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1

Mineralogical and Geochemical Anomalous Data of the K-T (Cretaceous-Tertiary) Boundary Samples.  

National Technical Information Service (NTIS)

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 di...

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

1988-01-01

2

Extended Period of K/T (Cretaceous/Tertiary) Boundary Mass Extinction in the Marine Realm.  

National Technical Information Service (NTIS)

The Cretaceous/Tertiary (K/T) boundary mass extinction has been widely recognized as a nearly instantaneous catastrophy among marine plankton such as foraminifera. However, the suddenness of this extinction event may have been overemphasized because most ...

G. Keller

1988-01-01

3

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

Microsoft Academic Search

The K\\/T transition is under geoscientific focus since many years. Ever since the discovery of the Chicxulub- Impact theory in the early 1980s, its ctrater and its subsurface structure in the late 1990s many scientists and media, Hollywood, and the general public have become convinced that a large meteorite caused the K\\/T boundary and killed the dinosaurs and other organisms

M. Harting; F. A. Wittler

2006-01-01

4

Impact and Extinction Signatures in Complete Cretaceous-Tertiary (K-T) Boundary Sections.  

National Technical Information Service (NTIS)

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 wer...

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

1988-01-01

5

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

USGS Publications Warehouse

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

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

2007-01-01

6

Cretaceous-Tertiary Boundary Biotic Crisis in the Basque Country.  

National Technical Information Service (NTIS)

The Zumaya section has been selected as a classic locality for the study of the Cretaceous-Tertiary (K-T) boundary due to its richness in microfaune, macrofaune, and nannoflora. The sections present similar good conditions for the study of the K-T boundar...

M. A. Lamolda

1988-01-01

7

Rock magnetic signature of the Cretaceous-Tertiary boundary  

Microsoft Academic Search

Black magnetic microspherules, commonly found in Cretaceous-Tertiary (K-T) boundary sediments and believed to be of an impact melt origin, were found to be responsible for a strong magnetic anomaly at the K-T boundary in Petriccio, Italy, and in almost all Deep Sea Drilling Project (DSDP) sediment cores investigated in which the K-T boundary was present. The enriched concentrations of magnetic

Horst-Ulrich Worm; Subir K. Banerjee

1987-01-01

8

Cretaceous-Tertiary (K/T) Impact: One or More Source Craters.  

National Technical Information Service (NTIS)

The Cretaceous-Tertiary (K/T) boundary is marked by signs of a worldwide catastrophe, marking the demise of more than 50 percent of all living species. Ever since Alvarez et al. found an enrichment of IR and other siderophile elements in rocks marking the...

C. Koeberl

1992-01-01

9

Seawater Strontium Isotopes at the Cretaceous-Tertiary Boundary.  

National Technical Information Service (NTIS)

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, ...

J. D. MacDougall E. Martin

1988-01-01

10

The Cretaceous/ Tertiary Boundary At Iridium Hill, Garfield County, Montana  

NSDL National Science Digital Library

The goal of this virtual field trip to Iridium Hill, Montana is to investigate the disappearance of dinosaur fossils above the Cretaceous/ Tertiary boundary. The site provides rock outcrop photos of Cretaceous and Tertiary strata (Hell Creek and Fort Union Formations), stratigraphic sections and supporting text for this classic iridium-bearing locality. Topics include the K/T boundary, iridium concentrations, stratigraphy, sedimentology and, fluvial and lacustrine depositional environments.

Limited, Athro

11

Step-Wise Extinctions at the Cretaceous-Tertiary Boundary and Their Climatic Implications.  

National Technical Information Service (NTIS)

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...

F. J. R. Maurrasse

1988-01-01

12

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

NASA Technical Reports Server (NTRS)

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

Koeberl, Christian

1992-01-01

13

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)

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.

Izett, G. A.

1988-01-01

14

Trace Element and Isotope Geochemistry of Cretaceous-Tertiary Boundary Sediments: Identification of Extra-Terrestrial and Volcanic Components.  

National Technical Information Service (NTIS)

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...

S. V. Margolis E. F. Doehne

1988-01-01

15

The Cretaceous\\/Tertiary boundary mass extinction in planktic foraminifera at Agost, (Spain)  

Microsoft Academic Search

The planktic foraminiferal mass extinction across the Cretaceous\\/Tertiary boundary at Agost (Spain) occurred over an extended period, with 7 species disappearing in the late Maastrichtian, 47 species extinct at the K\\/T boundary and 16 ranging into the earliest Danian. The species that became extinct at the K\\/T boundary are large, complex tropical and subtropical forms dwelling in deep and intermediate

Eustoquio Molina; Ignacio Arenillas; José A. Arz

1996-01-01

16

Mineralogy of Cretaceous/Tertiary Boundary Clays in the Chicxulub Structure in Northern Yucatan (Abstract Only).  

National Technical Information Service (NTIS)

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 t...

D. W. Ming V. L. Sharpton B. C. Schuraytz

1991-01-01

17

The Cretaceous\\/Tertiary boundary event in New Zealand: Profiling mass extinction  

Microsoft Academic Search

Of over 20 known Cretaceous\\/Tertiary (K\\/T) boundary sections in the New Zealand region, 6 in the northern South Island were selected for detailed biostratigraphic and paleoenvironmental study because of their apparent stratigraphic completeness and the range of depositional environments represented. These sections represent the only known southern high?latitude (55–60°S) transect of the K\\/T boundary transition from continental slope to terrestrial

Christopher J. Hollis

2003-01-01

18

The debate over the Cretaceous-Tertiary boundary  

NASA Astrophysics Data System (ADS)

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.

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

19

The debate over the Cretaceous-Tertiary boundary  

NASA Technical Reports Server (NTRS)

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.

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

1988-01-01

20

The Cretaceous\\/Tertiary boundary event in Ecuador: reduced biotic effects due to eastern boundary current setting  

Microsoft Academic Search

A multidisciplinary study of a new Cretaceous-Tertiary (K\\/T) boundary section near Guayaquil, Ecuador, reveals an unusually cool water, low diversity planktic foraminiferal fauna and a high diversity radiolarian fauna similar to those found in southern high-latitude K\\/T sequences despite the fact that this section was deposited near the Cretaceous equator. The K\\/T boundary is located by planktic foraminifera within a

Gerta Keller; Thierry Adatte; Chris Hollis; Martha Ordóñez; Italo Zambrano; Nelson Jiménez; Wolfgang Stinnesbeck; Antinor Aleman; Wendy Hale-Erlich

1997-01-01

21

Magnesioferrite from the Cretaceous-Tertiary boundary, Caravaca, Spain  

USGS Publications Warehouse

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

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

1986-01-01

22

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

Microsoft Academic Search

THEORIES that explain the extinctions characterizing the Cretaceous\\/Tertiary (K\\/T) boundary1-3 need to be tested by analyses of thoroughly sampled biotas. Palynological studies are the primary means for stratigraphic placement of the terrestrial boundary and for estimates of plant extinction4-12, but have not been combined with quantitative analyses of fossil leaves (megaflora). Megafloral studies complement palynology by representing local floras with

Kirk R. Johnson; Douglas J. Nichols; Moses Attrep; Charles J. Orth

1989-01-01

23

Cretaceous-Tertiary boundary planktic foraminiferal mass extinction and biochronology at La Ceiba and Bochil, Mexico, and El Kef, Tunisia  

Microsoft Academic Search

Micropaleontology studies across the Cretaceous-Tertiary (K-T) boundary from sections at La Ceiba, Bochil, Mexico, and El Kef, Tunisia, suggest a close cause and effect relationship between the Chicxulub impact and the K-T planktic foraminiferal mass extinction. The K-T planktic foraminiferal biostratigraphy and assemblage turn- over in Mexico was examined and the approximate deposition timing of K-T-related material (clastic unit) was

Ignacio Arenillas; Laia Alegret; Carlos Liesa; Alfonso Melendez; Ana R. Soria

24

Major wildfires at the Cretaceous-Tertiary boundary  

NASA Technical Reports Server (NTRS)

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.

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

1991-01-01

25

Emplacement of cretaceous-tertiary boundary shocked quartz from chicxulub crater.  

PubMed

Observations on shocked quartz in Cretaceous-Tertiary (K-T) boundary sediments compellingly tied to Chicxulub crater raise three problems. First, in North America shocked quartz occurs above the main K-T ejecta layer. Second, shocked quartz is more abundant west than east of Chicxulub. Third, shocked quartz reached distances requiring initial velocities up to 8 kilometers per second, corresponding to shock pressures that would produce melt, not the moderate-pressure shock lamellae observed. Shock devolatilization and the expansion of carbon dioxide and water from impacted wet carbonate, producing a warm, accelerating fireball after the initial hot fireball of silicate vapor, may explain all three problems. PMID:17807728

Alvarez, W; Claeys, P; Kieffer, S W

1995-08-18

26

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

Microsoft Academic Search

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

Dean A. Pearson; Terry Schaefer; Kirk R. Johnson; Douglas J. Nichols

2001-01-01

27

Ignition of global wildfires at the Cretaceous/Tertiary boundary  

NASA Technical Reports Server (NTRS)

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.

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

1990-01-01

28

Vertebrate extinctions and survival across the Cretaceous-Tertiary boundary  

NASA Astrophysics Data System (ADS)

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.

Buffetaut, Eric

1990-01-01

29

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

Microsoft Academic Search

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

Alfonso Pardo; Thierry Adatte; Gerta Keller; Hedi Oberhänsli

1999-01-01

30

Presence of an iron-rich nanophase material in the upper layer of the Cretaceous-Tertiary boundary clay  

Microsoft Academic Search

We report new geochemical evidence from ten Cretaceous-Tertiary boundary sites in North America and Europe, indicating the presence of a material remnant of a large asteroid or comet that struck the Earth at 65.0 Ma. Mössbauer spectroscopic data reveals that a ubiquitous iron-rich nanophase material exists at the uppermost part of the K-T boundary layer in the Western Hemisphere and

Thomas J. Wdowiak; Lawrence P. Armendarez; David G. Agresti; Manson L. Wade; Suzanne Y. Wdowiak; Philippe Claeys; Glenn Izett

2001-01-01

31

Comparison of the Cretaceous-Tertiary Boundary Impact Events and the 0.77-Ma Australasian Tektite Event: Relevance to Mass Extinction.  

National Technical Information Service (NTIS)

Cretaceous-Tertiary (K-T) boundary sections provide records of events of the K-T transition: retreat of the Cretaceous marine sea that left continents dotted with peat swamps, and impacts that left craters on exposed land and the ocean floor. In order to ...

E. C. T. Chao

1992-01-01

32

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

Microsoft Academic Search

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

G. Keller; L. Li; N. MacLeod

1996-01-01

33

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

USGS Publications Warehouse

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.

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

2001-01-01

34

Modelling of Dispersal and Deposition of Impact Glass Spherules from the Cretaceous-Tertiary Boundary Deposit.  

National Technical Information Service (NTIS)

The dispersal of glass spherules or tektites from a bolide impact with the Earth is modelled as ballistic trajectories in standard atmosphere. Ballistic dispersal of Cretaceous-Tertiary boundary impact glass spherules found in Haiti and Mimbral, Mexico re...

J. M. Espindola S. Carey H. Sigurdsson

1993-01-01

35

New links between the Chicxulub impact structure and the Cretaceous/Tertiary boundary  

USGS Publications Warehouse

THE 200-km-diameter Chicxulub structure1-3 in northern Yucatan, Mexico has emerged as the prime candidate for the Cretaceous/Tertiary (K/T) boundary impact crater3-6. Concentric geophysical anomalies associated with enigmatic occurrences of Upper Cretaceous breccias and andesitic rocks led Penfield and Camargo1 to suspect that this structure was a buried impact basin. More recently, the discovery of shocked quartz grains in a Chicxulub breccia3, and chemical similarities between Chicxulub rocks and K/T tektite-like glasses3-6 have been advanced as evidence that the Chicxulub structure is a K/T impact site. Here we present evidence from core samples that Chicxulub is indeed a K/T source crater, and can apparently account for all the evidence of impact distributed globally at the K/T boundary without the need for simultaneous multiple impacts or comet showers. Shocked breccia clasts found in the cores are similar to shocked lithic fragments found worldwide in the K/T boundary ejecta layer7,8. The Chicxulub melt rocks that we studied contain anomalously high levels of iridium (up to 13.5 parts per 109), also consistent with the indium-enriched K/T boundary layer9. Our best estimate of the crystallization age of these melt rocks, as determined by 40Ar/39Ar analyses, is 65.2??0.4 (1??) Myr, in good agreement with the mean plateau age of 64.98 ?? 0.05 Myr recently reported10. Furthermore, these melt rocks acquired a remanent magnetization indicating that they cooled during an episode of reversed geomagnetic polarity. The only such episode consistent with 40Ar/39Ar constraints is chron 29R, which includes the K/T boundary.

Sharpton, V. L.; Dalrymple, G. B.; Marin, L. E.; Ryder, G.; Schuraytz, B. C.; Urrutia-Fucugauchi, J.

1992-01-01

36

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

USGS Publications Warehouse

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

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

1989-01-01

37

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

PubMed

Large amounts of apparently extraterrestrial amino acids have been detected recently in rocks at the Cretaceous/Tertiary (K/T) boundary at Stevns Klint, Denmark. The amino acids were found a few tens of centimetres above and below the boundary layer, but were absent in the boundary clay itself. If one supposes that these compounds were carried to the Earth by the giant meteorite thought to have impacted at the end of the Cretaceous, some puzzling questions are raised: why weren't the amino acids incinerated in the impact, and why are they not present in the boundary clay itself? Here we suggest that the amino acids were actually deposited with the dust from a giant comet trapped in the inner Solar System, a fragment of which comprised the K/T impactor. Amino acids or their precursors in the comet dust would have been swept up by the Earth both before and after the impact, but any conveyed by the impactor itself would have been destroyed. The observed amino acid layers would thus have been deposited without an impact. PMID:11536472

Zahnle, K; Grinspoon, D

1990-11-01

38

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

USGS Publications Warehouse

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.

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

1989-01-01

39

Dinosaur Bone Beds and Mass Mortality: Implications for the K-T (Cretaceous-Tertiary) Extinction.  

National Technical Information Service (NTIS)

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 ma...

K. Carpenter

1988-01-01

40

Major wildfires at the Cretaceous-Tertiary boundary  

NASA Technical Reports Server (NTRS)

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.

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

1989-01-01

41

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

USGS Publications Warehouse

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.

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

1992-01-01

42

Ocean alkalinity and the Cretaceous/Tertiary boundary  

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

43

Geochemical evidence for suppression of pelagic marine productivity at the Cretaceous/Tertiary boundary  

USGS Publications Warehouse

The normal, biologically productive ocean is characterized by a gradient of the 13C/12C ratio from surface to deep waters. Here we present stable isotope data from planktonic and benthic micro-fossils across the Cretaceous/Tertiary boundary in the North pacific, which reveal a rapid and complete breakdown in this biologically mediated gradient. The fluxes of barium (a proxy for organic carbon) and CaCO3 also decrease significantly at the time of the major marine plankton extinctions. The implied substantial reduction in oceanic primary productivity persisted for ???0.5 Myr before the carbon isotope gradient was gradually re-established. In addition, the stable isotope and preservational data indicate that environmental change, including cooling, began at least 200 kyr before the Cretaceous/Tertiary boundary, and a peak warming of ???3 ??C occurred 600 kyr after the boundary event. ?? 1989 Nature Publishing Group.

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

1989-01-01

44

38. SUMMARY OF CRETACEOUS\\/TERTIARY BOUNDARY STUDIES, DEEP SEA DRILLING PROJECT SITE 577, SHATSKY RISE1  

Microsoft Academic Search

Continuous, expanded, and undisturbed Cretaceous\\/Tertiary boundary sequences were recovered in three holes drilled at Deep Sea Drilling Project Site 577 (32°26.51'N, 157°43.40'E) on Shatsky Rise. The Cretaceous\\/Tertiary boundary lies at a sub-bottom depth of approximately 109.6 m in a white calcareous ooze. It was identified biostrati- graphically within the magnetic C-29R subchron using nannofossils and is characterized by an iridium

Audrey A. Wright; Ulrich Bleil; Simonetta Monechi; Helen V. Michel; N. J. Shackleton; Bernd R. T. Simoneit; James C. Zachos

1985-01-01

45

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

USGS Publications Warehouse

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.

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

46

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

PubMed Central

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.”

Wolfe, Jack A.; Upchurch, Garland R.

1987-01-01

47

A new Cretaceous-Tertiary boundary site at Flaxbourne River, New Zealand - Biostratigraphy and geochemistry  

NASA Technical Reports Server (NTRS)

On the basis of biostratigraphy data, it is shown that the Flaxbourne River Cretaceous-Tertiary boundary is among the most complete and least disturbed marine sequences yet found; this is particularly true with respect to its post-Ir anomaly and prelowermost Paleocene sequence. INAA and ICP analyses reveal that the boundary clay is also enriched in Cr and Ni, mainly from meteoritic material, and As, Co, Cu, Sb, and Zn from terrestrial sources. It is found that Zn/Sb, As/Sb, and Zn/As ratios generally fall between crustal and oceanic values, suggesting contributions from both sources.

Strong, C. P.; Brooks, Robert R.; Wilson, Shane M.; Reeves, Roger D.; Orth, Charles J.

1987-01-01

48

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

USGS Publications Warehouse

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.

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

1984-01-01

49

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

NASA Technical Reports Server (NTRS)

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.

Pope, Kevin O.

1995-01-01

50

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

NASA Astrophysics Data System (ADS)

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.

Pope, Kevin O.

1994-05-01

51

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

NASA Technical Reports Server (NTRS)

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.

Pope, Kevin O.

1994-01-01

52

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

NASA Astrophysics Data System (ADS)

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

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

1994-11-01

53

Spheroids at the Cretaceous-Tertiary boundary are altered impact droplets of basaltic composition  

SciTech Connect

Sand-size spheroids of K-feldspar in the Cretaceous-Tertiary (C-T) boundary clay at Caravaca, southern Spain, were interpreted by Smit and Klaver as having solidified from a melt resulting from the impact of a large extraterrestrial body. Sand-size spheroids of K-feldspar, glauconite, and magnetite-quartz have been found in the C-T boundary clay in northern Italy, and spheroids of K-feldspar and pyrite were found in the boundary clay at Deep Sea Drilling Project Site 465A, in the central Pacific. These spheroids have textures similar to those of rapidly crystallized feldspar and mafic silicates. They are interpreted as diagenetically altered microcrystalline spherules of basaltic composition produced by the impact of a large asteroid in an ocean basin at the end of the Cretaceous. They are analogous to the glassy microtektites produced by impacts on more siliceous target rocks. 21 references, 4 figures.

Montanari, A.; Hay, R.L.; Alvarez, W.; Asaro, F.; Michel, H.V.; Alvarez, L.W.; Smit, J.

1983-11-01

54

Mineralogic evidence for an impact event at the cretaceous-tertiary boundary  

USGS Publications Warehouse

A thin claystone layer found in nonmarine rocks at the palynological Cretaceous-Tertiary boundary in eastern Montana contains an anomalously high value of iridium. The nonclay fraction is mostly quartz with minor feldspar, and some of these grains display planar features. These planar features are related to specific crystallographic directions in the quartz lattice. The shocked quartz grains also exhibit asterism and have lowered refractive indices. All these mineralogical features are characteristic of shock metamorphism and are compelling evidence that the shocked grains are the product of a high velocity impact between a large extraterrestrial body and the earth. The shocked minerals represent silicic target material injected into the stratosphere by the impact of the projectile.

Bohor, B. F.; Foord, E. E.; Modreski, P. J.; Triplehorn, D. M.

1984-01-01

55

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

USGS Publications Warehouse

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

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

1994-01-01

56

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

SciTech Connect

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

Blum, J.D.; Chamberlain, C.P. (Dartmouth Coll, Hanover, NH (United States))

1992-08-21

57

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

SciTech Connect

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.

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

58

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

NASA Astrophysics Data System (ADS)

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

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

1986-11-01

59

Chicxulub impact predates the K-T boundary mass extinction  

PubMed Central

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 ?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.

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

2004-01-01

60

Chicxulub impact predates the K-T boundary mass extinction.  

PubMed

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

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

2004-03-16

61

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

NASA Technical Reports Server (NTRS)

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.

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

1991-01-01

62

Elemental anomalies at the Cretaceous-Tertiary boundary, Woodside Creek, New Zealand  

NASA Astrophysics Data System (ADS)

Iridium and 26 other elements were determined in shale from the Cretaceous-Tertiary boundary at the locus classicus (for iridium anomalies) at Woodside Creek, New Zealand. Iridium, gold, copper, cobalt, chromium, nickel, arsenic, molybdenum, and iron were enriched in the basal 2 millimeters of the 8-millimeter shale parting as compared with the rest of the stratigraphic column. No other shale partings in the column had anomalous concentrations of any element when the data were expressed on a carbonate-free basis. The boundary material showed striking compositional similarities with the Stevns Klint Danish boundary shale. Elemental concentrations were in general much higher in the New Zealand material than in nonboundary shales from elsewhere in the world. The high concentration of iridium (153 nanograms per gram) in the basal layer of the boundary, together with the enrichment of other siderophile elements supports the idea of an exterrestrial source for much of the material. The iridium/gold ratio of 2.1 is also in accordance with such a source. The iridium content of the basal layer is higher than for any other marine boundary shale obtained on land. The integrated iridium value is 187 nanograms per square centimeter of boundary surface.

Brooks, R. R.; Reeves, R. D.; Neall, V. E.; Lee, J.; Yang, X.-H.; Ryan, D. E.; Holzbecher, J.; Collen, J. D.

1984-11-01

63

Review of The Hell Creek Formation and the Cretaceous-Tertiary Boundary in the Northern Great Plains: An Integrated Continental Record of the End of the Cretaceous Edited by Joseph H. Hartman, Kirk R. Johnson, And Douglas J. Nichols  

Microsoft Academic Search

The Hell Creek Formation (especially near the Fork Peck Reservoir and the Cedar Creek Anticline in east-central Montana) has been extensively studied over the years to evaluate changes in terrestrial floras and faunas across the Cretaceous-Tertiary (K-T) boundary. The research round in this volume, however, contains important new data from the lesser studied eastern outcrop area of western North Dakota,

Russell Jacobson

2005-01-01

64

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

NASA Technical Reports Server (NTRS)

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

Alvarez, Walter; Asaro, Frank; Montanari, Alessandro

1990-01-01

65

The Cretaceous-Tertiary boundary at Gubbio revisited - Vertical extent of the Ir anomaly  

NASA Astrophysics Data System (ADS)

The classical Gubbio (Italy) Cretaceous-Tertiary boundary section has been resampled for both magnetostratigraphy and iridium. Paleomagnetic samples were taken over 7 m in the Maastrichtian and 6 m in the Paleocene. Previous results obtained a decade ago are confirmed. The reversal sequence is well defined and the individual reversals are somewhat more precisely located. A noticeable difference is the location of the position of the 29N/29R limit which may be lowered by 20-30 cm in the stratigraphic column. This would imply that the KTB occurs near the middle of chron 29 R. Iridium measurements were made on samples from both shales and surrounding limestone beds from 2 m below to 3 m above the boundary: these measurements indicate that Ir is associated with clay minerals. Concentrations in the two types of samples are indeed compatible when reduced to a carbonate-free basis. Iridium concentrations stand above background over almost 3 m of section, corresponding to half a million years based on magnetostratigraphy. This is likely to indicate a protracted duration of the (external or internal) source of iridium, on top of which the main (short-lived) KTB anomaly proper stands.

Rocchia, Robert; Bonte, Ph.; Jehanno, C.; Boclet, D.; Chen, Yan

1990-08-01

66

The Cretaceous-Tertiary Boundary and the Last of the Dinosaurs  

Microsoft Academic Search

Disaster theories of the K-T extinctions, more specifically dinosaur extinctions, are presently engendering much controversy. They require (inter alia) that those extinctions were sudden and simultaneous worldwide and that they coincided with an allegedly causal disaster at the K-T boundary. This paper reviews the evidence for and against those temporal requirements. The other major requirement is of a biological nature,

A. J. Charig

1989-01-01

67

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

PubMed

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

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

1992-08-01

68

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

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.

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

69

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

NASA Technical Reports Server (NTRS)

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.

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

1993-01-01

70

Impact Mineralogy and Chemistry of the Cretaceous-Tertiary Boundary at DSDP Site 576.  

National Technical Information Service (NTIS)

We have identified the K/T boundary in pelagic clay sediments from cores at DSDP Site 576 in the western North Pacific. Detailed geochemical and trace mineralogical analyses of this boundary section are in progress and initial results indicate similaritie...

J. A. Bostwick F. T. Kyte

1993-01-01

71

The Cretaceous/Tertiary Extinction Controversy Reconsidered.  

ERIC Educational Resources Information Center

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)

McCartney, Kevin; Nienstedt, Jeffrey

1986-01-01

72

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

NASA Technical Reports Server (NTRS)

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

Ryder, Graham

1996-01-01

73

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

NASA Astrophysics Data System (ADS)

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.

Adatte, T.; Keller, G.

2012-04-01

74

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

NASA Technical Reports Server (NTRS)

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.

Ward, Peter D.; Macleod, Kenneth

1988-01-01

75

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

USGS Publications Warehouse

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

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

1986-01-01

76

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

Microsoft Academic Search

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

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

2008-01-01

77

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

NASA Technical Reports Server (NTRS)

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.

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

1988-01-01

78

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

NASA Technical Reports Server (NTRS)

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

Bostwick, Jennifer A.; Kyte, Frank T.

1993-01-01

79

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

USGS Publications Warehouse

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

Izett, G. A.

1991-01-01

80

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

NASA Technical Reports Server (NTRS)

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

Keller, G.

1988-01-01

81

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

PubMed

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

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

2007-11-01

82

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

NASA Technical Reports Server (NTRS)

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).

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

1988-01-01

83

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

NASA Technical Reports Server (NTRS)

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

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

2003-01-01

84

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

NASA Technical Reports Server (NTRS)

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.

Keller, G.; Benjamini, C.

1988-01-01

85

The K\\/T boundary at Beloc (Haiti): Compared stratigraphic distributions of the boundary markers  

Microsoft Academic Search

At Beloc, Haiti the Cretaceous-Tertiary boundary (KTB) is characterized by a spherule bed containing glass particles. These particles are considered by some authors as remains of tektites resulting from a nearby impact. However, because of the stratigraphic complexity of the Beloc sections the genetic link between the KTB cosmic event and the spherule bed is not obvious. In this paper,

Hugues Leroux; Robert Rocchia; Laurence Froget; Xavier Orue-Etxebarria; Jean-Claude Doukhan; Eric Robin

1995-01-01

86

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)

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.

