One of them, at the Cretaceous/Tertiary (K/T) boundary, was responsible for the demise of about 5% of genera and 75% of species, including the dinosaurs. These drastic and abrupt changes in the development of life on Earth puzzled paleontologists in the past. Many a cause was put forward to account for them, amongst them climate changes, disease, or overspecialization. About 20 years ago, Alvarez et al. [1980] discovered a high iridium concentration in an Italian K/T boundary clay layer. They proposed that the iridium was derived from an extra-terrestrial impact 65 Ma ago and that the impact was the cause for the K/T boundary extinctions. The iridium layer was subsequently found at K/T boundary locations worldwide. Further evidence for a K/T impact came from the discovery of shocked quartz, nano-diamonds, glass spherules, and nickel-rich spinels in microkrystites in the iridium-rich layer. There was evidence for an impact event, but no crater.

  1. Vertebrate time-tree elucidates the biogeographic pattern of a major biotic change around the K-T boundary in Madagascar.

    PubMed

    Crottini, Angelica; Madsen, Ole; Poux, Celine; Strauss, Axel; Vieites, David R; Vences, Miguel

    2012-04-01

    The geographic and temporal origins of Madagascar's biota have long been in the center of debate. We reconstructed a time-tree including nearly all native nonflying and nonmarine vertebrate clades present on the island, from DNA sequences of two single-copy protein-coding nuclear genes (BDNF and RAG1) and a set of congruent time constraints. Reconstructions calculated with autocorrelated or independent substitution rates over clades agreed in placing the origins of the 31 included clades in Cretaceous to Cenozoic times. The two clades with sister groups in South America were the oldest, followed by those of a putative Asian ancestry that were significantly older than the prevalent clades of African ancestry. No colonizations from Asia occurred after the Eocene, suggesting that dispersal and vicariance of Asian/Indian groups were favored over a comparatively short period during, and shortly after, the separation of India and Madagascar. Species richness of clades correlates with their age but those clades that have a large proportion of species diversity in rainforests are significantly more species-rich. This finding suggests an underlying pattern of continuous speciation through time in Madagascar's vertebrates, with accelerated episodes of adaptive diversification in those clades that succeeded radiating into the rainforests. PMID:22431616

  2. Discovery and focused study of the Chicxulub impact crater

    NASA Astrophysics Data System (ADS)

    Urrutia-Fucugauchi, Jaime; Camargo-Zanoguera, Antonio; Pérez-Cruz, Ligia

    2011-06-01

    Three decades ago, a landmark paper by Alvarez et al. [1980] proposed that an asteroid impact 65.5 million years ago was the cause of the mass extinction of about 75% of species, including the dinosaurs, at the boundary between the Cretaceous and Paleogene periods (K-Pg), formerly known as the Cretaceous-Tertiary (K-T) boundary. Alvarez et al. used geochemical studies on carbonate sequences from Italy, Denmark, and New Zealand to study the boundary layer, which was enriched in iridium and other platinum group elements (PGEs) at concentrations well above background levels. They associated these enrichments with the collision of an asteroid that injected large amounts of pulverized debris into the atmosphere, resulting in blockage of solar radiation, global cooling, and a shutdown of photosynthesis.

  3. Performance of the NOνA Data Acquisition and Trigger Systems for the full 14 kT Far Detector

    NASA Astrophysics Data System (ADS)

    Norman, A.; Davies, G. S.; Ding, P. F.; Dukes, E. C.; Duyan, H.; Frank, M. J.; R. C. Group; Habig, A.; Henderson, W.; Niner, E.; Mina, R.; Moren, A.; Mualem, L.; Oksuzian, Y.; Rebel, B.; Shanahan, P.; Sheshukov, A.; Tamsett, M.; Tomsen, K.; Vinton, L.; Wang, Z.; Zamorano, B.; Zirnstien, J.

    2015-12-01

    The NOvA experiment uses a continuous, free-running, dead-timeless data acquisition system to collect data from the 14 kT far detector. The DAQ system readouts the more than 344,000 detector channels and assembles the information into an raw unfiltered high bandwidth data stream. The NOvA trigger systems operate in parallel to the readout and asynchronously to the primary DAQ readout/event building chain. The data driven triggering systems for NOvA are unique in that they examine long contiguous time windows of the high resolution readout data and enable the detector to be sensitive to a wide range of physics interactions from those with fast, nanosecond scale signals up to processes with long delayed coincidences between hits which occur at the tens of milliseconds time scale. The trigger system is able to achieve a true 100% live time for the detector, making it sensitive to both beam spill related and off-spill physics.

  4. Impact-induced devolatilization of CaSO4 anhydrite and implications for K-T extinctions: Preliminary results

    NASA Technical Reports Server (NTRS)

    Tyburczy, James A.; Ahrens, Thomas J.

    1993-01-01

    The recent suggestions that the target area for the K-T bolide may have been a sulfate-rich evaporite and that the resulting sulfuric acid-rich aerosol was responsible for the subsequent cooling of the Earth and the resulting biological extinctions has prompted us to experimentally examine the impact-induced devolatization of the sulfate minerals anhydrite (CaSO4) and gypsum (CaSO4(2H2O)). Preliminary results for anhydrite are reported. Up to 42 GPa peak shock pressure, little or no devolatilization occurs, consistent with chemical thermodynamic calculations. Calculation of the influence of the partial pressure of the gas species on impact-induced devolatilization suggests that an even greater amount of sulfur than that proposed by Brett could have been released to the atmosphere by an impact into a sulfate-rich layer. Solid recovery, impact-induced devolatilization experiments were performed on the Caltech 20mm gun using vented, stainless steel sample assemblies.

  5. Clustering dynamics in water/methanol mixtures: a nuclear magnetic resonance study at 205 k<295 k.

    PubMed

    Corsaro, Carmelo; Spooren, Jeroen; Branca, Caterina; Leone, Nancy; Broccio, Matteo; Kim, Chansoo; Chen, Sow-Hsin; Stanley, H Eugene; Mallamace, Francesco

    2008-08-28

    Proton nuclear magnetic resonance (1H NMR) experiments have been performed to measure the spin-lattice, T1, and spin-spin, T2, relaxation times of the three functional groups in water/methanol mixtures at different methanol molar fractions (XMeOH=0, 0.04, 0.1, 0.24, 0.5, 1) as a function of temperature in the range 205 K<295 K. The measured relaxation times in the mixtures, at all the methanol molar fractions, are faster than those of pure water and methanol because of strong interactions, resulting in a complex hydrogen bonding dynamics that determines their thermodynamic properties. In particular, we observe how the interplay between hydrophobicity and hydrophilicity changes with temperature and influences the peculiar thermal behavior of the NMR relaxation times of the solution. The obtained results are interpreted in terms of the existence of stable water-methanol clusters at high temperature whereas, upon cooling to low temperature, clusters of single species are present in the mixture. PMID:18672927

  6. Cretaceous Tertiary convergence and continental collision, Sanandaj Sirjan Zone, western Iran

    NASA Astrophysics Data System (ADS)

    Mohajjel, M.; Fergusson, C. L.; Sahandi, M. R.

    2003-01-01

    The Sanandaj-Sirjan Zone contains the metamorphic core of the Zagros continental collision zone in western Iran. The zone has been subdivided into the following from southwest to northeast: an outer belt of imbricate thrust slices (radiolarite, Bisotun, ophiolite and marginal sub-zones, which consist of Mesozoic deep-marine sediments, shallow-marine carbonates, oceanic crust and volcanic arc, respectively) and an inner complexly deformed sub-zone (late Palaeozoic-Mesozoic passive margin succession). Rifting and sea-floor spreading of Tethys occurred in the Permian to Triassic but in the Sanandaj-Sirjan Zone extension-related successions are mainly of Late Triassic age. Subduction of Tethyan sea floor in the Late Jurassic to Cretaceous produced deformation, metamorphism and unconformities in the marginal and complexly deformed sub-zones. Deformation climaxed in the Late Cretaceous when a major southwest-vergent fold belt formed associated with greenschist facies metamorphism and post-dated by abundant Palaeogene granitic plutons. In the southwest of the zone a Late Cretaceous island arcpassive margin collision occurred with ophiolite emplacement onto the northern Arabian margin similar to that in Oman. Final closure of Tethys was not completed until the Miocene when Central Iran collided with the northeast Arabian margin.

  7. Cretaceous-Tertiary structural evolution of the north central Lhasa terrane, Tibet

    NASA Astrophysics Data System (ADS)

    Volkmer, John E.; Kapp, Paul; Guynn, Jerome H.; Lai, Qingzhou

    2007-12-01

    In the north central Lhasa terrane of Tibet, two distinct structural levels of an east-west striking thrust system are exposed along the north trending late Cenozoic Xiagangjiang rift. Upper Paleozoic strata deformed by the south directed Langgadong La thrust, and Cretaceous strata involved in variably north and south directed thrusting characterize these lower and upper structural levels, respectively. These two structural levels are separated by the Tagua Ri passive roof thrust. Balanced cross section restoration suggests that the thrust system accommodated 103 km (53%) shortening. The 40Ar/39Ar results, together with an interpretation of synthrust deposition of Upper Cretaceous strata, suggest that the majority of shortening occurred during the Late Cretaceous-Paleocene. Cretaceous strata lie unconformable on Permian rocks; volcanic tuffs directly above the unconformity yield U-Pb zircon ages of 131 Ma. Upper Cretaceous strata record a change from shallow marine to nonmarine deposition, indicating uplift above sea level during this time. The overall south directed vergence of the thrust belt is consistent with substantial crustal thickening in central Tibet by large-scale northward underthrusting of Lhasa terrane basement beneath the Qiantang terrane prior to the Indo-Asian collision. The documented decoupling of contractional deformation at shallow crustal levels appears to be a regional characteristic of Tibet from at least the Bangong suture in the north to the Tethyan Himalaya to the south. This style of deformation explains the absence of basement exposures and major denudation in this region despite substantial crustal shortening.

  8. Hydrogeologic characterization of the cretaceous-tertiary Coastal Plain sequence at the Savannah River Site

    SciTech Connect

    Aadland, R.K.

    1990-01-01

    Several hydrostratigraphic classification schemes have been devised to describe the hydrogeology at the Savannah River Site SRS. Central to these schemes is the one-to-one fixed relationship between the hydrostratigraphic units and the lithostratigraphic units currently favored for the Site. This fixed relationship has proven difficult to apply in studies of widely separated locations at the Site due to the various facies observed in the updip Coastal Plain sequence. A detailed analysis and synthesis of the geophysical, core, and hydrologic data available from more than 164 deep wells from 23 cluster locations both on the Site and in the surrounding region was conducted to provide the basis for a hydrostratigraphic classification scheme which could be applied to the entire SRS region. As a result, an interim hydrostratigraphic classification was developed that defines the regional hydrogeologic characteristics of the aquifers underlying the Site (Aadland et al., 1990). The hydrostratigraphic code accounts for and accommodates the rapid lateral variation in lithofacies observed in the region, and eliminates all formal'' connection between the hydrostratigraphic nomenclature and the lithostratigraphic nomenclature. The code is robust and can be made as detailed as is needed to characterize the aquifer units and aquifer zones described in Site-specific studies. 15 refs., 2 figs.

  9. Biospheric effects of volatiles produced by the Chicxulub Cretaceous/Tertiary impact

    NASA Technical Reports Server (NTRS)

    Pope, Kevin O.

    1996-01-01

    The meteorite impact that formed the Chicxulub crater 65 million years ago caused a mass extinction of life. Analyses indicate that the projectile was either a 9.4-16.8 km diameter asteroid or a 14.2-24.0 km diameter comet. We estimate that 200 gigatons each of S02 and H2O were deposited globally in the stratosphere by the impact into water saturated sulfate-rich sediments. Conversion of these gases into sulfuric acid aerosols blocked an average of 68 percent of the sun's radiation for a period of 12 years. Global average temperatures probably dropped to near freezing in 5 years and remained near or below freezing for 7 years. Greenhouse warming due to impact-generated C02 was negligible, hence global cooling from sulfates was the major cause of climate change and contributed greatly to the mass extinction.

  10. Emergence of a Rival Paradigm to Account for the Cretaceous/Tertiary Event.

    ERIC Educational Resources Information Center

    McCartney, Kevin; Loper, David E.

    1989-01-01

    Discusses the origin of the catastrophic event as to whether it was an episodic process or of extraterrestrial or endogenous origin. Develops a model of a volcanic mechanism to produce shocked quartz like those found in the Deccan basalts. (MVL)

  11. The interaction of the cretaceous-tertiary extinction bolide with the atmosphere, ocean, and solid earth

    NASA Technical Reports Server (NTRS)

    Okeefe, J. D.; Ahrens, T. J.

    1981-01-01

    A number of investigations, including those reported by Orth et al. (1981), have provided physical evidence for the impact of an extraterrestrial object on earth 65 million years ago. This time corresponds to the end of the cretaceous period. This impact could, therefore, be responsible for the observed extinction of biological species at the end of the Mesozoic era. Among the species becoming extinct are found also flying and walking dinosaurs, which include all land animals that had masses greater than 25 kg. The present investigation is concerned with a study of the possibilities for the collision of earth with 10 km-size object, and the consequences produced by such a collision. It is found that the penetration of the atmosphere by the bolide creates a temporary hole in the atmosphere. The resulting flow fields can inject melt droplets and finely commuted solid particles into the atmosphere. Short-term effects of heating, followed by dust induced worldwide cooling, may provide several mechanisms for the observed extinction of the species.

  12. Petroleum geology of Cretaceous-Tertiary rift basins in Niger, Chad, and Central African Republic

    SciTech Connect

    Genik, G.J. )

    1993-08-01

    This overview of the petroleum geology of rift basins in Niger, Chad, and Central African Republic (CAR) is based on exploration work by Exxon and partners in the years 1969-1991. The work included 50,000 km of modern reflection seismic, 53 exploration wells, 1,000,000 km[sup 2] of aeromagnetic coverage, and about 10,500 km of gravity profiles. The results outline ten Cretaceous and Tertiary rift basins, which constitute a major part of the West and Central African rift system (WCARS). The rift basins derive from a multiphased geologic history dating from the Pan-African (approximately 750-550 Ma) to the Holocene. WCARS in the study area is divided into the West African rift subsystem (WAS) and the Central African rift subsystem (WAS) and the Central African rift subsystem (CAS). WAS basins in Niger and Chad are chiefly extensional, and are filled by up to 13,000 m of Lower Cretaceous to Holocene continental and marine clastics. The basins contain five oil (19-43[degrees]API) and two oil and gas accumulations in Upper Cretaceous and Eocene sandstone reservoirs. The hydrocarbons are sourced and sealed by Upper Cretaceous and Eocene marine and lacustrine shales. The most common structural styles and hydrocarbon traps usually are associated with normal fault blocks. CAS rift basins in Chad and CAR are extensional and transtensional, and are filled by up to 7500 m of chiefly Lower Cretaceous continental clastics. The basins contain eight oil (15-39[degrees]API) and one oil and gas discovery in Lower and Upper Cretaceous sandstone reservoirs. The hydrocarbons are sourced by Lower Cretaceous shales and sealed by interbedded lacustrine and flood-plain shales. Structural styles range from simple fault blocks through complex flower structures. The main hydrocarbon traps are in contractional anticlines. Geological conditions favor the discovery of potentially commercial volumes of oil in WCARS basins, of Niger, Chad and CAR. 108 refs., 24 figs., 4 tabs.

  13. Borehole gravity surveys in the Cretaceous-Tertiary Sagavanirktok Formation, Kuparuk River oil field, Alaska

    SciTech Connect

    Beyer, L.A. )

    1990-05-01

    Detailed borehole gravity surveys (sponsored by the US Department of Energy) were made in three wells in the Kuparuk River and westernmost Prudhoe Bay oil fields, Alaska from depths as shallow as 15 m to as great as 1,340 m through permafrost and underlying heavy oil bearing sandstones of the Sagavanirktok Formation. A subbituminous coal-bearing sequence and the stability field for methane hydrate occur partly within and partly below the permafrost zone, whose base, defined by the 0{degree}C isotherm, varies from 464 to 564 m. The surveys provided accurate, large-volume estimates of in-situ bulk density from which equivalent porosity was calculated using independent grain and pore-fluid density information. This density and porosity data helped to define the rock mass properties within the hydrate stability field and the thermal conductivity, seismic character, and compaction history of the permafrost. Bulk density of the unconsolidated to poorly consolidated sections ranges mostly from 1.9 to 2.3 g/cm{sup 3}. The shallow permafrost section appears to be slightly overcompacted in comparison to similar sedimentary sequences in nonpermafrost regions. The cause of this apparent overcompaction is unknown but may be due to freeze-thaw processes that have similarly affected sea floor and surficial deposits elsewhere in the Arctic. Fluctuations of bulk density appear to be controlled principally by (1) textural variations of the sediments, possibly exaggerated locally within the permafrost zone by excess ice, (2) presence or absence of carbonaceous material, and (3) type of pore-fluid (water-ice vs. water vs. hydrocarbons). As hypothetical models predict bulk-density is slightly lower opposite one interval of possible methane hydrate. Porosity may be as high as 40-45% for selected coarser grained units within the permafrost zone, and as high as 30-35% in a series of well sorted, heavy oil-bearing sandstones.

  14. Diagenesis and reservoir characterization of the Cretaceous-Tertiary sequence, eastern Venezuela

    SciTech Connect

    Aquado, B.; Ghosh, S.; Isea, A. )

    1990-05-01

    The giant El Furrial field Maturin subbasin is the most important oil field discovered in Venezuela in the last three decades. The average oil column has a thickness of 400 m and the reservoirs consist of essentially sandy siliciclastic sediments of nearshore-shallow marine origin. The oil's API gravity ranges from light to extra heavy and occurs in a stratified manner in the reservoirs. A total of 1,080 m of core from the producing sequence was studied through x-ray diffraction scanning electron microscopy, and petrography. This data, along with petrophysical measurements, show a clear differentiation between the Upper Cretaceous and the Oligocene reservoirs. The Upper Cretaceous reservoirs are characterized by relatively fine and uniform grain size, subarkosic composition with common volcanic rock fragments, high degree of chemical and mechanical compaction highly illitic mixed-layer I/S assemblage with less than 10% expandable layers, and ubiquitous baroque dolomite. Additionally, porosity and permeability values are persistently low. Clearly, the Cretaceous sediments are diagenetically mature and may indicate diagenetic transformation at greater depths or under a different thermal regime. In contrast the coarser grained Oligocene reservoirs of quartz arenitic composition show a lesser diagenetic overprint, and greater porosity and permeability. Porosity is dominantly secondary due to cement and grain (mostly quartz) dissolution, as well as tectonically induced grain fracturing. Common kaolinite and minor amounts of I/S with up to 20% of expandable layers attest to a lower diagenetic regime than in the Cretaceous reservoirs.

  15. The interaction of the cretaceous-tertiary extinction bolide with the atmosphere, ocean, and solid earth

    NASA Astrophysics Data System (ADS)

    Okeefe, J. D.; Ahrens, T. J.

    1981-10-01

    A number of investigations, including those reported by Orth et al. (1981), have provided physical evidence for the impact of an extraterrestrial object on earth 65 million years ago. This time corresponds to the end of the cretaceous period. This impact could, therefore, be responsible for the observed extinction of biological species at the end of the Mesozoic era. Among the species becoming extinct are found also flying and walking dinosaurs, which include all land animals that had masses greater than 25 kg. The present investigation is concerned with a study of the possibilities for the collision of earth with 10 km-size object, and the consequences produced by such a collision. It is found that the penetration of the atmosphere by the bolide creates a temporary hole in the atmosphere. The resulting flow fields can inject melt droplets and finely commuted solid particles into the atmosphere. Short-term effects of heating, followed by dust induced worldwide cooling, may provide several mechanisms for the observed extinction of the species.

  16. Accelerator mass spectrometry for heavy isotopes at Oxford (OSIRIS)

    NASA Astrophysics Data System (ADS)

    Chew, S. H.; Greenway, T. J. L.; Allen, K. W.

    1984-11-01

    The isotopic ratios 194Pt/195Pt/196Pt and 193Ir/194Pt/195Pt have been measured for samples from the Cretaceous-Tertiary boundary at Stevns Klint, Dania, Nye Klv in Denmark and at Hor Har Har in Israel, for iron meteorites Odessa and Buenaventura and for the carbonaceous chondrite Allende. Determination of the indium ratio 193/191 in a standard and in a sample from the Cretaceous-Tertiary boundary at Stevns Klint has also been made. Preliminary measurements of the ratio 188Os/189Os in laboratory prepared Os samples (abundance approximately 10 ppm), in the Odessa and Allende meteorites and in the Stevns Klint Cretaceous-Tertiary boundary have been carried out. An anomalous abundance of 193Ir, 194Pt, 195Pt and 189Os at the Cretaceous-Tertiary boundary at Stevns Klint has also been established.

  17. Joint design of kT-points trajectories and RF pulses under explicit SAR and power constraints in the large flip angle regime.

    PubMed

    Gras, Vincent; Luong, Michel; Amadon, Alexis; Boulant, Nicolas

    2015-12-01

    In Magnetic Resonance Imaging at ultra-high field, kT-points radiofrequency pulses combined with parallel transmission are a promising technique to mitigate the B1 field inhomogeneity in 3D imaging applications. The optimization of the corresponding k-space trajectory for its slice-selective counterpart, i.e. the spokes method, has been shown in various studies to be very valuable but also dependent on the hardware and specific absorption rate constraints. Due to the larger number of degrees of freedom than for spokes excitations, joint design techniques based on the fine discretization (gridding) of the parameter space become hardly tractable for kT-points pulses. In this article, we thus investigate the simultaneous optimization of the 3D blipped k-space trajectory and of the kT-points RF pulses, using a magnitude least squares cost-function, with explicit constraints and in the large flip angle regime. A second-order active-set algorithm is employed due to its demonstrated success and robustness in similar problems. An analysis of global optimality and of the structure of the returned trajectories is proposed. The improvement provided by the k-space trajectory optimization is validated experimentally by measuring the flip angle on a spherical water phantom at 7T and via Quantum Process Tomography. PMID:26619073

  18. Joint design of kT-points trajectories and RF pulses under explicit SAR and power constraints in the large flip angle regime

    NASA Astrophysics Data System (ADS)

    Gras, Vincent; Luong, Michel; Amadon, Alexis; Boulant, Nicolas

    2015-12-01

    In Magnetic Resonance Imaging at ultra-high field, kT-points radiofrequency pulses combined with parallel transmission are a promising technique to mitigate the B1 field inhomogeneity in 3D imaging applications. The optimization of the corresponding k-space trajectory for its slice-selective counterpart, i.e. the spokes method, has been shown in various studies to be very valuable but also dependent on the hardware and specific absorption rate constraints. Due to the larger number of degrees of freedom than for spokes excitations, joint design techniques based on the fine discretization (gridding) of the parameter space become hardly tractable for kT-points pulses. In this article, we thus investigate the simultaneous optimization of the 3D blipped k-space trajectory and of the kT-points RF pulses, using a magnitude least squares cost-function, with explicit constraints and in the large flip angle regime. A second-order active-set algorithm is employed due to its demonstrated success and robustness in similar problems. An analysis of global optimality and of the structure of the returned trajectories is proposed. The improvement provided by the k-space trajectory optimization is validated experimentally by measuring the flip angle on a spherical water phantom at 7T and via Quantum Process Tomography.

  19. The end-cretaceous mass extinction in the marine realm: year 2000 assessment

    NASA Astrophysics Data System (ADS)

    Keller, Gerta

    2001-07-01

    The current database indicates that the terminal decline and extinction, or near extinction, of many groups commonly attributed to an asteroid or comet impact at the Cretaceous-Tertiary (K-T) boundary (e.g., ammonites, bivalves, planktic foraminifera) began during the last 500 k.y. of the Maastrichtian. By the time of the K-T boundary, extinction-prone tropical and subtropical marine faunas and floras were almost gone, or had severely reduced species populations struggling to survive. The K-T boundary kill-effect was largely restricted to these struggling tropical and subtropical populations that accounted for 2/3 of the species among planktic foraminifera, but less than 10% of the total foraminiferal population. No significant extinctions occurred among ecological generalists that dominated across latitudes. No single kill mechanism can account for this mass extinction pattern. The last 500 k.y. of the Maastrichtian were characterized by a series of rapid and extreme climate changes characterized by 3-4C warming between 65.4 and 65.2 Ma, major volcanic activity between 65.4 and 65.2 Ma, a spherule-producing event between 65.3 and 65.2 Ma, and an impact at the K-T boundary ( 65.0 Ma). All of these events caused major environmental perturbations and biotic stresses that resulted in severe reductions in species populations and extinctions that culminated at the K-T boundary. The mass extinction pattern, and the parallel environmental changes during the last 500 k.y. of the Maastrichtian, suggest that both long-term (climate, sea-level) and short-term (impact, volcanism) events contributed to the K-T boundary mass extinction.

  20. Ground boundaries

    SciTech Connect

    Balluffi, R.W.; Bristowe, P.D.

    1990-01-01

    The present document is a progress report describing the work accomplished on the study of grain boundaries in Ag, Au, Ni, Si, and Ge. Research was focused on the following four major efforts: study of the atomic structure of grain boundaries by means of x-ray diffraction, transmission electron microscopy and computer modeling; grain boundary migration; short-circuit diffusion along grain boundaries; and development of Thin-Film Deposition/Bonding Apparatus for the manufacture of high purity bicrystals. 10 refs., 1 fig.

  1. Drilling Probes Past Carbon Cycle Perturbations on the Demerara Rise

    NASA Astrophysics Data System (ADS)

    Erbacher, Jochen; Mosher, David; Malone, Mitchell

    2004-02-01

    Ocean Drilling Program (ODP) Leg 207 recently cored sediments on the Demerara Rise at ~9N in the tropical Atlantic and successfully recovered continuous records of the Paleocene/Eocene Thermal Maximum (PETM), the Cretaceous/Tertiary boundary (K/T), and Cretaceous Ocean Anoxic Events (OAEs). The Demerara Rise, north of Suriname and French Guyana, South America, is an ideal drilling target because expanded sections of Cretaceous- and Paleogene-age deep-sea sediments are shallowly buried and exist with good stratigraphic control in expanded sections. Furthermore, the northwestern escarpment of the Demerara Rise offered the possibility of recovering sediments along a paleo-depth transect. The paleogeographic position of the Demerara Rise lies within the core of the tropics in a location near the Equatorial Atlantic Gateway between South America and Africa, which is believed to have played an important role in controlling changes in global climate during the Cretaceous.

  2. Drilling probes past carbon cycle perturbations on the Demerara Rise

    NASA Astrophysics Data System (ADS)

    ODP Leg 207 Scientific Party; Erbacher, Jochen; Mosher, David; Malone, Mitchell

    2004-02-01

    Ocean Drilling Program (ODP) Leg 207 recently cored sediments on the Demerara Rise at 9N in the tropical Atlantic and successfully recovered continuous records of the Paleocene/Eocene Thermal Maximum (PETM), the Cretaceous/Tertiary boundary (K/T), and Cretaceous Ocean Anoxic Events (OAEs). The Demerara Rise, north of Suriname and French Guyana, South America, is an ideal drilling target because expanded sections of Cretaceous- and Paleogene-age deep-sea sediments are shallowly buried and exist with good stratigraphic control in expanded sections. Furthermore, the northwestern escarpment of the Demerara Rise offered the possibility of recovering sediments along a paleo-depth transect. The paleogeographic position of the Demerara Rise lies within the core of the tropics in a location near the Equatorial Atlantic Gateway between South America and Africa, which is believed to have played an important role in controlling changes in global climate during the Cretaceous.

