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1

The Cretaceous-Tertiary Boundary (K-T) Interval in Badlands National Park, South Dakota  

NSDL National Science Digital Library

Philip W. Stoffer and USGS colleagues wrote this report (.pdf format) on the marine K-T boundary interval that occurs throughout the Badlands National Park region of South Dakota. Data from marine sediments (supported by paleontological correlation, sequence stratigraphy, magnetostratigraphy, and strontium isotope geochronology) suggest that several asteroid impacts may be preserved in the Badlands. The deposits are thought to represent late Maestrichtian events or possibly the terminal K-T event.

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

2001-01-01

2

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

NASA Astrophysics Data System (ADS)

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

Harting, M.; Wittler, F. A.

2006-05-01

3

High-resolution geochemical record of Cretaceous-Tertiary boundary sections in Mexico: New constraints on the K/T and Chicxulub events  

NASA Astrophysics Data System (ADS)

The investigation of eight Cretaceous-Tertiary (K/T) sections in Mexico, based on major and trace element, platinum group element (PGE), stable isotope, and multivariate statistical analysis, reveals a complex depositional history across the Chicxulub and K/T boundary events. At the biostratigraphically determined K/T boundary, a minor but significant Ir-dominated PGE anomaly (0.2 0.8 ng/g) is present in most sections. This Ir anomaly originated from an impact event and is always stratigraphically and geochemically decoupled from the underlying spherule-rich ejecta deposit related to the Chicxulub event. In all sections examined, one to three glass spherule ejecta layers and one or two chondrite-dominated PGE anomalies are separated by a bioturbated siliciclastic deposit and/or hemipelagic marl, which indicates the occurrence of at least two impact events separated by a considerable amount of time. In addition, bentonite layers and Pt and Pd-dominated PGE anomalies below and above the K/T boundary indicate volcanic activity. Above the K/T boundary, reduced bioproductivity is documented by a decrease in the biogenically bound fraction of nutrients and fluctuating ratios of immobile elements (e.g., Ti/Zr). Variations in detrital elements reflect changes in the depositional environment. Carbon and oxygen isotope and trace element distribution patterns indicate a gradually changing climate during the latest Maastrichtian, an abrupt change at the K/T boundary, and a slight recovery during the lowermost Paleocene.

Stüben, D.; Kramar, U.; Harting, M.; Stinnesbeck, W.; Keller, G.

2005-05-01

4

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

5

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

6

Osmium Isotopic Composition of the Sumbar Cretaceous- Tertiary Boundary, Turkmenia  

NASA Astrophysics Data System (ADS)

Turekian (1982) propagated the use of the osmium isotopic composition as a cosmic indicator for the origin of the high osmium (and iridium) layers at the K/T boundaries. He did not consider the osmium isotopic signature of the terrestrial mantle, which also has a chondritic evolution of the Re-Os system. Osmium cannot serve alone as an infallible indicator of the impact theory, but interesting results can be obtained from their investigation. Different K/T boundary section have been analyzed so far for ^187Os/^186Os. An overview of the values is presented in the table. Boundary Clay layer Os ratio Reference Stevns Klint fish clay 1.66 Luck and Turekian, 1983 Woodside Creek 1.12 Lichte et al., 1986 Raton Basin 1.23 Kraehenbuehl et al., 1988 Raton Basin (several) 1.15-1.23 Esser and Turekian, 1989 Sumbar (0-1 cm) 1.16 This work We obtained a complete marine section of the K/T boundary in southern Turkmenia (decribed by Alekseyev, 1988). It shows a very high Ir concentration (66 ppb) at the boundary layer and a remarkable Ir enrichment over crustal rocks continuing up to 30 cm above the boundary. Our aim of this investigation is to analyze several samples from above and below the boundary for the ^187Os/^186Os ratio to obtain a complete picture of the isotopic evolution of the section. We want to evaluate mixing of Os with chondritic ratios with Os from upper crustal rocks. Another goal is to investigate a mobilization of Os. So far only one sample has been analyzed with NTI-MS after fire assay digestion of the sample. The sample 0 to 1 cm has an ^187Os/^186Os ratio of 1.162 +- 13, which is quite low. We expect an even lower value for the boundary clay (0 cm) itself not taking into account a contribution of radiogenic osmium from the decay of terrestrial rhenium. This might put this K/T boundary section closest of all to the present day chondritic value (approx. 1.05). Further analysis will be presented at the meeting. References Alekseyev A. S., Nazarov M. A., Barsukova L. D., Koselov G. M., Nizhegorodova I. V. and Amanniyazov K. N. (1988) The Cretaceous- Paleogene boundary in southern Turkmenia and its geochemical characteristics. Int. Geol. Rev. 30, 121-135. Esser B. K. and Turekian K. K. (1989) Osmium isotopic composition of the Raton Basin Cretaceous-Tertiary boundary interval. 70, 717. Kraehenbuehl U., Geissbuehler M., Buehler F. and Eberhardt P. (1988) The measurement of osmium isotopes in samples from a Cretaceous/Tertiary (K/T) section of the Raton Basin, USA. Meteoritics 23, 282. Lichte F. E., Wilson S. M., Brooks R. R., Reeves R. D., Holzbecher J. and Ryan D. E. (1986) New method for the measurement of osmium isotopes applied to a New Zealand Cretaceous/Tertiary boundary shale. Nature 322, 816-817. Luck J. M. and Turekian K. K. (1983) Osmium-^187/Osmium-^186 in manganese nodules and the Cretaceous-Tertiary boundary. Science 222, 613- 615. Turekian K. K. (1982) Potential of ^187Os/^186Os as a cosmic versus terrestrial indicator in high iridium layers of sedimentary strata. Geol. Bull. Am. Spec. Pap. 190, 243-249.

