Sample records for cretaceous-tertiary k-t boundary

  1. 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.

  2. 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).

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

    NASA Astrophysics Data System (ADS)

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

    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.

  4. The Cretaceous/ Tertiary boundary: sedimentology and micropalaeontology at El Mulato section, NE Mexico

    E-print Network

    Royer, Dana

    The Cretaceous/ Tertiary boundary: sedimentology and micropalaeontology at El Mulato section, NE-8109, USA Introduction Numerous researchers have focused investigations on Cretaceous / Tertiary (K / T and therefore formation over a long period of time. Bolide impact is also the most widely accepted explanation

  5. The debate over the Cretaceous-Tertiary boundary

    Microsoft Academic Search

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

    1988-01-01

    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

  6. Faunal implications of an environmental change before the Cretaceous-Tertiary (K-T) transition in central Utah

    Microsoft Academic Search

    Rose Difley; A. A. Ekdale

    2002-01-01

    The North Horn Formation at North Horn Mountain in central Utah records a shift in the composition of the upper Maastrichtian vertebrate fossil assemblage below the Cretaceous-Tertiary (K-T) boundary. Dinosaurs (Alamosaurus,Tyrannosaurus , Torosaurus, and hadrosaurs), turtles (Basilemys), mammals, and lizards(Polyglyphanodon ) occur in the lowest unit of the formation. The environment changed from semi-arid to wetter conditions, and several of

  7. 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.

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

    Microsoft Academic Search

    Meixun Zhao; Jeffrey L. Bada

    1989-01-01

    SINCE the discovery1 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

  9. The debate over the Cretaceous-Tertiary boundary

    NASA Technical Reports Server (NTRS)

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

    1988-01-01

    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.

  10. A sequence of events across the Cretaceous-Tertiary boundary

    Microsoft Academic Search

    J. Smit; A. J. T. Romein

    1985-01-01

    The lithological and biological sequence of events across the Cretaceous-Tertiary (K\\/T), as developed in thick and complete landbased sections and termed the standard K\\/T event sequence, is also found in many DSDP cores from all over the globe. Microtektite-like spherules have been found in almost every core or outcrop with an iridium anomaly, forming a worldwide strewnfield. These ``microtektites'' are

  11. 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.

  12. An extraterrestrial event at the Cretaceous-Tertiary boundary

    Microsoft Academic Search

    J. Smit; J. Hertogen

    1980-01-01

    Closely spaced samples from an uninterrupted calcareous pelagic sequence across the Cretaceous-Tertiary boundary reveal that the extinction of planktonic Foraminifera and nannofossils was abrupt without any previous warning in the sedimentary record, and that the moment of extinction was coupled with anomalous trace element enrichments, especially of iridium and osmium. The rarity of these two elements in the crust of

  13. 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.

  14. 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.

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

    Microsoft Academic Search

    H. B. Vonhof; J. Smit

    1997-01-01

    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

  16. Deccan flood basalts and the Cretaceous\\/Tertiary boundary

    Microsoft Academic Search

    V. Courtillot; G. Féraud; H. Maluski; D. Vandamme; M. G. Moreau; J. Besse

    1988-01-01

    Courtillot et al.1 have presented palaeomagnetic, palaeontological and K-Ar data for the Deccan flood basalts which suggest that > 106 km3 of basalt may have been erupted in < 1 Myr, mostly in a reversed magnetic chron. This chron is argued to be 29R, the one which contains the Cretaceous\\/Tertiary boundary. Here we aim to test the hypothesis1-5 that the

  17. Impacts, tsunamis, and the Haitian Cretaceous-Tertiary boundary layer

    Microsoft Academic Search

    Florentin J.-M. Maurrasse; Gautam Sen

    1991-01-01

    The marker bed at the Cretaceous-Tertiary boundary of the Beloc Formation (Haiti) contains abundant coarse-grained microtektites and minor amounts of shocked quartz grains in the basal part. The upper part is composed of medium-grained marl with amalgamated microtektite lenses and finer-grained marl lenses disseminated throughout. Field and petrographic observations, and the distribution of planktonic foraminifera suggest that the bed formed

  18. 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.

  19. 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.

  20. Paleoenvironmental changes across the Cretaceous–Tertiary boundary at Koshak, Kazakhstan, based on planktic foraminifera and clay mineralogy

    Microsoft Academic Search

    Alfonso Pardo; Thierry Adatte; Gerta Keller; Hedi Oberhänsli

    1999-01-01

    The Koshak section of the Mangyshlack Peninsula, Kazakhstan, is one of the most complete Cretaceous–Tertiary (K–T) transitions known from the boreal Paratethys. Cretaceous species richness is low (11 to 13 species), except for a peak of 20 species near the K\\/T boundary in the uppermost Maastrichtian (top 50 cm) that represents the temporary incursion of low-latitude taxa. This maximum species

  1. Vertebrate extinctions and survival across the Cretaceous-Tertiary boundary

    NASA Astrophysics Data System (ADS)

    Buffetaut, Eric

    1990-01-01

    A critical analysis of the fossil vertebrate record across the Cretaceous-Tertiary boundary shows that the available evidence is far less accurate than that concerning invertebrates and microfossils. Far-reaching conclusions have been drawn from generalisations about vertebrate extinctions in the continental realm based on the local record from western North America, but little is known about patterns of terminal Cretaceous vertebrate extinctions in other parts of the world, and even the western North American record is ambiguous. Despite this unsatisfactory record, it clearly appears that terminal Cretaceous vertebrate extinctions were highly selective, with some groups (e.g. dinosaurs) becoming completely extinct, whereas others seem to be virtually unaffected. This argues against devastating catastrophes of the kind postulated by some recent impact scenarios. However, the survival of groups known to be sensitive to climatic deterioration (such as crocodilians and other non-dinosaurian reptiles) indicates that alternative hypotheses involving gradual but fairly important climatic changes on a world-wide scale are not convincing either. The pattern of extinction and survival among vertebrates across the Cretaceous-Tertiary boundary may be explained as a consequence of the disruption of some food chains following a crisis in the plant kingdom, which itself may have been the result of the atmospheric consequences of unusual extraterrestrial or internal events.

  2. The fern-spore abundance anomaly at the Cretaceous-Tertiary boundary: A regional bioevent in western North America

    Microsoft Academic Search

    R. Fleming; D. Nichols

    At most localities where the palynological Cretaceous-Tertiary (K-T) boundary has been located in continuous deposition sequences in nonmarine rocks, an anomalous abundance of fern spores occurs immediately above the boundary. The fern-spore anomaly is characterized by unusually high relative abundance of fern spores and dominance by only one of a few species at each locality; it is independent of lithology.

  3. The fern-spore abundance anomaly at the Cretaceous-Tertiary boundary: A regional bioevent in western North America

    Microsoft Academic Search

    R. F. Fleming; D. J. Nichols

    1990-01-01

    At most localities where the palynological Cretaceous-Tertiary (K-T) boundary has been located in continuous deposition sequences in nonmarine rocks, an anomalous abundance of fern spores occurs immediately above the boundary. The fern-spore anomaly is characterized by unusually high relative abundance of fern spores and dominance by only one of a few species at each locality; it is independent of lithology.

  4. 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

  5. The Cretaceous\\/Tertiary boundary stratotype section at El Kef, Tunisia: how catastrophic was the mass extinction?

    Microsoft Academic Search

    G. Keller; L. Li; N. MacLeod

    1996-01-01

    The Cretaceous\\/Tertiary (K\\/T) boundary stratotype section at El Kef, Tunisia, represents the most complete and expanded sedimentary record across this important mass extinction horizon presently known. High resolution analysis of planktic foraminifera in two outcrops (El Kef I—stratotype and El Kef II) along with comparisons between planktic and benthic foraminifera, calcareous nannofossils, ostracods, pollen and spores, and dinoflagellates indicate that

  6. Iridium, sulfur isotopes and rare earth elements in the Cretaceous-Tertiary boundary clay at Stevns Klint, Denmark

    Microsoft Academic Search

    Birger Schmitz; Per Andersson; Jeremy Dahl

    1988-01-01

    Microbial activity and redox-controlled precipitation have been of major importance in the process of metal accumulation in the strongly Ir-enriched Cretaceous-Tertiary (K-T) boundary clay, the Fish Clay, at Stevns Klint in Denmark. Two important findings support this view: 1. 1) Kerogen, recovered by leaching the Fish Clay in HCl and HF, shows an Ir concentration of 1100 ppb; this represents

  7. 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.

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

    SciTech Connect

    Gallagher, W.B. (New Jersey State Museum, Trenton (United States))

    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.

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

    NASA Astrophysics Data System (ADS)

    Zhao, Meixun; Bada, Jeffrey L.

    1989-06-01

    SINCE the discovery1 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 (>10 km in diameter) with the Earth1-11. Alternative explanations claim that extensive, violent volcanism12-14 can account for the Ir, and that other independent causes were responsible for the mass extinctions15,16. 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 Earth17. 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 ?-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 chondrites17,18. An extraterrestrial source is the most reasonable explanation for the presence of these amino acids.

  10. 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.

  11. 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.

  12. Stable isotope evidence for gradual environmental changes and species survivorship across the Cretaceous/Tertiary Boundary

    NASA Astrophysics Data System (ADS)

    Barrera, Enriqueta; Keller, Gerta

    1990-12-01

    High-resolution ?13C and ?18O records have been generated from analyses of the planktonic foraminiferal species Heterohelix globulosa and the benthonic foraminiferal taxon Lenticulina spp from 3 m of a cored section spanning the Cretaceous/Tertiary (K/T) boundary at Brazos River, Texas. These are the first stable isotope records across the K/T boundary based on monospecific and monogeneric foraminiferal samples. They show a gradual decrease in ?13C values of about 2.5 permil beginning at the K/T boundary, as defined by the first appearance of Tertiary planktonic foraminifera, and continuing 17-20 cm above the boundary, approximately 40,000 years later. Gradual 13C depletion contrasts with the sudden ?13C drop at the K/T boundary observed in many deep-sea sections. The surface-to-bottom ?13C gradient decreased to less than zero approximately 25,000-30,000 years after the K/T boundary and remained negative for at least the next 140,000 years. Concomitant with change in ?13C values is a gradual decrease of about 2.5 permil in ?18C values which has not been observed at other localities. This 18O depletion suggests changes in temperature and/or salinity in the earliest Paleocene Gulf of Mexico. No extinction of foraminiferal species is associated with the K/T boundary or the onset of 18O and 13C depletions. Instead, two phases of Cretaceous species extinctions occur. One extinction phase is below the K/T boundary and below the tsunami bed of Bourgeois et al. [1988] and may be linked to sea level regression and environmental perturbations. The second extinction phase coincides with the minimum in ?13C and ?18O values in the Early Danian (Zone P0/Pla) and appears directly related to environmental changes reflected in the isotopic record. H. globulosa, which is commonly present in Maastrichtian and Danian sediments, exhibits significantly lower 18O/16O and 13C/12C ratios in Tertiary sediments relative to specimens from Maastrichtian sediments, demonstrating the survival of this important Cretaceous taxon after the K/T boundary event.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. Leaf architectural profiles of angiosperm floras across the Cretaceous\\/Tertiary boundary

    Microsoft Academic Search

    W. A. Green; L. J. HICKEY

    2005-01-01

    The Cretaceous\\/Tertiary boundary extinction has long been consid- ered one of the most important identifiable events in the course of Phanerozoic evolution. At times, the dramatic evidence for this has obscured the fact that any extinction event is selective and may not affect all groups of organisms in the same way. In this paper we examine a North American plant

  18. 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.

  19. A Short Duration of the Cretaceous-Tertiary Boundary Event: Evidence from Extraterrestrial Helium3

    Microsoft Academic Search

    S. Mukhopadhyay; K. A. Farley; A. Montanari

    2001-01-01

    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

  20. 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.

  1. 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.

  2. 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.

  3. Stratigraphic occurrences of iridium anomalies at four Cretaceous\\/Tertiary boundary sites in New Zealand

    Microsoft Academic Search

    Robert R. Brooks; C. Percy Strong; Julian Lee; Charles J. Orth; James S. Gilmore; Douglas E. Ryan; Jiri Holzbecher

    1986-01-01

    Three new iridium anomaly sites have been discovered in Cretaceous\\/Tertiary boundary sequences in New Zealand. These are at Needles Point, Chancet Rocks, and Waipara, where integrated iridium deposition values were 165, 211, and 7 ng\\/cm2, respectively. In contrast to the previously reported Woodside Creek stratigraphic sequence that had an iridium anomaly of 187 ng\\/cm2, a ferruginous boundary clay is absent

  4. Shocked quartz in the cretaceous-tertiary boundary clays: Evidence for a global distribution

    USGS Publications Warehouse

    Bohor, B.F.; Modreski, P.J.; Foord, E.E.

    1987-01-01

    Shocked quartz grains displaying planar features were isolated from Cretaceous-Tertiary boundary days at five sites in Europe, a core from the north-central Pacific Ocean, and a site in New Zealand. At all of these sites, the planar features in the shocked quartz can be indexed to rational crystallographic planes of the quartz lattice. The grains display streaking indicative of shock in x-ray diffraction photographs and also show reduced refractive indices. These characteristic features of shocked quartz at several sites worldwide confirm that an impact event at the Cretaceous-Tertiary boundary distributed ejecta products in an earth-girdling dust cloud, as postulated by the Alvarez impact hypothesis.

  5. Main Deccan Trap Eruptions occurred close to the Cretaceous-Tertiary Boundary: increasing Multiproxy Evidence

    Microsoft Academic Search

    Thierry Adatte; Gerta Keller

    2010-01-01

    Recent studies indicate that the bulk (80%) of the Deccan trap eruptions occurred over less than 0.8 m.y. in magnetic polarity C29r spanning the Cretaceous-Tertiary boundary (KTB) (Chenet et al, 2007, 2008). Detailed multiproxy studies from several sections from southeastern India (Rajhamundry, Andhra Pradesh) and central India (Jilmili, Madhya Pradesh) place the KTB event near the end of the main

  6. 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.

  7. Time Structure of a Mass Extinction: The Cretaceous- Tertiary Boundary

    NASA Astrophysics Data System (ADS)

    Hansen, H. J.; Rasmussen, K. L.; Gwozdz, R.; Walaszczyk, K. I.

    1992-07-01

    The uppermost Cretaceous chalk series is well exposed in Central Poland and its magnetostratigraphy has been established (Hansen et al. 1990). In the field 2.5-cm-diameter plugs were drilled spaced at 5-cm intervals (i.e., 20 plugs per meter corresponding to almost 50% coverage). All plugs were measured for their magnetic susceptibility and plotted against stratigraphic depth. The resultant curve from the Cretaceous part of magnetochron 29R corresponds to a time interval around 400 ky (Berggren et al. 1985). Magnetochron 29R has ben assigned a duration of 570-800 ky and contains the K/T boundary, where 2/3 of the time interval is earlier than the K/T boundary. In Fig. 1A two different periodicities are present. The larger peaks correspond to roughly 100 ky while the smaller corresponds to ca. 20 ky. No other frequencies are found. We suggest that the pulses correspond to the ellipse-precession complex in the Milankovitch band (compare Fisher and Bottjer 1991). Eight samples were analyzed by instrumental neutron activation. Four samples were from a pulse maximum and four from the neighboring trough. The results show a trace element doubling in the peak relative to the trough. By contrast the CaCO3 showed a decrease of 7% in the peak along with an increase in Sr of 4.2%. The drop in CaCO3 is much too low to account for the differences in trace elements. We suggest that the change is caused by variations in the early supply of terrigenuous material, mainly clay, related to variations in precipitation. We made a parallel study of the uppermost Maastrichtian red paleosoils with dinosaur nests from the region of Aix-en- Provence, South France. It disclosed the same pattern in susceptibility signal as that found in Poland (Fig. 1B). Here the magnetostratigraphy is also known (Hansen et al. 1989). We are thus dealing with a pattern common to both shallow water marine chalk and paleosoils. The interference pattern between the 100- and 20-ky cycles are in agreement in the two areas. This suggests to us that we are dealing with identical phenomena, where precipitation may affect both types of environments. Our method of study allows correlation (with a resolution of better than 10 ky) between marine and terrestrial deposits, timing of extinctions, estimates of accumulation rates plus realistic time estimates of magnetochrons. A study of the Uppermost Cretaceous chalk at the locality Nye Klov in North Jylland allows us to fix the extinction pattern of marine benthic fossils in a time frame. Detailed analysis of the boundary bed at Stevns Klint Karlstrup Quarry and Caravaca, Spain point at presence of two sediment pulses indicating a duration of Fish Clay time of around 40 ky. References: Berggren W. A., Kent D. V., and Flynn J. J. (1985) In The chronology of the geological record (ed. N. J. Snelling) Geol. Soc. Amer. Mem. 10, 141-195. Fisher A. G. and Bottjer D. J. (1991) Orbital forcing and sedimentary sequences. J. Sed. Petr. 61, 1063-1069. Hansen H. J., Rasmussen K. L., and Gwordz R. (1989) Cahiers de la Reserve Geologique de Haute Provence 1, 83-90. Hansen H. J., Rasmussen K. L., Gwordz R., Hansen J. M., and Radwanski A. (190) Acta Geologica Polinica 39, 1-12.

  8. 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 ?13C 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 ?13C excursion reflects the longer recovery time of marine versus terrestrial ecosystems.

  9. INTRODUCTION Cretaceous-Tertiary (K-T) boundary strati-

    E-print Network

    but poorly preserved, although dinoflagellates are well preserved and common. Body fossils of invertebrates indicate their presence. Marine invertebrates are represented by a few fish teeth. The uppermost

  10. 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.

  11. 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.

  12. Leaf assemblages across the Cretaceous-Tertiary boundary in the Raton Basin, New Mexico and Colorado

    PubMed Central

    Wolfe, Jack A.; Upchurch, Garland R.

    1987-01-01

    Analyses of leaf megafossil and dispersed leaf cuticle assemblages indicate that major ecologic disruption and high rates of extinction occurred in plant communities at the Cretaceous-Tertiary boundary in the Raton Basin. In diversity increase, the early Paleocene vegetational sequence mimics normal short-term ecologic succession, but on a far longer time scale. No difference can be detected between latest Cretaceous and early Paleocene temperatures, but precipitation markedly increased at the boundary. Higher survival rate of deciduous versus evergreen taxa supports occurrence of a brief cold interval (<1 year), as predicted in models of an “impact winter.” PMID:16593859

  13. 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.

  14. Extended Cretaceous/Tertiary boundary extinctions and delayed population change in planktonic foraminifera from Brazos River, Texas

    NASA Astrophysics Data System (ADS)

    Keller, Gerta

    1989-06-01

    High-resolution planktonic foraminiferal analysis of three Brazos River sections indicates a nearly continuous Cretaceous/Tertiary [K/T] boundary sedimentary record second only to the world's most complete record at El Kef, Tunisia. Species extinctions occur over an extended period of time and with two major extinction episodes. The first extinction episode with 46% of the species extinct occurs at and just below [10-15 cm] a short hiatus at the base of a sandy shell hash and clay-sand unit which was interpreted by Bourgeois et al. [1988] to represent a tsunami bed generated by the K/T boundary bolide impact. The top of this tsunami bed is about 17-20 cm below the K/T boundary as defined by the first appearance of Tertiary planktonic foraminifera. The second extinction phase with 45% of the species extinct occurs 25 cm above the K/T boundary [Zone P0/P1a boundary]. Of the remaining seven surviving Cretaceous species, six gradually disappear during planktonic foraminiferal Subzones P1a and basal P1b. No species extinctions or major faunal assemblage changes are directly associated with the K/T boundary. Iridium distribution is ambiguous, with one peak in the upper part of the tsunami bed and a second peak at the micropaleontologically defined K/T boundary. Relative abundances of dominant species are stable through the Late Maastrichtian, and only minor abundance changes coincide with the first extinction episode or the K/T boundary. The first major faunal change in the dominant species group coincides with the second extinction episode and leads to decline and eventual extinction of this group in Subzone P1a. Species disappearing at the two extinction episodes [46% and 45%] constitute only a small percentage [8% and 5%] of the individuals of the total planktonic foraminiferal population. This suggests that weakened species with low numbers of individuals and sensitive to relatively minor environmental changes were primarily affected by these extinction episodes. Magnetostratigraphy indicates that the first extinction phase began about 310,000 years before the K/T boundary, and the second extinction phase occurred 50,000 years after the K/T boundary. This stepped pattern of species extinctions suggests a progressively stressed ecosystem in continental shelf settings which may be related to an observed sea level regression and global cooling. The hypothesis of a global catastrophic mass extinction at the K/T boundary caused by a large extraterrestrial impact is not supported by the Brazos River planktonic foraminiferal data.

  15. Macro-invertebrates and the Cretaceous-Tertiary boundary

    NASA Astrophysics Data System (ADS)

    Wiedmann, Jost

    Most of Cretaceous macro-invertebrate groups such as ammonites, inoceramids, belemnites, and rudists whow a gradual decline towards the C/T boundary, and some of them disappear long before the boundary level itself. As in the terrestrial vertebrates, their disappearance is unrelated to an extraterrestrial impact as suggested by the widespread iridium anomaly occurring at the boundary. It is also unrelated to fluctuations in temperature, which have been recognized near the boundary level but which can probably be better correlated with such an event. The decline of ammonites is gradual and at the same time periodic in nature. Periodic events occurring through the Upper Cretaceous and the Phanerozoic as a whole are sea level changes. Indeed, the pattern of global transgressions and regressions shows a striking similarity with increasing and decreasing ammonite diversity. In contrast, the turnover in calcareous plankton of oceanic surface waters as well as in angiosperms (Aquilapollenites Province) is a later and "instantaneous" event which can be related with observed fluctuations in temperature, the iridium anomaly, and presumed impact at the boundary level.

  16. 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.

  17. 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.

  18. 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.

  19. A non-catastrophist explanation for the iridium anomaly at the Cretaceous/Tertiary boundary

    NASA Technical Reports Server (NTRS)

    Rampino, M. R.

    1982-01-01

    The iridium (Ir) anomaly at the Cretaceous/Tertiary (C/T) boundary can be explained by dissolution of normal pelagic limestones producing an insoluble clay residue containing Ir-rich meteoritic material. Further concentration of Ir and other trace metals in the clay can be explained by deposition under reducing conditions. Clay-mineral analyses indicate that the boundary clay is similar to locally derived clays in the limestones above and below the boundary, and contains no detectable exotic components. This supports a terrestrial origin for the boundary clay. The genesis of the boundary clay is attributed to changes in ocean chemistry (pH and oxygenation), leading to an interval of widespread dissolution of carbonate sequences in the oceans, and culminating in the development of submarine pyritic hardgrounds and a disconformity of global extent.

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

    NASA Astrophysics Data System (ADS)

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

    1984-10-01

    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 ? 18O 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 ? 18O 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.

  1. Stratigraphic occurrences of iridium anomalies at four Cretaceous/Tertiary boundary sites in New Zealand

    SciTech Connect

    Brooks, R.R.; Strong, C.P.; Lee, J.; Orth, C.J.; Gilmore, J.S.; Ryan, D.E.; Holzbecher, J.

    1986-09-01

    Three new iridium anomaly sites have been discovered in Cretaceous/Tertiary boundary sequences in New Zealand. These are at Needles Point, Chancet Rocks, and Waipara, where integrated iridium deposition values were 165, 211, and 7 ng/cm/sup 2/, respectively. In contrast to the previously reported Woodside Creek stratigraphic sequence that had an iridium anomaly of 187 ng/cm/sup 2/, a ferruginous boundary clay is absent in the three new sites, though the base of the Tertiary is marked by limonite staining. The relatively weak anomaly at the Waipara section is probably due to extensive bioturbation coupled with a high sedimentation rate at the time of deposition. The discovery of these additional boundary rock sequences in New Zealand negates suggestions that the Woodside Creek iridium.

  2. Copper and copper(II) porphyrins of the Cretaceous-Tertiary boundary at Stevns Klint (Denmark)

    NASA Astrophysics Data System (ADS)

    Premovi?, Pavle I.; Nikoli?, Nikola D.; Tonsa, Ivana R.; Pavlovi?, Mirjana S.; Premovi?, Miroslav P.; Dulanovi?, Dejan T.

    2000-04-01

    High levels of copper(II) (Cu 2+) were found with the major part (>90%) of the total Cu located in the smectite (Cu: 175 ppm) and kerogen (Cu: up to 1000 ppm) of the basal black marl of the Cretaceous-Tertiary (KT) boundary informal type sedimentary rock: the Fish Clay at Stevns Klint, Denmark. Anomalous abundance (4000 ppm) of the kerogen Cu 2+-porphyrins in this marl was detected by electron spin resonance. A model is proposed in which the enormous acid rains (caused by the KT asteroid impact) washed out the humics (already enriched with Cu 2+/Cu 2+-porphyrins) of the top horizon of the nearby oxic soil into the Fish Clay Basin during the KT event.

  3. 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)

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

    SciTech Connect

    Smit, J. (Free Univ., Amsterdam (Netherlands)); Montanari, A.; Swinburne, N.H.M.; Alvarez, W. (Univ. of California, Berkeley (United States)); Hildebrand, A.R. (Univ. of Arizona, Tucson (United States)); Margolis, S.V.; Claeys, P. (Univ. of California, Davis (United States)); Lowrie, W. (Eidgenoessische Technische Hochschule, Zuerich (Switzerland)); Asaro, F. (Lawrence Berkeley Lab., CA (United States))

    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.

  5. 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 Yucatán, 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 Yucatán. PMID:11537752

  6. 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.

  7. 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.

  8. Cretaceous/Tertiary boundary event, El Kef Tunesia: a foraminiferal response

    SciTech Connect

    Chi, W.R.; Keller, G.

    1985-01-01

    The Cretaceous/Tertiary boundary extinction event affected benthic communities less than planktonic faunas. Only 9% of benthic species comprising 20% in relative abundance of the total population became extinct, but most species declined in abundance. Only one species, Gavelinella eriksdalensis rapidly increased in abundance through the Danian and Loxostomum and Alabamian dorsoplanata are common in the boundary clay. Two further extinction events of lesser magnitude are observed in the upper A. mayaroensis Zone where 2% of the species go extinct, or 9% of the population, and in the Globigerina engubina Zone where also 2% of the species go extinct or 4% of the population. Significant species abundance changes also accompany these extinction events. Similar stepwise extinction events are also observed in the planktonic foraminifers. Benthic foraminifers indicate that the C/T boundary event was accompanied by a shallowing environment from middle slope to outer shelf. Reducing conditions prevailed during deposition of the boundary clay as suggested by the abundance of pyrite. The authors study of the El Kef section suggests that the observed population turnovers in benthic and planktonic communities could be explained by a sea level fall and/or geotectonically induced changes in oceanic circulation accompanied by temperature and salinity fluctuations. Although they cannot rule out the possibility of impact induced extinction events, have found no evidence of microtektite-like spherules in the boundary clay.

  9. Iridium, sulfur isotopes and rare earth elements in the Cretaceous-Tertiary boundary clay at Stevns Klint, Denmark

    NASA Astrophysics Data System (ADS)

    Schmitz, Birger; Andersson, Per; Dahl, Jeremy

    1988-01-01

    Microbial activity and redox-controlled precipitation have been of major importance in the process of metal accumulation in the strongly Ir-enriched Cretaceous-Tertiary (K-T) boundary clay, the Fish Clay, at Stevns Klint in Denmark. Two important findings support this view: 1) Kerogen, recovered by leaching the Fish Clay in HCl and HF, shows an Ir concentration of 1100 ppb; this represents about 50% of the Ir present in the bulk sample Fish Clay. Strong organometallic complexes is the most probable carrier phase for this fraction of Ir. Kerogen separated from the K-T boundary clay at Caravaca, Spain, similarly exhibits enhanced Ir concentrations. 2) Sulfur isotope analyses of metal-rich pyrite spherules, which occur in extreme abundance (about 10% by weight) in the basal Fish Clay, give a ? 34S value of -32%.. This very low value shows that sulfide formation by anaerobic bacteria was intensive in the Fish Clay during early diagenesis. Since the pyrite spherules are major carriers of elements such as Ni, Co, As, Sb and Zn, microbial activity may have played an important role for concentrating these elements. In the Fish Clay large amounts of rare earth elements have precipitated from sea water on fish scales. Analyses reveal that, compared with sea water, the Fish Clay is only about four times less enriched in sea-water derived lanthanides than in Ir. This shows that a sea-water origin is plausible for elements that are strongly enriched in the clay, but whose origin cannot be accounted for by a lithogenic precursor.

  10. 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.

  11. 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)

  12. Multiple impacts across the CretaceousTertiary boundary G. Kellera,*, W. Stinnesbeckb

    E-print Network

    Keller, Gerta

    global warming of 3­4 jC in intermediate waters between 65.4 and 65.2 Ma, decrease in primary, is generally considered the K/T boundary impact that caused one of the major mass extinctions in the Earth understanding of these events may reconcile the two divergent K/T mass extinction hypotheses. The impact­extinction

  13. 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. (Univ. of California, Berkeley (United States)); Smit, J. (Free Univ. of Amsterdam (Netherlands)); Lowrie, W. (Inst. fuer Geophysik, Zuerich (Switzerland)); Asaro, F. (Lawrence Berkeley Lab., CA (United States)); Margolis, S.V.; Claeys, P. (Univ. of California, Davis (United States)); Kastner, M. (Univ. of California, San Diego (United States)); Hildebrand, A.R. (Geological Survey, Ottawa, Ontario (Canada))

    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.

  14. 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.

  15. Coexisting altered glass and Fe-Ni oxides at the Cretaceous-Tertiary boundary, Stevns Klint (Denmark): direct evidence of meteorite impact

    NASA Astrophysics Data System (ADS)

    Bauluz, Blanca; Peacor, Donald R.; Elliott, W. Crawford

    2000-10-01

    The Cretaceous-Tertiary (K-T) boundary at Stevns Klint, Denmark, is noteworthy for its large Ir anomaly that is taken as evidence of extraterrestrial components, but the origin of the smectite in this marl has been variously interpreted to have a detrital, meteorite impact, or volcanic origin. We have carried out scanning electron microscopy and transmission electron microscopy (TEM)/analytical electron microscopy observations of the impact and contiguous layers within the K-T marl at Stevns Klint. TEM images show abundant smectite, much of which occurs with layers curving around and grading into cores of nanometer-scale glass shards. The smectite composition is unusual in having both significant octahedral Al and Mg. The glass and smectite major element compositions are similar and unique relative to glasses of terrestrial and extraterrestrial origin with the exception for one kind of glass at the K-T boundary in Haiti. Abundant 10-20-nm diameter iron oxides having as much as 10% Ni and minor Zn are intergrown with smectite. We interpret these domains to be altered meteorite fragments, which formed when impact glass was transformed to smectite. The direct association of unique glass and meteorite fragments is unambiguous evidence for meteorite impact. These data may imply fall-out of globally distributed impact-derived particles over an extended time period. The relations imply that TEM observations may be a powerful tool in detecting other impact events in the geological record.

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

    PubMed

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

  17. 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.

  18. 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.