  3. Mass extinctions in the deep sea

    NASA Technical Reports Server (NTRS)

    Thomas, E.

    1988-01-01

    The character of mass extinctions can be assessed by studying extinction patterns of organisms, the fabric of the extinction, and assessing the environmental niche and mode of life of survivors. Deep-sea benthic foraminifera have been listed as little affected by the Cretaceous-Tertiary (K-T) mass extinction, but very few quantitative data are available. New data on deep-sea Late Maestrichtian-Eocene benthic foraminifera from Maud Rise (Antractica) indicate that about 10 percent of the species living at depths of 2000 to 2500 m had last appearances within 1 my of the Cretaceous-Tertiary (K-T) boundary, versus about 25 percent of species at 1000 to 1500 m. Many survivors from the Cretaceous became extinct in a period of global deep-sea benthic foraminiferal extinction at the end of the Paleocene, a time otherwise marked by very few extinctions. Preliminary conclusions suggest that the deep oceanic environment is essentially decoupled from the shallow marine and terrestrial environment, and that even major disturbances of one of these will not greatly affect the other. This gives deep-sea benthic faunas a good opportunity to recolonize shallow environments from greater depths and vice versa after massive extinctions. The decoupling means that data on deep-sea benthic boundary was caused by the environmental effects of asteriod impact or excessive volcanism. The benthic foraminiferal data strongly suggest, however, that the environmental results were strongest at the Earth's surface, and that there was no major disturbance of the deep ocean; this pattern might result both from excessive volcanism and from an impact on land.

  4. Boundary Layer

    NASA Technical Reports Server (NTRS)

    Loitsianskii. L. G.

    1956-01-01

    The fundamental, practically the most important branch of the modern mechanics of a viscous fluid or a gas, is that branch which concerns itself with the study of the boundary layer. The presence of a boundary layer accounts for the origin of the resistance and lift force, the breakdown of the smooth flow about bodies, and other phenomena that are associated with the motion of a body in a real fluid. The concept of boundary layer was clearly formulated by the founder of aerodynamics, N. E. Joukowsky, in his well-known work "On the Form of Ships" published as early as 1890. In his book "Theoretical Foundations of Air Navigation," Joukowsky gave an account of the most important properties of the boundary layer and pointed out the part played by it in the production of the resistance of bodies to motion. The fundamental differential equations of the motion of a fluid in a laminar boundary layer were given by Prandtl in 1904; the first solutions of these equations date from 1907 to 1910. As regards the turbulent boundary layer, there does not exist even to this day any rigorous formulation of this problem because there is no closed system of equations for the turbulent motion of a fluid. Soviet scientists have done much toward developing a general theory of the boundary layer, and in that branch of the theory which is of greatest practical importance at the present time, namely the study of the boundary layer at large velocities of the body in a compressed gas, the efforts of the scientists of our country have borne fruit in the creation of a new theory which leaves far behind all that has been done previously in this direction. We shall herein enumerate the most important results by Soviet scientists in the development of the theory of the boundary layer.

  5. Fingerprinting the K/T impact site and determining the time of impact by U-Pb dating of single shocked zircons from distal ejecta

    NASA Technical Reports Server (NTRS)

    Krogh, T. E.; Kamo, S. L.; Bohor, B. F.

    1993-01-01

    U-Pb isotopic dating of single 1 - 3 micrograms zircons from K/T distal ejecta from a site in the Raton Basin, Colorado provides a powerful new tool with which to determine both the time of the impact event and the age of the basement at the impact site. Data for the least shocked zircons are slightly displaced from the 544 +/- 5 Ma primary age for a component of the target site, while those for highly shocked and granular grains are strongly displaced towards the time of impact at 65.5 +/- 3.0 Ma. Such shocked and granular zircons have never been reported from any source, including explosive volcanic rocks. Zircon is refractory and has one of the highest thermal blocking temperatures; hence, it can record both shock features and primary and secondary ages without modification by post-crystallization processes. Unlike shocked quartz, which can come from almost anywhere on the Earth's crust, shocked zircons can be shown to come from a specific site because basement ages vary on the scale of meters to kilometers. With U-Pb zircon dating, it is now possible to correlate ejecta layers derived from the same target site, test the single versus multiple impact hypothesis, and identify the target source of impact ejecta. The ages obtained in this study indicate that the Manson impact site, Iowa, which has basement rocks that are mid-Proterozoic in age, cannot be the source of K/T distal ejecta. The K/T distal ejecta probably originated from a single impact site because most grains have the same primary age.

  6. Fingerprinting the K/T impact site and determining the time of impact by UPb dating of single shocked zircons from distal ejecta

    USGS Publications Warehouse

    Krogh, T.E.; Kamo, S.L.; Bohor, B.F.

    1993-01-01

    UPb isotopic dating of single 1-3 ??g zircons from K/T distal ejecta from a site in the Raton Basin, Colorado provides a powerful new tool with which to determine both the time of the impact event and the age of the basement at the impact site. Data for the least shocked zircons are slightly displaced from the 544 ?? 5 Ma primary age for a component of the target site, white those for highly shocked and granular grains are strongly displaced towards the time of impact at 65.5 ?? 3.0 Ma. Such shocked and granular zircons have never been reported from any source, including explosive volcanic rocks. Zircon is refractory and has one of the highest thermal blocking temperatures; hence, it can record both shock features and primary and secondary ages without modification by post-crystallization processes. Unlike shocked quartz, which can come from almost anywhere on the Earth's crust, shocked zircons can be shown to come from a specific site because basement ages vary on the scale of meters to kilometers. With UPb zircon dating, it is now possible to correlate ejecta layers derived from the same target site, test the single versus multiple impact hypothesis, and identify the target source of impact ejecta. The ages obtained in this study indicate that the Manson impact site, Iowa, which has basement rocks that are mid-Proterozoic in age, cannot be the source of K/T distal ejecta. The K/T distal ejecta probably originated from a single impact site because most grains have the same primary age. ?? 1993.

  7. Fossil gap analysis supports early Tertiary origin of trophically diverse avian orders

    NASA Astrophysics Data System (ADS)

    Bleiweiss, Robert

    1998-04-01

    Recent molecular studies have cited the general incompleteness of the fossil record to support claims that most extant avian orders diverged in the mid-Cretaceous, some 40 m.y. before their first fossil appearances in the early Cenozoic. To evaluate these assertions, I used gap analysis to estimate confidence intervals for the beginnings of the observed stratigraphic ranges for the related extant avian orders Strigiformes (owls), Caprimulgiformes (goatsuckers), and Apodiformes (swifts, hummingbirds), and for the origin of the common ancestor to this larger megaclade. Ninety-five percent confidence intervals for the origins of these groups extend no more than 2 m.y. before the Cretaceous-Tertiary (K-T) boundary and are contained within the Paleocene for strigiforms, apodiforms, and the common ancestor to the megaclade. The confidence level that these orders diverged from a common ancestor after the K-T boundary exceeds 99%. Thus, the quality of the fossil record is consistent with the classical view that trophically diverse extant bird orders arose and diversified rapidly following the widespread extinction of other terrestrial groups at the K-T boundary.

  8. The generation of tens kT magnetic fields by transport instability of laser generated electrons in a near critical preformed plasma

    NASA Astrophysics Data System (ADS)

    Toncian, Toma; Hegelich, Bjorn Manuel; Willi, Oswald; Lehmann, Goetz

    2014-10-01

    First direct measurements of the electron transport along extended wire targets by Quinn et al. [PRL 102 (2009)] revealed a charging current and associated magnetic field moving close to the speed of light away from focal volume of the employed heating laser. The motion of the electrons is bound electrostatic to the proximity of the solid. A return current compensating the escaping charge is formed at the surface of the solid, the overall current loop sustaining kT magnetic fields, with traversal decay lengths of ?m. In our study we show by means of numerical 2 dimensional particle in cell simulations that the motion of the hot electrons and dynamic of the charge compensating return current can be dramatically affected by a preformed ?m scale length plasma gradient on the solid surface. In particularly the two velocities distribution and two antiparallel currents developing in the near critical plasma are unstable in respect of two stream and Kevin Helmholtz instability. The particle motion becomes locally magnetized resulting in current eddies trapping particles and localized magnetic and electric fields with values of tens of kT and TV/m sustained on ?m scales and with characteristic decay times of ps.

  9. Iridium abundance measurements across bio-event horizons in the geological record

    NASA Technical Reports Server (NTRS)

    Orth, C. J.; Attrep, M., Jr.

    1988-01-01

    Geochemical studies have been performed on thousands of rock samples collected across bio-event horizons in the fossil record using INAA for about 40 common and trace elements and radiochemical isolation procedures for Os, Ir, Pt, and Au on selected samples. These studies were begun soon after the Alvarez team announced their discovery of the Cretaceous-Tertiary (K-T) Ir anomaly in marine rock sequences in Europe. With their encouragement the Authors searched for the anomaly in nearby continental (freshwater coal swamp) deposits. In collaboration with scientists from the U.S.G.S. in Denver, the anomaly was located and it was observed that a floral crisis occurred at the same stratigraphic position as the Ir spike. Further work in the Raton Basin has turned up numerous well-preserved K-T boundary sections. Although the Authors have continued to study the K-T boundary and provide geochemical measurements for other groups trying to precisely locate it, the primary effort was turned to examining the other bio-events in the Phanerozoic, especially to those that are older than the terminal Cretaceous. A list of horizons that were examined in collaboration with paleontologists and geologists is given. Results are also given and discussed.

  10. Complete mitochondrial DNA genome sequences show that modern birds are not descended from transitional shorebirds.

    PubMed Central

    Paton, Tara; Haddrath, Oliver; Baker, Allan J

    2002-01-01

    To test the hypothesis put forward by Feduccia of the origin of modern birds from transitional birds, we sequenced the first two complete mitochondrial genomes of shorebirds (ruddy turnstone and blackish oystercatcher) and compared their sequences with those of already published avian genomes. When corrected for rate heterogeneity across sites and non-homogeneous nucleotide compositions among lineages in maximum likelihood (ML), the optimal tree places palaeognath birds as sister to the neognaths including shorebirds. This optimal topology is a re-rooting of recently published ordinal-level avian trees derived from mitochondrial sequences. Using a penalized likelihood (PL) rate-smoothing process in conjunction with dates estimated from fossils, we show that the basal splits in the bird tree are much older than the Cretaceous-Tertiary (K-T) boundary, reinforcing previous molecular studies that rejected the derivation of modern birds from transitional shorebirds. Our mean estimate for the origin of modern birds at about 123 million years ago (Myr ago) is quite close to recent estimates using both nuclear and mitochondrial genes, and supports theories of continental break-up as a driving force in avian diversification. Not only did many modern orders of birds originate well before the K-T boundary, but the radiation of major clades occurred over an extended period of at least 40 Myr ago, thus also falsifying Feduccia's rapid radiation scenario following a K-T bottleneck. PMID:11958716

  11. Effect of environmental variables on body size evolution of crinoids between periods of mass extinctions

    NASA Astrophysics Data System (ADS)

    Jani, T.; Heim, N. A.; Payne, J.

    2013-12-01

    Body size plays a major role in determining whether or not an organism can sustain in its local environment. The ecosystem of an animal has a major effect on the fitness of organisms, and it would be interesting to note the degree to which various environmental factors alter body size. In my project, I identify three environmental factors that seem to affect body size of crinoids, marine invertebrates from phylum Echinodermata, and explore how these variables play out in the intervals between the five mass extinctions. The particular factors I study include atmospheric CO2 concentration (proxy for temperature), O2 concentration, and sea level. Although the r and p values for all of these factors were statistically insignificant to definitively make any correlation, there was a visual correlation. For O2, I noted a generally positive correlation with body size over time. CO2 trends suggested a negative correlation until the K-T boundary, but a positive correlation afterwards. Correlation with sea level was a little more complicated: correlation was positive from the start of the Phanerozoic to the Permian extinction; it turned negative until the Cretaceous-Tertiary boundary; afterwards, it again became positive. However, for all three variables, statistical values are too low to say definitively mark any correlation. Out of all three factors, CO2 levels had the highest correlation and lowest p-values in the most time intervals: from the start of the Phanerozoic to Ordovician-Silurian Extinction, from the Late Devonian to the Permian Extinction, and from the Cretaceous-Tertiary boundary to the present. When considering first differences, CO2 levels also had the highest correlation from the Permian Extinction to Triassic-Jurassic Extinction and from the Triassic-Jurassic Extinction to Cretaceous-Tertiary Extinction. Using PaleoTS, I found that body size evolution patterns either seemed to follow either an unbiased random walk (URW) or stasis in the intervals between mass extinctions. Put together, these results suggest that environmental factors may have an effect of body size, but it may be the consequence of several environmental factors in conjunction. That is a correlation between body size and an individual environmental factor is hard to determine, but several biotic and abiotic factors may work interdependently to alter body size of crinoids.

  12. Boundary issues

    NASA Astrophysics Data System (ADS)

    Townsend, Alan R.; Porder, Stephen

    2011-03-01

    What is our point of no return? Caesar proclaimed 'the die is cast' while crossing the Rubicon, but rarely does modern society find so visible a threshold in our continued degradation of ecosystems and the services they provide. Humans have always used their surroundings to make a living— sometimes successfully, sometimes not (Diamond 2005)—and we intuitively know that there are boundaries to our exploitation. But defining these boundaries has been a challenge since Malthus first prophesied that nature would limit the human population (Malthus 1798). In 2009, Rockström and colleagues tried to quantify what the 6.8 billion (and counting) of us could continue to get away with, and what we couldn't (Rockström et al 2009). In selecting ten 'planetary boundaries', the authors contend that a sustainable human enterprise requires treating a number of environmental thresholds as points of no return. They suggest we breach these Rubicons at our own peril, and that we've already crossed three: biodiversity loss, atmospheric CO2, and disruption of the global nitrogen (N) cycle. As they clearly hoped, the very act of setting targets has provoked scientific inquiry about their accuracy, and about the value of hard targets in the first place (Schlesinger 2009). Such debate is a good thing. Despite recent emphasis on the science of human-ecosystem interactions, understanding of our planetary boundaries is still in its infancy, and controversy can speed scientific progress (Engelhardt and Caplan 1987). A few weeks ago in this journal, Carpenter and Bennett (2011) took aim at one of the more controversial boundaries in the Rockström analysis: that for human alteration of the global phosphorus (P) cycle. Rockström's group chose riverine P export as the key indicator, suggesting that humans should not exceed a value that could trigger widespread marine anoxic events—and asserting that we have not yet crossed this threshold. There are defensible reasons for a marine-centric boundary (Filippelli 2008, Handoh and Lenton 2003). However, human alteration of the P cycle has multiple potential boundaries (figure 1), including P-driven freshwater eutrophication (Smith and Schindler 2009), the potential for world P supply to place an ultimate limit on food production (Smil 2000, Childers et al 2011), and depletion of soil P stocks in some world regions (MacDonald et al 2011). Carpenter and Bennett revisit the P boundary from the freshwater eutrophication perspective. Given the extraordinary variation in freshwater ecosystems across the globe, this is a challenging task, but the authors strengthen their analysis by using three different boundaries with relevance to eutrophication, along with two water quality targets and a range of estimates of P flow to the sea. In doing so, they make a compelling case that if freshwater eutrophication is indeed a Rubicon, we have already crossed it. Importantly, Carpenter and Bennett go beyond the calculation of new boundaries to make broader points about humanity's relationship with the P cycle. Disruptions of both the P and N cycles are mostly about our need for food (Galloway et al 2008, Cordell et al 2009), but unlike N, P supplies are finite and irreplaceable. Environmental concerns aside, we can fix all the N2 from the atmosphere we want—but deplete our economically viable P reserves and we're in trouble. Figure 1 Figure 1. Human alteration of the global P cycle has multiple possible boundaries. These include the environmental risks posed by freshwater eutrophication and marine anoxic events, and the food security risks that come from depletion of soil P stocks in some world regions, as well as finite global supplies of high-value mineral P reserves. Photo credits beyond authors: upper left, Shelby Riskin; upper right, Pedro Sanchez. In effect, Carpenter and Bennett argue that among P's multiple boundaries, the one for freshwaters is less forgiving of our current activities (but no less important) than is the one for oceans. Encouragingly, while they argue that we've already crossed one key boundary in the P cycle, they also suggest it's not a Rubicon moment. The inefficiencies in P use that motivate these boundary debates are also clear targets for improvement, and some world regions may be on a trajectory towards greater P use efficiency (Vitousek et al 2009). This is a critical step for society, because even absent concerns over freshwater eutrophication or marine anoxic events, accelerating rates of P mining and inefficiencies in agricultural P use would still pose very real threats. There is legitimate debate over when readily accessible P reserves may run out (Cordell et al 2009, Van Kauenbergh 2010), but nobody argues with their finite nature. Sooner or later, we will be forced to keep P out of our waterways, if only because we will have to keep it on our farms. Without such a shift, we may face severe P constraints to food security within just a few human generations. As current P reserves decline, rising economic values of low concentration P stores may catalyze their harvest, but without considerable policy interventions, that price hike would exacerbate already strong global inequities in the distribution and use of chemical fertilizers (Sanchez and Swaminathan 2005). The harvest of low concentration P reserves would also create substantial collateral damage to the surrounding environment. Furthermore, even without exhaustion of high-concentration P reserves, their location in only a few countries creates geopolitical risks from the demand for an increasingly valuable resource (Cordell et al 2009). Policies aimed at lowering P inputs to aquatic environments will not only reduce the eutrophication risks explored by Carpenter and Bennett, they will increase P retention in agricultural landscapes and slow the decline of finite P reserves. Shifts in human diets can also make a profound difference in the amount of P (and N) required to meet caloric needs. Society can (and ultimately must) learn to capture and re-use P in human and animal wastes. And, as Carpenter and Bennett highlight, inequities in P availability across world regions are not just a problem, they are an opportunity: transfers from P-rich to P-poor regions could simultaneously reduce environmental and food security risks. Above all, Carpenter and Bennett's analyses highlight the need for new management strategies that better target not only P's environmental risks, but also recognize the element's standing as an irreplaceable resource. Human society has been built from the massive alteration of four global biogeochemical cycles (C, N, H2O and P). We can replace carbon-based fuels, plant legumes in lieu of Haber-Bosch-based N fixation, and the rain will still fall. But for P, there is neither substitute nor renewal. Without an almost closed loop between fertilizer application, food consumption, and waste management, society could solve the remainder of the environmental threats Rockström and colleagues identify, and still be facing a bleak future. References Carpenter S R and Bennett E M 2011 Reconsideration of the planetary boundary for phosphorus Environ. Res. Lett. 6 014009 Childers C L, Corman J, Edwards M and Elser J J 2011 Sustainability challenges of phosphorus and food: solutions from closing the human phosphorus cycle BioScience 61 117-24 Cordell D, Drangert J-O and White S 2009 The story of phosphorus: Global food security and food for thought global Environmental Change 19 292-305 Diamond J 2005 Collapse: How Societies Choose to Fail or Succeed (New York: Viking) Engelhardt H T and Caplan A L (ed) 1987 Scientific Controversies: Case Studies in the Resolution and Closure of Disputes in Science and Technology (New York: Cambridge University Press) Filippelli G M 2008 The global phosphorus cycle: Past, present, and future Elements 4 89-95 Galloway J N, Townsend A R, Erisman J W, Bekunda M, Cai Z C, Freney J R, Martinelli L A, Seitzinger S P and Sutton M A 2008 Transformation of the nitrogen cycle: Recent trends, questions, and potential solutions Science 320 889-92 Handoh I C and Lenton T M 2003 Periodic mid-Cretaceous oceanic anoxic events linked by oscillations of the phosphorus and oxygen biogeochemical cycles global Biogeochemical Cycles 17 1092 MacDonald G K, Bennett E M, Potter P A and Ramankutty N 2011 Agronomic phosphorus imbalances across the world_s croplands Proc. Natl Acad. Sci. 108 3086-91 Malthus T 1798 An Essay on the Principle of Population (available at http://www.gutenberg.org/browse/authors/m\\#a1411 Smil V 2000 Phosphorus in the environment: Natural flows and human interferences Annu. Rev. Energy Environ. 25 53-88 Rockström J et al 2009 A safe operating space for humanity Nature 461 472-5 Sanchez P A and Swaminathan M S 2005 Cutting world hunger in half Science 307 357-9 Schlesinger W H 2009 Planetary boundaries: Thresholds risk prolonged degradation Nature Reports Climate Change doi:10.1038/climate.2009.93 Smith V H and Schindler D W 2009 Eutrophication science: where do we go from here? Trends in Ecology and Evolution 24 201-7 Van Kauenbergh S J 2010 World Phosphate Rock Reserves and Resources (Muscle Shoals, AL: International Fertilizer Development Center) Vitousek P M, Naylor R, Crews T, David M B, Drinkwater L E, Holland E, Johnes P J, Katzenberger J, Martinelli L A, Matson P A, Nziguheba G, Ojima D, Palm C A, Robertson G P, Sanchez P A, Townsend A R, Zhang F S 2009 Nutrient Imbalances in Agricultural Development Science 324 1519-20

  13. Comet impacts and chemical evolution on the bombarded earth

    NASA Technical Reports Server (NTRS)

    Oberbeck, Verne R.; Aggarwal, Hans

    1992-01-01

    Amino acids yields for previously published shock tube experiments are used with minimum Cretaceous-Tertiary (K/T) impactor mass and comet composition to predict AIB amino acid K/T boundary sediment column density. The inferred initial concentration of all amino acids in the K/T sea and in similar primordial seas just after 10 km comet impacts would have been at least 10 exp -7 M. However, sinks for amino acids must also be considered in calculating amino acid concentrations after comet impacts and in assessing the contribution of comets to the origin of life. The changing concentration of cometary amino acids due to ultraviolet light is compared with the equilibrium concentration of amino acids produced in the sea from corona discharge in the atmosphere, deposition in water, and degradation by ultraviolet light. Comets could have been more important than endogenous agents for initial evolution of amino acids. Sites favorable for chemical evolution of amino acids are examined, and it is concluded that chemical evolution could have occurred at or above the surface even during periods of intense bombardment of earth before 3.8 billion years ago.

  14. A Method to Obtain a Maxwell-Boltzmann Neutron Spectrum at kT = 30 keV for Nuclear Astrophysics Studies

    NASA Astrophysics Data System (ADS)

    Praena, J.; Mastinu, P. F.; Hernndez, G. Martn

    2009-09-01

    A method to shape the neutron energy spectrum at low-energy accelerators is proposed by modification of the initial proton energy distribution. A first application to the superconductive RFQ of the SPES project at Laboratori Nazionali di Legnaro is investigated for the production of a Maxwell-Boltzmann neutron spectrum at kT = 30 keV via the 7Li(p, n)7Be reaction. Concept, solutions and calculations for a setup consisting of a proton energy shaper and a lithium target are presented. It is found that a power dentisity of 3 kW cm-2 could be sustained by the lithium target and a forward-directed neutron flux higher than 1010 s-1 at the sample position could be obtained. In the framework of the SPES project the construction of a LEgnaro NeutrOn Source (LENOS) for Astrophysics and for validation of integral nuclear data is proposed, suited for activation studies on stable and unstable isotopes.

  15. A method to obtain a Maxwell-Boltzmann neutron spectrum at kT=30 keV for nuclear astrophysics studies

    NASA Astrophysics Data System (ADS)

    Mastinu, P. F.; Martn Hernndez, G.; Praena, J.

    2009-04-01

    A method based on shaping the proton beam energy in order to shape the neutron beam energy to a desired form for accelerator-based neutron sources is proposed. An application to a superconductive RFQ proton accelerator of 5 MeV and 50 mA for the production of a stellar neutron spectrum at thermal energy equal to 30 keV using the 7Li(p,n)7Be reaction is investigated. The chosen energy beam shaper is a carbon foil which shapes the quasi-monochromatic proton beam to a quasi-Gaussian distribution: after the carbon foil, the beam is still shaped by chopping the Gaussian distribution at the reaction energy threshold. The obtained proton beam is impinged in a metallic lithium target. The concepts of the energy shaper, the proposed lithium target and the calculations performed to remove their power load are presented. Calculations show that a power density of 3 kW/cm2 can be sustained by the target which produces a forward-directed neutron source of 7.31010 neutrons/s. The obtained neutron spectrum resembles a Maxwell-Boltzmann distribution at kT=30 keV with a coefficient of determination of 0.997. The method is intended to be applied in activation analysis for measuring the Maxwellian-averaged neutron capture cross-section of elements of interest for astrophysics and validation of integral neutron data in the epithermal energy range.

  16. The Yukon Flats Cretaceous(?)-Tertiary Extensional Basin, East-Central Alaska: Burial and Thermal History Modeling

    USGS Publications Warehouse

    Rowan, Elisabeth L.; Stanley, Richard G.

    2008-01-01

    One-dimensional burial and thermal history modeling of the Yukon Flats basin, east-central Alaska, was conducted as part of an assessment of the region's undiscovered oil and gas resources. No deep exploratory wells have been drilled in the Yukon Flats region, and the subsurface geology of the basin is inferred from seismic reflection, gravity and magnetic surveys, and studies of shallow core holes in the basin and outcrops in the surrounding region. A thick sequence of Upper Cretaceous(?) and Cenozoic nonmarine sedimentary rocks is believed to fill the basin; coal and organic-rich mudstone and shale within this sequence represent potential hydrocarbon source rocks. The burial and thermal history models presented here represent the sole source of information on the thermal maturity of these potential source rocks at depth. We present four alternative burial history scenarios for a hypothetical well through the deepest portion of Yukon Flats basin. They differ from each other in the thicknesses of Upper Cretaceous and Cenozoic strata, the timing of initial basin subsidence, and the timing of inferred unconformities. The burial modeling results suggest a present-day depth to the oil window of approximately 6,000 feet.

  17. PTt path in metamorphic rocks of the Khoy region (northwest Iran) and their tectonic significance for Cretaceous Tertiary continental collision

    NASA Astrophysics Data System (ADS)

    Azizi, H.; Moinevaziri, H.; Mohajjel, M.; Yagobpoor, A.

    2006-06-01

    Metamorphic rocks in the Khoy region are exposed between obducted ophiolites to the southwest and sedimentary rocks of Precambrian-Paleozoic age to the northeast. The Qom formation (Oligocene-Miocene) with a basal conglomerate transgressively overlies all of these rocks. The metamorphic rocks consist of both metasediments and metabasites. The metasediments are micaschist, garnet-staurolite schist and garnet-staurolite sillimanite schist with some meta-arkose, marble and quartzite. The metabasites are metamorphosed to greenschist and amphibolite facies from a basaltic and gabbroic protolith of tholeiitic and calc-alkaline rocks. Geothermobarometry based on the equivalence of minerals stability and their paragenesis in these rocks and microprobe analyses by several different methods indicate that metamorphism occurred in a temperature range between 450 and 680 °C at 5.5 and 7.5 kb pressure. Rims of minerals reveal a considerable decrease of pressure (<2 kb) and insignificant decrease of temperature. The PTt path of this metamorphism is normal. The MFG line passes above the triple junction of Al 2SiO 5 polymorphs, and the average geothermal gradient during metamorphism was from 27 to 37 °C/km, which is more concordant with the temperature regime of collision zones. We infer that crustal thickening during post-Cretaceous (possibly Eocene) collision of the Arabian plate and the Azerbaijan-Albourz block was the main factor that caused the metamorphism in the studied area.