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

2003-01-01

87

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

NASA Technical Reports Server (NTRS)

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

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

1997-01-01

88

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

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

89

Deccan volcanism and K-T boundary signatures  

NASA Technical Reports Server (NTRS)

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.

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

1988-01-01

90

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

PubMed

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

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

1992-08-14

91

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

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

92

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

USGS Publications Warehouse

Isotopic ratios and trace element abundances were measured on samples of Ir-enriched clay at the Cretaceous-Tertiary boundary, and in carbonate and marl from 5 cm below and 3 cm above the boundary. Samples were leached with acetic acid to remove carbonate, and with hydrochloric acid. Leachates and residues were measured. The Sr, Nd, O and H isotopic compositions of the boundary clay residues are distinct from those of the stratigraphically neighboring materials. The data indicate that most of the clay material was derived from a terrestrial source with relatively low 87Sr/86Sr and high 143Nd/144Nd ratios. The ??18O data suggest that the detritus has been modified by submarine weathering. K-Ca and Rb-Sr systematics, as well as O isotope ratios of K-feldspar spherules within the boundary clay, suggest that they are predominantly authigenic and may have formed after the time of deposition. However, Sm-Nd and Rb-Sr isotopic data indicate that the spherules contain relict material that provides information on the nature of the original detritus. The isotopic evidence for foreign terrestrial detritus in the boundary clay, the low rare earth element concentrations and high Ni concentration, support the hypothesis of a terminal Cretaceous asteroidal impact that produced a global layer of fallout. The data are most easily explained if the impact site was on oceanic crust rather than continental crust, and if a substantial fraction of the fallout was derived from relatively deep within the lithosphere (>3 km). This would probably require a single large impactor. ?? 1983.

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

1983-01-01

93

THE K\\/T BOUNDARY IMPACT LAYER IN CUBA: UPDATE OF AN  

Microsoft Academic Search

The Cretaceous\\/Tertiary Boundary (KTB) bolide impactor that allegedly created the Chixulub crater in Yucatan, should have produced a series of events that must be recorded in the sedimentary sections of the surrounding areas. Cuba is an excellent spot to study these sediments and events, as in the territory of the island, there are abundant deposits of the Latest Cretaceous and

M. Iturralde-Vinent; D. García Delgado; C. Díaz Otero; R. Rojas Consuegra; R. Tada; H. Takayama; S. Kiyokawa; San Miguel de Padron

94

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

NASA Technical Reports Server (NTRS)

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

Briggs, J. C.

1991-01-01

95

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

USGS Publications Warehouse

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

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

1987-01-01

96

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

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

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

1991-01-01

97

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

NASA Technical Reports Server (NTRS)

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

Rampino, Michael R.; Volk, Tyler

1988-01-01

98

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

NASA Astrophysics Data System (ADS)

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 1031 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.

Pope, Kevin O.

1997-08-01

99

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

NASA Astrophysics Data System (ADS)

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

Brett, Robin

1992-09-01

100

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

USGS Publications Warehouse

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

Brett, R.

1992-01-01

101

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

Microsoft Academic Search

It is generally believed that the Chicxulub impact caused the Cretaceous-Tertiary (K-T) mass extinction. However, strong evidence from Mexico and Texas shows that this impact predates the K-T boundary and caused no species extinctions or any other significant environmental effects (Keller et al., 2003, 2007). The Chicxulub impact and K-T mass extinction are thus two separate and unrelated events and

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

2008-01-01

102

Trace-Element Composition of Chicxulub Crater Melt Rock, K/T Tektites and Yucatan Basement.  

National Technical Information Service (NTIS)

The Cretaceous/Tertiary (K/T) boundary Chicxulub impact is the best preserved large impact in the geologic record. The Chicxulub crater has been buried with no apparent erosion of its intracrater deposits, and its ejecta blanket is known and is well prese...

A. R. Hildebrand D. C. Gregoire M. Attrep P. Claeys C. M. Thompson

1993-01-01

103

There are no Fullerenes in the K-T Boundary Layer  

Microsoft Academic Search

Careful re-examination of the Cretacous-Tertiary boundary layer material that was reported earlier to contain C60, confirms that there is a peak in the HPLC of the extract having a retention time similar to that of C60 (the basis of the earlier claim). However, mass spectrometric analysis shows this to be merely a mixture of hydrocarbons. No traces of either C60

Roger Taylor; Alaa K. Abdul-Sada

2000-01-01

104

The global Cretaceous-Tertiary fire: Biomass or fossil carbon  

NASA Technical Reports Server (NTRS)

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

Gilmour, Iain; Guenther, Frank

1988-01-01

105

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

NASA Astrophysics Data System (ADS)

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.

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

2010-05-01

106

Determination of rapid Deccan eruptions across the Cretaceous-Tertiary boundary using paleomagnetic secular variation: 2. Constraints from analysis of eight new sections and synthesis for a 3500-m-thick composite section  

NASA Astrophysics Data System (ADS)

The present paper completes a restudy of the main lava pile in the Deccan flood basalt province (trap) of India. Chenet et al. (2008) reported results from the upper third, and this paper reports the lower two thirds of the 3500-m-thick composite section. The methods employed are the same, i.e., combined use of petrology, volcanology, chemostratigraphy, morphology, K-Ar absolute dating, study of sedimentary alteration horizons, and as the main correlation tool, analysis of detailed paleomagnetic remanence directions. The thickness and volume of the flood basalt province studied in this way are therefore tripled. A total of 169 sites from eight new sections are reported in this paper. Together with the results of Chenet et al. (2008), these data represent in total 70% of the 3500-m combined section of the main Deccan traps province. This lava pile was erupted in some 30 major eruptive periods or single eruptive events (SEE), each with volumes ranging from 1000 to 20,000 km3 and 41 individual lava units with a typical volume of 1300 km3. Paleomagnetic analysis shows that some SEEs with thicknesses attaining 200 m were emplaced over distances in excess of 100 km (both likely underestimates, due to outcrop conditions) and up to 800 km. The total time of emission of all combined SEEs could have been (much) less than 10 ka, with most of the time recorded in a very small number of intervening alteration levels marking periods of volcanic quiescence (so-called "big red boles"). The number of boles, thickness of the pulses, and morphology of the traps suggest that eruptive fluxes and volumes were larger in the older formations and slowed down with more and longer quiescence periods in the end. On the basis of geochronologic results published by Chenet et al. (2007) and paleontological results from Keller et al. (2008), we propose that volcanism occurred in three rather short, discrete phases or megapulses, an early one at ˜67.5 ± 1 Ma near the C30r/C30n transition and the two largest around 65 ± 1 Ma, one entirely within C29r just before the K-T boundary, the other shortly afterward spanning the C29r/C29n reversal. We next estimate sulfur dioxide (likely a major agent of environmental stress) amounts and fluxes released by SEEs: they would have ranged from 5 to 100 Gt and 0.1 to 1 Gt/a, respectively, over durations possibly as short as 100 years for each SEE. The chemical input of the Chicxulub impact would have been on the same order as that of a very large single pulse. The impact, therefore, appears as important but incremental, neither the sole nor main cause of the Cretaceous-Tertiary mass extinctions.

Chenet, Anne-Lise; Courtillot, Vincent; Fluteau, FréDéRic; GéRard, Martine; Quidelleur, Xavier; Khadri, S. F. R.; Subbarao, K. V.; Thordarson, Thor

2009-06-01

107

Paleoecology of the Cretaceous–Tertiary mass extinction in planktonic foraminifera  

Microsoft Academic Search

Paleobiogeographic patterns of the Cretaceous–Tertiary (K–T) mass extinction in planktonic foraminifera in Tunisia, spanning environments from open marine upper bathyal, to shelf and shallow marginal settings, indicate a surprisingly selective and environmentally mediated mass extinction. This selectivity is apparent in all of the environmental proxies used to evaluate the mass extinction, including species richness, ecological generalists, ecological specialists, surface and

Gerta Keller; Thierry Adatte; W. Stinnesbeck; Valeria Luciani; Narjess Karoui-Yaakoub; Dalila Zaghbib-Turki

2002-01-01

108

Barium anomaly preceding K/T boundary: possible causes and implications on end Cretaceous events of K/T sections in Cauvery basin (India), Israel, NE-Mexico and Guatemala  

NASA Astrophysics Data System (ADS)

Maastrichtian Danian strata of the Cauvery basin as well as selected sections of NE-Mexico, Guatemala and Israel record Ba anomalies, away from the Cretaceous/Tertiary boundary (KTB) in addition to common occurrences of geochemical and stable isotopic anomalies across the KTB. Ba anomalies were recorded in monotonous shallow marine sandstones of the Cauvery basin (south India) which contain minor amounts of Ba-orthoclase. Barium anomalies were observed also in shallow marine carbonates in sections of Israel, NE-Mexico and Guatemala. Calculation of excess Ba with reference to PAAS (Post-Archaen Average Australian Shale), comparison of coeval geochemical anomalies, depositional pattern and associated petrographic and mineralogical features of the Cauvery basin revealed that while a first Ba peak was related to detrital influx, the second Ba peak was coincident with sea level fall which in turn may have been influenced by emission of volatile hydrocarbons and resultant climatic changes. In view of intrinsic involvement of Ba in various geochemical processes and occurrence of Ba anomalies in K/T sites distributed around the world (NE-Mexico, Guatemala and Israel), it is suggested that probable causes of such widespread Ba-anomalies should be taken into consideration while analyzing end Cretaceous events. These observations support the views espoused by many workers who have stated that the K/T boundary was also accompanied by many non-catastrophic events that might have contributed to environmental stress on marine fauna, as a result of which selective multi-stage extinctions occurred.

Ramkumar, M.; Harting, M.; Stüben, D.

2005-07-01

109

The Cretaceous/Tertiary Extinction Controversy.  

ERIC Educational Resources Information Center

The cause of the Cretaceous/Tertiary extinction has become a major geologic controversy. Current evidence for the two opposing views is reviewed to provide an introduction to the controversy and to form the basis for a seminar of discussion topic. (Author/JN)

McCartney, Kevin

1984-01-01

110

Rocks, Resolution, and the Record at the Terrestrial K/T (Cretaceous/Tertiary) Boundary, Eastern Montana and Western North Dakota.  

National Technical Information Service (NTIS)

Reconstructions of mass extinction events are based upon faunal patterns, reconstructed from numerical and diversity data ultimately derived from rocks. It follows that geological complexity must not be subsumed in the desire to establish patterns. This i...

D. E. Fastovsky

1988-01-01

111

Dawn of echinoid nonplanktotrophy: Coordinated shifts in development indicate environmental instability prior to the K-T boundary  

NASA Astrophysics Data System (ADS)

The fossil record of echinoids indicates that a nonplanktotrophic developmental pattern first evolved, and was independently adopted, in nine clades immediately prior to the Cretaceous-Tertiary boundary. These near-synchronous shifts in developmental mode, which occurred over a broad taxonomic and latitudinal range, point to increasing seasonality as a forcing factor and provide the first clear evidence that environmental change on a global scale can drive synchronized shifts in life-history strategy.

Jeffery, Charlotte H.

1997-11-01

112

Mineralogical Data of Shocked Quartz Materials from K/T Boundary and Impact Crater  

NASA Astrophysics Data System (ADS)

Shocked quartz minerals from the Cretaceous-Tertiary (K/T) boundary and impact craters have been mainly discussed from distribution of optical directions, mean optical refractive index, and X-ray data (1). The purpose of the present study is presentation of the detailed mineralogical data of shocked quartz found in the K/T boundaries and terrestrial impact craters (2,3,4,5). X-ray powder diffraction pattern of shocked quartz aggregate reveals that all Xray peaks are split into major three peaks composed of low-density quartz (LQ), normal quartz (Q), and shocked quartz with high density (SQ). X-ray peaks of (110), (200), (201), (202), and (211) in the hexagonal cell are also split into many peaks. The X-ray intensity among LQ, Q, and SQ phases indicates that the SQ phase shows 36% to 53% in six K/T boundary samples (5). The relative X-ray intensity ratio of shocked quartz to standard rock crystal decreases into 13% to 37%, which suggests that shocked quartz materials contain major parts of diaplectic amorphous phases (G1) in the K/T boundary and impact crater. Although the LQ and Q type quartz phases, which can be also obtained at artificial impact processes (2,3,4,5), could not be distinguished from magmatic terrestrial origins, the SQ type quartz with high density has been selected for X-ray structure analysis to obtain the atomic arrangement of shocked quartz crystal. The detailed X-ray structural analyses of the SQ type shocked quartz indicate that atomic distance between oxygen and oxygen is shrunk largely (-0.8% than standard quartz Q), but that between silicon and oxygen is shrunk relatively small (-0.3%). The structural shrinkage is considered to be major causes of high density value of the SQ parts (up to +0.8% of the density deviation) (4,5). The chemical composition of shocked quartz phase (SQ) from electron and ion microprobe analyzers shows almost pure silica without Al element, though amorphous silica glassy phases (G2) contain Al contamination (ca. 0.5 wt% Al2O3). Thus, four major parts of shocked quartz silica aggregates from the K/T boundary and impact crater are divided into amorphous silica glasses (G1), low-density quartz (LQ), normal standard quartz (Q), and high-density shocked quartz (SQ) that have been formed by artificial impact experiments (2,3,4,5) in the powder state, as follows: Shocked quartz aggregate (SQA) = SQ + Q + LQ + G1. Single grain of SQ type shocked quartz phases consists of crystalline phase (SQ) and diaplectic amorphous regions (G2), as follows: Shocked quartz grain (SQG) = SQ + G2. Diaplectic amorphous phases (G2) reveal from coarse-grained silica (as multiple sets of lamellae) to submicroscopic fine-grained silica phases throughout SQG grains. Anomalous experimental data of shocked quartz with high density and shrinkages of atomic arrangements (2,3,4,5) are observed only the SQ crystalline phase. Shocked quartz as crystalline mineral means only crystalline SQ phase, whereas mixed shocked silica materials are considered to be "shocked quartz grain (SQG)" or "shocked quartz aggregate (SQA)." The experimental values of mean refractive index and bulk density of shocked quartz materials (i.e., SQA powder of LQ+Q+SQ+G1 phases, and SQG single grain of SQ+G phases), therefore, show bulk data with lower values. The similar relic phases with high-density crystal and amorphous phases formed by impact processes can be found in shocked graphite, diamond, and coesite. References: (1) Bohor B.F., Foord E.E., Modreski P.J. and Triplehorn D.W. (1987) Science, 224, 867-869. (2) Miura Y. (1991) Shock Waves (Springer-Verlag), 1, 35-41. (3) Miura Y. (1991) Lunar Planet. Sci. (abstract), 22, 905-908. (4) Miura Y. and T. Kato (1992) Celestial Mechanics (July issue), 5 pp. (in press). (5) Imai M. (1992) Master Sci. Thesis, Yamaguchi University, 89 pp.

Miura, Y.; Kato, T.; Imai, M.

1992-07-01

113

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

NASA Technical Reports Server (NTRS)

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

Sweet, A. R.

1988-01-01

114

High-pressure phase of natural fullerene C 60 in iridium-rich Cretaceous-Tertiary boundary layers of Deccan intertrappean deposits, Anjar, Kutch, India  

NASA Astrophysics Data System (ADS)

We report here for the first time the presence of the natural, toluene-soluble C 60 and the toluene-insoluble high-pressure and temperature phase of fullerene C 60 in the carbonaceous matter extracted from the iridium-rich layers of the intertrappean sediments of Anjar, India. The toluene-insoluble form of fullerene is formed at high-temperature and pressure (HPT) and is distinguished from normal fullerene by UV-visible and Fourier-transform infrared (FT-IR) spectroscopic techniques. The C 60 fullerene has been identified by high-resolution electron-impact ionization mass spectrometric analysis, as well as by Fourier-transform infrared (FT-IR), UV-visible, and 13C-nuclear magnetic resonance (NMR) spectroscopy. In iridium-poor horizons of this section, fullerenes are absent, but complex hydrocarbons are sometimes present. The FT-IR spectroscopic studies on the insoluble fullerenes show strong absorption peaks at about 740 and 509 cm -1 and a number of weak peaks at 1380, 1300, 1205, 1120, 1000, 608, 554, and 441 cm -1, which are characteristic of a high-pressure and temperature C 60 fullerene. The UV-visible spectra of the toluene-soluble fullerene, as well as the insoluble fullerene, show strong absorption bands at 270 and 348 nm, which are characteristic of pristine fullerene C 60. The toluene-insoluble carbon-rich residue shows additional absorption bands at 710, 640, and 395 nm. These UV-visible bands independently confirm the presence of the high-pressure-temperature (HPT) phase of fullerene C 60. Conditions of high-pressure and temperature required for formation of the HPT fullerene phase can be created by an energetic impact event. Therefore, the presence of HPT fullerene in the KT boundary layer at Anjar is linked to the impact event at the KT transition.

Parthasarathy, G.; Bhandari, N.; Vairamani, M.; Kunwar, A. C.

2008-02-01

115

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

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

116

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

NASA Technical Reports Server (NTRS)

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.

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

1994-01-01

117

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

NASA Astrophysics Data System (ADS)

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 0.7-3.4×1031ergs 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° and 31°K, suggesting that global near-freezing conditions may have been reached. Impact-generated CO2 caused less than 1°K greenhouse warming and therefore was insignificant compared 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.

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

1997-09-01

118

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

PubMed

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

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

1997-09-25

119

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

NASA Technical Reports Server (NTRS)

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.

Sharpton, Virgil L.; Marin, Luis E.

1997-01-01

120

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

PubMed

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

Sharpton, V L; Marin, L E

1997-05-30

121

Resistance of spiders to Cretaceous-Tertiary extinction events.  

PubMed

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

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

2003-11-01

122

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

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

123

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

NASA Astrophysics Data System (ADS)

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

Marshall, Charles R.

1995-08-01

124

RESISTANCE OF SPIDERS TO CRETACEOUS–TERTIARY EXTINCTION EVENTS  

Microsoft Academic Search

Abstract. Throughout,Earth history a small number,of global catastrophic events leading to biotic crises have caused mass extinctions. Here, using a technique that combines taxonomic and numerical data, we consider the effects of the Cenomanian?Turonian and Cretaceous?Tertiary mass,extinctions on the terrestrial spider fauna in the light of new fossil data. We provide,the first evidence,that spiders suffered no decline at the family

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

2003-01-01

125

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

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

126

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

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

127

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

PubMed

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

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

2009-03-17

128

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

PubMed

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

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

2013-01-01

129

Limitations on K-T (Cretaceous Tertiary) Mass Extinction Theories Based Upon the Vertebrate Record.  

National Technical Information Service (NTIS)

Theories of extinction are only as good as the patterns of extinction that they purport to explain. Often such patterns are ignored. For the terminal Cretaceous events, different groups of organisms in different environments show different patterns of ext...

J. D. Archibald L. J. Bryant

1988-01-01

130

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

SciTech Connect

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

Levi, B.G.

1992-12-01

131

Cathodoluminescence of Shocked Quartz at the Cretaceous-Tertiary Boundary.  

National Technical Information Service (NTIS)

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...

M. R. Owen M. H. Anders

1988-01-01

132

Debate over the Cretaceous-Tertiary Boundary. (Abstract Only).  

National Technical Information Service (NTIS)

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 ...

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

1988-01-01

133

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

Microsoft Academic Search

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

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

1986-01-01

134

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

Microsoft Academic Search

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

D. A. Kring; W. V. Boynton

1991-01-01

135

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

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

136

Changes in Ocean Chemistry Across the K/T Boundary: A Laser-Ablation Study of a Marine Ferromanganese Crust  

NASA Astrophysics Data System (ADS)

The Cretaceaous/Tertiary transition at 65 Ma marks one of the most extensive Phanerozoic mass extinctions, most likely caused by a giant bolide impact, the eruption of the Deccan flood basalts, or a combination of both. In this study we analysed the major and minor element composition of a thick (106 mm) marine ferromanganese crust (CD29-2 from the central Pacific ocean) at high resolution. Element concentrations were determined along continuous sections of the crust using a 193 nm Excimer laser ablation unit attached to a quadrupole ICP-MS. The crust was previously dated by Os-isotope stratigraphy [1] which showed that the section representing the period between 72 and 48 Ma is continuous and undisturbed. The K/T boundary was clearly identified in this crust by its pronounced Os isotope minimum. We determined the concentrations of 35 elements. Particular attention was paid to hydrogenetic metals and platinum-group elements (Ir and Pt) in the 10 Myr section containing the K/T boundary. In order to avoid disturbing effects of short term changes in growth rate or dilution effects, all concentrations were normalised to those of Co, which provides a reliable measure for the fluxes of elements into ferromanganese crusts. Data were acquired for the entire crust and clearly reveal only one significant peak in Ir/Co, which coincides precisely with the K/T boundary and clearly documents an extraterrestrial contribution. The peak extends over 0.5 mm thickness and represents approximately 150,000 years of crust growth as deduced from Co constant flux modelling. In contrast, the Pt/Co profile does not reveal such a clearly defined maximum. As an example of other hydrogenetic metals, Ni/Co also shows a proniunced increase near the K/T boundary but the Ni/Co clearly leads the Ir/Co peak by about 300000 years. The data from this unique archive form the basis for a reconstruction of the sequence of changes in ocean chemistry across the K/T transition. [1] Klemm V. et al. (2005) E.P.S.L. 238, 42-48.

Frank, M.; Hattendorf, B.; Guenther, D.; Hein, J. R.

2006-12-01

137

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

SciTech Connect

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

Fastovsky, D.E. (Univ. of Rhode Island, Kingston, RI (United States)); Sheehan, P.M. (Milwaukee Public Museum, WI (United States))

1992-01-01

138

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

Microsoft Academic Search

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

Joel Cracraft

2001-01-01

139

Cosmic Genes in the Cretaceous-Tertiary transition  

NASA Astrophysics Data System (ADS)

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

Wallis, M. K.

2003-07-01

140

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)

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.

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

1993-01-01

141

Evolutionary Events and Phytoplankton Recovery After the K\\/T Mass Extinction  

Microsoft Academic Search

The recovery of the open ocean ecosystem after the Cretaceous-Tertiary boundary mass extinction (65 Ma) was extremely slow. The surface to deep carbon isotopic gradient remained below latest Cretaceous levels for more than three million years after the boundary event, suggesting suppressed rates of carbon cycling and low phytoplankton productivity. There is a rapid change in the carbon isotopic gradient

L. M. Fuqua; T. J. Bralower

2004-01-01

142

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

PubMed

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

Cracraft, J

2001-03-01

143

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

PubMed Central

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.

Cracraft, J.

2001-01-01

144

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

SciTech Connect

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.

Kring, D.A.; Boynton, W.V. (Univ. of Arizona, Tucson (United States))

1991-06-01

145

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

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

146

Plants with double genomes might have had a better chance to survive the Cretaceous-Tertiary extinction event.  

PubMed

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 approximately 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

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

2009-04-01

147

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

SciTech Connect

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.

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

1990-04-01

148

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

NASA Astrophysics Data System (ADS)

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

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

2004-05-01

149

Geochemistry of impact glasses from the K\\/T boundary in Haiti - Relation to smectites and a new type of glass  

Microsoft Academic Search

Detailed element analyses were carried out on 12 black and seven yellow glasses from the K\\/T boundary section at Beloc (Haiti), and of three samples from smectite mantles around black glasses. The results obtained for bulk black and yellow glasses show differences between these, confirming the results of Sigurdsson et al. (1991) and Izett (1991), and the results obtained on

Christian Koeberl; Haraldur Sigurdsson

1992-01-01

150

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

NASA Astrophysics Data System (ADS)

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

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

1996-03-01

151

Composition of 298 Baptistina: Implications for the K/T impactor link  

NASA Astrophysics Data System (ADS)

Bottke et al. (2007) suggested that the breakup of the Baptistina asteroid family (BAF) 160+30 /-20 Myr ago produced an “asteroid shower” that increased by a factor of 2-3 the impact flux of kilometer-sized and larger asteroids striking the Earth over the last ~120 Myr. This result led them to propose that the impactor that produced the Cretaceous/Tertiary (K/T) mass extinction event 65 Myr ago also may have come from the BAF. This putative link was based both on collisional/dynamical modeling work and on physical evidence. For the latter, the available broadband color and spectroscopic data on BAF members indicate many are likely to be dark, low albedo asteroids. This is consistent with the carbonaceous chondrite-like nature of a 65 Myr old fossil meteorite (Kyte 1998)and with chromium from K/T boundary sediments with an isotopic signature similar to that from CM2 carbonaceous chondrites. To test elements of this scenario, we obtained near-IR and thermal IR spectroscopic data of asteroid 298 Baptistina using the NASA IRTF in order to determine surface mineralogy and estimate its albedo. We found that the asteroid has moderately strong absorption features due to the presence of olivine and pyroxene, and a moderately high albedo (~20%). These combined properties strongly suggest that the asteroid is more like an S-type rather than Xc-type (Mothé-Diniz et al. 2005). This weakens the case for 298 Baptistina being a CM2 carbonaceous chondrite and its link to the K/T impactor. We also observed several bright (V Mag. ?16.8) BAF members to determine their composition.

Reddy, V.; Emery, J. P.; Gaffey, M. J.; Bottke, W. F.; Cramer, A.; Kelley, M. S.

2009-01-01

152

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

NASA Astrophysics Data System (ADS)

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

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

2005-05-01

153

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

NASA Technical Reports Server (NTRS)

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.

Rice, A. R.

1988-01-01

154

20. PALEOENVIRONMENTAL HISTORY OF THE WALVIS RIDGE AT THE CRETACEOUS TERTIARY TRANSITION, FROM MINERALOGICAL AND GEOCHEMICAL INVESTIGATIONS1  

Microsoft Academic Search

Detailed studies on clay mineralogy and inorganic geochemistry performed on late Campanian to late Paleocene sediments of DSDP Sites 525, 527, 528, and 529 provide paleoenvironmental information about the Cretaceous- Tertiary transition in the Walvis Ridge area. They suggest (1) the existence of an average hot and humidity-contrasted climate on adjacent land masses, favoring the development of coastal areas with

Hervé Chamley; Henri Maillot; Gerard Duée; Christian Robert

155

The K-T Transition in Meghalaya, NE India  

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

156

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

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

157

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

NASA Technical Reports Server (NTRS)

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.

Macdougall, J. D.

1988-01-01

158

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

NASA Astrophysics Data System (ADS)

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.