Meisel, T.; Krahenbuhl, U.; Nazarov, M. A.

1992-07-01

7

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

8

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

Microsoft Academic Search

SINCE the discovery1 nearly a decade ago that Cretaceous\\/Tertiary (K\\/T) boundary layers are greatly enriched in iridium, a rare element in the Earth's crust, there has been intense controversy on the relationship between this Ir anomaly and the massive extinction of organisms ranging from dinosaurs to marine plankton that characterizes the K\\/T boundary. Convincing evidence suggests that both the Ir

Meixun Zhao; Jeffrey L. Bada

1989-01-01

9

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

Microsoft Academic Search

The hypothesis that a catastrophic impact of an extraterrestrial body caused the terminal Cretaceous mass extinctions of dinosaurs, planktonic foraminfera and other species is now accepted as respectable following the discovery of a worldwide iridium enrichment in the Cretaceous-Tertiary (K-T) boundary clay1-5. In the basal lamina of the K-T boundary clay of Caravaca (Spain)7 numerous spherules were discovered composed of

J. Smit; G. Klaver

1981-01-01

10

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.

11

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

Microsoft Academic Search

An exceptionally complete rock sequence across the Cretaceous-Tertiary (K-T) boundary has been discovered near the Flaxbourne River, Marlborough Province, South Island, New Zealand. The boundary is marked by a large Ir anomaly with an integrated abundance of 134 ng\\/cm² after correction for background. Above the boundary there is a 30 cm transition zone, in which a few Cretaceous foraminiferal taxa

C. P. Strong; R. R. Brooks; S. M. Wilson; R. D. Reeves; C. J. Orth; Xueying Mao; L. R. Quintana; E. Anders

1987-01-01

12

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

13

An extraterrestrial event at the Cretaceous-Tertiary boundary  

Microsoft Academic Search

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

J. Smit; J. Hertogen

1980-01-01

14

Magnetic Susceptibility Variations across the Cretaceous - Tertiary Boundary in Oman  

Microsoft Academic Search

Approximately four meters of carbonates were sampled across the Cretaceous-Tertiary boundary in a little deformed platform sequence in Oman. The sample locality is in the Murka Formation (Roger et al., 1998) in the east flank of a N-S anticline west of Abat; geographically the area is near the south limit of the Oman Mountains, about 20 km west of Sur.

W. D. MacDonald; B. B. Ellwood; C. W. Wheeler; S. L. Benoist

2001-01-01

15

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

Microsoft Academic Search

A high-resolution late Maastrichtian early Danian seawater 87Sr\\/86Sr reference curve is constructed from two Cretaceous-Tertiary boundary (K-T boundary) sections: Bidart (France) and El Kef (Tunisia). The 87Sr\\/86Sr curve shows maxima at 0.3 0.4 Ma before the K-T boundary and at the K-T boundary. The first maximum could mark the onset of a major outflow of the Deccan Traps. The second

H. B. Vonhof; J. Smit

1997-01-01

16

Seawater Sr isotopes at the Cretaceous\\/Tertiary boundary  

Microsoft Academic Search

Seawater 87Sr\\/86Sr values increase abruptly by 28 × 10-6 across the Cretaceous\\/Tertiary boundary (KTB). This small, but rapid shift is superimposed on the larger scale structure of the seawater Sr isotope curve. The time scale of radiogenic Sr addition appears to be too rapid to reconcile with sources associated with volcanism, and we show that the amount of Sr required

E. E. Martin; J. D. MacDougall

1991-01-01

17

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

18

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

19

Terrestrial carbon and nitrogen isotopic ratios from cretaceous-tertiary boundary nanodiamonds.  