  18. Thermochronology and tectonics of the Central and Western Cordilleras of Colombia: Early Cretaceous-Tertiary evolution of the Northern Andes

    NASA Astrophysics Data System (ADS)

    Villagmez, Diego; Spikings, Richard

    2013-02-01

    New thermochronological data record a complex cooling history in the Central and Western Cordilleras of Colombia that is a function of Early Cretaceous to late Miocene tectonic events. Alkali-feldspar 40Ar/39Ar cooling ages of ~ 138-130 Ma immediately post-date the cessation of Jurassic arc-magmatism and a major unconformity within the retro-foreland region of the northern Andes. We interpret these ages as cooling driven by exhumation in response to either compression driven by subduction of a seamount, or extension and oceanward migration of the slab during the earliest Cretaceous, giving rise to the Lower Cretaceous Quebradagrande arc sequence. Biotite and alkali-feldspar 40Ar/39Ar data from the palaeocontinental margin reveal the presence of a younger cooling event at 117-107 Ma, which was contemporaneous with hornblende 40Ar/39Ar cooling ages obtained from medium-high P-T metamorphic relicts of a Late Jurassic-Early Cretaceous subduction channel. This cooling event is attributed to exhumation driven by the collision and accretion of a fringing arc against the continental margin, and obduction of the subduction channel onto the forearc. Inverse modelling of zircon and apatite fission track and (U-Th)/He data from throughout the Central and Western Cordilleras reveals three periods of rapid cooling since the Late Cretaceous. The earliest phase is recorded by Jurassic and Cretaceous granitoids that cooled rapidly during 75-65 Ma. We attribute cooling to exhumation of the continental margin during ~ 75-70 Ma (~ 1.6 km/My), which was forced by the collision and accretion of the Caribbean Large Igneous Province in the Campanian. The Central Cordillera exhumed at moderate rates of ~ 0.3 km/My during ~ 45-30 Ma, which are also observed over widely dispersed regions along the Andean chain, and were probably caused by an increase in continent-ocean plate convergence rates. Exhumation rates drastically increased in the middle-late Miocene, with the greatest amount occurring in southern Colombia as a consequence of the collision and subduction of the buoyant Carnegie Ridge at 15 Ma.

  19. Cretaceous-Tertiary paleobathymetry of Labrador and Baffin shelves, and its significance to evolution of Labrador Sea

    SciTech Connect

    Helenes, J.; Gradstein, F.

    1988-03-01

    The integrated micropaleontological and palynological analyses of 17 wells from offshore Labrador and southern Baffin Island allowed consistent assignments of biozones, ages, and depositional environments to the sections. Resolution attained is approximately at the stage level or finer. Interpretation of the foraminifera and palynomorphs from the Labrador Shelf indicates that the depositional environments were mainly neritic during the Early and early Late Cretaceous, changed to bathyal during the Maastrichtian to late Eocene, and returned to neritic during the Oligocene to Miocene. The sections drilled on the Baffin Shelf do not include Cretaceous sediments, but indicate bathyal environments from Paleocene to early Eocene, and neritic to nonmarine environments from late Eocene to Miocene. The Barremian to Campanian continental to neritic sediments from the Labrador Shelf correspond to the initial rifting phase of the Labrador-Greenland continental plate; whereas the Maastrichtian to late Eocene bathyal sediments correspond to the opening of the southern part of the Labrador Sea with the creation of oceanic crust. The Labrador Sea reached the Baffin shelf area during the Maastrichtian. The Oligocene to Miocene neritic to continental sediments of both the Labrador and Baffin Shelf areas correspond to the filling phase of the basin, with resulting buildup of the continental shelves and slopes.

  20. Impact production of CO2 by the Cretaceous/Tertiary extinction bolide and the resultant heating of the earth

    NASA Technical Reports Server (NTRS)

    O'Keefe, John D.; Ahrens, Thomas J.

    1989-01-01

    Various observations and data demonstrate that sea level at the end of the Cretaceous was 150-200 m higher than at present, suggesting the possibility that the extinction bolide struck a shallow marine carbonate-rich sedimentary section. It is shown here that the impact of such a bolide (about 5 km in radius) onto a carbonate-rich terrane would increase the CO2 content of the atmosphere by a factor of two to ten. Additional dissolution of CO2 from the ocean's photic zone could release much larger quantities of CO2. The impact-induced release of CO2, by itself, would enhance atmospheric greenhouse heating and give rise to a worldwide increase in temperature from 2 K to 10 K for periods of 10,000 to 100,000 years.

  1. Manson impact structure, Iowa: First geochemical results for drill core M-1

    NASA Technical Reports Server (NTRS)

    Koeberl, Christian; Anderson, Raymond R.; Hartung, Jack B.; Reimold, Wolf Uwe

    1993-01-01

    The Manson Impact Structure is a large complex impact crater centered ca. S km north of the town of Manson, Iowa. It is the largest intact impact structure recognized in the United States (35 km in diameter). Its Ar-40/Ar-39 age is indistinguishable from that of the Cretaceous-Tertiary (K-T) boundary. The Manson structure may be one element of the events at the K-T boundary. The crater is completely covered by Quaternary glacial sedimentary deposits that are normally underlain by Cretaceous clastic sediments and flat-lying carbonate sediments of Phanerozoic age, as well as Proterozoic red clastic, metamorphic, volcanic, and plutonic rock sequences. The study of a reflection seismic profile, provided by Amoco, was critical in interpreting the structure. In the 35 km diameter zone that marks the extension of the crater the normal rock sequence is disturbed due to the impact, and at the center of the structure granitic basement rocks are present that have been uplifted from about 4 km depth. Our studies consist of detailed petrological and geochemical characterization of all cores, with emphasis on a detailed description of all rock types found in the core samples and their relationship to target rocks. Geochemical data on samples from the Manson M-1 core are presented.

  2. Projectile-target mixing in melted ejecta formed during a hypervelocity impact cratering event

    NASA Technical Reports Server (NTRS)

    Evans, Noreen Joyce; Ahrens, Thomas J.; Shahinpoor, M.; Anderson, W. W.

    1993-01-01

    Tektites contain little to no projectile contamination while, in contrast, some distal ejecta deposits can be relatively projectile-rich (e.g. the Cretaceous-Tertiary (K-T) boundary clay). This compositional difference motivated an experimental study of hypervelocity target-projectile mixing processes. We hope to scale up the results from these experiments and apply them to terrestrial impact structures like the Chicxulub Crater, Yucutan, Mexico, the leading contender as the site for the impact that caused the mass extinction that marks the K-T boundary. Shock decomposition of the approximately 500m thickness of anhydrite, or greater thickness of limestone, in the target rocks at Chicxulub may have been a critical mechanism for either global cooling via SO3, and subsequently H2SO4, formation, or possibly, global warming via increased CO2 formation. Understanding target-projectile mixing processes during hypervelocity impact may permit more accurate estimates of the amount of potentially toxic, target-derived material reaching stratospheric heights.

  3. A Model of the Chicxulub Impact Basin Based on Evaluation of Geophysical Data, Well Logs, and Drill Core Samples

    NASA Technical Reports Server (NTRS)

    Sharpton, Virgil L.; Marin, Luis E.; Carney, John D.; Lee, Scott; Ryder, Graham; Schuraytz, Benjamin C.; Sikora, Paul; Spudis, Paul D.

    1996-01-01

    Abundant evidence now shows that the buried Chicxulub structure in northern Yucatan, Mexico, is indeed the intensely sought-after source of the ejecta found world-wide at the Cretaceous-Tertiary (K/T) boundary. In addition to large-scale concentric patterns in gravity and magnetic data over the structure, recent analyses of drill-core samples reveal a lithological assemblage similar to that observed at other terrestrial craters. This assemblage comprises suevite breccias, ejecta deposit breccias (Bunte Breccia equivalents), fine-grained impact melt rocks, and melt-matrix breccias. All these impact-produced lithologies contain diagnostic evidence of shock metamorphism, including planar deformation features in quartz, feldspar, and zircons; diaplectic glasses of quartz and feldspar; and fused mineral melts and whole-rock melts. In addition, elevated concentrations of Ir, Re, and Os, in meteoritic relative proportions, have been detected in some melt-rock samples from the center of the structure. Isotopic analyses, magnetization of melt-rock samples, and local stratigraphic constraints identify this crater as the source of K/T boundary deposits.

  4. Biodiversity changes in Cretaceous palynofloras of eastern Asia and western North America

    NASA Astrophysics Data System (ADS)

    Nichols, D. J.

    2003-06-01

    Palynology has great potential for providing comparative data and interpretations about changes in biodiversity during the Cretaceous Period. This is especially true for both eastern Asia and western North America because of strong floristic similarities that existed between these regions during Cretaceous time. Also, because palynomorphs of terrestrial origin can be deposited in offshore as well as terrestrial environments, significant potential exists for marine-to-continental palynostratigraphic correlations in both regions. Palynological biostratigraphy can improve the geologic dating of changes in biodiversity. During the Early Cretaceous, eastern Asia and western North America lay within the Cerebropollenites palynofloral province, a circumpolar phytogeographic zone characterized by distinctive palynological assemblages. During most of the Late Cretaceous, these regions lay within the palynofloristically unique Aquilapollenites Province, which was more restricted geographically than the Cerebropollenites Province. The most important development during Cretaceous time that is reflected in palynological assemblages was the rise of the angiosperms as the numerically and ecologically dominant forms of vegetation. The most striking short-term palynofloral event in the two regions was the sudden disappearance of species of Aquilapollenites and associated genera at the Cretaceous-Tertiary (K/T) boundary. Both of these occurrences produced major changes in biodiversity in the terrestrial realm. Geologic research in International Geological Correlation Program Project 434 can benefit from applications of palynostratigraphy. Palynologic research within Project 434 could include development of a comprehensive palynostratigraphic zonation for the Cretaceous, the definition of regional palynostratigraphic datums, and investigation of the record of floral change at the K/T boundary.

  5. Selective extinction of marine plankton at the end of the Mesozoic era: The fossil and stable isotope record

    NASA Technical Reports Server (NTRS)

    Herman, Y.; Bhattacharya, S. K.

    1988-01-01

    Floral, faunal and stable isotope evidence in a continuous sequence of latest Cretaceous and earliest Tertiary shallow water marine deposits in the Mangyshlak Peninsula, USSR suggest severe environmental changes at the Cretaceous/Tertiary (K/T) boundary. Time frame is provided by nanno, micro and macrofossils as well as by magnetic stratigraphy and an iridium spike. Oxygen isotopic analyses of the bulk sediments, composed of nanno and microplankton skeletal remains, show a sharp positive spike at the K/T boundary. This shift is primarily attributed to severe cooling possibly accompanied by increased salinities of the surface mixed layer. Floral and faunal extinctions were selective, affecting approximately 90 percent of the warm water calcareous phyto and zooplankton genera in the Tethyan-Paratethyan regions. These highly diverse taxa with many endemic representatives were at the peak of their evolutionary development. Geologic evidence indicates that the terminal Cretaceous temperature decline was coeval with widespread and intense volcanic activity which reached a peak at the close of the Mesozoic Era. Increased acidity temporarily prohibited calcite nucleation of the surface dwelling warm-water plankton. Superimposed upon decreased alkalinity, severe and rapid climatic changes caused the extinction of calcareous phyto and zooplankton.

  6. Petrology of Tullock Member, Fort Union Formation, Wyoming and Montana: Evidence for early Paleocene uplift of Bighorn Mountains

    SciTech Connect

    Brown, J.L.; Hansley, P.L. )

    1989-09-01

    New petrologic data collected from sandstones in the Paleocene Tullock Member of the Fort Union Formation above the Cretaceous/Tertiary boundary in the Powder River basin (PRB) and from the lowermost Paleocene in the Bighorn basin, Wyoming and Montana, compel reevaluation of the timing of the bighorn uplift, formerly thought to be middle Paleocene. The Cretaceous/Tertiary boundary is identified by regionally valid palynological and trace element geochemical criteria. Basin-wide outcrop and subsurface studies of the Tullock Member indicate deposition on a low-gradient alluvial plain extending toward the retreating Cannonball sea. Eastward-flowing, low-sinuosity paleostreams containing small, sandy, stable channels characterized the fluvial systems.

  7. Petromagnetic and paleomagnetic characterization deposits at Mesozoic/Cenozoic boundary: The Tetritskaro section (Georgia)

    NASA Astrophysics Data System (ADS)

    Pechersky, D. M.; Asanidze, B. Z.; Nourgaliev, D. K.; Sharonova, Z. N.

    2009-02-01

    Petromagnetic and magnetostratigraphic characteristics are obtained for the Tetritskaro section. The boundary layer at the Mesozoic/Cenozoic (K/T) boundary is fixed primarily by an abrupt rise in the paramagnetic magnetization (total Fe concentration) and, to a lesser degree, by an increase in the concentration of such magnetic minerals as goethite, hemoilmenite, and magnetite. The along-section distribution of titanomagnetite of volcanic origin and metallic iron of cosmic origin does not correlate with the K/T boundary and lithologic properties of the sediments. The boundary of the Mesozoic and Cenozoic geological eras lies within the reversed polarity chron C29r and is marked by an abrupt rise in the geomagnetic field paleointensity and an instability of paleomagnetic directions, rather than by a polarity change. The accumulation time of the boundary clay layer is about 1.5-2 kyr, while abrupt changes in the paleointensity and direction of the geomagnetic field encompass 30-40 kyr. Such long occurrence intervals of the events in question cannot be related to a short-term impact phenomenon.

  8. A scale of greatness and causal classification of mass extinctions: implications for mechanisms.

    PubMed

    Sengr, A M Cell; Atayman, Saniye; Ozeren, Sinan

    2008-09-16

    A quantitative scale for measuring greatness, G, of mass extinctions is proposed on the basis of rate of biodiversity diminution expressed as the product of the loss of biodiversity, called magnitude (M), and the inverse of time in which that loss occurs, designated as intensity (I). On this scale, the catastrophic Cretaceous-Tertiary (K-T) extinction appears as the greatest since the Ordovician and the only one with a probable extraterrestrial cause. The end-Permian extinction was less great but with a large magnitude (M) and smaller intensity (I); only some of its individual episodes involved some semblance of catastrophe. Other extinctions during the Phanerozoic, with the possible exception of the end-Silurian diversity plunge, were parts of a forced oscillatory phenomenon and seem caused by marine- and land-habitat destruction during continental assemblies that led to elimination of shelves and (after the Devonian) rain forests and enlargement of deserts. Glaciations and orogenies that shortened and thickened the continental crust only exacerbated these effects. During the Mesozoic and Cainozoic, the evolution of life was linearly progressive, interrupted catastrophically only at the K-T boundary. The end-Triassic extinction was more like the Paleozoic extinctions in nature and probably also in its cause. By contrast, the current extinction resembles none of the earlier ones and may end up being the greatest of all. PMID:18779562

  9. Decline of the Maastrichtian pelagic ecosystem based on planktic foraminifera assemblage change: Implication for the terminal Cretaceous faunal crisis

    NASA Astrophysics Data System (ADS)

    Abramovich, Sigal; Almogi-Labin, Ahuva; Benjamini, Chaim

    1998-01-01

    An outer shelf upper slope tropical Tethyan pelagic environment existed over southern Israel during Maastrichtian time. Planktic foraminifera in the >63 and >149 μm size fractions from four sections in this area were studied quantitatively for a high-resolution ecostratigraphic analysis of the pre Cretaceous-Tertiary (K-T) paleoenvironment. During the Maastrichtian, 41% of the planktic foraminifera species became extinct, mostly keeled Globotruncanidae, which also became quantitatively reduced near the end of the Maastrichtian from as much as 35% to only 5% of the planktic foraminifera population. Evolutionary replacement of extinct species by new forms nearly ceased in that interval. Two major opportunistic blooms of Guembelitria took place, associated with reduced abundances of keeled forms and the dominant species Heterohelix globulosa. The first bloom occurred within the upper Gansserina gansseri to lower Abathomphalus mayaroensis Zones and the second within the Plummerita hantkeninoides Zone. The extinctions, concomitant changes in faunal dominance, and opportunist blooms indicate that the pelagic ecosystem in the Negev area experienced multiple stresses during the Maastrichtian. The planktic foraminiferal assemblages were taxonomically impoverished and in decline prior to the K-T boundary crisis.

  10. Method for solving moving boundary value problems for linear evolution equations

    PubMed

    Fokas; Pelloni

    2000-05-22

    We introduce a method of solving initial boundary value problems for linear evolution equations in a time-dependent domain, and we apply it to an equation with dispersion relation omega(k), in the domain l(t)k)t]rho(k) along a time-dependent contour, or an integral of exp[ikx-iomega(k)t]rho(k, &kmacr;) over a fixed two-dimensional domain. The functions rho(k) and rho(k,&kmacr;) can be computed through the solution of a system of Volterra linear integral equations. This method can be generalized to nonlinear integrable partial differential equations. PMID:10990798

  11. NATIONAL FOREST BOUNDARIES

    EPA Science Inventory

    This dataset contains National Forest boundaries for the lower 48 states, including Puerto Rico. Alaska is maintained separately. This dataset includes administrative unit boundaries, derived primarily from the GSTC SOC data system, comprised of Cartographic Feature Files (CFFs...

  12. On boundary superalgebras

    SciTech Connect

    Doikou, Anastasia

    2010-04-15

    We examine the symmetry breaking of superalgebras due to the presence of appropriate integrable boundary conditions. We investigate the boundary breaking symmetry associated with both reflection algebras and twisted super-Yangians. We extract the generators of the resulting boundary symmetry as well as we provide explicit expressions of the associated Casimir operators.

  13. Numerical Boundary Condition Procedures

    NASA Technical Reports Server (NTRS)

    1981-01-01

    Topics include numerical procedures for treating inflow and outflow boundaries, steady and unsteady discontinuous surfaces, far field boundaries, and multiblock grids. In addition, the effects of numerical boundary approximations on stability, accuracy, and convergence rate of the numerical solution are discussed.

  14. Experimental evidence that an asteroid impact led to the extinction of many species 65 million years ago

    SciTech Connect

    Alvarez, L.W.

    1982-09-01

    The development of the theory that the mass extinction of the dinosaurs at the Cretaceous-Tertiary boundary was caused by an asteroid impact is reviewed. The personnel involved, the objections to the theory, and the evidence refuting those objections are presented chronologically. (ACR)

  15. Diachronism between extinction time of terrestrial and marine dinosaurs

    NASA Technical Reports Server (NTRS)

    Hansen, H. J.

    1988-01-01

    The dinosaur eggs of southern France occur in continental, fine-grained red-beds, rich in carbonate. The last eggs in the region occur in the magnetic polarity interval 30 normal. Estimates of the accumulation rate of these sediments on the basis of the magneto-stratigraphy leads to placement of the time of disappearance of the dinosaurs in this region of 200,000 to 400,000 years earlier than the Cretaceous-Tertiary boundary. In the Red Deer Valley, Canada, estimates of average accumulation rate lead to a time of disappearance of the dinosaurs of 135,000 to 157,000 years earlier than the Cretaceous-Tertiary boundary. In the central part of Poland, in the Nasilow Quarry, the paleomagnetic pattern shows 7 m of chalk of reversed polarity containing in its upper part the marine Cretaceous-Tertiary biostratigraphic boundary. A greensand deposit contains numerous re-deposited Maastrichtian fossils. The fossils show no signs of wear and are of very different sizes including 1 mm thick juvenile belemnites. The deposit was described as a lag-sediment. Among the various fossils are teeth of mosasaurs. Thus there is coincidence in time between the extinction of mosasaurs and other Cretaceous organisms. This leads to the conclusion, that extinction of terrestrial dinosaurs took place earlier than extinction of marine dinosaurs at the Cretaceous-Tertiary boundary.

  16. Experimental evidence that an asteroid impact LED to the extinction of many species 65 million years ago

    NASA Astrophysics Data System (ADS)

    Alvarez, L. W.

    1982-09-01

    The development of the theory that the mass extinction of the dinosaurs at the Cretaceous-Tertiary boundary was caused by as asteroid impact is reviewed. The scientists involved, the objections to the theory, and the evidence refuting those objections are presented chronologically.

  17. Boundary-layer transition

    NASA Astrophysics Data System (ADS)

    Matthews, R. K.

    The prediction of the boundary layer transition Reynolds number for the design of hypersonic vehicles is considered. The boundary layer state (laminar or turbulent) that approaches the vehicle control surfaces can significantly affect the control surface effectiveness. In addition, the heating rates associated with turbulent boundary layers are often ten times higher than those of laminar boundary layers. Unfortunately, the methodology to predict transition has eluded the aerodynamicist for over three decades, and there are still many unanswered questions. Many parameters that affect transition are considered and numerous references for those who are interested in specializing in this topic are provided. It is emphasized that during wind tunnel testing it is very important to know the boundary layer state. Typically, heat transfer distributions can provide this information; however, it is often necessary to artificially trip the flow to induce a turbulent boundary layer. The methodology of using trip spheres is discussed, and illustrative data are presented.

  18. Boundary lubrication: Revisited

    NASA Technical Reports Server (NTRS)

    Jones, W. R., Jr.

    1982-01-01

    A review of the various lubrication regimes, with particular, emphasis on boundary lubrication, is presented. The types of wear debris and extent of surface damage is illustrated for each regime. The role of boundary surface films along with their modes of formation and important physical properties are discussed. In addition, the effects of various operating parameters on friction and wear in the boundary lubrication regime are considered.

  19. Experimentally Shock-loaded Anhydrite: Unit-Cell Dimensions, Microstrain and Domain Size from X-Ray Diffraction

    NASA Technical Reports Server (NTRS)

    Skala, R.; Hoerz, F.

    2003-01-01

    Cretaceous Tertiary (K/T) boundary is traditionally associated with one of the most dramatic mass extinctions in the Earth history. A number of killing mechanisms have been suggested to contribute to the widespread extinctions of Cretaceous biota at this boundary, including severe, global deterioration of the atmosphere and hydrosphere from the shock-induced release of CO2 and SO(x) from carbonate- and sulfate-bearing target rocks, respectively. Recently carried out calculations revealed that the global warming caused by CO2 release was considerably less important than the cooling due to SO(x) gases release during the Chicxulub impact event. Considering apparent potential importance of the response of sulfates to the shock metamorphism, relative lack of the data on shock behavior of sulfates as well as some general difficulties encountered during thermodynamic modeling of the shock-induced CO2 loss from carbonates we subjected anhydrite to a series of shock experiments designed for complete recovery of the shocked material. We report here on the detail X-ray diffraction analysis of seven samples that were subjected to experimental shock-loading from 10 to 65 GPa.

  20. The Atmospheric Boundary Layer

    ERIC Educational Resources Information Center

    Tennekes, Hendrik

    1974-01-01

    Discusses some important parameters of the boundary layer and effects of turbulence on the circulation and energy dissipation of the atmosphere. Indicates that boundary-layer research plays an important role in long-term forecasting and the study of air-pollution meteorology. (CC)

  1. Rethinking the Boundaries

    ERIC Educational Resources Information Center

    Schuller, Tom

    2011-01-01

    The splintering of the public domain makes the development of a coherent lifelong learning system less likely. But while people might want to resist plans to dissolve the boundaries between the public, private and voluntary sectors, debate about the relationship between professionals and volunteers in adult education suggests those boundaries

  2. Measurement of the ratio of inclusive jet cross sections using the anti-kT algorithm with radius parameters R =0.5 and 0.7 in pp collisions at ?s =7 TeV

    NASA Astrophysics Data System (ADS)

    Chatrchyan, S.; Khachatryan, V.; Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Bergauer, T.; Dragicevic, M.; Er, J.; Fabjan, C.; Friedl, M.; Frhwirth, R.; Ghete, V. M.; Hartl, C.; Hrmann, N.; Hrubec, J.; Jeitler, M.; Kiesenhofer, W.; Knnz, V.; Krammer, M.; Krtschmer, I.; Liko, D.; Mikulec, I.; Rabady, D.; Rahbaran, B.; Rohringer, H.; Schfbeck, R.; Strauss, J.; Taurok, A.; Treberer-Treberspurg, W.; Waltenberger, W.; Wulz, C.-E.; Mossolov, V.; Shumeiko, N.; Suarez Gonzalez, J.; Alderweireldt, S.; Bansal, M.; Bansal, S.; Cornelis, T.; De Wolf, E. A.; Janssen, X.; Knutsson, A.; Luyckx, S.; Mucibello, L.; Ochesanu, S.; Roland, B.; Rougny, R.; Van Haevermaet, H.; Van Mechelen, P.; Van Remortel, N.; Van Spilbeeck, A.; Blekman, F.; Blyweert, S.; D'Hondt, J.; Heracleous, N.; Kalogeropoulos, A.; Keaveney, J.; Kim, T. J.; Lowette, S.; Maes, M.; Olbrechts, A.; Strom, D.; Tavernier, S.; Van Doninck, W.; Van Mulders, P.; Van Onsem, G. P.; Villella, I.; Caillol, C.; Clerbaux, B.; De Lentdecker, G.; Favart, L.; Gay, A. P. R.; Lonard, A.; Marage, P. E.; Mohammadi, A.; Perni, L.; Reis, T.; Seva, T.; Thomas, L.; Vander Velde, C.; Vanlaer, P.; Wang, J.; Adler, V.; Beernaert, K.; Benucci, L.; Cimmino, A.; Costantini, S.; Dildick, S.; Garcia, G.; Klein, B.; Lellouch, J.; Mccartin, J.; Ocampo Rios, A. A.; Ryckbosch, D.; Salva Diblen, S.; Sigamani, M.; Strobbe, N.; Thyssen, F.; Tytgat, M.; Walsh, S.; Yazgan, E.; Zaganidis, N.; Basegmez, S.; Beluffi, C.; Bruno, G.; Castello, R.; Caudron, A.; Ceard, L.; Da Silveira, G. G.; Delaere, C.; du Pree, T.; Favart, D.; Forthomme, L.; Giammanco, A.; Hollar, J.; Jez, P.; Komm, M.; Lemaitre, V.; Liao, J.; Militaru, O.; Nuttens, C.; Pagano, D.; Pin, A.; Piotrzkowski, K.; Popov, A.; Quertenmont, L.; Selvaggi, M.; Vidal Marono, M.; Vizan Garcia, J. M.; Beliy, N.; Caebergs, T.; Daubie, E.; Hammad, G. H.; Alves, G. A.; Correa Martins Junior, M.; Dos Reis Martins, T.; Pol, M. E.; Souza, M. H. G.; Ald Jnior, W. L.; Carvalho, W.; Chinellato, J.; Custdio, A.; Da Costa, E. M.; De Jesus Damiao, D.; De Oliveira Martins, C.; Fonseca De Souza, S.; Malbouisson, H.; Malek, M.; Matos Figueiredo, D.; Mundim, L.; Nogima, H.; Prado Da Silva, W. L.; Santaolalla, J.; Santoro, A.; Sznajder, A.; Tonelli Manganote, E. J.; Vilela Pereira, A.; Bernardes, C. A.; Dias, F. A.; Tomei, T. R. Fernandez Perez; Gregores, E. M.; Lagana, C.; Mercadante, P. G.; Novaes, S. F.; Padula, Sandra S.; Genchev, V.; Iaydjiev, P.; Marinov, A.; Piperov, S.; Rodozov, M.; Sultanov, G.; Vutova, M.; Dimitrov, A.; Glushkov, I.; Hadjiiska, R.; Kozhuharov, V.; Litov, L.; Pavlov, B.; Petkov, P.; Bian, J. G.; Chen, G. M.; Chen, H. S.; Chen, M.; Du, R.; Jiang, C. H.; Liang, D.; Liang, S.; Meng, X.; Plestina, R.; Tao, J.; Wang, X.; Wang, Z.; Asawatangtrakuldee, C.; Ban, Y.; Guo, Y.; Li, Q.; Li, W.; Liu, S.; Mao, Y.; Qian, S. J.; Wang, D.; Zhang, L.; Zou, W.; Avila, C.; Carrillo Montoya, C. A.; Chaparro Sierra, L. F.; Florez, C.; Gomez, J. P.; Gomez Moreno, B.; Sanabria, J. C.; Godinovic, N.; Lelas, D.; Polic, D.; Puljak, I.; Antunovic, Z.; Kovac, M.; Brigljevic, V.; Kadija, K.; Luetic, J.; Mekterovic, D.; Morovic, S.; Sudic, L.; Attikis, A.; Mavromanolakis, G.; Mousa, J.; Nicolaou, C.; Ptochos, F.; Razis, P. A.; Finger, M.; Finger, M.; Abdelalim, A. A.; Assran, Y.; Elgammal, S.; Ellithi Kamel, A.; Mahmoud, M. A.; Radi, A.; Kadastik, M.; Mntel, M.; Murumaa, M.; Raidal, M.; Rebane, L.; Tiko, A.; Eerola, P.; Fedi, G.; Voutilainen, M.; Hrknen, J.; Karimki, V.; Kinnunen, R.; Kortelainen, M. J.; Lampn, T.; Lassila-Perini, K.; Lehti, S.; Lindn, T.; Luukka, P.; Menp, T.; Peltola, T.; Tuominen, E.; Tuominiemi, J.; Tuovinen, E.; Wendland, L.; Tuuva, T.; Besancon, M.; Couderc, F.; Dejardin, M.; Denegri, D.; Fabbro, B.; Faure, J. L.; Ferri, F.; Ganjour, S.; Givernaud, A.; Gras, P.; Hamel de Monchenault, G.; Jarry, P.; Locci, E.; Malcles, J.; Nayak, A.; Rander, J.; Rosowsky, A.; Titov, M.; Baffioni, S.; Beaudette, F.; Busson, P.; Charlot, C.; Daci, N.; Dahms, T.; Dalchenko, M.; Dobrzynski, L.; Florent, A.; Granier de Cassagnac, R.; Min, P.; Mironov, C.; Naranjo, I. N.; Nguyen, M.; Ochando, C.; Paganini, P.; Sabes, D.; Salerno, R.; Sirois, Y.; Veelken, C.; Yilmaz, Y.; Zabi, A.; Agram, J.-L.; Andrea, J.; Bloch, D.; Brom, J.-M.; Chabert, E. C.; Collard, C.; Conte, E.; Drouhin, F.; Fontaine, J.-C.; Gel, D.; Goerlach, U.; Goetzmann, C.; Juillot, P.; Le Bihan, A.-C.; Van Hove, P.; Gadrat, S.; Beauceron, S.; Beaupere, N.; Boudoul, G.; Brochet, S.; Chasserat, J.; Chierici, R.; Contardo, D.; Depasse, P.; El Mamouni, H.; Fan, J.; Fay, J.; Gascon, S.; Gouzevitch, M.; Ille, B.; Kurca, T.; Lethuillier, M.; Mirabito, L.; Perries, S.; Ruiz Alvarez, J. D.; Sgandurra, L.; Sordini, V.; Vander Donckt, M.; Verdier, P.