  19. Main Deccan Trap Eruptions occurred close to the Cretaceous-Tertiary Boundary: increasing Multiproxy Evidence

    NASA Astrophysics Data System (ADS)

    Adatte, Thierry; Keller, Gerta

    2010-05-01

    Recent studies indicate that the bulk (80%) of the Deccan trap eruptions occurred over less than 0.8 m.y. in magnetic polarity C29r spanning the Cretaceous-Tertiary boundary (KTB) (Chenet et al, 2007, 2008). Detailed multiproxy studies from several sections from southeastern India (Rajhamundry, Andhra Pradesh) and central India (Jilmili, Madhya Pradesh) place the KTB event near the end of the main Deccan eruptive phase and indicate that Deccan volcanism could have been a major contributor to the mass extinction (Keller et al., 2008, 2009). Geochemical, mineralogical and micropaleontogical evidence from localities outside India suggest that this megapulse took place in the uppermost Maastrichtian C29r (CF2-CF1 transition). For example, a rapid shift in 187Os/188Os ratios observed in three deep-sea sections (Atlantic, Pacific and Indian Oceans) are interpreted to mark the onset of the main Deccan pulse in C29r (Robinson et al., 2009). Foraminiferal oxygen isotope data from DSDP Site 525 (South Atlantic) show a short rapid global warming in C29r (Li and Keller, 1998) coincident with the decline in 187Os/188Os ratios. This warming is also observed in the terrestrial plant record (Wilf 2003). A coeval increase in weathering observed in Site 525 and Tunisia (Adatte et al., 2002) is marked by dominant kaolinite clay assemblages. In the same interval a significant decrease in bulk carbonate content suggests acidification due to volcanic SO2. Enhanced dissolution is also observed at DSDP Site 527 and Gubbio, Italy. Calcareous microfossils (planktic foraminifera and nannofossils) experienced major stress conditions expressed by species dwarfing, decreased diversity and decreased abundance (Keller, 2005). These observations indicate that Deccan volcanism played a key role in increasing atmospheric CO2 levels that resulted in global warming and enhanced greenhouse effect, which coupled with high SO2 emission increased biotic stress and predisposed faunas to eventual extinction at the KTB. Adatte, T. Keller, G. & Stinnesbeck, W. (2002). PPP 178; 3-4, Pages 165-196. Chenet, A-L., Quidelleur, X., Fluteau, F., Courtillot, V., 2007. EPSL. 263, 1-15. Chenet, A-L., Fluteau, F., Courtillot, V., Gerard, M., Subbarao, K.V., 2008. J. Geophys. Res. 113, B04101. Li, L., Keller, G., 1998c. Geology 26, 995-998. Keller, G. 2005. Lithos, 79, 3-4, 317-341. Keller, G., Adatte, T., Gardin, S., Bartolini, A., Bajpai, S., 2008. EPSL 268, 293-311. Keller, G., Adatte, T., Bajpai, S., Mohabey, D.M., Widdowson, M., Khosla, A., Sharma, R., Khosla, S. C., Gertsch, B., Fleitmann, D., Sahni, A. 2009.. EPSL, 282, 1-4, 10-23 Robinson, Ravizza, G., Coccioni, R. Peucker-Ehrenbrink, B. Norris, R. 2009. EPSL, 281, 3-4, 159-158. Wilf, P., Johnson, K.R., Huber, B.T., 2003. PNAS 100, 599-604.

  20. 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.

  1. Records of post Cretaceous-Tertiary boundary millennial-scale cooling from the western Tethys: A smoking gun for the impact-winter hypothesis?

    Microsoft Academic Search

    Simone Galeotti; Henk Brinkhuis; Matthew Huber

    2004-01-01

    The record of both dinoflagellate cysts and benthic foraminifera across the Cretaceous-Tertiary boundary at El Kef, Tunisia, reveals a brief expansion of the Boreal bioprovince into the western Tethys, suggesting that an ˜2 k.y. cooling occurred during the earliest Danian. We show that this prolonged cooling phase is consistent with the oceanographic response to an impact winter.

  2. Journal of the Geological Society, London, Vol. 160, 2003, pp. 783795. Printed in Great Britain. Spherule deposits in CretaceousTertiary boundary sediments in Belize and

    E-print Network

    Keller, Gerta

    . 783 Spherule deposits in Cretaceous­Tertiary boundary sediments in Belize and Guatemala G. KELLER1 , W Guatemala Limited, 6a Av. 0­28 Zona 10, Guatemala 01010, Guatemala Abstract: Large spheroid deposits and eastern Guatemala have the same glass origin based on the presence of almost pure Cheto smectite derived

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

    Microsoft Academic Search

    V. Vajda; J. I. Raine

    2003-01-01

    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

  4. 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.

  5. 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.

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

    Microsoft Academic Search

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

    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

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

    NASA Astrophysics Data System (ADS)

    Gilmour, Iain; Boyd, Stuart R.

    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.

  8. Main Deccan volcanism phase ends near the K–T boundary: Evidence from the Krishna–Godavari Basin, SE India

    Microsoft Academic Search

    G. Keller; T. Adatte; S. Gardin; A. Bartolini; S. Bajpai

    2008-01-01

    Recent studies indicate that the bulk (80%) of the Deccan trap eruptions occurred over less than 0.8 m.y. in magnetic polarity C29r spanning the Cretaceous–Tertiary (K–T) boundary. Determining where within this major eruptive phase the K–T mass extinction occurred has remained problematic. For this reason, models estimating the biotic and environmental consequences have generally underestimated the rate and quantity of Deccan

  9. Biogeochemical modeling at mass extinction boundaries: Atmospheric carbon dioxide and ocean alkalinity at the K\\/T boundary

    Microsoft Academic Search

    Ken Caldeira; Michael Rampino; Tyler Volk; James Zachos

    The causes of mass extinctions and the importance of major bio-events in the history of life are subjects of considerable scientific interest. A large amount of geological, geochemical, and paleontological information now exists for the Cretaceous\\/Tertiary (K\\/T) boundary (66 Myr BP). These data are used here to constrain a newly developed time-dependent biogeochemical cycle model that is designed to study

  10. 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.

  11. Extended mitogenomic phylogenetic analyses yield new insight into crocodylian evolution and their survival of the Cretaceous-Tertiary boundary.

    PubMed

    Roos, Jonas; Aggarwal, Ramesh K; Janke, Axel

    2007-11-01

    The mitochondrial genomes of the dwarf crocodile, Osteolaemus tetraspis, and two species of dwarf caimans, the smooth-fronted caiman, Paleosuchus trigonatus, and Cuvier's dwarf caiman, Paleosuchus palpebrosus, were sequenced and included in a mitogenomic phylogenetic study. The phylogenetic analyses, which included a total of ten crocodylian species, yielded strong support to a basal split between Crocodylidae and Alligatoridae. Osteolaemus fell within the Crocodylidae as the sister group to Crocodylus. Gavialis and Tomistoma, which joined on a common branch, constituted a sister group to Crocodylus/Osteolaemus. This suggests that extant crocodylians are organized in two families: Alligatoridae and Crocodylidae. Within the Alligatoridae there was a basal split between Alligator and a branch that contained Paleosuchus and Caiman. The analyses also provided molecular estimates of various divergences applying recently established crocodylian and outgroup fossil calibration points. Molecular estimates based on amino acid data placed the divergence between Crocodylidae and Alligatoridae at 97-103 million years ago and that between Alligator and Caiman/Paleosuchus at 65-72 million years ago. Other crocodilian divergences were placed after the Cretaceous-Tertiary boundary. Thus, according to the molecular estimates, three extant crocodylian lineages have their roots in the Cretaceous. Considering the crocodylian diversification in the Cretaceous the molecular datings suggest that the extinction of the dinosaurs was also to some extent paralleled in the crocodylian evolution. However, for whatever reason, some crocodylian lineages survived into the Tertiary. PMID:17719245

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

    Microsoft Academic Search

    A. Z. Camargo; J. S. Juarez

    2004-01-01

    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

  13. Calcareous nannofossils at the K-T boundary, El Kef: No evidence for stepwise, gradual, or sequential extinctions

    Microsoft Academic Search

    James J. Pospichal

    1994-01-01

    A detailed quantitative study of well-preserved nannofossil assemblages in closely spaced samples across the Cretaceous-Tertiary (K-T) boundary at El Kef, Tunisia, reveals no extinctions of nannoplankton in the uppermost 4 m of Maastrichtian marls as has been reported for planktonic foraminifers from the same samples. Nannofossil assemblages below the boundary show no trends to indicate that ecologic stresses such as

  14. 40Ar-39Ar Ages of the Large Impact Structures Kara and Manicouagan and their Relevance to the Cretaceous-Tertiary and the Triassic-Jurassic Boundary

    NASA Astrophysics Data System (ADS)

    Trieloff, M.; Jessberger, E. K.

    1992-07-01

    Since the discovery of the iridium enrichment in Cretaceous- Tertiary boundary clays by Alvarez et al. (1980) the search for the crater of the K/T impactor is in progress. Petrographic evidence at the K/T boundary material points towards an impact into an ocean as well as onto the continental crust, multiple K/T impacts are now being considered (Alvarez and Asaro, 1990). One candidate is the Kara crater in northern Siberia of which Kolesnikov et al. (1988) determined a K-Ar isochrone age of 65.6 +- 0.5 Ma, regarding this as indicating that the Kara bolide is at least one of the K/T impactors. Koeberl et al. (1990) determined ^40Ar-^39Ar ages of six impact melts ranging from 70 to 82 Ma and suggested rather an association to the Campanian- Maastrichtian boundary, another important extinction horizon 73 Ma ago (Harland et al., 1982). We dated with the ^40Ar-^39Ar technique four impact melts, KA2- 306, KA2-305, SA1-302 and AN9-182. The spectra have rather well- defined plateaus, shown with highly extended age scales (Fig. 1). The plateau ages range from 69.3 to 71.7 Ma. Our data do not support an association either with the Cretaceous-Tertiary or with the Campanian-Maastrichtian boundary. We deduce an age of 69-71 Ma for the Kara impact structure. Nazarov et al. (1991) have demonstrated by isotopic hydrogen studies that the Kara bolide impacted on dry land, while the last regression at the target area before the end of the Cretaceous occurred 69-70 Ma ago. Our data are consistent with an impact shortly after the regression. We further dated impact metamorphic anorthosite samples (10BD5 and 10BD3C) of the Manicouagan crater, Canada, which may be related to the Triassic-Jurassic boundary (McLaren and Goodfellow, 1990). The samples consist of two different phases, one degassing at low temperatures yielding a plateau age of 212 Ma and another phase which was degassed during the cratering event to varying degrees with apparent ages increasing up to 950 Ma, the age of the target rocks (Wolfe, 1971). The low temperature plateaux are in agreement with the crater age of 212 Ma (Grieve, 1991) and do not improve the age of the impact structure. Anyway, while the crater age is quite accurate the ages of the adjacent geologic boundaries seem to be not. The last revision of the Triassic-Jurassic boundary (Harland et al., 1982) approved an age of 213 Ma, while later an age of 208 Ma was determined (Palmer, 1983). We think as far as ages are concerned it is not yet possible to conclude or exclude an association of the impact with the boundary until the age of the boundary is determined more precisely. References: Alvarez, L.W. , Alvarez, W., Asaro, F. and Michel, H.V. (1980) Science, 208, 1095-1108. Alvarez, L.W. and Asaro, F. (1990) Scient. Amer., 362. Grieve, R.A.F. (1991) Met., 26, 175- 194. Harland, W.B., Cox, A.V., Llewellyn, P.G., Pickton, C.A.G., Smith, A.G., and Walters, R. (1982) A geologic time scale. Cambridge Univ. Press. Koeberl, C., Sharpton, V.L., Murali, A.V. and Burke, K. (1990) Geology, 18, 50-53. Kolesnikov, E.M., Nazarov, M.A., Badjukov, D.D. and Shukolyukov, Y.A. (1988) Conf. on Glob. Catastr. in Earth Hist. LPI, Houston, Texas (abstract), 99-100. McLaren, D.J., and Goodfellow, W.D. (1990) Ann. Rev. Earth Planet. Sci., 18, 123-171. Nazarov, M.A., Devirts, A.L., Lagutina, E.P., Alekseev, A.S., Badjukov, D.D. and Shukolyukov, Y.A. (1991) Lunar Planet. Sci. (abstract) 22, 961. Palmer, A.R. (1983) Geology, 11, 503-504. Wolfe, S.H. (1971) J. Geophys. Res., 76, 5424-5436.

  15. Metal precipitation in the Cretaceous-Tertiary boundary clay at Stevns Klint, Denmark

    NASA Astrophysics Data System (ADS)

    Schmitz, B.

    1985-11-01

    The theory that enrichment of the Fish Clay in Denmark occurs by the precipitation of metals at a geochemical barrier is proposed. The compositions of the layers of the Fish Clay are described, and a table of the elemental concentrations in the Fish Clay is provided. Data supporting the precipitation of elements as sulfides at the redoxcline include: (1) the chalcophile element abundance pattern in the Fish Clay; (2) the precipitation of metals at the anoxic-oxic boundary; and (3) the large amount of small pyrite spheroids at the redoxcline. A precipitation model depicting the process of elemental enrichment in the Fish Clay, based on metal-bearing pore solutions losing their metals by precipitation upon passing the boundary between the oxic Cretaceous chalk and the overlying anoxic and hydrogen sulfide-rich Fish Clay, is examined.

  16. Paleoecology of the Cretaceous^Tertiary mass extinction in planktonic foraminifera

    E-print Network

    Keller, Gerta

    Paleoecology of the Cretaceous^Tertiary mass extinction in planktonic foraminifera Gerta Keller a Paleobiogeographic patterns of the Cretaceous^Tertiary (K^T) mass extinction in planktonic foraminifera in Tunisia; K^T planktonic foraminifera 1. Introduction The mass extinction in planktonic foraminifera across

  17. Mineralogical and geochemical anomalous data of the K-T boundary samples

    NASA Astrophysics Data System (ADS)

    Miura, Y.; Shibya, G.; Imai, M.; Takaoka, N.; Saito, S.

    Cretaceous-Tertiary boundary problem has been discussed previously from the geological research, mainly by fossil changes. Although geochemical bulk data of Ir anomaly suggest the extraterrestrial origin of the K-T boundary, the exact formation process discussed mainly by mineralogical and geochemical study has been started recently, together with noble gas contents. The K-T boundary sample at Kawaruppu River, Hokkaido was collected, in order to compare with the typical K-T boundary samples of Bubbio, Italy, Stevns Klint, Denmark, and El Kef, Tunisia. The experimental data of the silicas and calcites in these K-T boundary samples were obtained from the X-ray unit-cell dimension (i.e., density), ESR signal and total linear absorption coefficient, as well as He and Ne contents. The K-T boundary samples are usually complex mixture of the terrestrial activities after the K-T boundary event. The mineralogical and geochemical anomalous data indicate special terrestrial atmosphere at the K-T boundary formation probably induced by asteroid impact, followed the many various terrestrial activities (especially the strong role of sea-water mixture, compared with terrestrial highland impact and impact craters in the other earth-type planetary bodies).

  18. Mono and bicyclic alkanes and diamondoid hydrocarbons in the Cretaceous\\/Tertiary boundary sediments at Kawaruppu, Hokkaido, Japan

    Microsoft Academic Search

    AKIRA SHIMOYAMA; HIKARU YABUTA

    Sixty-two mono- and 4 bicyclic alkanes, and 11 diamondoid hydrocarbons were detected in the Creta- ceous-Tertiary (K\\/T) boundary sediments at Kawaruppu, Hokkaido, Japan. The monocyclic alkanes in- cluded series of n-alkylcyclohexanes, methyl-n-alkylcyclohexanes and n-alkylcyclopentanes, and other alkylcyclohexanes. The bicyclic alkanes included bicyclo(3.3.1)nonane, trans-decalin, and methyldecalins. The diamondoid hydrocarbons included adamantane, and methyl- and dimethyladamantanes, and diamantane and methyldiamantanes. These mono-

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. Shock-induced microdeformations in quartz and other mineralogical indications of an impact event at the Cretaceous-Tertiary boundary

    USGS Publications Warehouse

    Bohor, B.F.

    1990-01-01

    The event terminating the Cretaceous period and the Mesozoic era caused massive extinctions of flora and fauna worldwide. Theories of the nature of this event can be classed as endogenic (volcanic, climatic, etc.) or exogenic (extraterrestrial causes). Mineralogical evidence from the boundary clays and claystones strongly favor the impact of an extraterrestrial body as the cause of this event. Nonmarine KT boundary claystones are comprised of two separate layers-an upper layer composed of high-angle ejecta material (shocked quartz, altered glass and spinel) and a basal kaolinitic layer containing spherules, clasts, and altered glass, together with some shocked grains. Recognition of this dual-layered nature of the boundary clay is important for the determination of the timing and processes involved in the impact event and in the assignment and interpretation of geochemical signatures. Multiple sets of shock-induced microdeformations (planar features) in quartz grains separated from KT boundary clays provide compelling evidence of an impact event. This mineralogical manifestation of shock metamorphism is associated worldwide with a large positive anomaly of iridium in these boundary clays, which has also been considered indicative of the impact of a large extraterrestrial body. Global distributions of maximum sizes of shocked quartz grains from the boundary clays and the mineralogy of the ejecta components favor an impact on or near the North American continent. Spinel crystals (magnesioferrite) occur in the boundary clays as micrometer-sized octahedra or skeletal forms. Their composition differs from that of spinels found in terrestrial oceanic basalts. Magnesioferrite crystals are restricted to the high-angle ejecta layer of the boundary clays and their small size and skeletal morphology suggest that they are condensation products of a vaporized bolide. Hollow spherules ranging up to 1 mm in size are ubiquitously associated with the boundary clays. In nonmarine sections, where a high-angle ejecta layer and an underlying kaolinitic layer can be distinguished, the spherules are found only in the kaolinitic layer. The morphologies and surface features of these spherules suggest that they are original forms, and not secondary growths or algal bodies. These impact spherules closely resemble microtektites in size and shape. All of these features of the boundary clay are uniquely associated with impact, and cannot have been formed by volcanic or other terrestrial processes. ?? 1990.

  5. The stratigraphic distribution of Ni-rich spinels in Cretaceous-Tertiary boundary rocks at EL Kef (Tunisia), Caravaca (Spain) and Hole 761 (Leg 122)

    Microsoft Academic Search

    E. Robin; D. Boclet; Ph. Bonte; L. Froget; C. Jehanno; R. Rocchia

    1991-01-01

    The stratigraphic distributions of Ni-rich spinels at three widely scattered K-T sites are presented, and the implications in the present understanding of the K-T boundary event are discussed. The various Ni-rich spinel and carbonate distributions are interpreted as the result of an infall of extraterrestrial material occurring in close coincidence with the global mass extinctions. The duration of the pulse

  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. 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.

  8. The stratigraphic distribution of Ni-rich spinels in Cretaceous-Tertiary boundary rocks at EL Kef (Tunisia), Caravaca (Spain) and Hole 761 (Leg 122)

    NASA Astrophysics Data System (ADS)

    Robin, E.; Boclet, D.; Bonte, Ph.; Froget, L.; Jehanno, C.; Rocchia, R.

    1991-12-01

    The stratigraphic distributions of Ni-rich spinels at three widely scattered K-T sites are presented, and the implications in the present understanding of the K-T boundary event are discussed. The various Ni-rich spinel and carbonate distributions are interpreted as the result of an infall of extraterrestrial material occurring in close coincidence with the global mass extinctions. The duration of the pulse was very brief on the geological time scale, with upper limits ranging from 100 to 3000 years. Long-duration estimates (50 ka to 1 Ma), derived from the distribution of iridium, and probably other chemical markers, are found to be misleading and meaningless because of disturbance by postdepositional chemical processes. The volcanic crisis associated with Deccan Trap formation, whose duration greatly exceeds even the present upper limit of 3000 yr, should be rejected. Strong evidence for a collisional event occurring at the close of the Cretaceous is provided.

  9. Cretaceous eutherians and Laurasian origin for placental mammals near the K/T boundary.

    PubMed

    Wible, J R; Rougier, G W; Novacek, M J; Asher, R J

    2007-06-21

    Estimates of the time of origin for placental mammals from DNA studies span nearly the duration of the Cretaceous period (145 to 65 million years ago), with a maximum of 129 million years ago and a minimum of 78 million years ago. Palaeontologists too are divided on the timing. Some support a deep Cretaceous origin by allying certain middle Cretaceous fossils (97-90 million years old) from Uzbekistan with modern placental lineages, whereas others support the origin of crown group Placentalia near the close of the Cretaceous. This controversy has yet to be addressed by a comprehensive phylogenetic analysis that includes all well-known Cretaceous fossils and a wide sample of morphology among Tertiary and recent placentals. Here we report the discovery of a new well-preserved mammal from the Late Cretaceous of Mongolia and a broad-scale phylogenetic analysis. Our results exclude Cretaceous fossils from Placentalia, place the origin of Placentalia near the Cretaceous/Tertiary (K/T) boundary in Laurasia rather than much earlier within the Cretaceous in the Southern Hemisphere, and place afrotherians and xenarthrans in a nested rather than a basal position within Placentalia. PMID:17581585

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

    Microsoft Academic Search

    K. Sharma

    2004-01-01

    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

  11. 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.

  12. 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.

  13. Cretaceous-Tertiary findings, paradigms and problems

    NASA Astrophysics Data System (ADS)

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

    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.

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

    PubMed

    Pope, K O; Baines, K H; Ocampo, A C; Ivanov, B 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, indicate that between 0.4 and 7.0 x 10(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 Wm-2, which far exceeded the +8 Wm-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. PMID:11539442

  15. 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.

  16. Enregistrement des événements remarquables de la limite Crétacé Tertiaire dans la coupe d'Ellès (Tunisie)Characteristic events record of the K/T boundary in the Ellès section (Tunisia).

    NASA Astrophysics Data System (ADS)

    Zaghbib-Turki, Dalila; Karoui-Yaakoub, Narjess; Rocchia, Robert; Robin, Eric; Belayouni, Habib

    2000-07-01

    The review of the Cretaceous-Paleogene interval deposits of the Ellès section based on a detailed sampling gives a good characterization of the K/T boundary and reconstitution of the geological events underlining this boundary. Thus, the discovery of a thin Ir-rich layer, with Ni and Cr-rich spinel and shocked quartz is a well preserved record of the known cosmic event that occurred at that time. This sudden event is also corroborated by the quantitative and qualitative organic components distribution along the K/T interval. Added to some other long-term events (e.g. climatic, eustatic), it generated a mass extinction, at the K/T boundary, of specialists among the Globotruncanids and Heterohelicids planktic foraminifera species. Following this biological crisis, the biotic turnover into the Danian is slow. The underlining of all the Cretaceous-Tertiary interval biozones attests that the Ellès section is complete. If compared to the K/T stratotype and El Kef II sections, the Ellès section is found to display a better exposure of the K/T interval and shows more expanded zones and subzones. Such characteristics promote the Ellès section to be considered as a parastratotype.

  17. Cretaceous/Tertiary Impact Ejecta in the Yucatan Basin and the Caribbean: Leg 165 of the Ocean Drilling Project

    NASA Astrophysics Data System (ADS)

    Shipboard Scientific Party

    1996-03-01

    This communication is a report of the results of drilling and sampling and preliminary analysis of the Cretaceous/Tertiary boundary impact ejecta deposit at three sites in the Yucatan Basin, Colombia Basin and on the lower Nicaragua Rise in the Caribbean Sea, recovered during Leg 165 of the Ocean Drilling Program.

  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. 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.

  20. 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.

  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. Extraterrestrial Cause for the Cretaceous-Tertiary Extinction

    Microsoft Academic Search

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

    1980-01-01

    Platinum metals are depleted in the earth's crust relative to their cosmic abundance; concentrations of these elements in deep-sea sediments may thus indicate influxes of extraterrestrial material. Deep-sea limestones exposed in Italy, Denmark, and New Zealand show iridium increases of about 30, 160, and 20 times, respectively, above the background level at precisely the time of the Cretaceous-Tertiary extinctions, 65

  3. Magnetic Analysis of K/T Boundary Layer Clay from Stevns Klint, Denmark

    NASA Astrophysics Data System (ADS)

    Morden, S. J.

    1993-09-01

    Following the distribution at The 53rd Annual Meeting of the Meteoritical Society of 40 kg of Cretaceous-Tertiary boundary layer clay (Fish Clay) recovered from Stevns Klint, Denmark, a magnetic analysis of both the coarse and fine fractions was carried out. The magnetic mineralogy was found to be complex, consisting of single-domain magnetite and fine-grained sulphides of Fe. The Fe sulphide was present as ferrimagnetic pyrrhotite (Fe7S8) and other sulphides that decayed on heating to produce magnetite. A magnetic fraction of the material was separated by using a strong hand magnet. The separate from the coarse fraction was found to contain low-Ni,Fe (TC = 750-770 °C) in trace quantities. Since contamination seems unlikely, it must be concluded that the Fe has an extraterrestrial origin. Whilst partially-degraded cosmic spherules may add to the signal, their input is believed to be insignificant. The other obvious source is debris from the vapourization of a K/F impactor.

  4. Independent Mammalian Genome Contractions Following the KT Boundary Mina Rho,* Mo Zhou,* Xiang Gao, Sun Kim,* Haixu Tang,* and Michael Lynch

    E-print Network

    Lynch, Michael

    substantial, independent reductions in genome size following the Cretaceous­Tertiary (KT) boundary, a period in genome size have occurred in multiple lineages of mammals subsequent to the Cretaceous­ Tertiary (KT

  5. Chicxulub impact predates K–T boundary: New evidence from Brazos, Texas

    Microsoft Academic Search

    Gerta Keller; Thierry Adatte; Zsolt Berner; Markus Harting; Gerald Baum; Michael Prauss; Abdel Tantawy; Doris Stueben

    2007-01-01

    Multidisciplinary studies, including stratigraphy, sedimentology, mineralogy and geochemistry, of the new core Mullinax-1 and outcrops along the Brazos River and Cottonmouth Creek, Falls County, Texas, reveal the complex history of the Chicxulub impact, the event deposit and the K–T boundary event. The K–T boundary, as identified by the negative ?13C shift, first occurrence of Danian planktic foraminifera and palynomorphs occurs

  6. 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

  7. 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.

  8. Deccan flood basalts at the Cretaceous\\/Tertiary boundary?

    Microsoft Academic Search

    Vincent Courtillot; Jean Besse; Didier Vandamme; Raymond Montigny; Jean-Jacques Jaeger; Henri Cappetta

    1986-01-01

    Joint consideration of new paleomagnetic, paleontological and geochronological data from the Deccan continental flood basalts in India and critical discussion of earlier results lead us to suggest that volcanic activity may have lasted less than 1 Ma, thus possibly ranking as one of the largest volcanic catastrophes in the last 200 Ma. Available data are best satisfied if volcanism spanned

  9. Placental mammal diversification and the CretaceousTertiary boundary

    E-print Network

    Eizirik, Eduardo

    extinction of dinosaurs. Discriminating among these models is critical for understanding the historical- ordinal divergences in excess of 100 million years ago (mya), ``before or shortly after the appearance

  10. 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.

  11. Fires at the K/T boundary - Carbon at the Sumbar, Turkmenia, site

    NASA Technical Reports Server (NTRS)

    Wolbach, Wendy S.; Anders, Edward; Nazarov, Michael A.

    1990-01-01

    Results are reported on carbon analysis and on C and Ir correlations in samples from the marine K-T boundary site SM-4 at the Sumbar River in Turkmenia (USSR), which has the largest known Ir anomaly (580 ng/cq cm). In addition, the boundary clay is thick, and is undisturbed by bioturbation. Kerogen and delta-C-13 elemental carbon in the boundary clay were resolved using a Cr2O7(2-) oxidation method of Wolbach and Anders (1989). It was found that Ir and shocked quartz, both representing impact ejecta, rise sharply at the boundary, peak in the basal layer, and then decline. On the other hand, soot and total elemental C show a similar spike in the basal layer but then rise rather than fall, peking at 7 cm. Results indicate that fires at the SM-4 K-T boundary site started before the basal layer had settled, implying that ignition and spreading of major fires became possible at the time of or very soon after the meteorite impact.

  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. 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.

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

    Microsoft Academic Search

    Joel Cracraft

    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. Phylogenetic relationships of basal

  15. CretaceousTertiary geodynamics: a North Atlantic exercise Trond H. Torsvik,1,2

    E-print Network

    Torsvik, Trond Helge

    Cretaceous­Tertiary geodynamics: a North Atlantic exercise Trond H. Torsvik,1,2 Jon Mosar1 reconstructions are presented for the Cretaceous­Early Tertiary North Atlantic using a combination described misfits between the North Atlantic Plate elements at successive intervals during this time period

  16. 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

  17. Mineralogy and phase-chemistry of the Cretaceous/Tertiary section in the Lattengebirge, Bavarian Alps

    NASA Technical Reports Server (NTRS)

    Graup, G.

    1988-01-01

    The Lattengebirge K/T section reveals three distinct Ir spikes. Two of them are contained in the K/T transition zone sensu-strictu termed clayey interval, with 4.4 ppb Ir at the actual K/T boundary, and 2.8 ppb Ir 10 cm above the boundary. The highest Ir enrichment of 9 ppb, however, was detected in semi-cleaned organic material from a thin sandstone layer of Upper Maastrichtian age at 16 cm below the boundary. In this layer various discernible phases are preserved, contrasting with the worldwide observed K/T transition zones which are generally entirely composed of diagenetically altered materials. Given that, important clues to understanding the Cretaceous terminal events may be provided. The phases of the Cretaceous Ir bearing layer at Lattengebirge consist of: sandstone fragmental minerals in a carbonate matrix, coal which is partly burnt, melt glasses presumably of combustion-metamorphic origin, and sulfides, mainly chalcopyrite, contained in the coal. Like many known K/T sections and the Lattengebirge boundary sensu-strictu, the Cretaceous horizon is enriched in Ir and chalcophile elements as well. Although the Lattengebirge section offers the freshest materials, including melt glasses, of all K/T localities investigated, no unequivocal evidence of formation by impact has been found there.

  18. 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

  19. 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.

  20. Plants with double genomes might have had a better chance to survive the Cretaceous–Tertiary 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 Cretaceous–Tertiary (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

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

    SciTech Connect

    Lehman, T.M. (Texas Tech Univ., Lubbock (USA))

    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.

  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. 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 ?m) 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.

  4. 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.

  5. No Evidence For Autochtonous Maastrichtian Sediment Above Chicxulub Suevitic Ejecta in The Yaxcopoil-1 Core: The Chicxulub Impact is the K\\/T Boundary Impact

    Microsoft Academic Search

    J. Smit

    2006-01-01

    No Evidence for Autochthonous Maastrichtian Sediment Above Chicxulub Suevitic Ejecta in the Yaxcopoil-1 Core: The Chicxulub Impact is the K\\/T Boundary Impact. J. Smit, Dept. of Sedimentology, Faculty of Earth and Life Sciences FALW, Vrije Universiteit, de Boelelaan 1085, 1081HV Amsterdam, Netherlands Recently(1), it was suggested that the Chicxulub crater might precede the K\\/T boundary by about 300kyrs. Initially, the

  6. 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.

  7. Geochemistry of K/T-boundary Chicxulub ejecta of NE-Mexico

    NASA Astrophysics Data System (ADS)

    Harting, M.; Deutsch, A.; Rickers, K.

    2003-12-01

    Many K/T sections all over the world contain impact spherules supposed related to the Chicxulub event. This study focus on ejecta layers in NE-Mexican profiles. We carried out systematic XRF and synchrotron radiation measurements on such spherules at the HASYLAB and ANKA facilities as well as microprobe analyses (CAMECA SX50). Area scans on tektite-like material of the Bochil section reveal a pronounced zonation in the inner part, dominated by Ba and Sr whereas secondary CaCO3 dominates in the altered margin. The composition of the spherules from the Mesa-Juan Perez section differ significantly from the Beloc (Haiti) and Bochil tektite glasses. At Mesa-Juan Perez, spherules are either extremely rich in Fe and Ca or consist of smectite, some of those carry carbonate inclusions. Yttrium, La and Ce are zoned within the smectite with concentrations below the detection limit and up to 20 æg/g The Ca-rich inclusions are enriched in Y (up to 35 æg/g) and La (18 æg/g) and, compared to the surrounding smectite, also in Ce (up to 34 æg/g). The Ce enrichment in spherules from the Mesa-Juan Perez section indicates impact-melted carbonates of the Yucatan carbonate platform as possible precursor rocks. Recent investigations focus on the chemistry of melt rock samples from the PEMEX wells Yucatan-6 and Chicxulub-1: Their average composition (mean of 250 data points in wt-percent ) is 61.6 for SiO2, 0.16 for TiO2, 18.07 for Al2O3, 0.01 for Cr2O3, 1.98 for Na2O, 1.5 for FeO, 0.05 for MnO, 0.01 for NiO, 0.31 for MgO, 9.14 for K2O, 3.44 for CaO, and 0.01 for SO2. These results are in some cases comparable to the geochemistry of ejecta glasses, e.g. from Beloc (Haiti).