PubMed

One hypothesis for the origin of the nanometer-size diamonds found at the Cretaceous-Tertiary (K-T) boundary is that they are relict interstellar diamond grains carried by a postulated asteroid. The (13)C/(12)C and (15)N/(14)N ratios of the diamonds from two sites in North America, however, show that the diamonds are two component mixtures differing in carbon and nitrogen isotopic composition and nitrogen abundance. Samples from a site from Italy show no evidence for either diamond component. All the isotopic signatures obtained from the K-T boundary are material well distinguished from known meteoritic diamonds, particularly the fine-grain interstellar diamonds that are abundant in primitive chondrites. The K-T diamonds were most likely produced during the impact of the asteroid with Earth or in a plasma resulting from the associated fireball. PMID:17742530

Gilmour, I; Russell, S S; Arden, J W; Lee, M R; Franchi, I A; Pillinger, C T

1992-12-01

20

Event Stratigraphy across the Cretaceous-Tertiary Boundary  

NASA Astrophysics Data System (ADS)

The Cretaceous-Tertiary (K-T) transition, that spans paleomagnetic Chron 29R, is one of the most widely studied intervals in Earth history. This interval spans a number of globally correlatable events, such as geochemical anomalies (iridium, PGE's), stable isotopes (carbon 13 shift, climate change), lithological changes (red and black clay layers), and biotic events (species evolution and extinction, the mass extinction of tropical and subtropical planktic foraminifera and calcareous nannoplankton). In addition, there are important, though regionally restricted correlatable events in Central America and the Caribbean that include multiple spherule-rich layers in the latest Maastrichtian and in the early Danian, and early Danian Ir and PGE anomalies. Integration of these diverse correlatable events provides high-resolution and globally reliable event stratigraphy for the K-T transition. Event stratigraphy reveals the relative ordering of a sequence of events through time, the higher the number of correlatable events in a stratigraphic sequence, the better the age resolution is. Events may be missing due to erosion or a hiatus, insufficient sample resolution, or tectonic disturbance, though the relative ordering of the remaining events remains the same. Chronostratigraphic ages for the various events can be derived based on paleomagnetic and radiometric dating, and extrapolation based on the assumption of constant sediment accumulation rates. Although uncertainties associated with each of the derived ages for the correlatable events provides significant error margins, the overall sequence of closely spaced events across the K-T transition provides high resolution time control.

Keller, G.

2001-05-01

21

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

22

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

NASA Astrophysics Data System (ADS)

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

Smit, J.; Klaver, G.

1981-07-01

23

Pollen and spores in marine Cretaceous\\/Tertiary boundary sediments at mid?Waipara River, North Canterbury, New Zealand  

Microsoft Academic Search

Terrestrial pollen and spores in late Maastrichtian to early Paleocene marine strata at mid?Waipara, New Zealand, permit reconstruction of contemporary vegetation and paleoclimates. During the latest Cretaceous, spore?pollen assemblages reflect a temperate rainforest with a prominent podocarp and tree ferns component, angiosperm pollen being mainly represented by Nothofagus and Proteaceae. Disruption of the vegetation at the Cretaceous\\/Tertiary (K\\/T) boundary is

Vivi Vajda; J. Ian Raine

2003-01-01

24

Oceanic primary productivity and dissolved oxygen levels at the Cretaceous\\/Tertiary boundary: Their decrease, subsequent warming, and recovery  

Microsoft Academic Search

Thirty-six different geochemical and foraminiferal analyses were conducted on samples collected at closely spaced intervals across the Cretaceous\\/Tertiary (K\\/T) boundary exposed at Caravaca, Spain. A rapid reduction in the gradient between delta13C values in fine fraction carbonate and benthic foraminiferal calcite and a decrease in the abundance of phosphorus (a proxy for organic carbon) and calcium were recorded in sediments

Kunio Kaiho; Yoshimichi Kajiwara; Kazue Tazaki; Masato Ueshima; Nobuyori Takeda; Hodaka Kawahata; Tetsuya Arinobu; Ryoshi Ishiwatari; Akio Hirai; Macros A. Lamolda

1999-01-01

25

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

Microsoft Academic Search

The hypothesis of Cretaceous-Tertiary (K-T) boundary impact on Yucatán, Mexico, predicts that nearby sites should show evidence of proximal impact ejecta and disturbance by giant waves. An outcrop along the Arroyo el Mimbral in northeastern Mexico contains a layered clastic unit up to 3 m thick that interrupts a biostratigraphically complete pelagic-marl sequence deposited at more than 400 m water

Jan Smit; Alessandro Montanari; Nicola H. M. Swinburne; Walter Alvarez; Alan R. Hildebrand; Stanley V. Margolis; Philippe Claeys; William Lowrie; Frank Asaro

1992-01-01

26

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

Microsoft Academic Search

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

Birger Schmitz; Per Andersson; Jeremy Dahl

1988-01-01

27

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

28

Biogeochemical and ecological consequences of dissolved organic carbon released from soot particles from global firestorms at the Cretaceous\\/Tertiary boundary: Was the Strangelove Ocean a blackwater ocean?  