    2014-10-01

    Measurements of the inclusive jet cross section with the anti-kT clustering algorithm are presented for two radius parameters, R =0.5 and 0.7. They are based on data from LHC proton-proton collisions at ?s =7 TeV corresponding to an integrated luminosity of 5.0 fb-1 collected with the CMS detector in 2011. The ratio of these two measurements is obtained as a function of the rapidity and transverse momentum of the jets. Significant discrepancies are found comparing the data to leading-order simulations and to fixed-order calculations at next-to-leading order, corrected for nonperturbative effects, whereas simulations with next-to-leading-order matrix elements matched to parton showers describe the data best.

  3. Measurement of the ratio of inclusive jet cross sections using the anti-kT algorithm with radius parameters R=0.5 and 0.7 in pp collisions ats=7TeV

    DOE PAGESBeta

    Chatrchyan, S.; Khachatryan, V.; Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Bergauer, T.; Dragicevic, M.; Erö, J.; Fabjan, C.; Friedl, M.; et al

    2014-10-16

    Measurements of the inclusive jet cross section with the anti-kT clustering algorithm are presented for two radius parameters, R = 0.5 and 0.7. They are based on data from LHC proton-proton collisions at √s = 7  TeV corresponding to an integrated luminosity of 5.0  fb⁻¹ collected with the CMS detector in 2011. The ratio of these two measurements is obtained as a function of the rapidity and transverse momentum of the jets. Significant discrepancies are found comparing the data to leading-order simulations and to fixed-order calculations at next-to-leading order, corrected for nonperturbative effects, whereas simulations with next-to-leading-order matrix elements matched to partonmore » showers describe the data best.« less

  4. Phenomenological applications of kT factorization

    NASA Astrophysics Data System (ADS)

    Keum, Yong-Yeon

    2004-12-01

    We discuss applications of the perturbative QCD approach in the exclusive non-leptonic two-body B-meson decays. We briefly review its ingredients and some important theoretical issues on the factorization approach. PQCD results are compatible with present experimental data for charmless B-meson decays. We predict the possibility of large direct CP asymmetry in B^0 rightarrow pi^+pi^- (23 pm 7%) and B^0 rightarrow K^+ pi^- (-17 pm 5%). We also investigate the branching ratios, CP asymmetry and isospin symmetry breaking in radiative B rightarrow (K^* /rho)gamma decays.

  5. K-T Transition into Chaos.

    ERIC Educational Resources Information Center

    McLean, Dewey M.

    1988-01-01

    Discusses the destabilizing influences that affect feedback systems in the earth and trigger disorganization. Presents information that integrates mantle degassing with feed-back systems, and the Sun-Earth-Space energy flow system which is the primary source of energy that drives the Earth's biosphere. (RT)

  6. Evolution of Modern Birds Revealed by Mitogenomics: Timing the Radiation and Origin of Major Orders

    PubMed Central

    Pacheco, M. Andrena; Battistuzzi, Fabia U.; Lentino, Miguel; Aguilar, Roberto F.; Kumar, Sudhir; Escalante, Ananias A.

    2011-01-01

    Mitochondrial (mt) genes and genomes are among the major sources of data for evolutionary studies in birds. This places mitogenomic studies in birds at the core of intense debates in avian evolutionary biology. Indeed, complete mt genomes are actively been used to unveil the phylogenetic relationships among major orders, whereas single genes (e.g., cytochrome c oxidase I [COX1]) are considered standard for species identification and defining species boundaries (DNA barcoding). In this investigation, we study the time of origin and evolutionary relationships among Neoaves orders using complete mt genomes. First, we were able to solve polytomies previously observed at the deep nodes of the Neoaves phylogeny by analyzing 80 mt genomes, including 17 new sequences reported in this investigation. As an example, we found evidence indicating that columbiforms and charadriforms are sister groups. Overall, our analyses indicate that by improving the taxonomic sampling, complete mt genomes can solve the evolutionary relationships among major bird groups. Second, we used our phylogenetic hypotheses to estimate the time of origin of major avian orders as a way to test if their diversification took place prior to the Cretaceous/Tertiary (K/T) boundary. Such timetrees were estimated using several molecular dating approaches and conservative calibration points. Whereas we found time estimates slightly younger than those reported by others, most of the major orders originated prior to the K/T boundary. Finally, we used our timetrees to estimate the rate of evolution of each mt gene. We found great variation on the mutation rates among mt genes and within different bird groups. COX1 was the gene with less variation among Neoaves orders and the one with the least amount of rate heterogeneity across lineages. Such findings support the choice of COX 1 among mt genes as target for developing DNA barcoding approaches in birds. PMID:21242529

  7. Boundary Layer Relaminarization Device

    NASA Technical Reports Server (NTRS)

    Creel, Theodore R. (Inventor)

    1993-01-01

    Relamination of a boundary layer formed in supersonic flow over the leading edge of a swept airfoil is accomplished using at least one band, especially a quadrangular band, and most preferably a square band. Each band conforms to the leading edge and the upper and lower surfaces of the airfoil as an integral part thereof and extends perpendicularly from the leading edge. Each band has a height of about two times the thickness of the maximum expected boundary layer.

  8. Iridium in sediments containing large abundances of Australasian microtektites from DSDP hole 758B in the Eastern Indian Ocean and from DSDP hole 769A in the Sulu Sea

    NASA Technical Reports Server (NTRS)

    Schmidt, Gerhard; Zhou, Lei; Wasson, John T.

    1993-01-01

    Excess Ir found in sediments at the Cretaceous/Tertiary (K/T) boundary and in other (e.g., Pliocene) sediments from deep sea drilling cores is widely interpreted as evidence of major impact events. The Australasian tektites originated in an impact event approximately 0.77 Ma ago; microtektites have been found in deep-sea sediment cores from throughout the Indian Ocean, the Philippine Sea, and western Pacific Ocean, but Ir has not been previously reported in these horizons. The deep-sea record of tektites is of particular interest, because in contrast to most continental occurrences, the stratigraphy preserves the original depositional position. Recently several cores having exceptionally high contents of Australasian microtektites have been investigated, Glass and Wu found shocked quartz associated with the microtektites. We used neutron activation to determine concentrations of Ir and other elements in two cores bearing microtektites, one from Deep Sea Drilling Project (DSDP) hole 758B in the Eastern Indian Ocean and one from DSDP hole 769A in the Sulu Sea (near Mindanao, Philippines). The sedimentation age for the microtektite layers in core 758B lies between 0.73 - 0.78 Ma and agrees well with the mean laser-fusion Ar-40/Ar-39 age of Australasian tektites of 0.77 +/- 0.02 Ma by Izett et al. We are able to resolve a small positive Ir enhancement in 758B. Core 769A shows too much scatter to allow resolution of an Ir peak.

  9. Periodic Explosive Expansion of Human Retroelements Associated with the Evolution of the Hominoid Primate

    PubMed Central

    Kim, Tae-Min; Hong, Seung-Jin

    2004-01-01

    Five retroelement families, L1 and L2 (long interspersed nuclear element, LINE), Alu and MIR (short interspersed nuclear element, SINE), and LTR (long terminal repeat), comprise almost half of the human genome. This genome-wide analysis on the time-scaled expansion of retroelements sheds light on the chronologically synchronous amplification peaks of each retroelement family in variable heights across human chromosomes. Especially, L1s and LTRs in the highest density on sex chromosomes Xq and Y, respectively, disclose peak activities that are obscured in autosomes. The periods of young L1, Alu, LTR, and old L1 peak activities calibrated based on sequence divergence coincide with the divergence of the three major hominoid divergence as well as early eutherian radiation while the amplification peaks of old MIR and L2 account for the marsupial-placental split. Overall, the peaks of autonomous LINE (young and old L1s and L2s) peaks and non-autonomous SINE (Alus and MIRs) have alternated repeatedly for 150 million years. In addition, a single burst of LTR parallels the Cretaceous-Tertiary (K-T) boundary, an exceptional global event. These findings suggest that the periodic explosive expansions of LINEs and SINEs and an exceptional burst of LTR comprise the genome dynamics underlying the macroevolution of the hominoid primate lineage. PMID:15082888

  10. Placenta-specific protein 1 is conserved throughout the Placentalia under purifying selection.

    PubMed

    Devor, Eric J

    2014-01-01

    Placental mammals (Placentalia) are a very successful group that, today, comprise 94% of all mammalian species. Recent phylogenetic analyses, coupled with new, quite complete fossils, suggest that the crown orders were all established rapidly from a common ancestor just after the Cretaceous/Tertiary (K/T) boundary 65 million years ago. Extensive molecular and morphologic evidence has led to a description of the common ancestor of all Placentalia in which a two-horned uterus and a hemochorial placenta are present. Thus, the process of placentation in which the placenta invades and anchors to the uterine epithelium was already established. One factor that has been suggested as a crucial component of this process is placenta-specific protein 1 (PLAC1). A phylogenetic analysis of the PLAC1 protein in 25 placental mammal species, representing nine of the sixteen crown orders of the Placentalia, suggests that this protein was present in the placental common ancestor in the form we see it today, that it evolved in the Placentalia and has been subject to the effects of purifying selection since its appearance. PMID:25180201

  11. Placenta-Specific Protein 1 Is Conserved throughout the Placentalia under Purifying Selection

    PubMed Central

    Devor, Eric J.

    2014-01-01

    Placental mammals (Placentalia) are a very successful group that, today, comprise 94% of all mammalian species. Recent phylogenetic analyses, coupled with new, quite complete fossils, suggest that the crown orders were all established rapidly from a common ancestor just after the Cretaceous/Tertiary (K/T) boundary 65 million years ago. Extensive molecular and morphologic evidence has led to a description of the common ancestor of all Placentalia in which a two-horned uterus and a hemochorial placenta are present. Thus, the process of placentation in which the placenta invades and anchors to the uterine epithelium was already established. One factor that has been suggested as a crucial component of this process is placenta-specific protein 1 (PLAC1). A phylogenetic analysis of the PLAC1 protein in 25 placental mammal species, representing nine of the sixteen crown orders of the Placentalia, suggests that this protein was present in the placental common ancestor in the form we see it today, that it evolved in the Placentalia and has been subject to the effects of purifying selection since its appearance. PMID:25180201

  12. Mammalian phylogeny reveals recent diversification rate shifts.

    PubMed

    Stadler, Tanja

    2011-04-12

    Phylogenetic trees of present-day species allow investigation of the rate of evolution that led to the present-day diversity. A recent analysis of the mammalian phylogeny challenged the view of explosive mammalian evolution after the Cretaceous-Tertiary (K/T) boundary (65 Mya). However, due to lack of appropriate methods, the diversification (speciation minus extinction) rates in the more recent past of mammalian evolution could not be determined. In this paper, I provide a method that reveals that the tempo of mammalian evolution did not change until ∼ 33 Mya. This constant period was followed by a peak of diversification rates between 33 and 30 Mya. Thereafter, diversification rates remained high and constant until 8.55 Mya. Diversification rates declined significantly at 8.55 and 3.35 Mya. Investigation of mammalian subgroups (marsupials, placentals, and the six largest placental subgroups) reveals that the diversification rate peak at 33-30 Mya is mainly driven by rodents, cetartiodactyla, and marsupials. The recent diversification rate decrease is significant for all analyzed subgroups but eulipotyphla, cetartiodactyla, and primates. My likelihood approach is not limited to mammalian evolution. It provides a robust framework to infer diversification rate changes and mass extinction events in phylogenies, reconstructed from, e.g., present-day species or virus data. In particular, the method is very robust toward noise and uncertainty in the phylogeny and can account for incomplete taxon sampling. PMID:21444816

  13. Behavior of carbonate shelf communities in the Upper Triassic of Nevada: Evidence of impact mediated faunal turnover

    SciTech Connect

    Hogler, J.A. . Museum of Paleontology)

    1993-04-01

    The carbonate shelf sediments of the Luning and Gabbs Formations of Nevada span the last several million years of the Triassic. This richly fossiliferous sequence provides a relatively continuous record of benthic community behavior during a long interval of global biotic turnover. Upper Carnian-Lower Norian and Upper Norian sea floors in this region were inhabited by a variety of invertebrate communities, all of them mollusc-dominated. Across a range of offshore shelf to basinal environments and throughout repeated community replacements, the most abundant and diverse taxa were infaunal and epifaunal bivalves and ammonites. The sequence of Upper Triassic molluscan communities was interrupted by a Lower or Middle Norian interval of brachiopod-dominated faunas. Although preserved in similar offshore carbonate shelf sediments, these communities are nearly devoid of the infaunal bivalves and ammonites that characterize both older and younger assemblages in the section. This pattern, of a temporary replacement of molluscan communities by brachiopod faunas, mimics that reported for some shelf assemblages across the Cretaceous-Tertiary boundary. That brief resurgence of brachiopods is linked to a sharp drop in marine primary productivity, which suggests that a disruption of planktonic food chains may also have occurred early in the Norian. The timing and pattern of Carnian-Norian faunal and physical events and their resemblance to K/T sequences are consistent with the proposal that an asteroid impact played a role in the Upper Triassic faunal transition.

  14. Accretion rate of extraterrestrial matter: Iridium deposited over the last 70 million years

    NASA Technical Reports Server (NTRS)

    Kyte, Frank T.

    1988-01-01

    In order to quantify the accretion rate of extraterrestrial matter during the Cenozoic, Ir concentrations were measured in a continuous series of 450 samples across most of the length of piston core LL44-GPC3. LL44-GPC3 is a 25-meter-long, large-diameter piston core of abyssal clay from the central North Pacific. This core contains a nearly continuous record of sedimentation over the last 70 Ma, as this site migrated from a region near the Equator in the late Cretaceous to its present position north of Hawaii. The first-cut survey across the core is nearing completion, and all of the conclusions of the earlier study, in which was reported the concentrations of Ir, Co, and Sb across 9 meters of this core, remain unchanged. The only strongly enhanced Ir concentrations occur at the Cretaceous-Tertiary (K-T) boundary and outside the K-T boundary Ir correlates well with Co, a terrestrial element which is largely present in hydrogenous ferromanganese oxide precipitates from seawater. Concentrations of both elements appear to be inversely correlated with the sedimentation rate. Although the K-T Ir anomaly is unique in magnitude in this core, there are several small bumps in the Ir profile which may reflect smaller accretionary events. The most promising Ir enhancement was observed in a 30 cm section approximately 1 m below the K-T boundary. Preliminary data suggest deposition of an excess across this interval at a time estimate to be approximate 1 Ma before the K-T impact event, but there is insufficient evidence at present to prove that this reflects enhanced accretion of extraterrestrial matter. A detailed model is being prepared of the chemical record of sedimentation in this core using a combined database of 39 elements in approximately 450 samples across the Cenozoic. Preliminary working model indicates that the only sedimentary sources which contribute significantly to the Ir budget in this core are the hydrogenous precipitates and extraterrestrial particulates.

  15. Boundary-type quadrature and boundary element method

    NASA Astrophysics Data System (ADS)

    He, T.-X.; Zhang, R.; Zhou, Y. S.

    2003-06-01

    In this paper, we apply a boundary-type quadrature technique to derive a type of boundary element scheme, which is used to solve the boundary-value problems of partial differential equations. Numerical examples for solving the exterior boundary-value problem of Helmholtz equation by using the spline approximation and the spline wavelet approximation are given.

  16. An Investigation of the Effect of a Highly Favorable Pressure Gradient on Boundary-Layer Transition as Caused by Various Types of Roughnesses on a 10-foot-Diameter Hemisphere at Subsonic Speeds

    NASA Technical Reports Server (NTRS)

    Peterson, John B., Jr.; Horton, Elmer A.

    1959-01-01

    Tests were made on a 10-foot-diameter hemispherical nose at Reynolds numbers up to 10 x 10(exp 6) and at a maximum Mach number of about 0.1 to determine the effects of a highly favorable pressure gradient on boundary-layer transition caused by roughness. Both two-dimensional and three-dimensional roughness particles were used, and the transition of the boundary layer was determined by hot-wire anemometers. The roughness Reynolds number for transition R(sub k,t) caused by three-dimensional particles such as Carborundum grains, spherical particles, and rimmed craters was found. The results show that for particles immersed in the boundary layer, R(sub k,t) is independent of the particle size or position on the hemispherical nose and depends mainly on the height-to-width ratio of the particle. The values of R(sub k,t) found on the hemispherical nose compare closely with those previously found on a flat plate and on airfoils with roughness. For two-dimensional roughness, the ratio of roughness height to boundary-layer displacement thickness necessary to cause transition was found to increase appreciably as the roughness was moved forward on the nose. Also included in the investigation were studies of the spread of turbulence behind a single particle of roughness and the effect of holes such as pressure orifices.

  17. Upper Cretaceous-Tertiary subduction dynamics from the Balkan to the Aegean and W-Anatolia region: input of mineralization and related magmatism

    NASA Astrophysics Data System (ADS)

    Menant, Armel; Jolivet, Laurent; Bertrand, Guillaume; Guillou-Frottier, Laurent

    2013-04-01

    In the eastern Mediterranean, the dynamics of the Tertiary subduction of African plate below Eurasia is still largely debated, notably in the region extending from the Balkan to the Aegean and western part of Anatolia. To understand this evolution since the late Cretaceous, an additional feature should be considered: the spatial and temporal evolution of arc- and back-arc-related ore deposits. Indeed, the type of mineralization, their magmatic environment and their relationships with large-scale structures, can provide insights on subduction-related processes from deep mantle to surface. In the eastern Mediterranean, a clear evolution through time can be observed. First, during the late Cretaceous and Paleocene, magmatism and mineralization were located in the Balkans with dominant calc-alkaline rocks and related porphyry Cu deposits. These syn-extensional occurrences emplaced in a back-arc environment that developed in response to a low slab retreat. In opposition, from 35-30 Ma, slab retreat accelerated, inducing a significant back-arc extension from the Rhodope massif to the south Aegean domain. Analysis of metallogenic data demonstrates that, during this second stage, mineralization consists mainly in low-sulphidation epithermal Au deposits related to shoshonitic volcanism in NW-Anatolia. The Au stored in the lithospheric mantle during the first stage was remobilized by melting of the lithospheric mantle, thus suggesting a significant thermal event that could result from wide lithospheric extension, possible slab breakoff and asthenospheric influx. From the middle Miocene, alkaline volcanism appeared in western Anatolia and progressively developed in the east of the Aegean domain and some syn-extensional plutonic intrusions were emplaced in the Cyclades up to the upper Miocene. Associated ore deposits are variable with porphyry, skarn and epithermal occurrences and late hydrothermal veins, depending upon various parameters such as the depth of the intrusions. These occurrences developed during the fast clockwise rotation of the western Aegean that is a probable consequence of the slab tear shown by tomographic models below western Anatolia. The related major asthenospheric influx followed the rotating slab and invaded the whole Aegean domain from ~17 Ma ago until 9 Ma. This mantle flow induced the partial melting of the base of continental crust to form the Cycladic plutonic intrusions and related ore deposits.

  18. Turbulent boundary layers over nonstationary plane boundaries

    NASA Technical Reports Server (NTRS)

    Roper, A. T.

    1976-01-01

    Methods of predicting integral parameters and skin-friction coefficients of turbulent boundary layers developing over moving-ground-planes are evaluated using test information from three different wind tunnel facilities at the NASA Langley Research Center. These data include test information from the VSTOL tunnel which is presented for the first time. The three methods evaluated were: (1) relative integral parameter method, (2) relative power law method, and (3) modified law of the wall method. Methods (1) and (2) can be used to predict moving-ground-plane shape factors with an expected accuracy of + or - 10%. They may also be used to predict moving-ground-plane displacement and momentum thicknesses with lower expected accuracy. This decrease in accuracy can be traced to the failure of approximations upon which these methods are based to prove universal when compared with VSTOL tunnel test results.

  19. The open boundary equation

    NASA Astrophysics Data System (ADS)

    Diederen, D.; Savenije, H. H. G.; Toffolon, M.

    2015-06-01

    We present a new equation describing the hydrodynamics in infinitely long tidal channels (i.e., no reflection) under the influence of oceanic forcing. The proposed equation is a simple relationship between partial derivatives of water level and velocity. It is formally derived for a progressive wave in a frictionless, prismatic, tidal channel with a horizontal bed. Assessment of a large number of numerical simulations, where an open boundary condition is posed at a certain distance landward, suggests that it can also be considered accurate in the more natural case of converging estuaries with nonlinear friction and a bed slope. The equation follows from the open boundary condition and is therefore a part of the problem formulation for an infinite tidal channel. This finding provides a practical tool for evaluating tidal wave dynamics, by reconstructing the temporal variation of the velocity based on local observations of the water level, providing a fully local open boundary condition and allowing for local friction calibration.

  20. Probabilistic boundary element method

    NASA Technical Reports Server (NTRS)

    Cruse, T. A.; Raveendra, S. T.

    1989-01-01

    The purpose of the Probabilistic Structural Analysis Method (PSAM) project is to develop structural analysis capabilities for the design analysis of advanced space propulsion system hardware. The boundary element method (BEM) is used as the basis of the Probabilistic Advanced Analysis Methods (PADAM) which is discussed. The probabilistic BEM code (PBEM) is used to obtain the structural response and sensitivity results to a set of random variables. As such, PBEM performs analogous to other structural analysis codes such as finite elements in the PSAM system. For linear problems, unlike the finite element method (FEM), the BEM governing equations are written at the boundary of the body only, thus, the method eliminates the need to model the volume of the body. However, for general body force problems, a direct condensation of the governing equations to the boundary of the body is not possible and therefore volume modeling is generally required.

  1. Boundary layer simulator improvement

    NASA Technical Reports Server (NTRS)

    Praharaj, Sarat C.; Schmitz, Craig P.; Nouri, Joseph A.

    1989-01-01

    Boundary Layer Integral Matrix Procedure (BLIMPJ) has been identified by the propulsion community as the rigorous boundary layer program in connection with the existing JANNAF reference programs. The improvements made to BLIMPJ and described herein have potential applications in the design of the future Orbit Transfer Vehicle engines. The turbulence model is validated to include the effects of wall roughness and a way is devised to treat multiple smooth-rough surfaces. A prediction of relaminarization regions is examined as is the combined effects of wall cooling and surface roughness on relaminarization. A turbulence model to represent the effects of constant condensed phase loading is given. A procedure is described for thrust decrement calculation in thick boundary layers by coupling the T-D Kinetics Program and BLIMPJ and a way is provided for thrust loss optimization. Potential experimental studies in rocket nozzles are identified along with the required instrumentation to provide accurate measurements in support of the presented new analytical models.

  2. USACE DIVISION AND DISTRICT BOUNDARIES

    EPA Science Inventory

    The USACE Division and District Boundary data contains the delination of Corps Division and District boundaries. District and Division Boundaries are based on the US political and watershed boundaries. In the mid 1990's, WES created the file by digitizing the 1984 Civil Wor...

  3. Biodiversity changes in Cretaceous palynofloras of eastern Asia and western North America

    USGS Publications Warehouse

    Nichols, D.J.

    2003-01-01

    Palynology has great potential for providing comparative data and interpretations about changes in biodiversity during the Cretaceous Period. This is especially true for both eastern Asia and western North America because of strong floristic similarities that existed between these regions during Cretaceous time. Also, because palynomorphs of terrestrial origin can be deposited in offshore as well as terrestrial environments, significant potential exists for marine-to-continental palynostratigraphic correlations in both regions. Palynological biostratigraphy can improve the geologic dating of changes in biodiversity. During the Early Cretaceous, eastern Asia and western North America lay within the Cerebropollenites palynofloral province, a circumpolar phytogeographic zone characterized by distinctive palynological assemblages. During most of the Late Cretaceous, these regions lay within the palynofloristically unique Aquilapollenites Province, which was more restricted geographically than the Cerebropollenites Province. The most important development during Cretaceous time that is reflected in palynological assemblages was the rise of the angiosperms as the numerically and ecologically dominant forms of vegetation. The most striking short-term palynofloral event in the two regions was the sudden disappearance of species of Aquilapollenites and associated genera at the Cretaceous-Tertiary (K/T) boundary. Both of these occurrences produced major changes in biodiversity in the terrestrial realm. Geologic research in International Geological Correlation Program Project 434 can benefit from applications of palynostratigraphy. Palynologic research within Project 434 could include development of a comprehensive palynostratigraphic zonation for the Cretaceous, the definition of regional palynostratigraphic datums, and investigation of the record of floral change at the K/T boundary. ?? 2002 Elsevier Science Ltd. All rights reserved.