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

159

Paleosol barometer indicates extreme fluctuations in atmospheric CO2 across the Cretaceous-Tertiary boundary  

Microsoft Academic Search

We present an atmospheric pCO2 (p is partial pressure) curve showing extreme fluctuations for the interval between ca. 77 and 63 Ma in southern Alberta, Canada, using a paleosol barometer. Paleosol carbonate nodules (micrite) were collected from 40 Bk horizons among 6 stratigraphic sections for stable carbon isotope analysis. Based on results from the study area, declining atmospheric pCO2 from

Lee Nordt; Stacy Atchley; S. I. Dworkin

2002-01-01

160

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)

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.

Smit, J.

2006-05-01

161

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)

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.

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

2012-08-01

162

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

USGS Publications Warehouse

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.

Higley, Debra K.

2004-01-01

163

A theoretical exercise in the modeling of ground-level ozone resulting from the K–T asteroid impact: Its possible link with the extinction selectivity of terrestrial vertebrates  

Microsoft Academic Search

The extinction pattern of the Maastrichtian indicates that long-term and short-term events contributed to the Cretaceous–Tertiary (K–T) mass extinction at 65Ma. However, it is not clear how the impact events are linked with the extinction selectivity; e.g. non-avian dinosaurs became extinct, whereas birds survived. The post-impact air quality is discussed, and attention is focused on the then land vertebrates. Although

Ryunosuke Kikuchi; Maarten Vanneste

2010-01-01

164

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

USGS Publications Warehouse

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.

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

1986-01-01

165

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

PubMed

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

Bottke, William F; Vokrouhlický, David; Nesvorný, David

2007-09-01

166

Ejecta of Multiple Impacts Found Across the K/T Boundary in Deep-Sea Cores LL44- GPC3 and DSDP 91-596 from the Northern and Southern Pacific Ocean  

NASA Astrophysics Data System (ADS)

Cores of brown pelagic clay recovered from sites LL44-GPC3 (30°19.9'N, 157°49.4'W) and DSDP 91- 596 (23°51.2'S, 169°39.3'W) in the abyssal Pacific Ocean include the K/T boundary at 20.56 and 20.10 mbsf, respectively. The boundary has been identified in both cores by peak Ir and magnetic susceptibility anomalies, and by ichthyolith fossils. Abundant shocked quartz, magnesioferrite spinels, and microspherules were also found within the cores' K/T boundary sediments. Although lacking high-resolution stratigraphies, abyssal sediment cores have advantages for recovering impact ejecta, mainly slow accumulation rates, uniform composition, and the general absence of coarse-grained detrital minerals. Corliss and Hollister [1] initially reported finding small (~20 ?m) cristobalite "spheres" scattered in the lower part of core GPC3 between 22 and 24 mbsf. Similarly, between 21.79 and 24.12 mbsf, we have found numerous large (often >100 ?m) euhedral crystals of feldspar, iron oxide, apatite, and SiO2 (few), in addition to microkrystite spherules, microtektite spherules (some with quenched textures), and several pieces of amorphous carbon. Dozens of the more common feldspar crystals contain smaller iron oxide and/or apatite crystals that were ballistically "shot" into the feldspar crystals, clearly fracturing them. The microkrystites include mineral grains of Cr-rich spinel, olivine, feldspar, Mg-silicate, Fe-sulfide, Fe-Ti oxide, and SiO2. In core 596 between 19.85 and 20.97 mbsf, including the K/T boundary at 20.10 mbsf, we found abundant microspherules and microkrystites at 8 of 9 levels sampled. In addition, Pb spherules were found 17 cm above and 51 cm below the boundary level. The isotopic compositions of the two Pb spherules (206Pb/204Pb=19.23 and 19.27; 207Pb/204Pb=15.67 and 15.72; and 208Pb/204Pb=38.63 and 38.75) are indistinguishable from common MORB Pb isotopic compositions, plotting at the intersection of values for DM, EMI, EMII, and HIMU mantle sources. The Pb composition for the spherules also places them within the Pb isotopic field for modern pelagic sediments. Between 24.00 and 24.46 mbsf in core 596, ~4 m below the K/T boundary, we also found large pieces (>400 ?m) of platy FeO and microkrystite spherules. The sedimentation rate in both cores has been estimated to be between 20 to 30 cm per Myr, and we provisionally interpret the ejecta found across the K/T boundary in core 596 to be from multiple impact events that occurred between ~68 and ~64 Ma, some possibly in the ancient Pacific Ocean. An earlier impact event might also have occurred 16 to 18 Myr before (~4 m below) the K/T event. We infer that the pre-K/T mineral crystals, microkrystites, and microspherules in core GPC3 are vapor-phase condensates, microtektites and possibly fine target particulates entrained in the fireball from a large oceanic impact at ~68 Ma, perhaps nearby to the east on seafloor now subducted beneath western North America. Dispersal of the mineral crystals in core GPC3 between 22 and 24 mbsf might have been caused by seismically-induced slumping and megatsunami associated with the nearby impact. [1] Corliss and Hollister, Nature, 282, p. 707.

Hagstrum, J. T.; Premo, W. R.; Bullen, T. D.; Abbott, D. H.

2008-12-01

167

Biogeochemical modeling at mass extinction boundaries  

NASA Technical Reports Server (NTRS)

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.

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

1991-01-01

168

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

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

169

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

NASA Technical Reports Server (NTRS)

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

Johnson, Kirk R.; Hickey, Leo J.

1988-01-01

170

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)

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.

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

2011-04-01

171

Iridium abundance patterns across extinction boundaries  

SciTech Connect

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

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

1985-01-01

172

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

NASA Astrophysics Data System (ADS)

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

Murillo-Muñeton, G.; Grajales-Nishimura, J. M.; Velasquillo-Martínez, L. G.; García-Hernández, J.

2013-05-01

173

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

174

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

NASA Astrophysics Data System (ADS)

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. 10-2 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 1016 to 6 x 1017 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.

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

1994-12-01

175

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

NASA Technical Reports Server (NTRS)

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.

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

1994-01-01

176

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

NASA Technical Reports Server (NTRS)

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.

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

1993-01-01

177

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

PubMed Central

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.

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

2011-01-01

178

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

NASA Astrophysics Data System (ADS)

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

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

2007-10-01

179

Diversification of Ramphastinae (Aves, Ramphastidae) prior to the Cretaceous\\/Tertiary boundary as shown by molecular clock of mtDNA sequences  

Microsoft Academic Search

Partial cytochrome b and 12S rDNA mitochondrial DNA sequences of eight representatives of the Ramphastidae family were analyzed. We applied the linearized tree method to identify sequences evolving at similar rates and estimated the divergence times among some of the taxa analyzed. After excluding Ramphastos tucanus and Capito dayi from our data set, the remaining taxa presented a constant rate

Laila Alves Nahum; Sérgio Luiz Pereira; Flora Maria de Campos Fernandes; Sergio Russo Matioli; Anita Wajntal

2003-01-01

180

Coeval Ar40\\/Ar39 ages of 65.0 million years ago from Chicxulub crater melt rock and Cretaceous-Tertiary boundary tektites  

Microsoft Academic Search

Ar-40\\/Ar-39 dating of drill-core samples of a glassy melt rock recovered from beneath a massive impact breccia contained with the 180-kilometer subsurface Chicxulub crater yields well-behaved incremental heating spectra with a mean plateau age of 64.98 +\\/- 0.05 million years ago (Ma). The glassy melt rock of andesitic composition was obtained from core 9 (1390 to 1393 meters) in the

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

1992-01-01

181

Search for extractable fullerenes in clays from the Cretaceous/Tertiary boundary of the Woodside Creek and Flaxbourne River sites, New Zealand  

NASA Astrophysics Data System (ADS)

When fullerenes were first discovered to form spontaneously in condensing carbon vapors ( KROTO et al., 1985), it was suggested that they might be widely distributed in the Universe. Searches for fullerenes in meteorites (see DEVRIES et al., 1993) were unsuccessful, but C 60 and C 70 were reported to occur on Earth in samples of shungite, a meta-anthracite from a deposit near Shunga, Russia ( BUSECK et al., 1992), and in "fulgurite", a substance formed when lightning strikes certain soils or rocks ( DALY et al., 1993). The occurrence of fullerenes in shungite is particularly surprising since fullerene synthesis in the laboratory has always involved gas phase chemistry at temperatures over 1000°C. Such conditions may be attained during lightning strikes, but shungite is believed to have formed from carbonaceous material creeping into fissures of a Precambrian rock which metamorphosed under extreme pressures. If the original carbonaceous material did not already contain fullerenes perhaps from wildfires, they must have formed during the metamorphism by as yet unknown solid- or liquid-phase mechanisms.

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

1994-08-01

182

A new look at the nature of the transitional layer at the K\\/T boundary near Gams, Eastern Alps, Austria, and the problem of the mass extinction of the biota  

Microsoft Academic Search

(1) The results of detailed biostratigraphic, lithological, isotopic-geochemical, and petro- magnetic analysis of the sedimentary sequence at the Cretaceous-Paleogene boundary in the Gams area, Eastern Alps, Austria, point to two stages in the evolution of the transi- tional layer at the Cretaceous-Paleogene boundary. During the earlier one of these stages (which lasted for approximately 1500 years, as follows from conservative

A. F. Grachev; O. A. Korchagin; H. A. Kollmann; D. M. Pechersky; V. A. Tsel'movich

2005-01-01

183

Shock-synthesized hexagonal diamonds in Younger Dryas boundary sediments.  

PubMed

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

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

2009-08-01

184

Rubey Colloquium Paper Impact at the Permo-Triassic Boundary: A Critical Evaluation  

Microsoft Academic Search

The recognition in 1980 of a signature of an extraterrestrial impact at the Cretaceous-Tertiary boundary and its apparent involvement with the mass extinction generated considerable en- thusiasm for impacts at other mass extinctions. Numerous claims of impact evidence for the Permo-Triassic mass extinction (251.6 Ma), the largest of the Phanerozoic mass extinctions, have generally been rejected, found wanting, or been

DOUGLAS H. ERWIN

185

Sudden productivity collapse associated with the Triassic-Jurassic boundary mass extinction.  

PubMed

The end-Triassic mass extinction is one of the five most catastrophic in Phanerozoic Earth history. Here we report carbon isotope evidence of a pronounced productivity collapse at the boundary, coincident with a sudden extinction among marine plankton, from stratigraphic sections on the Queen Charlotte Islands, British Columbia, Canada. This signal is similar to (though smaller than) the carbon isotope excursions associated with the Permian-Triassic and Cretaceous-Tertiary events. PMID:11349146

Ward, P D; Haggart, J W; Carter, E S; Wilbur, D; Tipper, H W; Evans, T

2001-05-11

186

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

PubMed

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

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

2011-09-13

187

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

NASA Technical Reports Server (NTRS)

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.

Cisowski, Stanley M.

1988-01-01

188

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

Microsoft Academic Search

Stratigraphic and mineralogic studies of Cretaceous-Tertiary (K-T) boundary sections demonstrate that the offshore oil-producing breccias and seals from oil fields in the Campeche marine platform are of K-T boundary age and that their mode of formation is probably related to the K-T impact event at Chicxulub. The oil-producing carbonate breccia and the overlying dolomitized ejecta layer (seal) found in several

José M. Grajales-Nishimura; Esteban Cedillo-Pardo; Carmen Rosales-Domínguez; Dante J. Morán-Zenteno; Walter Alvarez; Philippe Claeys; José Ruíz-Morales; Jesús García-Hernández; Patricia Padilla-Avila; Antonieta Sánchez-Ríos

2000-01-01

189

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

USGS Publications Warehouse

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

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

1999-01-01

190

Three-point susceptibilities ?n(k;t) and ?ns(k;t) : Mode-coupling approximation  

NASA Astrophysics Data System (ADS)

Recently, it was argued that a three-point susceptibility equal to the density derivative of the intermediate scattering function, ?n(k;t)=dF(k;t)/dn , enters into an expression for the divergent part of an integrated four-point dynamic density correlation function of a colloidal suspension [Berthier , J. Chem. Phys. 126, 184503 (2007)]. We show that, within the mode-coupling theory, the equation of motion for ?n(k;t) is essentially identical as the equation of motion for the q?0 limit of the three-point susceptibility ?q(k;t) introduced by Biroli [Phys. Rev. Lett. 97, 195701 (2006)]. We present a numerical solution of the equation of motion for ?n(k;t) . We also derive and numerically solve an equation of motion for the density derivative of the self-intermediate scattering function, ?ns(k;t)=dFs(k;t)/dn . We contrast the wave vector dependence of ?n(k;t) and ?ns(k;t) .

Szamel, Grzegorz; Flenner, Elijah

2009-02-01

191

Hamiltonicity of Graphs G(n,k,t).  

National Technical Information Service (NTIS)

G(n,k,t) denotes the graph with k-sets of an n-set as vertices and with two vertices joined if and only if the corresponding k-sets intersect in exactly t elements. In this paper the conjecture of Chen and Lih that the graph G(n,k,t) is hamiltonian for an...

C. Hoede

1996-01-01

192

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

NASA Astrophysics Data System (ADS)

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

Barash, M. S.

2011-08-01

193

Impact Event at the Permian-Triassic Boundary: Evidence from Extraterrestrial Noble Gases in Fullerenes  

NASA Astrophysics Data System (ADS)

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.

Becker, Luann; Poreda, Robert J.; Hunt, Andrew G.; Bunch, Theodore E.; Rampino, Michael

2001-02-01

194

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

PubMed

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

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

2001-02-23

195

Primate Origins: Implications of a Cretaceous Ancestry  

Microsoft Academic Search

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

Robert D. Martin; Christophe Soligo; Simon Tavaré

2007-01-01

196

Impacts, volcanism and mass extinction: random coincidence or cause and effect?  

Microsoft Academic Search

Large impacts are credited with the most devastating mass extinctions in Earth's history and the Cretaceous - Tertiary (K\\/T) boundary impact is the strongest and sole direct support for this view. A review of the five largest Phanerozoic mass extinctions provides no support that impacts with craters up to 180 km in diameter caused significant species extinctions. This includes the

G. Keller

2005-01-01

197

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

NASA Astrophysics Data System (ADS)

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

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

1995-03-01

198

QCD jet rates with the inclusive generalized k t algorithms  

NASA Astrophysics Data System (ADS)

We derive generating functions, valid to next-to-double logarithmic accuracy, for QCD jet rates according to the inclusive forms of the k t , Cambridge/Aachen and anti- k t algorithms, which are equivalent at this level of accuracy. We compare the analytical results with jet rates and average jet multiplicities from the SHERPA event generator, and study the transition between Poisson-like and staircase-like behaviour of jet ratios.

Gerwick, Erik; Schumann, Steffen; Gripaios, Ben; Webber, Bryan

2013-04-01

199

The end-cretaceous mass extinction in the marine realm: year 2000 assessment  

Microsoft Academic Search

The current database indicates that the terminal decline and extinction, or near extinction, of many groups commonly attributed to an asteroid or comet impact at the Cretaceous–Tertiary (K–T) boundary (e.g., ammonites, bivalves, planktic foraminifera) began during the last 500k.y. of the Maastrichtian. By the time of the K–T boundary, extinction-prone tropical and subtropical marine faunas and floras were almost gone,

Gerta Keller

2001-01-01

200

Determination of rapid Deccan eruptions across the Cretaceous-Tertiary boundary using paleomagnetic secular variation: 2. Constraints from analysis of eight new sections and synthesis for a 3500-m-thick composite section  

Microsoft Academic Search

The present paper completes a restudy of the main lava pile in the Deccan flood basalt province (trap) of India. Chenet et al. (2008) reported results from the upper third, and this paper reports the lower two thirds of the 3500-m-thick composite section. The methods employed are the same, i.e., combined use of petrology, volcanology, chemostratigraphy, morphology, K-Ar absolute dating,

Anne-Lise Chenet; Vincent Courtillot; Frédéric Fluteau; Martine Gérard; Xavier Quidelleur; S. F. R. Khadri; K. V. Subbarao; Thor Thordarson

2009-01-01

201

Primary Mineralogical and Chemical Characteristics of the Major K/T and Late Eocene Impact Deposits  

NASA Astrophysics Data System (ADS)

Three well-characterized, distal impact deposits at the K/T boundary and in upper Eocene sediments serve as a baseline for understanding other proposed impact deposits. All contain abundant spherules, evidence of shock metamorphism, and the largest have significant extraterrestrial components (ETCs). The K/T and the Eocene cpx-spherule (cpxS) deposits are global - likely from the events that produced the 180 km Chicxulub and 100 km Popigai craters. The Eocene North American microtektite (NAM) deposit is regional and likely from the event that produced the 45 km Chesapeake Bay crater. These deposits all contain abundant spherules formed from both shock-melted target and mixtures of target and projectile in the ejecta plume. Spherules constitute most of the mass of the distal ejecta. K/T spherules in regional deposits around the Gulf of Mexico are from low-velocity, target-rich ejecta. These can be a few mm in size and form deposits 10s of cm thick. Globally deposited K/T spherules from the plume (typically a few hundred micron size) are both target- and projectile- rich. When well preserved, the global deposits are 3 mm thick. Eocene cpxS deposits are similar to distal K/T with both target- and projectile-rich varieties (i.e., glassy microtektite, and cpx spherules). They are smaller on average than K/T spherules, concentrated in the 125-250 micron and smaller fractions. They are invariably bioturbated, but the initial deposit was probably less than 1 mm thick. The NAM are composed entirely of target-rich glass. They are similar in size to the cpxS. Size is an important criterion for distal ejecta because droplet size in the impact plume is proportional to the energy of the impact. Both the K/T and cpxS deposits are characterized by well-defined ETCs, commonly measured by Ir. The total Ir deposited is about 55 ng per square cm in K/T sediments, and about 11 ng for the cpxS layer. This 5/1 proportion in Ir is generally consistent with the ~1.8/1 ratio in crater diameters. The NAM have no significant ETC. This may be a function of the smaller impact. It indicates there was no significant projectile-rich plume deposit. All three deposits also contain evidence of shock metamorphism, including quartz with planar deformation features, and coesite. K/T and NAM deposits are also known to contain shocked feldspar and zircon. Shocked minerals are not as ubiquitous as spherules, although in K/T deposits they are found in the Pacific, North America, and in trace amounts in Europe. Shocked minerals are only a small fraction of the total mass (typically less than 1 mg/g). These diagnostic criteria are clearly demonstrated by numerous labs on samples from a large number of K/T and Eocene sites. At present, such evidence of impact is not ubiquitous in P/T or T/J boundary sediments. Scattered reports of very small spherules (less than 100 microns) in P/T boundaries do not include abundance data. There are no convincing Ir anomalies that would represent a large ETC. Reported traces of meteorite fragments or anomalous noble gases, while intriguing, could be derived from non-impact sources (e.g., interplanetary dust particles). A few reports of shocked quartz in P/T boundaries are also intriguing, but this author won't be convinced of their accuracy until confirmed by TEM analysis. A problem with searching for evidence of impact at the P/T and T/J boundaries is the paucity of good localities with continuous sediment records and the fact that they are unavailable to most researchers. Those who wish to advance impact at the T/J and P/T need to work to get key samples distributed the broader impact community.

Kyte, F. T.

2004-12-01

202

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

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

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

2009-01-01

203

Did the European dinosaurs disappear before the K-T event? Magnetostratigraphic evidence  

NASA Astrophysics Data System (ADS)

Debate on the non-catastrophic or catastrophic extinction of the dinosaurs by an asteroid impact, K-T event, remains a controversy and is mainly based on the interpretation of the sedimentary continental sequences in the North American Western Interior. The global aspect of this event needs to be tested in sedimentary record from all continents where continuous terrestrial deposits through the Cretaceous-Paleogene are well preserved. In the western Mediterranean realm, recognition of the Cretaceous-Paleogene boundary is limited by the lack of biostratigraphic data in the upper Cretaceous-lower Tertiary continental sedimentary sequences. New magnetostratigraphic results were obtained from the analysis of two sections in southern France and compared to previous results in northern Spain. The last occurrence of in situ dinosaurs eggshells, the only dinosaur remains found, is located in Chron 30n (southeast France) or 31n (southwest France and northern Spain). This last occurrence could demonstrate that the extinction of the European dinosaurs occurred prior to the Cretaceous-Paleogene boundary, and would therefore support the idea of a gradual or stepwise extinction unlinked to the K-T event.

Galbrun, Bruno

1997-05-01

204

New Analysis Of The Baptistina Asteroid Family: Implications For Its Link With The K/t Impactor  

NASA Astrophysics Data System (ADS)

The Baptistina Asteroid Family (BAF) is the result of the breakup of an asteroid roughly 100 million years ago. This family is the source of meteoroids and near-Earth asteroids and likely caused an asteroid shower of impactors on our Earth. Bottke et al. (2007) proposed a link between the BAF and the K/T impactor, based on the favorable timing, large probability of a terrestrial impact of one 10-km BAF asteroid, and the Sloan colors of the BAF members, indicating that the BAF may have composition consistent with the K/T impactor (CM2-type carbonaceous meteorite, as inferred from chromium studies at different K/T boundary sites; Alvarez et al. 1980, Kring et al. 2007). The relationship between the BAF and K/T impactor is now controversial. Masiero et al. (2011) found that the albedo of BAF family members is 0.15, significantly higher than expected for a dark carbonaceous parent body. Also, Reddy et al. (2011) reported the spectroscopic observations of (298) Baptistina and objects in the general neighborhood of the BAF, and suggested the BAF includes a mixture of spectroscopic types that is not very different from the background (mostly S-type asteroids in the background Flora family). Unfortunately, Reddy et al. observed only the large asteroids near (298) Baptistina, and not the K/T-impactor-size BAF members with D 10 km. Using WISE albedos, Sloan colors and newly obtained spectroscopic observations of BAF members, here we show that (1) the large objects in the BAF are mostly BAF interlopers, (2) that BAF has an homogeneous composition consistent with an X-type class. We discuss the implications of the link between the BAF and the K/T impactor.

Delbo, Marco; Nesvorny, D.; Licandro, J.; Ali-Lagoa, V.

2012-10-01

205

Nanofósiles del límite Cretácico\\/Terciario cerca de Beloc (Haití): bioestratigrafía, composición de las asociaciones e implicaciones paleoclimáticas  

Microsoft Academic Search

Abstract The Beloc Formation, (Southern Peninsula of Haiti) includes a well preserved record of the Cretaceous\\/Tertiary boundary ma- terials with a distinct spherulithic layer interpreted as a result of the Chicxulub impact. A quantitative nannofossil study of four sections spanning the K\\/T boundary,has led to identify the interval corresponding,to the Micula murus\\/Nephrolithus frequens (CC25c\\/CC26a) Subzones and a thick Micula prinsii(CC26b)

Roque Aguado; Marcos A. Lamolda; Florentin J-M; R. Maurrasse

206

kT-Scale interactions between supported lipid bilayers.  

PubMed

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

Everett, W Neil; Bevan, Michael A

2014-01-14

207

Aftermath of the end-Cretaceous mass extinction: Possible biogeochemical stabilization of the carbon cycle and climate  

Microsoft Academic Search

In the aftermath of the Cretaceous\\/Tertiary (K\\/T) boundary event (~65 m.y. ago), pelagic carbonate productivity was greatly reduced for several hundred thousand years. A decrease in carbonate productivity by a factor greater than 3, in the absence of some mechanism to remove excess carbonate from the ocean, should have resulted in the accumulation of carbon and alkalinity in the oceans.

Ken Caldeira; Michael R. Rampino

1993-01-01

208

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

NASA Technical Reports Server (NTRS)

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.

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

2003-01-01

209

Definitive fossil evidence for the extant avian radiation in the Cretaceous  

Microsoft Academic Search

Long-standing controversy surrounds the question of whether living bird lineages emerged after non-avian dinosaur extinction at the Cretaceous\\/Tertiary (K\\/T) boundary or whether these lineages coexisted with other dinosaurs and passed through this mass extinction event. Inferences from biogeography and molecular sequence data (but see ref. 10) project major avian lineages deep into the Cretaceous period, implying their `mass survival' at

Julia A. Clarke; Claudia P. Tambussi; Jorge I. Noriega; Gregory M. Erickson; Richard A. Ketcham

2005-01-01

210

Primary Mineralogical and Chemical Characteristics of the Major K/T and Late Eocene Impact Deposits  

NASA Technical Reports Server (NTRS)

Three well-characterized, distal impact deposits at the WT boundary and in upper Eocene sediments serve as a baseline for understanding other proposed impact deposits. All contain abundant spherules, evidence of shock metamorphism, and the largest have significant extraterrestrial components (ETCs). The K/T and the Eocene cpx-spherule (cpxS) deposits are global - likely from the events that produced the 180 km Chicxulub and 100 km Popigai craters. The Eocene North American microtektite (NAM) deposit is regional and likely from the event that produced the 45 km Chesapeake Bay crater. These deposits all contain abundant spherules formed from both shock-melted target and mixtures of target and projectile in the ejecta plume. Spherules constitute most of the mass of the distal ejecta. K/T spherules in regional deposits around the Gulf of Mexico are from low-velocity, target-rich ejecta. These can be a few mm in size and form deposits 10s of cm thick. Globally deposited KIT spherules from the plume (typically a few hundred micron size) are both target- and projectile-rich. When well preserved, the global deposits are 3 mm thick. Eocene cpxS deposits are similar to distal K/T with both target- and projectile-rich varieties (Le., glassy microtektite, and cpx spherules). They are smaller on average than WT spherules, concentrated in the 125-250 micron and smaller fractions. They are invariably bioturbated, but the initial deposit was probably less than 1 mm thick. The NAM are composed entirely of target-rich glass. They are similar in size to the cpxS. Size is an important criterion for distal ejecta because droplet size in the impact plume is proportional to the energy of the impact. Both the JUT and cpxS deposits are characterized by well-defined ETCs, commonly measured by Ir. The total Ir deposited is about 55 ng per square cm in WT sediments, and about 11 ng for the cpxS layer. This 5/1 proportion in Ir is generally consistent with the approx.1.8/1 ratio in crater diameters. The NAM have no significant ETC. This may be a function of the smaller impact. It indicates there was no significant projectile-rich plume deposit.

Kyte, Frank T.

2004-01-01

211

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

NASA Astrophysics Data System (ADS)

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

Adatte, T.; Keller, G.

2006-05-01

212

What Caused the Mass Extinction Recorded at the K-T Boundary  

NSDL National Science Digital Library

Exploring Earth Investigations are Internet-based activities that use animations, interactive graphics, and unique imagery to help students gather information about a particular Earth science theme, issue, or concept.