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

    NASA Technical Reports Server (NTRS)

    Kring, David A.; Boynton, William V.

    1991-01-01

    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.

  9. Geochemical constraints on source region of Cretaceous/Tertiary impact glasses

    NASA Astrophysics Data System (ADS)

    Sigurdsson, H.; Bonte, Ph.; Turpin, L.; Chaussidon, M.; Metrich, N.; Steinberg, M.; Pradel, Ph.; D'Hondt, S.

    1991-10-01

    New trace elements and stable and radiogenic isotope data are presented which show that the silicic black glass spherules from the K/T boundary layer at Beloc in Haiti are derived from continental crust of andesitic composition, whereas the high-Ca glass formed by melting of evaporite-rich sediment. This is confirmed by melting experiments with evaporite and andesite at 1200-1400 C which approximately reproduce the high-Ca glass. The temperature-dependent variation of sulfur content in synthetic high-Ca glasses indicates a formation temperature of 1300 C for the Haiti glasses. The geology of the impact site inferred from the geochemistry of the Haiti glasses matches the lithologies found in the 180-km Chicxulub structure which occurs in Cretaceous evaporite deposits in Mexico. The high sulfur content of the calcic glasses suggests that the impact may have generated significant emissions of sulfur dioxide to the atmosphere, causing short-term global cooling.

  10. 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 world’s 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.

  11. An atmospheric pCO2 reconstruction across the Cretaceous-Tertiary boundary from

    E-print Network

    Royer, Dana

    for review October 29, 2001) The end-Cretaceous mass extinctions, 65 million years ago, pro- foundly evidence for major climatic warming after the KTB impact and implies that severe and abrupt global warming-Cretaceous period, 65 million years (Myr) ago, was marked by one of the five largest mass extinction events in Earth

  12. Palynological assemblages across the Cretaceous\\/Tertiary boundary in northern Jiangsu, eastern China

    Microsoft Academic Search

    Song Zhichen; Zheng Yahui; Liu Jinling

    1995-01-01

    Palynological assemblages from the uppermost Cretaceous (Taizhou Formation) and the basal Tertiary (First Member of Funing Formation) in northern Jiangsu are described, and the distribution of some distinctive palynomorphs, including Consoliduspollenites, Crassimarginpollenites, Taizhoupollis, Jiangsupollis, Jianghanpollis, Morinoipollenites, Aquilapollenites and Extratriporopollenites is discussed. Some species of these genera are redescribed. The plants that produced them must have become extinct shortly before, or

  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. 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.

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

    Microsoft Academic Search

    Ronald G. Prinn; Bruce Fegley 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

  16. 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.

  17. 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.

  18. 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.

  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. 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.

  1. 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.

  2. 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.

  3. No Evidence For Autochtonous Maastrichtian Sediment Above Chicxulub Suevitic Ejecta in The Yaxcopoil-1 Core: The Chicxulub Impact is the K/T Boundary Impact.

    NASA Astrophysics Data System (ADS)

    Smit, J.

    2006-05-01

    No Evidence for Autochthonous Maastrichtian Sediment Above Chicxulub Suevitic Ejecta in the Yaxcopoil-1 Core: The Chicxulub Impact is the K/T Boundary Impact. J. Smit, Dept. of Sedimentology, Faculty of Earth and Life Sciences FALW, Vrije Universiteit, de Boelelaan 1085, 1081HV Amsterdam, Netherlands Recently(1), it was suggested that the Chicxulub crater might precede the K/T boundary by about 300kyrs. Initially, the idea was based on multiple layers of (mostly altered) impact glass spherules that were found up to 11 m below and at the base of a sandstone interval and an iridium anomaly occurs at the top. Normal hemipelagic deposits of the Mendez shale would separate the multiple spherule layers. However, those layers are slumped and discontinuous, and separated by displaced layers of Mendez shale. The sandstone deposits in between spherules and iridium anomaly betray very rapid deposition (thick climbing ripple units), probably deposited in a few days at most, compatible with a single impact (at Chicxulub). The Yaxcopoil-1 core in the Chicxulub crater recovered a complete core interval of the same time period, and a similar controversy erupted. The critical interval in the Yaxcopoil-1 core is a short, 64cm long core-segment overlying the highest (displaced) suevitic ejecta (794.75m), and underlying uncontested deep-water crater-fill sediments of basal Paleocene age (794.11m). The interval includes an interval of cross-bedded dolomitic sand, alternating with fine-grained parallel laminated dolomitic sand, overlain by a 9cm thick bored dolomitic hard ground. A 2cm thick, dark clay-layer with dissolution features overlies the hard ground, followed by micritic basal Paleocene wackestones. The clay layer is often linked with the K/T boundary However, the evidence suggesting that the 64 cm interval is an authigenic, pelagic, micritic sediment of upper Maastichtian age is seriously flawed. This idea is based on four arguments: 1) presence of abundant latest Maastrichtian foraminifers, 2) presence of multiple layers of glauconite, 3) presence of pelagic micrite, 4) presence of an stable isotope shift, comparable to an identical shift at the K/T boundary elsewhere. We have made four thin sections of each of the 13 samples (yax306-318) of that contested interval, and subjected these slides to SEM backscatter, microprobe, XRD, Cathode luminescence and microscopic analysis. In these thin sections we were unable to distinguish 1) Even a single specimen of a Maastrichtian planktic foraminifer, and found: 2) Smectite instead of glauconite in all layers except the dissolved clay layer at the top, and found: 3) No evidence for micrite, and found out that 4) the shift in stable isotopes across the clay layer is due to measurements of diagenetic sparry calcite pore-filling below, and pelagic micrite above the isotopic shift. Thus, in conclusion, we reject all evidence for a Maastrichtian age of sediments overlying the Chicxulub ejecta in the Yaxcopoil-1 core. 1. Stinnesbeck, W.,et al., 2004. Yaxcopoil-1 and the Chicxulub impact. Int. Jour. of Earth Sci., 93. 1042-1065.

  4. 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.

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

    PubMed

    Bottke, William F; Vokrouhlický, David; Nesvorný, 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

  6. 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.

  7. Proportions of coarse and fine clay across the Cretaceous-Tertiary boundary in Milam, Falls, and Travis Counties, Texas 

    E-print Network

    Smith, John Charles

    1966-01-01

    for the investigation Explanation of Proposed Method Location of Clay Units Investigated Previous Investigations Methods of Investigation Eield Investigations Laboratory Investigations Hesults of the lnvcstigation 15 26 Locality I Locality II Locality III... and fine clay expressed as percentages of the total clay i'rection from Locality I . 30 Lattice spacings, mineral composition, indices, and intensities of typical samples from Locality I 33 Proportions for duplicate fractionations of coarse and fine...

  8. GEOLOGY, TAPHONOMY, AND PALEOECOLOGY OF A UNIQUE UPPER CRETACEOUS BONEBED NEAR THE CRETACEOUS-TERTIARY BOUNDARY IN SOUTH DAKOTA

    E-print Network

    DePalma, Robert Anthony

    2010-04-27

    This research examines a Konzentrat-Lagerstätte, the Bone Butte site, in the Upper Cretaceous Hell Creek Formation of South Dakota. Field data from a diverse multispecific bonebed in Harding County, South Dakota, including ...

  9. Proportions of coarse and fine clay across the Cretaceous-Tertiary boundary in Milam, Falls, and Travis Counties, Texas

    E-print Network

    Smith, John Charles

    1966-01-01

    has offered one of the best solutions to the correlation of clays and shales, but many times it is also inconclusive. For these and other reasons geologists, soil sci. ent, ists, civil engineers, and related physical scientists have initiated...-' the If varro and. Eidway Groups exposed =. t Loc" lity I ar e il lustr atcd in Figure 3, The lithologic description of' thi; section is giver. below. Tertiary System 1'iidway Group Kincaid Formation Tn 1 cJnr ir' f'e~ 4 F. C' ay; yellowi. sh-brown, we...

  10. A unique geochemical record at the Permian\\/Triassic boundary

    Microsoft Academic Search

    William T. Holser; Hans-Peter Schoenlaub; Peter Klein; Moses Attrep Jr.; Klaus Boeckelmann; Mordeckai Magaritz; Charles J. Orth; Alois Fenninger; Catherine Jenny; Martin Kralik; Hermann Mauritsch; Edwin Pak; Josef-Michael Schramm; Karl Stattegger; Rupert Schmöller

    1989-01-01

    A 330-m core drilled through the marine Permian\\/Triassic boundary in the Austrian Carnic Alps has been used to make closely correlated studies of geochemistry, petrography, and paleontology across that boundary. The isotope shifts and metal concentrations are found to be extended, multiple, and complex, and do not resemble those seen at the Cretaceous\\/Tertiary boundary. Both the carbon isotope shifts and

  11. 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. (Indiana Univ., Bloomington (United States))

    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.

  12. Cosmic particles (micrometeorites) and nanospheres from the Cretaceous-Paleogene (K/T) boundary clay layer at the Stevns Klint Section, Denmark

    NASA Astrophysics Data System (ADS)

    Korchagin, O. A.; Tsel'Movich, V. A.

    2011-04-01

    This paper presents new data on numerous small metallic particles of iron, copper, Fe-Ni, Fe-Ni-Co, and Fe-Cr alloys, magnetite, and aluminosilicate balls of cosmic origin found in the black clay boundary layer between the Cretaceous and Paleogene in the Stevns Klint Section (Denmark). The findings imply that a fall of an asteroid to Earth 65 Ma ago was accompanied with falling of finely dispersed metallic particles of extraterrestrial nature related to the asteroid fragments or to micrometeorites following the asteroid or to the intense supply of cosmic dust. The huge amount of finely dispersed matter that fell to Earth at that time should be considered in further reconstructions of events at the boundary of the Cretaceous and Paleogene.

  13. 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.

  14. 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.

  15. The carbon-isotope shift at the Permian\\/Triassic boundary in the southern Alps is gradual

    Microsoft Academic Search

    Mordeckai Magaritz; Richard Bart; Aymon Baud; William T. Holser

    1988-01-01

    Carbon isotope ratios in marine carbonate rocks have been shown to shift at some of the time boundaries associated with extinction events; for example, Cretaceous\\/Tertiary1 and Ordovician\\/ Silurian2. The Permian\\/Triassic boundary, the greatest extinction event of the Phanerozoic3, is also marked by a large delta13C depletion4,5. New carbon isotope results from sections in the southern Alps show that this depletion

  16. 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.

  17. Inquiring into indicators and origin of catastrophic events at stratigraphic boundaries.

    PubMed

    Zhang, Q; Xu, D

    1996-01-01

    Since 1982, numerous indicators of catastrophic events have been observed at the main stratigraphic boundaries in China during the Phanerozoic, i.e. Precambrian-Cambrian, Permian-Triassic, Cretaceous-Tertiary as well as Ordovician-Silurian and Devonian-Carboniferous boundaries. These markers are boundary clay layer, microspherules, high Ir anomaly, mass extinction of organisms and impact of meteorite. We support the hypothesis of the extraterrestrial origin of catastrophic events and suggest that the events at different stratigraphic boundaries might be different in features and processes. PMID:12747349

  18. 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.

  19. 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

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

    Microsoft Academic Search

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

    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

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

    Microsoft Academic Search

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

    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 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

  2. Primate Origins: Implications of a Cretaceous Ancestry

    Microsoft Academic Search

    Robert D. Martin; Christophe Soligo; Simon Tavaré

    2007-01-01

    It has long been accepted that the adaptive radiation of modern placental mammals, like that of modern birds, did not begin until after the Cretaceous\\/Tertiary (K\\/T) boundary 65 million years (Ma) ago, following the extinction of the dinosaurs. The first undoubted fossil relatives of modern primates appear in the record 55 Ma ago. However, in agreement with evidence from molecular

  3. Rubey Colloquium Paper Cenozoic Bolide Impacts and Biotic Change in North American Mammals

    Microsoft Academic Search

    JOHN ALROY

    North American mammals experienced a major mass extinction at the Cretaceous\\/Tertiary (K\\/T) boundary that is tied unambiguously to the Chicxulub impact event. Immediately af- terwards, there was an immense adaptive radiation that greatly expanded taxonomic diver- sity and the range of body sizes and ecological strategies. However, ties between later, Ceno- zoic impact events and specific episodes in mammalian evolution

  4. Impact event at the Permian-Triassic boundary: evidence from extraterrestrial noble gases in fullerenes.

    PubMed

    Becker, L; Poreda, R J; Hunt, A G; Bunch, T E; Rampino, M

    2001-02-23

    The Permian-Triassic boundary (PTB) event, which occurred about 251.4 million years ago, is marked by the most severe mass extinction in the geologic record. Recent studies of some PTB sites indicate that the extinctions occurred very abruptly, consistent with a catastrophic, possibly extraterrestrial, cause. Fullerenes (C60 to C200) from sediments at the PTB contain trapped helium and argon with isotope ratios similar to the planetary component of carbonaceous chondrites. These data imply that an impact event (asteroidal or cometary) accompanied the extinction, as was the case for the Cretaceous-Tertiary extinction event about 65 million years ago. PMID:11222855

  5. 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.

  6. Genesis of the K/T section of stevns klint

    NASA Astrophysics Data System (ADS)

    Zijlstra, Hans

    A numerical model that was developed for the simulation of the genesis of Maastrichtian wavy-bedded (Tuffaceous) Chalk precession cycles of Maastricht (SE Netherlands) and the Gironde Estuary (SW France), is used to explain the sedimentology of the wavy-bedded Maastrichtian-Danian (Tuffaceous) Chalk sequence of Stevns Klint (Denmark). It appears that the Stevns Klint K/T boundary Fish Clay with an abnormally high iridium concentration reflects the dissolution of carbonate and the concentration of insoluble authigenic minerals (condensation) during a period of exceptionally low deposition rates, that presumably coincided with a rather low-energetic precession period, during a sudden change of tectonic regime.

  7. 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.

  8. Locating the K\\/T boundary impact crater(s)

    Microsoft Academic Search

    Susan M. Bush

    1990-01-01

    Stratigraphic, mineralogical, chemical and isotopic evidence have led to the large (˜10-km) asteroid or comet impact theory as the cause of the Cretaceous period coming to an end. However, a suitable crater has not yet been found. Although the crater may have been destroyed because half of what was then the ocean floor has since been subducted, researchers are still

  9. ADAPTIVE K-T BLAST/K-T SENSE FOR ACCELERATING CARDIAC PERFUSION MRI Alexei Samsonov1

    E-print Network

    Utah, University of

    ADAPTIVE K-T BLAST/K-T SENSE FOR ACCELERATING CARDIAC PERFUSION MRI Alexei Samsonov1 , Ed DiBella2 Laboratory of Cardio Energetics, NIH, Bethesda, Maryland, USA Introduction: Recently proposed k-t BLAST wall motion in cine cardiac MRI. The periodicity permits acquiring training data prior to actual scan

  10. Are Nanodiamonds Evidence for a Younger Dryas Impact Event?

    Microsoft Academic Search

    J. Kennett; D. J. Kennett; T. E. Bunch; T. W. Stafford Jr.; W. S. Wolbach

    2009-01-01

    Nanodiamonds (NDs), including hexagonal diamonds (lonsdaleite) have been discovered at the Tunguska impact site and in the Cretaceous-Tertiary (K\\/T) boundary layer, which also contains cubic diamonds. Similarly, for the Younger Dryas boundary layer (YDB) that dates to the onset of the Younger Dryas (YD) cooling event at ~12.9 ka, NDs (cubics and lonsdaleite) are found broadly at multiple locations over

  11. Chicxulub Impact Crater and Yucatan Carbonate Platform - Stratigraphy and Petrography of PEMEX Borehole Cores

    Microsoft Academic Search

    A. G. Gutierrez-Cirlos; G. Perez-Drago; L. Perez-Cruz; J. Urrutia-Fucugauchi

    2008-01-01

    Chicxulub impact crater is the best preserved of the three large multi-ring structures documented in the terrestrial record. Chicxulub, formed 65 Ma ago, is associated with the Cretaceous\\/Tertiary (K\\/T) boundary layer and the impact related to the organism extinctions and events marking the boundary. The crater is buried under Tertiary sediments in the Yucatan carbonate platform in the southern Gulf

  12. The Chicxulub Impact and K-T Mass Extinction in Texas *Gerta Keller, Department of Geosciences, Princeton University, Princeton NJ 08544

    E-print Network

    Keller, Gerta

    of three tectonically undisturbed and stratigraphically well-separated events: the Chicxulub impact sequences comparable to the K-T boundary stratotype section at El Kef, Tunisia. (c) the absence of significant tectonic activity, (d) excellent preservation of microfossils

  13. 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.

  14. 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.

  15. 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.

  16. boundaries

    Microsoft Academic Search

    Paolo Moretti; Lasse Laurson; Mikko J. Alava

    The dynamics of dislocation assemblies in deforming crystals indicate the emergence of collective phenomena, intermittent fluctuations and strain avalanches. In polycrystalline materials, the understanding of plastic deformation mechanisms depends on grasping the role of grain boundaries on dislocation motion. Here the interaction of dislocations and elastic, low angle grain boundaries is studied in the framework of a discrete dislocation representation.

  17. End-Cretaceous devastation of terrestrial flora in the boreal Far East

    NASA Astrophysics Data System (ADS)

    Saito, T.; Yamanoi, T.; Kaiho, K.

    1986-09-01

    Terrestrial palynomorphs from the Hokkaido marime sedimentary sequence spanning the Cretaceous/Tertiary (K/T) boundary record sudden changes in the floristic composition at the exact base of the boundary claystone layer; pollen abundance declines that are accompanied by an abrupt rise in the proportion of fern spores are noted to resemble the palynologically defined K/T boundary in the western interior of North America, which coincides with the top of an IR-rich clay layer. The possible synchronous occurrence of analogous floral changes at such widely separated regions implies a devastation of the land flora which although brief was intercontinental in scope, such as a catastrophic meteorite impact.

  18. Geochemical environmental changes and dinosaur extinction during the Cretaceous-Paleogene (K\\/T) transition in the Nanxiong Basin, South China: Evidence from dinosaur eggshells

    Microsoft Academic Search

    ZiKui Zhao; XueYing Mao; ZhiFang Chai; GaoChuang Yang; FuCheng Zhang; Zheng Yan

    2009-01-01

    The complex patterns of trace elements including Ir and isotope distributions in the three K\\/T sections of the Nanxiong Basin\\u000a prove the existence of two environmental events in the latest Cretaceous and earliest Paleocene. The first geochemical environmental\\u000a event occurred at about 2 Ma prior to the K\\/T boundary interval, where the dinosaur diversity was hardly reduced, except that\\u000a a

  19. Benthic foraminifera across the K/Pg boundary in the Brazos River area (Texas) and Stevns Klint (Denmark): sequence stratigraphy, sea level change and extinctions.

    NASA Astrophysics Data System (ADS)

    Hart, Malcolm; Smart, Christopher; Searle, Sarah; Feist, Sean; Leighton, Andrew; Price, Gregory; Twitchett, Richard

    2010-05-01

    While the majority of micropalaeontologists have concentrated on the planktic foraminifera of the Brazos River succession (in order to define the position of the K/T boundary), there are relatively few studies of the benthic foraminifera published. There are a number of sites available for study, including the Brazos River itself and the tributaries of Cottonmouth Creek and Darting Minnow Creek. There have also been a number of drill cores recovered from the area including the Mullinax - 1 core which we have studied. Almost all of the benthic foraminifera recovered from the Mullinax - 1 core were described by Joseph Cushman (1946) in his monograph. The Corsicana Formation (Kemp Formation of the State Geological Map) of latest Maastrichtian age is overlain by the Littig Member of the Kincaid Formation which includes, at its base, the so-called "Event Bed". The base of this unit is the "impact-defined K/T boundary" of many authors (e.g., Yancey, 1996). The "Event Bed" contains a number of discreet (but thin) sedimentary units including spherule-rich layers, shell lags and a number of hummocky sandstone beds (Gale, 2006). In a recent paper, Keller et al. (2009) have identified an "impact" layer below the "Event Bed" and a K/T boundary higher in the succession that most other authors. In the Mullinax - 1 core, there is a diverse fauna of benthic foraminifera, although the species count is much less than that described by Cushman (1946). This is almost certainly the result of the small sample size available in the small diameter core. There is a distinctive assemblage of mid-outer shelf taxa, including agglutinated foramininfera (Tritaxia, Verneuilina, Plectina, etc.) and aragonitic taxa (Epistomina). The numbers of agglutinated taxa in the Mullinax - 1 core are much reduced at the level of the "Event Bed" and this, coupled with the changes in the planktic fauna, indicates a (fairly) marked drop in sea level. Both Yancey (1996) and Gale (2006) argue that this brings the sea floor into the range of storm wave base and that this is what is indicated by the "Event Bed". There are a number of water-depth changes in the famous Stevns Klint succession in Denmark, although the majority of the benthic taxa are different. All belong to the normal Chalk Sea assemblage of North West Europe. The planktic assemblage in Denmark is limited and there are no aragonitic taxa (preservation problems). Benthic foraminifera are rare, though generally more abundant in the chalks immediately below the K/T boundary. Work on material from Denmark and the Brazos River successions is on-going including a more detailed assessment of the various morphogroups represented. The presence of an unusual "foraminiferal sand" within the lowermost Paleocene of the Cottonmouth Creek succession has yet to be fully described and its presence is not fully understood (environmental control or re-deposition?). A sequence stratigraphical interpretation of the successions in Texas and Denmark has shown parallel changes in sea level (of the same magnitude in both areas) that are coincident with the major lithological changes. The most significant feature is a fall in sea level some tens of thousands of years before the K/Pg boundary. Cushman, J. A. 1946. Upper Cretaceous Foraminifera of the Gulf Coastal Region of the United States and adjacent areas. U. S. Geological Survey, Professional Paper, 206, 1 - 241. Gale, A. S. 2006. The Cretaceous-Palaeogene boundary on the Brazos River, Falls County, Texas: is there evidence for impact-induced tsunami sedimentation? Proceedings of the Geologists' Association, London, 117, 173 - 185. Keller, G., Abramovich, S., Berner, Z. & Adatte, T. 2009. Biotic effects of the Chicxulub Impact, K-T catastrophe and sea level change in Texas. Palaegeography, Palaeoclimatology, Palaeoecology, 271, 52 - 68. Yancey, T. E. 1996. Stratigraphy and depositional environments of the Cretaceous-Tertiary Boundary Complex and Basal Paleocene section, Brazos River, Texas. Tran

  20. Nonlinear k_t factorisation: recent progress and perspectives

    E-print Network

    W. Schäfer

    2006-11-07

    Hard scattering in a strongly absorptive regime requires a novel nonlinear k_t -- factorization. Here we discuss two recent developments: firstly the evaluation of radiative corrections to single particle spectra, and secondly an extension of the formalism to address topological cross sections and unitarity cutting rules.

  1. Heavy quark impact factor in kT-factorization

    E-print Network

    Grigorios Chachamis; Michal Deak; German Rodrigo

    2013-10-24

    We present the calculation of the finite part of the heavy quark impact factor at next-to-leading logarithmic accuracy in a form suitable for phenomenological studies such as the calculation of the cross-section for single bottom quark production at the LHC within the kT-factorization scheme.

  2. Improving temporal fidelity in k-t BLAST MRI reconstruction.

    PubMed

    Sigfridsson, Andreas; Andersson, Mats; Wigström, Lars; Kvitting, John-Peder Escobar; Knutsson, Hans

    2007-01-01

    Studies of myocardial motion using magnetic resonance imaging usually require multiple breath holds and several methods have been proposed in order to reduce the scan time. Rapid imaging using k-t BLAST has gained much attention with its high reduction factors and image quality. Temporal smoothing, however, may reduce the accuracy when assessing cardiac function. In the present work, a modified reconstruction filter is proposed, that preserves more of the high temporal frequencies. Artificial decimation of a fully sampled data set was used to evaluate the reconstruction filter. Compared to the conventional k-t BLAST reconstruction, the modified filter produced images with sharper temporal delineation of the myocardial walls. Quantitative analysis by means of regional velocity estimation showed that the modified reconstruction filter produced more accurate velocity estimations. PMID:18044592

  3. Pion Form Factor in the $k_T$ Factorization Formalism

    E-print Network

    T. Huang; X. G. Wu; X. H. Wu

    2004-06-12

    Based on the light-cone (LC) framework and the $k_T$ factorization formalism, the transverse momentum effects and the different helicity components' contributions to the pion form factor $F_{\\pi}(Q^2)$ are recalculated. In particular, the contribution to the pion form factor from the higher helicity components ($\\lambda_1+\\lambda_2=\\pm 1$), which come from the spin-space Wigner rotation, are analyzed in the soft and hard energy regions respectively. Our results show that the right power behavior of the hard contribution from the higher helicity components can only be obtained by fully keeping the $k_T$ dependence in the hard amplitude, and that the $k_T$ dependence in LC wave function affects the hard and soft contributions substantially. As an example, we employ a model LC wave function to calculate the pion form factor and then compare the numerical predictions with the experimental data. It is shown that the soft contribution is less important at the intermediate energy region.

  4. 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

  5. kT-Scale interactions between supported lipid bilayers.

    PubMed

    Everett, W Neil; Bevan, Michael A

    2014-01-14

    We use total internal reflection microscopy (TIRM) and confocal laser scanning microscopy (CSLM) to study supported lipid bilayer (SLB)-modified silica colloids with various SLB compositions (e.g., PEGylated vs. non-PEGylated) that control colloidal and bilayer stability. Measured and predicted potentials accurately capture stable configurations. For unstable conditions when SLBs adhere, fuse, or spread between surfaces, SLB structures are connected to effective potentials as well as time-dependent behavior. In all cases, directly measured and inferred interactions are well described by steric interactions between PEG brushes and van der Waals weakened by substrate roughness. Our findings quantify non-specific kT-scale interactions between SLB-modified colloids and surfaces, which enables the design of such systems for use in biomedical applications and studies of biomolecular interactions. PMID:24652312

  6. 0016-7622/2011-78-5-399/$ 1.00 GEOL. SOC. INDIA JOURNAL GEOLOGICAL SOCIETY OF INDIA

    E-print Network

    Keller, Gerta

    with the rapid global warming and subsequent cooling near the end of the Maastrichtian. The mass extinction began, November 2011, pp.399-428 Deccan Volcanism Linked to the Cretaceous-Tertiary Boundary Mass Extinction: New in the Cretaceous-Tertiary boundary (KTB) mass extinction. Here we report on the stratigraphy and biologic effects

  7. Global Effects of the Chicxulub Impact on Terrestrial Vegetation -Review of the

    E-print Network

    Vajda, Vivi

    Record from New Zealand Cretaceous/Tertiary Boundary Vivi Vajda1 , J. Ian Raine2 , Christopher J. Hollis2 of the land plants in close association with the Cretaceous-Tertiary boundary (KTB) event. The turnover of the period of fern-dominance is here calculated to have lasted for ca. 8000-20,000 years, based

  8. and Mlr is the primary mass in solar mass units. Inside the Hill's sphere, the motion of the satellite is con-

    E-print Network

    Vajda, Vivi

    Indication of Global Deforestation at the Cretaceous-Tertiary Boundary by New Zealand Fern Spike Vivi Vajda,1 of a bolide impact at the Cretaceous-Tertiary boundary is shown in fossil pollen and spore assem- blages by a diverse flora being abruptly replaced by one dominated by a few species of fern. Well documented in North

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

    Microsoft Academic Search

    Michael R. Rampino; Tyler Volk

    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

  10. Cretaceous eutherians and Laurasian origin for placental mammals near the K\\/T boundary

    Microsoft Academic Search

    J. R. Wible; G. W. Rougier; M. J. Novacek; R. J. Asher

    2007-01-01

    Estimates of the time of origin for placental mammals from DNA studies span nearly the duration of the Cretaceous period (145 to 65million years ago), with a maximum of 129million years ago and a minimum of 78million years ago. Palaeontologists too are divided on the timing. Some support a deep Cretaceous origin by allying certain middle Cretaceous fossils (97-90million years

  11. 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.

  12. THE CRETACEOUSTERTIARY MASS EXTINCTION: THEORIES AND CONTROVERSIES

    E-print Network

    Keller, Gerta

    activity. The cause(s) for the end-Cretaceous mass extinction following this long period of globallyTHE CRETACEOUS­TERTIARY MASS EXTINCTION: THEORIES AND CONTROVERSIES GERTA KELLER Department: The Cretaceous­Tertiary boundary (KTB) mass extinction is primarily known for the demise of the dinosaurs

  13. Boundary conditions effects by Discontinuous Galerkin Solvers for Boltzmann-Poisson models of

    E-print Network

    defines insulating boundaries) is imposed by: fspec (x, k, t) = f(x, k , t) for (x, k) - N , t > 0. (I.4 of gas dynamics. The distribution function at the Inflow boundary is proportional to a Maxwellian [4 of the momentum p(k), as in [5]. A. BP system with k coordinate transformation assuming a Kane Energy Band

  14. 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.

  15. High temperature structural study of Gd-doped ceria by synchrotron X-ray diffraction (673 K ? T ? 1073 K).

    PubMed

    Artini, Cristina; Pani, Marcella; Lausi, Andrea; Masini, Roberto; Costa, Giorgio A

    2014-10-01

    The crystallographic features of Gd-doped ceria were investigated at the operating temperature of solid oxides fuel cells, where these materials are used as solid electrolytes. (Ce(1-x)Gd(x))O(2-x/2) samples (x = 0.1, 0.3, 0.5, 0.7) were prepared by coprecipitation of mixed oxalates, treated at 1473 K in air, and analyzed by synchrotron X-ray diffraction in the temperature range 673 K ? T ? 1073 K at the Elettra synchrotron radiation facility located in Trieste, Italy. In the whole temperature span a boundary was found at x ? 0.2 between a CeO2-based solid solution (for x ? 0.2) and a structure where Gd2O3 microdomains grow within the CeO2 matrix, taking advantage of the similarity between Gd(3+) and Ce(4+) sizes; the existence of the boundary at x ? 0.2 was confirmed also by measurements of ionic conductivity performed by impedance spectroscopy. Similar to what observed at room temperature, the trend of the cell parameter shows the presence of a maximum; with increasing temperature, the composition corresponding to the maximum moves toward lower Gd content. This evidence can be explained by analyzing the behavior of the coefficient of thermal expansion as a function of composition. PMID:25192043

  16. 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

  17. Futures in Accelerator-Based Physics K.T. McDonald

    E-print Network

    McDonald, Kirk

    Futures in Accelerator-Based Physics K.T. McDonald Princeton U. U. Ioannina, Greece May 21, 2004. McDonald U. Ioannina, May 21, 2004 1 #12;From the Cathode Ray Tube to a Muon Collider 1897 Braun cooling. 1993 Mikhailichenko, Zolotorev: Optical stochastic cooling. Kirk T. McDonald U. Ioannina, May 21

  18. Shock-induced vaporization of anhydrite and global cooling from the K/T impact

    E-print Network

    Stewart, Sarah T.