  4. Carbonate-silicate cycle models of the long-term carbon cycle, carbonate accumulation in the oceans, and climate

    SciTech Connect

    Caldeira, K.G.

    1991-01-01

    Several models of the long-term carbon cycle, incorporating models of the carbonate-silicate cycle, were developed and utilized to investigate issues relating to global climate and the causes and consequences of changes in calcium carbonate accumulation in the oceans. Model results indicate that the marked mid-Cretaceous (120 Ma) global warming could be explained by increased rates of release of carbon dioxide from subduction-zone metamorphism and mid-ocean-ridges, in conjunction with paleogeographic factors. Since the mid-Cretaceous, the primary setting for calcium carbonate accumulation in the oceans has shifted from shallow-water to deep-water environments. Model results suggest that this shift could have major consequences for the carbonate-silicate cycle and climate, and lead to significant increases in the flux of metamorphic carbon dioxide to the atmosphere. Increases in pelagic carbonate productivity, and decreases in tropical shallow-water area available for neritic carbonate accumulation, have both been proposed as the primary cause of this shift. Two lines of evidence developed here (one involving a statistical analysis of Tertiary carbonate-accumulation and oxygen-isotope data, and another based on modeling the carbonate-silicate cycle and ocean chemistry) suggest that a decrease in tropical shallow-water area was more important than increased pelagic productivity in explaining this shift. Model investigations of changes in ocean chemistry at the Cretaceous/Tertiary (K/T) boundary (66 Ma) indicate that variations in deep-water carbonate productivity may affect shallow-water carbonate accumulation rates through a mechanism involving surface-water carbonate-ion concentration. In the aftermath of the K/T boundary event, deep-water carbonate production and accumulation were significantly reduced as a result of the extinction of calcareous plankton.

  5. 2000 CENSUS BLOCK BOUNDARIES

    EPA Science Inventory

    This data set is a polygon shapefile of the boundaries of Census Blocks in New England derived from U.S. Census Bureau 2000 TIGER/Line data. Numerous attributes pertaining to population are included. TIGER, TIGER/Line, and Census TIGER are registered trademarks of the Bureau o...

  6. Dialogic Bonds and Boundaries.

    ERIC Educational Resources Information Center

    Khawaja, Mabel

    A study of literature cannot be divorced from cultural contexts, nor can it ignore the humanist vision in interpreting literary texts. To discover dialogic bonds and boundaries between the reader and the text, or the writer and the audience, English classes should have two objectives: (1) to explore the diversity of perspectives, and (2) to relate

  7. Rethinking the Boundaries

    ERIC Educational Resources Information Center

    Schuller, Tom

    2011-01-01

    The splintering of the public domain makes the development of a coherent lifelong learning system less likely. But while people might want to resist plans to dissolve the boundaries between the public, private and voluntary sectors, debate about the relationship between professionals and volunteers in adult education suggests those boundaries…

  8. Boundary Changing without Acrimony

    ERIC Educational Resources Information Center

    Gunnell, Thomas J.

    2011-01-01

    In December 2009, a rapid-growth school district on the Texas Gulf Coast shifted its paradigm of rezoning. Even though half of the Katy Independent School District (Katy ISD) was affected, it achieved a genuine ownership for boundary changes that would affect more than 11,500 students at five schools. Katy ISD accomplished this by seeking

  9. A compilation of information and data on the Manson impact structure

    NASA Technical Reports Server (NTRS)

    Hartung, Jack B.; Anderson, Raymond R.

    1988-01-01

    A problem for the impact hypothesis for the Cretaceous-Tertiary (K-T) mass extinction is the apparent absence of an identifiable impact site. The Manson Impact Structure is a candidate because it is the largest recognized in the U.S.; it is relatively close to the largest and most abundant shocked quartz grains found at the K-T boundary; and its age is indistinguishable from that of the K-T boundary based on paleontological evidence, fission track dates, and preliminary Ar-40/Ar-39 measurements. The region of northwest central Iowa containing the Manson Impact Structure is covered by Quaternary glacial deposits underlain by Phanerozoic sedimentary rocks (mostly flat-lying carbonates) and Proterozoic red clastic, metamorphic, volcanic, and plutonic rocks. In a circular area about 22 miles (35 km) in diameter around Manson, Iowa, this normal sequence is absent or disturbed and near the center of the disturbed area granitic basement rocks have been uplifted some 20,000 ft (6000m). Attention was drawn to Manson initially by the unusual quality of the groundwater there. Within the structure three roughly concentric zones of rock associations have been identified: (1) displaced strata; (2) completely disrupted strata, and igneous and metamorphic rocks. Manson was established as an impact structure based on its circular shape, its central uplift, and the presence of shocked quartz within the granitic central uplift. A gravity survey identified locations of low-density brecciated rocks and high-density uplifted crystalline rocks, but the outer boundary of the structure could not be established. Aeromagnetic and ground magnetic surveys showed locations and depths of shallowly buried crystalline rock and the locations of faults. A refraction seismic survey identified the crystalline central uplift, determined that the average elevation of bedrock is 70 ft (20 m) higher outside the structure than within, and was used to map the bedrock topography within the structure. A connection between the Manson impact and the K-T boundary may be established or refuted through study of the impact energy, the impact time, and composition of host rock, possible impactors, and impact melts.

  10. Boundary layer simulator improvement

    NASA Technical Reports Server (NTRS)

    Praharaj, S. C.; Schmitz, C.; Frost, C.; Engel, C. D.; Fuller, C. E.; Bender, R. L.; Pond, J.

    1984-01-01

    High chamber pressure expander cycles proposed for orbit transfer vehicles depend primarily on the heat energy transmitted from the combustion products through the thrust wall chamber wall. The heat transfer to the nozzle wall is affected by such variables as wall roughness, relamarization, and the presence of particles in the flow. Motor performance loss for these nozzles with thick boundary layers is inaccurate using the existing procedure coded BLIMPJ. Modifications and innovations to the code are examined. Updated routines are listed.

  11. Boundary integral operators and boundary value problems for Laplace's equation

    NASA Astrophysics Data System (ADS)

    Chang, Tongkeun; Lewis, John L.

    2011-10-01

    In this paper, we define boundary single and double layer potentials for Laplace's equation in certain bounded domains with d-Ahlfors regular boundary, considerably more general than Lipschitz domains. We show that these layer potentials are invertible as mappings between certain Besov spaces and thus obtain layer potential solutions to the regularity, Neumann, and Dirichlet problems with boundary data in these spaces.

  12. SOLE SOURCE AQUIFER BOUNDARY DATA

    EPA Science Inventory

    There are 7 polygons representing 6 individual sole source aquifer boundaries and one streamflow source area in California, Arizona, and Nevada. Various efforts were combined to create the final product, which represents the Federal Register boundary description. Sole source aqu...

  13. Cell boundary fault detection system

    DOEpatents

    Archer, Charles Jens (Rochester, MN); Pinnow, Kurt Walter (Rochester, MN); Ratterman, Joseph D. (Rochester, MN); Smith, Brian Edward (Rochester, MN)

    2009-05-05

    A method determines a nodal fault along the boundary, or face, of a computing cell. Nodes on adjacent cell boundaries communicate with each other, and the communications are analyzed to determine if a node or connection is faulty.

  14. Maritime boundaries and ocean resources

    SciTech Connect

    Blake, G.

    1987-01-01

    International maritime boundaries have become a major issue in international politics with the increasing exploitation of maritime resources, including mineral extraction from the sea bed, and the associated exstention of territorial waters and zones of exclusive economic activity. This book examines this important international problem. It considers the growth in the exploration of marine resources. It examines particular boundary disputes in different parts of the world and discusses the implications for international law, international politics and maritime activity and management. Contents. Antarctic maritime boundary problems; the law of the sea and the mediterranean; historical geography and the world court line of delimitation across the Gulf of Maine; maritime boundary delimitation worldwide: the current state of play; technical delimitation problems in the Mediterranean Sea; offshore boundaries and mineral resources; maritime boundaries and the emerging regional bases of world ocean management; recent delimitation decisions and trends in international law; maritime boundary problems in the Barents Sea; local government boundaries in U.K. coastal areas.

  15. Boundary conditions as dynamical fields

    NASA Astrophysics Data System (ADS)

    Karabali, Dimitra; Nair, V. P.

    2015-12-01

    The possibility of treating boundary conditions in terms of a bilocal dynamical field is formalized in terms of a boundary action. This allows for a simple path-integral perturbation theory approach to physical effects such as radiation from a time-dependent boundary. The nature of the action which governs the dynamics of the bilocal field is investigated for a limited case (which includes the Robin boundary conditions).

  16. Boundary terms for causal sets

    NASA Astrophysics Data System (ADS)

    Buck, Michel; Dowker, Fay; Jubb, Ian; Surya, Sumati

    2015-10-01

    We propose a family of boundary terms for the action of a causal set with a spacelike boundary. We show that in the continuum limit one recovers the Gibbons-Hawking-York boundary term in the mean. We also calculate the continuum limit of the mean causal set action for an Alexandrov interval in flat spacetime. We find that it is equal to the volume of the codimension-2 intersection of the two light-cone boundaries of the interval.

  17. Teaching Educators to Respect Boundaries.

    ERIC Educational Resources Information Center

    Summy, Sarah E.; Bunsen, Teresa D.

    1996-01-01

    Introduces to teachers the concept of defining boundaries, traditionally referred to as appropriate limits, in the relationship between helper and client. Defines the concept of boundaries within current school systems and addresses the importance of boundary issues within all educator training programs, especially in training programs for special…

  18. Word Boundary Tasks for Beginners.

    ERIC Educational Resources Information Center

    Mason, George E.; Mickish, Virginia L.

    A sample of 100 first graders participated in a study of the relationship between three types of spacing used in written sentences for segmenting word boundaries and pupil errors in completing word-boundary tasks. The results indicated that eliminating printer's word boundaries in written sentences had a significant effect on first graders'

  19. Anisotropy across Superplume Boundaries

    NASA Astrophysics Data System (ADS)

    Cottaar, S.; Romanowicz, B. A.

    2011-12-01

    Sdiff data sets are presented for paths that run parallel to the African and the Pacific superplume boundaries. Objective clustering of waveforms illustrates sharp changes across these boundaries. The African plume shows a sharp offset in travel times in the SHdiff phase, while a more gradual offset towards slower arrivals is seen in the case of the Pacific superplume. Additionally, Pdiff phases display no offset around the African plume and a weak one around the Pacific plume. Here we focus mainly on another striking feature observed in both cases: outside of the superplume the Sdiff particle motion is strongly elliptical, but becomes linear within the superplume (first noticed by To et al. 2005 in the African superplume case). For the African plume we argue that these observations of delayed SV at large distances (~120 degrees) are indicative of the occurrence of azimuthal anisotropy. The SV arrivals have similar polarity as SH, opposite from what their radiation pattern predicts. Azimuthal anisotropy causes SH energy to be converted to SV (Maupin, 1994), explaining the travel time, polarity and amplitude. Forward modeling through different isotropic and anisotropic models supports this statement, although there are trade-offs between direction and magnitude of azimuthal anisotropy. The strong elliptical particle motions are also observed outside the Pacific plume, but at shorter distances (95-105 degrees). Elliptical motions can occur in the absence of anisotropy when strong velocity deviations or layering occurs close to the CMB, which, based on velocity profiles with depth in global tomographic models would be more likely within the superplume rather than on the fast side. The elliptical particle motions here can be modelled with a simple transverse isotropic model with VSH>VSV, but azimuthal anisotropy cannot be ruled out. The complexities within the Pacific superplume, including strong amplitude drop and existence of a post-cursor, are likely caused by an ultra low velocity zone (Cottaar and Romanowicz, this meeting) and make it difficult to constrain anisotropy within the Pacific superplume. Notably, however, in both cases, elliptical particle motions become more linear, and thus anisotropy decreases, from the fast side towards the slow side across superplume boundaries. Possibly this is caused by a rotation in the deformational regime, causing rotation of the pre-existing anisotropic fast directions. Forward modeling of deformation using tracers in mantle convection models, considering different mineral physics scenarios (Wenk et al., 2011) suggest that the boundaries in anisotropy from downwellings to upwellings can be sharp, and could possibly contribute to explaining the sharp boundary in VSH, in addition to effects of lateral variations in temperature and composition. Moreover the model for post-perovskite with (001)-slip predicts anti-correlation between S and P wave anisotropy. Variation in VPH due to anisotropy would then be anti-correlated with the variation caused by temperature, and this could explain the lack of correlation in the variations of VSH and VPH across the superplume boundary. Our modeling shows that care must be taken when computing R=dlnVs/dlnVp in the presence of anisotropy.

  20. Open boundary molecular dynamics

    NASA Astrophysics Data System (ADS)

    Delgado-Buscalioni, R.; Sabli?, J.; Praprotnik, M.

    2015-09-01

    This contribution analyzes several strategies and combination of methodologies to perform molecular dynamic simulations in open systems. Here, the term open indicates that the total system has boundaries where transfer of mass, momentum and energy can take place. This formalism, which we call Open Boundary Molecular Dynamics (OBMD), can act as interface of different schemes, such as Adaptive Resolution Scheme (AdResS) and Hybrid continuum-particle dynamics to link atomistic, coarse-grained (CG) and continuum (Eulerian) fluid dynamics in the general framework of fluctuating Navier-Stokes equations. The core domain of the simulation box is solved using all-atom descriptions. The CG layer introduced using AdResS is located at the outer part of the open box to make feasible the insertion of large molecules into the system. Communications between the molecular system and the outer world are carried out in the outer layers, called buffers. These coupling preserve momentum and mass conservation laws and can thus be linked with Eulerian hydro- dynamic solvers. In its simpler form, OBMD allows, however, to impose a local pressure tensor and a heat flux across the system's boundaries. For a one component molecular system, the external normal pressure and temperature determine the external chemical potential and thus the independent parameters of a grand-canonical ensemble simulation. Extended ensembles under non-equilibrium stationary states can also be simulated as well as time dependent forcings (e.g. oscillatory rheology). To illustrate the robustness of the combined OBMD-AdResS method, we present simulations of star-polymer melts at equilibrium and in sheared flow.

  1. Boundaries and Boundary Marks - Substantive Cultural Heritage of Extensive Importance

    NASA Astrophysics Data System (ADS)

    Waldhaeusl, P.; Koenig, H.; Mansberger, R.

    2015-08-01

    The Austrian Society for surveying and Geoinformation (ASG) has proposed to submit "Boundaries and Boundary Marks" for the UNESCO World Heritage title. It was time that boundaries, borders and limits of all types as well as ownership rights would find the proper attention in the global public. Landmarks symbolize the real property and the associated rights and obligations, in a figurative sense, the property generally and all legal limits. A democratic state of law is impossible at today's population density without a functioning land administration system with surveying and jurisdiction. As monumental World Heritage representatives of the geodetic artwork "Boundaries and Boundary Marks" are specifically proposed: remaining monuments of the original cadastral geodetic network, the first pan-Austrian surveying headquarters in Vienna, and a specific selection of outstanding boundary monuments. Landmarks are monuments to the boundaries which separate rights and obligations, but also connect the neighbors peacefully after written agreement. "And cursed be he who does not respect the boundaries" you wrote already 3000 years ago. Boundaries and Boundary Marks are a real thing; they all belong to the tangible or material heritage of human history. In this context also the intangible heritage is discussed. This refers to oral tradition and expressions, performing arts; social practices, rituals and festive events; as well as to knowledge and practices handling nature and the universe. "Boundaries and Boundary Marks" do not belong to it, but clearly to the material cultural world heritage. "Boundary and Boundary Marks" is proposed to be listed according to the criteria (ii),(iv),(vi).

  2. U-Pb isotopic results for single shocked and polycrystalline zircons record 550-65.5-Ma ages for a K-T target site and 2700-1850-Ma ages for the Sudbury impact event

    NASA Technical Reports Server (NTRS)

    Krogh, T. E.; Kamo, S. L.; Bohor, B. F.

    1992-01-01

    The refractory mineral zircon develops distinct morphological features during shock metamorphism and retains these features under conditions that would anneal them in other minerals. In addition, weakly shocked zircon grains give primary ages for the impact site, while highly reconstituted (polycrystalline) single grains give ages that approach the age of the impact event. Data for a series of originally coeval grains will define a mixing line that gives both of these ages providing that no subsequent geological disturbances have overprinted the isotopic systematics. In this study, we have shown that the three zircon grain types described by Bohor, from both K-T distal ejecta (Fireball layer, Raton Basin, Colorado) and the Onaping Formation, represent a progressive increase in impact-related morphological change that coincides with a progressive increase in isotopic resetting in zircons from the ejecta and basement rocks. Unshocked grains are least affected by isotopic resetting while polycrystalline grains are most affected. U-Pb isotopic results for 12 of 14 single zircon grains from the Fireball layer plot on or close to a line recording a primary age of 550 +/- 10 Ma and a secondary age of 65.5 +/- 3 Ma. Data for the least and most shocked grains plot closest to the primary and secondary ages respectively. The two other grains each give ages between 300 and 350 Ma. This implies that the target ejecta was dominated by 550-Ma rocks and that the recrystallization features of the zircon were superimposed during the impact event at 65.5 Ma. A predominant age of 550 Ma for zircons from the Fireball layer provides an excellent opportunity to identify the impact site and to test the hypothesis that multiple impacts occurred at this time. A volcanic origin for the Fireball layer is ruled out by shock-related morphological changes in zircon and the fact that the least shocked grains are old. Basement Levack gneisses north of the Sudbury structure have a primary age of 2711 Ma. Data for three single zircons from this rock, which record a progressive increase in shock features, are displaced 24, 36, and 45 percent along a Pb-loss line toward the 1850 +/- 1 Ma minimum age for the impact as defined by the age of the norite. Southeast of the structure three shocked grains from the Murray granite record a primary age of 2468 Ma and are displaced 24, 41, and 56 percent toward the 1853 +/- 4 Ma even as defined by coexisting titanite.

  3. Vortex boundary-layer interactions

    NASA Technical Reports Server (NTRS)

    Bradshaw, P.

    1986-01-01

    The interaction of a turbulent boundary layer (on a flat plate) with a strong artificially-generated longitudinal vortex, which may or may not actually enter the boundary layer, was studied. Experiments, including extensive hot-wire measurements, were completed for the case in which the vortex does enter the boundary layer, and measurements for the somewhat simpler cases in which the boundary layer and vortex remain distinct are now in progress. Contours of total pressure (recently acquired) and of turbulent kinetic energy at various downstream positions are presented to show the overall development of the vortex imbedded in the boundary layer.

  4. A classification of ecological boundaries

    USGS Publications Warehouse

    Strayer, D.L.; Power, M.E.; Fagan, W.F.; Pickett, S.T.A.; Belnap, J.

    2003-01-01

    Ecologists use the term boundary to refer to a wide range of real and conceptual structures. Because imprecise terminology may impede the search for general patterns and theories about ecological boundaries, we present a classification of the attributes of ecological boundaries to aid in communication and theory development. Ecological boundaries may differ in their origin and maintenance, their spatial structure, their function, and their temporal dynamics. A classification system based on these attributes should help ecologists determine whether boundaries are truly comparable. This system can be applied when comparing empirical studies, comparing theories, and testing theoretical predictions against empirical results.

  5. Boundary layer transition studies

    NASA Technical Reports Server (NTRS)

    Watmuff, Jonathan H.

    1995-01-01

    A small-scale wind tunnel previously used for turbulent boundary layer experiments was modified for two sets of boundary layer transition studies. The first study concerns a laminar separation/turbulent reattachment. The pressure gradient and unit Reynolds number are the same as the fully turbulent flow of Spalart and Watmuff. Without the trip wire, a laminar layer asymptotes to a Falkner & Skan similarity solution in the FPG. Application of the APG causes the layer to separate and a highly turbulent and approximately 2D mean flow reattachment occurs downstream. In an effort to gain some physical insight into the flow processes a small impulsive disturbance was introduced at the C(sub p) minimum. The facility is totally automated and phase-averaged data are measured on a point-by-point basis using unprecedently large grids. The evolution of the disturbance has been tracked all the way into the reattachment region and beyond into the fully turbulent boundary layer. At first, the amplitude decays exponentially with streamwise distance in the APG region, where the layer remains attached, i.e. the layer is viscously stable. After separation, the rate of decay slows, and a point of minimum amplitude is reached where the contours of the wave packet exhibit dispersive characteristics. From this point, exponential growth of the amplitude of the disturbance is observed in the detached shear layer, i.e. the dominant instability mechanism is inviscid. A group of large-scale 3D vortex loops emerges in the vicinity of the reattachment. Remarkably, the second loop retains its identify far downstream in the turbulent boundary layer. The results provide a level of detail usually associated with CFD. Substantial modifications were made to the facility for the second study concerning disturbances generated by Suction Holes for laminar flow Control (LFC). The test section incorporates suction through interchangeable porous test surfaces. Detailed studies have been made using isolated holes in the impervious test plate that used to establish the Blasius base flow. The suction is perturbed harmonically and data are averaged on the basis of the phase of the disturbance, for conditions corresponding to strong suction and without suction. The technique was enhanced by using up to nine multiple probes to reduce the experimental run-time. In both cases, 3D contour surfaces in the vicinity of the hole show highly 3D TS waves which fan out in the spanwise direction forming bow-shaped waves downstream. The case without suction has proved useful for evaluating calculation methods. With suction, the perturbations on the centerline are much stronger and decay less rapidly, while the TS waves in the far field are similar to the case without suction. Downstream, the contour surfaces of the TS waves develop spanwise irregularities which eventually form into clumps. The spanwise clumping is evidence of a secondary instability that could be associated with suction vortices. Designers of porous surfaces use Goldsmith's Criterion to minimize cross-stream interactions. It is shown that partial TS wave cancellation is possible, depending on the hole spacing, disturbance frequency and free-stream velocity. New high-performance Constant Temperature Hot-Wire Anemometers were designed and built, based on a linear system theory analysis that can be extended to arbitrary order. The motivation was to achieve the highest possible frequency reponse while ensuring overall system stability. The performance is equal to or superior to commercially available instruments at about 10% of the cost. Details, such as fabrication drawings and a parts list, have been published to enable the instrument to be construced by others.

  6. Critical frequencies at ocean boundaries

    NASA Astrophysics Data System (ADS)

    Clarke, Allan J.; Shi, Chuan

    1991-06-01

    Past theoretical work has shown that for low-frequency flow at a given ocean boundary location, a critical frequency ωc exists such that for ω > ωc unforced motion is trapped to the coast while for ω; < ωc energy leaves the coast. Alternatively, for motion of a given frequency ω on the boundary, there exists a critical latitude such that the motion is trapped to the coast poleward of that latitude but equatorward it is not. This theory is discussed physically for both meridional and nonmeridional boundaries. The simple formula for critical frequency along a nonmeridional boundary is used to document critical periods for the eastern and western Atlantic, Pacific, and Indian Ocean boundaries. The theory occasionally breaks down when boundary curvature is too large.

  7. Boundary terms of conformal anomaly

    NASA Astrophysics Data System (ADS)

    Solodukhin, Sergey N.

    2016-01-01

    We analyze the structure of the boundary terms in the conformal anomaly integrated over a manifold with boundaries. We suggest that the anomalies of type B, polynomial in the Weyl tensor, are accompanied with the respective boundary terms of the Gibbons-Hawking type. Their form is dictated by the requirement that they produce a variation which compensates the normal derivatives of the metric variation on the boundary in order to have a well-defined variational procedure. This suggestion agrees with recent findings in four dimensions for free fields of various spins. We generalize this consideration to six dimensions and derive explicitly the respective boundary terms. We point out that the integrated conformal anomaly in odd dimensions is non-vanishing due to the boundary terms. These terms are specified in three and five dimensions.

  8. Modeling the urban boundary layer

    NASA Technical Reports Server (NTRS)

    Bergstrom, R. W., Jr.

    1976-01-01

    A summary and evaluation is given of the Workshop on Modeling the Urban Boundary Layer; held in Las Vegas on May 5, 1975. Edited summaries from each of the session chairpersons are also given. The sessions were: (1) formulation and solution techniques, (2) K-theory versus higher order closure, (3) surface heat and moisture balance, (4) initialization and boundary problems, (5) nocturnal boundary layer, and (6) verification of models.

  9. Boundary degeneracy of topological order

    NASA Astrophysics Data System (ADS)

    Wang, Juven C.; Wen, Xiao-Gang

    2015-03-01

    We introduce the concept of boundary degeneracy, as the ground state degeneracy of topologically ordered states on a compact orientable spatial manifold with gapped boundaries. We emphasize that the boundary degeneracy provides richer information than the bulk degeneracy. Beyond the bulk-edge correspondence, we find the ground state degeneracy of the fully gapped edge modes depends on boundary gapping conditions. By associating different types of boundary gapping conditions as different ways of particle or quasiparticle condensations on the boundary, we develop an analytic theory of gapped boundaries. By Chern-Simons theory, this allows us to derive the ground state degeneracy formula in terms of boundary gapping conditions, which encodes more than the fusion algebra of fractionalized quasiparticles. We apply our theory to Kitaev's toric code and Levin-Wen string-net models. We predict that the Z2 toric code and Z2 double-semion model [more generally, the Zk gauge theory and the U (1) kU (1) -k nonchiral fractional quantum Hall state at even integer k ] can be numerically and experimentally distinguished, by measuring their boundary degeneracy on an annulus or a cylinder.

  10. Symbolic Boundary Work in Schools: Demarcating and Denying Ethnic Boundaries

    ERIC Educational Resources Information Center

    Tabib-Calif, Yosepha; Lomsky-Feder, Edna

    2014-01-01

    This article examines the symbolic boundary work that is carried out at a school whose student population is heterogeneous in terms of ethnicity and class. Based on ethnography, the article demonstrates how the school's staff seeks to neutralize ethnic boundaries and their accompanying discourse, while the pupils try to bring ethnic

  11. Symbolic Boundary Work in Schools: Demarcating and Denying Ethnic Boundaries

    ERIC Educational Resources Information Center

    Tabib-Calif, Yosepha; Lomsky-Feder, Edna

    2014-01-01

    This article examines the symbolic boundary work that is carried out at a school whose student population is heterogeneous in terms of ethnicity and class. Based on ethnography, the article demonstrates how the school's staff seeks to neutralize ethnic boundaries and their accompanying discourse, while the pupils try to bring ethnic…

  12. Boundary-Layer & health

    NASA Astrophysics Data System (ADS)

    Costigliola, V.