TERC (www.terc.edu)

213

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

SciTech Connect

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

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

1990-08-01

214

What Effect Do They Have? Direct Hit at the K-T Boundary  

NSDL National Science Digital Library

This is a lesson about the effects of large impacts. Learners will use critical thinking skills to evaluate and apply data from a narrative to a scientific selection process, will demonstrate or visualize simulations of some of the effects of a huge impact, and will write a point of view narrative. Materials and vocabulary lists, and advanced preparation and procedural tips are included. This is lesson 14 of 19 in Exploring Meteorite Mysteries.

215

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)

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

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

2010-05-01

216

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

USGS Publications Warehouse

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

Wingard, G. Lynn

1993-01-01

217

Restoration of k T factorization for low p T hadron hadroproduction  

Microsoft Academic Search

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

Chun-Peng Chang; Hsiang-Nan Li

2011-01-01

218

Fullerenes and Interplanetary Dust at the Permian-Triassic Boundary  

NASA Astrophysics Data System (ADS)

We recently presented new evidence that an impact occurred ~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 3He-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 3He vs. giant impact for fullerene).

Poreda, Robert J.; Becker, Luann

2003-01-01

219

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

NASA Astrophysics Data System (ADS)

The clinical utility of myocardial perfusion MR imaging (MPI) is often restricted by the inability of current acquisition schemes to simultaneously achieve high spatio-temporal resolution, good volume coverage, and high signal to noise ratio. Moreover, many subjects often find it difficult to hold their breath for sufficiently long durations making it difficult to obtain reliable MPI data. Accelerated acquisition of free breathing MPI data can overcome some of these challenges. Recently, an algorithm termed as k - t SLR has been proposed to accelerate dynamic MRI by exploiting sparsity and low rank properties of dynamic MRI data. The main focus of this paper is to further improve k - t SLR and demonstrate its utility in considerably accelerating free breathing MPI. We extend its previous implementation to account for multi-coil radial MPI acquisitions. We perform k - t sampling experiments to compare different radial trajectories and determine the best sampling pattern. We also introduce a novel augmented Lagrangian framework to considerably improve the algorithm’s convergence rate. The proposed algorithm is validated using free breathing rest and stress radial perfusion data sets from two normal subjects and one patient with ischemia. k - t SLR was observed to provide faithful reconstructions at high acceleration levels with minimal artifacts compared to existing MPI acceleration schemes such as spatio-temporal constrained reconstruction and k - t SPARSE/SENSE.

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

2013-10-01

220

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

Microsoft Academic Search

We discuss the applicability of the $k_T$ factorization theorem to low-$p_T$\\u000ahadron production in hadron-hadron collision in a simple toy model, which\\u000ainvolves only scalar particles and gluons. It has been shown that the $k_T$\\u000afactorization for high-$p_T$ hadron hadroproduction is broken by soft gluons in\\u000athe Glauber region, which are exchanged among a transverse-momentum-dependent\\u000a(TMD) parton density and other

Chun-peng Chang; Hsiang-nan Li

2009-01-01

221

Restoration of k T factorization for low p T hadron hadroproduction  

NASA Astrophysics Data System (ADS)

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.

Chang, Chun-Peng; Li, Hsiang-Nan

2011-06-01

222

Sparsity transform k-t principal component analysis for accelerating cine three-dimensional flow measurements.  

PubMed

Time-resolved three-dimensional flow measurements are limited by long acquisition times. Among the various acceleration techniques available, k-t methods have shown potential as they permit significant scan time reduction even with a single receive coil by exploiting spatiotemporal correlations. In this work, an extension of k-t principal component analysis is proposed utilizing signal differences between the velocity encodings of three-directional flow measurements to further compact the signal representation and hence improve reconstruction accuracy. The effect of sparsity transform in k-t principal component analysis is demonstrated using simulated and measured data of the carotid bifurcation. Deploying sparsity transform for 8-fold undersampled simulated data, velocity root-mean-square errors were found to decrease by 52 ± 14%, 59 ± 11%, and 16 ± 32% in the common, external, and internal carotid artery, respectively. In vivo, errors were reduced by 15 ± 17% in the common carotid artery with sparsity transform. Based on these findings, spatial resolution of three-dimensional flow measurements was increased to 0.8 mm isotropic resolution with prospective 8-fold undersampling and sparsity transform k-t principal component analysis reconstruction. Volumetric data were acquired in 6 min. Pathline visualization revealed details of helical flow patterns partially hidden at lower spatial resolution. PMID:22887065

Knobloch, Verena; Boesiger, Peter; Kozerke, Sebastian

2013-07-01

223

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

USGS Publications Warehouse

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

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

1988-01-01

224

Off-gas treatment system Process Experimental Pilot Plant (PREPP) k-t evaluation  

Microsoft Academic Search

The scope of work for this task involves a systems' evaluation, using the Kepner-Tregoe (K-T) decision analysis methodology, of off-gas treatment alternatives for a Process Experimental Pilot Plant (PREPP). Two basic systems were evaluated: (1) a wet treatment system using a quencher and scrubber system; and (2) a dry treatment system using a spray dryer and baghouse arrangement. Both systems

T. G. Hedahl; C. H. Cargo; A. L. Ayers

1982-01-01

225

Measurement of left ventricular dimensions with contrast-enhanced three-dimensional cine imaging facilitated by k-t SENSE  

PubMed Central

Aim To compare three-dimensional (3D) k-t sensitivity encoded (k-t SENSE) cine cardiovascular magnetic resonance (CMR), before and after contrast administration, against standard 2D imaging for the assessment of left ventricular volumes and mass. Method Twenty-six subjects (14 volunteers, 12 patients) underwent multiple breathhold 2D balanced turbo-field echo cine CMR in addition to k-t SENSE accelerated 3D imaging (acceleration factor 5; 5× k-t SENSE), performed before and after administration of a high-relaxivity gadolinium-based contrast agent (Gadobutrolum). k-t acceleration factors of 7 and 10 were also assessed in six volunteers. Left ventricular end diastolic volume (EDV), end systolic volume (ESV), mass, and ejection fraction (EF) were calculated for each method. Results There was at least moderate agreement between the EDV, ESV, mass and EF calculated by 2D and 3D 5× k-t SENSE methods before contrast (concordance coefficients 0.92, 0.95, 0.97, 0.92, respectively). Agreement improved following contrast (concordance coefficients 0.97, 0.99, 0.98, 0.93, respectively). The 3D method underestimated all parameters compared to 2D (mean bias pre-contrast 6.1 ml, 0.6 ml, 3.5 g, 2.0% respectively). 3D image quality scores were significantly poorer than 2D, showing a non-significant trend to improvement following contrast administration. Parameters derived with k-t acceleration factors of 7 and 10 showed poorer agreement with 2D values. Conclusion Left ventricular volumes and mass are reliably assessed using 3D 5× k-t SENSE accelerated CMR. Contrast administration further improves agreement between 5× k-t SENSE and 2D-derived measurements. k-t acceleration factors greater than 5, though feasible, produce poorer agreement with 2D values.

Maredia, Neil; Kozerke, Sebastian; Larghat, Abdul; Abidin, Nik; Greenwood, John P; Boesiger, Peter; Plein, Sven

2008-01-01

226

Accelerated phase-contrast cine MRI using k-t SPARSE-SENSE.  

PubMed

Phase-contrast (PC) cine MRI is a promising method for assessment of pathologic hemodynamics, including cardiovascular and hepatoportal vascular dynamics, but its low data acquisition efficiency limits the achievable spatial and temporal resolutions within clinically acceptable breath-hold durations. We propose to accelerate PC cine MRI using an approach which combines compressed sensing and parallel imaging (k-t SPARSE-SENSE). We validated the proposed 6-fold accelerated PC cine MRI against 3-fold accelerated PC cine MRI with parallel imaging (generalized autocalibrating partially parallel acquisitions). With the programmable flow pump, we simulated a time varying waveform emulating hepatic blood flow. Normalized root mean square error between two sets of velocity measurements was 2.59%. In multiple blood vessels of 12 control subjects, two sets of mean velocity measurements were in good agreement (mean difference = -0.29 cm/s; lower and upper 95% limits of agreement = -5.26 and 4.67 cm/s, respectively). The mean phase noise, defined as the standard deviation of the phase in a homogeneous stationary region, was significantly lower for k-t SPARSE-SENSE than for generalized autocalibrating partially parallel acquisitions (0.05 ± 0.01 vs. 0.19 ± 0.06 radians, respectively; P < 0.01). The proposed 6-fold accelerated PC cine MRI pulse sequence with k-t SPARSE-SENSE is a promising investigational method for rapid velocity measurement with relatively high spatial (1.7 mm × 1.7 mm) and temporal (?35 ms) resolutions. PMID:22083998

Kim, Daniel; Dyvorne, Hadrien A; Otazo, Ricardo; Feng, Li; Sodickson, Daniel K; Lee, Vivian S

2012-04-01

227

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

NASA Technical Reports Server (NTRS)

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.

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

1988-01-01

228

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

PubMed

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

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

1993-09-17

229

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

NASA Technical Reports Server (NTRS)

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.

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

230

Erice International Seminars on Planetary Emergencies. 17th Workshop: The Collision of an Asteroid or Comet with the Earth  

NASA Astrophysics Data System (ADS)

Participating papers of this workshop included: K/T Mass Extinctions: Some Astronomical Constraints; The dynamical Properties of Near-Earth Objects; Predicting Close Earth Approaches of Asteroids and Comets; Australasian Near-Earth Object Programs; The Cosmic Impact Hazard: Overview; Large Body Impacts And Mass Extinction Events: Evidence from the Cretaceous/Tertiary Boundary and a Possible General Relationship; Historical Perspectives on Impact Hazards; Research Activities on Asteroids and Comets conducted in Japan; Physical and Chemical Properties of Near-Earth Objects; and Search for Near-Earth Objects with Ground-Based Electro-Optical Deep Space Surveillance (GEODSS) Assets. An abstract of each is contained herein.

1993-05-01

231

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

PubMed

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

Kendall, Kevin; Dhir, Aman; Du, Shangfeng

2009-07-01

232

Highly-Accelerated Real-Time Cardiac Cine MRI Using k-t SPARSE-SENSE  

PubMed Central

For patients with impaired breath-hold capacity and/or arrhythmias, real-time cine MRI may be more clinically useful than breath-hold cine MRI. However, commercially available real-time cine MRI methods using parallel imaging typically yield relatively poor spatio-temporal resolution due to their low image acquisition speed. We sought to achieve relatively high spatial resolution (~2.5mm × 2.5mm) and temporal resolution (~40ms), to produce high-quality real-time cine MR images that could be applied clinically for wall motion assessment and measurement of left ventricular (LV) function. In this work, we present an 8-fold accelerated real-time cardiac cine MRI pulse sequence using a combination of compressed sensing and parallel imaging (k-t SPARSE-SENSE). Compared with reference, breath-hold cine MRI, our 8-fold accelerated real-time cine MRI produced significantly worse qualitative grades (1–5 scale), but its image quality and temporal fidelity scores were above 3.0 (adequate) and artifacts and noise scores were below 3.0 (moderate), suggesting that acceptable diagnostic image quality can be achieved. Additionally, both 8-fold accelerated real-time cine and breath-hold cine MRI yielded comparable LV function measurements, with coefficient of variation < 10% for LV volumes. Our proposed 8-fold accelerated real-time cine MRI with k-t SPARSE-SENSE is a promising modality for rapid imaging of myocardial function.

Feng, Li; Srichai, Monvadi B.; Lim, Ruth P.; Harrison, Alexis; King, Wilson; Adluru, Ganesh; Dibella, Edward VR.; Sodickson, Daniel K.; Otazo, Ricardo; Kim, Daniel

2012-01-01

233

NLO twist-3 contributions to B?? form factors in kT factorization  

NASA Astrophysics Data System (ADS)

In this paper, we calculate the next-to-leading-order (NLO) twist-3 contribution to the form factors of B?? transitions by employing the kT factorization theorem. All the infrared divergences regulated by the logarithms ln(kiT2) cancel between those from the quark diagrams and from the effective diagrams for the initial B meson wave function and the final pion meson wave function. An infrared finite NLO hard kernel is, therefore, obtained, which confirms the application of the kT factorization theorem to the B meson semileptonic decays at the twist-3 level. From our analytical and numerical evaluations, we find that the NLO twist-3 contributions to the form factors f+,0(q2) of the B?? transition are similar in size but have an opposite sign with the NLO twist-2 contribution, which leads to a large cancellation between these two NLO parts. For the case of f+(0), for example, the 24% NLO twist-2 enhancement to the full LO prediction is largely canceled by the negative (about -17%) NLO twist-3 contribution, leaving a small and stable 7% enhancement to the full LO prediction in the whole range of 0?q2?12 GeV2. At the full NLO level, the perturbative QCD prediction is FB??(0)=0.269-0.050+0.054. We also study the possible effects on the perturbative QCD predictions when different sets of the B meson and pion distribution amplitudes are used in the numerical evaluation.

Cheng, Shan; Fan, Ying-Ying; Yu, Xin; Lü, Cai-Dian; Xiao, Zhen-Jun

2014-05-01

234

Highly accelerated real-time cardiac cine MRI using k-t SPARSE-SENSE.  

PubMed

For patients with impaired breath-hold capacity and/or arrhythmias, real-time cine MRI may be more clinically useful than breath-hold cine MRI. However, commercially available real-time cine MRI methods using parallel imaging typically yield relatively poor spatio-temporal resolution due to their low image acquisition speed. We sought to achieve relatively high spatial resolution (?2.5 × 2.5 mm(2)) and temporal resolution (?40 ms), to produce high-quality real-time cine MR images that could be applied clinically for wall motion assessment and measurement of left ventricular function. In this work, we present an eightfold accelerated real-time cardiac cine MRI pulse sequence using a combination of compressed sensing and parallel imaging (k-t SPARSE-SENSE). Compared with reference, breath-hold cine MRI, our eightfold accelerated real-time cine MRI produced significantly worse qualitative grades (1-5 scale), but its image quality and temporal fidelity scores were above 3.0 (adequate) and artifacts and noise scores were below 3.0 (moderate), suggesting that acceptable diagnostic image quality can be achieved. Additionally, both eightfold accelerated real-time cine and breath-hold cine MRI yielded comparable left ventricular function measurements, with coefficient of variation <10% for left ventricular volumes. Our proposed eightfold accelerated real-time cine MRI with k-t SPARSE-SENSE is a promising modality for rapid imaging of myocardial function. PMID:22887290

Feng, Li; Srichai, Monvadi B; Lim, Ruth P; Harrison, Alexis; King, Wilson; Adluru, Ganesh; Dibella, Edward V R; Sodickson, Daniel K; Otazo, Ricardo; Kim, Daniel

2013-07-01

235

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

NASA Technical Reports Server (NTRS)

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

Boston, P. J.

1988-01-01

236

Global blackout following the K/T Chicxulub impact: Results of impact and atmospheric modeling  

NASA Technical Reports Server (NTRS)

Several recent studies have suggested that shock decomposition of anhydrite (CaSO4) target rocks during the K/T Chicxulub impact would have ejected tremendous amounts of sulfur gas into the stratosphere. One of the many potential biospheric effects of this sulfur gas is the generation of a sulfuric acid (H2SO4) aerosol layer capable of causing darkness and severe disruption of photosynthesis for periods of years. In this paper we report the preliminary results of our modeling of shock pressures within the anhydrites and of light attenuation by the H2SO4 aerosol cloud. These models indicate that earlier studies over-estimated the amount of sulfur gas produced, but that more than enough was produced to extend global blackout conditions 4-6 times longer than the approximately 3 month predictions for silicate dust alone.

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

1993-01-01

237

Modeling study of infrasonic detection of 1 kT atmospheric blast  

SciTech Connect

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.

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

1998-12-31

238

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

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

239

Phenomenology of kT-factorization for inclusive Higgs boson production at LHC  

NASA Astrophysics Data System (ADS)

We investigate the inclusive Higgs boson production in proton-proton collisions at high energies in the framework of kT-factorization QCD approach. The attention is focused on the dominant off-shell gluon-gluon fusion subprocess g*g*?H???, where the transverse momentum of incoming gluons are taken into account. The transverse momentum dependent (or unintegrated) gluon densities of the proton are determined using the CCFM evolution equation as well as the Kimbe-Martin-Ryskin prescription. We study the theoretical uncertainties of our calculations and perform the comparison with the results of traditional pQCD evaluations. Our predictions agree well with the first experimental data taken by the ATLAS Collaboration at the LHC. We argue that further studies of the Higgs boson production are capable of constraining the unintegrated gluon densities of the proton.

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

2014-07-01

240

Mineralogical characterization of Baptistina Asteroid Family: Implications for K/T impactor source  

NASA Astrophysics Data System (ADS)

Bottke et al. [Bottke, W.F., Vokrouhlicky, D., Nesvorný, D., 2007. Nature 449, 48-53] linked the catastrophic formation of Baptistina Asteroid Family (BAF) to the K/T impact event. This linkage was based on dynamical and compositional evidence, which suggested the impactor had a composition similar to CM2 carbonaceous chondrites. However, our recent study [Reddy, V., Emery, J.P., Gaffey, M.J., Bottke, W.F., Cramer, A., Kelley, M.S., 2009. Meteorit. Planet. Sci. 44, 1917-1927] suggests that the composition of (298) Baptistina is similar to LL-type ordinary chondrites rather than CM2 carbonaceous chondrites. This rules out any possibility of it being related to the source of the K/T impactor, if the impactor was of CM-type composition. Mineralogical study of asteroids in the vicinity of BAF has revealed a plethora of compositional types suggesting a complex formation and evolution environment. A detailed compositional analysis of 16 asteroids suggests several distinct surface assemblages including ordinary chondrites (Gaffey SIV subtype), primitive achondrites (Gaffey SIII subtype), basaltic achondrites (Gaffey SVII subtype and V-type), and a carbonaceous chondrite. Based on our mineralogical analysis we conclude that (298) Baptistina is similar to ordinary chondrites (LL-type) based on olivine and pyroxene mineralogy and moderate albedo. S-type and V-type in and around the vicinity of BAF we characterized show mineralogical affinity to (8) Flora and (4) Vesta and could be part of their families. Smaller BAF asteroids with lower SNR spectra showing only a 'single' band are compositionally similar to (298) Baptistina and L/LL chondrites. It is unclear at this point why the silicate absorption bands in spectra of asteroids with formal family definition seem suppressed relative to background population, despite having similar mineralogy.

Reddy, Vishnu; Carvano, Jorge M.; Lazzaro, Daniela; Michtchenko, Tatiana A.; Gaffey, Michael J.; Kelley, Michael S.; Mothé-Diniz, Thais; Alvarez-Candal, Alvaro; Moskovitz, Nicholas A.; Cloutis, Edward A.; Ryan, Erin L.

2011-11-01

241

Electronic-structure modulation transistor: A new switch with few kT supply voltage  

NASA Astrophysics Data System (ADS)

We present a novel electronic-structure modulation transistor (EMT) for post-CMOS logic applications. The device is based on the electronic structure modulation of the channel by an external gate voltage. Its functionality is theoretically analyzed using single-band tight-binding model and non-equilibrium Green's function formalism. We report that the EMT is expected to have very large ON/OFF current ratio with reasonable self gain using a few kT Vdd. We provide an experimental proof-of-concept device of the proposed mechanism in a double gated structure using a 20 nm long and 10 um wide channel consisting of Au nanocrystals (NCs) and nitride traps. Putting negative charge on the NCs is results in wavefunction extension over larger distance due to lifting of the energy levels, resulting in reduction of the effective barrier. In transfer characteristics, we find a nonlinear dependence of the drain current on gate voltage and charge stored in the channel, which we attribute to the wavefunction modulation of the Au NCs due to charging.

Raza, Hassan; Raza, Tehseen; Hou, Tuo-Hung; Kan, Edwin

2009-03-01

242

Rapid assessment of regional and global left ventricular function using three-dimensional k-t BLAST imaging  

Microsoft Academic Search

ObjectiveTo test if three-dimensional (3D) cine spatial frequency-temporal frequency Broad-use Linear Acquisition Speed-up Technique (k-t BLAST) is suitable for rapid evaluation of global and regional left ventricular (LV) functional parameters and to evaluate the influence of gadolinium administration.

Steffen Huber; Raja Muthupillai; Hamid Mojibian; Benjamin Cheong; Marc Kouwenhoven; Scott D. Flamm

2008-01-01

243

Constraints on volatile production by the Chicxulub impact  

NASA Astrophysics Data System (ADS)

Vaporization of sulfates by the Chicxulub impact and the environmental effects resulting from atmospheric loading of sulfur dioxide are potential causes of the mass extinction at the Cretaceous/Tertiary (K/T) boundary. Recent advances in the study of the Chicxulub crater, impact simulations and experiments, and studies of acid rain at the K/T boundary provide new constraints on impact volatile production and help identify research areas where the greatest uncertainties lie. A conservative estimate of global sulfur dioxide loading is 200 Gt. The nature of the projectile (asteroid or comet), the effects of impact angle on vaporization, and sulfuric acid production in the vapor plume are important sources of uncertainty and require more research.

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

1997-03-01

244

What killed the dinosaurs?  

USGS Publications Warehouse

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

Glen, W.

1990-01-01

245

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

NASA Astrophysics Data System (ADS)

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

Grajales-Nishimura, José M.; Cedillo-Pardo, Esteban; Rosales-Domínguez, Carmen; Morán-Zenteno, Dante J.; Alvarez, Walter; Claeys, Philippe; Ruíz-Morales, José; García-Hernández, Jesús; Padilla-Avila, Patricia; Sánchez-Ríos, Antonieta

2000-04-01

246

Hydrogen production via the K-T (Koppers-Totzek) coal gasification process: current economic and technological aspects  

Microsoft Academic Search

The K-T process for partial oxidation of various coals, coke, char, tars, heavy residua, or light to heavy oils yields 300 Btu\\/cu ft syngas containing typically 50-55Vertical Bar3< CO and 30-35Vertical Bar3< Hâ from coal or 45Vertical Bar3< each CO and Hâ from liquid feedstocks. If hydrogen is desired as the end product, the raw syngas is treated with steam

H. J. Michaels; H. F. Leonards

1978-01-01

247

Image Reconstruction from Highly Undersampled (k, t)-Space Data with Joint Partial Separability and Sparsity Constraints  

PubMed Central

Partial separability (PS) and sparsity have been previously used to enable reconstruction of dynamic images from undersampled (k, t)-space data. This paper presents a new method to use PS and sparsity constraints jointly for enhanced performance in this context. The proposed method combines the complementary advantages of PS and sparsity constraints using a unified formulation, achieving significantly better reconstruction performance than using either of these constraints individually. A globally convergent computational algorithm is described to efficiently solve the underlying optimization problem. Reconstruction results from simulated and in vivo cardiac MRI data are also shown to illustrate the performance of the proposed method.

Zhao, Bo; Haldar, Justin P.; Christodoulou, Anthony G.; Liang, Zhi-Pei

2012-01-01

248

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

National Technical Information Service (NTIS)

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 ext...

K. O. Pope

1997-01-01

249

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

ERIC Educational Resources Information Center

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)

McCartney, Kevin; Loper, David E.

1989-01-01

250

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

Microsoft Academic Search

The Sanandaj–Sirjan Zone contains the metamorphic core of the Zagros continental collision zone in western Iran. The zone has been subdivided into the following from southwest to northeast: an outer belt of imbricate thrust slices (radiolarite, Bisotun, ophiolite and marginal sub-zones, which consist of Mesozoic deep-marine sediments, shallow-marine carbonates, oceanic crust and volcanic arc, respectively) and an inner complexly deformed

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

2003-01-01

251

Mantle degassing induced dead ocean in the cretaceous-tertiary transition  

Microsoft Academic Search

A treatment is presented of the terminal Cretaceous marine and Early Tertiary terrestrial dinosaur extinctions coincident with the Deccan Traps flood basalt volcanism in India. The rate of this basalt production was 4.91 cu km\\/yr as opposed to modern midocean ridge basalt production of 1.2 cu cm\\/yr. Deccan Traps total mantle CO2 release was about 5 x 10 to the

D. M. McLean

1985-01-01

252

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

NASA Technical Reports Server (NTRS)

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

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

1981-01-01

253

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

NASA Technical Reports Server (NTRS)

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.

Pope, Kevin O.

1996-01-01

254

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

PubMed

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

Xiao, Dan; Balcom, Bruce J

2014-06-01

255

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

NASA Astrophysics Data System (ADS)

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

Xiao, Dan; Balcom, Bruce J.

2014-06-01

256

Distribution of Siderophile and Other Trace Elements in Melt Rock at the Chicxulub Impact Structure.  

National Technical Information Service (NTIS)

Recent isotopic and mineralogical studies have demonstrated a temporal and chemical link between the Chicxulub multiring impact basin and ejecta at the Cretaceous-Tertiary boundary. A fundamental problem yet to be resolved, however, is identification of t...

B. C. Schuraytz D. J. Lindstrom R. R. Martinez V. L. Sharpton L. E. Marin

1994-01-01

257

Proviral Structure, Chromosomal Location, and Expression of HERV-K-T47D, a Novel Human Endogenous Retrovirus Derived from T47D Particles  

PubMed Central

We previously described that type B retrovirus-like particles released from the human mammary carcinoma cell line T47D are pseudotypes and package retroviral RNA of different origins (W. Seifarth, H. Skladny, F. Krieg-Schneider, A. Reichert, R. Hehlmann, and C. Leib-Mösch, J. Virol. 69:6408–6416, 1995). One preferentially packaged retroviral sequence, ERV-MLN, has now been used to isolate the corresponding full-length provirus from a human genomic library. The 9,315-bp proviral genome comprises a complete retroviral structure except for a 3? long terminal repeat (LTR) truncation. A lysine tRNA primer-binding site and phylogenetic analyses assign this human endogenous retroviral element, now called HERV-K-T47D, to the HML-4 subgroup of the HERV-K superfamily. The gag, prt, pol, and env genes exhibit 40 to 60% amino acid identity to HERV-K10. HERV-K-T47D is located on human chromosome 10, with five closely related elements on chromosomes 8, 9, 15, 16, and 19 and several hundred HERV-K-T47D-related solitary LTRs dispersed over the human genome. HERV-K-T47D-related sequences are detected in the genomes of higher primates and Old World monkeys but not in those of New World monkeys. High HERV-K-T47D transcription levels were observed in human placenta tissue, whereas transcription in T47D cells was strictly steroid dependent.