    Shock-induced vaporization of anhydrite and global cooling from the K/T impact Satish C. Gupta 1 Laboratory, California Institute of Technology, Pasadena, CA 91125, USA Received 24 August 2000; received present new data on the vaporization criteria of anhydrite. These are based on the reanalysis of the shock

  19. Restoration of $k_T$ factorization for low $p_T$ hadron hadroproduction

    E-print Network

    Chun-peng Chang; Hsiang-nan Li

    2011-06-10

    We discuss the applicability of the $k_T$ factorization theorem to low-$p_T$ hadron production in hadron-hadron collision in a simple toy model, which involves only scalar particles and gluons. It has been shown that the $k_T$ factorization for high-$p_T$ hadron hadroproduction is broken by soft gluons in the Glauber region, which are exchanged among a transverse-momentum-dependent (TMD) parton density and other subprocesses of the collision. We explain that the contour of a loop momentum can be deformed away from the Glauber region at low $p_T$, so the above residual infrared divergence is factorized by means of the standard eikonal approximation. The $k_T$ factorization is then restored in the sense that a TMD parton density maintains its universality. Because the resultant Glauber factor is independent of hadron flavors, experimental constraints on its behavior are possible. The $k_T$ factorization can also be restored for the transverse single-spin asymmetry in hadron-hadron collision at low $p_T$ in a similar way, with the residual infrared divergence being factorized into the same Glauber factor.

  20. Princeton/BaBar/TNDC9756 C. Lu and K.T. McDonald

    E-print Network

    McDonald, Kirk

    of Aluminum Wire 1 Update of Creep Measurements Most creep measurements were obtained by stretching the wirePrinceton/BaBar/TNDC­97­56 C. Lu and K.T. McDonald Feb. 6, 1997 The Effect of Annealing on Creep that the creep be less than 10% in the first 10 days. 40 30 20 10 0 Days 1.8 1.6 1.4 1.2 1.0 0.8 Tension

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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)

  6. Plants with double genomes might have had a better chance to survive the CretaceousTertiary

    E-print Network

    Gent, Universiteit

    have been suggested for several plant species whose genome sequence is not available but large ESTPlants with double genomes might have had a better chance to survive the Cretaceous Genome-wide analyses provide overwhelming evidence that plants have undergone one or more whole genome

  7. Diagenesis and reservoir characterization of the Cretaceous-Tertiary sequence, eastern Venezuela

    SciTech Connect

    Aquado, B.; Ghosh, S.; Isea, A. (Intevep, S.A., Caracas (Venezeula))

    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.

  8. The Cretaceous-Tertiary sea floor off Dronning Maud Land, Antarctica

    NASA Astrophysics Data System (ADS)

    Rao, D. Gopala; Chaubey, A. K.; Ramprasad, T.

    1992-05-01

    A study of the bathymetric and linear magnetic anomalies between Dronning Maud Land, Antarctica and the South West Indian Ridge (SWIR) revealed a Mesozoic sequence of linear magnetic anomalies, M0 to M12 (108-126 Ma), a fracture zone offset (˜- 130 km), and the Cretaceous magnetic quiet zone between isochrons M0 (108 Ma) and 34 (80 Ma). The study sheds light on: (1) the evolution of an anomalous "stretched" pattern of seafloor anomalies during magnetic isochrons M0 and 34, and the associated offset (> 10°) in some segments of the northeastern part of the SWIR; (2) continuation of a proposed buried fracture zone to the south, where it abuts the Astrid Ridge off Dronning Maud Land. The history of spreading is related to declining dynamic pressures at the plate margin due to the Kergeulen-Heard mantle plume during Cretaceous time (˜-110 Ma).

  9. Improved k-t BLAST for fast fMR imaging.

    PubMed

    Sinha, Neelam; Saranathan, Manojkumar; Ramakrishnan, A G

    2010-06-01

    A popular dynamic imaging technique, k-t BLAST (ktB) is studied here for fMR imaging. ktB utilizes correlations in k-space and time, to reconstruct the image time series with only a fraction of the data. The algorithm works by unwrapping the aliased Fourier conjugate space of k-t (y-f-space). The unwrapping process utilizes the estimate of the true y-f-space, by acquiring densely sampled low k-space data. The drawbacks of this method include separate training scan, blurred training estimates and aliased phase maps. The proposed changes are incorporation of phase information from the training map and using generalized-series-extrapolated training map. The proposed technique is compared with ktB on real fMRI data. The proposed changes allow for ktB to operate at an acceleration factor of 6. Performance is evaluated by comparing activation maps obtained using reconstructed images. An improvement of up to 10 dB is observed in the PSNR of activation maps. Besides, a 10% reduction in RMSE is obtained over the entire time series of fMRI images. Peak improvement of the proposed method over ktB is 35%, averaged over five data sets. PMID:20382056

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

    PubMed

    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). PMID:19531867

  11. 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.

  12. Blast From the Past

    NSDL National Science Digital Library

    A recently recovered deep-sea core supports theories that an asteroid collided with the earth 65 million years ago, around the time of the extinction of the dinosaurs. The Smithsonian Institution National Museum of Natural History's new site, Blast from the Past, contains details on this cataclysmic event. Colorful graphics provide conceptual illustrations of the asteroid impact and aftermath, accompanied by photographs of the deep-sea core. Text summaries, followed by bibliographic references, describe the asteroid hypothesis, the Cretaceous/Tertiary (K/T) boundary, and the utility of deep-sea cores. With links to other paleobiological sites and related museum exhibits, this site is a useful resource for those wanting to know more about fateful asteroid impacts.

  13. Fluid acceleration effects on suspended sediment transport in the J. A. Puleo, K. T. Holland, and N. G. Plant

    E-print Network

    Slinn, Donald

    Fluid acceleration effects on suspended sediment transport in the swash zone J. A. Puleo, K. T-energy steep beach were used to investigate the importance of fluid accelerations to suspended sediment transport. Swash flow acceleration was nearly constant at about one-half downslope gravitational

  14. The Target System Baseline H.G. Kirk (BNL) and K.T. McDonald (Princeton U.)

    E-print Network

    McDonald, Kirk

    channel field strength 1.5T Length of transition between 20 T and 1.5 T 15 m This target concept has been1 The Target System Baseline H.G. Kirk (BNL) and K.T. McDonald (Princeton U.) (Feb. 4, 2011) Abstract The document summarizes the present baseline of the target system for a 4-MW proton beam

  15. Photon impact factor and $k_T$-factorization for DIS in the next-to-leading order

    E-print Network

    Ian Balitsky; Giovanni A. Chirilli

    2014-07-27

    The photon impact factor for the BFKL pomeron is calculated in the next-to-leading order (NLO) approximation using the operator expansion in Wilson lines. The result is represented as a NLO $k_T$-factorization formula for the structure functions of small-$x$ deep inelastic scattering.

  16. Bl k t T h l F l C l dBlanket Technology, Fuel Cycle and Tritium Self Sufficiency

    E-print Network

    Abdou, Mohamed

    Bl k t T h l F l C l dBlanket Technology, Fuel Cycle and Tritium Self Sufficiency M h d Abd.fusion.ucla.edu JASON Study on Tritium Production in FusionJASON Study on Tritium Production in Fusion San Diego, CA, June 27-28, 2011 1 #12;Summary Points · The importance of tritium breeding blankets has been recognized

  17. NITROGEN SECRETION INTO THE DIGESTIVE TRACT IN SHEEP J. VARADY K. BODA, K.T. TASENOV J. FEJES

    E-print Network

    Paris-Sud XI, Université de

    NITROGEN SECRETION INTO THE DIGESTIVE TRACT IN SHEEP J. VARADY K. BODA, K.T. TASENOV J. FEJES protein and non-protein nitrogenous compounds not only from food, i.e. of exogenous origin, but also those is important from the point of view of nitrogen circulation, its balance and nitrogen enonomy

  18. Symmetry and Stability of Plutonium: The Influence of Electronic Structure K. T. Moore,1,* P. Soderlind,1

    E-print Network

    Laughlin, David E.

    Symmetry and Stability of Plutonium: The Influence of Electronic Structure K. T. Moore,1,* P. So-functional theory, we calculate the bond strengths between the 12 nearest neighbors in plutonium for both pure Pu rather than face-centered cubic Fm3m, showing that the anomalously large anisotropy of plutonium

  19. Late Cretaceous to early Paleocene climate and sea-level uctuations: the Tunisian record

    E-print Network

    Keller, Gerta

    Late Cretaceous to early Paleocene climate and sea-level £uctuations: the Tunisian record Thierry August 2001 Abstract Climate and sea-level fluctuations across the Cretaceous^Tertiary (K^T) transition hiatus at Ain Settara where most of P0 is missing and a period of non-deposition and erosion in the lower

  20. Palaeontology Dinosaur extinction

    E-print Network

    Sargis, Eric J.

    Palaeontology Dinosaur extinction: closing the `3 m gap' Tyler R. Lyson1,2,*, Antoine Bercovici3- avian dinosaurs was ignited by the publication of the Cretaceous­Tertiary (K­T) asteroid impact theory and has seen 30 years of dispute over the position of the stratigraphically youngest in situ dinosaur

  1. Princeton/BaBar/TNDC-97-56 C. Lu and K.T. McDonald

    E-print Network

    McDonald, Kirk

    of Aluminum Wire 1 Update of Creep Measurements Most creep measurements were obtained by stretching the wirePrinceton/BaBar/TNDC-97-56 C. Lu and K.T. McDonald Feb. 6, 1997 The Effect of Annealing on Creep that the creep be less than 10% in the first 10 days. 403020100 Days 1.8 1.6 1.4 1.2 1.0 0.8 Tensionreduction

  2. R&D Towards a Muon Collider H. Guler (undergraduate student), C. Lu, K.T. McDonald,

    E-print Network

    McDonald, Kirk

    R&D Towards a Muon Collider H. Guler (undergraduate student), C. Lu, K.T. McDonald, E.J. Prebys, S.E. Vahsen (graduate student) Princeton U. May 26, 1998 Muon Collider main page: http://www.cap.bnl.gov/mumu/mu home page.html Princeton muon collider page: http://www.hep.princeton.edu/~mcdonald/mumu 1 #12;Options

  3. R&D Towards a Muon Collider H. Guler (undergraduate student), C. Lu, K.T. McDonald,

    E-print Network

    McDonald, Kirk

    R&D Towards a Muon Collider H. Guler (undergraduate student), C. Lu, K.T. McDonald, E.J. Prebys, S.E. Vahsen (graduate student) Princeton U. May 26, 1998 Muon Collider main page: http://www.cap.bnl.gov/mumu/mu home page.html Princeton muon collider page: http://www.hep.princeton.edu/�mcdonald/mumu 1 #12; Options

  4. 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.

  5. Security Boundaries

    Microsoft Academic Search

    Stephen Farrell

    2008-01-01

    Security boundaries are usually defined by a set of systems that are under a single administrative control. These boundaries occur at various levels, and vulnerabilities can become apparent as data crosses each boundary. In this inaugural column on practical security, boundaries from smaller to larger are discussed and a couple of vulnerabilities are described. A potential path forward to tackling

  6. 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

  7. Lemma 4.1-revised: Let y satisfy + K(t, s) y(s) ds + E(t) + F(t), (30)

    E-print Network

    Lamm, Patricia K.

    Lemma 4.1-revised: Let y satisfy y(t) = - t 0 k(t, s) + K(t, s) y(s) ds + E(t) + F(t), (30) a, ) := 0, t ds = - t 0 (t - , ) 0 k(, s) + K(, s) y(s) ds d + (t, )(E(t) + F(t)) = - t 0 t s (t - , ) k(, s) + K(, s

  8. 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.

  9. 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.

  10. 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.

  11. New Constraints on the Asteroid 298 Baptistina, the Alleged Family Member of the K/T Impactor

    E-print Network

    Majaess, Daniel J; Molnar, Larry A; Haegert, Melissa J; Lane, David J; Turner, David G; Nielsen, Inga

    2008-01-01

    In their study Bottke et al. (2007) suggest that a member of the Baptistina asteroid family was the probable source of the K/T impactor which ended the reign of the Dinosaurs 65 Myr ago. Knowledge of the physical and material properties pertaining to the Baptistina asteroid family are, however, not well constrained. In an effort to begin addressing the situation, data from an international collaboration of observatories were synthesized to determine the rotational period of the family's largest member, asteroid 298 Baptistina (P_r = 16.23+-0.02 hrs). Discussed here are aspects of the terrestrial impact delivery system, implications arising from the new constraints, and prospects for future work.

  12. New Constraints on the Asteroid 298 Baptistina, the Alleged Family Member of the K/T Impactor

    E-print Network

    Daniel J. Majaess; David Higgins; Larry A. Molnar; Melissa J. Haegert; David J. Lane; David G. Turner; Inga Nielsen

    2008-11-02

    In their study Bottke et al. (2007) suggest that a member of the Baptistina asteroid family was the probable source of the K/T impactor which ended the reign of the Dinosaurs 65 Myr ago. Knowledge of the physical and material properties pertaining to the Baptistina asteroid family are, however, not well constrained. In an effort to begin addressing the situation, data from an international collaboration of observatories were synthesized to determine the rotational period of the family's largest member, asteroid 298 Baptistina (P_r = 16.23+-0.02 hrs). Discussed here are aspects of the terrestrial impact delivery system, implications arising from the new constraints, and prospects for future work.

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

    PubMed Central

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

    2012-01-01

    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

  14. 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

  15. Plate Boundaries

    NSDL National Science Digital Library

    This site provides information on plate boundaries, which are found at the edge of the lithospheric plates and are of three types: convergent, divergent and conservative. Wide zones of deformation are usually characteristic of plate boundaries because of the interaction between two plates. The three boundaries are characterized by their distinct motions which are described in the text and depicted with block diagram illustrations, all of which are animated. There are also two maps that show the direction of motion of the plates. Active links lead to more information on plate tectonics.

  16. Paleoenvironmental Changes linked to Deccan Volcanism and the K-T Mass Extinction across India and their Correlations with more distant Areas

    NASA Astrophysics Data System (ADS)

    Adatte, T.; Keller, G.; Gerstch, B.; Gardin, S.; Bartolini, A.; Bajpai, S.

    2009-04-01

    Recent studies indicate that the bulk (80%) of the Deccan Trap eruptions occurred over a relatively short time period coinciding with the KT mass extinction. Here we present results based on multiproxy data from intertrappean sediments located at Anjar, Kutch, western India, Jhilmili, Madhya Pradesh, central India, and Rajahmundry, SE India. We compare these results with a KT sequence in Meghalya, NE India, about 800 km from the Deccan volcanic province and more distant areas (e.g. South Atlantic, Tunisia, Kazakhstan) . Intertrappean sediments at Anjar consist mainly of lacustrine sediments and paleosoils, which exhibit at least three PGE anomalies with high Pd contents but only one with a significant Ir enrichment. The presence of dinosaur eggshells and bone fragments above the Ir anomaly implies an upper Maastrichtian age for these sediments. Thus, the PGE anomalies do not coincide with the KT boundary, nor are they of cosmic origin because normalized PGE values suggest a flood basalt origin. Clay minerals consist mainly of smectite and palygorskite and reflect arid conditions, probably linked to higher surface temperatures on a young volcanic landscape subjected to effusive volcanic activity. In the Rajhamundry area, two Deccan basalt flows, known as the Rajahmundry traps, mark the most extensive lava flows extending 1000 km across the Indian continent. The sediments directly overlying the lower trap contain the earliest Danian planktic foraminifera of zones P0-P1a and mark the initial evolution in the aftermath of the KT mass extinction. The upper trap was deposited during zone P1b corresponding to the lower part of magnetic polarity C29n. Sedimentological, mineralogical data reveal that deposition occurred in a shallow estuarine to inner neritic environment with periods of subaerial deposition marked by paleosoils. Clay minerals consist exclusively of smectite, typical of vertisol developed under semi-arid conditions. Outcrop correlation reveals an incised valley estuarine system. At Jhilmili, multidisciplinary analyses reveal the KT boundary at or close to the lower trap basalt in C29R and the upper trap near the C29R/C29N transition. Intertrappean deposition occurred in predominantly terrestrial environments. But a short aquatic interval of fresh water ponds and lakes followed by shallow estuarine marine conditions with brackish ostracods and early Danian zone P1a planktic foraminifera mark this interval close to the K-T boundary. Clays from paleosoils and sediments consist of smectite and palygorskyte and indicate sub-humid to semi-arid conditions. In Meghalaya to the northeast, the KT transition consists of Upper Cretaceous sediments dominated by sandstone, shale, sandy shale and rare coal layers, which indicate deposition in a shallow marine environment with high detrital influx from nearby continental areas. The KTB is characterized by major PGE anomalies in Ir (11.8 ppb), Ru (108 ppb), Rh (93 ppb) and Pd (75 pbb). Contrary to the sections located in the Deccan traps, dominant kaolinite in clay mineral assemblages indicates high humidity and high runoff, which is likely linked with increased warming (greenhouse effect) due to Deccan activity on the mainland. Such climatic conditions have been observed worldwide (e.g. Tunisia, Kazakhstan, South Atlantic). The contemporaneous semi-arid climate conditions that are observed in the Deccan Traps province are not observed elsewhere and therefore appear to be restricted to areas of volcanic activity.

  17. Global Climate Change Resulting From Voluminous Intrusive Basaltic Volcanism in Sedimentary Basins: the Methane Production Potential

    Microsoft Academic Search

    S. Planke; H. Svensen; A. Malthe-Srenssen; T. Rasmussen; B. Jamtveit

    2003-01-01

    Large igneous provinces are often temporarily associated with global warming and mass extinction events, for instance (1) the Siberian Traps and the Permian-Triassic boundary, (2) the Karoo igneous event and the Early Toacian anoxic event, (3) the Deccan Traps and the Cretaceous-Tertiary boundary, and (4) the North Atlantic Volcanic Province (NAVP) and the initial Eocene thermal maximum (IETM). We propose

  18. 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.

  19. Theory and Design of tError Correcting, k-Error Detecting and d-Unidirectional Error Detecting Codes with d > k > t

    Microsoft Academic Search

    Dimitris Nikolos; Alexandros Krokos

    1992-01-01

    The fundamental theory of t-error correcting, k-error detecting, and d-unidirectional error detecting codes with d>k>t (t-EC\\/k-ED\\/d-UED codes) is presented. The authors give a family of methods for designing systematic t-EC\\/ k-ED\\/d-UED codes, with d>k>t, and they reveal the methods which give the more efficient, with respect to redundancy, codes for the various values of t, k, and d. The error

  20. A Planetary Ring Around Earth as Source for the Ir-Enrichment at the KT-Boundary

    NASA Astrophysics Data System (ADS)

    Stage, M.; Rasmussen, K. L.

    1992-07-01

    Since the discovery of the Ir enrichment at the Cretaceous- Tertiary boundary a majority of the researchers have claimed a meteorite impact as origin of the event. But up till now the search for an impact crater has not been conclusive, and alternative explanations have been suggested, e.g., a volcanic origin (Hansen 1990). If, however, we maintain that the KT- boundary material is extraterrestrial, the missing crater constitutes a problem. The missing-crater-problem can be solved by postulating the existence of a temporary planetary ring around the Earth. We suggest the following scenario: an incoming asteroid is captured by the Earth inside the Roche limit, and the breakup of the asteroid creates a planetary ring. Atmospheric drag and partially inelastic collisions between particles cause the ring particles to lose energy and slowly accrete onto Earth. Once the asteroid is decomposed, the atmospheric drag on the ring particles will primarily drain the smaller particles from the ring. The figure shows residence times as a function of starting position. Each curve represents one particle size. Thus the needed amount of Ir is brought down to Earth as a gentle rain lasting perhaps thousands of years, without major crater production. Our 3D computer simulations of the ring dynamics show accretion profiles, which are comparable to the Ir profiles at the KT boundary. In our model partially inelastic collisions occur between ring particles (Brahic, 1976, 1977) and the particles experience a slight atmospheric drag (10^-14 atm at 0.75 Earth radii). The particles are injected into randomly oriented orbits near the Earth upper atmosphere, from 0.1 to 0.75 Earth radii. The number and the density profile of the inward spiralling particles are calculated, until the distance from the Earth is small enough to assure that they are lost to the Earth surface within a few hours. The profile reflects the composition of the ring, and thereby the asteroid. In conclusion we suggest that a planetary ring formed around the Earth prior to the KT boundary event, and that the Ir enrichment at the KT boundary layer is formed by a slow accretion from a planetary ring rather than from a giant impact. This explains the gradual rise in Ir content prior to the peak event at the boundary layer (Hansen et al. 1988) and the gradual decrease in Ir content found in the sediments after the peak event. References Brahic A. (1976) J. of Computational Physics 22, 171-188. Brahic, A. (1977) Astr. Astrophys. 54, 895-907. Hansen, H.J., Gwozdz, R., and Rasmussen, K.L. (1988). Revista Espanola Paleontologia. extra vol., 21-29. Hansen, H.J. (1990) Geological Soc. Am. Spec. Pap. 247, 417-423. Figure 1, which in the hard copy appears here, shows the atmospheric drag on ring particles.

  1. Interface mechanics of adhesiveless microtransfer printing processes H.-J. Kim-Lee, A. Carlson, D. S. Grierson, J. A. Rogers, and K. T. Turner

    E-print Network

    Rogers, John A.

    electronics, advanced packaging schemes, and complex 3D microstructures that cannot be realizedInterface mechanics of adhesiveless microtransfer printing processes H.-J. Kim-Lee, A. Carlson, D microtransfer printing processes H.-J. Kim-Lee,1,a) A. Carlson,2 D. S. Grierson,1,b) J. A. Rogers,2 and K. T

  2. The Muon Collider/Neutrino Factory Target System H.G. Kirk (BNL) and K.T. McDonald (Princeton U.)

    E-print Network

    McDonald, Kirk

    /Jet Angle 27 mrad Capture Solenoid (SC-1) Field Strength 20 T This target concept has been validated by RThe Muon Collider/Neutrino Factory Target System H.G. Kirk (BNL) and K.T. McDonald (Princeton U.) (Aug. 14, 2010) Abstract We outline a program of engineering design and simulation for a target station

  3. Integrated High Power Electro-Optic Lens/Scanner for Spaced-Based K. T. Gahagan', j. L. Casson', v. Gopalanb, D. A. Scrymgeour'', and J. M. Robinson"

    E-print Network

    Gopalan, Venkatraman

    light into or out of channel waveguide or fiber optic systems. We will discuss the expected performance applications is the modulation, deflection, and focusing of laser light. Integrated electro-optic devicesIntegrated High Power Electro-Optic Lens/Scanner for Spaced-Based Platforms K. T. Gahagan', j. L

  4. Design and construction of a novel quad tilt-wing UAV E. Cetinsoy, S. Dikyar, C. Hancer, K.T. Oner, E. Sirimoglu, M. Unel

    E-print Network

    Ã?nel, Mustafa

    Design and construction of a novel quad tilt-wing UAV E. Cetinsoy, S. Dikyar, C. Hancer, K.T. Oner 12 March 2012 Available online xxxx Keywords: UAV Quad tilt-wing Aerodynamic design Carbon composite VehIcle). SUAVI is an electric powered quad tilt-wing UAV that is capable of vertical takeoff

  5. investigate boundaries?

    E-print Network

    ; Paradigm ffl Time­averaged motion statistics identical throughout ex­ periment. ffl Difference between to motion­defined form (this study , Lamme et al 1994, Marcar and Cowey 1992) Feedback from MT ontoPURPOSE To investigate the processing of motion boundaries in the hu­ man occipital lobe using

  6. Cenozoic bolide impacts and biotic change in North American mammals.

    PubMed

    Alroy, John

    2003-01-01

    North American mammals experienced a major mass extinction at the Cretaceous/Tertiary (K/T) boundary that is tied unambiguously to the Chicxulub impact event. Immediately afterwards, there was an immense adaptive radiation that greatly expanded taxonomic diversity and the range of body sizes and ecological strategies. However, ties between later, Cenozoic impact events and specific episodes in mammalian evolution cannot be demonstrated. A time series of maximum known crater sizes within 1.0-million-year-long temporal bins is shown not to cross-correlate with five separate measures of taxonomic turnover rate, one measure of change in relative taxonomic composition, and four measures of change in body mass distributions. The lack of correlation persists even after excluding the volatile Paleocene mammalian data, adding dummy data to represent intervals without known craters, or lagging the time series against each other for up to 5 million years. Furthermore, the data fail to support broad-brush correspondences between ages of major (>20 km in diameter) craters and the timing of five key, post-K/T biotic transitions, including medium-sized extinction episodes during the late Paleocene and latest Miocene. The results challenge the idea that extraterrestrial impacts drive all, most, or even many extinction and radiation episodes in terrestrial organisms, and add to other evidence that natural, long-term biotic changes are often independent of changes in the physical environment. PMID:12804369

  7. Boundary inflation

    SciTech Connect

    Lukas, Andre [Department of Physics, Theoretical Physics, University of Oxford, 1 Keble Road, Oxford OX1 3NP, (United Kingdom)] [Department of Physics, Theoretical Physics, University of Oxford, 1 Keble Road, Oxford OX1 3NP, (United Kingdom); Ovrut, Burt A. [Department of Physics, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6396 (United States)] [Department of Physics, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6396 (United States); Waldram, Daniel [Department of Physics, Joseph Henry Laboratories, Princeton University, Princeton, New Jersey 08544 (United States)] [Department of Physics, Joseph Henry Laboratories, Princeton University, Princeton, New Jersey 08544 (United States)

    2000-01-15

    Inflationary solutions are constructed in a specific five-dimensional model with boundaries motivated by heterotic M theory. We concentrate on the case where the vacuum energy is provided by potentials on those boundaries. It is pointed out that the presence of such potentials necessarily excites bulk fields. We distinguish a linear and a non-linear regime for those modes. In the linear regime, inflation can be discussed in an effective four-dimensional theory in the conventional way. This effective action is derived by integrating out the bulk modes. Therefore, these modes do not give rise to excited Kaluza-Klein modes from a four-dimensional perspective. We lift a four-dimensional inflating solution up to five dimensions where it represents an inflating domain wall pair. This shows explicitly the inhomogeneity in the fifth dimension. We also demonstrate the existence of inflating solutions with unconventional properties in the non-linear regime. Specifically, we find solutions with and without an horizon between the two boundaries. These solutions have certain problems associated with the stability of the additional dimension and the persistence of initial excitations of the Kaluza-Klein modes. (c) 1999 The American Physical Society.

  8. 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 bound

  9. letters to nature 290 NATURE |VOL 411 |17 MAY 2001 |www.nature.com

    E-print Network

    Massachusetts at Amherst, University of

    Cretaceous. Geology 29, 159±162 (2001). 23. Arens, N. C. & Jahren, A. H. Carbon isotope excursion in atmospheric CO2 at the Cretaceous-Tertiary boundary: evidence from terrestrial sediments. Palaios 15, 314 in the present climate4 . Here we present a high-resolution record of oxygen isotope variations, for the period

  10. Environmental perturbations caused by the impacts of asteroids andcomets

    Microsoft Academic Search

    Owen B. Toon; Kevin Zahnle; David Morrison; Richard P. Turco; Curt Covey

    1997-01-01

    We review the major impact-associated mechanisms proposed to cause extinctions at the Cretaceous-Tertiary geological boundary. We then discuss how the proposed extinction mechanisms may relate to the environmental consequences of asteroid and comet impacts in general. Our chief goal is to provide relatively simple prescriptions for evaluating the importance of impacting objects over a range of energies and compositions, but

  11. 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.

  12. Environmental perturbations caused by the impacts of asteroids and comets

    Microsoft Academic Search

    Owen B. Toon; Kevin Zahnle; David Morrison; Richard P. Turco; Curt Covey

    1997-01-01

    We review the major impact-associated mechanisms proposed to cause extinctions at the Cretaceous-Tertiary geological boundary. We then discuss how the proposed extinction mechanisms may relate to the environmental consequences of asteroid and comet impacts in general. Our chief goal is to provide relatively simple prescriptions for evaluating the importance of impacting objects over a range of energies and compositions, but

  13. Microtektites, microkrystites, and spinels from a late Pliocene asteroid impact in the southern ocean

    Microsoft Academic Search

    S. V. Margolis; P. Claeys; F. T. Kyte

    1991-01-01

    The properties of glassy spherules found in sedimentary deposits of a late Pliocene asteroid impact into the southeast Pacific are similar to those of both microtektites and microkrystites. These spherules probably formed from molten silicate droplets that condensed from an impact-generated vapor cloud. The spherules contain inclusions of magnesioferrite spinels similar to those in spherules found at the Cretaceous-Tertiary boundary,

  14. 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.

  15. Evidence for a Large Bolide Impact in the Proto-Pacific Ocean Preceding the Chicxulub Impact by About 2 Million Years

    Microsoft Academic Search

    J. T. Hagstrum; D. Abbott

    2002-01-01

    Although the Cretaceous-Tertiary (K-T) transition is generally accepted as having been caused by a single large asteroid impact at ~65 Ma near Chicxulub on the Yucatán Peninsula, a `comet shower' or multiple-impact hypothesis has also been proposed to explain multiple extinction pulses in latest Cretaceous time. The contributory effects of contemporaneous Deccan volcanism and rapid sea level changes also remain

  16. MS Exam Solution: ECE265 (Spring 2014) 3 pts for noise power in kT, 2 pts for final answer

    E-print Network

    California at San Diego, University of

    MS Exam Solution: ECE265 (Spring 2014) a. 3 pts for noise power in kT, 2 pts for final answer b. 3 pts for the SFDR, 2 pts for final answer c. 4 pts for noise factor cascade, 2 pts for final answer d. or 3 dBm 4 pts for the IIP3 cascade of power, 1pts for each term of IIP3 term , 2 pts for final answer

  17. THE MERIT HIGHPOWER TARGET EXPERIMENT AT THE CERN PS K.T. McDonald, # Princeton University, Princeton, NJ 08544, U.S.A.

    E-print Network

    McDonald, Kirk

    , Princeton, NJ 08544, U.S.A. H.G. Kirk, H. Park, T. Tsang, BNL, Upton, NY 11973, U.S.A. I. Efthymiopoulos, A 37831, U.S.A. P.H. Titus, Princeton Plasma Physics Laboratory, Princeton, NJ 08543, U.S.A. JTHE MERIT HIGH­POWER TARGET EXPERIMENT AT THE CERN PS K.T. McDonald, # Princeton University

  18. Critical evaluation of K-epsilon and K-T turbulence models in two-dimensional flow over a backward-facing step

    Microsoft Academic Search

    Kenichi Ichinose; Hiroshi Tokunaga; Nobuyuki Satofuka

    1993-01-01

    The capability of two-equation K-epsilon and K-T models to predict separated flows is investigated from the computational standpoint. The flow over a backward-facing step is chosen as a test problem. A method of lines approach is adopted as a numerical method. The spatial derivatives are discretized by the second order central and upwind difference approximations. As a time integration scheme

  19. 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.

  20. 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.

  1. Time-like pion electromagnetic form factors in $k_{T}$ factorization with the Next-to-leading-order twist-3 contribution

    E-print Network

    Shan Cheng; Zhen-Jun Xiao

    2015-05-12

    We calculate the time-like pion electromagnetic form factor in the $k_T$ factorization formalism with the inclusion of the next-to-leading-order(NLO) corrections to the leading-twist and sub-leading-twist contributions. It's found that the total NLO correction can enhance (reduce) the magnitude (strong phase) of the leading order form factor by $20\\% - 30\\%$ ( $ 5$ GeV$^2$, and the NLO twist-3 correction play the key role to narrow the gap between the pQCD predictions and the measured values for the time-like pion electromagnetic form factor.

  2. 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.