Microsoft Academic Search

Phytoplankton productivity in the oceans was suppressed for about 200,000 years after the Cretaceous\\/Tertiary (K\\/T) boundary event, and many species of marine calcareous plankton became extinct at the boundary. Proposed causes for what has been called the \\

D. M. McKnight; C. Steinberg; J. S. Baron

2002-01-01

29

Seawater Sr isotopes at the Cretaceous/Tertiary boundary  

NASA Astrophysics Data System (ADS)

Seawater 87Sr/ 86Sr values increase abruptly by 28 × 10 -6 across the Cretaceous/Tertiary boundary (KTB). This small, but rapid shift is superimposed on the larger scale structure of the seawater Sr isotope curve. The time scale of radiogenic Sr addition appears to be too rapid to reconcile with sources associated with volcanism, and we show that the amount of Sr required to produce even this small increase is too large to be derived from: (1) a KT bolide of the size constrained by the Ir anomaly, (2) continental crust ejecta from the impact of such a bolide, (3) soot from global wildfires initiated by an impact, or (4) any combination of these sources. The probable source of the radiogenic Sr is enhanced continental weathering, but the high rate of increase appears to rule out processes such as sea level regression, glaciation or tectonism. A plausible mechanism for rapid addition of radiogenic Sr to the oceans is enhanced weathering associated with globally distributed acid rain (pH ˜ 1) which is a proposed by-product of a bolide impact [51, EPSL Vol. 83].

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

1991-06-01

30

The Cretaceous-Tertiary boundary events: External or internal causes?  

NASA Astrophysics Data System (ADS)

Alvarez [1986] recently summarized in Eos the evidence for the hypothesis that an impact was actually responsible for the terminal Cretaceous events. Alvarez reviewed the physical and chemical evidence for an impact; at the same time, he provided an interesting account of how quickly ideas evolved after the original discovery, by himself and his colleagues [Alvarez et al., 1980], of a conspicuous iridium anomaly at the Cretaceous-Tertiary boundary (also known as the KTB). An alternate hypothesis is a volcanic (either quiet basaltic or violent siliceous) origin for the KTB [e.g, Officer and Drake, 1983, 1985]. Alvarez summarized his observations with a table [Alvarez, 1986, Table 1, p. 649] in which each hypothesis is tested against the following evidence: iridium, spherules, shocked quartz, soot, and worldwide distribution. The “yes” and “no” answers to these tests are, of course, a function of present data and knowledge. The purpose of this article is to stress that answers have changed rapidly in recent years and may still evolve, and also that Alvarez's declaration that the case for a volcanic cause is extinct may be somewhat premature.

Courtillo, Vincent E.; Cisowski, Stanley

31

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

NASA Astrophysics Data System (ADS)

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

Pospichal, James J.

1996-03-01

32

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

NASA Astrophysics Data System (ADS)

SINCE the discovery1 nearly a decade ago that Cretaceous/Tertiary (K/T) boundary layers are greatly enriched in iridium, a rare element in the Earth's crust, there has been intense controversy on the relationship between this Ir anomaly and the massive extinction of organisms ranging from dinosaurs to marine plankton that characterizes the K/T boundary. Convincing evidence suggests that both the Ir spike and the extinction event were caused by the collision of a large bolide (>10 km in diameter) with the Earth1-11. Alternative explanations claim that extensive, violent volcanism12-14 can account for the Ir, and that other independent causes were responsible for the mass extinctions15,16. We surmise that the collision of a massive extraterrestrial object with the Earth may have produced a unique organic chemical signature because certain meteorites, and probably comets, contain organic compounds which are either rare or non-existent on the Earth17. In contrast, no organic compounds would be expected to be associated with volcanic processes. Here we find that K/T boundary sediments at Stevns Klint, Denmark, contain both ?-amino-isobutyric acid [AIB, (CH3)2CNH2COOH] and racemic isovaline [ISOVAL, CH3CH2(CH3)CNH2COOH], two amino acids that are exceedingly rare on the Earth but which are major amino acids in carbonaceous chondrites17,18. An extraterrestrial source is the most reasonable explanation for the presence of these amino acids.

Zhao, Meixun; Bada, Jeffrey L.

1989-06-01

33

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

SciTech Connect

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

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

1991-10-01

34

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

SciTech Connect

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

Habib, D. (City Univ. of New York, Flushing (United States)); Moshkovitz, S. (Geological Survey of Israel, Jerusalem (Israel)); Kramer, C. (Hamilton College, Clinton, NY (United States))

1992-02-01

35

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

NASA Astrophysics Data System (ADS)