    2010-09-01

    It has long been known that specific atmospheric processes, such as weather and longer-term climatic fluctuations, affect human health. The biometeorological literature refers to this relationship as meteorotropism, defined as a change in an organism that is correlated with a change in atmospheric conditions. Plenty of (patho)physiological functions are affected by those conditions - like the respiratory diseases - and currently it is difficult to put any limits for pathologies developed in reply. Nowadays the importance of atmospheric boundary layer and health is increasingly recognised. A number of epidemiologic studies have reported associations between ambient concentrations of air pollution, specifically particulate pollution, and adverse health effects, even at the relatively low concentrations of pollution found. Since 1995 there have been over twenty-one studies from four continents that have explicitly examined the association between ambient air pollutant mixes and daily mortality. Statistically significant and positive associations have been reported in data from various locations around the world, all with varying air pollutant concentrations, weather conditions, population characteristics and public health policies. Particular role has been given to atmospheric boundary layer processes, the impact of which for specific patient-cohort is, however, not well understood till now. Assessing and monitoring air quality are thus fundamental to improve Europe's welfare. One of current projects run by the "European Medical Association" - PASODOBLE will develop and demonstrate user-driven downstream information services for the regional and local air quality sectors by combining space-based and in-situ data with models in 4 thematic service lines: - Health community support for hospitals, pharmacies, doctors and people at risk - Public information for regions, cities, tourist industry and sporting event organizers - Compliance monitoring support on particulate matter for regional environmental agencies - Local forecast model evaluation support for local authorities and city bodies. Giving value to the above listed aspects, PASODOBLE objectives are following: - Evolution of existing and development of new sustainable air quality services for Europe on regional and local scales - Development and testing of a generic service framework for coordinated input data acquisition and customizable user-friendly access to services - Utilization of multiple cycles of delivery, use and assessment versus requirements and market planning in cooperation with users - Promotion and harmonisation of best practise tools for air quality communities. Further European multidisciplinary projects should be created to better understand the most prevalent atmospheric factors to be impacted in predictive, preventive and personalised medicine considered as the central concept for future medicine.

  13. Dependence of Boundary Layer Mixing On Lateral Boundary Conditions

    NASA Astrophysics Data System (ADS)

    Straub, D.

    Ocean circulation models often show strong mixing in association with lateral bound- ary layers. Such mixing is generally considered to be artifactual rather than real. Fur- thermore, the severity of the problem is boundary condition dependent. For example, an inconsistency between geostrophy and insulating boundary conditions on tempera- ture and salinity cause many modelers to opt for the no slip, rather than slip boundary condtion on the tangential component of momentum. As modellers increasingly move into the eddy revealing regime, biharmonic, rather than harmonic dissipative operators are likely to become more common. Biharmonic operators, however, require specifi- cation of additional boundary conditions. For example, there are several `natural ex- tensions' to each of the slip and no slip conditions. Here, these various possiblities are considered in the context of a simple model. Particular attention is payed to how mixing (and the associated overturning cell) is affected by the choice of boundary condition.

  14. Boundary Condtions of Gravity

    NASA Astrophysics Data System (ADS)

    Goradia, Shantilal

    2014-03-01

    Our quantum mechanical derivation of the strong coupling using modified Newtonian inverse square logic in (1) and the fine structure constant (ALPHA) using Boltzmann expression in our book (2) come close to Einstein's 1919 paper merging nuclear force with gravitation and retracting his cosmological constant. Its conflict with the inflationary aspect of the universe can be reconciled with the possibility that the light coming from the receding galaxies follow a curvilinear path increasing in length due to its ever increasing curvature without receding only in the radial direction. In (1), we implicitly show gravity as nothing but the cumulative effect of quantum mechanical forces, making G vary at different locations in the universe. The subsequent effects of gravitational variation would be on the curvature of the paths of the geodesics they create. Further investigation along these lines is warranted as we do not have unification, evidence of graviton, quantum gravity or anything else very concrete after a century of hard work. Strong coupling and ALPHA may be the boundary conditions of gravitational constants.

  15. Boundary Condtions of Gravity

    NASA Astrophysics Data System (ADS)

    Goradia, Shantilal

    2014-05-01

    Our quantum mechanical derivation of the strong coupling using modified Newtonian inverse square logic in (1) and the fine structure constant (ALPHA) using Boltzmann expression in our book (2) come close to Einstein (1919) merging nuclear force with gravitation and retracting his cosmological constant. Its conflict with the inflationary aspect of the universe can be reconciled with the possibility that the light coming from the receding galaxies follow a curvilinear path increasing in length due to its ever increasing curvature without receding only in the radial direction. In (1), we implicitly show gravity as nothing but the cumulative effect of quantum mechanical forces, making G vary at different locations in the universe. The subsequent effects of gravitational variation would be on the curvature of the paths of the geodesics they create. Further investigation along these lines is warranted as we do not have unification, evidence of graviton, quantum gravity or anything else very concrete after a century of hard work. Strong coupling and ALPHA may be the boundary conditions of gravitational constants. Newtonian Gravity in Natural Units, Journal of Physical Science and Application 2 (7) (2012)265-268, [2] Quantum Consciousness - The Road to Reality by S. Goradia, 4/27/20.

  16. Le Crtac-Palogne du Blake Nose (marge atlantique de la Floride, campagne ODP 171 B): un enregistrement exemplaire de la transition Maastrichtien-Danien

    NASA Astrophysics Data System (ADS)

    Bellier, Jean-Pierre; Marca, Sandra; Norris, Richard D.; Kroon, Dick; Klaus, Adam; Alexander, Ian T.; Bardot, Lon Paul; Barker, Charles E.; Blome, Charles D.; Clarke, Leon J.; Erbacher, Jochen; Faul, Kristina L.; Holmes, Mary Anne; Huber, Brian T.; Kate, Miriam E.; MacLeod, Kenneth G.; Martinez-Ruiz, Francisca C.; Mita, Isao; Nakai, Mutsumi; Ogg, James G.; Pak, Dorothy K.; Pletsch, Thomas K.; Self-Trail, Jean M.; Shackleton, Nicholas J.; Smit, Jan; Ussler, William; Watkins, David K.; Widmark, Joen; Wilson, Paul A.

    1997-10-01

    During ODP Leg 171B, devoted to the analysis of the Blake Plateau margin in front of Florida, 16 holes have been drilled in 5 distinct sites. The sites have documented a sedimentary succession ranging in age from Aptian to Eocene. Emphasis has been put on critical periods, comprising the Paleocene-Eocene transition, the Cretaceous-Tertiary boundary which has been cored in excellent conditions, the middle Maastrichtian extinctions and the Albian anoxic episodes.

  17. Alvarez, Luis Walter (1911-88)

    NASA Astrophysics Data System (ADS)

    Murdin, P.

    2000-11-01

    Physicist and astronomer, born in San Francisco, CA, professor at the University of California, Nobel prizewinner (1968) for his discoveries in particle physics. Used cosmic rays to `x-ray' the pyramids of Egypt, finding in particular that the tombs in the Great Pyramid at Giza had no hidden rooms. Alvarez (and his son) discovered globally distributed iridium at the Cretaceous/Tertiary boundary i...

  18. Cell boundary fault detection system

    DOEpatents

    Archer, Charles Jens (Rochester, MN); Pinnow, Kurt Walter (Rochester, MN); Ratterman, Joseph D. (Rochester, MN); Smith, Brian Edward (Rochester, MN)

    2011-04-19

    An apparatus and program product determine a nodal fault along the boundary, or face, of a computing cell. Nodes on adjacent cell boundaries communicate with each other, and the communications are analyzed to determine if a node or connection is faulty.

  19. Calculation of State Specific Rate Coefficients for Non-Equilibrium Hypersonics Applications: from H(Psi) = E(Psi) to k(T) = A *exp(-E(sub a)/RT)

    NASA Technical Reports Server (NTRS)

    Jaffe, Richard; Schwenke, David; Chaban, Galina; Panesi, Marco

    2014-01-01

    Development of High-Fidelity Physics-Based Models to describe hypersonic flight through the atmospheres of Earth and Mars is underway at NASA Ames Research Center. The goal is to construct chemistry models of the collisional and radiative processes that occur in the bow shock and boundary layers of spacecraft during atmospheric entry that are free of empiricism. In this talk I will discuss our philosophy and describe some of our progress. Topics to be covered include thermochemistry, internal energy relaxation, collisional dissociation and radiative emission and absorption. For this work we start by solving the Schrodinger equation to obtain accurate interaction potentials and radiative properties. Then we invoke classical mechanics to compute state-specific heavy particle collision cross sections and reaction rate coefficients. Finally, phenomenological rate coefficients and relaxation times are determined from master equation solutions.

  20. Improved boundary tracking by off-boundary detection

    NASA Astrophysics Data System (ADS)

    Chen, Alex

    2012-11-01

    This work discusses an improvement to the boundary tracking algorithm introduced by Chen et al 2011. This method samples points in an image locally and utilizes the CUSUM algorithm to reduce tracking problems due to noise or texture. However, when tracking problems do arise, the local nature of the algorithm does not give any mechanism in which to recover. This work introduces a second CUSUM algorithm to detect off-boundary movement, compensating for such movement by backtracking. Boundary tracking results comparing the two algorithms are presented, including both image data and a numerical comparison of the effectiveness of the algorithms.

  1. Dimension of fractal basin boundaries

    SciTech Connect

    Park, B.S.

    1988-01-01

    In many dynamical systems, multiple attractors coexist for certain parameter ranges. The set of initial conditions that asymptotically approach each attractor is its basin of attraction. These basins can be intertwined on arbitrary small scales. Basin boundary can be either smooth or fractal. Dynamical systems that have fractal basin boundary show final state sensitivity of the initial conditions. A measure of this sensitivity (uncertainty exponent {alpha}) is related to the dimension of the basin boundary d = D - {alpha}, where D is the dimension of the phase space and d is the dimension of the basin boundary. At metamorphosis values of the parameter, there might happen a conversion from smooth to fractal basin boundary (smooth-fractal metamorphosis) or a conversion from fractal to another fractal basin boundary characteristically different from the previous fractal one (fractal-fractal metamorphosis). The dimension changes continuously with the parameter except at the metamorphosis values where the dimension of the basin boundary jumps discontinuously. We chose the Henon map and the forced damped pendulum to investigate this. Scaling of the basin volumes near the metamorphosis values of the parameter is also being studied for the Henon map. Observations are explained analytically by using low dimensional model map.

  2. The Cantarell Breccia System, Southern Gulf Of Mexico: Structural Evolution And Support For An Origin Relarted To The Chixculub Meteorite Impact

    NASA Astrophysics Data System (ADS)

    Ricoy, V.

    2003-04-01

    The Upper Cretaceous within the Campeche Basin, southern Gulf of Mexico hosts a world class petroleum system. Cantarell is the most important reservoir that consists of a complex brecciated carbonate reservoir deposited at or around the Cretaceous-Tertiary boundary. Previous sedimentological studies suggests that the Upper Cretaceous Carbonate breccias found in the Cantarell oilfield system and through the Bay of Campeche, were the result of a catastrophic shelf collapse event triggered by the Chixculub meteorite impact. This work presents new evidence from structural and stratigraphic interpretation of 3D seismic and 2D lines which gives light to features that support the platform collapse model. The reservoir consists of thick (up to 300 m), heterogeneous, monomyctic and polymictic breccias developed at the K-T boundary, and widely distributed throughout the Campeche Basin. The timing, internal architecture, widespread deposition and distance to the platform margin source (over 30 kms) of the breccia unit, combined with a contorted irregular seismic reflector near the base of the Cretaceous carbonate platform, suggests that the geological processes accountable for the emplacement of the breccias relates to the massive catastrophic collapse of the Cretaceous platform as a result of the Chixculub meteorite impact. Structural interpretation of the 3D seismic data, together with well stratigraphic markers unraveled a complex Oligocene-Miocene structural deformation history of the Cantarell field, which resulted in several discrete reservoir blocks partitioned by a complex array of thrusts, normal and reverse faults. It is proposed that the structural deformation of the area controlled to a large extent the distribution of the reservoir properties found in the Cantarell area. This idea is tested using the structural model matched against the well log porosity data.

  3. Vortex boundary-layer interactions

    NASA Technical Reports Server (NTRS)

    Bradshaw, P.

    1985-01-01

    The interaction of a turbulent boundary layer on a flat plate with a strong artificially generated longitudinal vortex which may or may not actually enter the boundary layer is studied. The vortices are generated by a delta wing suspended ahead of the test plate, so that the configuration is approximately that of a close coupled carnard with zero main-wing sweep and an invisible body. All necessary configuration and parametric checks are completed, and data acquisition and analysis on the first configuration chosen for detailed study, in which the vortex starts to merge with the boundary layer a short distance downstream of the leading edge of the test plate, are nearly complete.

  4. Boundary Conditions in Elementary Mechanics.

    ERIC Educational Resources Information Center

    Gonzalez, Alejandro D.

    1991-01-01

    Uses the problem of determining when a car and truck traveling at the same speed will collide after the truck has applied its brakes to illustrate the need to consider boundary conditions when solving problems in elementary mechanics. (MDH)

  5. Boundary Layer Control on Airfoils.

    ERIC Educational Resources Information Center

    Gerhab, George; Eastlake, Charles

    1991-01-01

    A phenomena, boundary layer control (BLC), produced when visualizing the fluidlike flow of air is described. The use of BLC in modifying aerodynamic characteristics of airfoils, race cars, and boats is discussed. (KR)

  6. Removing Boundary Layer by Suction

    NASA Technical Reports Server (NTRS)

    Ackeret, J

    1927-01-01

    Through the utilization of the "Magnus effect" on the Flettner rotor ship, the attention of the public has been directed to the underlying physical principle. It has been found that the Prandtl boundary-layer theory furnishes a satisfactory explanation of the observed phenomena. The present article deals with the prevention of this separation or detachment of the flow by drawing the boundary layer into the inside of a body through a slot or slots in its surface.

  7. Changing the Structure Boundary Geometry

    SciTech Connect

    Karasev, Viktor; Dzlieva, Elena; Ivanov, Artyom

    2008-09-07

    Analysis of previously obtained results shows that hexagonal crystal lattice is the dominant type of ordering, in particular, in striated glow discharges. We explore the possibility for changing the dust distribution in horizontal cross sections of relatively highly ordered structures in a glow-discharge. Presuming that boundary geometry can affect dust distribution, we used cylindrical coolers held at 0 deg. C and placed against a striation containing a structure, to change the geometry of its outer boundary. By varying the number of coolers, their positions, and their separations from the tube wall, azimuthally asymmetric thermophoretic forces can be used to form polygonal boundaries and vary the angles between their segments (in a horizontal cross section). The corner in the structure's boundary of 60 deg. stimulates formation of hexagonal cells. The structure between the supported parallel boundaries is also characterized by stable hexagonal ordering. We found that a single linear boundary segment does not give rise to any sizable domain, but generates a lattice extending from the boundary (without edge defects). A square lattice can be formed by setting the angle equal to 90 deg. . However, angles of 45 deg. and 135 deg. turned out easier to form. Square lattice was created by forming a near-135 deg. corner with four coolers. It was noted that no grain ordering is observed in the region adjacent to corners of angles smaller than 30 deg. , which do not promote ordering into cells of any shape. Thus, manipulation of a structure boundary can be used to change dust distribution, create structures free of the ubiquitous edge defects that destroy orientation order, and probably change the crystal lattice type.

  8. Pyramidal inversion domain boundaries revisited

    SciTech Connect

    Remmele, T.; Albrecht, M.; Irmscher, K.; Fornari, R.; Strassburg, M.

    2011-10-03

    The structure of pyramidal inversion domain boundaries in GaN:Mg was investigated by aberration corrected transmission electron microscopy. The analysis shows the upper (0001) boundary to consist of a single Mg layer inserted between polarity inverted GaN layers in an abcab stacking. The Mg bound in these defects is at least one order of magnitude lower than the chemical Mg concentration. Temperature dependent Hall effect measurements show that up to 27% of the Mg acceptors is electrically compensated.

  9. Boundary Condition for Modeling Semiconductor Nanostructures

    NASA Technical Reports Server (NTRS)

    Lee, Seungwon; Oyafuso, Fabiano; von Allmen, Paul; Klimeck, Gerhard

    2006-01-01

    A recently proposed boundary condition for atomistic computational modeling of semiconductor nanostructures (particularly, quantum dots) is an improved alternative to two prior such boundary conditions. As explained, this boundary condition helps to reduce the amount of computation while maintaining accuracy.

  10. Tidal boundary conditions in SEAWAT.

    PubMed

    Mulligan, Ann E; Langevin, Christian; Post, Vincent E A

    2011-01-01

    SEAWAT, a U.S. Geological Survey groundwater flow and transport code, is increasingly used to model the effects of tidal motion on coastal aquifers. Different options are available to simulate tidal boundaries but no guidelines exist nor have comparisons been made to identify the most effective approach. We test seven methods to simulate a sloping beach and a tidal flat. The ocean is represented in one of the three ways: directly using a high hydraulic conductivity (high-K) zone and indirect simulation via specified head boundaries using either the General Head Boundary (GHB) or the new Periodic Boundary Condition (PBC) package. All beach models simulate similar water fluxes across the upland boundary and across the sediment-water interface although the ratio of intertidal to subtidal flow is different at low tide. Simulating a seepage face results in larger intertidal fluxes and influences near-shore heads and salinity. Major differences in flow occur in the tidal flat simulations. Because SEAWAT does not simulate unsaturated flow the water table only rises via flow through the saturated zone. This results in delayed propagation of the rising tidal signal inland. Inundation of the tidal flat is delayed as is flow into the aquifer across the flat. This is severe in the high-K and PBC models but mild in the GHB models. Results indicate that any of the tidal boundary options are fine if the ocean-aquifer interface is steep. However, as the slope of that interface decreases, the high-K and PBC approaches perform poorly and the GHB boundary is preferable. PMID:21275984

  11. Squirmer dynamics near a boundary.

    PubMed

    Ishimoto, Kenta; Gaffney, Eamonn A

    2013-12-01

    The boundary behavior of axisymmetric microswimming squirmers is theoretically explored within an inertialess Newtonian fluid for a no-slip interface and also a free surface in the small capillary number limit, preventing leading-order surface deformation. Such squirmers are commonly presented as abridged models of ciliates, colonial algae, and Janus particles and we investigate the case of low-mode axisymmetric tangential surface deformations with, in addition, the consideration of a rotlet dipole to represent torque-motor swimmers such as flagellated bacteria. The resulting boundary dynamics reduces to a phase plane in the angle of attack and distance from the boundary, with a simplifying time-reversal duality. Stable swimming adjacent to a no-slip boundary is demonstrated via the presence of stable fixed points and, more generally, all types of fixed points as well as stable and unstable limit cycles occur adjacent to a no-slip boundary with variations in the tangential deformations. Nonetheless, there are constraints on swimmer behavior-for instance, swimmers characterized as pushers are never observed to exhibit stable limit cycles. All such generalities for no-slip boundaries are consistent with observations and more geometrically faithful simulations to date, suggesting the tangential squirmer is a relatively simple framework to enable predications and classifications for the complexities associated with axisymmetric boundary swimming. However, in the presence of a free surface, with asymptotically small capillary number, and thus negligible leading-order surface deformation, no stable surface swimming is predicted across the parameter space considered. While this is in contrast to experimental observations, for example, the free-surface accumulation of sterlet sperm, extensive surfactants are present, most likely invalidating the low capillary number assumption. In turn, this suggests the necessity of surface deformation for stable free-surface three-dimensional finite-size microswimming, as previously highlighted in a two-dimensional mathematical study of singularity swimmers [Crowdy et al., J. Fluid Mech. 681, 24 (2011)]. PMID:24483481

  12. Undulatory microswimming near solid boundaries

    NASA Astrophysics Data System (ADS)

    Schulman, R. D.; Backholm, M.; Ryu, W. S.; Dalnoki-Veress, K.

    2014-10-01

    The hydrodynamic forces involved in the undulatory microswimming of the model organism C. elegans are studied in proximity to solid boundaries. Using a micropipette deflection technique, we attain direct and time-resolved force measurements of the viscous forces acting on the worm near a single planar boundary as well as confined between two planar boundaries. We observe a monotonic increase in the lateral and propulsive forces with increasing proximity to the solid interface. We determine normal and tangential drag coefficients for the worm, and find these to increase with confinement. The measured drag coefficients are compared to existing theoretical models. The ratio of normal to tangential drag coefficients is found to assume a constant value of 1.5 0.1(5) at all distances from a single boundary, but increases significantly as the worm is confined between two boundaries. In response to the increased drag due to confinement, we observe a gait modulation of the nematode, which is primarily characterized by a decrease in the swimming amplitude.

  13. Physics of magnetospheric boundary layers

    NASA Technical Reports Server (NTRS)

    Cairns, Iver H.

    1995-01-01

    This final report was concerned with the ideas that: (1) magnetospheric boundary layers link disparate regions of the magnetosphere-solar wind system together; and (2) global behavior of the magnetosphere can be understood only by understanding its internal linking mechanisms and those with the solar wind. The research project involved simultaneous research on the global-, meso-, and micro-scale physics of the magnetosphere and its boundary layers, which included the bow shock, the magnetosheath, the plasma sheet boundary layer, and the ionosphere. Analytic, numerical, and simulation projects were performed on these subjects, as well as comparisons of theoretical results with observational data. Other related activity included in the research included: (1) prediction of geomagnetic activity; (2) global MHD (magnetohydrodynamic) simulations; (3) Alfven resonance heating; and (4) Critical Ionization Velocity (CIV) effect. In the appendixes are list of personnel involved, list of papers published; and reprints or photocopies of papers produced for this report.

  14. Watershed Boundary Dataset for Mississippi

    USGS Publications Warehouse

    Wilson, K. Van, Jr.; Clair, Michael G., II; Turnipseed, D. Phil; Rebich, Richard A.

    2009-01-01

    The U.S. Geological Survey, in cooperation with the Mississippi Department of Environmental Quality, U.S. Department of Agriculture-Natural Resources Conservation Service, Mississippi Department of Transportation, U.S. Department of Agriculture-Forest Service, and the Mississippi Automated Resource Information System developed a 1:24,000-scale Watershed Boundary Dataset for Mississippi including watershed and subwatershed boundaries, codes, names, and areas. The Watershed Boundary Dataset for Mississippi provides a standard geographical framework for water-resources and selected land-resources planning. The original 8-digit subbasins (Hydrologic Unit Codes) were further subdivided into 10-digit watersheds (62.5 to 391 square miles (mi2)) and 12-digit subwatersheds (15.6 to 62.5 mi2) - the exceptions being the Delta part of Mississippi and the Mississippi River inside levees, which were subdivided into 10-digit watersheds only. Also, large water bodies in the Mississippi Sound along the coast were not delineated as small as a typical 12-digit subwatershed. All of the data - including watershed and subwatershed boundaries, subdivision codes and names, and drainage-area data - are stored in a Geographic Information System database, which are available at: http://ms.water.usgs.gov/. This map shows information on drainage and hydrography in the form of U.S. Geological Survey hydrologic unit boundaries for water-resource 2-digit regions, 4-digit subregions, 6-digit basins (formerly called accounting units), 8-digit subbasins (formerly called cataloging units), 10-digit watershed, and 12-digit subwatersheds in Mississippi. A description of the project study area, methods used in the development of watershed and subwatershed boundaries for Mississippi, and results are presented in Wilson and others (2008). The data presented in this map and by Wilson and others (2008) supersede the data presented for Mississippi by Seaber and others (1987) and U.S. Geological Survey (1977).

  15. 3D grain boundary migration

    NASA Astrophysics Data System (ADS)

    Becker, J. K.; Bons, P. D.

    2009-04-01

    Microstructures of rocks play an important role in determining rheological properties and help to reveal the processes that lead to their formation. Some of these processes change the microstructure significantly and may thus have the opposite effect in obliterating any fabrics indicative of the previous history of the rocks. One of these processes is grain boundary migration (GBM). During static recrystallisation, GBM may produce a foam texture that completely overprints a pre-existing grain boundary network and GBM actively influences the rheology of a rock, via its influence on grain size and lattice defect concentration. We here present a new numerical simulation software that is capable of simulating a whole range of processes on the grain scale (it is not limited to grain boundary migration). The software is polyhedron-based, meaning that each grain (or phase) is represented by a polyhedron that has discrete boundaries. The boundary (the shell) of the polyhedron is defined by a set of facets which in turn is defined by a set of vertices. Each structural entity (polyhedron, facets and vertices) can have an unlimited number of parameters (depending on the process to be modeled) such as surface energy, concentration, etc. which can be used to calculate changes of the microstructre. We use the processes of grain boundary migration of a "regular" and a partially molten rock to demonstrate the software. Since this software is 3D, the formation of melt networks in a partially molten rock can also be studied. The interconnected melt network is of fundamental importance for melt segregation and migration in the crust and mantle and can help to understand the core-mantle differentiation of large terrestrial planets.

  16. AC conductivity scaling behavior in grain and grain boundary response regime of fast lithium ionic conductors

    NASA Astrophysics Data System (ADS)

    Mariappan, C. R.

    2014-05-01

    AC conductivity spectra of Li-analogues NASICON-type Li1.5Al0.5Ge1.5P3O12 (LAGP), Li-Al-Ti-P-O (LATP) glass-ceramics and garnet-type Li7La2Ta2O13 (LLTO) ceramic are analyzed by universal power law and Summerfield scaling approaches. The activation energies and pre-exponential factors of total and grain conductivities are following the Meyer-Neldel (M-N) rule for NASICON-type materials. However, the garnet-type LLTO material deviates from the M-N rule line of NASICON-type materials. The frequency- and temperature-dependent conductivity spectra of LAGP and LLTO are superimposed by Summerfield scaling. The scaled conductivity curves of LATP are not superimposed at the grain boundary response region. The superimposed conductivity curves are observed at cross-over frequencies of grain boundary response region for LATP by incorporating the exp ( {{{ - (EAt - EAg )} {{{ - (EAt - EAg )} {kT}}} ) factor along with Summerfield scaling factors on the frequency axis, where EAt and EAg are the activation energies of total and grain conductivities, respectively.

  17. Nonparallel stability of boundary layers

    NASA Technical Reports Server (NTRS)

    Nayfeh, Ali H.

    1987-01-01

    The asymptotic formulations of the nonparallel linear stability of incompressible growing boundary layers are critically reviewed. These formulations can be divided into two approaches. The first approach combines a numerical method with either the method of multiple scales, or the method of averaging, of the Wentzel-Kramers-Brillouin (WKB) approximation; all these methods yield the same result. The second approach combined a multi-structure theory with the method of multiple scales. The first approach yields results that are in excellent agreement with all available experimental data, including the growth rates as well as the neutral stability curve. The derivation of the linear stability of the incompressible growing boundary layers is explained.

  18. 15 CFR 923.31 - Inland boundary.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 15 Commerce and Foreign Trade 3 2011-01-01 2011-01-01 false Inland boundary. 923.31 Section 923.31... ZONE MANAGEMENT PROGRAM REGULATIONS Boundaries § 923.31 Inland boundary. (a) The inland boundary of a... the region; (5) Beaches—The area affected by wave action directly from the sea. Examples are...

  19. Boundaries and the Exploration of Self

    ERIC Educational Resources Information Center

    Gharabaghi, Kiaras

    2008-01-01

    Boundaries and the exploration of self are conceptualized within the agency-structure problem first articulated in social theory during the 1970s. Constructing boundaries as a professional issue within the discipline has to take account the agency embedded within boundaries. Multiple boundary dilemmas are discussed within the framework of the…

  20. Boundaries and the Exploration of Self

    ERIC Educational Resources Information Center

    Gharabaghi, Kiaras

    2008-01-01

    Boundaries and the exploration of self are conceptualized within the agency-structure problem first articulated in social theory during the 1970s. Constructing boundaries as a professional issue within the discipline has to take account the agency embedded within boundaries. Multiple boundary dilemmas are discussed within the framework of the

  1. Nucleation of small-angle boundaries

    SciTech Connect

    Nabarro, F.R.N.; Wilsdorf, D.K.

    1996-12-01

    The internal stresses induced by the strain gradients in an array of lattice cells delineated by low-angle dislocation boundaries are partially relieved by the creation of new low-angle boundaries. This is shown to be a first-order transition, the new boundaries having finite misorientations. The calculated misorientations both of the new boundaries and of the existing boundaries which provoke the transition agree well with observations.