Seifarth, Wolfgang; Baust, Corinna; Murr, Andreas; Skladny, Heyko; Krieg-Schneider, Frank; Blusch, Jurgen; Werner, Thomas; Hehlmann, Rudiger; Leib-Mosch, Christine

1998-01-01

258

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

NASA Technical Reports Server (NTRS)

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

Tyburczy, James A.; Ahrens, Thomas J.

1993-01-01

259

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

NASA Astrophysics Data System (ADS)

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

Tyburczy, James A.; Ahrens, Thomas J.

1993-03-01

260

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)

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.

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

2009-04-01

261

Do Impacts Really Cause Most Mass Extinctions?  

Microsoft Academic Search

For the past 28 years, the trendy “bandwagon” in the geosciences has attempted to explain most mass extinctions by extraterrestrial\\u000a impact events. However, the past decade of research has shown no significant evidence of impacts at any mass extinction horizon\\u000a except for the Cretaceous-Tertiary boundary at 65 Ma. In fact, numerous paleontologists have even questioned whether the Cretaceous-Tertiary\\u000a impact was

Donald R. Prothero

262

Petrogenesis of an augite-bearing melt rock in the Chicxulub structure and its relationship to K\\/T impact spherules in Haiti  

Microsoft Academic Search

The link between the Chicxulub structure and the K\\/T impact is strengthened here by a showing that a simple chemical relationship exists between glassy tektitelike relics and an augite-bearing melt rock found within the structure. It is argued that the composition of this melt rock could not easily have been produced by volcanic processes.

David A. Kring; William V. Boynton

1992-01-01

263

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.

264

Palaeontological data and identifying mass extinctions.  

PubMed

It is often assumed that mass extinctions may be read directly from the fossil record. However, recent work on the Cretaceous-Tertiary (K-T) boundary has shown the difficulty of doing this. For example, it is hard to tell whether the stratigraphic ranges of taxa are complete or not, and what the shape of an extinction really is. Range completeness may be assessed by (1) a statistical approach to the relative completeness of ranges of taxa, and (2) tests based on collecting effort near the ends of ranges. Tests carried out recently suggest that the record is good in parts and getting better. Hence, palaeontologists ought to be able to document the nature of extinction events ever more precisely. PMID:21236813

Benton, M J

1994-05-01

265

Mass extinctions in the deep sea  

NASA Technical Reports Server (NTRS)

The character of mass extinctions can be assessed by studying extinction patterns of organisms, the fabric of the extinction, and assessing the environmental niche and mode of life of survivors. Deep-sea benthic foraminifera have been listed as little affected by the Cretaceous-Tertiary (K-T) mass extinction, but very few quantitative data are available. New data on deep-sea Late Maestrichtian-Eocene benthic foraminifera from Maud Rise (Antractica) indicate that about 10 percent of the species living at depths of 2000 to 2500 m had last appearances within 1 my of the Cretaceous-Tertiary (K-T) boundary, versus about 25 percent of species at 1000 to 1500 m. Many survivors from the Cretaceous became extinct in a period of global deep-sea benthic foraminiferal extinction at the end of the Paleocene, a time otherwise marked by very few extinctions. Preliminary conclusions suggest that the deep oceanic environment is essentially decoupled from the shallow marine and terrestrial environment, and that even major disturbances of one of these will not greatly affect the other. This gives deep-sea benthic faunas a good opportunity to recolonize shallow environments from greater depths and vice versa after massive extinctions. The decoupling means that data on deep-sea benthic boundary was caused by the environmental effects of asteriod impact or excessive volcanism. The benthic foraminiferal data strongly suggest, however, that the environmental results were strongest at the Earth's surface, and that there was no major disturbance of the deep ocean; this pattern might result both from excessive volcanism and from an impact on land.

Thomas, E.

1988-01-01

266

The fossil record and molecular clocks: basal radiations within the Neornithes  

Microsoft Academic Search

The fossil record of the extant clades of birds (Neornithes) is critical to understanding both the timing and pattern of the evolutionary divergences within this major verte- brate group. Interpretations of the fossil record have indicated that this radiation occurred in the aftermath of the Cretaceous-Tertiary (K-T) extinction event. However, the use of 'molecular clocks' to estimate the timing of

Gareth J. Dyke

2003-01-01

267

Computation and analysis of the transverse current autocorrelation function, Ct(k,t), for small wave vectors: A molecular-dynamics study for a Lennard-Jones fluid  

NASA Astrophysics Data System (ADS)

Molecular-dynamics (MD) calculations are reported for three thermodynamic states of a Lennard-Jones fluid. Systems of 2048 particles and 105 integration steps were used. The transverse current autocorrelation function, Ct(k,t), has been determined for wave vectors of the range 0.5<||k||?<1.5. Ct(k,t) was fitted by hydrodynamic-type functions. The fits returned k-dependent decay times and shear viscosities which showed a systematic behavior as a function of k. Extrapolation to the hydrodynamic region at k=0 gave shear viscosity coefficients in good agreement with direct Green-Kubo results obtained in previous work. The two-exponential model fit for the memory function proposed by other authors does not provide a reasonable description of the MD results, as the fit parameters show no systematic wave-vector dependence, although the Ct(k,t) functions are somewhat better fitted. Similarly, the semiempirical interpolation formula for the decay time based on the viscoelastic concept proposed by Akcasu and Daniels fails to reproduce the correct k dependence for the wavelength range investigated herein.

Vogelsang, R.; Hoheisel, C.

1987-02-01

268

Osmium-Iridium Correlation and Osmium Isotopic Composition in Some Geological Boundaries and Meteorites  

NASA Astrophysics Data System (ADS)

Since the pioneering study of Alvarez et al. on K/T boundary event, Ir has long been considered to be the main indicator of extraterrestrial materials in boundaries, while little work about Os and its isotopic composition have been done. In this work a sophisticated radiochemical separation procedure together with neutron activation analsis (NAA) method was established for the determination of Os in some geological boundaries (P epsilon/epsilon, K/T, D/C, O/S, P/T). Combined with our early work--determination of Ir abundances [1], the sources of boundary events were deciphered by using the Os/Ir ratios. Simultaneously ^184Os/^190Os ratios in K/T boundaries, as well as inclusions of Allende chondrite and acid-insoluble residues of iron meteorites (Nandan, Jianshi, Longchang) were determined to search for the Os isotopic composition anomalies resulted from the extrasolar components by RNAA. The results show that the Os abundances exhibit a positive correlation with the Ir abundances for overall K/T boundary samples, but only the Os/Ir ratios of K/T boundaries, with the average of 0.98 +- 0.55, are in excellent agreement with 1.01 of the solar system [2], Accordingly, it provides new evidence for an extraterrestrial source of the K/T event. The results of ^184Os/^190Os ratios, with uncertainties of less than 1%, indicate there is no remarkable ^184Os/^190Os ratio anomaly in the K/T boundary samples, which implies the impacting matter may be from the solar system not the extrasolar, while no anomaly exists in the inclusions of Allende chondrite and acid-insoluble residues of iron meteorites, which disagree with the results obtained by Goel [3]. REFERENCES [1] Chai Chifang (1988) Isotopenpraxis 24, pp. 257-272. [2] Anders E. and Grevesse N. (l989) Geochim. Cosmochim. Acta 53, 197-214. [3] Goel P.S.(1987) Proc. Indian Acad. Sci. (Earth Planet. Sci), 96, pp. 81-102.

Liu, Y. Z.; Wang, J. X.; Mao, X. Y.; Chai, C. F.

1992-07-01

269

Grain boundaries  

SciTech Connect

The present document is a progress report describing the work accomplished to date during the second year of our four-year grant (February 15, 1990--February 14, 1994) to study grain boundaries. The research was focused on the following three major efforts: Study of the atomic structure of grain boundaries by means of x-ray diffraction, transmission electron microscopy and computer modeling; study of short-circuit diffusion along grain boundaries; and development of a Thin-film Deposition/Bonding Apparatus for the manufacture of high purity bicrystals.

Balluffi, R.W.; Bristowe, P.D.

1991-01-01

270

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)

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.

Krogh, T. E.; Kamo, S. L.; Bohor, B. F.

1993-01-01

271

Cretaceous-Tertiary paleobathymetry of Labrador and Baffin shelves, and its significance to evolution of Labrador Sea  

SciTech Connect

The integrated micropaleontological and palynological analyses of 17 wells from offshore Labrador and southern Baffin Island allowed consistent assignments of biozones, ages, and depositional environments to the sections. Resolution attained is approximately at the stage level or finer. Interpretation of the foraminifera and palynomorphs from the Labrador Shelf indicates that the depositional environments were mainly neritic during the Early and early Late Cretaceous, changed to bathyal during the Maastrichtian to late Eocene, and returned to neritic during the Oligocene to Miocene. The sections drilled on the Baffin Shelf do not include Cretaceous sediments, but indicate bathyal environments from Paleocene to early Eocene, and neritic to nonmarine environments from late Eocene to Miocene. The Barremian to Campanian continental to neritic sediments from the Labrador Shelf correspond to the initial rifting phase of the Labrador-Greenland continental plate; whereas the Maastrichtian to late Eocene bathyal sediments correspond to the opening of the southern part of the Labrador Sea with the creation of oceanic crust. The Labrador Sea reached the Baffin shelf area during the Maastrichtian. The Oligocene to Miocene neritic to continental sediments of both the Labrador and Baffin Shelf areas correspond to the filling phase of the basin, with resulting buildup of the continental shelves and slopes.

Helenes, J.; Gradstein, F.

1988-03-01

272

PTt path in metamorphic rocks of the Khoy region (northwest Iran) and their tectonic significance for Cretaceous Tertiary continental collision  

NASA Astrophysics Data System (ADS)

Metamorphic rocks in the Khoy region are exposed between obducted ophiolites to the southwest and sedimentary rocks of Precambrian-Paleozoic age to the northeast. The Qom formation (Oligocene-Miocene) with a basal conglomerate transgressively overlies all of these rocks. The metamorphic rocks consist of both metasediments and metabasites. The metasediments are micaschist, garnet-staurolite schist and garnet-staurolite sillimanite schist with some meta-arkose, marble and quartzite. The metabasites are metamorphosed to greenschist and amphibolite facies from a basaltic and gabbroic protolith of tholeiitic and calc-alkaline rocks. Geothermobarometry based on the equivalence of minerals stability and their paragenesis in these rocks and microprobe analyses by several different methods indicate that metamorphism occurred in a temperature range between 450 and 680 °C at 5.5 and 7.5 kb pressure. Rims of minerals reveal a considerable decrease of pressure (<2 kb) and insignificant decrease of temperature. The PTt path of this metamorphism is normal. The MFG line passes above the triple junction of Al 2SiO 5 polymorphs, and the average geothermal gradient during metamorphism was from 27 to 37 °C/km, which is more concordant with the temperature regime of collision zones. We infer that crustal thickening during post-Cretaceous (possibly Eocene) collision of the Arabian plate and the Azerbaijan-Albourz block was the main factor that caused the metamorphism in the studied area.

Azizi, H.; Moinevaziri, H.; Mohajjel, M.; Yagobpoor, A.

2006-06-01

273

High pT direct photon and pi0 triggered azimuthal jet correlations and measurement of kT for isolated direct photons in p+p collisions at s=200GeV  

Microsoft Academic Search

Correlations of charged hadrons of 1kT, is obtained by comparing to a model incorporating a Gaussian kT smearing. The sensitivity of the associated charged hadron spectra to

A. Adare; S. Afanasiev; C. Aidala; N. N. Ajitanand; Y. Akiba; H. Al-Bataineh; J. Alexander; K. Aoki; L. Aphecetche; R. Armendariz; S. H. Aronson; J. Asai; E. T. Atomssa; R. Averbeck; T. C. Awes; B. Azmoun; V. Babintsev; M. Bai; G. Baksay; L. Baksay; A. Baldisseri; K. N. Barish; P. D. Barnes; B. Bassalleck; A. T. Basye; S. Bathe; S. Batsouli; V. Baublis; C. Baumann; A. Bazilevsky; S. Belikov; R. Bennett; A. Berdnikov; Y. Berdnikov; A. A. Bickley; J. G. Boissevain; H. Borel; K. Boyle; M. L. Brooks; H. Buesching; V. Bumazhnov; G. Bunce; S. Butsyk; C. M. Camacho; S. Campbell; B. S. Chang; W. C. Chang; J.-L. Charvet; S. Chernichenko; J. Chiba; C. Y. Chi; M. Chiu; I. J. Choi; R. K. Choudhury; T. Chujo; P. Chung; A. Churyn; V. Cianciolo; Z. Citron; C. R. Cleven; B. A. Cole; M. P. Comets; M. Connors; P. Constantin; M. Csanád; T. Csörgo; T. Dahms; S. Dairaku; K. Das; G. David; M. B. Deaton; K. Dehmelt; H. Delagrange; A. Denisov; D. D'Enterria; A. Deshpande; E. J. Desmond; O. Dietzsch; A. Dion; M. Donadelli; O. Drapier; A. Drees; K. A. Drees; A. K. Dubey; A. Durum; D. Dutta; V. Dzhordzhadze; Y. V. Efremenko; J. Egdemir; F. Ellinghaus; W. S. Emam; T. Engelmore; A. Enokizono; H. En'Yo; S. Esumi; K. O. Eyser; B. Fadem; D. E. Fields; M. Finger Jr.; F. Fleuret; S. L. Fokin; Z. Fraenkel; J. E. Frantz; A. Franz; A. D. Frawley; K. Fujiwara; Y. Fukao; T. Fusayasu; S. Gadrat; I. Garishvili; A. Glenn; H. Gong; M. Gonin; J. Gosset; Y. Goto; R. Granier de Cassagnac; N. Grau; S. V. Greene; M. Grosse Perdekamp; T. Gunji; H.-Å. Gustafsson; T. Hachiya; A. Hadj Henni; C. Haegemann; J. S. Haggerty; H. Hamagaki; R. Han; H. Harada; E. P. Hartouni; K. Haruna; E. Haslum; R. Hayano; M. Heffner; T. K. Hemmick; T. Hester; X. He; H. Hiejima; J. C. Hill; R. Hobbs; M. Hohlmann; W. Holzmann; K. Homma; B. Hong; T. Horaguchi; D. Hornback; S. Huang; T. Ichihara; R. Ichimiya; H. Iinuma; Y. Ikeda; K. Imai; J. Imrek; M. Inaba; Y. Inoue; D. Isenhower; L. Isenhower; M. Ishihara; T. Isobe; M. Issah; A. Isupov; D. Ivanischev; B. V. Jacak; J. Jia; J. Jin; O. Jinnouchi; B. M. Johnson; K. S. Joo; D. Jouan; F. Kajihara; S. Kametani; N. Kamihara; J. Kamin; M. Kaneta; J. H. Kang; H. Kanou; J. Kapustinsky; D. Kawall; A. V. Kazantsev; T. Kempel; A. Khanzadeev; K. M. Kijima; J. Kikuchi; B. I. Kim; D. H. Kim; D. J. Kim; E. Kim; S. H. Kim; E. Kinney; K. Kiriluk; Á. Kiss; E. Kistenev; A. Kiyomichi; J. Klay; C. Klein-Boesing; L. Kochenda; V. Kochetkov; B. Komkov; M. Konno; J. Koster; D. Kotchetkov; A. Kozlov; A. Král; A. Kravitz; J. Kubart; G. J. Kunde; N. Kurihara; K. Kurita; M. Kurosawa; M. J. Kweon; Y. Kwon; G. S. Kyle; R. Lacey; Y. S. Lai; J. G. Lajoie; D. Layton; A. Lebedev; D. M. Lee; K. B. Lee; M. K. Lee; T. Lee; M. J. Leitch; M. A. L. Leite; B. Lenzi; P. Liebing; T. Liska; A. Litvinenko; H. Liu; M. X. Liu; X. Li; B. Love; D. Lynch; C. F. Maguire; Y. I. Makdisi; A. Malakhov; M. D. Malik; V. I. Manko; E. Mannel; Y. Mao; L. Masek; H. Masui; F. Matathias; M. McCumber; P. L. McGaughey; N. Means; B. Meredith; Y. Miake; P. Mikes; K. Miki; T. E. Miller; A. Milov; S. Mioduszewski; M. Mishra; J. T. Mitchell; M. Mitrovski; A. K. Mohanty; Y. Morino; A. Morreale; D. P. Morrison; T. V. Moukhanova; D. Mukhopadhyay; J. Murata; S. Nagamiya; Y. Nagata; J. L. Nagle; M. Naglis; M. I. Nagy; I. Nakagawa; Y. Nakamiya; T. Nakamura; K. Nakano; J. Newby; M. Nguyen; T. Niita; B. E. Norman; R. Nouicer; A. S. Nyanin; E. O'Brien; S. X. Oda; C. A. Ogilvie; H. Ohnishi; K. Okada; M. Oka; O. O. Omiwade; Y. Onuki; A. Oskarsson; M. Ouchida; K. Ozawa; R. Pak; D. Pal; A. P. T. Palounek; V. Pantuev; V. Papavassiliou; W. J. Park; S. F. Pate; H. Pei; J.-C. Peng; H. Pereira; V. Peresedov; D. Yu. Peressounko; C. Pinkenburg; M. L. Purschke; A. K. Purwar; H. Qu; J. Rak; A. Rakotozafindrabe; I. Ravinovich; K. F. Read; S. Rembeczki; M. Reuter; K. Reygers; V. Riabov; Y. Riabov; D. Roach; G. Roche; S. D. Rolnick; A. Romana; M. Rosati; S. S. E. Rosendahl; P. Rosnet; P. Rukoyatkin; P. Ruzicka; V. L. Rykov; B. Sahlmueller; N. Saito; T. Sakaguchi; S. Sakai; K. Sakashita; H. Sakata; V. Samsonov; S. Sato; T. Sato; S. Sawada; K. Sedgwick; J. Seele; R. Seidl; A. Yu. Semenov; V. Semenov; R. Seto; D. Sharma; I. Shein; A. Shevel; T.-A. Shibata; K. Shigaki; M. Shimomura; K. Shoji; P. Shukla; A. Sickles; C. L. Silva; D. Silvermyr; C. Silvestre; K. S. Sim; B. K. Singh; C. P. Singh; V. Singh; S. Skutnik; M. Slunecka; A. Soldatov; R. A. Soltz; W. E. Sondheim; S. P. Sorensen; I. V. Sourikova; F. Staley; P. W. Stankus; E. Stenlund; M. Stepanov; A. Ster; S. P. Stoll; T. Sugitate; C. Suire; A. Sukhanov; J. Sziklai; T. Tabaru; S. Takagi; E. M. Takagui; A. Taketani; R. Tanabe; Y. Tanaka; S. Taneja; K. Tanida; M. J. Tannenbaum; A. Taranenko; P. Tarján; H. Themann; T. L. Thomas; M. Togawa; A. Toia; J. Tojo; L. Tomásek; Y. Tomita; H. Torii; R. S. Towell; V.-N. Tram; I. Tserruya; Y. Tsuchimoto; C. Vale; H. Valle

2010-01-01

274

Mass extinctions: Ecological selectivity and primary production  

NASA Astrophysics Data System (ADS)

If mass extinctions were caused by reduced primary productivity, then extinctions should be concentrated among animals with starvation-susceptible feeding modes, active lifestyles, and high-energy budgets. The stratigraphic ranges (by stage) of 424 genera of bivalves and 309 genera of articulate brachiopods suggest that there was an unusual reduction of primary productivity at the Cretaceous/Tertiary (K/T) boundary extinction. For bivalves at the K/T, there were (1) selective extinction of suspension feeders and other susceptible trophic categories relative to deposit feeders and other resistant categories, and (2) among suspension feed-ers, selective extinction of bivalves with active locomotion. During the Permian-Triassic (P/Tr) extinction and Jurassic background time, extinction rates among suspension feeders were greater for articulate brachiopods than for bivalves. But during the K/T event, extinction rates of articulates and suspension-feeding bivalves equalized, possibly because the low-energy budgets of articulates gave them an advantage when food was scarce.

Rhodes, Melissa Clark; Thayer, Charles W.

1991-09-01

275

Measurement of the k(T) distribution of particles in jets produced in pp collisions at sqrt(s)=1.96 TeV.  

PubMed

We present a measurement of the transverse momentum with respect to the jet axis (k(t)) of particles in jets produced in pp collisions at sqrt(s)=1.96 TeV. Results are obtained for charged particles in a cone of 0.5 radians around the jet axis in events with dijet invariant masses between 66 and 737 GeV/c(2). The experimental data are compared to theoretical predictions obtained for fragmentation partons within the framework of resummed perturbative QCD using the modified leading log and next-to-modified leading log approximations. The comparison shows that trends in data are successfully described by the theoretical predictions, indicating that the perturbative QCD stage of jet fragmentation is dominant in shaping basic jet characteristics. PMID:19658924

Aaltonen, T; Adelman, J; Akimoto, T; Alvarez González, B; Amerio, S; Amidei, D; Anastassov, A; Annovi, A; Antos, J; Apollinari, G; Apresyan, A; Arisawa, T; Artikov, A; Ashmanskas, W; Attal, A; Aurisano, A; Azfar, F; Azzurri, P; Badgett, W; Barbaro-Galtieri, A; Barnes, V E; Barnett, B A; Bartsch, V; Bauer, G; Beauchemin, P-H; Bedeschi, F; Beecher, D; Behari, S; Bellettini, G; Bellinger, J; Benjamin, D; Beretvas, A; Beringer, J; Bhatti, A; Binkley, M; Bisello, D; Bizjak, I; Blair, R E; Blocker, C; Blumenfeld, B; Bocci, A; Bodek, A; Boisvert, V; Bolla, G; Bortoletto, D; Boudreau, J; Boveia, A; Brau, B; Bridgeman, A; Brigliadori, L; Bromberg, C; Brubaker, E; Budagov, J; Budd, H S; Budd, S; Burke, S; Burkett, K; Busetto, G; Bussey, P; Buzatu, A; Byrum, K L; Cabrera, S; Calancha, C; Campanelli, M; Campbell, M; Canelli, F; Canepa, A; Carls, B; Carlsmith, D; Carosi, R; Carrillo, S; Carron, S; Casal, B; Casarsa, M; Castro, A; Catastini, P; Cauz, D; Cavaliere, V; Cavalli-Sforza, M; Cerri, A; Cerrito, L; Chang, S H; Chen, Y C; Chertok, M; Chiarelli, G; Chlachidze, G; Chlebana, F; Cho, K; Chokheli, D; Chou, J P; Choudalakis, G; Chuang, S H; Chung, K; Chung, W H; Chung, Y S; Chwalek, T; Ciobanu, C I; Ciocci, M A; Clark, A; Clark, D; Compostella, G; Convery, M E; Conway, J; Cordelli, M; Cortiana, G; Cox, C A; Cox, D J; Crescioli, F; Cuenca Almenar, C; Cuevas, J; Culbertson, R; Cully, J C; Dagenhart, D; Datta, M; Davies, T; de Barbaro, P; De Cecco, S; Deisher, A; De Lorenzo, G; Dell'orso, M; Deluca, C; Demortier, L; Deng, J; Deninno, M; Derwent, P F; di Giovanni, G P; Dionisi, C; Di Ruzza, B; Dittmann, J R; D'Onofrio, M; Donati, S; Dong, P; Donini, J; Dorigo, T; Dube, S; Efron, J; Elagin, A; Erbacher, R; Errede, D; Errede, S; Eusebi, R; Fang, H C; Farrington, S; Fedorko, W T; Feild, R G; Feindt, M; Fernandez, J P; Ferrazza, C; Field, R; Flanagan, G; Forrest, R; Frank, M J; Franklin, M; Freeman, J C; Furic, I; Gallinaro, M; Galyardt, J; Garberson, F; Garcia, J E; Garfinkel, A F; Genser, K; Gerberich, H; Gerdes, D; Gessler, A; Giagu, S; Giakoumopoulou, V; Giannetti, P; Gibson, K; Gimmell, J L; Ginsburg, C M; Giokaris, N; Giordani, M; Giromini, P; Giunta, M; Giurgiu, G; Glagolev, V; Glenzinski, D; Gold, M; Goldschmidt, N; Golossanov, A; Gomez, G; Gomez-Ceballos, G; Goncharov, M; González, O; Gorelov, I; Goshaw, A T; Goulianos, K; Gresele, A; Grinstein, S; Grosso-Pilcher, C; Grundler, U; Guimaraes da Costa, J; Gunay-Unalan, Z; Haber, C; Hahn, K; Hahn, S R; Halkiadakis, E; Han, B-Y; Han, J Y; Happacher, F; Hara, K; Hare, D; Hare, M; Harper, S; Harr, R F; Harris, R M; Hartz, M; Hatakeyama, K; Hays, C; Heck, M; Heijboer, A; Heinrich, J; Henderson, C; Herndon, M; Heuser, J; Hewamanage, S; Hidas, D; Hill, C S; Hirschbuehl, D; Hocker, A; Hou, S; Houlden, M; Hsu, S-C; Huffman, B T; Hughes, R E; Husemann, U; Hussein, M; Husemann, U; Huston, J; Incandela, J; Introzzi, G; Iori, M; Ivanov, A; James, E; Jayatilaka, B; Jeon, E J; Jha, M K; Jindariani, S; Johnson, W; Jones, M; Joo, K K; Jun, S Y; Jung, J E; Junk, T R; Kamon, T; Kar, D; Karchin, P E; Kato, Y; Kephart, R; Keung, J; Khotilovich, V; Kilminster, B; Kim, D H; Kim, H S; Kim, H W; Kim, J E; Kim, M J; Kim, S B; Kim, S H; Kim, Y K; Kimura, N; Kirsch, L; Klimenko, S; Knuteson, B; Ko, B R; Kondo, K; Kong, D J; Konigsberg, J; Korytov, A; Kotwal, A V; Kreps, M; Kroll, J; Krop, D; Krumnack, N; Kruse, M; Krutelyov, V; Kubo, T; Kuhr, T; Kulkarni, N P; Kurata, M; Kwang, S; Laasanen, A T; Lami, S; Lammel, S; Lancaster, M; Lander, R L; Lannon, K; Lath, A; Latino, G; Lazzizzera, I; Lecompte, T; Lee, E; Lee, H S; Lee, S W; Leone, S; Lewis, J D; Lin, C-S; Linacre, J; Lindgren, M; Lipeles, E; Lister, A; Litvintsev, D O; Liu, C; Liu, T; Lockyer, N S; Loginov, A; Loreti, M; Lovas, L; Lucchesi, D; Luci, C; Lueck, J; Lujan, P; Lukens, P; Lungu, G; Lyons, L; Lys, J; Lysak, R; Macqueen, D; Madrak, R; Maeshima, K; Makhoul, K; Maki, T; Maksimovic, P; Malde, S; Malik, S; Manca, G; Manousakis-Katsikakis, A; Margaroli, F; Marino, C; Marino, C P; Martin, A; Martin, V; Martínez, M; Martínez-Ballarín, R; Maruyama, T; Mastrandrea, P; Masubuchi, T; Mathis, M; Mattson, M E; Mazzanti, P; McFarland, K S; McIntyre, P; McNulty, R; Mehta, A; Mehtala, P; Menzione, A; Merkel, P; Mesropian, C; Miao, T; Miladinovic, N; Miller, R; Mills, C; Milnik, M; Mitra, A; Mitselmakher, G; Miyake, H; Moggi, N; Moon, C S; Moore, R; Morello, M J; Morlok, J; Movilla Fernandez, P; Mülmenstädt, J; Mukherjee, A; Muller, Th; Mumford, R; Murat, P; Mussini, M; Nachtman, J; Nagai, Y; Nagano, A; Naganoma, J; Nakamura, K; Nakano, I; Napier, A; Necula, V; Nett, J; Neu, C; Neubauer, M S; Neubauer, S; Nielsen, J; Nodulman, L; Norman, M; Norniella, O; Nurse, E; Oakes, L; Oh, S H; Oh, Y D; Oksuzian, I; Okusawa, T; Orava, R; Pagan Griso, S; Palencia, E; Papadimitriou, V; Papaikonomou, A; Paramonov, A A; Parks, B; Pashapour, S; Patrick, J

2009-06-12

276

Next-to-leading order versus quark off-shellness and intrinsic kT in the Drell-Yan process  

NASA Astrophysics Data System (ADS)

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?? behavior of the cross section in these approaches, we find that the effects of quark off-shellness and intrinsic-kT 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 pT-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.