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

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

2003-04-01

36

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

37

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

SciTech Connect

An exceptionally complete rock sequence across the Cretaceous-Tertiary (K-T) boundary has been discovered near the Flaxbourne River, Marlborough Province, South Island, New Zealand. The boundary is marked by a large Ir anomaly with an integrated abundance of 134 ng/cm{sup 2} after correction for background. Above the boundary there is a 30 cm transition zone, in which a few Cretaceous foraminiferal taxa such as Hedbergella monmouthensis and Guembelitria cretacea survived, though with reduced abundance and size, apparently reflecting environmental stress. INAA and ICP analyses show that, in addition to Ir, the boundary clay is also enriched in Cr and Ni, mainly from meteoritic material, and As, Co, Cu, Sb, and Zn from terrestrial sources. Volcanic sources, even when scaled to the 10{sup 7} km{sup 3} volume of the Deccan basalts, fail by three orders of magnitude to account for the Ir and As at the K-T boundary and by even larger factors for Sb, Zn, Cu, etc. Comparison of their data with those from six other K-T boundary sites shows that the Zn/Sb, As/Sb, and Zn/As ratios generally fall between crustal and oceanic values, suggesting contributions from both sources. Mass balance calculations show that As and Sb could be derived from only 300-500 m of ocean water or also for modest amounts (20-36 g/cm{sup 2}) of average crustal rock. Copper and Zn, on the other hand, can only be derived from crustal or mantle rock (5-15 g/cm{sup 2}), presumably impact ejecta. Such an amount of ejecta is fairly close to the global fallout of boundary clay (2-5 g/cm{sup 2}).

Strong, C.P. (New Zealand Geological Survey, Lower Hutt (New Zealand)); Brooks, R.R.; Wilson, S.M.; Reeves, R.D. (Massey Univ., Palmerston North (New Zealand)); Orth, C.J.; Mao, Xueying; Quintana, L.R. (Los Alamos National Lab., NM (USA)); Anders, E. (Univ. of Chicago, IL (USA))

1987-10-01

38

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

National Technical Information Service (NTIS)

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 abru...

G. Ryder

1996-01-01

39

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

NASA Astrophysics Data System (ADS)

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

Vonhof, H. B.; Smit, J.

1997-04-01

40

Assessing the Evidence for Extensive Wildfires at the Cretaceous-Tertiary Boundary  

NASA Astrophysics Data System (ADS)

Models of the Cretaceous-Tertiary impact at Chicxulub have suggested that the thermal radiation released by the impact would have been sufficient to ignite extensive wildfires. Eight non-marine K-T sequences stretching from New Mexico to Saskatchewan have been studied in order to test this hypothesis. A multi-proxy approach has been devised by identifying and using key palaeo wildfire proxies (charcoal, soot and polyaromatic hydrocarbons (PAH's)) in combination to assess the extent of biomass burning as part of the K-T events. Soot and PAH's cannot be used to indicate fire location, as soot and PAH's from one large fire could be spread globally. The morphology of the soot and nature of the PAH's present can be used to determine their source, allowing identification of those created by biomass burning versus those from coal, gas and hydrocarbons in the K-T rocks. In contrast to soot and PAH's charcoal is a product uniquely produced by the combustion of vegetation. Charcoal in non-marine rocks provides an excellent tool to record the distribution of wildfires and therefore assess the extent of any thermal radiation associated with the impact at Chicxulub. Quantitative data from three different measures of charcoal abundance (in situ in polished blocks of rock and macro- and microscopic charcoal particles released from sieving of demineralised sediment) reveal that the K-T boundary rocks across the Western Interior of North America contain significantly less charcoal than is typical of the Cretaceous background of this area. The Cretaceous sedimentary rocks contain between 4 and 9 times (according to the measure used) more charcoal particles than the K-T sedimentary rocks. Taphonomic factors do not explain this difference. Furthermore non-charred plant remains are also abundant in the K-T rock layers. Re-assessment of the record of soot and PAH's reported in the K-T rocks suggests that the morphology of the soot and the signature of the PAH's is more consistent with them being sourced from the vaporization of hydrocarbon material rather than biomass burning. We conclude that there was no significant wildfire across North America as part of the K-T events. The below background levels of charcoal in the K-T rocks allows the ground temperatures following the K-T impact to be constrained to no more than 545° C at any point and not above 325° C for any significant period. This indicates that the impact at Chicxulub did not generate sufficient thermal power to ignite extensive wildfires.

Belcher, C. M.; Collinson, M. E.; Finch, P.; Scott, A. C.