  2. Prosodic Boundaries in Alaryngeal Speech

    ERIC Educational Resources Information Center

    van Rossum, M. A.; Quene, H.; Nooteboom, S. G.

    2008-01-01

    Alaryngeal speakers (speakers in whom the larynx has been removed) have inconsistent control over acoustic parameters such as F[subscript 0] and duration. This study investigated whether proficient tracheoesophageal and oesophageal speakers consistently convey phrase boundaries. It was further investigated if these alaryngeal speakers used the…

  3. NEVADA RCRA TSD FACILITY BOUNDARIES

    EPA Science Inventory

    Polygon coverage of RCRA TSD facility boundaries in Nevada. These are derived from original maps and descriptions located in the US EPA Region 9 Records Center files. Current TSD facility designations were extracted from the ARIS (RCRIS) database in June 1998. Auxiliary tables i...

  4. CALIFORNIA RCRA TSD FACILITY BOUNDARIES

    EPA Science Inventory

    Polygon coverage of RCRA TSD facility boundaries in California. These are derived from original maps and descriptions located in the US EPA Region 9 Records Center files. Current TSD facility designations were extracted from the ARIS (RCRIS) database in June 1998. Auxiliary tabl...

  5. HAWAII RCRA TSD FACILITY BOUNDARIES

    EPA Science Inventory

    Polygon coverage of RCRA TSD facility boundaries in Hawaii. These are derived from original maps and descriptions located in the US EPA Region 9 Records Center files. Current TSD facility designations were extracted from the ARIS (RCRIS) database in June 1998. Auxiliary tables i...

  6. ARIZONA RCRA TSD FACILITY BOUNDARIES

    EPA Science Inventory

    Polygon coverage of RCRA TSD facility boundaries in Arizona. These are derived from original maps and descriptions located in the US EPA Region 9 Records Center files. Current TSD facility designations were extracted from the ARIS (RCRIS) database in June 1998. Auxiliary tables ...

  7. Boundary Element Programming in Mechanics

    NASA Astrophysics Data System (ADS)

    Gao, Xiao-Wei; Davies, Trevor G.

    2002-03-01

    This monograph describes the application of boundary element methods (BEM) in solid mechanics, beginning with basic theory and then explaining the numerical implementation of BEM in nonlinear stress analysis. In addition, the authors have developed state-of-the-art BEM source code, available for the first time on a CD-ROM included with the book.

  8. The seismotectonics of plate boundaries

    NASA Technical Reports Server (NTRS)

    Berger, J.; Brune, J. N.; Goodkind, J.; Wyatt, F.; Agnew, D. C.; Beaumont, C.

    1981-01-01

    Research on the seismotectonics of plate boundaries is summarized. Instrumental development and an observational program designed to study various aspects of the seismotectonics of southern California and the northern Gulf of California are described. A unique superconducting gravimeter was further developed and supported under this program for deployment and operation at several sites. Work on Earth tides is also discussed.

  9. Science beyond the Classroom Boundaries

    ERIC Educational Resources Information Center

    Feasey, Rosemary; Bianchi, Lynne

    2011-01-01

    There have been many years of innovation in primary science education. Surprisingly, however, most of this has taken place within the confines of the classroom. What primary science has not yet done with universal success is step outside the classroom boundaries to use the school grounds for teaching and learning across all aspects of the science

  10. Prosodic Boundaries in Alaryngeal Speech

    ERIC Educational Resources Information Center

    van Rossum, M. A.; Quene, H.; Nooteboom, S. G.

    2008-01-01

    Alaryngeal speakers (speakers in whom the larynx has been removed) have inconsistent control over acoustic parameters such as F[subscript 0] and duration. This study investigated whether proficient tracheoesophageal and oesophageal speakers consistently convey phrase boundaries. It was further investigated if these alaryngeal speakers used the

  11. Boundary elements for structural analysis

    NASA Technical Reports Server (NTRS)

    1989-01-01

    The intent here is to discuss the status of the boundary element method (BEM) for structural analysis, both in terms of the present and anticipated capabilities of the method and in terms of the incorporation of the method in the design/analysis process, particularly for gas turbine engine components.

  12. Patients, friends, and relationship boundaries.

    PubMed Central

    Rourke, J. T.; Smith, L. F.; Brown, J. B.

    1993-01-01

    When patient and physician are close friends, both professional and personal relationships can suffer. Jointly exploring and setting explicit boundaries can help avoid conflict and maintain these valuable relationships. This is particularly important when the physician practises in a small community where such concurrent relationships are unavoidable. PMID:8292931

  13. Physics of magnetospheric boundary layers

    NASA Technical Reports Server (NTRS)

    Cairns, I. H.

    1993-01-01

    The central ideas of this grant are that the magnetospheric boundary layers link disparate regions of the magnetosphere together, and the global behavior of the magnetosphere can be understood only by understanding the linking mechanisms. Accordingly the present grant includes simultaneous research on the global, meso-, and micro-scale physics of the magnetosphere and its boundary layers. These boundary layers include the bow shock, magnetosheath, the plasma sheet boundary layer, and the ionosphere. Analytic, numerical and simulation projects have been performed on these subjects, as well as comparison of theoretical results with observational data. Very good progress has been made, with four papers published or in press and two additional papers submitted for publication during the six month period 1 June - 30 November 1993. At least two projects are currently being written up. In addition, members of the group have given papers at scientific meetings. The further structure of this report is as follows: section two contains brief accounts of research completed during the last six months, while section three describes the research projects intended for the grant's final period.

  14. Squirmer dynamics near a boundary

    NASA Astrophysics Data System (ADS)

    Ishimoto, Kenta; Gaffney, Eamonn A.

    2013-12-01

    The boundary behavior of axisymmetric microswimming squirmers is theoretically explored within an inertialess Newtonian fluid for a no-slip interface and also a free surface in the small capillary number limit, preventing leading-order surface deformation. Such squirmers are commonly presented as abridged models of ciliates, colonial algae, and Janus particles and we investigate the case of low-mode axisymmetric tangential surface deformations with, in addition, the consideration of a rotlet dipole to represent torque-motor swimmers such as flagellated bacteria. The resulting boundary dynamics reduces to a phase plane in the angle of attack and distance from the boundary, with a simplifying time-reversal duality. Stable swimming adjacent to a no-slip boundary is demonstrated via the presence of stable fixed points and, more generally, all types of fixed points as well as stable and unstable limit cycles occur adjacent to a no-slip boundary with variations in the tangential deformations. Nonetheless, there are constraints on swimmer behaviorfor instance, swimmers characterized as pushers are never observed to exhibit stable limit cycles. All such generalities for no-slip boundaries are consistent with observations and more geometrically faithful simulations to date, suggesting the tangential squirmer is a relatively simple framework to enable predications and classifications for the complexities associated with axisymmetric boundary swimming. However, in the presence of a free surface, with asymptotically small capillary number, and thus negligible leading-order surface deformation, no stable surface swimming is predicted across the parameter space considered. While this is in contrast to experimental observations, for example, the free-surface accumulation of sterlet sperm, extensive surfactants are present, most likely invalidating the low capillary number assumption. In turn, this suggests the necessity of surface deformation for stable free-surface three-dimensional finite-size microswimming, as previously highlighted in a two-dimensional mathematical study of singularity swimmers [Crowdy , J. Fluid Mech.JFLSA70022-112010.1017/jfm.2011.223 681, 24 (2011)].

  15. Absorbing boundary conditions for exterior problems

    NASA Technical Reports Server (NTRS)

    Hariharan, S. I.

    1985-01-01

    Elliptic and hyperbolic problems in unbounded regions are considered. These problems, when one wants to solve them numerically, have the difficulty of prescribing boundary conditions at infinity. Computationally, one needs a finite region in which to solve these problems. The corresponding conditions at infinity imposed on the finite distance boundaries should dictate the boundary condition at infinity and be accurate with respect to the interior numerical scheme. Such boundary conditions are commonly referred to as absorbing boundary conditions. A treatment is given of these boundary conditions for wave-like equations.

  16. Cloud boundaries during FIRE 2

    NASA Technical Reports Server (NTRS)

    Uttal, Taneil; Shaver, Scott M.; Clothiaux, Eugene E.; Ackerman, Thomas P.

    1993-01-01

    To our knowledge, previous observations of cloud boundaries have been limited to studies of cloud bases with ceilometers, cloud tops with satellites, and intermittent reports by aircraft pilots. Comprehensive studies that simultaneously record information of cloud top and cloud base, especially in multiple layer cases, have been difficult, and require the use of active remote sensors with range-gated information. In this study, we examined a 4-week period during which the NOAA Wave Propagation Laboratory (WPL) 8-mm radar and the Pennsylvania State University (PSU) 3-mm radar operated quasi-continuously, side by side. By quasi-continuously, we mean that both radars operated during all periods when cloud was present, during both daytime and nighttime hours. Using this data, we develop a summary of cloud boundaries for the month of November for a single location in the mid-continental United States.

  17. Boundary Preserving Dense Local Regions.

    PubMed

    Kim, Jaechul; Grauman, Kristen

    2015-05-01

    We propose a dense local region detector to extract features suitable for image matching and object recognition tasks. Whereas traditional local interest operators rely on repeatable structures that often cross object boundaries (e.g., corners, scale-space blobs), our sampling strategy is driven by segmentation, and thus preserves object boundaries and shape. At the same time, whereas existing region-based representations are sensitive to segmentation parameters and object deformations, our novel approach to robustly sample dense sites and determine their connectivity offers better repeatability. In extensive experiments, we find that the proposed region detector provides significantly better repeatability and localization accuracy for object matching compared to an array of existing feature detectors. In addition, we show our regions lead to excellent results on two benchmark tasks that require good feature matching: weakly supervised foreground discovery and nearest neighbor-based object recognition. PMID:26353319

  18. Stability of compressible boundary layers

    NASA Technical Reports Server (NTRS)

    Nayfeh, Ali H.

    1989-01-01

    The stability of compressible 2-D and 3-D boundary layers is reviewed. The stability of 2-D compressible flows differs from that of incompressible flows in two important features: There is more than one mode of instability contributing to the growth of disturbances in supersonic laminar boundary layers and the most unstable first mode wave is 3-D. Whereas viscosity has a destabilizing effect on incompressible flows, it is stabilizing for high supersonic Mach numbers. Whereas cooling stabilizes first mode waves, it destabilizes second mode waves. However, second order waves can be stabilized by suction and favorable pressure gradients. The influence of the nonparallelism on the spatial growth rate of disturbances is evaluated. The growth rate depends on the flow variable as well as the distance from the body. Floquet theory is used to investigate the subharmonic secondary instability.

  19. Transition in hypersonic boundary layers

    NASA Astrophysics Data System (ADS)

    Zhang, Chuanhong; Zhu, Yiding; Chen, Xi; Yuan, Huijing; Wu, Jiezhi; Chen, Shiyi; Lee, Cunbiao; Gad-el-Hak, Mohamed

    2015-10-01

    Transition and turbulence production in a hypersonic boundary layer is investigated in a Mach 6 wind tunnel using Rayleigh-scattering visualization, fast-response pressure measurements, and particle image velocimetry. It is found that the second-mode instability is a key modulator of the transition process. Although the second-mode is primarily an acoustic wave, it causes the formation of high-frequency vortical waves, which triggers a fast transition to turbulence.

  20. Equilibrium composition of interphase boundaries

    SciTech Connect

    Wynblatt, P.

    1990-01-01

    Two modeling approaches have been used to investigate segregation effects at interphase boundaries. The first approach is based on the nearest neighbor bond model, used in conjunction with the regular solution approximation, and is an extension of an earlier framework developed to address segregation phenomena at free surfaces. In order to model a semicoherent interphase boundary, we have employed a second modeling approach, based on Monte Carol simulation, in conjunction with the embedded atom method (EAM). The EAM is a powerful new method for describing interatomic interactions in metallic systems. It includes certain many-body interactions that depend on the local environment of an atom. The Monte Carol approach has been applied to semicoherent interphase boundaries in Cu-Ag-Au alloys dilute in Au. These alloys consist of coexisting Cu-rich and Ag-rich phases, which differ in lattice constant by about 12%, such that good matching across in interface occurs when nine structural units of the Cu-rich phase are opposed to eight structural units of the Ag-rich phase. Thus far, interfaces with two different orientations have been studied: {l brace}001{r brace}-Cu//{l brace}001{r brace}-Ag, {l angle}110{r angle}-Cu//{l angle}110{r angle}-Ag; and {l brace}111{r brace}-Cu//{l brace}111{r brace}-Ag, {l angle}110{r angle}-Cu//{l angle}110{r angle}-Ag. These two interfaces will be referred to as the (001) and (111) interphase boundaries, for short. 18 refs.

  1. Solitons induced by boundary conditions

    SciTech Connect

    Zhou, R.L.

    1987-01-01

    Although soliton phenomena have attracted wide attention since 1965, there are still not enough efforts paid to mixed-boundary - initial-value problems that are important in real physical cases. The main purpose of this thesis is to study carefully the various boundary-induced soliton under different initial conditions. The author states with three sets of nonlinear equations: KdV equations and Boussinesq equations (for water); two-fluid equations for cold-ion plasma. He was interested in four types of problems involved with water solitons: excitation by different time-dependent boundary conditions under different initial conditions; head-on and over-taking collisions; reflection at a wall and the excitation by pure initial conditions. For KdV equations, only cases one and four are conducted. The results from two fully nonlinear KdV and Boussinesq equations are compared, and agree extremely well. The Boussinesq equations permit solition head-on collisions and reflections, studied the first time. The results from take-over collision agree with KdV results. For the ion-acoustic plasma, a set of Boussinesq-type equations was derived from the standard two-fluid equations for the ion-acoustic plasma. It theoretically proves the essential nature of the solitary wave solutions of the cold-ion plasma. The ion acoustic solitons are also obtained by prescribing a potential phi/sub 0/ at one grid point.

  2. Event boundaries and memory improvement.

    PubMed

    Pettijohn, Kyle A; Thompson, Alexis N; Tamplin, Andrea K; Krawietz, Sabine A; Radvansky, Gabriel A

    2016-03-01

    The structure of events can influence later memory for information that is embedded in them, with evidence indicating that event boundaries can both impair and enhance memory. The current study explored whether the presence of event boundaries during encoding can structure information to improve memory. In Experiment 1, memory for a list of words was tested in which event structure was manipulated by having participants walk through a doorway, or not, halfway through the word list. In Experiment 2, memory for lists of words was tested in which event structure was manipulated using computer windows. Finally, in Experiments 3 and 4, event structure was manipulated by having event shifts described in narrative texts. The consistent finding across all of these methods and materials was that memory was better when the information was distributed across two events rather than combined into a single event. Moreover, Experiment 4 demonstrated that increasing the number of event boundaries from one to two increased the memory benefit. These results are interpreted in the context of the Event Horizon Model of event cognition. PMID:26780472

  3. Jupiter's deep magnetotail boundary layer

    NASA Astrophysics Data System (ADS)

    Nicolaou, G.; McComas, D. J.; Bagenal, F.; Elliott, H. A.; Ebert, R. W.

    2015-06-01

    In 2007 the New Horizons (NH) spacecraft flew by Jupiter for a gravity assist en route to Pluto. After closest approach on day of year (DOY) 58, 2007, NH followed a tailward trajectory that provided a unique opportunity to explore the deep jovian magnetotail and the surrounding magnetosheath. After DOY 132, 16 magnetopause crossings were observed between 1654 and 2429 Jupiter radii (Rj) along the dusk flank tailward of the planet. In some cases the crossings were identified as rapid transitions from the magnetotail to the magnetosheath and vice versa. In other cases a boundary layer was observed just inside the magnetopause. Solar Wind Around Pluto (SWAP) is an instrument on board NH that obtained spectra of low energy ions during the flyby period. We use a forward model including the SWAP instrument response to derive plasma parameters (density, temperature and velocity) which best reproduce the observations. We also vary the plasma parameters in our model in order to fit the observations more accurately on occasions where the measurements exhibit significant variability. We compare the properties of the plasma in the boundary layer with those of the magnetosheath plasma derived in our earlier work. We attempt to estimate the magnetic field in the boundary layer assuming pressure balance between it and the magnetosheath. Finally, we investigate several possible scenarios to assess if magnetopause movement and structure could cause the variations seen in the data.

  4. Boundary detection via dynamic programming

    NASA Astrophysics Data System (ADS)

    Udupa, Jayaram K.; Samarasekera, Supun; Barrett, William A.

    1992-09-01

    This paper reports a new method for detecting optimal boundaries in multidimensional scene data via dynamic programming (DP). In its current form the algorithm detects 2-D contours on slices and differs from other reported DP-based algorithms in an essential way in that it allows freedom in 2-D for finding optimal contour paths (as opposed to a single degree of freedom in the published methods). The method is being successfully used in segmenting object boundaries in a variety of medical applications including orbital volume from CT images (for craniofacial surgical planning), segmenting bone in MR images for kinematic analysis of the joints of the foot, segmenting the surface of the brain from the inner surface of the cranial vault, segmenting pituitary gland tumor for following the effect of a drug on the tumor, segmenting the boundaries of the heart in MR images, and segmenting the olfactory bulb for verifying hypotheses related to the size of this bulb in certain disease states.

  5. Boundary layer receptivity and control

    NASA Technical Reports Server (NTRS)

    Hill, D. C.

    1993-01-01

    Receptivity processes initiate natural instabilities in a boundary layer. The instabilities grow and eventually break down to turbulence. Consequently, receptivity questions are a critical element of the analysis of the transition process. Success in modeling the physics of receptivity processes thus has a direct bearing on technological issues of drag reduction. The means by which transitional flows can be controlled is also a major concern: questions of control are tied inevitably to those of receptivity. Adjoint systems provide a highly effective mathematical method for approaching many of the questions associated with both receptivity and control. The long term objective is to develop adjoint methods to handle increasingly complex receptivity questions, and to find systematic procedures for deducing effective control strategies. The most elementary receptivity problem is that in which a parallel boundary layer is forced by time-harmonic sources of various types. The characteristics of the response to such forcing form the building blocks for more complex receptivity mechanisms. The first objective of this year's research effort was to investigate how a parallel Blasius boundary layer responds to general direct forcing. Acoustic disturbances in the freestream can be scattered by flow non-uniformities to produce Tollmien-Schlichting waves. For example, scattering by surface roughness is known to provide an efficient receptivity path. The present effort is directed towards finding a solution by a simple adjoint analysis, because adjoint methods can be extended to more complex problems. In practice, flows are non-parallel and often three-dimensional. Compressibility may also be significant in some cases. Recent developments in the use of Parabolized Stability Equations (PSE) offer a promising possibility. By formulating and solving a set of adjoint parabolized equations, a method for mapping the efficiency with which external forcing excites the three-dimensional motions of a non-parallel boundary layer was developed. The method makes use of the same computationally efficient formulation that makes the PSE currently so appealing. In the area of flow control, adjoint systems offer a powerful insight into the effect of control forces. One of the simplest control strategies for boundary layers involves the application of localized mean wall suction.

  6. Regional variations in seismic boundaries

    NASA Astrophysics Data System (ADS)

    Shumlyanska, Ludmila

    2010-05-01

    Dividing of the Earth into zones in the frame one-dimensional velocity model was proposed Jeffreys and Gutenberg is the first half of XX century. They recovered the following zones: A - the crust; B - zone in the depth interval 33-413 km, C - zone 413-984 km, D - zone 984-2898 km, E - 2898-4982 km, F - 4982-5121 km, G - 5121-6371 km (centre of the Earth). These zones differ in their seismic properties. Later, zone D was divided to the areas D' (984-2700 km) and D" (2700-2900 km). At present, this scheme is significantly modified and only the layer D" is in wide use. The more seismological studies are carried out, the more seismic boundaries appear. Boundaries at 410, 520, 670, and 2900 km, at which increase in the velocity of the seismic waves is particularly noticeable are considered as having global significance. Moreover, there are indications of the existence of geophysical boundaries at 800, 1200-1300, 1700, 1900-2000 km. Using 3D P-velocity model of the mantle based on Taylor approximation method for solving of the inverse kinematics multi-dimensional seismic task we have obtained seismic boundaries for the area covering 20-55 E 40-55 N. Data on the time of first arrivals of P waves from earthquakes and nuclear explosions recorded at ISC stations during 1964-2002 were used as input to construct a 3-D model. The model has two a priori limits: 1) the velocity is a continuous function of spatial coordinates, 2) the function v(r)/r where r is a radius in the spherical coordinate system r, ?, ? decreases with depth. The first limitation is forced since velocity leaps can not be sustainably restored from the times of first arrival; the second one follows from the nature of the observed data. Results presented as horizontal sections of the actual velocity every 25 km in the depth interval 850-2850 km, and as the longitudinal and latitudinal sections of the discrepancy on the 1-D reference model, obtained as a result of solving of the inversion task at 1 in the same depth interval [1, 2]. A general approach to the solving of the seismic tomography task by the method of Taylor's approximation is as follows: construction of a generalized field of mid-point of arrival times of waves at the observation station; construction of mid-points travel-time curves, i.e. cross-sections of the generalized field of mid-point of the arrival times of waves; inversion of travel time of the mid-point curve into speed curve. Due to the imposed limitations there are no abrupt velocity leaps in the model in use. First derivatives of the velocity for each curve were calculated points of local extreme were identified in order to determine the seismic boundaries. Maps of depths of occurrences of seismic boundaries at about 410 km, 670 km, 1700 km, and 2800 km were constructed. In general there is a deviation from generally accepted values beneath regions with different geodynamic regimes. There is a correlation of the 410 km and 670 km boundaries behaviour with the observed heat flow anomalies and gravitational field. [1] V.Geyko, T. Tsvetkova, L. Shymlanskaya, I. Bugaienko, L. Zaets Regional 3-D velocity model of the mantle of Sarmatia (south-west of the East European Platform). Geophysical Journal, 2005, iss. 6, P. 927-939. (In Russian) [2] V. Geyko, L. Shymlanskaya, T. Tsvetkova, I.Bugaenko, L.Zaets Three-dimensional model of the upper mantle of Ukraine constructed from the times of P waves arrival. Geophysical Journal, 2006, iss. 1, P. 3-16. (In Russian)

  7. Characterization of grain boundaries in silicon

    NASA Technical Reports Server (NTRS)

    Cheng, L. J.; Shyu, C. M.; Stika, K. M.; Daud, T.; Crotty, G. T.

    1983-01-01

    Zero-bias conductance and capacitance measurements at various temperatures were used to study trapped charges and potential barrier height at the boundaries. Deep-level transient spectroscopy (DLTS) was applied to measure the density of states at the boundary. A study of photoconductivity of grain boundaries in p-type silicon demonstrated the applicability of the technique in the measurement of minority carrier recombination velocity at the grain boundary. Enhanced diffusion of phosphorus at grain boundaries in three cast polycrystalline photovoltaic materials was studied. Enhancements for the three were the same, indicating that the properties of boundaries are similar, although grown by different techniques. Grain boundaries capable of enhancing the diffusion were found always to have strong recombination activities; the phenomena could be related to dangling bonds at the boundaries. Evidence that incoherent second-order twins of (111)/(115) type are diffusion-active is presented.

  8. Boundary Channel of the Potomac River

    USGS Multimedia Gallery

    The Boundary Channel of the Potomac River, which forms the boundary between the District of Columbia and the Commonwealth of Virginia. On the right of the image is the Lyndon Baines Johnson Memorial Grove on the Potomac....

  9. Nonequilibrium chemistry boundary layer integral matrix procedure

    NASA Technical Reports Server (NTRS)

    Tong, H.; Buckingham, A. C.; Morse, H. L.

    1973-01-01

    The development of an analytic procedure for the calculation of nonequilibrium boundary layer flows over surfaces of arbitrary catalycities is described. An existing equilibrium boundary layer integral matrix code was extended to include nonequilibrium chemistry while retaining all of the general boundary condition features built into the original code. For particular application to the pitch-plane of shuttle type vehicles, an approximate procedure was developed to estimate the nonequilibrium and nonisentropic state at the edge of the boundary layer.

  10. Outline of research on oscillating boundary layers

    NASA Technical Reports Server (NTRS)

    Cousteix, J.

    1979-01-01

    The state of the art in the field of unsteady boundary layers is outlined with emphasis on turbulent boundary layers. The unsteady flows considered are mainly periodic with the external velocity varying around a zero or nonzero mean time value. The principal results obtained on laminar boundary layers are also presented.

  11. Solute redistribution by a migrating grain boundary

    SciTech Connect

    Lillo, T.M.; Siclen, C.DeW. van; Wright, R.N.

    1998-05-05

    Although the role of volume diffusion during homogenization of as-cast microstructures is fairly well understood, the effect of grain boundaries on the homogenization process is largely unknown. To address the role of moving grain boundaries in homogenization, the authors have monitored grain boundary migration in a chill-cast Cu-8wt% Ni alloy at temperatures around 0.6 T{sub mp} where volume diffusion is expected to be minimal. Energy dispersive x-ray spectra (EDS) taken from both sides of mobile grain boundaries were used to assess homogenization of the as-cast microstructure by grain boundary diffusion. The degree of homogenization due to migration, given by the change in the minimum and maximum values of Ni concentration on opposite sides of a migrated grain boundary, is expected to reflect the grain boundary diffusivity and the grain boundary velocity. A relationship incorporating these parameters was obtained from a simple model describing solute redistribution within a moving grain boundary. This relationship allows calculation of the grain boundary diffusivity from experimentally-determined solute concentration profiles ahead of and behind the grain boundary and the migration velocity. The free energy change due to the reduction in compositional inhomogeneity is also calculated from the compositional free energy densities associated with the composition profiles. Estimates of the grain boundary mobility are then calculated assuming that this change in free energy is the major contributor to the driving force.

  12. 15 CFR 923.34 - Interstate boundary.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 15 Commerce and Foreign Trade 3 2012-01-01 2012-01-01 false Interstate boundary. 923.34 Section...) NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION, DEPARTMENT OF COMMERCE OCEAN AND COASTAL RESOURCE MANAGEMENT COASTAL ZONE MANAGEMENT PROGRAM REGULATIONS Boundaries 923.34 Interstate boundary. States...

  13. 15 CFR 923.34 - Interstate boundary.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 15 Commerce and Foreign Trade 3 2014-01-01 2014-01-01 false Interstate boundary. 923.34 Section...) NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION, DEPARTMENT OF COMMERCE OCEAN AND COASTAL RESOURCE MANAGEMENT COASTAL ZONE MANAGEMENT PROGRAM REGULATIONS Boundaries 923.34 Interstate boundary. States...

  14. 15 CFR 923.34 - Interstate boundary.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 15 Commerce and Foreign Trade 3 2010-01-01 2010-01-01 false Interstate boundary. 923.34 Section...) NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION, DEPARTMENT OF COMMERCE OCEAN AND COASTAL RESOURCE MANAGEMENT COASTAL ZONE MANAGEMENT PROGRAM REGULATIONS Boundaries 923.34 Interstate boundary. States...

  15. Turbulent boundary layer of an airfoil

    NASA Technical Reports Server (NTRS)

    Fediaevsky, K

    1937-01-01

    A need has arisen for a new determination of the velocity profiles in the boundary layer. Assuming that the character of the velocity distribution depends to a large extent on the character of the shear distribution across the boundary layer, we shall consider the nature of the shear distribution for a boundary layer with a pressure gradient.

  16. Mean Flow Boundary Conditions for Computational Aeroacoustics

    NASA Technical Reports Server (NTRS)

    Hixon, R.; Nallasamy, M.; Sawyer, S.; Dyson, R.