  3. Next-to-leading order vs. quark off-shellness and intrinsic k_T in the Drell-Yan process

    E-print Network

    O. Linnyk; S. Leupold; U. Mosel

    2006-11-20

    We calculate the effects of next-to-leading order perturbative QCD as well as of the quark transverse motion and off-shellness on the Drell-Yan process cross section. By studying the s->infinity behaviour of the cross section in these approaches, we find that the effects of quark off-shellness and intrinsic-k_T parametrize those of higher twists. In particular, the off-shellness of partons generates part of the K-factor type corrections to the leading order cross section. Higher twist contributions to the p_T-spectrum of the Drell-Yan pairs are found to be large for presently accessible energies. The evolution of quark off-shellness distribution with the hard scale is also studied.

  4. Grain Boundary Diffusion in Copper Nanocrystals under Tensile Stress

    NASA Astrophysics Data System (ADS)

    Crosby, Kevin

    2003-03-01

    Recent experiments on the microstructure of copper thin films suggest that the ? 3 twin grain boundary accounts for roughly 42% of all high angle boundaries. As grain boundaries provide high-mobility paths for mass-transport, diffusion near grain boundaries is a significant obstacle in integrated circuit technologies. Typically, in ultra-large scale integrated circuit (ULSIC) technologies, copper interconnects are under large tensile stresses (hundreds of MPa) due to thermal mismatch with an underlying substrate or overlying passivation layer. Using embedded atom potentials, I have examined diffusion near the ? 3 <111> twin boundary for a range of applied strains. The effective, strain-dependent activation enthalpy for diffusion is computed and compared with a generalized Fick-type relation for diffusivity due to vacancy migration in elastic media under tensile strain. The analytic model predicts an exponential dependence of diffusivity on strain of the form D(?)=D(0)(1+?)^2 e^??/kT, where ? is the tensile strain component, D(0) is the usual Arrhenius diffusivity, and ? is proportional to the vacancy formation energy.

  5. 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

  6. 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

  7. Behavior of carbonate shelf communities in the Upper Triassic of Nevada: Evidence of impact mediated faunal turnover

    SciTech Connect

    Hogler, J.A. (Univ. of California, Berkeley, CA (United States). 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.

  8. Evolution of Modern Birds Revealed by Mitogenomics: Timing the Radiation and Origin of Major Orders

    PubMed Central

    Pacheco, M. Andreína; 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

  9. 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

  10. 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...

  11. Integrated stratigraphy from the Vallcebre Basin (southeastern Pyrenees, Spain): New insights on the continental Cretaceous?Tertiary transition in southwest Europe

    Microsoft Academic Search

    O. Oms; J. Dinarès-Turell; E. Vicens; R. Estrada; B. Vila; À. Galobart; A. M. Bravo

    2007-01-01

    An integrated sedimentological, magnetostratigraphic, and paleontological study of the Vallcebre section (south eastern Pyrenees, Spain) is carried out in order to define and portray the transition from the Cretaceous to the Tertiary in a continental setting. A robust magnetostratigraphy is correlated to the standard polarity scale in light of known biochronological constraints (charophyte, marine invertebrates, eggshells and other dinosaur remains).

  12. Multiple volcanic episodes of flood basalts caused by thermochemical mantle plumes

    Microsoft Academic Search

    Shu-Chuan Lin; Peter E. van Keken

    2005-01-01

    The hypothesis that a single mushroom-like mantle plume head can generate a large igneous province within a few million years has been widely accepted. The Siberian Traps at the Permian-Triassic boundary and the Deccan Traps at the Cretaceous-Tertiary boundary were probably erupted within one million years. These large eruptions have been linked to mass extinctions. But recent geochronological data reveal

  13. 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.

  14. On boundary superalgebras

    SciTech Connect

    Doikou, Anastasia [Department of Engineering Sciences, University of Patras, GR-26500 Patras (Greece)

    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.

  15. Domain boundary engineering

    Microsoft Academic Search

    Ekhard Salje; Huali Zhang

    2009-01-01

    We review the idea that domain boundaries, rather than domains, can carry information and act as memory devices. Domains are bulk objects; their large response to changing external fields is related to their change in volume, which implies the movement of domain boundaries. In many cases, the design of ‘optimal’ domain structures corresponds to ‘optimal’ domain boundaries with parameters such

  16. 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.

  17. NATIONAL PARK BOUNDARIES

    EPA Science Inventory

    The National Park Service has produced a data base of boundaries for its National Parks. A copy of this data was downloaded from the National Parks Service ftp site by Region 10. These digital boundaries represent the best guess and data that could be collected in a short time....

  18. Chemostratigraphic Evidence of Deccan Volcanism from the Marine Osmium Isotope Record

    Microsoft Academic Search

    G. Ravizza; B. Peucker-Ehrenbrink

    2003-01-01

    Continental flood basalt (CFB) volcanism is hypothesized to have played a causative role in global climate change and mass extinctions. Uncertainties associated with radiometric dating preclude a clear chronological assessment of the environmental consequences of CFB volcanism. Our results document a 25% decline in the marine 187Os\\/188Os record that predates the Cretaceous-Tertiary boundary (KTB) and coincides with late Maastrichtian warming.

  19. Untangling the Palaeocene climatic rhythm: an astronomically calibrated Early Palaeocene magnetostratigraphy and biostratigraphy at Zumaia (Basque basin, northern Spain)

    Microsoft Academic Search

    Jaume Dinarès-Turell; Juan Ignacio Baceta; Victoriano Pujalte; Xabier Orue-Etxebarria; Gilen Bernaola; Stefano Lorito

    2003-01-01

    The magnetostratigraphy of a 54-m-long section above the Cretaceous–Tertiary boundary at the sea-cliff section of Zumaia in the Basque basin (northern Spain) has been established. The section encompasses the entire Danian and the lower part of the Selandian stages as indicated by calcareous plankton biostratigraphy. The studied interval consists of (hemi)pelagic limestone–marl alternations in the form of couplets and bundles,

  20. Survival of the Fittest?

    NSDL National Science Digital Library

    In this lesson plan students will investigate the evidence from modern and prehistoric crocodilians like SuperCroc (Sarcosuchus imperator) to determine the causes of survival and mass extinction at the Cretaceous/Tertiary boundary about 65 million years ago. Students will research and take notes on questions about modern and prehistoric crocodilians, and write papers providing their opinions of why crocodilians have survived so long, including evidence from their research.

  1. Possible Climatic Perturbations Produced by Impacting Asteroids and Comets

    Microsoft Academic Search

    D. A. Kring; H. J. Melosh; D. M. Hunten

    1995-01-01

    Studies of the Chicxulub impact event suggest that large volumes of evaporites and carbonates in the target may have been vaporized, enhancing concentrations of S-rich aerosols and CO2 in the atmosphere, which may have, in turn, been partly responsible for the mass extinction that occurred at the Cretaceous-Tertiary boundary. We note that in this and other impact events the projectile

  2. Le Crétacé-Paléogène du Blake Nose (marge atlantique de la Floride, campagne ODP 171 B): un enregistrement exemplaire de la transition Maastrichtien-Danien

    Microsoft Academic Search

    Jean-Pierre Bellier; Sandra Marca; Richard D. Norris; Dick Kroon; Adam Klaus; Ian T. Alexander; Léon Paul Bardot; Charles E. Barker; Charles D. Blome; Leon J. Clarke; Jochen Erbacher; Kristina L. Faul; Mary Anne Holmes; Brian T. Huber; Miriam E. Kate; Kenneth G. MacLeod; Francisca C. Martinez-Ruiz; Isao Mita; Mutsumi Nakai; James G. Ogg; Dorothy K. Pak; Thomas K. Pletsch; Jean M. Self-Trail; Nicholas J. Shackleton; Jan Smit; William Ussler; David K. Watkins; Joen Widmark; Paul A. Wilson

    1997-01-01

    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

  3. Meteoric smoke fallout over the Holocene epoch revealed by iridium and platinum in Greenland ice

    Microsoft Academic Search

    Paolo Gabrielli; Carlo Barbante; John M. C. Plane; Anita Varga; Sungmin Hong; Giulio Cozzi; Vania Gaspari; Frédéric A. M. Planchon; Warren Cairns; Christophe Ferrari; Paul Crutzen; Paolo Cescon; Claude F. Boutron

    2004-01-01

    An iridium anomaly at the Cretaceous\\/Tertiary boundary layer has been attributed to an extraterrestrial body that struck the Earth some 65million years ago. It has been suggested that, during this event, the carrier of iridium was probably a micrometre-sized silicate-enclosed aggregate or the nanophase material of the vaporized impactor. But the fate of platinum-group elements (such as iridium) that regularly

  4. The Blake Nose Cretaceous-Paleogene (Florida Atlantic margin, ODP Leg 171B): an exemplar record of the Maastrichtian-Danian transition

    USGS Publications Warehouse

    Bellier, J.-P.; Marca, S.; Norris, R.D.; Kroon, D.; Klaus, A.; Alexander, I.T.; Bardot, L.P.; Barker, C.E.; Blome, C.D.; Clarke, L.J.; Erbacher, J.; Faul, K.L.; Holmes, M.A.; Huber, B.T.; Katz, M.E.; MacLeod, K.G.; Martinez-Ruiz, F. C.; Mita, I.; Nakai, M.; Ogg, J.G.; Pak, D.K.; Pletsch, T.K.; Self-Trail J.M.; Shackleton, N.J.; Smit, J.; Ussler, W., III; Watkins, D.K.; Widmark, J.; Wilson, P.A.

    1997-01-01

    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.

  5. Physicochemical conditions of sedimentation of the Fish Clay from Stevns Klint, Denmark, and its detrital nature: Vanadium and other supportive evidence

    NASA Astrophysics Data System (ADS)

    Premovi?, Pavle I.; Pavlovi?, Nebojša Z.; Pavlovi?, Mirjana S.; Nikoli?, Nikola D.

    1993-04-01

    Cretaceous-Tertiary (K/T) boundary samples of the Fish Clay in Denmark from three sites (Stevns Klint, Nye Kløv and Dania) have been analyzed mineralogically and chemically. All samples contain major amounts of biogenic calcite and smectite. In some samples, minor amounts of authigenic pyrite and siderite (Stevns Klint), and lepidocrocite (Dania) are also present. To obtain an indication of the chemical nature of the V present in the Danish boundaries, the samples were analysed for V and vanadyl (VO 2+) at various stages of selective leaching. The results obtained indicate that the bulk of V is associated with the smectite fractions (?47% of total V); all VO 2+ resides in the smectite portions. From the chemistry of VO 2+, pyrite and carbonates, it is deduced that the oxidation potential and pH of the interstitial seawater of the Stevns Klint boundary was approximately 0.0 to -0.2 V and 6 to 7, respectively, during the accumulation of the lower black basal part, but rose during the accumulation of the upper grey part. The geochemical data do support the hypothesis that the Danish boundary smectite represents weathered clay (along with some asteroid and local material) that was redeposited to the Danish boundary sites after the K/T event. Substantial proportions of the VO 2+ contents of the Nye Kløv and Dania smectite were probably already contained in the detrital clay arriving at the site of boundary sedimentation, but at the Stevns Klint site they have been significantly augmented by uptake from the interfacial and interstitial seawaters through the humic substances involvement. Abundances and major mineralogical residences have been determined for trace metals: Cr, Ni, Co and Ga; and minor Fe. Much of these elements is located in the boundary smectite structure as the corresponding ionic forms (CrOH 2+, Ni 2+, Co 2+, Ga 3+ and Fe 3+) and is strictly detrital in character, i.e., having been transported to the Danish boundary sites already contained in smectite. All these metals in the Danish boundary smectite are well above normal abundances in clays.

  6. Palaeocene oceans and climate: An isotopic perspective

    NASA Astrophysics Data System (ADS)

    Corfield, R. M.

    1994-12-01

    The early Cenozoic was a time of climatic and oceanographic transition from the Cretaceous "Greenhouse" world to the "Icehouse" world of the Neogene. ? 18O measurements shed light on ocean temperature and possible polar ice fluctuations during this interval, while ? 13C measurements monitor fluctuations in ocean productivity, deep water circulation and atmospheric CO 2. The major features from ? 18O analysis of the early Cenozoic are general cooling of surface waters, with some evidence for transient cooling across the K/T boundary. Surface water temperatures were at a Cenozoic maximum in the early Eocene, whereas deep waters cooled then warmed during the Palaeocene. The ? 13C of bulk carbonates is at a minimum at the start of the Cenozoic due to the profound crisis in ocean surface water productivity associated with the extinctions of marine plankton at the Cretaceous/Tertiary boundary, thereafter ? 13C values increase (in bulk carbonates, as well as planktonic and benthonic foraminifera) to their Cenozoic maximum in the late Palaeocene (c. 60 Ma), after which time they again decrease over an interval of c. 4.5 m.y. to a Cenozoic low in the early Eocene. The increase in ? 13C values characteristic of the Palaeocene period is probably related to a combination of increasing surface water productivity and accelerated burial of organic carbon, conversely the decline in ? 13C into the early Eocene is probably related to a decrease in ocean productivity and a deceleration in the rate of organic carbon burial. Benthic ? 13C comparisons suggest that deep waters appear to have been predominantly formed in the high southern latitudes with the exception of a short lived interval near the Palaeocene/ Eocene boundary possibly associated with a transient climatic anomaly (The "Late Palaeocene Thermal Maximum"). The thermal change of Palaeocene deep waters may be related to the changing productivity of surface waters by controlling atmospheric CO 2 flux in a similar way to that proposed for the control of the Pleistocene glacial cycles.

  7. Discovering Plate Boundaries

    NSDL National Science Digital Library

    Alison Henning

    Students are initially assigned to one of four maps of the world: Seismology, Volcanology, Geochronology or Topography. They are also given a map of the world's plate boundaries and are asked to classify the boundaries based upon the data from their assigned map. Students are then assigned to a tectonic plate, such that each plate group contains at least one "expert" on each map. As a group, they must classify their plate's boundaries using data from all four maps. Recent volcanic and seismic events are discussed in the plate tectonic context. Has minimal/no quantitative component Uses geophysics to solve problems in other fields

  8. Measurement of the inclusive jet cross section using the kT algorithm in pp¯ collisions at s=1.96TeV with the CDF II detector

    Microsoft Academic Search

    A. Abulencia; J. Adelman; T. Affolder; T. Akimoto; M. G. Albrow; D. Ambrose; S. Amerio; D. Amidei; A. Anastassov; K. Anikeev; A. Annovi; J. Antos; M. Aoki; G. Apollinari; J.-F. Arguin; T. Arisawa; A. Artikov; W. Ashmanskas; A. Attal; F. Azfar; P. Azzi-Bacchetta; P. Azzurri; N. Bacchetta; W. Badgett; A. Barbaro-Galtieri; V. E. Barnes; B. A. Barnett; S. Baroiant; V. Bartsch; G. Bauer; F. Bedeschi; S. Behari; S. Belforte; G. Bellettini; J. Bellinger; A. Belloni; D. Benjamin; A. Beretvas; J. Beringer; T. Berry; A. Bhatti; M. Binkley; D. Bisello; R. E. Blair; C. Blocker; B. Blumenfeld; A. Bocci; A. Bodek; V. Boisvert; G. Bolla; A. Bolshov; D. Bortoletto; J. Boudreau; A. Boveia; B. Brau; L. Brigliadori; C. Bromberg; E. Brubaker; J. Budagov; H. S. Budd; S. Budd; S. Budroni; K. Burkett; G. Busetto; P. Bussey; K. L. Byrum; S. Cabrera; M. Campanelli; M. Campbell; F. Canelli; A. Canepa; S. Carillo; D. Carlsmith; R. Carosi; S. Carron; M. Casarsa; A. Castro; P. Catastini; D. Cauz; M. Cavalli-Sforza; A. Cerri; L. Cerrito; S. H. Chang; Y. C. Chen; M. Chertok; G. Chiarelli; G. Chlachidze; F. Chlebana; I. Cho; K. Cho; D. Chokheli; J. P. Chou; G. Choudalakis; S. H. Chuang; K. Chung; W. H. Chung; Y. S. Chung; M. Ciljak; C. I. Ciobanu; M. A. Ciocci; A. Clark; D. Clark; M. Coca; G. Compostella; M. E. Convery; J. Conway; B. Cooper; K. Copic; M. Cordelli; G. Cortiana; F. Crescioli; C. Cuenca Almenar; J. Cuevas; R. Culbertson; J. C. Cully; D. Cyr; S. Daronco; M. Datta; S. D'Auria; T. Davies; M. D'Onofrio; D. Dagenhart; P. de Barbaro; S. de Cecco; A. Deisher; G. de Lentdecker; M. Dell'Orso; F. Delli Paoli; L. Demortier; J. Deng; M. Deninno; D. de Pedis; P. F. Derwent; G. P. di Giovanni; C. Dionisi; B. di Ruzza; J. R. Dittmann; P. Dituro; C. Dörr; S. Donati; M. Donega; P. Dong; J. Donini; T. Dorigo; S. Dube; J. Efron; R. Erbacher; D. Errede; S. Errede; R. Eusebi; H. C. Fang; S. Farrington; I. Fedorko; W. T. Fedorko; R. G. Feild; M. Feindt; J. P. Fernandez; R. Field; G. Flanagan; A. Foland; S. Forrester; G. W. Foster; M. Franklin; J. C. Freeman; I. Furic; M. Gallinaro; J. Galyardt; J. E. Garcia; F. Garberson; A. F. Garfinkel; C. Gay; H. Gerberich; D. Gerdes; S. Giagu; P. Giannetti; A. Gibson; K. Gibson; J. L. Gimmell; C. Ginsburg; N. Giokaris; M. Giordani; P. Giromini; M. Giunta; G. Giurgiu; V. Glagolev; D. Glenzinski; M. Gold; N. Goldschmidt; J. Goldstein; A. Golossanov; G. Gomez; G. Gomez-Ceballos; M. Goncharov; O. González; I. Gorelov; A. T. Goshaw; K. Goulianos; A. Gresele; M. Griffiths; S. Grinstein; C. Grosso-Pilcher; U. Grundler; J. Guimaraes da Costa; Z. Gunay-Unalan; C. Haber; K. Hahn; S. R. Hahn; E. Halkiadakis; B.-Y. Han; J. Y. Han; R. Handler; F. Happacher; K. Hara; M. Hare; S. Harper; R. F. Harr; R. M. Harris; M. Hartz; K. Hatakeyama; J. Hauser; A. Heijboer; B. Heinemann; J. Heinrich; C. Henderson; M. Herndon; J. Heuser; D. Hidas; C. S. Hill; D. Hirschbuehl; A. Hocker; A. Holloway; S. Hou; M. Houlden; S.-C. Hsu; B. T. Huffman; R. E. Hughes; U. Husemann; J. Huston; J. Incandela; G. Introzzi; M. Iori; Y. Ishizawa; A. Ivanov; B. Iyutin; E. James; D. Jang; B. Jayatilaka; D. Jeans; H. Jensen; E. J. Jeon; S. Jindariani; M. Jones; K. K. Joo; S. Y. Jun; J. E. Jung; T. R. Junk; T. Kamon; P. E. Karchin; Y. Kato; Y. Kemp; R. Kephart; U. Kerzel; V. Khotilovich; B. Kilminster; D. H. Kim; H. S. Kim; J. E. Kim; M. J. Kim; S. B. Kim; S. H. Kim; Y. K. Kim; N. Kimura; L. Kirsch; S. Klimenko; M. Klute; B. Knuteson; B. R. Ko; K. Kondo; D. J. Kong; J. Konigsberg; A. Korytov; A. V. Kotwal; A. Kovalev; A. C. Kraan; J. Kraus; I. Kravchenko; M. Kreps; J. Kroll; N. Krumnack; M. Kruse; V. Krutelyov; T. Kubo; S. E. Kuhlmann; T. Kuhr; Y. Kusakabe; S. Kwang; A. T. Laasanen; S. Lai; S. Lami; S. Lammel; M. Lancaster; R. L. Lander; K. Lannon; A. Lath; G. Latino; I. Lazzizzera; T. Lecompte; J. Lee; Y. J. Lee; S. W. Lee; R. Lefèvre; N. Leonardo; S. Leone; S. Levy; J. D. Lewis; C. Lin; M. Lindgren; E. Lipeles; A. Lister; D. O. Litvintsev; T. Liu; N. S. Lockyer; A. Loginov; M. Loreti; P. Loverre; R.-S. Lu; D. Lucchesi; P. Lujan; P. Lukens; G. Lungu; L. Lyons; J. Lys; R. Lysak; E. Lytken; P. Mack; D. MacQueen; R. Madrak; K. Maeshima; K. Makhoul; T. Maki; P. Maksimovic; S. Malde; G. Manca; F. Margaroli; R. Marginean; C. Marino; A. Martin; M. Martin; V. Martin; M. Martínez; T. Maruyama; P. Mastrandrea; T. Masubuchi; H. Matsunaga; M. E. Mattson; R. Mazini; P. Mazzanti; K. S. McFarland; P. McIntyre; R. McNulty; A. Mehta; P. Mehtala; S. Menzemer; A. Menzione; P. Merkel; C. Mesropian; A. Messina; T. Miao; N. Miladinovic; J. Miles; R. Miller; C. Mills; M. Milnik; A. Mitra; G. Mitselmakher; A. Miyamoto; S. Moed; N. Moggi; B. Mohr; R. Moore; M. Morello; P. Movilla Fernandez; J. Mülmenstädt; A. Mukherjee; Th. Muller; R. Mumford; P. Murat; J. Nachtman; A. Nagano; J. Naganoma; I. Nakano; A. Napier; V. Necula; C. Neu; M. S. Neubauer; J. Nielsen

    2007-01-01

    We report on measurements of the inclusive jet production cross section as a function of the jet transverse momentum in pp¯ collisions at s=1.96TeV, using the kT algorithm and a data sample corresponding to 1.0fb-1 collected with the Collider Detector at Fermilab in run II. The measurements are carried out in five different jet rapidity regions with |yjet|<2.1 and transverse

  9. A k t u e l N a t u r v i d e n s k a b | 5 | 2 0 0 4 Atomfysik p CERN har

    E-print Network

    Uggerhøj, Ulrik I.

    10 A k t u e l N a t u r v i d e n s k a b | 5 | 2 0 0 4 10 Atomfysik på CERN har altid været en- svarende små eksperimenter. Til gengæld har disse små eksperi- menter det til fælles, at de for en beskeden investering har vakt stor opsigt og givet et betydeligt videnskabeligt afkast. De atom- fysiske eksperimenter

  10. Boundary degeneracy of topological order

    E-print Network

    Wen, Xiao-Gang

    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 ...

  11. Mapping Plate Tectonic Boundaries

    NSDL National Science Digital Library

    Michael Kerwin

    To prepare for this activity, students do background reading on Plate Tectonics from the course textbook. Students also participate in a lecture on the discovery and formulation of the unifying theory of plate tectonics, and the relationship between plate boundaries and geologic features such as volcanoes. Lastly, in lecture, students are introduced to a series of geologic hazards caused by certain plate tectonic interactions. The activity gives students practices at identifying plate boundaries and allows them to explore lesser known tectonically active regions.

  12. 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.

  13. 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...

  14. The Chicxulub event - sulfur-bearing minerals and lithologies

    NASA Astrophysics Data System (ADS)

    Strauss, H.; Deutsch, A.

    2003-04-01

    Evaporates form a major target lithology at the Chicxulub impact site. One of the postulated effects of the impact event at the Cretaceous/Tertiary boundary is the impact-induced dissociation of anhydrite to form sulfur-oxides and a solid residue; large isotope fractionation effects in sulfur should accompany this process. We have analyzed the sulfur isotope composition of (i) annealed anhydrite clasts in impact melt breccias of PEMEX core Yucatan-6 N 19, (ii) unshocked anhydrite from the CSDP well Yaxcopoil-1, which belong to the megabreccia below the suevite layer (YAX-1 1369, and 1376 m depth), and (iii) sulfide grains of hydrothermal origin in a finest-grained breccia, which transects a large limestone block of this megabreccia at a depth of 1369 m. Samples of groups (i) and (ii) yielded ?34S values between 18.0 and 19.8 ppm CDT (unweighted mean is 18.3 ppm, n=7), with one slightly lower value of 15.3 ppm for an anhydrite clast in Y-6 N19/Part 6. These data are in agreement with the ?34S value for the Late Cretaceous seawater (Strauss 1999). The ?34S obviously remained unchanged despite the fact that textural features indicate a severe annealing of the clasts in the impact melt. Sulfides of group (iii) show ?34S values around 41 ppm CDT (n=7), which are quite unusual values if these minerals are of non-biogenic origin. In contrast, ?34S for the yellow glass from the K/T boundary at Haiti range from 1.5 to 13.2 ppm (Chaussidon et al. 1996). Using this preliminary evidence, we conclude that only distant ejecta lithologies, and probably secondary material inside the crater, may display impact-related fractionation of sulfur isotopes. This observation is consistent with petrologic data, modeling results as well as of shock recovery and annealing experiments: anhydrite obviously is quite resistant to shock-related dissociation.

  15. Biodiversity during the Deccan volcanic eruptive episode

    NASA Astrophysics Data System (ADS)

    Khosla, A.; Sahni, A.

    2003-06-01

    This paper gives a detailed overview of biotic assemblages recovered from the Deccan trap intercalated sedimentary sequences (infra- and intertrappean beds) of peninsular India as a result of extensive research done during the last 20 years. The infra- and intertrappean beds contain remnants of Gondwanan forms such as myobatrachinae frogs, pelomedusid turtles, dinosaurs (i.e. titanosaurids and abelisaurids), and mammals. Apart from these Gondwanan elements, the infra- and intertrappean beds also contain forms of Laurasian affinity though recently doubt has been cast on such relationships. Based on previous fossil records, Laurasiatic forms were considered to be represented by a great variety of micro- and megavertebrate assemblages such as discoglossid and pelobatid frogs, anguid lizards, alligatorid crocodiles, palaeoryctid mammals, charophytes and ostracodes. The biotic assemblages show a remarkable similarity between the infra- and intertrappean beds indicating a short time period for the deposition of these Deccan volcano-sedimentary beds. The recovered biotic assemblages strongly indicate a Maastrichtian age for the initiation of Deccan volcanic activity and the sedimentary beds associated with it. The Cretaceous/Tertiary boundary as such remains to be defined in any known sections in sedimentary sequences in so far investigated localities of peninsular India. What have been identified are Maastrichtian age beds in the east-central and western Narmada river region on the basis of pollens, vertebrate assemblage and planktonic foraminiferas in infratrappean offshore sequences. A Palaeocene intertrappean bed at Lalitpur (Uttar Pradesh) that is among those lacking dinosaurian remains but having palynological assemblages similar to those from well established Palaeocene sequences, suggests the presence of Palaeocene intertrappeans, but the K/T boundary is yet to be properly defined.

  16. 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.

  17. Recycling prosodic boundaries.

    PubMed

    Hirose, Yuki

    2003-03-01

    The present study investigates the role of prosodic structure in selecting a syntactic analysis at different stages of parsing in silent reading of Japanese relative clauses. Experiments 1 and 2 (sentence-completion questionnaires) revealed an effect of the length of the sentence-initial constituent on the resolution of a clause boundary ambiguity in Japanese. Experiment 3 (fragment-reading) showed that this length manipulation is also reflected in prosodic phrasing in speech. Its influence on ambiguity resolution is attributed to "recycling" of prosodic boundaries established during the first-pass parse. This explanation is based on the implicit prosody proposals of Bader (1998) and Fodor (1998). Experiment 4 (self-paced reading) demonstrated the immediacy of the influence on ambiguity resolution on-line. Experiment 5 (self-paced reading) found support for the additional prediction that when no boundary is available to be recycled, processing the relative clause construction is more difficult. PMID:12690830

  18. Attraction, with boundaries

    NASA Astrophysics Data System (ADS)

    Chakraborty, Avik; Krishnan, Chethan

    2014-02-01

    We study the basin of attraction of static extremal black holes, in the concrete setting of the STU model. By finding a connection to a decoupled Toda-like system and solving it exactly, we find a simple way to characterize the attraction basin via competing behaviors of certain parameters. The boundaries of attraction arise in the various limits where these parameters degenerate to zero. We find that these boundaries are generalizations of the recently introduced (extremal) subtracted geometry: the warp factors still exhibit asymptotic integer power law behaviors, but the powers can be different from one. As we cross over one of these boundaries (‘generalized subttractors’), the solutions turn unstable and start blowing up at finite radius and lose their asymptotic region. Our results are fully analytic, but we also solve a simpler theory where the attraction basin is lower dimensional and easy to visualize, and present a simple picture that illustrates many of the basic ideas.

  19. Discovering Plate Boundaries

    NSDL National Science Digital Library

    Rice University's Earth Science Department offers the Discovering Plate Boundaries educational activity. The exercise is described as a "data rich exercise to help students discover the processes that occur at plate tectonic boundaries" and has been used successfully with 5th graders to undergraduates. The site provides the necessary downloads of maps; earthquake, volcanic, seafloor, topographic, and bathymetric data; and teacher guides and complete instructions. Because the activity can be geared towards such a large range of students, is well designed, and is easily accessible, educators will definitely appreciate the site.

  20. Periodic boundary conditions

    NSDL National Science Digital Library

    Iacovella, Christopher R.

    2006-09-24

    Schematic of periodic boundary conditions. When using periodic boundary conditions, a particle which exits the system on the right, will reappear on the left. In the schematic, our simulation volume is colored in red. As the yellow particle exits on the right, it will re-enter on the left. This can be thought of as having identical simulation boxes surrounding the system. As the yellow particle enters the next simulation on the right, a particle from the periodic image on the left will enter.

  1. 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.

  2. Detection of Boundary Films.

    PubMed

    Wise, W S; Munro, R E; King, P P

    1960-12-16

    Results, obtained with a photoelectric refractometer and sucrose solutions, indicate that a concentrated surface layer rapidly builds up when sucrose solutions are allowed to stand under conditions where evaporation can occur from the surface. The phenomenon is similar to the formation of a cool boundary film which has recently been shown to occur on the surface of the ocean. PMID:17797363

  3. Flashover and boundary properties

    Microsoft Academic Search

    Alan N. Beard

    2010-01-01

    A non-linear model of flashover, FLASHOVER A1, which has been described in earlier work, has been used to explore the dependence of the critical heat release rate (Qfc) for flashover on the properties of the boundary of the enclosure. The compartment is assumed to have a single ventilation opening stretching from floor to ceiling. Specifically, the dependence of Qfc upon

  4. Bolt in bore boundaries

    NASA Technical Reports Server (NTRS)

    Butler, T. G.

    1983-01-01

    The factors that must be taken into consideration when applying NASTRAN's linear analysis to structures whose principle boundaries are formed by bolting, and for which localized stress peaking is important are discussed. An illustration is given in an application to a mounting bracket.

  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. Boundary Ambiguity in Stepfamilies

    ERIC Educational Resources Information Center

    Stewart, Susan D.

    2005-01-01

    Family boundary ambiguity refers to a lack of clarity as to who is in and who is out of the family system. Few studies have examined this concept in the stepfamily context, which is problematic because such definitional problems hinder our understanding of close relationships in stepfamilies. Based on a nationally representative sample of…

  7. Tectonic Plates and Plate Boundaries

    NSDL National Science Digital Library

    WGBH Educational Foundation

    2005-12-17

    This interactive activity adapted from NASA features world maps that identify different sections of the Earth's crust called tectonic plates. The locations of different types of plate boundaries are also identified, including convergent, divergent, and transform boundaries.

  8. 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...

  9. 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.

  10. Axisymmetric free boundary problems

    NASA Astrophysics Data System (ADS)

    Sussman, Mark; Smereka, Peter

    1997-06-01

    We present a number of three-dimensional axisymmetric free boundary problems for two immiscible fluids, such as air and water. A level set method is used where the interface is the zero level set of a continuous function while the two fluids are solutions of the incompressible Navier Stokes equation. We examine the rise and distortion of an initially spherical bubble into cap bubbles and toroidal bubbles. Steady solutions for gas bubbles rising in a liquid are computed, with favourable comparisons to experimental data. We also study the inviscid limit and compare our results with a boundary integral method. The problems of an air bubble bursting at a free surface and a liquid drop hitting a free surface are also computed.