2004-12-01

41

Shocked Quartz Aggregates of the Cretaceous-Tertiary Boundary at Colorado, USA  

NASA Astrophysics Data System (ADS)

Shock-metamorphosed quartz (i.e., shocked quartz) at the Cretaceous-Tertiary boundary (K/T) at Colorado [1,2] reveals the following mineralogical data by X-ray diffractometry and high-resolution electron micrograph with energy- dispersive spectrometry. 1. Shocked quartz is not normal (perfect crystalline) quartz mineral but various quartz aggregates that show relatively low X-ray intensity (i.e., imperfect crystalline) and shock lamellae with crystalline quartz and amorphous glass [3]. 2. Analytical electron micrographs indicate that crystalline quartz silica with spotty dislocation features is included in dendritic amorphous glasses of potassium (K) feldspar composition. Various compositions of glassy materials are found in shocked quartz aggregates as matrix or alternate shock lamellae, which is important to estimate the target rock of impact. The composition of glassy matrix is dendritic K-feldspar in the K/T boundary at Clear Creak North (CCN), Colorado, whereas that in the Barringer Crater is quartz-rich composition from the target rock of sandstone (or some mixture with iron meteorite), and that in artificial impact rock [3] is dendritic silica composition. It is found in this study that shocked quartz aggregates from the CCN K/T boundary samples are supplied from quartz and K-feldspar-bearing target rock at impact event (Table 1). Table 1, which appears here in the hard copy, shows the compositions, texture, and origin of shocked quartz aggregates. References: [1] Alvarez L. W. et al. (1980) Science, 208, 1095-1107. [2] Izett G. (1989) GSA Spec. Pap. 249, 1-194. [3] Miura Y. (1991) Shock Waves, 1, 35-41, Springer-Verlag.

Miura, Y.; Okamoto, M.; Iancu, O. G.

1993-07-01

42

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

Microsoft Academic Search

Analyses of marine carbonates through the interval 63.9 to 65.4 million years ago indicate a near-constant flux of extraterrestrial helium-3, a tracer of the accretion rate of interplanetary dust to Earth. This observation indicates that the bolide associated with the Cretaceous-Tertiary (K-T) extinction event was not accompanied by enhanced solar system dustiness and so could not have been a member

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

2001-01-01

43

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

Microsoft Academic Search

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

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

1994-01-01

44

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

NASA Astrophysics Data System (ADS)

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 in Europe in marine and continental fine-grained sedimentary rock. The high surface-to-volume ratio of nanophase material suggests that it may be the carrier of the iridium abundance enhancement that marks the K-T boundary. Even more provocative is the possibility that the discovered nanophase material is, for the most part, composed of the vaporized impactor after the impact-generated high-temperature vapor plume rose and cooled above the atmosphere.

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

2001-01-01

45

ESR Spectra of Limestones from the Cretaceous-Tertiary Boundary: Traces of a Catastrophe  

Microsoft Academic Search

ESR studies have been carried out on limestones collected at or near the Cretaceous-Tertiary (KT) boundary, a stratigraphic bedding plane in the rocks marking the instant in geological time 65 million years ago when the dinosaurs and many marine species became extinct. It is more than coincidence that the giant Chicxulub crater (~200 km in diameter) has been discovered bur-

D. L. Griscom; V. Beltrán-López

46

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

USGS Publications Warehouse

Indium concentrations are anomalously high at the palynological Cretaceous-Tertiary boundary in fluvial sedimentary rocks of the lower part of the Raton Formation at several localities in the Raton Basin of New Mexico and Colorado. The iridium anomaly is associated with a thin bed of kaolinitic claystone in a discontinuous carbonaceous shale and coal sequence.

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

1984-01-01

47

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

USGS Publications Warehouse

At the fossil-pollen-defined Cretaceous-Tertiary boundary in the Raton Basin of New Mexico and Colorado, an iridium abundance anomaly and excess scandium, titanium, and chromium are associated with a thin ash or dust fallout bed (now kaolinitic clay) that was preserved in freshwater coal swamps. ?? 1984 Nature Publishing Group.

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

1984-01-01

48

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

NASA Astrophysics Data System (ADS)

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

Carlisle, David B.; Braman, Dennis R.

1991-08-01

49

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

Microsoft Academic Search

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

W. Alvarez; A. Montanari; F. Asaro

1990-01-01

50

Trace Elements in Cretaceous-Tertiary Boundary Clay at Gubbio, Italy  

NASA Astrophysics Data System (ADS)