Linnyk, O.; Leupold, S.; Mosel, U.

2007-01-01

277

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

NASA Astrophysics Data System (ADS)

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.

Stage, M.; Rasmussen, K. L.

1992-07-01

278

A Model of the Chicxulub Impact Basin Based on Evaluation of Geophysical Data, Well Logs, and Drill Core Samples  

NASA Technical Reports Server (NTRS)

Abundant evidence now shows that the buried Chicxulub structure in northern Yucatan, Mexico, is indeed the intensely sought-after source of the ejecta found world-wide at the Cretaceous-Tertiary (K/T) boundary. In addition to large-scale concentric patterns in gravity and magnetic data over the structure, recent analyses of drill-core samples reveal a lithological assemblage similar to that observed at other terrestrial craters. This assemblage comprises suevite breccias, ejecta deposit breccias (Bunte Breccia equivalents), fine-grained impact melt rocks, and melt-matrix breccias. All these impact-produced lithologies contain diagnostic evidence of shock metamorphism, including planar deformation features in quartz, feldspar, and zircons; diaplectic glasses of quartz and feldspar; and fused mineral melts and whole-rock melts. In addition, elevated concentrations of Ir, Re, and Os, in meteoritic relative proportions, have been detected in some melt-rock samples from the center of the structure. Isotopic analyses, magnetization of melt-rock samples, and local stratigraphic constraints identify this crater as the source of K/T boundary deposits.

Sharpton, Virgil L.; Marin, Luis E.; Carney, John D.; Lee, Scott; Ryder, Graham; Schuraytz, Benjamin C.; Sikora, Paul; Spudis, Paul D.

1996-01-01

279

Primate origins: implications of a cretaceous ancestry.  

PubMed

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 phylogenies calibrated with dates from denser parts of the fossil record, a statistical analysis of the primate record allowing for major gaps now indicates a Cretaceous origin of euprimates 80-90 Ma ago. If this interpretation is correct, primates overlapped with dinosaurs by some 20 Ma prior to the K/T boundary, and the initial radiation of primates was probably truncated as part of the major extinction event that occurred at the end of the Cretaceous. Following a review of evidence for an early origin of primates, implications of this are discussed with respect to the likely ancestral condition for primates, including a southern continental area of origin and moderately large body size. The known early Tertiary primates are re-interpreted as northern continental offshoots of a 'second wave' of primate evolution. PMID:17855783

Martin, Robert D; Soligo, Christophe; Tavaré, Simon

2007-01-01

280

Selective extinction of marine plankton at the end of the Mesozoic era: The fossil and stable isotope record  

NASA Technical Reports Server (NTRS)

Floral, faunal and stable isotope evidence in a continuous sequence of latest Cretaceous and earliest Tertiary shallow water marine deposits in the Mangyshlak Peninsula, USSR suggest severe environmental changes at the Cretaceous/Tertiary (K/T) boundary. Time frame is provided by nanno, micro and macrofossils as well as by magnetic stratigraphy and an iridium spike. Oxygen isotopic analyses of the bulk sediments, composed of nanno and microplankton skeletal remains, show a sharp positive spike at the K/T boundary. This shift is primarily attributed to severe cooling possibly accompanied by increased salinities of the surface mixed layer. Floral and faunal extinctions were selective, affecting approximately 90 percent of the warm water calcareous phyto and zooplankton genera in the Tethyan-Paratethyan regions. These highly diverse taxa with many endemic representatives were at the peak of their evolutionary development. Geologic evidence indicates that the terminal Cretaceous temperature decline was coeval with widespread and intense volcanic activity which reached a peak at the close of the Mesozoic Era. Increased acidity temporarily prohibited calcite nucleation of the surface dwelling warm-water plankton. Superimposed upon decreased alkalinity, severe and rapid climatic changes caused the extinction of calcareous phyto and zooplankton.

Herman, Y.; Bhattacharya, S. K.

1988-01-01

281

Manson impact structure, Iowa: First geochemical results for drill core M-1  

NASA Technical Reports Server (NTRS)

The Manson Impact Structure is a large complex impact crater centered ca. S km north of the town of Manson, Iowa. It is the largest intact impact structure recognized in the United States (35 km in diameter). Its Ar-40/Ar-39 age is indistinguishable from that of the Cretaceous-Tertiary (K-T) boundary. The Manson structure may be one element of the events at the K-T boundary. The crater is completely covered by Quaternary glacial sedimentary deposits that are normally underlain by Cretaceous clastic sediments and flat-lying carbonate sediments of Phanerozoic age, as well as Proterozoic red clastic, metamorphic, volcanic, and plutonic rock sequences. The study of a reflection seismic profile, provided by Amoco, was critical in interpreting the structure. In the 35 km diameter zone that marks the extension of the crater the normal rock sequence is disturbed due to the impact, and at the center of the structure granitic basement rocks are present that have been uplifted from about 4 km depth. Our studies consist of detailed petrological and geochemical characterization of all cores, with emphasis on a detailed description of all rock types found in the core samples and their relationship to target rocks. Geochemical data on samples from the Manson M-1 core are presented.

Koeberl, Christian; Anderson, Raymond R.; Hartung, Jack B.; Reimold, Wolf Uwe

1993-01-01

282

Joint Spatial-Spectral Reconstruction and k-t Spirals for Accelerated 2D Spatial/1D Spectral Imaging of 13C Dynamics  

PubMed Central

Purpose To develop a novel imaging technique to reduce the number of excitations and required scan time for hyperpolarized 13C imaging. Methods A least-squares based optimization and reconstruction is developed to simultaneously solve for both spatial and spectral encoding. By jointly solving both domains, spectral imaging can potentially be performed with a spatially oversampled single echo spiral acquisition. Digital simulations, phantom experiments, and initial in vivo hyperpolarized [1-13C]pyruvate experiments were performed to assess the performance of the algorithm as compared to a multi-echo approach. Results Simulations and phantom data indicate that accurate single echo imaging is possible when coupled with oversampling factors greater than six (corresponding to a worst case of pyruvate to metabolite ratio < 9%), even in situations of substantial T2* decay and B0 heterogeneity. With lower oversampling rates, two echoes are required for similar accuracy. These results were confirmed with in vivo data experiments, showing accurate single echo spectral imaging with an oversampling factor of 7 and two echo imaging with an oversampling factor of 4. Conclusion The proposed k-t approach increases data acquisition efficiency by reducing the number of echoes required to generate spectroscopic images, thereby allowing accelerated acquisition speed, preserved polarization, and/or improved temporal or spatial resolution. Magn Reson Med

Gordon, Jeremy W.; Niles, David J.; Fain, Sean B.; Johnson, Kevin M.

2014-01-01

283

Impact Theory of Mass Extinctions and the Invertebrate Fossil Record  

Microsoft Academic Search

There is much evidence that the Cretaceous-Tertiary boundary was marked by a massive meteorite impact. Theoretical consideration of the consequences of such an impact predicts sharp extinctions in many groups of animals precisely at the boundary. Paleontological data clearly show gradual declines in diversity over the last 1 to 10 million years in various invertebrate groups. Reexamination of data from

Walter Alvarez; Erle G. Kauffman; Finn Surlyk; Luis W. Alvarez; Frank Asaro; Helen V. Michel

1984-01-01

284

Crossing boundaries  

PubMed Central

ABSTRACT OBJECTIVE To explore the tensions between professional and personal boundaries and how they affect the work and private lives of family physicians. DESIGN Qualitative case study using semistructured interviews. SETTING Province of New Brunswick. PARTICIPANTS Forty-eight family physicians from across the province. METHODS A collective case-study approach was developed, with 24 cases of 2 individuals per case. Cases were selected based on sex, location (urban or rural), language (French or English), and number of years since medical school graduation (< 10 years, 10 to 20 years, or > 20 years). Physicians were interviewed in either French or English. Participants were recruited using the College of Physicians and Surgeons of New Brunswick’s physician directory. Based on the rates of response and participation, some cases were overrepresented, while others were not completed. All interviews were audiotaped, transcribed verbatim, and analyzed thematically using a categorical aggregation approach. A coding scheme for the thematic analysis was developed by the research team before the interviews were transcribed. MAIN FINDINGS Almost all of the family physicians interviewed discussed how their profession negatively affected their personal lives. Many struggled with issues such as heavy workloads, the adverse effects of their profession on their family lives, and the trespassing of patients onto their personal lives in small towns and rural communities. Some physicians had developed strategies to balance their personal lives with their professional demands; however, this often meant reducing work hours or terminating certain shifts, such as those in the emergency department or after-hours clinics. CONCLUSION Family physicians struggle to keep their profession from intruding too much into their private lives. These struggles are important to acknowledge and address in order to avoid physician burnout and premature retirement from clinical practice.

Miedema, Baukje; Easley, Julie; Fortin, Pierrette; Hamilton, Ryan; Tatemichi, Sue

2009-01-01

285

Method for Solving Moving Boundary Value Problems for Linear Evolution Equations  

Microsoft Academic Search

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

A. S. Fokas; B. Pelloni

2000-01-01

286

Boundary streaming with Navier boundary condition  

NASA Astrophysics Data System (ADS)

In microfluidic applications involving high-frequency acoustic waves over a solid boundary, the Stokes boundary-layer thickness ? is so small that some non-negligible slip may occur at the fluid-solid interface. This paper assesses the impact of this slip by revisiting the classical problem of steady acoustic streaming over a flat boundary, replacing the no-slip boundary condition with the Navier condition u |y =0=Ls?yu |y =0, where u is the velocity tangent to the boundary y =0, and the parameter Ls is the slip length. A general expression is obtained for the streaming velocity across the boundary layer as a function of the dimensionless parameter Ls/?. The limit outside the boundary layer provides an effective slip velocity satisfied by the interior mean flow. Particularizing to traveling and standing waves shows that the boundary slip respectively increases and decreases the streaming velocity.

Xie, Jin-Han; Vanneste, Jacques

2014-06-01

287

Two-gluon correlations in heavy-light ion collisions: Energy and geometry dependence, IR divergences, and kT-factorization  

NASA Astrophysics Data System (ADS)

We study the properties of the cross section for two-gluon production in heavy-light ion collisions derived in our previous paper [1] in the saturation/Color Glass Condensate framework. Concentrating on the energy and geometry dependence of the corresponding correlation functions we find that the two-gluon correlator is a much slower function of the center-of-mass energy than the one- and two-gluon production cross sections. The geometry dependence of the correlation function leads to stronger azimuthal near- and away-side correlations in the tip-on-tip U+U collisions than in the side-on-side U+U collisions, an exactly opposite behavior from the correlations generated by the elliptic flow of the quark-gluon plasma: a study of azimuthal correlations in the U+U collisions may thus help to disentangle the two sources of correlations. We demonstrate that the cross section for two-gluon production in heavy-light ion collisions contains a power-law infrared (IR) divergence even for fixed produced gluon momenta: while saturation effects in the target regulate some of the power-law IR-divergent terms in the lowest-order expression for the two-gluon correlator, other power-law IR-divergent terms remain, possibly due to absence of saturation effects in the dilute projectile. Finally we rewrite our result for the two-gluon production cross-section in a kT-factorized form, obtaining a new factorized expression involving a convolution of one- and two-gluon Wigner distributions over both the transverse momenta and impact parameters. We show that the two-gluon production cross-section depends on two different types of unintegrated two-gluon Wigner distribution functions.

Kovchegov, Yuri V.; Wertepny, Douglas E.

2014-05-01

288

A scale of greatness and causal classification of mass extinctions: implications for mechanisms.  

PubMed

A quantitative scale for measuring greatness, G, of mass extinctions is proposed on the basis of rate of biodiversity diminution expressed as the product of the loss of biodiversity, called magnitude (M), and the inverse of time in which that loss occurs, designated as intensity (I). On this scale, the catastrophic Cretaceous-Tertiary (K-T) extinction appears as the greatest since the Ordovician and the only one with a probable extraterrestrial cause. The end-Permian extinction was less great but with a large magnitude (M) and smaller intensity (I); only some of its individual episodes involved some semblance of catastrophe. Other extinctions during the Phanerozoic, with the possible exception of the end-Silurian diversity plunge, were parts of a forced oscillatory phenomenon and seem caused by marine- and land-habitat destruction during continental assemblies that led to elimination of shelves and (after the Devonian) rain forests and enlargement of deserts. Glaciations and orogenies that shortened and thickened the continental crust only exacerbated these effects. During the Mesozoic and Cainozoic, the evolution of life was linearly progressive, interrupted catastrophically only at the K-T boundary. The end-Triassic extinction was more like the Paleozoic extinctions in nature and probably also in its cause. By contrast, the current extinction resembles none of the earlier ones and may end up being the greatest of all. PMID:18779562

Sengör, A M Celâl; Atayman, Saniye; Ozeren, Sinan

2008-09-16

289

Ontogenetic niche shifts in dinosaurs influenced size, diversity and extinction in terrestrial vertebrates.  

PubMed

Given the physiological limits to egg size, large-bodied non-avian dinosaurs experienced some of the most extreme shifts in size during postnatal ontogeny found in terrestrial vertebrate systems. In contrast, mammals--the other dominant vertebrate group since the Mesozoic--have less complex ontogenies. Here, we develop a model that quantifies the impact of size-specific interspecies competition on abundances of differently sized dinosaurs and mammals, taking into account the extended niche breadth realized during ontogeny among large oviparous species. Our model predicts low diversity at intermediate size classes (between approx. 1 and 1000 kg), consistent with observed diversity distributions of dinosaurs, and of Mesozoic land vertebrates in general. It also provides a mechanism--based on an understanding of different ecological and evolutionary constraints across vertebrate groups--that explains how mammals and birds, but not dinosaurs, were able to persist beyond the Cretaceous-Tertiary (K-T) boundary, and how post-K-T mammals were able to diversify into larger size categories. PMID:22513279

Codron, Daryl; Carbone, Chris; Müller, Dennis W H; Clauss, Marcus

2012-08-23

290

Cenozoic bolide impacts and biotic change in North American mammals.  

PubMed

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

Alroy, John

2003-01-01

291

A dual-layer Chicxulub ejecta sequence with shocked carbonates from the Cretaceous–Paleogene (K–Pg) boundary, Demerara Rise, western Atlantic  

Microsoft Academic Search

An up to ?2-cm thick Chicxulub ejecta deposit marking the Cretaceous–Paleogene (K–Pg) boundary (the “K–Tboundary) was recovered in six holes drilled during ODP Leg 207 (Demerara Rise, tropical western Atlantic). Stunning features of this deposit are its uniformity over an area of 30km2 and the total absence of bioturbation, allowing documentation of the original sedimentary sequence. High-resolution mineralogical, petrological,

Schulte Peter; A. Deutsch; T. Salge; J. Berndt; A. Kontny; K. G. MacLeod; R. D. Neuser; S. Krumm

2009-01-01

292

Boundary Models in DPD  

Microsoft Academic Search

We present a model for treating solid boundaries of a DPD fluid. The basic idea is to model the stick boundary conditions by assuming that a layer of DPD particles is stuck on the boundary. By taking a continuum limit of this layer effective dissipative and stochastic forces on the fluid DPD particles are obtained. The boundary model is tested

M. Revenga; I. Zúñiga; P. Español; I. Pagonabarraga

1998-01-01

293

The palaeoclimatology, palaeoecology and palaeoenvironmental analysis of mass extinction events  

Microsoft Academic Search

Although there is a continuum in magnitude of diversity loss between the smallest and largest biotic crisis, typically most authors refer to the largest five Phanerozoic events as “mass extinctions”. In the past 25 years the study of these mass extinction events has increased dramatically, with most focus being on the Cretaceous–Tertiary (K–T) event, although study of the end-Permian event

Richard J. Twitchett

2006-01-01

294

Mammals from the end of the age of dinosaurs in North Dakota and southeastern Montana, with a reappraisal of geographic differentiation among Lancian mammals  

Microsoft Academic Search

An end-Cretaceous nonavian dinosaur extinction and an early Paleocene mam- malian radiation is documented primarily in stratigraphic sequences in eastern Mon- tana. To determine how representative these sequences are, we extended investigation of this Cretaceous-Tertiary (K-T) transition to new areas. Studies in southwestern North Dakota and southeastern Montana provide new records of mammals through the last 1.32-1.68 million years of

John P. Hunter

295

Comparative analysis of SV40 17kT and LT function in vivo demonstrates that LT's C-terminus re-programs hepatic gene expression and is necessary for tumorigenesis in the liver  

PubMed Central

Transformation by Simian Virus 40 (SV40) large T antigen (LT) is mediated in large part by its interaction with a variety of cellular proteins at distinct binding domains within LT. While the interaction of LT's N-terminus with the tumor suppressor Rb is absolutely required for LT-dependent transformation, the requirement for the interaction of LT's C-terminus with p53 is less clear and cell- and context-dependent. Here, we report a line of transgenic mice expressing a doxycycline-inducible liver-specific viral transcript that produces abundant 17kT, a naturally occurring SV40 early product that is co-linear with LT for the first 131 amino acids and that binds to Rb, but not p53. Comparative analysis of livers of transgenic mice expressing either 17kT or full length LT demonstrates that 17kT stimulates cell proliferation and induces hepatic hyperplasia but is incapable of inducing hepatic dysplasia or promoting hepatocarcinogenesis. Gene expression profiling demonstrates that 17kT and LT invoke a set of shared molecular signatures consistent with the action of LT's N-terminus on Rb-E2F-mediated control of hepatocyte transcription. However, 17kT also induces a unique set of genes, many of which are known transcriptional targets of p53, while LT actively suppresses them. LT also uniquely deregulates the expression of a subset of genes within the imprinted network and rapidly re-programs hepatocyte gene expression to a more fetal-like state. Finally, we provide evidence that the LT/p53 complex provides a gain-of-function for LT-dependent transformation in the liver, and confirm the absolute requirement for LT's C-terminus for liver tumor development by demonstrating that phosphatase and tensin homolog (PTEN)-deficiency readily cooperates with LT, but not 17kT, for tumorigenesis. These results confirm independent and inter-dependent functions for LT's N- and C-terminus and emphasize differences in the requirements for LT's C-terminus in cell-type dependent transformation.

Comerford, S A; Schultz, N; Hinnant, E A; Klapproth, S; Hammer, R E

2012-01-01

296

Reconstructing large regions of an ancestral mammalian genome in silico  

Microsoft Academic Search

It is believed that most modern mammalian lineages arose from a series of rapid speciation events near the Cretaceous-Tertiary boundary. It is shown that such a phylogeny makes the common ancestral genome sequence an ideal target for reconstruction. Simulations suggest that with methods currently available, we can expect to get 98% of the bases correct in reconstructing megabase-scale euchromatic regions

Mathieu Blanchette; Eric D. Green; Webb Miller; David Haussler

2008-01-01

297

Environmental perturbations caused by the impacts of asteroids andcomets  

Microsoft Academic Search

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

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

1997-01-01

298

Geological implications of impacts of large asteroids and comets on the earth  

Microsoft Academic Search

The present conference discusses such topics as large object fluxes in near-earth space and the probabilities of terrestrial impacts, the geological record of impacts, dynamics modeling for large body impacts on continents and oceans, physical, chemical, and biological models of large impacts atmospheric effects, dispersed impact ejecta and their signatures, general considerations concerning mass biological extinctions, the Cretaceous\\/Tertiary boundary event,

L. T. Silver; P. H. Schultz

1982-01-01

299

TERRESTRIAL BIOTIC CRISES: PALEOBOTANICAL RECORD AND INTERPRETATION  

Microsoft Academic Search

The controversial problem of biotic crises is considered in relation to the Cretaceous - Tertiary and Permian - Triassic transboundary events in the non- marine sequence of Far East and the Russian platform, respectively. In both cases, the floristic changes across the critical boundaries proceeded in few steps, none of which indicated a catastrophic destruction of plant communities. Rather the

300

Experimental evidence that an asteroid impact LED to the extinction of many species 65 million years ago  

Microsoft Academic Search

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.

L. W. Alvarez

1982-01-01

301

Experimental evidence that an asteroid impact led to the extinction of many species 65 million years ago  

SciTech Connect

The development of the theory that the mass extinction of the dinosaurs at the Cretaceous-Tertiary boundary was caused by an asteroid impact is reviewed. The personnel involved, the objections to the theory, and the evidence refuting those objections are presented chronologically. (ACR)

Alvarez, L.W.

1982-09-01

302

Sniffing for Clues to the Dinosaurs Demise: Measurement of Osmium Isotope Compositions and Platinum Group Element Abundances in Volcanic Emissions  

Microsoft Academic Search

Platinum Group Elements (PGE: Os, Ir, Rh, Ru, Pt, Pd) and osmium isotopes measured in marine and terrestrial sediment, snow and ice records are important paleo-tracers of riverine, hydrothermal, extraterrestrial, volcanic and anthropogenic inputs into the global surficial environment. For instance, the marine Os isotope record across the Cretaceous-Tertiary Boundary (KTB) indicates that the onset of the main phase of

K. W. Sims; B. Peucker-Ehrenbrink; T. Mather; D. Pyle; R. Martin; P. Gauthier; A. Aiuppa

2005-01-01

303

Diachronism between extinction time of terrestrial and marine dinosaurs  

NASA Technical Reports Server (NTRS)

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.

Hansen, H. J.

1988-01-01

304

Environmental perturbations caused by the impacts of asteroids and comets  

Microsoft Academic Search

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

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

1997-01-01

305

Mitogenomic analyses place the gharial (Gavialis gangeticus) on the crocodile tree and provide pre-K/T divergence times for most crocodilians.  

PubMed

Based on morphological analyses, extant members of the order Crocodylia are divided into three families, Alligatoridae, Crocodylidae, and Gavialidae. Gavialidae includes one species, the gharial, Gavialis gangeticus. In this study we have examined crocodilian relationships in phylogenetic analyses of seven mitochondrial genomes that have been sequenced in their entirety. The analyses did not support the morphologically acknowledged separate position of the gharial in the crocodilian tree. Instead the gharial joined the false gharial (Tomistoma schlegelii) on a common branch that was shown to constitute a sister group to traditional Crocodylidae (less Tomistoma). Thus, the analyses suggest the recognition of only two Crocodylia families, Alligatoridae and Crocodylidae, with the latter encompassing traditional Crocodylidae plus Gavialis/Tomistoma. A molecular dating of the divergence between Alligatoridae and Crocodylidae suggests that this basal split among recent crocodilians took place approximately 140 million years before present, at the Jurassic/Cretaceous boundary. The results suggest that at least five crocodilian lineages survived the mass extinction at the KT boundary. PMID:16211427

Janke, Axel; Gullberg, Anette; Hughes, Sandrine; Aggarwal, Ramesh K; Arnason, Ulfur

2005-11-01

306

Evaluating the accretion of meteoritic debris and interplanetary dust particles in the GPC-3 sediment core using noble gas and mineralogical tracers  

NASA Astrophysics Data System (ADS)

Extraterrestrial (ET) noble gases (helium and neon) in 35 sediment samples from Central Pacific core LL-44 GPC-3 demonstrate the variable flux of interplanetary dust particles (IDPs) and major meteorite impacts over the past 70 Ma (21-72 Ma). Spinel mineralogical and chemical compositions clearly distinguish major impact events from the continuous flux of IDPs, including the well-established Cretaceous/Tertiary (K/T) and late Eocene (E/O) impact boundaries. No spinel grains with chemical or mineralogical evidence of a distinctly ET origin were found in an extensive survey of 'background' samples (i.e. non E/O or K/T boundary) suggesting that either the carrier grains for ET noble gas occur within the Fe-Ti oxide mineral fraction observed in this study (found to include ilmenite and ulvospinel) or are too small for identification by SEM. The presence of ilmenite and ulvospinel suggest lunar regolith is a potential source for ET noble gas-rich particles. Noble gas analysis on both the EMF (extractable magnetic fraction) and the Bulk minus EMF (Bulk - EMF) show that the He and Ne compositions are consistent with partially degassed noble gas signatures of zero-age magnetic grains (Z-MAG) and stratospheric interplanetary dust particles (IDPs). Conclusive evidence for a 'planetary' (Ne-A) noble gas signature is found only in the bulk sediments at the K/T boundary, although all GPC-3 K/T fractions (Bulk, EMF, and HF Digestion) plot along a mixing line between planetary (Ne-A) and solar wind (SW). Spinels from major impact boundaries (K/T; E/O) exhibit dendritic texture and elevated [Ni], consistent with previous reports. In contrast to the otherwise consistent [3He] signal from IDPs, the [3He] at the known impact boundaries (K/T and E/O) actually decreases. These anomalously low [3He] are accompanied by significantly elevated [Ne] and significantly lower (3He/20Ne)solar ratios (˜10× lower) produced by both preferentially degassing of He relative to Ne at times of increased flux of larger ET material. Degassed ("degassed-He/enriched-Ne profile") noble gas characteristics occur in two sample intervals that do not correspond to any known impact events (47 and 71 Ma), explained by an influx of larger particles. SEM analysis of the 47 Ma sample shows spinels with dendritic textures, but without distinctive markers of large meteorite impacts (e.g. elevated Ni). Particle size increases and degassed signatures may be caused by major bolides, micrometeorites, comet showers; or simply a flux of larger IDPs, potentially with a different source.