  11. Boundary Element Method Tutorial

    NSDL National Science Digital Library

    Dwyer, Jerry

    2004-09-21

    The Boundary Element Method is a numerical scheme for solving partial differential equations. In this tutorial, we illustrate this method using the example of temperature distribution in a two dimensional plate. The tutorial was developed by Professor Jerry Dwyer and Kathy Hichcock of the Mathematics Departments of the University of Tennessee and Leonard Gray of the Mathematical Sciences Section of Oak Ridge National Laboratory . The zip file contains a word file.

  12. 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.

  13. Boundary layers in centrifugal compressors

    Microsoft Academic Search

    R. C. Dean Jr.

    1974-01-01

    The utility of boundary-layer theory in the design of centrifugal compressors is demonstrated. Boundary-layer development in the diffuser entry region is shown to be important to stage efficiency. The result of an earnest attempt to analyze this boundary layer with the best tools available is displayed. Acceptable prediction accuracy was not achieved. The inaccuracy of boundary-layer analysis in this case

  14. Discovering Plate Boundaries

    NSDL National Science Digital Library

    Dale Sawyer

    1997-09-15

    Discovering Plate Boundaries is based on 5 world maps containing earthquake, volcano, topography, satellite gravity, and seafloor age data. The novel aspect of the exercise is the "jigsaw" manner in which student groups access the maps and use them to discover, classify, and describe plate boundary types. The exercise is based only on observation and description, which makes it useful at a wide variety of levels; it has been used successfully in 5th grade classes, as well as in non-major earth science classes. The exercise is based on a set of wall maps that are not consumed during the exercise. Other inexpensive materials required include two 11x17 black and white copies per student and colored pencils. Because the exercise is not based on student access to the web, it is not dependent on classroom technology equipment. The exercise takes three 50-minute class periods to complete, and involves the students in making presentations to one another in small groups as well as to the whole class. The students come away from the exercise with knowledge of the key features of each type of plate boundary and a sense of why each looks and acts the way it does.

  15. Superstrings with boundary fermions

    E-print Network

    P. S. Howe; U. Lindstrom; L. Wulff

    2005-06-06

    The Green-Schwarz action for an open superstring with additional boundary fermions, representing Chan-Paton factors, is studied at the classical level. The boundary geometry is described by a bundle, with fermionic fibres, over the super worldvolume of a D-brane together with a map from the total space into the type II target superspace. This geometry is constrained by the requirement of kappa-symmetry on the boundary together with the use of the equations of motion for the fermions. There are two constraints which are formally similar to those that arise in the abelian case but which differ because of the dependence on the additional coordinates. The model, when quantised, would be a candidate for a fully kappa-symmetric theory of a stack of coincident D-branes including a non-abelian Born-Infeld sector. The example of the D9-brane in a flat background is studied. The constraints on the non-abelian field strength are shown to be in agreement with those derived from the pure spinor approach to the superstring. A covariant formalism is developed and the problem of quantisation is discussed.

  16. 2. System boundaries; Balance equations

    E-print Network

    Zevenhoven, Ron

    1/28 2. System boundaries; Balance equations Ron Zevenhoven Åbo Akademi University Thermal and flow | Finland 2/28 2.1 System boundaries Åbo Akademi University | Thermal and Flow Engineering | 20500 Turku | Finland #12;3/28 Systems and boundaries /1 Any engineering device can be denoted as a system, separated

  17. South Campus Boundary/Landscape

    E-print Network

    Brownstone, Rob

    of the Agenda 7:05 - 7:20 Principles of the South Campus Boundary/Landscape from the Feb 21 Design Charette 7 Campus Boundary/Landscape from the Feb 21 Design Charette #12;#12;#12;#12;#12;#12;#12;#12;#12;#12;Preferences From Most `Likes' to Least `Likes' Ideas from South campus Boundary/Landscape on Feb 21 Design

  18. Boundary energy and boundary states in integrable quantum field theories

    NASA Astrophysics Data System (ADS)

    LeClair, A.; Mussardo, G.; Saleur, H.; Skorik, S.

    1995-02-01

    We study the ground-state energy of integrable 1 + 1 quantum field theories with boundaries (the genuine Casimir effect). In the scalar case, this is done by introducing a new "R-channel TBA", where the boundary is represented by a boundary state, and the thermodynamics involves evaluating scalar products of boundary states with all the states of the theory. In the non-scalar, sine-Gordon case, this is done by generalizing the method of Destri and De Vega. The two approaches are compared. Miscellaneous other results are obtained, in particular formulas for the overall normalization and scalar products of boundary states, exact partition functions for the critical Ising model in a boundary magnetic field, and also results for the energy, excited states and boundary S-matrix of O( n) and minimal models.

  19. International Boundary News Database (IBRU)

    NSDL National Science Digital Library

    The International Boundaries Research Unit (IBRU) at the University of Durham maintains the International Boundary News Database, which consists of more than 10,000 documents related to international boundaries, "including their delimitation, demarcation and management." The documents, spanning from 1991 to the present, are compiled from news sources worldwide. The database may be queried through a simple keyword search or via the Boundary Field, which retrieves all records associated with an international boundary. Searches yield summarized news items, generally one paragraph in length.

  20. The Hale solar sector boundary

    NASA Technical Reports Server (NTRS)

    Svalgaard, L.; Wilcox, J. M.

    1976-01-01

    A Hale solar-sector boundary is defined as that half (northern hemisphere or southern hemisphere) of a sector boundary in which the change of sector-magnetic-field polarity is the same as the change of polarity from a preceding spot to a following spot. Above a Hale sector boundary the green corona has maximum brightness, while above a non-Hale boundary the green corona has a minimum brightness. The Hale portion of a photospheric sector boundary tends to have maximum magnetic-field strength, while the non-Hale portion has minimum field strength.

  1. 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.

  2. Boundary conditions for incompressible flows

    NASA Astrophysics Data System (ADS)

    Orszag, Steven A.; Israeli, Moshe; Deville, Michel O.

    A general framework is presented for the formulation and analysis of rigid no-slip boundary conditions for numerical schemes for the solution of the incompressible Navier-Stokes equations. It is shown that fractional-step (splitting) methods are prone to introduce a spurious numerical boundary layer that induces substantial time differencing errors. High-order extrapolation methods are analyzed to reduce these errors. Both improved pressure boundary condition and velocity boundary condition methods are developed that allow accurate implementation of rigid no-slip boundary conditions.

  3. Black holes without boundaries

    E-print Network

    Alex B. Nielsen

    2008-09-10

    We discuss some of the drawbacks of using event horizons to define black holes and suggest ways in which black holes can be described without event horizons, using trapping horizons. We show that these trapping horizons give rise to thermodynamic behavior and possibly Hawking radiation too. This raises the issue of whether the event horizon or the trapping horizon should be seen as the true boundary of a black hole. This difference is important if we believe that quantum gravity will resolve the central singularity of the black hole and clarifies several of the issues associated with black hole thermodynamics and information loss.

  4. Subduction at Convergent Boundary

    NSDL National Science Digital Library

    The representation depicts subduction. The narrated animated movie (simulation) shows subduction of the Indian Plate as the Indian Plate and the Eurasian Plate converge at the plate boundary. The segment begins showing a world view of the Earth's plates and zooms in on the highlighted Indian and Eurasian plate activity. The animation transitions to a cross-sectional view, giving an inside-the-Earth look at what happens as these plates converge. The movie can be viewed in two ways- in continuous play or step by step.

  5. 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.; Erö, J.; Fabjan, C.; Friedl, M.; Frühwirth, R.; Ghete, V. M.; Hartl, C.; Hörmann, N.; Hrubec, J.; Jeitler, M.; Kiesenhofer, W.; Knünz, V.; Krammer, M.; Krätschmer, I.; Liko, D.; Mikulec, I.; Rabady, D.; Rahbaran, B.; Rohringer, H.; Schöfbeck, 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.; Léonard, A.; Marage, P. E.; Mohammadi, A.; Perniè, 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.; Aldá Júnior, W. L.; Carvalho, W.; Chinellato, J.; Custódio, 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.; Müntel, M.; Murumaa, M.; Raidal, M.; Rebane, L.; Tiko, A.; Eerola, P.; Fedi, G.; Voutilainen, M.; Härkönen, J.; Karimäki, V.; Kinnunen, R.; Kortelainen, M. J.; Lampén, T.; Lassila-Perini, K.; Lehti, S.; Lindén, T.; Luukka, P.; Mäenpää, 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.; Miné, 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.; Gelé, 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.

  6. The Magnetopause Boundary

    NSDL National Science Digital Library

    Sten Odenwald

    In this activity students explore in a quantitative way, how the distance to the bowshock balance point depends on the solar wind pressure acting on the Earth's magnetic field. They will explore the changes using actual satellite data, by both an algebraic and a graphical process. Students will discover that as the solar wind flows past the Earth, it applies pressure to the magnetic field of the earth, sweeping it back into a comet-like shape on the nighttime side of the planet and that the brunt of the solar wind pressure is exerted on the dayside field, compressing it; only the restorative pressure of the magnetic field pushes against the solar wind, and a rough balance of these pressures occurs. Students also learn that this balance moves towards the Earth when the solar wind pressure increases, and it moves outwards toward the sun as the solar wind pressure slackens. This line is called the magnetopause boundary. During this activity students use simple algebra to calculate the distance to the boundary where the solar wind presses on Earth's magnetosphere.

  7. Chicxulub Impact Crater and Yucatan Carbonate Platform - Stratigraphy and Petrography of PEMEX Borehole Cores

    NASA Astrophysics Data System (ADS)

    Gutierrez-Cirlos, A. G.; Perez-Drago, G.; Perez-Cruz, L.; Urrutia-Fucugauchi, J.

    2008-12-01

    Chicxulub impact crater is the best preserved of the three large multi-ring structures documented in the terrestrial record. Chicxulub, formed 65 Ma ago, is associated with the Cretaceous/Tertiary (K/T) boundary layer and the impact related to the organism extinctions and events marking the boundary. The crater is buried under Tertiary sediments in the Yucatan carbonate platform in the southern Gulf of Mexico. The structure was initially recognized from gravity and magnetic anomalies in the PEMEX exploration surveys of the northwestern Yucatan peninsula. The exploration program included eight deep boreholes completed from 1952 through the 1970s. The investigations showing Chicxulub as a large complex impact crater formed at the K/T boundary have relayed on the PEMEX decades-long exploration program. However, despite frequent use of PEMEX information and core samples, significant parts of the database and cores remain to be evaluated, analyzed and incorporated with results from recent efforts. Access to PEMEX Core Repository has permitted to study the cores and collect new samples from some of the boreholes. We analyzed cores from Yucatan-6, Chicxulub-1, Sacapuc-1, Ticul-1, Yucatan-1 and Yucatan-4 boreholes to make new detailed stratigraphic correlations and petrographic characterization, using information from PEMEX database and the recent studies. In C-1 cores, breccias show 4-8 cm clasts of fine grained altered melt dispersed in a medium to coarse grained matrix composed of pyroxene and feldspar with little macroscopic alteration. Clasts contain 0.2 to 0.1 cm fragments of silicate material (basement) that show variable degrees of digestion. Melt samples from C-1 N10 comes from interval 1,393-1,394 m, and show a fine-to-medium grained coherent microcrystalline groundmass. Melt and breccias in Y-6 extend from about 1,100 m to more than 1,400 m. Sequence is well sorted, with an apparent gradation in both the lithic and melt clasts. In this presentation we report on initial results from this new joint project for the carbonate sequences and impact lithologies.

  8. Size effects in thin gold films: Discrimination between electron-surface and electron-grain boundary scattering by measuring the Hall effect at 4 K

    NASA Astrophysics Data System (ADS)

    Munoz, Raul C.; Henriquez, R.; Moraga, L.; Kremer, G.; Flores, M.; Espinosa, A.

    2014-03-01

    We report the Hall effect measured in gold films evaporated onto mica substrates, the samples having an average grain diameter D that ranges between 12 and 174 nm, and a thickness t of approximately 50 nm and 100 nm. The Hall mobility was determined at low temperatures T (4K <= T <= 50K). By tuning the grain size during sample preparation, we discriminate whether the dominant collision mechanism controlling the resistivity of the samples at 4 K is electron-surface or electron-grain boundary scattering, based upon whether the Hall mobility depends linearly on film thickness t or on grain diameter D. Funding from FONDECYT 1120198 is gratefully acknowledged.

  9. 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.

  10. Minimalist turbulent boundary layer model.

    PubMed

    Moriconi, L

    2009-04-01

    We discuss an elementary model of a turbulent boundary layer over a flat surface given as a vertical random distribution of spanwise Lamb-Oseen vortex configurations placed over a nonslip boundary-condition line. We are able to reproduce several important features of realistic flows, such as the viscous and logarithmic boundary sublayers, and the general behavior of the first statistical moments (turbulent intensity, skewness, and flatness) of the streamwise velocity fluctuations. As an application, we advance some heuristic considerations on the boundary layer underlying kinematics that could be associated with the phenomenon of drag reduction by polymers, finding a suggestive support from its experimental signatures. PMID:19518332

  11. Deriving grain boundary character distributions and relative grain boundary

    E-print Network

    Rohrer, Gregory S.

    -dimensional electron backscatter diffraction data, obtained by serial sectioning a nickel­ base superalloy, has been of the procedures. The procedures are applied to data from a Ni base superalloy with a high degree of twining and GBED are inversely correlated. Keywords: Grain boundaries, Grain boundary energy, Superalloy, EBSD

  12. Improved boundary integral method for inviscid boundary condition applications

    Microsoft Academic Search

    P. Koumoutsakos; A. Leonard

    1993-01-01

    The present computational treatment of the potential component of an unsteady, incompressible viscous flow around an arbitrary configuration, as well as the enforcement of the no-throughflow boundary condition, employs a solver to account for the convective and viscous part of the flow. This rigorous approach involves the application of the internal Neumann boundary condition, and is noted not to increase

  13. 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…

  14. Identification of grain boundary dislocations

    Microsoft Academic Search

    C. T. Forwood; P. Humble

    1975-01-01

    The simultaneous two-beam method for identifying defects in grain boundaries developed in Part I is demonstrated by using image matching to determine the Burgers vectors of GBDs introduced into coherent twin boundaries in copper by deformation at room temperature. The choice of this special twin system involves no loss of generality in the identification procedure, but provides an idealized test

  15. Boundary elements and nuclear organization

    Microsoft Academic Search

    Maya Capelson; Victor G. Corces

    2004-01-01

    Functional compartmentalization of eukaryotic genomes is thought to be necessary for the proper regulation of gene expression. Chromatin insulators or boundary elements have been implicated in the establishment of this compartmentalization, as they may be involved in creating independent chromatin domains. Recent advances in understanding the mechanisms of insulator function suggest a role for boundary elements in determining transcriptional identity

  16. 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.

  17. 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.

  18. Brain response to prosodic boundary cues depends on boundary position

    PubMed Central

    Holzgrefe, Julia; Wellmann, Caroline; Petrone, Caterina; Truckenbrodt, Hubert; Höhle, Barbara; Wartenburger, Isabell

    2013-01-01

    Prosodic information is crucial for spoken language comprehension and especially for syntactic parsing, because prosodic cues guide the hearer's syntactic analysis. The time course and mechanisms of this interplay of prosody and syntax are not yet well-understood. In particular, there is an ongoing debate whether local prosodic cues are taken into account automatically or whether they are processed in relation to the global prosodic context in which they appear. The present study explores whether the perception of a prosodic boundary is affected by its position within an utterance. In an event-related potential (ERP) study we tested if the brain response evoked by the prosodic boundary differs when the boundary occurs early in a list of three names connected by conjunctions (i.e., after the first name) as compared to later in the utterance (i.e., after the second name). A closure positive shift (CPS)—marking the processing of a prosodic phrase boundary—was elicited for stimuli with a late boundary, but not for stimuli with an early boundary. This result is further evidence for an immediate integration of prosodic information into the parsing of an utterance. In addition, it shows that the processing of prosodic boundary cues depends on the previously processed information from the preceding prosodic context. PMID:23882234

  19. Brain response to prosodic boundary cues depends on boundary position.

    PubMed

    Holzgrefe, Julia; Wellmann, Caroline; Petrone, Caterina; Truckenbrodt, Hubert; Höhle, Barbara; Wartenburger, Isabell

    2013-01-01

    Prosodic information is crucial for spoken language comprehension and especially for syntactic parsing, because prosodic cues guide the hearer's syntactic analysis. The time course and mechanisms of this interplay of prosody and syntax are not yet well-understood. In particular, there is an ongoing debate whether local prosodic cues are taken into account automatically or whether they are processed in relation to the global prosodic context in which they appear. The present study explores whether the perception of a prosodic boundary is affected by its position within an utterance. In an event-related potential (ERP) study we tested if the brain response evoked by the prosodic boundary differs when the boundary occurs early in a list of three names connected by conjunctions (i.e., after the first name) as compared to later in the utterance (i.e., after the second name). A closure positive shift (CPS)-marking the processing of a prosodic phrase boundary-was elicited for stimuli with a late boundary, but not for stimuli with an early boundary. This result is further evidence for an immediate integration of prosodic information into the parsing of an utterance. In addition, it shows that the processing of prosodic boundary cues depends on the previously processed information from the preceding prosodic context. PMID:23882234

  20. Emeralds in the Eastern Cordillera of Colombia: Two tectonic settings for one mineralization

    NASA Astrophysics Data System (ADS)

    Branquet, Yannick; Laumonier, Bernard; Cheilletz, Alain; Giuliani, Gaston

    1999-07-01

    Colombian emeralds are formed through a hydrothermal-sedimentary process. On the western side of the Eastern Cordillera, the deposits are linked by tear faults and associated thrusts developed during a compressive tectonic phase that occurred at the time of the Eocene-Oligocene boundary, prior to the major uplift of the Cordillera during the Andean phase (middle Miocene). On the eastern side of the Cordillera, emerald mineralization occurred earlier, at the time of the Cretaceous-Tertiary boundary, during a thin-skinned extensional tectonic event linked to evaporite dissolution. This event predates the Andean phase, during which this part of the chain was folded and thrust over the Llanos foreland.

  1. 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.

  2. Molecular wall effects: Are conditions at a boundary ``boundary conditions''?

    Microsoft Academic Search

    Howard Brenner; Venkat Ganesan

    2000-01-01

    This paper addresses and answers ``no'' to the question of whether the literal molecular-dynamically-derived species velocities prevailing at a solid surface bounding a two-component fluid continuum undergoing molecular diffusion constitute the appropriate species-velocity boundary conditions to be imposed upon the fluid continuum. In a broader context, generic boundary condition issues arising from the presence of different length scales in continuum-mechanical

  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 stability under nonequilibrium conditions

    SciTech Connect

    Not Available

    1993-01-01

    Purpose of this work is to study microscopic, nanometer-scale behavior of interfaces under nonequilibrium conditions prevailing during service or materials processing. The need is to study grain boundary and surface/thin film instabilities under applied stress and chemical diffusion. This document is divided into: grain boundaries (stability, dislocations under applied stress, structural stability of grain boundaries during DIGM and under applied stress) and surfaces/thin films (hillock growth on microcrystalline and single crystal surfaces, plate edge instabilities, coherently strained islands). 31 refs.

  5. 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.

  6. Boundary conditions for quadrupolar metamaterials

    NASA Astrophysics Data System (ADS)

    Silveirinha, Mário G.

    2014-08-01

    One of the long-standing problems in effective medium theories is using the knowledge of the bulk material response to predict the behavior of the electromagnetic fields at the material boundaries. Here, using a first principles approach, we derive the boundary conditions satisfied by the macroscopic fields at interfaces between reciprocal metamaterials with a quadrupolar-type response. Our analysis reveals that in addition to the usual Maxwellian-type boundary conditions for the tangential fields, in general—to ensure the conservation of the power flow and Lorentz reciprocity—it is necessary to enforce an additional boundary condition (ABC) at an interface between a quadrupolar material and a standard dielectric. It is shown that the ABC is related to the emergence of an additional wave in the bulk quadrupolar medium.

  7. Academy Colloquium "Immersed Boundary Methods

    E-print Network

    Lindken, Ralph

    for Compressible Flows 16.20-16.40 Break 16.40-17.00 H. Hartmann, M. Borsboom and I. Wenneker A First Step Towards. Wenneker Implementation of Boundary Conditions on an Irregular Geometry by Extrapolation to the Staircase

  8. ConcepTest: Divergent Boundary

    NSDL National Science Digital Library

    The figures below show the location of a plate boundary (dashed line) and the distribution of earthquake foci (filled circles). The color of the filled circle indicates the depth of the earthquake focus. Given the ...

  9. 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)

  10. The plasma sheet boundary layer

    NASA Technical Reports Server (NTRS)

    Eastman, T. E.; Frank, L. A.; Peterson, W. K.; Lennartsson, W.

    1984-01-01

    A spatially distinct, temporally variable, transition region between the magnetotail lobes and the central plasma sheet designated the plasma sheet boundary layer has been identified from a survey of particle spectra and three-dimensional distributions as sampled by the ISEE 1 LEPEDEA. The instrumentation and data presentation are described, and the signatures of the magnetotail plasma regimes are presented and discussed for the central plasma sheet and lobe and the plasma sheet boundary layer. Comparisons of plasma parameters and distribution fucntions are made and the evolution of ion velocity distributions within the plasma sheet boundary layer is discussed. The spatial distribution of the plasma sheet boundary layer is considered and ion composition measurements are presented.

  11. ConcepTest: Transform Boundary

    NSDL National Science Digital Library

    A and B are located on two plates separated by a transform boundary (see diagram below). What direction is plate B moving if plate A is moving northeast (NE)? a. northeast b. northwest c. southwest d. southeast

  12. Thermal boundary condition effects on compressible turbulent boundary layers

    NASA Astrophysics Data System (ADS)

    Beekman, Izaak; Martin, Pino

    2013-11-01

    Numerous questions about the physics of compressible boundary layers, and their modeling remain open. While Morkovin's hypothesis has proven remarkably robust for zero pressure gradient, smooth wall, compressible, turbulent boundary layers, accounting correctly for thermal energy transport and its impact on the density and momentum fields remains challenging. We use spatially developing DNS data over strongly and weakly adiabatic walls at Mach 3 and Mach 7. The strongly adiabatic boundary condition further stresses common assumptions of weak direct compressibility and weak total temperature fluctuations. We observe non-trivial differences between the two cases. The simulations are performed at Re? ~ 500 on very large domains in the streamwise and spanwise directions, approximately 50 by 10?inlet , with a rescaling method providing the inflow. We examine the effects of this boundary condition on common scaling laws, temperature-velocity relations, and suggest improvements, where possible. A dimensionless parameter is proposed, the ``fluctuation Nusselt number,'' to quantify the impact of the wall material for laboratory and engineering flows and relate it to these idealized, numerical boundary conditions. Numerous questions about the physics of compressible boundary layers, and their modeling remain open. While Morkovin's hypothesis has proven remarkably robust for zero pressure gradient, smooth wall, compressible, turbulent boundary layers, accounting correctly for thermal energy transport and its impact on the density and momentum fields remains challenging. We use spatially developing DNS data over strongly and weakly adiabatic walls at Mach 3 and Mach 7. The strongly adiabatic boundary condition further stresses common assumptions of weak direct compressibility and weak total temperature fluctuations. We observe non-trivial differences between the two cases. The simulations are performed at Re? ~ 500 on very large domains in the streamwise and spanwise directions, approximately 50 by 10?inlet , with a rescaling method providing the inflow. We examine the effects of this boundary condition on common scaling laws, temperature-velocity relations, and suggest improvements, where possible. A dimensionless parameter is proposed, the ``fluctuation Nusselt number,'' to quantify the impact of the wall material for laboratory and engineering flows and relate it to these idealized, numerical boundary conditions. Supported by AFOSR grant AF/9550-10-1-0535 STW 21 - Revitalization of the hypersonics testing and evaluation workforce.

  13. Changing the Structure Boundary Geometry

    SciTech Connect

    Karasev, Viktor; Dzlieva, Elena; Ivanov, Artyom [St.-Petersburg State University, Physics Faculty, Ulianovskaya 1, Peterhof, St. Petersburg, 198504 (Russian Federation)

    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.

  14. Boundary lubrication by associative mucin.

    PubMed

    Wang, Xiang; Du, Miao; Han, Hongpeng; Song, Yihu; Zheng, Qiang

    2015-04-28

    Mucus lubricants are widely distributed in living organisms. Such lubricants consist of a gel structure constructed by associative mucin. However, limited tribological studies exist on associative mucin fluids. The present research is the first to investigate the frictional behavior of a typical intact vertebrate mucin (loach skin mucin), which can recover the gel structure of mucus via hydrophobic association under physiological conditions (5-10 mg/mL loach skin mucin dissolved in water). Both rough hydrophobic and hydrophilic polydimethylsiloxane (PDMS) rubber plates were used as friction substrates. Up to 10 mg/mL loach skin mucin dissolved in water led to a 10-fold reduction in boundary friction of the two substrates. The boundary-lubricating ability for hydrophilic PDMS decreased with rubbing time, whereas that for hydrophobic PDMS remained constant. The boundary-lubricating abilities of the mucin on hydrophobic PDMS and hydrophilic PDMS showed almost similar responses toward changing concentration or sodium dodecyl sulfate (SDS). The mucin fluids reduced boundary friction coefficients (?) only at concentrations (c) in which intermucin associations were formed, with a relationship shown as ? ? c(-0.7). Destroying intermucin associations by SDS largely impaired the boundary-lubricating ability. Results reveal for the first time that intermolecular association of intact mucin in bulk solution largely enhances boundary lubrication, whereas tightly adsorbed layer plays a minor role in the lubrication. This study indicates that associated mucin should contribute considerably to the lubricating ability of biological mucus in vivo. PMID:25843576

  15. Tidal Boundary Conditions in SEAWAT

    USGS Publications Warehouse

    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.

  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. Non-reflecting boundary conditions for waveguides

    Microsoft Academic Search

    A. Bendali; Ph. Guillaume

    1999-01-01

    New non-reflecting boundary conditions are introduced for the solution of the Helmholtz equation in a waveguide. These boundary condi- tions are perfectly transparent for all propagating modes. They do not require the determination of these propagating modes but only their propagation con- stants. A quasi-local form of these boundary conditions is well suited as termi- nating boundary condition beyond nite

  18. Sinh-Gordon Boundary TBA and Boundary Liouville Reflection Amplitude

    E-print Network

    Z. Bajnok; Chaiho Rim; Al. Zamolodchikov

    2007-12-26

    The ground state energy of the sinh-Gordon model defined on the strip is studied using the boundary thermodynamic Bethe ansatz equation. Its ultraviolet (small width of the strip) behavior is compared with the one obtained from the boundary Liouville reflection amplitude. The results are in perfect agreement in the allowable range of the parameters and provide convincing support for both approaches. We also describe how the ultraviolet limit of the effective central charge can exceed one in the parameter range when the Liouville zero mode forms a bound state.

  19. 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.

  20. 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.

  1. Boundary layer control for airships

    NASA Technical Reports Server (NTRS)

    Pake, F. A.; Pipitone, S. J.

    1975-01-01

    An investigation is summarized of the aerodynamic principle of boundary layer control for nonrigid LTA craft. The project included a wind tunnel test on a BLC body of revolution at zero angle of attack. Theoretical analysis is shown to be in excellent agreement with the test data. Methods are evolved for predicting the boundary layer development on a body of revolution and the suction pumping and propulsive power requirements. These methods are used to predict the performance characteristics of a full-scale airship. The analysis indicates that propulsive power reductions of 15 to 25 percent and endurance improvements of 20 to 40 percent may be realized in employing boundary-layer control to nonrigid airships.

  2. 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).

  3. 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.

  4. Iridium in sea-water.

    PubMed

    Fresco, J; Weiss, H V; Phillips, R B; Askeland, R A

    1985-08-01

    Iridium in sea-water has been measured (after isolation from the saline matrix by reduction with magnesium) by neutron bombardment, radiochemical purification and high-resolution gamma-ray spectroscopy. The concentration obtained in a Pacific coastal water was 1.02 +/- 0.26 x 10(-14) g per g of sea-water. At such extremely low concentrations, seawater is an extremely unlikely source for anomalously high iridium concentrations measured in the Cretaceous-Tertiary boundary layer of deep-sea sediments. PMID:18964014

  5. Boundary crises, fractal basin boundaries, and electric power collapses

    Microsoft Academic Search

    Sura H. C. Marcos; Sérgio R. Lopes; Ricardo L. Viana

    2003-01-01

    Electric power systems are frequently nonlinear and, when faced with increasing power demands, may behave in unpredictable and rather irregular ways. We investigated the nonlinear dynamics of a single machine infinite bus power system model in order to study the appearance of coexistent periodic and chaotic attractors, characterizing multi-stable behavior. The corresponding basins of attraction present fractal boundaries, for which

  6. Integrable nonlinear boundary value problems

    NASA Astrophysics Data System (ADS)

    Leon, Jérôme

    1992-11-01

    We construct an extension of the spectral transform theory that allows us to build nonlinear systems of coupled wave which are integrable for arbitrary boundary values. These problems occur in many areas of physics and model generic processes of interaction of radiation (for which boundary values are prescribed) with matter (for which an initial value is given). We treat the example of interaction of electromagnetic waves with the ion-acoustic wave in plasmas and prove the total reflexivity due to stimulated Brillouin scattering.

  7. 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.

  8. Grain boundaries in complex oxides

    SciTech Connect

    Chiang, Yet-Ming.

    1993-05-01

    A quantitative comparison was achieved between space charge theory and segregation at grain boundaries in the model system TiO[sub 2]. The ionic space charge can be titrated from negative to positive potential. A space charge model was developed that includes the lattice defect chemistry. Defect formation energies in the Frenkel pair for TiO[sub 2] were studied. Grain boundary enthalpy was measured during coarsening. It was shown that it is the barium vacancy that forms near surfaces in donor-doped BaTiO[sub 3] electroceramics during oxidative-cooling.

  9. Laminar boundary layer over riblets

    NASA Astrophysics Data System (ADS)

    Djenidi, L.; Anselmet, F.; Liandrat, J.; Fulachier, L.

    1994-09-01

    Laser doppler anemometry (LDA) measurements and numerical calculations have been made for a laminar boundary layer on triangular riblets. Calculated mean velocity distributions along the riblet contour are in good agreement with the measured ones. The results show that no transversal motion exists above and within the riblet valleys (e.g., no secondary motion). It is found that despite the large wetted area increase, the frictional drag is not increased on riblets relative to a smooth wall. This result suggests that the viscous effects are at play in the drag reduction for a turbulent boundary layer, in the sense that they compensate for the increase in wetted area.

  10. On the Structure of Tilt Grain Boundaries in Cubic Metals II. Asymmetrical Tilt Boundaries

    Microsoft Academic Search

    A. P. Sutton; V. Vitek

    1983-01-01

    The results of the study of symmetrical tilt boundaries, reported in the preceding part I, are generalized to asymmetrical tilt boundaries. A classification of tilt boundaries in cubic crystals is developed that reveals which boundaries to choose in order to study equilibrium faceting or intrinsic grain boundary dislocations (g.b.ds) accommodating a misorientation. Two series of atomistic studies of asymmetrical tilt

  11. Are Nanodiamonds Evidence for a Younger Dryas Impact Event?

    NASA Astrophysics Data System (ADS)

    West, A.; Kennett, J.; Kennett, D. J.; Bunch, T. E.; Stafford, T. W., Jr.; Wolbach, W. S.