In 1980, Alvarez et al. reported high Ir concentrations for the Cretaceous-Tertiary (hereafter, K/T) boundary layer, suggesting an impact of extraterrestrial material as a possible cause of the sudden mass extinction at the end of the Cretaceous period. Since then, high Ir abundances have been reported for K/T layers all over the world. Iridium enrichments were alternatively explained in terms of volcanic eruptions (Officer and Drake, 1982) or sedimentation (Zoller et al, 1982). Thus, abundances of Ir only cannot be critical in explaining the cause of the mass extinctions at the K/T boundary. In contrast to the fairly large number of Ir data for K/T boundary geological materials, only limited data are available for other siderophile elements. Relative abundances of siderophiles must be more informative in considering the causes of extinction, and provide further data on the type of extraterrestrial material of the projectile if siderophile abundances are in favor of an impact as the cause of the mass extinction at the K/T boundary. Thus, we analyzed additional K/T boundary materials for trace elements, including some of the siderophiles. A total of 7 samples collected from the K/T boundary near Gubbio, Italy (three from Bottaccione, four from Contessa) were analyzed. For comparison, we analyzed three additional samples, one from a Cretaceous sediment layer and the remaining two from a Tertiary layer. Four siderophile elements (Ir, Pt, Au, and Pd) were measured by RNAA and more than 25 elements, including 9 lanthanoids, were measured by INAA. The siderophiles listed above and Ni were found to be present in all of the boundary clay samples. They have C1-normalized abundances of 0.02 for Ni, Ir, and Pt, 0.04 for Pd, and Au was exceptionally depleted at 0.005. Both Ni and Ir show fairly small variations in abundances among the clay samples, whereas the other three elements show quite large variations, exceeding error limits. We believe that similar enrichments for these siderophiles in the K/T boundary clays were caused by an impact of extraterrestrial material having siderophiles that have not been largely fractionated. Similar abundance patterns of REE were confirmed not only for clay samples but also for the Cretaceous and Tertiary sediments. This suggests that sedimentation continued in similar circumstances without a large disturbance at the K/T boundary. We confirmed excellent correlations among Ir, As, and Sb abundances in the K/T samples, suggesting that they had a similar solution chemistry when sedimentation occurred. Both As and Sb show similar abundances, even for the Cretaceous as well as the Tertiary sediments, while Ir does not. Neither Pd nor Pt shows any correlation with these elements or with each other. This suggests that Ir was trapped into the clay together with As and Sb, but not with Pd or Pt. It is highly unlikely that these siderophiles were supplied only from sea water, and were eventually greatly enriched in clay materials, with the relative elemental abundances coinciding with those in chondrites. Thus, our data strongly suggest that a large impact of extraterrestrial material (chondritic?) caused the enrichment of siderophiles at K/T boundary. Acknowledgment. We are indebted to M. Ozima and S. Amari for samples analyzed in this work. References Alvarez, L.W., Alvarez, W., Asaro, F., and Michel, H.V. (1980) Science 208, 1095-1108. Officer, C.B. and Drake, C.L. (1982) Science 219, 1383-1390. Zoller, W.H., Parrington, J.R., and Kotra, J.M.P. (1983) Science 222, 1118-1120.

Ebihara, M.; Miura, T.

1992-07-01

51

The Chicxulub Impact Crater and the Cretaceous/Tertiary Boundary: Results from the Drilling Projects  

NASA Astrophysics Data System (ADS)

Chicxulub crater has attracted considerable attention as one of the three largest terrestrial impact structures and its association with the Cretaceous/Tertiary boundary. Chicxulub is a 200 km-diameter multi-ring structure formed 65 Ma ago in the Yucatan carbonate platform in the southern Gulf of Mexico and which has since been buried by Tertiary carbonates. The impact lithologies and carbonate sequence have been cored as part of several drilling projects. Here we analyze the stratigraphy of Chicxulub from the borehole data and core analyses, with particular reference to studies on CSDP Yaxcopoil-1 and UNAM Santa Elena boreholes. Analyses of core samples have examined the stratigraphy of the cover carbonate sequence, impact breccia contact and implications for impact age, K/T global correlations and paleoenvironmental conditions following impact. The K/T age for Chicxulub has been supported from different studies, including Ar/Ar dating, magnetic polarity stratigraphy, geochemistry and biostratigraphy. A Late Maastrichtian age has also been proposed for Chicxulub from studies in Yaxcopoil-1 basal Paleocene carbonates, with impact occurring 300 kyr earlier predating the K/T boundary. This proposal calls attention to the temporal resolution of stratigraphic and chronological methods, and the need for further detailed analyses of the basal carbonate sections in existing boreholes and new drilling/coring projects. Stratigraphy of impact ejecta and basal sediments in Yaxcopoil-1 and UNAM boreholes indicates a hiatus in the basal sequence. Modeling of post- impact processes suggest erosion effects due to seawater back surge, block slumping and partial rim collapse of post-impact crater modification. Analyses of stable isotopes and magnetostratigraphic data for the Paleocene carbonate sequences in Yaxcopoil-1 and Santa Elena boreholes permit to investigate the post- impact processes, depositional conditions and age of basal sediments. Correlation of stable isotopes with the global pattern for marine carbonate sediments provides a stratigraphic framework for the basal Paleocene carbonates.

Fucugauchi, J. U.; Perez-Cruz, L.