Darrah, Thomas H.; Poreda, Robert J.

2012-05-01

307

Method for solving moving boundary value problems for linear evolution equations  

PubMed

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

Fokas; Pelloni

2000-05-22

308

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...

309

On boundary superalgebras  

SciTech Connect

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.

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

2010-04-15

310

International Rivers as Boundaries  

Microsoft Academic Search

International rivers serve a number of purposes, the most obvious are the navigational and non-navigational uses. Less noticed is the fact that international rivers are also used to delimit boundaries between nations. The immediate question that would arise is: Where are such boundaries actually drawn across the river? Boundaries, however, are established by treaties and the answer to this question

Salman M. A. Salman

2000-01-01

311

Experimentally Shock-loaded Anhydrite: Unit-Cell Dimensions, Microstrain and Domain Size from X-Ray Diffraction  

NASA Technical Reports Server (NTRS)

Cretaceous Tertiary (K/T) boundary is traditionally associated with one of the most dramatic mass extinctions in the Earth history. A number of killing mechanisms have been suggested to contribute to the widespread extinctions of Cretaceous biota at this boundary, including severe, global deterioration of the atmosphere and hydrosphere from the shock-induced release of CO2 and SO(x) from carbonate- and sulfate-bearing target rocks, respectively. Recently carried out calculations revealed that the global warming caused by CO2 release was considerably less important than the cooling due to SO(x) gases release during the Chicxulub impact event. Considering apparent potential importance of the response of sulfates to the shock metamorphism, relative lack of the data on shock behavior of sulfates as well as some general difficulties encountered during thermodynamic modeling of the shock-induced CO2 loss from carbonates we subjected anhydrite to a series of shock experiments designed for complete recovery of the shocked material. We report here on the detail X-ray diffraction analysis of seven samples that were subjected to experimental shock-loading from 10 to 65 GPa.

Skala, R.; Hoerz, F.

2003-01-01

312

Boundary lubrication: Revisited  

NASA Technical Reports Server (NTRS)

A review of the various lubrication regimes, with particular, emphasis on boundary lubrication, is presented. The types of wear debris and extent of surface damage is illustrated for each regime. The role of boundary surface films along with their modes of formation and important physical properties are discussed. In addition, the effects of various operating parameters on friction and wear in the boundary lubrication regime are considered.

Jones, W. R., Jr.

1982-01-01

313

Generalized supersymetric boundary state  

NASA Astrophysics Data System (ADS)

Following our previous paper (hep-th/9909027), we generalize a supersymmetric boundary state so that arbitrary configuration of the gauge field coupled to the boundary of the worldsheet is incorpolated. This generalized boundary state is BRST invariant and satisfies the non-linear boundary conditions with non-constant gauge field strength. This boundary state contains divergence which is identical with the loop divergence in a superstring sigma model. Hence vanishing of the beta function in the superstring sigma model corresponds to a well-defined boundary state with no divergence. The coupling of a single closed superstring massless mode with multiple open string massless modes is encoded in the boundary state, and we confirm that derivative correction to the D-brane action in this sector vanishes up to the first non-trivial order O(alpha'partial2). Combining T-dualities, we incorpolate also general configurations of the scalar fields on the D-brane, and construct boundary states representing branes stuck to another D-brane, with use of BIon configuration.

Hashimoto, Koji

2000-04-01

314

The Atmospheric Boundary Layer  

ERIC Educational Resources Information Center

Discusses some important parameters of the boundary layer and effects of turbulence on the circulation and energy dissipation of the atmosphere. Indicates that boundary-layer research plays an important role in long-term forecasting and the study of air-pollution meteorology. (CC)

Tennekes, Hendrik

1974-01-01

315

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....

316

About positivity of green's functions for nonlocal boundary value problems with impulsive delay equations.  

PubMed

The impulsive delay differential equation is considered (Lx)(t) = x'(t) + ?(i=1)(m) p(i)(t)x(t - ?(i) (t)) = f(t), t ? [a, b], x(t j) = ?(j)x(t(j - 0)), j = 1,…, k, a = t0 < t1 < t2 < ?k < t k+1 = b, x(?) = 0, ? ? [a, b], with nonlocal boundary condition lx = ?(a)(b) ?(s)x'(s)ds + ?x(a) = c, ? ? L ? [a, b]; ?, c ? R. Various results on existence and uniqueness of solutions and on positivity/negativity of the Green's functions for this equation are obtained. PMID:24719584

Domoshnitsky, Alexander; Volinsky, Irina

2014-01-01

317

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

PubMed Central

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.

Pacheco, M. Andreina; Battistuzzi, Fabia U.; Lentino, Miguel; Aguilar, Roberto F.; Kumar, Sudhir; Escalante, Ananias A.

2011-01-01

318

Upper Cretaceous-Tertiary subduction dynamics from the Balkan to the Aegean and W-Anatolia region: input of mineralization and related magmatism  

NASA Astrophysics Data System (ADS)

In the eastern Mediterranean, the dynamics of the Tertiary subduction of African plate below Eurasia is still largely debated, notably in the region extending from the Balkan to the Aegean and western part of Anatolia. To understand this evolution since the late Cretaceous, an additional feature should be considered: the spatial and temporal evolution of arc- and back-arc-related ore deposits. Indeed, the type of mineralization, their magmatic environment and their relationships with large-scale structures, can provide insights on subduction-related processes from deep mantle to surface. In the eastern Mediterranean, a clear evolution through time can be observed. First, during the late Cretaceous and Paleocene, magmatism and mineralization were located in the Balkans with dominant calc-alkaline rocks and related porphyry Cu deposits. These syn-extensional occurrences emplaced in a back-arc environment that developed in response to a low slab retreat. In opposition, from 35-30 Ma, slab retreat accelerated, inducing a significant back-arc extension from the Rhodope massif to the south Aegean domain. Analysis of metallogenic data demonstrates that, during this second stage, mineralization consists mainly in low-sulphidation epithermal Au deposits related to shoshonitic volcanism in NW-Anatolia. The Au stored in the lithospheric mantle during the first stage was remobilized by melting of the lithospheric mantle, thus suggesting a significant thermal event that could result from wide lithospheric extension, possible slab breakoff and asthenospheric influx. From the middle Miocene, alkaline volcanism appeared in western Anatolia and progressively developed in the east of the Aegean domain and some syn-extensional plutonic intrusions were emplaced in the Cyclades up to the upper Miocene. Associated ore deposits are variable with porphyry, skarn and epithermal occurrences and late hydrothermal veins, depending upon various parameters such as the depth of the intrusions. These occurrences developed during the fast clockwise rotation of the western Aegean that is a probable consequence of the slab tear shown by tomographic models below western Anatolia. The related major asthenospheric influx followed the rotating slab and invaded the whole Aegean domain from ~17 Ma ago until 9 Ma. This mantle flow induced the partial melting of the base of continental crust to form the Cycladic plutonic intrusions and related ore deposits.

Menant, Armel; Jolivet, Laurent; Bertrand, Guillaume; Guillou-Frottier, Laurent

2013-04-01

319

From the Cover: Plants with double genomes might have had a better chance to survive the Cretaceous-Tertiary extinction event  

Microsoft Academic Search

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

Jeffrey A. Fawcett; Steven Maere; Yves van de Peer

2009-01-01

320

PTt path in metamorphic rocks of the Khoy region (northwest Iran) and their tectonic significance for Cretaceous–Tertiary continental collision  

Microsoft Academic Search

Metamorphic rocks in the Khoy region are exposed between obducted ophiolites to the southwest and sedimentary rocks of Precambrian–Paleozoic age to the northeast. The Qom formation (Oligocene–Miocene) with a basal conglomerate transgressively overlies all of these rocks. The metamorphic rocks consist of both metasediments and metabasites. The metasediments are micaschist, garnet–staurolite schist and garnet–staurolite sillimanite schist with some meta-arkose, marble

H. Azizi; H. Moinevaziri; M. Mohajjel; A. Yagobpoor

2006-01-01

321

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

Microsoft Academic Search

Both the bolide impact hypothesis and the volcanism hypothesis suggest, as one of the major environmental consequences, the release of large amounts of SO2 and CO2 into the atmosphere, with consequent lowering of the pH of ocean water. In the study of rare earth elements (REEs) in seawater and in carbonate sediments, we found that the Ce in seawater is

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

1996-01-01

322

Cretaceous Tertiary phenomena in the context of seafloor rearrangements and P(CO2) fluctuations over the past 100 m.y  

Microsoft Academic Search

Both the bolide impact hypothesis and the volcanism hypothesis suggest, as one of the major environmental consequences, the release of large amounts of SO2 and CO2 into the atmosphere, with consequent lowering of the pH of ocean water. In the study of rare earth elements (REEs) in seawater and in carbonate sediments, we found that the Ce in seawater is

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

1996-01-01

323

Improving boundary conditions for the Child-Langmuir sheath model  

NASA Astrophysics Data System (ADS)

A collision-free space-charge sheath formed by cold ions at a negative surface is considered. The method of matched asymptotic expansions is applied, small parameter being the ratio of the electron temperature to the sheath voltage. Two expansions are considered, one describing bulk of the sheath where the electron density is exponentially small as compared to the ion density, and another describing the outer section of the sheath in which the electron and ion densities are comparable. Boundary conditions for equations describing the bulk are obtained by matching with a solution describing the outer section. A choice is found of the boundary conditions such that the model have exponential accuracy. A physical meaning of these conditions is that the ions are accelerated in the outer section from the Bohm velocity to twice the Bohm velocity and that the voltage drop in the outer section equals 3/2frackT_ee. The model predicts the electric field and ion velocity at the surface and the thickness of the ion layer to the accuracy of several per cent for sheath voltages exceeding 3 kT_e/e. The validity of the derived boundary conditions is not restricted to the case of a collisionless sheath: they are applicable also in cases when collisions play a role in the bulk of the sheath, provided that the Debye length in the quasineutral plasma is much smaller than the mean free path for collisions of ions and neutral particles.

Benilov, M. S.

2000-10-01

324

Periodic Explosive Expansion of Human Retroelements Associated with the Evolution of the Hominoid Primate  

PubMed Central

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.

Kim, Tae-Min; Hong, Seung-Jin

2004-01-01

325

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

SciTech Connect

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.

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

1993-04-01

326

?-Aminoisobutyric Acid and Isovaline in Tokyo Bay Sediments  

NASA Astrophysics Data System (ADS)

Two nonprotein amino acids, 2-amino-2-methylpropionic acid (?-aminoisobutyric acid, ?AiBA) and 2-amino-2-methylbutanoic acid (isovaline, iVal) were found in modern Tokyo bay sediments together with several protein amino acids. Concentrations of the two nonprotein amino acids were approximately 1 nmol per g of dry sediment, and the protein amino acids were several hundred to slightly over one thousand nmol per g. iVal was found to be nearly racemic, whereas the protein amino acids were predominantly in the L-form. We do not consider the two nonprotein amino acids to be of extraterrestrial origin as suggested by the study of the Cretaceous/Tertiary (K/T) boundary sediments at Stevns Klint ( Zhao and Bada 1989) and propose a terrestrial origin. The source of the two nonprotein amino acids is not biological because the iVal is racemic. They may come from industrial waste water containing C-5 substituted hydantoins which then hydrolyzed to give ?AiBA and racemic iVal.

Mita, Hajime; Shimoyama, Akira

1998-01-01

327

Mammalian phylogeny reveals recent diversification rate shifts.  

PubMed

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

Stadler, Tanja

2011-04-12

328

The noncommutative Choquet boundary  

NASA Astrophysics Data System (ADS)

Let S be an operator system-a self-adjoint linear subspace of a unital C^* -algebra A such that 1in S and A=C^*(S) is generated by S . A boundary representation for S is an irreducible representation pi of C^*(S) on a Hilbert space with the property that pirestriction_S has a unique completely positive extension to C^*(S) . The set partial_S of all (unitary equivalence classes of) boundary representations is the noncommutative counterpart of the Choquet boundary of a function system Ssubseteq C(X) that separates points of X . It is known that the closure of the Choquet boundary of a function system S is the Silov boundary of X relative to S . The corresponding noncommutative problem of whether every operator system has ``sufficiently many" boundary representations was formulated in 1969, but has remained unsolved despite progress on related issues. In particular, it was unknown if partial_Sneqemptyset for generic S . In this paper we show that every separable operator system has sufficiently many boundary representations. Our methods use separability in an essential way.

Arveson, William

2008-10-01

329

Defining Regional Boundaries  

NSDL National Science Digital Library

The purpose of this resource is to identify a reqion for study as a system, and to establish a list of characteristics and features useful for determining the boundaries of regional systems. Students discuss their current understanding of what Earth systems are and how they work, and consider how to identify the boundaries of a region for Earth system study. In small groups, they select a region for recommendation to the class, and they make a list of characteristics and features that can mark the boundaries of regional systems. After presentations by each group, the class chooses one region for study as an Earth system. Then they mark the boundaries of their chosen region on their Landsat image, topographic map, or other map.

The GLOBE Program, University Corporation for Atmospheric Research (UCAR)

2003-08-01

330

Mapping Plate Tectonic Boundaries  

NSDL National Science Digital Library

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.

Kerwin, Michael

331

Boundary detection in multidimensions.  

PubMed

The development of image processing algorithms for time-varying imagery and computerized tomography data calls for generalization of the concepts of adjacency, connectivity, boundary, etc., to three and four-dimensional discrete spaces. This paper defines these basic concepts in unified terminology and presents algorithms for a boundary detection task in multidimensional space. The performance of these algorithms is discussed with respect to theoretical maximum complexity, and is illustrated with simulated computerized tomography data. PMID:21869001

Udupa, J K; Srihari, S N; Herman, G T

1982-01-01

332

Graphs with small boundary  

Microsoft Academic Search

For a pair of vertices x and y in a graph G, we denote by dG(x,y) the distance between x and y in G. We call x a boundary vertex of y if x and y belong to the same component and dG(y,v)?dG(y,x) for each neighbor v of x in G. A boundary vertex of some vertex is simply called

Yoko Hasegawa; Akira Saito

2007-01-01

333

Separated laminar boundary layers  

NASA Technical Reports Server (NTRS)

Classical boundary layer theory is inadequate to deal with the problem of flow separation owing to its underlying assumption that the boundary layer has an insignificant effect on the external stream. This difficulty is resolved by a theory which includes interaction with the external flow. This theory is described from the viewpoint of the asymptotic triple deck structure. Several triple deck studies are reviewed with emphasis on results of interest in aeronautical applications.

Burggraf, O. R.

1976-01-01

334

Psychodynamic Perspective on Therapeutic Boundaries  

PubMed Central

Discussion of boundaries in therapeutic work most often focuses on boundary maintenance, risk management factors, and boundary violations. The psychodynamic meaning and clinical management of boundaries in therapeutic relationships remains a neglected area of discourse. Clinical vignettes will illustrate a psychodynamic, developmental-relational perspective using boundary dilemmas to deepen and advance the therapeutic process. This article contributes to the dialogue about the process of making meaning and constructing therapeutically useful and creative boundaries that further the psychotherapeutic process.

Bridges, Nancy A.

1999-01-01

335

Biodiversity changes in Cretaceous palynofloras of eastern Asia and western North America  

USGS Publications Warehouse

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.

Nichols, D. J.

2003-01-01

336

Phenomenological Application of $k_T$ factorization  

Microsoft Academic Search

We discuss applications of the perturbative QCD approach in the exclusive non-leptonic two body B-meson decays. We briefly review its ingredients and some important theoretical issues on the factorization approaches. PQCD results are compatible with present experimantal data for the charmless B-meson decays. We predict the possibility of large direct CP asymmetry in $B^0 \\\\to \\\\pi^{+}\\\\pi^{-}$ $(23\\\\pm7 %)$ and $B^0\\\\to

Yong-Yeon Keum

2004-01-01

337

K-T Transition into Chaos.  

ERIC Educational Resources Information Center

Discusses the destabilizing influences that affect feedback systems in the earth and trigger disorganization. Presents information that integrates mantle degassing with feed-back systems, and the Sun-Earth-Space energy flow system which is the primary source of energy that drives the Earth's biosphere. (RT)

McLean, Dewey M.

1988-01-01

338

Economics of the K-T process  

Microsoft Academic Search

The average gas cost of intermediate and high Btu gas produced in the Koppers-Totzek coal gasification process (for the production of a clean gaseous fuel and synthesis products such as hydrogen, ammonia, and methanol) was calculated. The coal preparation and gasification process is described, along with the processes of gas cooling and cleaning and sulfur removal. Costs associated with the

D. M. Mitsak; J. F. Farnsworth; R. Wintrell

1975-01-01

339

Melt droplet formation in energetic impact events  

NASA Astrophysics Data System (ADS)

It was recently shown that geological materials initially shocked to high pressure approach the liquid-vapor phase boundary from the liquid side as they decompress, breaking up into an expanding spray of liquid droplets. A simple theory is presented here for estimating the sizes of these droplets as a function of impactor size and velocity. It is shown that these sizes are consistent with observations of microtektites and spherules found in the Cretaceous/Tertiary boundary layer.

Melosh, H. J.; Vickery, A. M.

1991-04-01

340

Terrestrial and Extraterrestrial Fullerenes  

Microsoft Academic Search

This paper reviews reports of occurrences of fullerenes in circumstellar media, interstellar media, meteorites, interplanetary dust particles (IDPs), lunar rocks, hard terrestrial rocks from Shunga (Russia), Sudbury (Canada) and Mitov (Czech Republic), coal, terrestrial sediments from the Cretaceous?Tertiary?Boundary and Permian?Triassic?Boundary, fulgurite, ink sticks, dinosaur eggs, and a tree char. The occurrences are discussed in the context of known and postulated

D. Heymann; L. W. Jenneskens; J. Jehli?ka; Carola Koper; E. J. Vlietstra

2003-01-01

341

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...

342

Probabilistic boundary element method  

NASA Technical Reports Server (NTRS)

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.

Cruse, T. A.; Raveendra, S. T.

1989-01-01

343

Road boundary detection  

NASA Technical Reports Server (NTRS)

A method for extracting road boundaries using the monochrome image of a visual road scene is presented. The statistical information regarding the intensity levels present in the image along with some geometrical constraints concerning the road are the basics of this approach. Results and advantages of this technique compared to others are discussed. The major advantages of this technique, when compared to others, are its ability to process the image in only one pass, to limit the area searched in the image using only knowledge concerning the road geometry and previous boundary information, and dynamically adjust for inconsistencies in the located boundary information, all of which helps to increase the efficacy of this technique.

Sowers, J.; Mehrotra, R.; Sethi, I. K.

1989-01-01

344

Boundary layer simulator improvement  

NASA Technical Reports Server (NTRS)

Boundary Layer Integral Matrix Procedure (BLIMPJ) has been identified by the propulsion community as the rigorous boundary layer program in connection with the existing JANNAF reference programs. The improvements made to BLIMPJ and described herein have potential applications in the design of the future Orbit Transfer Vehicle engines. The turbulence model is validated to include the effects of wall roughness and a way is devised to treat multiple smooth-rough surfaces. A prediction of relaminarization regions is examined as is the combined effects of wall cooling and surface roughness on relaminarization. A turbulence model to represent the effects of constant condensed phase loading is given. A procedure is described for thrust decrement calculation in thick boundary layers by coupling the T-D Kinetics Program and BLIMPJ and a way is provided for thrust loss optimization. Potential experimental studies in rocket nozzles are identified along with the required instrumentation to provide accurate measurements in support of the presented new analytical models.

Praharaj, Sarat C.; Schmitz, Craig P.; Nouri, Joseph A.

1989-01-01

345

Periodic boundary conditions  

NSDL National Science Digital Library

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.

Iacovella, Christopher R.

2006-09-24

346

Cartographic Boundary Files  

NSDL National Science Digital Library

The Cartographic Boundary Files Web site from the US Census Bureau contains "generalized extracts from the Census Bureau's TIGER geographic database for use in a Geographic Information System (GIS) or similar mapping systems." The files are mainly from the 2000 census and contain such things as Congressional Districts, School Districts, Urbanized Areas, and more. The Descriptions and Metadata link gives users an idea of what is contained in each file before downloading, and the Download Boundary Files link lists each file that can than be downloaded, all available in several formats.

2001-01-01

347

Organic-Chemical Clues to the Theory of Impacts as a Cause of Mass Extinctions  

NASA Astrophysics Data System (ADS)

The reasons for the mass extinctions, which occur from time to time in Earth's history-as, e.g., the dinosaur extinction at the Cretaceous/Tertiary boundary 65 myr ago - are still not satisfactorily cleared up. A possible reason might be the impact of one or several comets of several kilometers in diameter. In this paper the astrophysical background of this hypothesis and organic-chemical processes during an impact will be discussed. Quantitative estimations are given, which show that the amount of organic substances brought to the Earth may be of the same order of magnitude as the normal biological production of organic material. Investigations are proposed to examine the organic-chemical composition of profiles of the Cretaceous/Tertiary boundary and other boundaries, at which mass extinction had occurred, in order to find anomalies as consequences of impacts.

Sack, N. J.

1988-11-01

348

Flashover and boundary properties  

Microsoft Academic Search

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

Alan N. Beard

2010-01-01

349

Boundary counterterms in supergravity  

Microsoft Academic Search

Quantum supergravity may be described in terms of the amplitude to go from data given on an initial spacelike hypersurface to data on a final surface, instead of the usual S-matrix formulation. One might expect this description to involve more infinities than the usual one, since additional counterterms might be formed from data on the boundary surfaces. Such counterterms are

P. D. D'Eath

1986-01-01

350

Axisymmetric free boundary problems  

Microsoft Academic Search

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

Mark Sussman; Peter Smereka

1997-01-01

351

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...

352

Boundary Ambiguity in Stepfamilies  

ERIC Educational Resources Information Center

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…

Stewart, Susan D.

2005-01-01

353

Study of Boundary Structures.  

National Technical Information Service (NTIS)

The project extends previous studies on structures of a 2-D grain boundary (g.b.). The basic analytical tool is the cluster variation method (CVM) and the path probability method (PPM), both developed by the author. In the CVM, the free energy is minimize...

R. Kikuchi

1987-01-01

354

Interstellar Boundary Explorer Lithograph  

NSDL National Science Digital Library

This is a lithograph that outlines the major mission highlights of the Interstellar Boundary Explorer, or IBEX, mission, a Small Explorer Earth-orbiting spacecraft that is designed to map the distant boundary between the solar wind from our Sun and the interstellar medium, the material between the stars. Short educational activities are included on the back of the lithograph. Learners will use a ball to represent the Earth to investigate the concepts of size and scale in relation to the IBEX mission: the size of the Moon compared to Earth, the distance from the Earth to the Moon on the same scale, the distance to the farthest point in IBEX's orbit, and the distance to the Sun and the edge of the heliosphere, also on the same scale.

355

Boundary layer stability calculations  

NASA Technical Reports Server (NTRS)

In this paper numerical calculation of the spatial stability of disturbances in the parallel and nonparallel Blasius boundary layers is considered. Chebyshev polynomials are used for discretization. The problem with the boundary condition at infinity is overcome, and the resulting nonlinear matrix eigenvalue problem is attacked directly. The secondary eigenvalue problem for three-dimensional disturbances is shown to be uniformly stable, and particular solutions of this problem generated by the Orr-Sommerfeld equation are shown. A numerical solution of the nonparallel problem is considered using Chebyshev polynomials. The matrix equations are analyzed directly and the problem of uniqueness of the nonparallel correction is settled by careful application of the Fredholm alternative. Nonparallel corrections to the streamwise eigenfunction are shown.

Bridges, Thomas J.; Morris, Philip J.

1987-01-01

356

Boundary Element Method Tutorial  

NSDL National Science Digital Library

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.

Dwyer, Jerry; Hitchcock, Kathy; Gray, Leonard

2004-09-21

357

Boundary layer simulator improvement  

NASA Technical Reports Server (NTRS)

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.

Praharaj, S. C.; Schmitz, C.; Frost, C.; Engel, C. D.; Fuller, C. E.; Bender, R. L.; Pond, J.

1984-01-01

358

The Atmospheric Boundary Layer  

NASA Astrophysics Data System (ADS)

A comprehensive and lucid account of the physics and dynamics of the lowest one to two kilometers of the Earth's atmosphere in direct contact with the Earth's surface, known as the atmospheric boundary layer (ABL). Dr. Garratt emphasizes the application of the ABL problems to numerical modeling of the climate, which makes this book unique among recent texts on the subject. He begins with a brief introduction to the ABL before leading to the development of mean and turbulence equations and the many scaling laws and theories that are the cornerstone of any serious ABL treatment. Modeling of the ABL is crucially dependent for its realism on the surface boundary conditions, so chapters four and five deal with aerodynamic and energy considerations, with attention given to both dry and wet land surfaces and the sea. The author next treats the structure of the clear-sky, thermally stratified ABL, including the convective and stable cases over homogeneous land, the marine ABL, and the internal boundary layer at the coastline. Chapter seven then extends this discussion to the cloudy ABL. This is particularly relevant to current research because the extensive stratocumulus regions over the subtropical oceans and stratus regions over the Arctic have been identified as key players in the climate system. In the final chapters, Dr. Garratt summarizes the book's material by discussing appropriate ABL and surface parameterization schemes in general circulation models of the atmosphere that are being used for climate stimulation.

Garratt, J. R.

1994-05-01

359

Discovering Plate Boundaries  

NSDL National Science Digital Library

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.

Sawyer, Dale

1997-09-15

360

Cell boundary fault detection system  

DOEpatents

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.

Archer, Charles Jens (Rochester, MN) [Rochester, MN; Pinnow, Kurt Walter (Rochester, MN) [Rochester, MN; Ratterman, Joseph D. (Rochester, MN) [Rochester, MN; Smith, Brian Edward (Rochester, MN) [Rochester, MN

2009-05-05

361

Tectonic Plates and Plate Boundaries  

NSDL National Science Digital Library

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.

Foundation, Wgbh E.