    2009-12-01

    Nanodiamonds (NDs), including hexagonal diamonds (lonsdaleite) have been discovered at the Tunguska impact site and in the Cretaceous-Tertiary (K/T) boundary layer, which also contains cubic diamonds. Similarly, for the Younger Dryas boundary layer (YDB) that dates to the onset of the Younger Dryas (YD) cooling event at ~12.9 ka, NDs (cubics and lonsdaleite) are found broadly at multiple locations over North America and Europe. The NDs are proposed to result from a cosmic impact event that triggered widespread biomass-burning, which produced peaks at multiple sites in charcoal, grape-cluster soot, carbon spherules (CS), glass-like carbon, ammonium, and nitrate at the onset of the YD. The question is whether or not a cosmic impact is the best or only explanation for the YDB nanodiamonds. For example, could volcanism or intense wildfires have produced them? WILDFIRES: There is evidence for widespread fires at 12.9 ka: (1) The YDB also contains variable concentrations and sizes of CS, which are carbon-rich spheres produced through intense heat in high-stand wildfires. (2) Greenland ice cores exhibit spikes in ammonium and nitrate at the YD onset, that are interpreted as proxies for biomass-burning and collectively form the largest such peak known from late Quaternary ice cores. (3) Nearly all of 74 North American lakes examined exhibit peaks in charcoal representing evidence for wildfires at or close to ~12.9 ka, within the limits of radiocarbon dating. (4) High levels of soot have been detected in the YDB layer at five sites across North America (CA, AZ, OK, TX, and SC). NANODIAMONDS: For Tunguska, K/T sites, and the YDB, NDs have been found either embedded within or closely associated with CS. Experimental research demonstrates that ND formation requires extreme physical conditions generated either in the laboratory or during an ET impact, and not otherwise found on Earth’s surface. These conditions include transient high temperatures, hypoxic atmospheric conditions, and rapid quenching, thus excluding regular wildfires, where oxic conditions would destroy NDs. The available evidence supports formation of nanodiamonds by cosmic impact at 12.9 ka for the following reasons: (A) Lonsdaleite has never been found associated with any volcanic or igneous rocks or with mantle-derived terrestrial diamonds; (B) Lonsdaleite has been found only inside meteorites or impact craters; (C) NDs have never been found in association with non-impact wildfires; (D) No CS that contain NDs have been observed above or below known impact boundaries, e.g., the K/T and Tunguska layers; (E) In the entire geologic record, there are only two known continental layers containing both NDs and soot - the K/T boundary and the YDB. Thus, existing aggregate evidence supports an as-yet undefined cosmic event as the most compelling explanation for the YDB, and it argues against wildfires or volcanism as alternative causes.

  12. 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.

  13. Grain boundary structure in alumina

    Microsoft Academic Search

    Shiue

    1985-01-01

    In liquid phase sintered aluminas, basal twins and glass phase at boundary regions are very common. The microstructures of a very glassy alumina show that coarse ledges (up to several hundred angstroms in height) are usually present at the AlâOâ\\/glass interface and the preferred ledge plane is (0001). This result suggests that the basal plane is the most stable plane

  14. 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.

  15. Pricing Options With Curved Boundaries

    Microsoft Academic Search

    Naoto Kunitomo; Masayuki Ikeda

    1992-01-01

    This paper provides a general valuation method for the European options whose payoff is restricted by curved boundaries contractually set on the underlying asset price process when it follows the geometric Brownian motion. Our result is based on the generalization of the Levy formula on the Brownian motion by T. W. Anderson in sequential analysis. We give the explicit probability

  16. 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.

  17. Localized receptivity of boundary layers

    Microsoft Academic Search

    J. D. Crouch

    1992-01-01

    The boundary-layer receptivity resulting from acoustic forcing over a flat plate with a localized surface irregularity is analyzed using perturbation methods. The length-scale reduction, essential to acoustic receptivity, is captured within the framework of the classical stability theory. At first order, two disturbances are calculated: an unsteady disturbance resulting from the acoustic forcing and a steady disturbance resulting from the

  18. 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...

  19. 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 ...

  20. 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...

  1. 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...

  2. 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…

  3. 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…

  4. Atlas of Historical County Boundaries

    NSDL National Science Digital Library

    So you'd like to know the boundaries of Washington's King County in the early 20th century? Or perhaps you'd like to know more about the shape of Nassau County in New York back in the 19th century? The Atlas of Historical County Boundaries can provide you such details. The project is housed at the William M. Scholl Center for American History and Culture at The Newberry Library in Chicago and it was completed in 2010. The Atlas includes such features as all boundary changes in states and countries, non-county areas, separate map or polygon files for every different county configuration, and other helpful features. Users can get started by clicking on different states of interest and just exploring as they see fit. It's also useful to read over the Using the Atlas area for additional assistance. Finally, visitors can also look at the Publications section for more information on the source material for these county boundaries.

  5. Lagrangian Variational Framework for Boundary Value Problems

    E-print Network

    Alexander Figotin; Guillermo Reyes

    2014-07-29

    A boundary value problem is commonly associated with constraints imposed on a system at its boundary. We advance here an alternative point of view treating the system as interacting "boundary" and "interior" subsystems. This view is implemented through a Lagrangian framework that allows to account for (i) a variety of forces including dissipative acting at the boundary; (ii) a multitude of features of interactions between the boundary and the interior fields when the boundary fields may differ from the boundary limit of the interior fields; (iii) detailed pictures of the energy distribution and its flow; (iv) linear and nonlinear effects. We provide a number of elucidating examples of the structured boundary and its interactions with the system interior. We also show that the proposed approach covers the well known boundary value problems.

  6. Molecular wall effects: are conditions at a boundary "boundary conditions"?

    PubMed

    Brenner, H; Ganesan, V

    2000-06-01

    This paper addresses and answers "no" to the question of whether the literal molecular-dynamically-derived species velocities prevailing at a solid surface bounding a two-component fluid continuum undergoing molecular diffusion constitute the appropriate species-velocity boundary conditions to be imposed upon the fluid continuum. In a broader context, generic boundary condition issues arising from the presence of different length scales in continuum-mechanical descriptions of physical phenomena are clarified. This is achieved by analyzing a model problem involving the steady-state diffusion of a dilute system of Brownian spheres (the latter envisioned as tractable models of solute "molecules") through a quiescent viscous solvent continuum bounded laterally by solid plane walls. Both physicochemical (potential energy) and hydrodynamic (steric) wall interaction effects experienced by the Brownian spheres are explicitly accounted for in our refined, microscale continuum model of the diffusion process. Inclusion of these "solid-wall-fluid" (s-f ) boundary-generated forces [above and beyond the usual "fluid-fluid" (f-f ) intermolecular forces implicit in the conventional Fick's law macroscale continuum description] serves to simulate the comparable s-f molecular boundary forces modeled in molecular dynamics simulations of the diffusional process. A singular perturbation framework is used to clarify the physical interpretation to be ascribed to "continuum-mechanical boundary conditions." In this same spirit we also clearly identify the origin of the physical concept of a "surface field" as well as of the concomitant surface transport conservation equation for strongly adsorbed species at solid walls. Our analysis of such surface phenomena serves to emphasize the fact that these are asymptotic, surface-excess, macroscale concepts assigned to a surface, rather than representing literal molecular material entities physically confined to the surface. Overall, this paper serves to illustrate the manner in which molecular simulations need to account for these different length scales and corresponding scale-dependent concepts if such analyses are to avoid drawing incorrect inferences regarding the molecular origins of continuum-mechanical boundary conditions. PMID:11088381

  7. Molecular wall effects: Are conditions at a boundary ``boundary conditions''?

    NASA Astrophysics Data System (ADS)

    Brenner, Howard; Ganesan, Venkat

    2000-06-01

    This paper addresses and answers ``no'' to the question of whether the literal molecular-dynamically-derived species velocities prevailing at a solid surface bounding a two-component fluid continuum undergoing molecular diffusion constitute the appropriate species-velocity boundary conditions to be imposed upon the fluid continuum. In a broader context, generic boundary condition issues arising from the presence of different length scales in continuum-mechanical descriptions of physical phenomena are clarified. This is achieved by analyzing a model problem involving the steady-state diffusion of a dilute system of Brownian spheres (the latter envisioned as tractable models of solute ``molecules'') through a quiescent viscous solvent continuum bounded laterally by solid plane walls. Both physicochemical (potential energy) and hydrodynamic (steric) wall interaction effects experienced by the Brownian spheres are explicitly accounted for in our refined, microscale continuum model of the diffusion process. Inclusion of these ``solid-wall-fluid'' (s-f ) boundary-generated forces [above and beyond the usual ``fluid-fluid'' (f-f ) intermolecular forces implicit in the conventional Fick's law macroscale continuum description] serves to simulate the comparable s-f molecular boundary forces modeled in molecular dynamics simulations of the diffusional process. A singular perturbation framework is used to clarify the physical interpretation to be ascribed to ``continuum-mechanical boundary conditions.'' In this same spirit we also clearly identify the origin of the physical concept of a ``surface field'' as well as of the concomitant surface transport conservation equation for strongly adsorbed species at solid walls. Our analysis of such surface phenomena serves to emphasize the fact that these are asymptotic, surface-excess, macroscale concepts assigned to a surface, rather than representing literal molecular material entities physically confined to the surface. Overall, this paper serves to illustrate the manner in which molecular simulations need to account for these different length scales and corresponding scale-dependent concepts if such analyses are to avoid drawing incorrect inferences regarding the molecular origins of continuum-mechanical boundary conditions.

  8. Boundary learning by optimization with topological constraints

    E-print Network

    Helmstaedter, Moritz N.

    Recent studies have shown that machine learning can improve the accuracy of detecting object boundaries in images. In the standard approach, a boundary detector is trained by minimizing its pixel-level disagreement with ...

  9. Boundaries and Lenition in Yuman Languages

    ERIC Educational Resources Information Center

    Langdon, Margaret

    1975-01-01

    This article discusses the role of boundaries in Yuman languages and gives a general idea of Yuman phonology. Basic units in the morphology and syntax are also delimited, as a result of the examination of boundaries. (CLK)

  10. 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.

  11. 15 CFR 922.150 - Boundary.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ...adjacent to Indian reservations, State and county owned lands; in such case, the coastal boundary is the mean lower low water line. La Push harbor is excluded from the Sanctuary boundary shoreward of the International Collision at Sea...

  12. 50 CFR 600.105 - Intercouncil boundaries.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ...c) South Atlantic and Gulf of Mexico Councils. The boundary coincides with the line of demarcation between the Atlantic Ocean and the Gulf of Mexico, which begins at the intersection of the outer boundary of the EEZ, as specified...

  13. 50 CFR 600.105 - Intercouncil boundaries.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ...c) South Atlantic and Gulf of Mexico Councils. The boundary coincides with the line of demarcation between the Atlantic Ocean and the Gulf of Mexico, which begins at the intersection of the outer boundary of the EEZ, as specified...

  14. ConcepTest: Divergent Boundary Sketch

    NSDL National Science Digital Library

    The figure below was drawn by a student to show the relationship between earthquake epicenters (filled circles) and a divergent plate boundary (red line). The figure represents a boundary between two oceanic ...

  15. 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....

  16. Quasilinear singularly perturbed problem with boundary perturbation.

    PubMed

    Mo, Jia-qi

    2004-09-01

    A class of quasilinear singularly perturbed problems with boundary perturbation is considered. Under suitable conditions, using theory of differential inequalities we studied the asymptotic behavior of the solution for the boundary value problem. PMID:15323011

  17. Unsteady boundary-layer injection

    NASA Technical Reports Server (NTRS)

    Telionis, D. P.; Jones, G. S.

    1981-01-01

    The boundary-layer equations for two-dimensional incompressible flow are integrated numerically for the flow over a flat plate and a Howarth body. Injection is introduced either impulsively or periodically along a narrow strip. Results indicate that injection perpendicular to the wall is transmitted instantly across the boundary layer and has little effect on the velocity profile parallel to the wall. The effect is a little more noticeable for flows with adverse pressure gradients. Injection parallel to the wall results in fuller velocity profiles. Parallel and oscillatory injection appears to influence the mean. The amplitude of oscillation decreases with distance from the injection strip but further downstream it increases again in a manner reminiscent of an unstable process.

  18. Casimir energy for spherical boundaries

    NASA Astrophysics Data System (ADS)

    Hagen, C. R.

    2000-03-01

    Calculations of the Casimir energy for spherical geometries which are based on integrations of the stress tensor are critically examined. It is shown that despite their apparent agreement with numerical results obtained from mode summation methods, they are subject to criticism on several points. Specifically, these include (1) an improper application of the stress tensor to spherical boundaries, (2) the neglect of pole terms in contour integrations, and (3) the imposition of inappropriate boundary conditions upon the relevant propagators. A calculation which is based on the stress tensor and which avoids such problems is shown to be possible. It is, however, equivalent to the mode summation method and does not therefore constitute an independent calculation of the Casimir energy.

  19. Flaring Solar Hale Sector Boundaries

    NASA Astrophysics Data System (ADS)

    Svalgaard, L.; Hannah, I. G.; Hudson, H. S.

    2011-05-01

    The sector structure that organizes the magnetic field of the solar wind into large-scale domains has a clear pattern in the photospheric magnetic field as well. The rotation rate, 27-28.5 days, implies an effectively rigid rotation originating deeper in the solar interior than the sunspots. The photospheric magnetic field is known to be concentrated near that portion (the Hale boundary) in each solar hemisphere, where the change in magnetic sector polarity matches that between the leading and following sunspot polarities in active regions in the respective hemispheres. We report here that flares and microflares also concentrate at the Hale boundaries, implying that flux emergence and the creation of free magnetic energy in the corona also have a direct cause in the deep interior.

  20. Tectonic Plates and Plate Boundaries

    NSDL National Science Digital Library

    Continents were once thought to be static, locked tight in their positions in Earth's crust. Similarities between distant coastlines, such as those on opposite sides of the Atlantic, were thought to be the work of a scientist's overactive imagination, or, if real, the result of erosion on a massive scale. This interactive feature shows 11 tectonic plates and their names, the continents that occupy them, and the types of boundaries between them.

  1. 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.

  2. Grain Boundary Self-Diffusion in Nickel

    Microsoft Academic Search

    R. F. Canon; J. P. Stark

    1969-01-01

    High-purity nickel bicrystals with controlled grain boundary misorientations have been grown from the melt using an electron beam floating-zone technique. These bicrystals have symmetrical tilt grain boundaries with 10° misorientation between {111} planes tilted about a ?112? axis, and 10° twist about a {111} axis. The diffusion of nickel-63 in these boundaries and similar sintered grain boundaries has been studied

  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. Plasma boundaries in the inner magnetosphere

    Microsoft Academic Search

    J. L. Horwitz; S. Menteer; J. Turnley; J. L. Burch; J. D. Winningham; C. R. Chappell; J. D. Craven; L. A. Frank; D. W. Slater

    1986-01-01

    Plasma boundaries in the inner magnetosphere are investigated with measurements chiefly by the DE 1 and 2 spacecraft. The boundaries studied here are: (1) the low-energy (or thermal) ion transition (LEIT) frequently observed at or near the conventional plamapause density gradient, defined here as the outer boundary of observable, cold, isotropic light ions and transition to warm field-aligned ions; (2)

  5. Boundary element formulation for thermoelastohydrodynamic contact problems

    Microsoft Academic Search

    A. Gakwaya; D. Despres

    1991-01-01

    This paper presents a boundary element formulation and numerical solution of lubricated contact problems. It uses the full Navier-Stokes equation for thermoviscous incompressible lubricant fluid and the thermoelastic equations for the contacting solids. These equations form a coupled system that is written into equivalent boundary-domain integral equations which are then discretized using both conforming and nonconforming boundary elements. The resulting

  6. 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.

  7. Title: Boundary File: GTA (Greater Toronto Area) Data Creator /

    E-print Network

    Municipal Boundary shapefiles: Municipal Boundary ­ Upper Tier and District, and Municipal Boundary ­ Lower Municipality of Durham, Regional Municipality of York Data Type: Digital Vector Data Format: Shapefile Datum

  8. 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.

  9. 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)

  10. 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.…

  11. Twin boundaries and incoherent steps on twin boundaries in body-centered-cubic metals

    Microsoft Academic Search

    M. Yamaguchi; V. Vitek

    1976-01-01

    The atomistic structure of coherent {112} twin boundaries and of incoherent steps on these boundaries is studied by computer simulation. The interatomic interaction is described by four different central force laws. It is found that for strong binding the boundary for which the first layer of the twin is sheared by 1\\/12?111? is preferred to the boundary where all the

  12. 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.

  13. New bifurcations of basin boundaries involving Wada and a smooth Wada basin boundary

    NASA Astrophysics Data System (ADS)

    Zou, Hai-Lin; Xu, Jian-Xue; Jiang, Jun

    2008-01-01

    This paper demonstrates and analyses double heteroclinic tangency in a three-well potential model, which can produce three new types of bifurcations of basin boundaries including from smooth to Wada basin boundaries, from fractal to Wada basin boundaries in which no changes of accessible periodic orbits happen, and from Wada to Wada basin boundaries. In a model of mechanical oscillator, it shows that a Wada basin boundary can be smooth.

  14. Stagnation Flow in Streamer Boundaries

    NASA Technical Reports Server (NTRS)

    Suess, Steven T.; Nerney, S. F.; Whitaker, Ann F. (Technical Monitor)

    2001-01-01

    Flow tubes adjacent to closed magnetic field lines on the boundaries of streamers can have spreading factors which change rapidly with height. Numerical models in this thin layer are subject to uncertainties. Here we use an analytic model of magnetically closed and adjacent open regions to compute the spreading factor close to the closed field lines and the flow on the open field lines. We axe able to recover the shape of the closed field region, or helmet, and show the evolution of the helmet under slowly increasing temperature. We also show why and when stagnation flow can occur in the vicinity of the cusp at the top of the helmet.

  15. 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.

  16. 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.

  17. Seismic link at plate boundary

    NASA Astrophysics Data System (ADS)

    Ramdani, Faical; Kettani, Omar; Tadili, Benaissa

    2015-06-01

    Seismic triggering at plate boundaries has a very complex nature that includes seismic events at varying distances. The spatial orientation of triggering cannot be reduced to sequences from the main shocks. Seismic waves propagate at all times in all directions, particularly in highly active zones. No direct evidence can be obtained regarding which earthquakes trigger the shocks. The first approach is to determine the potential linked zones where triggering may occur. The second step is to determine the causality between the events and their triggered shocks. The spatial orientation of the links between events is established from pre-ordered networks and the adapted dependence of the spatio-temporal occurrence of earthquakes. Based on a coefficient of synchronous seismic activity to grid couples, we derive a network link by each threshold. The links of high thresholds are tested using the coherence of time series to determine the causality and related orientation. The resulting link orientations at the plate boundary conditions indicate that causal triggering seems to be localized along a major fault, as a stress transfer between two major faults, and parallel to the geothermal area extension.

  18. Boundary effects in Cherenkov radiation

    NASA Astrophysics Data System (ADS)

    García de Abajo, F. J.; Rivacoba, A.; Zabala, N.; Yamamoto, N.

    2004-04-01

    The effect of dielectric boundaries on the Cherenkov radiation (CR) produced when a fast point charge moves inside or near a material is analyzed for different shapes of the sample. Calculations are offered for a charge moving near both planar and nonplanar surfaces. CR is found to be produced even when the external charge moves outside a semi-infinite medium. For charges moving near planar boundaries, the reflected radiation interferes with the direct CR, leading to oscillations in the emission probability as a function of the impact parameter relative to the interfaces. Thin-film guided modes are excited by penetrating electrons and our calculations agree reasonably well with available experiments. The bulk limit in the emission probability is recovered for charges passing by the center of cylinders or spheres of increasingly large radius. Recent experiments of energy loss of electrons passing near dielectric spheres are explained thanks to the inclusion of retardation effects in the sphere response. These effects lead to an efficient channel of radiative energy losses. Finally, the diffraction of CR in void inclusions is proposed as a tool for providing information on otherwise inaccessible buried structures.

  19. Boundaries in Miniature: Two Examples from Soil

    NSDL National Science Digital Library

    JAYNE BELNAP, CHRISTINE V. HAWKES, and MARY K. FIRESTONE (; )

    2003-08-01

    This peer-reviewed article from BioScience journal is about the effects of soil boundaries water, carbon, nitrogen, and oxygen dynamics. Transitions between atmosphere and soil, and between soil and roots, are two examples of small-scale boundaries across which the nutrient, water, and gas dynamics of ecosystems are modulated. Most atmospheric inputs to ecosystems have to pass through the soil; thus, the atmosphere-soil boundary influences the type and amount of materials and energy entering the soil. Belowground plant inputs occur through the rhizosphere, the zone of soil immediately adjacent to the root. This soil boundary layer affects root inputs to soil and root extraction of water and nutrients from soil. We discuss how water, carbon, nitrogen, and oxygen dynamics are affected by atmosphere-soil and soil-root boundaries and how light, soil pH, and dust are affected by the atmosphere-soil boundary. (We also examine pH with regard to the root-soil boundary, but not in a separate section.) We examine the linkages between these small-scale boundaries and landscape ecology and discuss how the understanding of small-scale boundaries can contribute to the emerging field of boundary theory.

  20. Non-local effects of prosodic boundaries

    PubMed Central

    Carlson, Katy; Clifton, Charles; Frazier, Lyn

    2009-01-01

    Placing a prosodic boundary before a phrase may influence its syntactic analysis. However, the effect of the boundary depends on the presence, size, and position of other, earlier, prosodic boundaries (Carlson et al., 2001, Clifton et al., 2002). Three experiments are reported that extend previous results about the effect of the position of the early boundary. In sentences where a final phrase may modify either a local verb or an earlier verb, a boundary immediately after the first verb leads to more first verb attachments than when the earlier boundary is placed in some other position between the first verb and the local verb (Experiments 1,2). This effect cannot be attributed to weaker effects of more distant boundaries (Experiment 2), but is likely due to the first verb being more prominent when a boundary immediately follows it, since similar effects are observed when the verb is accented (Experiment 3). The results further support the Informative Boundary hypothesis, and show that the impact of earlier, nonlocal boundaries is not fully uniform. PMID:19744940

  1. Momentum transfer of a Boltzmann-lattice fluid with boundaries

    Microsoft Academic Search

    M'hamed Bouzidi; Mouaouia Firdaouss; Pierre Lallemand

    2001-01-01

    We study the velocity boundary condition for curved boundaries in the lattice Boltzmann equation (LBE). We propose a LBE boundary condition for moving boundaries by combination of the ``bounce-back'' scheme and spatial interpolations of first or second order. The proposed boundary condition is a simple, robust, efficient, and accurate scheme. Second-order accuracy of the boundary condition is demonstrated for two

  2. The complex variable boundary element method: Applications in determining approximative boundaries

    USGS Publications Warehouse

    Hromadka, T.V., II

    1984-01-01

    The complex variable boundary element method (CVBEM) is used to determine approximation functions for boundary value problems of the Laplace equation such as occurs in potential theory. By determining an approximative boundary upon which the CVBEM approximator matches the desired constant (level curves) boundary conditions, the CVBEM is found to provide the exact solution throughout the interior of the transformed problem domain. Thus, the acceptability of the CVBEM approximation is determined by the closeness-of-fit of the approximative boundary to the study problem boundary. ?? 1984.

  3. Paleoecology of the Late Cretaceous of southern Limburg

    SciTech Connect

    MacKenzie, G.J.

    1985-01-01

    Geochemical, sedimentological and paleontological criteria were used to determine changing paleoenvironmental conditions in southern Limburg during Campanian and Maastrichtian times. To this end a 100 meter composite sequence exposing Middle Campanian to Cretaceous/Tertiary boundary sediments was sampled. Relatively rapid variations in temperature and water depth over this stratigraphic interval are suggested by the faunal assemblage. This shows greater affinity for warmer, shallower waters toward the Cretaceous-Tertiary boundary. Boreal indicators such as belemnites are superseded by rudists, corals and orbitoid foramanifera during climatic amelioration. Profuse algal growth and accompanying rapid benthonic biomass generation at higher levels, indicative of shallow water deposition, contrasts strongly with the less fossiliferous, muddy-bottom, older biofacies dominated by nekton. Strontium, magnesium, manganese, sodium and stable isotope measurements were made on the carbonate soluble fraction of the sediment and contained macrofauna. Although other interpretations may be placed on the geochemical data, progressive increases in the Sr/Ca and Mg/Ca ratios seen through into the lower Upper Maastrichtian offer support for conclusions based on paleontological data. In younger sediments a gradual decline in the Sr/Ca ratio possibly indicate terminal Cretaceous cooling, although without a supporting parallel trend in the Mg/Ca ratio this is less certain.

  4. Who's Afraid of the Hill Boundary?

    NASA Astrophysics Data System (ADS)

    Montgomery, Richard

    2014-11-01

    The Jacobi-Maupertuis metric allows one to reformulate Newton's equations as geodesic equations for a Riemannian metric which degenerates at the Hill boundary. We prove that a JM geodesic which comes sufficiently close to a regular point of the boundary contains pairs of conjugate points close to the boundary. We prove the conjugate locus of any point near enough to the boundary is a hypersurface tangent to the boundary. Our method of proof is to reduce analysis of geodesics near the boundary to that of solutions to Newton's equations in the simplest model case: a constant force. This model case is equivalent to the beginning physics problem of throwing balls upward from a fixed point at fixed speeds and describing the resulting arcs, see Fig. 2.

  5. HMK 1_Plate Boundaries: Present, future, & past

    NSDL National Science Digital Library

    Brian Hampton

    Prior to this homework assignment, students will have been exposed (for ~2-3 in class activities and lectures) to general concepts in plate tectonics, plate boundaries, hot spot volcanoes, use of earthquake/volcano trends at plate boundaries, as well as GPS as a modern use to document plate motion. Students receive this activity as a homework assignment to be completed outside of class. Their task is to use provided topographic/bathymetric data, earthquake and volcano distribution, GPS data, as well as ocean floor and hot spot age trends to characterize plate motion in modern, future, and ancient plate boundaries. This is a three-part exercise that involves a modern plate boundary study form the eastern margin of the Pacific plate, a potential future plate boundary in eastern Africa, and a identification of possible ancient plate boundaries in the Eurasian plate.

  6. Mechanical Behavior of Grain Boundary Engineered Copper

    SciTech Connect

    Carter, S B; Hodge, A M

    2006-08-08

    A grain boundary engineered copper sample previously characterized by Electron Backscatter Diffraction (EBSD) has been selected for nanoindentation tests. Given the fact that grain boundaries have thicknesses in the order of 1 micron or less, it is essential to use nanomechanics to test the properties of individual grain boundaries. The Hysitron nanoindenter was selected over the MTS nanoindenter due to its superior optical capabilities that aid the selection and identification of the areas to be tested. An area of 2mm by 2mm with an average grain size of 50 microns has been selected for the study. Given the EBSD mapping, grains and grain boundaries with similar orientations are tested and the hardness and modulus are compared. These results will give a relationship between the mechanical properties and the engineered grain boundaries. This will provide for the first time a correlation between grain boundary orientation and the mechanical behavior of the sample at the nanoscale.

  7. Hamiltonian boundary term and quasilocal energy flux

    SciTech Connect

    Chen, C.-M.; Nester, James M.; Tung, R.-S. [Department of Physics, National Central University, Chungli 32054, Taiwan (China); Department of Physics and Institute of Astronomy, National Central University, Chungli 32054, Taiwan (China); Center for Astrophysics, Shanghai Normal University, 100 Guilin Road, Shanghai 200234 (China)

    2005-11-15

    The Hamiltonian for a gravitating region includes a boundary term which determines not only the quasilocal values but also, via the boundary variation principle, the boundary conditions. Using our covariant Hamiltonian formalism, we found four particular quasilocal energy-momentum boundary term expressions; each corresponds to a physically distinct and geometrically clear boundary condition. Here, from a consideration of the asymptotics, we show how a fundamental Hamiltonian identity naturally leads to the associated quasilocal energy flux expressions. For electromagnetism one of the four is distinguished: the only one which is gauge invariant; it gives the familiar energy density and Poynting flux. For Einstein's general relativity two different boundary condition choices correspond to quasilocal expressions which asymptotically give the ADM energy, the Trautman-Bondi energy and, moreover, an associated energy flux (both outgoing and incoming). Again there is a distinguished expression: the one which is covariant.

  8. Microgravity Effects on Plant Boundary Layers

    NASA Technical Reports Server (NTRS)

    Stutte, Gary; Monje, Oscar

    2005-01-01

    The goal of these series of experiment was to determine the effects of microgravity conditions on the developmental boundary layers in roots and leaves and to determine the effects of air flow on boundary layer development. It is hypothesized that microgravity induces larger boundary layers around plant organs because of the absence of buoyancy-driven convection. These larger boundary layers may affect normal metabolic function because they may reduce the fluxes of heat and metabolically active gases (e.g., oxygen, water vapor, and carbon dioxide. These experiments are to test whether there is a change in boundary layer associated with microgravity, quantify the change if it exists, and determine influence of air velocity on boundary layer thickness under different gravity conditions.

  9. Grain-boundary plane reorientation in copper

    Microsoft Academic Search

    Valerie Randle; P. Davies; B. Hulm

    1999-01-01

    This paper describes an experiment to 'fine tune' or reorient grain-boundary planes in the interior of a copper specimen after annealing in air, focusing on the Sigma-3 boundaries. The initial heat treatment consisted of annealing in air at 900oC for 1h. This resulted in a population of Sigma-3 boundaries which was mainly displaced from low-energy configurations and was a 'snapshot'

  10. The equilibrium boundary between grahite and diamond

    Microsoft Academic Search

    C. Scott Kennedy; George C. Kennedy

    1976-01-01

    The equilibrium boundary between diamond and graphite has been determined over the temperature interval 1100°C-1625°C. A piston-cylinder apparatus and a ''zero-friction'' cell were used. Pressures were computed by force\\/area measurements and are independent of any calibration points. Visual observations of diamond dissolution or diamond growth were used in fixing the position of the boundary. Our newly determined boundary has the

  11. Identification and Characterization of Adolescents’ Sexual Boundaries

    PubMed Central

    Wolf, Hilary T.; Morrell, Holly E. R.; Halpern-Felsher, Bonnie L.

    2013-01-01

    Purpose Adolescents’ decisions to have sex may be based on a priori boundaries placed on sex. This study addresses: (1) to what extent adolescents set vaginal sexual boundaries; (2) the types of sexual boundaries most and least likely to be endorsed; and (3) to what extent sexual boundaries vary by sex, race/ethnicity, and sexual experience. Methods A cross-sectional study of 518 students attending 10th grade. Survey measures queried about demographics, ever having sex, and existence of sexual boundaries (e.g., being in love, having an attractive partner) that must be in place before having vaginal sex. Results The most frequently endorsed boundaries were maturity, commitment, trust, love, and marriage. These boundaries were more frequently endorsed than having a safer-sex method. Compared to females, males were more likely to choose boundaries based on partner attractiveness (p<.001) and avoiding trouble (p<.04). Compared to Asians and Pacific Islanders, Whites were more likely to endorse wanting to be a certain age to have sex (p<.01 and p<.05, respectively); Asians and Pacific Islanders were more likely to choose sexual boundaries based on marriage (p’s<.05). Adolescents who were sexually experienced were more likely than inexperienced adolescents to endorse boundaries related to relationship characteristics and partner attractiveness (OR=2.5), and less likely to endorse boundaries related to feeling mature (OR=0.34) and waiting until marriage (OR=0.34). Conclusions Identifying adolescents’ sexual boundaries should assist healthcare professionals better understand under what circumstances adolescents are more or less likely to have sex; and this information should ultimately inform the development of new interventions. PMID:23481297

  12. Turbulent boundary layer behind a separation zone

    Microsoft Academic Search

    P. Wauschkuhn; V. I. Vasanta Ram

    1975-01-01

    The turbulent boundary layer after reattachment following separation on a backward-facing step in incompressible flow has been studied experimentally. Hot-wire measurements of the velocity and shear-stress distribution in the boundary layer were made. Furthermore the local wall shear stress was measured by a sub-layer fence. For a considerable distance downstream of reattachment the boundary layer exhibits a region not obeying

  13. B R I E F I N G B O O K T H E O F F I C E O F G O V E R N M E N T R E L A T I O N S

    E-print Network

    Matsuda, Noboru

    B R I E F I N G B O O K T H E O F F I C E O F G O V E R N M E N T R E L A T I O N S 2 0 1 1 #12;G O V E R N M E N T R E L AT I O N S 1 C O N T E N T S Pittsburgh Office Carnegie Mellon University-268-7778 Email: tpm@andrew.cmu.edu Stan Caldwell Director of State Relations Phone: 412-268-9505 Email: stanleyc@andrew

  14. 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.