    2003-01-01

    In this work, a new type of boundary condition for time-accurate Computational Aeroacoustics solvers is described. This boundary condition is designed to complement the existing nonreflective boundary conditions while ensuring that the correct mean flow conditions are maintained throughout the flow calculation. Results are shown for a loaded 2D cascade, started with various initial conditions.

  17. K/T age for the popigai impact event

    NASA Technical Reports Server (NTRS)

    Deino, A. L.; Garvin, J. B.; Montanari, S.

    1991-01-01

    The multi-ringed POPIGAI structure, with an outer ring diameter of over 100 km, is the largest impact feature currently recognized on Earth with an Phanerozoic age. The target rocks in this relatively unglaciated region consist of upper Proterozoic through Mesozoic platform sediments and igneous rocks overlying Precambrian crystalline basement. The reported absolute age of the Popigai impact event ranges from 30.5 to 39 Ma. With the intent of refining this age estimate, a melt-breccia (suevite) sample from the inner regions of the Popigai structure was prepared for total fusion and step-wise heating Ar-40/Ar-39 analysis. Although the total fusion and step-heating experiments suggest some degree of age heterogeneity, the recurring theme is an age of around 64 to 66 Ma.

  18. Stable isotopes of carbon from basaltic rocks and their possible relation to atmospheric isotope excursions

    NASA Astrophysics Data System (ADS)

    Hansen, Hans Jrgen

    2006-11-01

    Repeated short-time negative excursions from the general trend of organic carbon isotopes occur at, and shortly after, the Permo-Triassic and Cretaceous-Tertiary mass extinctions. The cause of these excursions is unexplained since an extinction event can only explain one excursion at each boundary. At the P/T boundary one negative excursion occurs shortly before the boundary proper followed by one at the boundary, followed by several excursions that can be correlated in both marine and terrestrial environments over larger geographical distances. Also at the K/T boundary negative excursions in organic carbon, which can be correlated, occur after the boundary in both marine and terrestrial settings. As both mass extinctions occurred contemporaneously with major continental flood basalts, the present study focuses on the possible effect of eruption of flood basalts on the atmospheric carbon isotopic budget. The carbon isotopic compositions of forty different basalts, from the time span of Albian to the Recent, and predominantly continental flood, were measured. The isotopic composition of the CO 2 gas released by basalts is generally accepted as being rather heavy (- 5 PDB) based on observations from Hawaii. This is in strong contrast to the observed values in this study, which showed that the gas released had an average isotopic value of around - 23 PDB. Acid digestion by HF left a residue of elemental carbon with isotopic values in the range of - 24 to almost - 28 PDB. This corresponds to the carbon released during stepped heating experiments in the temperature range from 200 to 600 C. Since basalt in a molten state has a temperature of > 600 C and since the most negative carbon (i.e. the elemental carbon) is released below that temperature, it suggests that the most isotopically negative component is not present as elemental carbon above temperatures of 600 C. In view of the recorded isotopic composition of - 24 for gas collected at a temperature between 700 and 800 C from Mauna Loa, it seems that the generally assumed - 5 is unrepresentative for flood basalts. It is therefore possible that high intensity volcanic episodes have caused the repeated negative excursions. It is further suggested that the short-time non-secular isotopic variation pattern of organic carbon through time may be a record of volcanic activity. The episodic nature of volcanism precludes it from being causally related to the secular variations. Elemental carbon from four different kimberlites yielded carbon isotopic values similar to those from basalts. It is suggested that the Boudouard reaction (2CO = C + CO 2) may be responsible for the formation of the elemental carbon.

  19. Iridium and Spherules in Late Eocene Impact Deposits

    NASA Technical Reports Server (NTRS)

    Kyte, F. T.; Liu, S.

    2002-01-01

    We have been independently examining the Ir (FTK) and spherule (SL) contents of recently discovered late Eocene impact deposits from the south Atlantic and western Indian oceans. These include ODP Sites 1090 [14,15], 709 [lo], and 699 [Liu in prep.]. Iridium abundances at these sites are within the typical range reported for late Eocene deposits, with peak concentrations between 100 and 1000 pg/g. In Table 1 we present estimated net Ir fluences (in ng Ir/cm ) for these and nine other sites. Although there are fewer sites than the K/T boundary, the average of 9 ng Ir/cm2 is probably a good estimate of the late Eocene global flux. This is enough Ir for a 6 km comet (assuming 250 ng/g Ir, p=1.5), is sufficient to produce the Popigai or Chesapeake Bay structures, and is 16% of the flux estimated for the K/T boundary (55 ng/cm2 [ 161). Figure 1 shows the relative abundances of Ir, glassy microtektites and cpx-bearing spherules in sediments from Sites 699 and 1090, which are separated by only 3100 km. Although these two sites have similar Ir anomalies, the abundances of spherules are quite different. Site 1090 has well-defined peaks for both types of spherules, with a peak of 562 cpx spheruledg, while Site 699 contains only a few glassy microtektites and no cpx spherules. While the different abundances of spherules may reflect a heterogeneous distribution of spherules on the Earth s surface, an equally likely cause of this difference may be differential preservation of spherules in the sediment. recovered are only a trace residue of the initial impact deposit. Earlier work found 0.22 ng/g Ir in glassy microtektites from Site 689 [17], an insufficient concentration to support 0.16 ng/g in the bulk sediment at this site. We measured 15 ng/g Ir in a group of 95 cpx spherules from Site 1090 with sizes from 63 to -200 pm, a set typical of the size distribution at this site. Although this is a significant concentration it also cannot support the Ir peak. We presently lack quantitative data on the mass concentration of cpx spherules in Site 1090 sediments, but it is certainly <1 mg/g in The impact record in the late Eocene is very different from that at the Cretaceous-Tertiary In contrast, the late Eocene probably experienced multiple impact events.

  20. Boundary Scattering in Ballistic Graphene

    NASA Astrophysics Data System (ADS)

    Masubuchi, Satoru; Iguchi, Kazuyuki; Yamaguchi, Takehiro; Onuki, Masahiro; Arai, Miho; Watanabe, Kenji; Taniguchi, Takashi; Machida, Tomoki

    2012-07-01

    We report magnetotransport measurements in ballistic graphene mesoscopic wires where the charge carrier mean free path is comparable to the wire width W. Magnetoresistance curves show characteristic peak structures where the peak field scales with the ratio of cyclotron radius Rc and wire width W as W/Rc=0.90.1, due to diffusive boundary scattering. The obtained proportionality constant between Rc and W differs from that of a classical semiconductor two-dimensional electron system in which W/Rc=0.55.

  1. Grain Boundary Rotations in Solids

    NASA Astrophysics Data System (ADS)

    Bobylev, S. V.; Ovid'ko, I. A.

    2012-10-01

    A new physical mechanism of plastic flow in solids is suggested and theoretically described. The mechanism represents stress-driven rotations of grain boundaries (GBs) in subsurface areas of solids. The stress and energy characteristics of the GB rotations are calculated. In the case of nickel, we find that such rotations are energetically favorable processes in a wide range of GB parameters. Our theory is consistent with the experimental observation [D. Jang and J. R. Greer, Scr. Mater. 64, 77 (2011).SCMAF71359-646210.1016/j.scriptamat.2010.09.010] of GB rotations in deformed nanocrystalline nickel nanopillars.

  2. Phase Boundaries in Algebraic Conformal QFT

    NASA Astrophysics Data System (ADS)

    Bischoff, Marcel; Kawahigashi, Yasuyuki; Longo, Roberto; Rehren, Karl-Henning

    2016-01-01

    We study the structure of local algebras in relativistic conformal quantum field theory with phase boundaries. Phase boundaries are instances of a more general notion of boundaries that give rise to a variety of algebraic structures. These can be formulated in a common framework originating in Algebraic QFT, with the principle of Einstein Causality playing a prominent role. We classify the phase boundary conditions by the centre of a certain universal construction, which produces a reducible representation in which all possible boundary conditions are realized. For a large class of models, the classification reproduces results obtained in a different approach by Fuchs et al. before.

  3. Computing region moments from boundary representations

    NASA Technical Reports Server (NTRS)

    Wilf, J. M.; Cunningham, R. T.

    1979-01-01

    The class of all possible formulas for computing arbitrary moments of a region from the region's boundary is derived. The selection of a particular formula depends on the choice of an independent parameter. Several choices of this parameter are explored for region boundaries approximated by polygons. The parameter choice that minimizes computation time for boundaries represented by chain code is derived. Algorithms are presented for computing arbitrary moments for a region from a polygonal approximation of its boundary and for computing low order moments from chain encoded boundaries.

  4. Mechanism for diffusion induced grain boundary migration

    SciTech Connect

    Balluffi, R.W.; Cahn, J.W.

    1980-08-01

    Grain boundaries are found to migrate under certain conditions when solute atoms are diffused along them. This phenomenon, termed diffusion induced grain boundary migration (DIGM), has now been found in six systems. The observed phenomenon and empirical data are used to discard certain concepts for the driving force and the mechanism. A mechanism is proposed in which differences in the diffusion coefficients of the diffusing species along the grain boundary cause a self-sustaining climb of grain boundary dislocations and motion of their associated grain boundary steps.

  5. Work-Family Boundary Strategies: Stability and Alignment between Preferred and Enacted Boundaries

    ERIC Educational Resources Information Center

    Ammons, Samantha K.

    2013-01-01

    Are individuals bounding work and family the way they would like? Much of the work-family boundary literature focuses on whether employees are segmenting or integrating work with family, but does not explore the boundaries workers would like to have, nor does it examine the fit between desired and enacted boundaries, or assess boundary stability.

  6. Problems with the Younger Dryas Boundary (YDB) Impact Hypothesis

    NASA Astrophysics Data System (ADS)

    Boslough, M.

    2009-12-01

    One breakthrough of 20th-century Earth science was the recognition of impacts as an important geologic process. The most obvious result is a crater. There are more than 170 confirmed terrestrial impact structures with a non-uniform spatial distribution suggesting more to be found. Many have been erased by tectonics and erosion. Deep water impacts do not form craters, and craters in ice sheets disappear when the ice melts. There is growing speculation that such hidden impacts have caused frequent major environmental events of the Holocene, but this is inconsistent with the astronomically-constrained population of Earth-crossing asteroids. Impacts can have consequences much more significant than excavation of a crater. The K/T boundary mass extinction is attributed to the environmental effects of a major impact, and some researchers argue that other extinctions, abrupt climate changes, and even civilization collapses have resulted from impacts. Nuclear winter models suggest that 2-km diameter asteroids exceed a "global catastrophe threshold" by injecting sufficient dust into the stratosphere to cause short-term climate changes, but would not necessarily collapse most natural ecosystems or cause mass extinctions. Globally-catastrophic impacts recur on timescales of about one million years. The 1994 collision of Comet Shoemaker-Levy 9 with Jupiter led us recognize the significance of terrestrial airbursts caused by objects exploding violently in Earth’s atmosphere. We have invoked airbursts to explain rare forms of non-volcanic glasses and melts by using high-resolution computational models to improve our understanding of atmospheric explosions, and have suggested that multiple airbursts from fragmented impactors could be responsible for regional effects. Our models have been cited in support of the widely-publicized YDB impact hypothesis. Proponents claim that a broken comet exploded over North America, with some fragments cratering the Laurentide Ice Sheet. They suggest an abrupt climate change caused by impact-triggered meltwater forcing, along with massive wildfires, resulted in megafaunal extinctions and collapse of the Clovis culture. We argue that the physics of fragmentation, dispersion, and airburst is not consistent with the hypothesis; that observations are no more compatible with impact than with other causes; and that the probability of the scenario is effectively nil. Moreover, millennial-scale climate events are far more frequent than catastrophic impacts, and pose a much greater threat to humanity. Sandia is a multiprogram laboratory operated by Sandia Corp, a Lockheed Martin Company, for the US DOE under Contract DE-AC04-94AL85000. Probability density for largest asteroid impact since Last Glacial Maximum based on power-law size distribution. Comets are orders of magnitude less likely. Grazing trajectory or recent fragmentation further reduces probability.

  7. Characterization of grain boundaries in silicon

    SciTech Connect

    Cheng, L.J.; Shyu, C.M.; Stika, K.M.; Crotty, G.T.

    1983-11-15

    Results from several research activities on properties of grain boundaries in silicon materials are reported. Zero-bias conductance and capacitance measurements at various temperatures were used to study trapped charges and potential barrier height at the boundaries. Deep-level transient spectroscopy (DLTS) was applied to measure the density of states at the boundary. The result is consistent with the model in which the density of states increases as the states become deeper. Anomalous phenomena have been observed by DLTS and other methods, which can be only explained by a new model in which the spatial distribution of the localized states is not uniform along the boundary in the microscopic scale. A study of photoconductivity of grain boundaries in p-type silicon demonstrated the applicability of the technique in the measurement of minority carrier recombination velocity at the grain boundary. The data are consistent with the concept of recombination velocity increasing with boundary-state density and light intensity. Enhanced diffusion of phosphorus at grain boundaries in three cast polycrystalline photovoltaic materials was studied. Enhancements for the three were the same, indicating that the properties of boundaries are similar, although grown by different techniques. Grain boundaries capable of enhancing the diffusion were found always to have strong recombination activities; the phenomena could be related to dangling bonds at the boundaries. The present study gives the first evidence that incoherent second-order twins of (111)/(115) type are diffusion-active.

  8. Modelling the transitional boundary layer

    NASA Technical Reports Server (NTRS)

    Narasimha, R.

    1990-01-01

    Recent developments in the modelling of the transition zone in the boundary layer are reviewed (the zone being defined as extending from the station where intermittency begins to depart from zero to that where it is nearly unity). The value of using a new non-dimensional spot formation rate parameter, and the importance of allowing for so-called subtransitions within the transition zone, are both stressed. Models do reasonably well in constant pressure 2-dimensional flows, but in the presence of strong pressure gradients further improvements are needed. The linear combination approach works surprisingly well in most cases, but would not be so successful in situations where a purely laminar boundary layer would separate but a transitional one would not. Intermittency-weighted eddy viscosity methods do not predict peak surface parameters well without the introduction of an overshooting transition function whose connection with the spot theory of transition is obscure. Suggestions are made for further work that now appears necessary for developing improved models of the transition zone.

  9. Transcending boundaries with Ira Hirsh

    NASA Astrophysics Data System (ADS)

    Singh, Punita G.

    2002-05-01

    Ira Hirsh has made many contributions to various fields of acoustics from speech, hearing, psychological and physiological acoustics, to musical and architectural acoustics. It was a privilege for me to have been his student in all these areas, and to have had him as a guide through masters and doctoral degree programs that focused on topics that lie at the boundaries connecting these disciplines. Ira was not a prescriptive advisor, imposing particular research topics or procedures on his graduate students. Rather, he encouraged originality, innovation, and personal goal setting. He would subtly suggest starting points and provide landmarks as references, rather than explicit directions leading to them. One had to navigate the path by ones own wits. This approach encouraged lateral, out-of-the box thinking, while also leading to respectful appreciation of historic trajectories in scientific research. During our time together, we worked on several aspects of music, including, rhythm, melody, pitch, and timber perception. Some of this work will be recapitulated, highlighting Ira's role in its exposition and development. His multidimensional personality, astute insights, colorful remarks, wry humor, care, and concern are qualities to be cherished-beyond the boundaries of campus, city, country, and contemporaneity.

  10. Boundary Conditions of the Heliosphere

    NASA Technical Reports Server (NTRS)

    Slavin, Jonathan D.; Frisch, Priscilla C .

    2001-01-01

    We present new calculations of the ionization of the Local Interstellar Cloud (LIC) by directly observed sources including nearby stellar extreme ultraviolet (EUV) sources and the diffuse emission of the Soft X-ray Background (SXRB). In addition, we model the important, unobserved EUV emission both from the hot gas responsible for the SXRB and from a possible evaporative boundary between the LIC and the hot gas. We show that these ionization sources can provide the necessary ionization and heating of the cloud to match observations. Including the radiation from the conductive boundary, while not required, does improve the agreement with observations of the temperature of the LIC. The ionization predicted in our models shows good agreement with pickup ion results, interstellar absorption line data towards epsilon CMa, and EUV opacity measurements of nearby white dwarf stars. The areas of disagreement point to a possible underabundance (relative to solar abundance) of neon in the LIC. The presence of dust in the cloud, or at least depleted abundances, is necessary to maintain the heating/cooling balance and reach the observed temperature.

  11. Model Reduction by Manifold Boundaries

    PubMed Central

    Transtrum, Mark K.; Qiu, Peng

    2015-01-01

    Understanding the collective behavior of complex systems from their basic components is a difficult yet fundamental problem in science. Existing model reduction techniques are either applicable under limited circumstances or produce black boxes disconnected from the microscopic physics. We propose a new approach by translating the model reduction problem for an arbitrary statistical model into a geometric problem of constructing a low-dimensional, submanifold approximation to a high-dimensional manifold. When models are overly complex, we use the observation that the model manifold is bounded with a hierarchy of widths and propose using the boundaries as submanifold approximations. We refer to this approach as the manifold boundary approximation method. We apply this method to several models, including a sum of exponentials, a dynamical systems model of protein signaling, and a generalized Ising model. By focusing on parameters rather than physical degrees of freedom, the approach unifies many other model reduction techniques, such as singular limits, equilibrium approximations, and the renormalization group, while expanding the domain of tractable models. The method produces a series of approximations that decrease the complexity of the model and reveal how microscopic parameters are systematically compressed into a few macroscopic degrees of freedom, effectively building a bridge between the microscopic and the macroscopic descriptions. PMID:25216014

  12. Progress in boundary element methods. Volume 2

    NASA Astrophysics Data System (ADS)

    Brebbia, C. A.

    Nonlinear potential problems are considered along with wave propagation phenomena, aspects of fracture mechanics stress analysis, the boundary element method applied to two-dimensional contact problems, fluid structure interaction, and viscoplasticity and creep using boundary elements. An investigation is conducted of liner isotropic elasticity with body forces, taking into account governing equations, the boundary integral formulation, two-dimensional elasticity problems, a fundamental solution, boundary points, internal points, three-dimensional elasticity problems, two-dimensional body forces, three-dimensional body forces, and a direct computation of three-dimensional body force kernels. Boundary integral equations for the bending of thin plates are discussed, giving attention to thin plate reciprocal work identity, natural boundary integral equations, special fundamental solutions for corners and cracks. Augmented boundary integral equations, and the discretization of the equations. For individual items see A83-33853 to A83-33859

  13. Local Geometrical Boundary Data for Einstein's Equations

    NASA Astrophysics Data System (ADS)

    Winicour, Jeffrey

    2014-03-01

    An outstanding issue in the treatment of boundaries in general relativity is the lack of a local geometric interpretation of the necessary boundary data. For the Cauchy problem, the initial data is supplied by the 3-metric and extrinsic curvature of the initial Cauchy hypersurface, subject to constraints. This Cauchy data determine a solution to Einstein's equations which is unique up to a diffeomorphism. In joint work with H.-O. Kreiss, we show how three pieces of unconstrained boundary data, which are associated locally with the geometry of the boundary, likewise determine a solution of the initial-boundary value problem which is unique up to a diffeomorphism. One piece of this data, constructed from the extrinsic curvature of the boundary, determines the dynamical evolution of the boundary. The other two pieces constitute a conformal class of rank-2 metrics, which represent the two gravitational degrees of freedom. Research supported by NSF grant PHY-1201276 to the University of Pittsburgh.

  14. Vortex rings impinging on permeable boundaries

    NASA Astrophysics Data System (ADS)

    Mujal-Colilles, Anna; Dalziel, Stuart B.; Bateman, Allen

    2015-01-01

    Experiments with vortex rings impinging permeable and solid boundaries are presented in order to investigate the influence of permeability. Utilizing Particle Image Velocimetry, we compared the behaviour of a vortex ring impinging four different reticulated foams (with permeability k 26 - 85 10-8 m2) and a solid boundary. Results show how permeability affects the stretching phenomena of the vortex ring and the formation and evolution of the secondary vortex ring with opposite sign. Moreover, permeability also affects the macroscopic no-slip boundary condition found on the solid boundary, turning it into an apparent slip boundary condition for the most permeable boundary. The apparent slip-boundary condition and the flux exchange between the ambient fluid and the foam are jointly responsible for both the modified formation of the secondary vortex and changes on the vortex ring diameter increase.

  15. Evolutionary and Ecological Sequelae of Mass Extinctions: Examples From the Continental Triassic-Jurassic Boundary

    NASA Astrophysics Data System (ADS)

    Olsen, P. E.; Whiteside, J. H.

    2003-12-01

    The Triassic-Jurassic boundary at ˜200 Ma marks one of the five major mass-extinctions of the Phanerozoic and, depending on the metrics used, was similar in magnitude to the K-T mass extinction. In continental environments about 50% of all tetrapod families are eliminated and although floral diversity change is difficult to gauge, a similar proportion of palynomorph taxa disappear at the boundary. The extinction event appears to have been very abrupt, followed by a roughly 900 ky super-greenhouse period characterized by increased precipitation. We hypothesize a series of biological consequences of the drop in diversity and associated super-greenhouse based on observations of the earliest Jurassic assemblages, largely from eastern North America. 1) The drop in diversity results in a collapse of ecological interactions that tend to stabilize the composition of regional biotas and buffer them from invading forms. Triassic assemblages show considerable biogeographic provinciality despite the existence of Pangea, but the earliest Jurassic assemblages were extraordinarily homogenous with many vertebrate genera being essentially global in distribution. 2) Initially the post-boundary terrestrial assemblages were comprised of eurytopic trophic generalists, with animal communities with few herbivores, but abundant carnivores and detritivores subsisting on aquatic-based food webs. The earliest Jurassic tetrapod footprint record is overwhelmingly dominated by the footprints of ceratosaurian theropod dinosaurs, the latter having skull characteristics usually associated at least in part with piscivory. 3) The dramatic size changes over very short periods of time were likely due to an absence of competition (i.e., ecological release). The maximum size of theropod dinosaur footprints increased by about 25% within 10 ky following the boundary, corresponding to a doubling of mass. 4) Representatives of clades with intrinsically high rates of speciation tend to form species flocks after the boundary. Species flocks of semionotid fishes dominated earliest Jurassic giant rift lakes in eastern North America, but not Triassic or later Early Jurassic lakes in the same basins. Based on footprint data, it is quite possible that there were also species flocks of morphologically similar ceratosaurian theropod dinosaurs in the Early Jurassic.

  16. The new boundaries of the "boundaryless" company.

    PubMed

    Hirschhorn, L; Gilmore, T

    1992-01-01

    In an economy founded on innovation and change, one of the premier challenges of management is to design more flexible organizations. For many executives, a single metaphor has come to embody this managerial challenge and to capture the kind of organization they want to create: the "corporation without boundaries." According to Larry Hirschhorn and Thomas Gilmore of the Wharton Center for Applied Research, managers are right to break down the boundaries that make organizations rigid and unresponsive. But they are wrong if they think that doing so eliminates the need for boundaries altogether. Once the traditional boundaries of hierarchy, function, and geography disappear, a new set of boundaries becomes important. These new boundaries are more psychological than organizational. They aren't drawn on a company's organizational chart but in the minds of its managers and employees. And instead of being reflected in a company's structure, they must be "enacted" over and over again in a manager's relationships with bosses, subordinates, and peers. In this article, Hirschhorn and Gilmore provide a guide to the boundaries that matter in the "boundaryless" company. They explain how these new boundaries are essential for both managers and employees in coping with the demands of flexible work. They describe the typical mistakes that managers make in their boundary relationships. And they show how executives can become effective boundary managers by paying attention to a source of data they have often overlooked in the past: their own gut feelings about work and the people with whom they do it. PMID:10117998

  17. Synthetic Grain Boundaries in Rock Forming Minerals

    NASA Astrophysics Data System (ADS)

    Heinemann, S.; Wirth, R.; Dresen, G.

    2003-12-01

    A grain boundary may be defined as the zone separating two crystals differing in crystallographic orientation, composition, or dimension of the crystal lattice. In polycrystalline, multiphase materials, grain boundaries or phase boundaries are present in many different configurations forming three-dimensional networks very much like the networks of liquid films that A constitute foams. Physical properties of rocks, as for example, strength, electrical conductivity and diffusivity are largely controlled by grain boundary properties. Most of our present knowledge on grain boundaries stems from studies of metals and alloys. Likewise, the structure and properties of grain or phase boundaries in ceramics consisting of complex ionic and covalent compounds are well investigated. However, relatively little is known about the structure and physical properties of grain boundaries in rocks. For example, grain boundary diffusivity and mobility depend on orientation, and they are different for low and high angle grain boundaries. We successfully synthesized bicrystals of rock-forming minerals with defined grain boundaries to investigate their physical properties. We used the direct bonding technique to avoid plastic deformation of the grain boundary region. We synthesized quartz, periclase (MgO), forsterite and feldspar bicrystals. In addition, we successfully produced a forsterite bicrystal directly from a melt using the Czochralski method. For each direct bonded bicrystal two oriented mineral single crystals were joined at room temperature and annealed at 400oC for one week. All bicrystals were cut in two parts and one part was annealed further at 0.9 Tm for 48h. Specimens were prepared for investigation in the transmission electron microscope (TEM) using the focused ion beam (FIB) technique. High-resolution TEM studies reveal similar grain boundary structures produced at 400oC and at 0.9 Tm between undisturbed crystals. This suggests that bonding of bicrystals was effective at or below 400oC. Common structural elements of the synthetic grain boundaries encompass dislocations, steps and disconnections. }

  18. Vortex boundary-layer interactions

    NASA Technical Reports Server (NTRS)

    Bradshaw, P.

    1986-01-01

    Parametric studies to identify a vortex generator were completed. Data acquisition in the first chosen configuration, in which a longitudinal vortex pair generated by an isolated delta wing starts to merge with a turbulent boundary layer on a flat plate fairly close to the leading edge is nearly completed. Work on a delta-wing/flat-plate combination, consisting of a flow visualization and hot wire measurements taken with a computer controlled traverse gear and data logging system were completed. Data taking and analysis have continued, and sample results for another cross stream plane are presented. Available data include all mean velocity components, second order mean products of turbulent fluctuations, and third order mean products. Implementation of a faster data logging system was accomplished.

  19. Plasma transport near material boundaries

    SciTech Connect

    Singer, C.E.

    1985-06-01

    The fluid theory of two-dimensional (2-d) plasma transport in axisymmetric devices is reviewed. The forces which produce flow across the magnetic field in a collisional plasma are described. These flows may lead to up-down asymmetries in the poloidal rotation and radial fluxes. Emphasis is placed on understanding the conditions under which the known 2-d plasma fluid equations provide a valid description of these processes. Attempts to extend the fluid treatment to less collisional, turbulent plasmas are discussed. A reduction to the 1-d fluid equations used in many computer simulations is possible when sources or boundary conditions provide a large enough radial scale length. The complete 1-d fluid equations are given in the text, and 2-d fluid equations are given in the Appendix.

  20. Positron trapping at grain boundaries

    SciTech Connect

    Dupasquier, A. ); Romero, R.; Somoza, A. )

    1993-10-01

    The standard positron trapping model has often been applied, as a simple approximation, to the interpretation of positron lifetime spectra in situations of diffusion-controlled trapping. This paper shows that this approximation is not sufficiently accurate, and presents a model based on the correct solution of the diffusion equation, in the version appropriate for studying positron trapping at grain boundaries. The model is used for the analysis of new experimental data on positron lifetime spectra in a fine-grained Al-Ca-Zn alloy. Previous results on similar systems are also discussed and reinterpreted. The analysis yields effective diffusion coefficients not far from the values known for the base metals of the alloys.