2005-12-17

362

THE SURVEYOR AND THE BOUNDARY  

Microsoft Academic Search

The preamble of the paper draws attention to the concept and importance of boundaries from the early creation, reminding us about the role that boundaries played in the ejection of Adam and Eve from the Garden of Eden. The paper therefore traces the origin of the concept of boundary from the time of Adam. Over the years however, the legal

Francis O. KORKOR

363

Anisotropy across Superplume Boundaries  

NASA Astrophysics Data System (ADS)

Sdiff data sets are presented for paths that run parallel to the African and the Pacific superplume boundaries. Objective clustering of waveforms illustrates sharp changes across these boundaries. The African plume shows a sharp offset in travel times in the SHdiff phase, while a more gradual offset towards slower arrivals is seen in the case of the Pacific superplume. Additionally, Pdiff phases display no offset around the African plume and a weak one around the Pacific plume. Here we focus mainly on another striking feature observed in both cases: outside of the superplume the Sdiff particle motion is strongly elliptical, but becomes linear within the superplume (first noticed by To et al. 2005 in the African superplume case). For the African plume we argue that these observations of delayed SV at large distances (~120 degrees) are indicative of the occurrence of azimuthal anisotropy. The SV arrivals have similar polarity as SH, opposite from what their radiation pattern predicts. Azimuthal anisotropy causes SH energy to be converted to SV (Maupin, 1994), explaining the travel time, polarity and amplitude. Forward modeling through different isotropic and anisotropic models supports this statement, although there are trade-offs between direction and magnitude of azimuthal anisotropy. The strong elliptical particle motions are also observed outside the Pacific plume, but at shorter distances (95-105 degrees). Elliptical motions can occur in the absence of anisotropy when strong velocity deviations or layering occurs close to the CMB, which, based on velocity profiles with depth in global tomographic models would be more likely within the superplume rather than on the fast side. The elliptical particle motions here can be modelled with a simple transverse isotropic model with VSH>VSV, but azimuthal anisotropy cannot be ruled out. The complexities within the Pacific superplume, including strong amplitude drop and existence of a post-cursor, are likely caused by an ultra low velocity zone (Cottaar and Romanowicz, this meeting) and make it difficult to constrain anisotropy within the Pacific superplume. Notably, however, in both cases, elliptical particle motions become more linear, and thus anisotropy decreases, from the fast side towards the slow side across superplume boundaries. Possibly this is caused by a rotation in the deformational regime, causing rotation of the pre-existing anisotropic fast directions. Forward modeling of deformation using tracers in mantle convection models, considering different mineral physics scenarios (Wenk et al., 2011) suggest that the boundaries in anisotropy from downwellings to upwellings can be sharp, and could possibly contribute to explaining the sharp boundary in VSH, in addition to effects of lateral variations in temperature and composition. Moreover the model for post-perovskite with (001)-slip predicts anti-correlation between S and P wave anisotropy. Variation in VPH due to anisotropy would then be anti-correlated with the variation caused by temperature, and this could explain the lack of correlation in the variations of VSH and VPH across the superplume boundary. Our modeling shows that care must be taken when computing R=dlnVs/dlnVp in the presence of anisotropy.

Cottaar, S.; Romanowicz, B. A.

2011-12-01

364

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.

365

A classification of ecological boundaries  

USGS Publications Warehouse

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.

Strayer, D. L.; Power, M. E.; Fagan, W. F.; Pickett, S. T. A.; Belnap, J.

2003-01-01

366

Streamer Brightness Boundary  

NASA Technical Reports Server (NTRS)

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 analyze the spreading factor close to the closed field lines. The model is based on the one-temperature, isothermal flow model of Pneuman (1968), extended to calculate spreading factors and plasma beta, and to better explain streamer evolution with increasing temperature.

Suess, S. T.; Nerney, S.

1999-01-01

367

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.

368

Endogenous versus Exogenous Origins of Crises  

Microsoft Academic Search

Are large biological extinctions such as the Cretaceous\\/Tertiary KT boundary due to a meteorite, extreme volcanic activity\\u000a or self-organized critical extinction cascades? Are commercial successes due to a progressive reputation cascade or the result\\u000a of a well orchestrated advertisement? Determining the chain of causality for Xevents in complex systems requires disentangling\\u000a interwoven exogenous and endogenous contributions with either no clear

Didier Sornette; V. I. Yukalov; E. P. Yukalova; J.-Y. Henry; D. Schwab

2004-01-01

369

Robust Time Estimation Reconciles Views of the Antiquity of Placental Mammals  

Microsoft Academic Search

BackgroundMolecular studies have reported divergence times of modern placental orders long before the Cretaceous–Tertiary boundary and far older than paleontological data. However, this discrepancy may not be real, but rather appear because of the violation of implicit assumptions in the estimation procedures, such as non-gradual change of evolutionary rate and failure to correct for convergent evolution.Methodology\\/Principal FindingsNew procedures for divergence-time

Yasuhiro Kitazoe; Hirohisa Kishino; Peter J. Waddell; Noriaki Nakajima; Takahisa Okabayashi; Teruaki Watabe; Yoshiyasu Okuhara; Matthew Hahn

2007-01-01

370

New dinosaur sites correlated with Upper Maastrichtian pelagic deposits in the Spanish Pyrenees: implications for the dinosaur extinction pattern in Europe  

Microsoft Academic Search

Six new dinosaurs sites have been found close to the Cretaceous\\/Tertiary boundary in Arén (south-central Pyrenees, Huesca, Spain) in coastal and non-marine deposits of the Arén and Tremp Formations. The sites contain articulated remains (skull elements, vertebrae, hind-limb bones) and isolated teeth and bones of hadrosaurids, three types of theropod teeth, one sauropod, at least seven types of eggshells (six

Nieves López-Mart??nez; José Ignacio Canudo; Llu??s Ardèvol; Xabier Pereda Suberbiola; Xabier Orue-Etxebarria; Gloria Cuenca-Bescós; José Ignacio Ruiz-Omeñaca; Xabier Murelaga; Monique Feist

2001-01-01

371

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

NASA Astrophysics Data System (ADS)

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.

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

1997-10-01

372

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.

373

The Blake Nose Cretaceous-Paleogene (Florida atlantic margin, ODP Leg 171 B): An exemplar record of the Maastrichtian-Danian transition [Le Cre??tace??-Pale??oge??ne du Blake Nose (marge atlantique de la Floride, campagne ODP 171 B) : Un enregistrement exemplaire de la transition Maastrichtien-Danien  

USGS Publications Warehouse

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.

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, III, W.; Watkins, D. K.; Widmark, J.; Wilson, P. A.

1997-01-01

374

Organic-chemical clues to the theory of impacts as a cause of mass extinctions  

Microsoft Academic Search

The reasons for the mass extinctions, which occur from time to time in Earth's history-as, e.g., the dinosaur extinction at the Cretaceous\\/Tertiary boundary 65 myr ago - are still not satisfactorily cleared up. A possible reason might be the impact of one or several comets of several kilometers in diameter. In this paper the astrophysical background of this hypothesis and

N. J. Sack

1988-01-01

375

Organic-Chemical Clues to the Theory of Impacts as a Cause of Mass Extinctions  

Microsoft Academic Search

The reasons for the mass extinctions, which occur from time to time in Earth's history-as, e.g., the dinosaur extinction at the Cretaceous\\/Tertiary boundary 65 myr ago - are still not satisfactorily cleared up. A possible reason might be the impact of one or several comets of several kilometers in diameter. In this paper the astrophysical background of this hypothesis and

N. J. Sack

1988-01-01

376

Rapid (10-yr) recovery of terrestrial productivity in a simulation study of the terminal Cretaceous impact event  

Microsoft Academic Search

Investigations of short-term (up to 103 yr) environmental change across the Cretaceous–Tertiary boundary provide evidence for reduced temperatures, consistent with the injection of debris and sulphate aerosols into the upper atmosphere by a large impact event. Concomitant with this was a postulated massive addition of CO2 to the atmospheric carbon reservoir by impact vaporisation of the Chicxulub carbonate platform. Taken

Barry Lomax; David Beerling; Garland Upchurch Jr; Bette Otto-Bliesner

2001-01-01

377

Possible Climatic Perturbations Produced by Impacting Asteroids and Comets  

Microsoft Academic Search

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

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

1995-01-01

378

The Magnetopause Boundary  

NSDL National Science Digital Library

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.

Odenwald, Sten

379

Nanoscale Boundary Lubrication Studies  

NASA Astrophysics Data System (ADS)

Boundary films are formed by physisorption, chemisorption, and chemical reaction. With physisorption, no exchange of electrons takes place between the molecules of the adsorbate and those of the adsorbant. The physisorption process typically involves van der Waals forces, which are relatively weak. In chemisorption, there is an actual sharing of electrons or electron interchange between the chemisorbed species and the solid surface. The solid surfaces bond very strongly to the adsorption species through covalent bonds. Chemically reacted films are formed by the chemical reaction of a solid surface with the environment. The physisorbed film can be either monomolecularly or polymolecularly thick. The chemisorbed films are monomolecular, but stoichiometric films formed by chemical reaction can have a large film thickness. In general, the stability and durability of surface films decrease in the following order: chemically reacted films, chemisorbed films, and physisorbed films. A good boundary lubricant should have a high degree of interaction between its molecules and the sliding surface. As a general rule, liquids are good lubricants when they are polar and, thus, able to grip solid surfaces (or be adsorbed). In this chapter, we focus on perfluoropolyethers (PFPEs). We first introduce details of the commonly used PFPE lubricants; then present a summary of nanodeformation, molecular conformation, and lubricant spreading studies; followed by an overview of nanotribological properties of polar and nonpolar PFPEs studied by atomic force microscopy (AFM) and some concluding remarks.

Bhushan, Bharat; Liu, Huiwen

380

Nanoscale Boundary Lubrication Studies  

NASA Astrophysics Data System (ADS)

Boundary films are formed by physisorption, chemisorption, and chemical reaction. With physisorption, no exchange of electrons takes place between the molecules of the adsorbate and those of the adsorbant. The physisorption process typically involves van der Waals forces, which are relatively weak. In chemisorption, there is an actual sharing of electrons or electron interchange between the chemisorbed species and the solid surface. The solid surfaces bond very strongly to the adsorption species through covalent bonds. Chemically reacted films are formed by the chemical reaction of a solid surface with the environment. The physisorbed film can be either monomolecularly or polymolecularly thick. The chemisorbed films are monomolecular, but stoichiometric films formed by chemical reaction can have a large film thickness. In general, the stability and durability of surface films decrease in the following order: chemically reacted films, chemisorbed films, and physisorbed films. A good boundary lubricant should have a high degree of interaction between its molecules and the sliding surface. As a general rule, liquids are good lubricants when they are polar and, thus, able to grip solid surfaces (or be adsorbed). In this chapter, we focus on PFPEs. We first introduce details of the commonly used PFPE lubricants; then present a summary of nanodeformation, molecular conformation, and lubricant spreading studies; followed by an overview of nanotribological properties of polar and nonpolar PFPEs studied by atomic force microscopy (AFM) atomic force microscope (AFM) and some concluding remarks.

Bhushan, Bharat; Liu, Huiwen

381

The Boundary Layer Radiometer  

NASA Astrophysics Data System (ADS)

The Boundary Layer Radiometer is a small, low mass (<1kg) radiometer with only a single moving part - a scan/calibration mirror. The instrument consists of a three mirror telescope system incorporating an intermediate focus for use with miniature infrared and visible filters. It also has an integrated low power blackbody calibration target to provide long-term calibration stability The instrument may be used as an upward looking boundary layer radiometer for both the terrestrial and Martian atmospheres with appropriate filters for the mid-infrared carbon dioxide band, as well as a visible channel for the detection of aerosol components such as dust. The scan mirror may be used to step through different positions from the local horizon to the zenith, allowing the vertical temperature profile of the atmosphere to be retrieved. The radiometer uses miniature infrared filter assemblies developed for previous space-based instruments by Oxford, Cardiff and Reading Universities. The intermediate focus allows for the use of upstream blocking filters and baffles, which not only simplifies the design of the filters and focal plane assembly, but also reduces the risk of problems due to stray light. Combined with the calibration target this means it has significant advantages over previous generations of small radiometers.

Irshad, Ranah; Bowles, N. E.; Calcutt, S. B.; Hurley, J.

2010-10-01

382

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

NASA Astrophysics Data System (ADS)

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 controversial. We have discovered spherule layers several meters below the K-T boundary (Chicxulub impact layer) in giant piston core GPC-3 and in DSDP drill cores 576-8-1 (43-45 cm) and 596-3-6 (142-144 cm) from the northern and southern Pacific Ocean, respectively. We have also found a spherule layer ~8 cm below the peak K-T Ir anomaly in core 596-3-4 (50-51 cm); this layer contains the farthest known spherules from the Chicxulub crater (>10,000 km at 65 Ma). Corliss and Hollister [Nature, 282, 1979, p. 707-9] initially reported small (~20 ?m) cristobalite spherules in core GPC-3 within a zone of disrupted layering, between ~2 m below the K-T boundary and the core bottom (~2 m thick), but considered them of volcanic origin. We have found larger spherules and mineral crystals (up to >200 ?m) dispersed within this disturbed zone. The spherule layers found ~5.5 m below the peak K-T Ir anomaly in hole 576, and ~3.8 m below the peak K-T Ir anomaly in hole 596 are relatively undisturbed. Hole GPC-3 is the easternmost on Mesozoic crust in the Pacific Ocean, and we interpret the pre-K-T spherules and mineral crystals as ejecta and vapor-phase condensates, respectively, from an oceanic impact site farther east on crust now subducted beneath western North America. Apparently, the pre-K-T spherule layers are related to an earlier large impact because of the size of the condensed particles (>100 ?m) in the GPC-3 core, and because some of the particles have chemical compositions (Fe-Ti-C-O) that are not of volcanic origin. Disruption of the sediments and dispersal of the spherules and mineral grains in core GPC-3 were probably caused by megatsunami waves associated with nearby impact. Such waves (initially up to 4 km high) might account for an abrupt anomaly in the seawater 87Sr/86Sr ratio, also preceding the K-T boundary by several m.y., because the waves likely washed vast amounts of 87Sr-rich continental soils into the oceans. In addition, erosion of shallow continental margins or deposition of higher-energy sediments by megatsunami waves left a stratigraphic record that may be erroneously interpreted as indicating a regression-transgression pulse in sea level near the time of impact.

Hagstrum, J. T.; Abbott, D.

2002-12-01

383

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)

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.

Krogh, T. E.; Kamo, S. L.; Bohor, B. F.

1992-01-01

384

Boundary layer transition studies  

NASA Technical Reports Server (NTRS)

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.

Watmuff, Jonathan H.

1995-01-01

385

A Classification of Ecological Boundaries  

NSDL National Science Digital Library

This peer-reviewed article from BioScience is about defining ecological boundaries. 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.

DAVID L. STRAYER, MARY E. POWER, WILLIAM F. FAGAN, STEWARD T. A. PICKETT, and JAYNE BELNAP (;)

2003-08-01

386

Meteors and Meteorites  

NSDL National Science Digital Library

This resource covers meteors; meteor showers, such as Leonids; the relationship between meteor showers and comets; fireballs; classification of meteorites into chondrite, iron and carbonaceous chondrite meteorites; and meteorite impacts, including their velocities. There is information on a meteorite that may have come from the asteroid Vesta; a Mars meteorite that may hold evidence of life; the relation between the Cretaceous-Tertiary mass extinction (commonly known as the K-T Event), the Chicxulub crater in the Yucatan region of Mexico, and dinosaur extinction; and antarctic meteorites. There is also a video clip of the Peekskill fireball of 1992, and a photograph of the Barringer Crater of Arizona.

2007-06-05

387

Grain boundary finite length faceting  

Microsoft Academic Search

We study symmetrical and asymmetrical aluminium grain boundary faceting with molecular dynamics simulations employing two embedded atom method potentials. Facet formation, coarsening, and the reversible phase transition of ?3{110} boundary into ?3{112} twin, and vice versa, are demonstrated in the simulations and the results are consistent with earlier experimental studies and theoretical models. The ?11{002}1\\/{667}2 boundary shows faceting into {225}1\\/{441}2

Z. X. Wu; Y. W. Zhang; D. J. Srolovitz

2009-01-01

388

Adaptive Multilingual Sentence Boundary Disambiguation  

Microsoft Academic Search

The sentence is a standard textual unit in natual language processing applications. In many language the punctuation mark that indicates the end-of-sentence boundary is ambiguous; thus the tokenizers of most NLP systems must be equipped with special sentence boundary recognition rules for every new text collection.As an alternative, this article presents an efficient, trainable system for sentence boundary disambiguation. The

David D. Palmer; Marti A. Hearst

1997-01-01

389

Biodiversity during the Deccan volcanic eruptive episode  

NASA Astrophysics Data System (ADS)

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.

Khosla, A.; Sahni, A.

2003-06-01

390

Boundary-Layer & health  

NASA Astrophysics Data System (ADS)

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.

Costigliola, V.

2010-09-01

391

Boundary Tides in the Kattegat  

Microsoft Academic Search

IN order to facilitate observations on the vertical movements of the boundary surface far from the shore a recording boundary gauge has been constructed. A commercial steel barrel of about 200 litres capacity used for kerosene was provided with an axial tube of two inches width running through the barrel and having its ends welded to the flat ends of

Hans Pettersson; Börje Kullenberg

1933-01-01

392

Impedance boundary conditions in ultrasonics  

Microsoft Academic Search

A generalized impedance boundary condition (GIBC) is developed to approximate the scattering of a plane acoustic wave from a bone structure such as a rib. In particular, the rib and surrounding tissue are modeled as a viscoelastic cylinder of infinite length immersed in an infinite, inviscid fluid medium. In order to determine the scattered pressure wave, appropriate boundary conditions are

John D. Shumpert; Thomas B. A. Senior

2000-01-01

393

Graphs with four boundary vertices  

Microsoft Academic Search

A vertex v of a graph G is a boundary vertex if there exists a vertex u such that the distance in G from u to v is at least the distance from u to any neighbour of v. We give a full description of all graphs that have exactly four boundary vertices, which answers a question of Hasegawa and

Tobias Müller; A. Por; J.-S. Sereni

2011-01-01

394

Cell boundary fault detection system  

DOEpatents

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.

Archer, Charles Jens (Rochester, MN) [Rochester, MN; Pinnow, Kurt Walter (Rochester, MN) [Rochester, MN; Ratterman, Joseph D. (Rochester, MN) [Rochester, MN; Smith, Brian Edward (Rochester, MN) [Rochester, MN

2011-04-19

395

Foreshock Compressional Boundary: THEMIS Observations  

NASA Astrophysics Data System (ADS)

Ahead of our planet, a bow shock and a foreshock region form due to the interaction of the Solar Wind with the terrestrial magnetosphere. Inside the foreshock there are a variety of phenomena such as the foreshock compressional boundary (FCB) that has recently been discovered in global hybrid simulations and in CLUSTER data. The FCB represents a transition region between different plasma regimes, and it can be located at the edges of the foreshock or within it. Using the multispacecraft capabilities of the THEMIS mission we study the properties (field, density, velocity and orientation) of a sample of FCBs, as well as ion distributions inside them and at their surroundings. We also explore a possible relationship between the FCBs and other well known internal foreshock boundaries: the ion foreshock boundary, the ULF wave boundary, and the intermediate ion boundary.

Rojas Castillo, D. I.; Blanco-Cano, X.; Omidi, N.; Kajdic, P.

2013-05-01

396

Brain response to prosodic boundary cues depends on boundary position.  

PubMed

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

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

2013-01-01

397

On the X-ray emitting boundary layer of the dwarf nova VW Hydri  

NASA Technical Reports Server (NTRS)

The temperature and luminosity of the boundary layer of VW Hyi are constrained to kT(BL) of about 10.5 eV, and L(BL) of about 6 x 10 to the 32nd (d/65 pc)squared ergs/sec. This is based on Voyager far- and extreme-ultraviolet spectrophotometry and a measurement of the column density of neutral hydrogen, combined with Exosat LE filter observations. Results are compared with the accretion-disk luminosity found by Polidan et al. (1990) using concurrent optical, IUE, and Voyager spectrophotometric observations. The value of zeta is found to be about 0.04, although theoretical predictions show comparable luminosities at the boundary layer and the accretion disk - zeta is identical to L(BL)/L(disk), which is about 1 - unless the white dwarf rotates very rapidly. Severe contamination of filter observations due to light from the inner accretion disk is also found. This contamination had previously been understood as a result of the luminous ultrasoft boundary layer.

Mauche, Christopher W.; Wade, Richard A.; Polidan, Ronald S.; Van Der Woerd, Hans; Paerels, Frits B. S.

1991-01-01

398

Parts and boundaries.  

PubMed

Within the framework of Conceptual Semantics, a family of conceptual features and functions is developed that accounts for phenomena in the semantics of noun phrases such as the mass-count distinction, plurality, the partitive construction (a leg of the table), the constitutive construction (a house of wood), the "Universal Packager" (three coffees), and boundary words such as end, edge, and crust. Using the strong formal parallelism between noun phrase semantics and event structure that is a hallmark of the Conceptual Semantics approach, the features and functions of the NP system are applied to a wide range of problems in event structure, for example the analysis of the Vendler classes, the meaning of the progressive, the "imperfective paradox", and "aktionsarten" such as the syntactically unexpressed sense of repetition in The light flashed until dawn. Crucial to the analysis is that these features and functions can be expressed in syntactic structure either by being part of lexical conceptual structure, or by use of a morphological affix, or by being associated with the meaning of a construction such as N of NP or nominal compounding. Alternatively, they may remain unexpressed altogether, being introduced into the conceptual structure of a phrase by "rules of construal". This shows that lexical semantics and phrasal semantics interpenetrate deeply, and that there is no strict one-to-one correspondence between syntactic and semantic structures. In addition, the analysis provides further evidence that natural language semantics must be based on a psychological view of meaning--it must be concerned with how language users are constructed to understand and schematize the world. PMID:1790657

Jackendoff, R

1991-12-01

399

Vortex boundary-layer interactions  

NASA Technical Reports Server (NTRS)

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.

Bradshaw, P.

1985-01-01

400

ConcepTest: Convergent Boundary  

NSDL National Science Digital Library

A and B represent locations on two separate plates. The curved black line represents the plate boundary. The arrows show the directions of plate motion and the rates of motion are indicated. a. transform b. ...

401

Poiseuille Flows with Boundary Disturbances.  

National Technical Information Service (NTIS)

Direct numerical solutions were obtained for steady Stokes flow in planar and axisymmetric channels with boundary disturbances. The flows with the disturbances considered, straightsided grooves in the wall or projections into the channel of various height...

V. O'Brien

1966-01-01

402

Magnetic clouds at sector boundaries  

SciTech Connect

Eight of the 14 magnetic clouds in the period August 1978 to February 1982, previously identified in solar wind data by their smooth magnetic field rotations, were encountered at sector boundaries. Most of these differed from those not encountered at sector boundaries in two ways. First, the accompanying counterstreaming electrons, indicating closed magnetic topology, on average spanned intervals more than twice as long as the identified clouds. Second, the field rotations within the identified clouds appear to form part of larger-scale rotations beyond the cloud boundaries that roughly coincide with the counterstreaming electrons. The results suggest that the documented clouds were parts of larger transient structures that are best observed in their entirety at sector boundaries. The data are consistent with spacecraft passages through both the leading and trailing sections of kinematically distorted flux rope loops rooted to the Sun. {copyright} 1998 American Geophysical Union

Crooker, N.U. [Center for Space Physics, Boston University, Boston, Massachusetts (United States)] [Center for Space Physics, Boston University, Boston, Massachusetts (United States); Gosling, J.T. [Los Alamos National Laboratory, Los Alamos, New Mexico (United States)] [Los Alamos National Laboratory, Los Alamos, New Mexico (United States); Kahler, S.W. [Phillips Laboratory, Hanscom Air Force Base, Massachusetts (United States)] [Phillips Laboratory, Hanscom Air Force Base, Massachusetts (United States)

1998-01-01

403

ConcepTest: Convergent 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 ...

404

Boundary Conditions in Elementary Mechanics.  

ERIC Educational Resources Information Center

Uses the problem of determining when a car and truck traveling at the same speed will collide after the truck has applied its brakes to illustrate the need to consider boundary conditions when solving problems in elementary mechanics. (MDH)

Gonzalez, Alejandro D.

1991-01-01

405

Boundary Condition for Modeling Semiconductor Nanostructures  

NASA Technical Reports Server (NTRS)

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.

Lee, Seungwon; Oyafuso, Fabiano; von Allmen, Paul; Klimeck, Gerhard

2006-01-01

406

Thermal boundaries analysis program document  

NASA Technical Reports Server (NTRS)

The digital program TBAP has been developed to provide thermal boundaries in the DD/M-relative velocity (D-V), dynamic pressure-relative velocity (q-V), and altitude-relative velocity (h-V) planes. These thermal boundaries are used to design and/or analyze shuttle orbiter entry trajectories. The TBAP has been used extensively in supporting the Flight Performance Branch of NASA in evaluating candidate trajectories for the thermal protection system design trajectory.

Evans, M. E.

1975-01-01

407

Pyramidal inversion domain boundaries revisited  

SciTech Connect

The structure of pyramidal inversion domain boundaries in GaN:Mg was investigated by aberration corrected transmission electron microscopy. The analysis shows the upper (0001) boundary to consist of a single Mg layer inserted between polarity inverted GaN layers in an abcab stacking. The Mg bound in these defects is at least one order of magnitude lower than the chemical Mg concentration. Temperature dependent Hall effect measurements show that up to 27% of the Mg acceptors is electrically compensated.

Remmele, T.; Albrecht, M.; Irmscher, K.; Fornari, R. [Leibniz-Institut fuer Kristallzuechtung, Max-Born-Str. 2, 12489 Berlin (Germany); Strassburg, M. [OSRAM Optical Semiconductors GmbH, Leibniz Strasse 4, 93055 Regensburg (Germany)

2011-10-03

408

Boundary Labeling with Octilinear Leaders  

Microsoft Academic Search

An illustration with textual labels may be hard to read if the labels overlap parts of the illustration. Boundary labeling\\u000a addresses this problem by attaching the labels to the boundary of a rectangle that contains all features. Then, each feature\\u000a should be connected to its associated label through a polygonal line, called leader, such that no two leaders intersect.\\u000a \\u000a \\u000a In

Michael A. Bekos; Michael Kaufmann; Martin Nöllenburg; Antonios Symvonis

2010-01-01

409

Interplanetary sector boundaries, 1971 - 1973  

NASA Technical Reports Server (NTRS)

Eighteen interplanetary sector boundary crossings observed at 1 AU by the magnetometer on the IMP-6 spacecraft are discussed. The events were examined on many different time scales ranging from days on either side of the boundary to high resoluti