  15. Radiation-viscous boundary layer

    NASA Technical Reports Server (NTRS)

    Arav, Nahum; Begelman, Mitchell C.

    1992-01-01

    A viscous boundary layer (BL) is studied which is most likely to occur in astrophysical systems dominated by radiation pressure, in particular compact objects surrounded by a very optically thick envelope and radiating at close to the Eddington limit. Calculations are reported which show that a BL due to radiation viscosity behaves very differently from a 'classical' incompressible BL for flows with Mach number M much greater than unity far from the BL. In these flows the width of the BL is much larger than its incompressible value and scales as M-squared times the width of the imcompressible BL. The density inside the BL is much lower than that in the undisturbed fluid and scales as 1/M-squared with respect to the value far away from the BL. It is concluded that under certain circumstances a cocoon of low-density material will develop between a jet and its surrounding medium.

  16. 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.

  17. Stagnation Flow in Streamer Boundaries

    NASA Technical Reports Server (NTRS)

    Suess, S. T.; Nerney, S. F.

    2002-01-01

    It is possible for flow tubes adjacent to closed magnetic field lines on the boundaries of streamers to have spreading factors that change rapidly according to height. Mathematical models in this thin layer are prone to uncertainties. In this paper we use an analytical model of magnetically closed and adjacent open regions to calculate the spreading factor close to the closed field lines and near the flow on the open field lines. We recovered the shape of the closed field region, or helmet, and show the evolution of the helmet under increasing temperature. We also show why and when stagnation flow can occur in the area of the cusp at the top of the helmet.

  18. Development of perturbations in the boundary layer

    NASA Technical Reports Server (NTRS)

    Dovgal, A. V.; Kachanov, Y. S.; Kozlov, V. V.; Levchenko, V. Y.; Maksimov, V. P.

    1986-01-01

    The transition of laminar flows into turbulent flows in a boundary layer is discussed. The individual aspects of the transition process, observed under controllable model conditions are examined. The aspect of this problem, namely the development or excitation of the natural oscillations in the boundary layer, the so-called Tollmin-Schlichting waves is covered. Three types of excitation of these waves are considered: (1) distributed generation throughout the boundary layer; (2) generation in the vicinity of the forward edge of a model, having either a sharp edge or an edge with a large radius or curvature, and (3) generation in a developed boundary layer by means of a focused effect.

  19. Advection diffusion equation with absorbing boundary

    E-print Network

    John Grant; Michael Wilkinson

    2014-12-15

    We consider a spatially homogeneous advection-diffusion equation in which the diffusion tensor and drift velocity are time-independent, but otherwise general. We derive asymptotic expressions, valid at large distances from a steady point source, for the flux onto a completely permeable boundary and onto an absorbing boundary. The absorbing case is treated by making a source of antiparticles at the boundary. In both cases there is an exponential decay as the distance from the source increases; we find that the exponent is the same for both boundary conditions.

  20. Numerical simulation of a controlled boundary layer

    NASA Technical Reports Server (NTRS)

    Zang, Thomas A.; Hussaini, M. Yousuff

    1986-01-01

    The problem of interest is the boundary layer over a flat plate. The three standard laminar flow control (LFC) techniques are pressure gradient, suction, and heating. The parameters used to describe the amount of control in the context of the boundary layer equations are introduced. The numerical method required to find the mean flow, the linear eigenvalues of the Orr-Sommerfeld equation, and the full, nonlinear, 3-D solution of the Navier-Stokes equations are outlined. A secondary instability exists for the parallel boundary subject to uniform pressure gradient, suction, or heating. Selective control of the spanwise mode reduces the secondary instability in the parallel boundary layer at low Reynolds number.

  1. Gapped symmetric boundaries of topological insulators

    NASA Astrophysics Data System (ADS)

    Lee, Dung-Hai; Lu, Yuan-Ming

    2014-03-01

    Topological insulators (TIs) are gapped quantum phases which host symmetry-protected gapless boundary excitations. On the other hand, the boundary states can be gapped by spontaneously breaking symmetry. We show that topological defects on the symmetry-broken boundary cannot proliferate due to their fractional statistics. A gapped symmetric boundary, however, can be achieved between a TI phase and certain fractionalized phase by condensing the bound state of a topological defect and an anyon. Such a hybrid structure containing TI and fractionalized phase generally support ground state degeneracy on torus.

  2. Plasma boundaries in the inner magnetosphere

    SciTech Connect

    Horwitz, J.L.; Menteer, S.; Turnley, J.; Burch, J.L.; Winningham, J.D.; Chappell, C.R.; Craven, J.D.; Frank, L.A.; Slater, D.W.

    1986-08-01

    Plasma boundaries in the inner magnetosphere are investigated with measurements chiefly by the DE 1 and 2 spacecraft. The boundaries studied here are: (1) the low-energy (or thermal) ion transition (LEIT) frequently observed at or near the conventional plamapause density gradient, defined here as the outer boundary of observable, cold, isotropic light ions and transition to warm field-aligned ions; (2) the earthward or inner edges of the plasma sheet electrons having pitch angles near 90/sup 0/ and the three energies 100 eV, 1 keV, and 10 keV; and (3) the equatorward boundaries of precipitating auroral oval electrons at those same energies.

  3. Scalar discrete nonlinear multipoint boundary value problems

    NASA Astrophysics Data System (ADS)

    Rodriguez, Jesus; Taylor, Padraic

    2007-06-01

    In this paper we provide sufficient conditions for the existence of solutions to scalar discrete nonlinear multipoint boundary value problems. By allowing more general boundary conditions and by imposing less restrictions on the nonlinearities, we obtain results that extend previous work in the area of discrete boundary value problems [Debra L. Etheridge, Jesus Rodriguez, Periodic solutions of nonlinear discrete-time systems, Appl. Anal. 62 (1996) 119-137; Debra L. Etheridge, Jesus Rodriguez, Scalar discrete nonlinear two-point boundary value problems, J. Difference Equ. Appl. 4 (1998) 127-144].

  4. Boundary assessment under uncertainty: A case study

    USGS Publications Warehouse

    Pawlowsky, V.; Olea, R.A.; Davis, J.C.

    1993-01-01

    Estimating certain attributes within a geological body whose exact boundary is not known presents problems because of the lack of information. Estimation may result in values that are inadmissible from a geological point of view, especially with attributes which necessarily must be zero outside the boundary, such as the thickness of the oil column outside a reservoir. A simple but effective way to define the boundary is to use indicator kriging in two steps, the first for the purpose of extrapolating control points outside the body, the second to obtain a weighting function which expresses the uncertainty attached to estimations obtained in the boundary region. ?? 1993 International Association for Mathematical Geology.

  5. Effects of grain boundary constraints on properties of polycrystalline materials

    NASA Astrophysics Data System (ADS)

    McGarrity, Kimberly; McGarrity, Erin; Duxbury, Phillip; Reed, Bryan; Holm, Elizabeth

    2007-03-01

    Grain boundary networks are engineered by increasing the fraction of boundaries which have favorable properties. Favorable boundaries have either low grain boundary misorientation or they are special boundaries, such as coincident site lattice boundaries. Significant improvement in properties such as corrosion resistance, critical current in superconductors and mechanical strength and toughness occur, provided percolating grain or grain boundary structures can be engineered. We demonstrate that grain boundary constraints shift percolation thresholds from their uncorrelated values and that the behavior near threshold is also modified. The origin of these behaviors is an enhanced clustering of weak boundaries induced by grain boundary constraints.

  6. Work-family boundary strategies: Stability and alignment between preferred and enacted boundaries

    PubMed Central

    Ammons, Samantha K.

    2015-01-01

    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. In this study, 23 respondents employed at a large Fortune 500 company were interviewed about their work-family boundaries before and after their teams underwent a cultural change initiative that sought to loosen workplace norms and allow employees more autonomy to decide when and where they performed their job tasks. Four distinct boundary strategies emerged from the data, with men and parents of young children having better alignment between preferred and enacted boundaries than women and those without these caregiving duties. Implications for boundary theory and research are discussed. PMID:25620801

  7. The Influence of Grain Boundary Type upon Damage Evolution at Grain Boundary Interfaces

    SciTech Connect

    Perez-Bergquist, Alejandro G [Los Alamos National Laboratory; Brandl, Christian [Los Alamos National Laboratory; Escobedo, Juan P [Los Alamos National Laboratory; Trujillo, Carl P [Los Alamos National Laboratory; Cerreta, Ellen K [Los Alamos National Laboratory; Gray III, George T [Los Alamos National Laboratory; Germann, Timothy C [Los Alamos National Laboratory

    2012-07-09

    In a prior work, it was found that grain boundary structure strongly influences damage evolution at grain boundaries in copper samples subjected to either shock compression or incipient spall. Here, several grain boundaries with different grain boundary structures, including a {Sigma}3 (10-1) boundary, are interrogated via conventional transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) to investigate the effects of atomic-scale structural differences on grain boundary strength and mobility. Boundaries are studied both before and after shock compression at a peak shock stress of 10 GPa. Results of the TEM and HRTEM work are used in conjunction with MD modeling to propose a model for shock-induced damage evolution at grain boundary interfaces that is dependent upon coincidence.

  8. Grain Boundary Character Distributions In Isostructural Materials

    NASA Astrophysics Data System (ADS)

    Ratanaphan, Sutatch

    Anisotropic grain boundary character distributions (GBCDs), which influence macroscopic materials properties, are thought to be controlled by the grain boundary energy anisotropy. Structurally, grain boundary could be viewed as two free surfaces joined together. Grain boundary energy could be simply defined by the total excess energy for creating two free surfaces minus the energy gained when new bonds are formed between these surfaces. This implies that different crystal structure should have different GBEDs and GBCDs. It was recently discovered that grain boundary energy distributions (GBED) in isostructural materials, a class of materials that share the same crystal structure, are directly related to one another. This suggests that GBCDs in isostructural materials might also be related in a similar way. To test this hypothesis, electron backscatter diffraction (EBSD) was used to map grain orientations in Ag, Au, Cu, Fe, and Mo. The GBCDs were determined from the stereological interpretation of EBSD maps containing on the order of 100,000 grains. It was found that the GBCDs of face-centered cubic (FCC) metals are statistically correlated, while the GBCDs of body-centered cubic (BCC) Fe and Mo are not correlated to the GBCD of FCC metals. The degree of the correlations among the FCC metals is weaker if there are significant differences in grain shape or texture. For example, Ag has the weakest correlation to the other FCC materials and also has quantitatively different grain shapes and texture. The relationship between the populations and energies of grain boundaries was also studied. By comparing the GBCDs of Al, Au, Cu, and Ni to the energies of 388 grain boundaries previously calculated by the Embedded Atom Method (EAM), we observed a moderately inverse correlation between the relative areas of grain boundaries and their energies. Interestingly, there are strong inverse correlations between the energies and populations of the most common grain boundaries (Sigma3, Sigma9, and Sigma27). Because the enhancement of twin related boundaries due to the prevalence Sigma3 boundaries results in a decrease in the grain boundary populations for the other boundary types, this inverse correlation is influenced by the crystallographic constraints at triple junctions. In other words, having an anisotropic misorientation distribution with strong maxima for certain boundaries biases the inverse correlation between grain boundary population and energy for other boundaries and causes different slopes at each misorientation. Interestingly, the inverse correlation at each misorientation is consistent with the Boltzmann distribution. Based on our results, it is possible to predict the GBCDs and GBEDs in isostructural polycrystalline materials by using a single GBCD and GBED. This principle is demonstrated by predicting the GBCD and GBED of Actinium (Ac). To investigate the GBED in the isostructural BCC metals, the energies of 408 grain boundaries in Fe and Mo were computed using atomistic simulations based on the embedded-atom method (EAM) potential. We found that the calculated boundary energies in Fe and Mo were strongly correlated and scaled with the ratio of the cohesive energy divided by the square of the lattice constant (Ecoh/a02). We would expect that the GBCD of Fe and Mo might be correlated in a similar manner to that of FCC metals. To test this hypothesis, we compared the GBCDs of Fe and Mo. We found that the GBCDs of Fe and Mo are moderately and strongly correlated when all boundary types and only Sigma3 boundaries were considered, respectively. In this thesis, the results demonstrated that the GBCDs of isostructural materials are correlated with one another and the magnitudes of correlation coefficients varied. Reduced correlations were observed when there were differences in the microstructure and crystallographic texture. The inverse relationship between grain boundary population and energy is more strongly correlated at each misorientation than over the entire five macroscopic parameters of grain boundary, especially when t

  9. Optimal Regularity and the Free Boundary in the Parabolic Signorini ...

    E-print Network

    2015-05-28

    Introduction. 1. 1.1. Overview of the main results. 3. 1.2. Related problems. 5. 1.3. Structure of the .... ment has appeared earlier in the book [PSU12, Chapter 9]. The bound ? ...... fk = ??(x)[? ?k ? ?t?k]+[vk(x, t) ? ?k(x ,t)]?? + 2[?vk ? ??k]?

  10. TBA boundary flows in the tricritical Ising field theory

    E-print Network

    Rafael I. Nepomechie; Changrim Ahn

    2002-07-04

    Boundary S matrices for the boundary tricritical Ising field theory (TIM), both with and without supersymmetry, have previously been proposed. Here we provide support for these S matrices by showing that the corresponding boundary entropies are consistent with the expected boundary flows. We develop the fusion procedure for boundary RSOS models, with which we derive exact inversion identities for the TIM. We confirm the TBA description of nonsupersymmetric boundary flows of Lesage et al., and we obtain corresponding descriptions of supersymmetric boundary flows.

  11. Strain Induced Grain Boundary Premelting along Twin Boundaries in Copper Polycrystals

    Microsoft Academic Search

    F. Inoko; T. Okada; T. Nishimura; M. Ohomori; T. Yoshikawa

    1999-01-01

    A polycrystalline copper sample was compressed at room temperature, then the temperature was raised to 873 K in a vacuum and annealed without unloading. Grain boundary cracks were found at S 3 coherent twin boundaries. The formation of these cracks can be interpreted based on the idea of strain induced grain boundary premelting (SIGBPM). It is emphasized that S 3

  12. A new discriminant analysis based on boundary\\/non-boundary pattern separation

    Microsoft Academic Search

    Jin Hee Na; Myoung Soo Park; Jin Young Choi

    2009-01-01

    In this paper, we propose a new discriminant analysis, named as linear boundary discriminant analysis (LBDA), which increases the class separability by differently emphasizing the boundary and non-boundary patterns. This is achieved by defining two novel scatter matrices and solving eigenproblem on the criterion described by these scatter matrices. As a result, the classification performance using the extracted features can

  13. Prediction Error and Event Boundaries 1 Running Head: PREDICTION ERROR AND EVENT BOUNDARIES

    E-print Network

    Zacks, Jeffrey M.

    Prediction Error and Event Boundaries 1 Running Head: PREDICTION ERROR AND EVENT BOUNDARIES A computational model of event segmentation from perceptual prediction. Jeremy R. Reynolds, Jeffrey M. Zacks, and Todd S. Braver Washington University Manuscript #12;Prediction Error and Event Boundaries 2 People tend

  14. Far field boundary conditions for compressible flows

    Microsoft Academic Search

    A. Bayliss; E. Turkel

    1982-01-01

    A family of boundary conditions which simulate outgoing radiation are derived. These boundary conditions are applied to the computation of steady state flows and are shown to significantly accelerate the convergence to steady state. Numerical results are presented. Extensions of this theory is problems in duct geometries are indicated.

  15. Boundary layer variational principles: a case study.

    PubMed

    Grmela, Miroslav; Karlin, Iliya V; Zmievski, Vladimir B

    2002-07-01

    Considering the model heat conduction problem in the setting of Grad's moment equations, we demonstrate a crossover in the structure of minima of the entropy production within the boundary layer. Based on this observation, we formulate and compare variation principles for solving the problem of boundary conditions in nonequilibrium thermodynamics. PMID:12241345

  16. 78 FR 15883 - Standard Time Zone Boundaries

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-03-13

    ...DOT-OST-2012-0159] RIN 2105-AE20 Standard Time Zone Boundaries AGENCY: Office of the...and amends the Department's standard time zone boundaries regulations to reflect changes that Congress made to the Uniform Time Act. The purpose of this update is...

  17. Boundary Conditions in Particle Swarm Optimization Revisited

    Microsoft Academic Search

    Shenheng Xu; Yahya Rahmat-Samii

    2007-01-01

    In order to enforce particles to search inside the solution space of interest during the optimization procedure, various boundary conditions are currently used in particle swarm optimization (PSO) algorithms. The performances, however, vary considerably with the dimensionality of the problem and the location of the global optimum in the solution space. In this paper, different boundary conditions are categorized into

  18. A Semigroup Approach to Boundary Feedback Systems

    Microsoft Academic Search

    Valentina Casarino; Klaus-Jochen Engel; Rainer Nagel; Gregor Nickel

    2003-01-01

    In this paper we convert a (linear ) initial boundary value problem into an abstract Cauchy problem on some product space and use semigroup methods to solve it. In particular, we apply spectral theory in order to discuss stability under boundary feedback.

  19. Measuring Trust between Organizational Boundary Role Persons

    Microsoft Academic Search

    Steven C. Currall; Timothy A. Judge

    1995-01-01

    Theoretical writings on trust and interorganizational collaboration have neglected the measurement aspects of trust. Defining trust as an individual?s behavioral reliance on another person under a condition of risk, we developed and tested the construct validity of a questionnaire measure that assessed trust between the individuals who provide the linking mechanism across organizational boundaries, namely, boundary role persons (BRPs). The

  20. Three-dimensional receptivity of boundary layers

    Microsoft Academic Search

    Yury S. Kachanov

    2000-01-01

    The paper presents a review of results of some recent (mainly experimental) studies devoted to a quantitative investigation of the problem of receptivity of the 2D and 3D boundary layers with respect to various 3D (in general) external perturbations. The paper concentrates on the mechanisms of excitation and development of stationary and travelling instability modes in a 3D boundary layer

  1. Flexibility of Event Boundaries in Autobiographical Memory

    PubMed Central

    Hohman, Timothy J.; Peynircio?lu, Zehra F.; Beason-Held, Lori L.

    2014-01-01

    Events have clear and consistent boundaries that are defined during perception in a manner that influences memory performance. The natural process of event segmentation shapes event definitions during perception, and appears to play a critical role in defining distinct episodic memories at encoding. However, the role of retrieval processes in modifying event definitions is not clear. We explored how such processes changed event boundary definitions at recall. In Experiment 1 we showed that distance from encoding is related to boundary flexibility. Participants were more likely to move self-reported event boundaries to include information reported beyond those boundaries when recalling more distant events compared to more recent events. In Experiment 2, we showed that age also influenced boundary flexibility. Older Age adults were more likely to move event boundaries than College Age adults, and the relationship between distance from encoding and boundary flexibility seen in Experiment 1 was present only in College Age and Middle Age adults. These results suggest that factors at retrieval have a direct impact on event definitions in memory and that, although episodic memories may be initially defined at encoding, these definitions are not necessarily maintained in long-term memory. PMID:22989194

  2. Transgressions and Transcendence: Surpassing Disciplinary Boundaries.

    ERIC Educational Resources Information Center

    Wughalter, Emily H.

    2002-01-01

    Discusses how women such as Amy Morris Homans, Susan B. Anthony, Elizabeth Cady Stanton, and Mary Wollstonecraft transgressed boundaries, allowing others to transcend old boundary limitations in physical education, examining the Boston Normal School of Gymnastics established for training women as directors of physical education over 100 years ago…

  3. Boundary Fragment Matching Articulated Pose Under Occlusion

    E-print Network

    Howe, Nicholas

    Silhouette-based Body-part Hypotheses Kwatra, Bobick, & Johnson, CVPR 2001 #12;Occlusion Ruins Everything ­ Efficient: best fragment matching approximated via EMD embedding [5] Assume for the moment that we knowAssume for the moment that we know which parts of the boundary arewhich parts of the boundary are ""realreal"" #12

  4. Dislocation interactions mediated by grain boundaries

    Microsoft Academic Search

    Paolo Moretti; Lasse Laurson; Mikko J. Alava

    2008-01-01

    The dynamics of dislocation assemblies in deforming crystals indicates the emergence of collective phenomena, intermittent fluctuations and strain avalanches. In polycrystalline materials, the understanding of plastic deformation mechanisms depends on grasping the role of grain boundaries on dislocation motion. Here the interaction of dislocations and elastic, low-angle grain boundaries is studied in the framework of a discrete dislocation representation. We

  5. Boundary Issues in Global Virtual Teams

    ERIC Educational Resources Information Center

    Wu, Wenxia

    2009-01-01

    The purpose of this dissertation is to develop a better understanding of boundary issues in global virtual teams, especially in higher education settings. Although previous research in the past decade has studied various aspects of global virtual teams, there is no comprehensive review of boundary issues and their impact. This dissertation…

  6. Boundary conditions for the subdiffusion equation

    SciTech Connect

    Shkilev, V. P., E-mail: shkilevv@ukr.net [National Academy of Sciences of Ukraine, Institute of Surface Chemistry (Ukraine)

    2013-04-15

    The boundary conditions for the subdiffusion equations are formulated using the continuous-time random walk model, as well as several versions of the random walk model on an irregular lattice. It is shown that the boundary conditions for the same equation in different models have different forms, and this difference considerably affects the solutions of this equation.

  7. EPA REGION 6 NPL SITE BOUNDARIES

    EPA Science Inventory

    This dataset includes boundaries for sites on the EPA's National Priority List (NPL) as of 05/01/2005, although boundaries for all sites are not included. The field "Status" provides a description of each site's current status, i.e. Proposed, Final, Deleted, o...

  8. Image registration using binary boundary maps

    NASA Technical Reports Server (NTRS)

    Andrus, J. F.; Campbell, C. W.; Jayroe, R. R.

    1978-01-01

    Registration technique that matches binary boundary maps extracted from raw data, rather than matching actual data, is considerably faster than other techniques. Boundary maps, which are digital representations of regions where image amplitudes change significantly, typically represent data compression of 60 to 70 percent. Maps allow average products to be computed with addition rather than multiplication, further reducing computation time.

  9. Boundary integral operators for the heat equation

    Microsoft Academic Search

    Martin Costabel

    1990-01-01

    We study the integral operators on the lateral boundary of a space-time cylinder that are given by the boundary values and the normal derivatives of the single and double layer potentials defined with the fundamental solution of the heat equation. For Lipschitz cylinders we show that the 2×2 matrix of these operators defines a bounded and positive definite bilinear form

  10. Stably stratified boundary layer over longitudinal ridges

    Microsoft Academic Search

    L. Falcomer; V. Armenio; G. C. Carnevale

    2003-01-01

    It is well known that a boundary layer (BL) developing over a topography behaves very differently from an analogous, plane BL. On the other hand, in geophysical applications topographic effects are often predominant. We analyze the turbulent boundary layer developing over a longitudinally-ridged wall in presence of stable stratification. The analysis is performed numerically, using large eddy simulation (LES). A

  11. Evaluation of Boundary Conditions for Computational Aeroacoustics

    NASA Technical Reports Server (NTRS)

    Hixon, R.; Shih, S.-H.; Mankbadi, Reda R.

    1995-01-01

    The performance of three boundary conditions for aeroacoustics were investigated, namely, (1) Giles-1990; (2) Tam and Webb-1993, and (3) Thompson-1987. For each boundary condition, various implementations were tested to study the sensitivity of their performance to the implementation procedure. Details of all implementations are given. Results are shown for the acoustic field of a monopole in a uniform freestream.

  12. Record-Boundary Discovery in Web Documents

    Microsoft Academic Search

    David W. Embley; Y. S. Jiang; Yiu-Kai Ng

    1999-01-01

    Extraction of information from unstructured or semistructured Web documentsoften requires a recognition and delimitation of records. (By "record" we mean agroup of information relevant to some entity.) Without first chunking documentsthat contain multiple records according to record boundaries, extraction of recordinformation will not likely succeed. In this paper we describe a heuristic approach todiscovering record boundaries in Web documents. In

  13. Professional boundary violations: a literature review.

    PubMed

    Manfrin-Ledet, Linda; Porche, Demetrius J; Eymard, Amanda S

    2015-06-01

    The purpose of this article is to review the nursing literature related to professional boundary violations in nursing. A search was conducted using CINAHL, MEDLINE, Ebscohost, and NCSBN. The key words searched were professional boundaries, boundary violation, boundary crossings, nurse, home health nurses, and home nursing. The search returned over 40 publications related specifically to boundary violations and nursing although only four of them are published research studies and one as a dissertation. Seven common characteristics emerged from the nonresearch nursing articles on professional boundaries: (1) Dual relations/role reversal, (2) Gifts and money, (3) Excessive self-disclosure, (4) Secretive behavior, (5) Excessive attention/overinvolvement, (6) Sexual behavior, and (7) Social media. Additional nursing research is greatly needed in the area of professional boundaries. The nurse-patient relationship should always be maintained for the benefit of the patient and not the personal gain of the nurse. Ongoing education in nursing practice regarding professional boundaries is needed. Nurses need to be mindful of state practice acts, codes of conduct, and employer policies. PMID:26034824

  14. SPECTRAL PROBLEMS IN ELASTICITY. SINGULAR BOUNDARY PERTURBATIONS

    E-print Network

    Paris-Sud XI, Université de

    SPECTRAL PROBLEMS IN ELASTICITY. SINGULAR BOUNDARY PERTURBATIONS S.A.NAZAROV AND J optimization and inverse problems. Keywords: Singular perturbations; Spectral problem; Asymptotics be regarded as singular perturbations of the interior piece of the boundary of the body. In this way we can

  15. Special holonomy sigma models with boundaries

    E-print Network

    P. S. Howe; U. Lindstrom; V. Stojevic

    2005-12-15

    A study of (1,1) supersymmetric two-dimensional non-linear sigma models with boundary on special holonomy target spaces is presented. In particular, the consistency of the boundary conditions under the various symmetries is studied. Models both with and without torsion are discussed.

  16. New boundary conditions for granular fluids

    E-print Network

    Mark D. Shattuck

    2007-03-22

    We present experimental evidence, which contradicts the the standard boundary conditions used in continuum theories of non-cohesive granular flows for the velocity normal to a boundary u.n=0, where n points into the fluid. We propose and experimentally verify a new boundary condition for u.n, based on the observation that the boundary cannot exert a tension force Fb on the fluid. The new boundary condition is u.n=0 if Fb.n>=0 else n.P.n=0, where P is the pressure tensor. This is the analog of cavitation in ordinary fluids, but due the lack of attractive forces and dissipation it occurs frequently in granular flows.

  17. The boundary characteristics of lucid dreamers.

    PubMed

    Galvin, F

    1990-06-01

    Based on the previously established personality correlates of frequent lucid dreaming and frequent nightmare dreaming, several hypotheses were generated regarding the boundary characteristics of these dreamers relative to each other and to a control group of non-lucid and comparatively nightmare-free dreamers. The data from Hartmann's Boundary Questionnaire obtained from 40 subjects in each dreamer group (who were individually matched for sex, age, and background as far as possible) were analyzed. The results of the study give evidence that lucid dreamers have "thin" boundaries in many of the same senses that nightmare sufferers do, but can be differentiated from nightmare dreamers by the greater degree of coherence of their psychological sense of self as measured on the Self-Coherence Subscale of the Boundary Questionnaire. The suggestion is made that, given the similarity of "thin" boundaries, perhaps nightmare sufferers could become lucid dreamers and possibly resolve their nightmare condition while in the dream state. PMID:2374791

  18. Tectonic Plates and Plate Boundaries (WMS)

    NSDL National Science Digital Library

    Eric Sokolowsky

    2004-06-14

    The earths crust is constantly in motion. Sections of the crust, called plates, push against each other due to forces from the molten interior of the earth. The areas where these plates collide often have increased volcanic and earthquake activity. These images show the locations of the plates and their boundaries in the earths crust. Convergent boundaries are areas where two plates are pushing against each other and one plate may be subducting under another. Divergent boundaries have two plates pulling away from each other and indicate regions where new land could be created. Transform boundaries are places where two plates are sliding against each other in opposite directions, and diffuse boundaries are places where two plates have the same relative motion. Numerous small microplates have been omitted from the plate image. These images have been derived from images made available by the United States Geological Surveys Earthquake Hazards Program.

  19. Exact boundary condition for time-dependent wave equation based on boundary integral

    NASA Astrophysics Data System (ADS)

    Teng, Zhen-Huan

    2003-09-01

    An exact non-reflecting boundary conditions based on a boundary integral equation or a modified Kirchhoff-type formula is derived for exterior three-dimensional wave equations. The Kirchhoff-type non-reflecting boundary condition is originally proposed by L. Ting and M.J. Miksis [J. Acoust. Soc. Am. 80 (1986) 1825] and numerically tested by D. Givoli and D. Cohen [J. Comput. Phys. 117 (1995) 102] for a spherically symmetric problem. The computational advantage of Ting-Miksis boundary condition is that its temporal non-locality is limited to a fixed amount of past information. However, a long-time instability is exhibited in testing numerical solutions by using a standard non-dissipative finite-difference scheme. The main purpose of this work is to present a new exact boundary condition and to eliminate the long-time instability. The proposed exact boundary condition can be considered as a limit case of Ting-Miksis boundary condition when the two artificial boundaries used in their method approach each other. Our boundary condition is actually a boundary integral equation on a single artificial boundary for wave equations, which is to be solved in conjunction with the interior wave equation. The new boundary condition needs only one artificial boundary, which can be of any shape, i.e., sphere, cubic surface, etc. It keeps all merits of the original Kirchhoff boundary condition such as restricting the temporal non-locality, free of numerical evaluation of any special functions and so on. Numerical approximation to the artificial boundary condition on cubic surface is derived and three-dimensional numerical tests are carried out on the cubic computational domain.

  20. Effects of grain boundary constraint on properties of polycrystalline materials

    NASA Astrophysics Data System (ADS)

    McGarrity, E. S.; McGarrity, K. S.; Duxbury, P. M.; Reed, B. W.; Holm, E. A.

    2007-06-01

    Grain boundary networks are engineered by increasing the fraction of boundaries which exhibit improved properties. Favourable boundaries have either low grain boundary misorientation or they are special boundaries, such as coincident site lattice boundaries. Significant improvement in properties such as corrosion resistance, critical current in superconductors and mechanical strength and toughness occur, provided percolating grain or grain boundary structures can be engineered. We develop computational models for grain boundary engineered polycrystals and demonstrate that grain boundary constraints modify the behaviour near the percolation threshold. We postulate that this is due to an enhanced clustering of weak boundaries induced by grain boundary constraints. In random grain structures the fraction of strong grain boundaries may be measured in two ways, either the length fraction, c, or the edge fraction ce. We find that grain boundary constraint shifts the length fraction threshold, c*, of Potts model polycrystals to higher values, while the edge fraction, ce*, remains almost the same in both correlated and uncorrelated grain structures.