2008-12-01

52

Cretaceous/Tertiary boundary in the Eastern Carpathians: evidence from stable isotopes, mineralogy and calcareous nannoplancton  

NASA Astrophysics Data System (ADS)

This study presents the first integrated analyses of stable isotopes, mineralogical, and calcareous nannofossil data from a continuous Upper Campanian to Maastrichtian red bed sequence, including the K/T boundary interval, situated in the bend area of the Romanian Carpathians. The semi-quantitative calcareous nannofossil investigations have focused on six taxonomic groups, such as Watznaueria barnesae, Micula spp., Boreal nannofossils, Tethyan nannofossils, Braarudosphaera bigelowii, and the calcareous dinoflagellate genus Thoracosphaera. The nannofosil investigations show that the sequence spans the Upper Campanian and the whole Maastrichtian stage, including the K/T boundary. Calcite is present in all samples and varies from values up to 70 % down to 2 %. Its concentration varies in opposite direction with the concentration of layer silicates (smectite, chlorite, illite). Quartz and feldspars are plotted together and their content varies between 20 and 40 % and show no systematic fluctuations or long term trends. The delta 13C and d18O values are constant in the Upper Campanian and lower Maastrichtian red marls of the Gura Beliei Formation. In the upper Maastrichtian, lithological, mineralogical and nannofossil changes, together with several negative delta 13C and delta 18O excursions suggest instability of the ecosystems related to climatic changes and/or late Cretaceous tectonic phase. At the Cretaceous/Tertiary boundary, both d13C and d18O values show a negative excursion. Above the Cretaceous nannofossil mass extinction, successive blooms of the dinoflagellate genus Thoracosphaera and of the nannofossil species Braarudosphaera bigelowii were identified. Each of these blooms is marked by successive increases in productivity and positive delta 13C excursions.

Bojar, A.-V.; Melinte-Dobrinescu, M. C.; Bojar, H.-P.

2009-04-01

53

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

Microsoft Academic Search

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

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

1986-01-01

54

Magnetic characterization of Cretaceous-Tertiary boundary sediments  

NASA Astrophysics Data System (ADS)

Rock magnetic properties across several K-T boundary sections have been investigated to reveal any possible magnetic signature associated with the remains of the impact event at the end of the Cretaceous. Studied sections' locations vary in distance to the Chicxulub structure from distal (Agost and Caravaca, Spain), through closer (ODP Hole 1049A, Blake Nose, North Atlantic), to proximal (El Mimbral and La Lajilla, Mexico). A clear magnetic signature is associated with the fireball layer in the most distal sections, consisting of a sharp increase in susceptibility and saturation isothermal remanent magnetization (SIRM), and a decrease in remanence coercivity. Magnetic properties in these sections point to a distinctive ferrimagnetic phase, probably corresponding to the reported Mg- and Ni-rich, highly oxidized spinels of meteoritic origin. At closer and proximal sections magnetic properties are different. Although there is an increase in susceptibility and SIRM associated with a rusty layer placed on top of the siliciclastic deposit in proximal sections, and with a similar limonitic layer on top of the spherule bed that defines the boundary at Blake Nose, the magnetic properties indicate a mixture of iron oxyhydroxides dominated by fine-grained goethite. Based on previous geochemical studies at Blake Nose and new geochemical and PGE abundance measurements performed in this work at El Mimbral, this goethite-rich layer can be interpreted as an effect of diagenetic remobilization and precipitation of Fe. There is not enough evidence to assert that this Fe concentration layer at proximal sections is directly related to deposition of fine meteoritic material. Magnetic, geochemical, and iridium data reject it as a primary meteoritic phase.

Villasante-Marcos, Víctor; Martínez-Ruiz, Francisca; Osete, María Luisa; Urrutia-Fucugauchi, Jaime

55

Ejecta layer at the Cretaceous-Tertiary boundary, Bass River, New Jersey (Ocean Drilling Program Leg 174AX)  

NASA Astrophysics Data System (ADS)

A continuously cored borehole drilled at Bass River, New Jersey, recovered a Cretaceous-Tertiary (K-T) succession with a 6-cm-thick spherule layer immediately above the boundary. Below the spherule layer, the Cretaceous glauconitic clay is extensively burrowed and contains the uppermost Maastrichtian Micula prinsii calcareous nannofossil zone. Spherical impressions of spherules at the top of the Cretaceous indicate nearly instantaneous deposition of ejecta from the Chicxulub impact. The thickest ejecta layer shows clearly that a single impact occurred precisely at K-T boundary time. Above the spherule layer, the glauconitic clay contains the planktonic foraminiferal P0 and P-alpha Zones, indicating (1) a complete K-T succession and (2) continuous deposition interrupted only by fallout of the ejecta layer. Clay clasts within a 6 cm interval above the spherule layer contain Cretaceous microfossils and may be rip-up clasts from a tsunami or possibly a megastorm event. Extinction of the Cretaceous planktonic foraminifers and burrowing organisms occurs abruptly at the K-T boundary. Thus, the Bass River K-T succession unequivocally links the Chicxulub bolide impact to the mass extinctions at the end of the Mesozoic.

Olsson, Richard K.; Miller, Kenneth G.; Browning, James V.; Habib, Daniel; Sugarman, Peter J.

1997-08-01

56

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

USGS Publications Warehouse

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

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

1987-01-01

57

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

PubMed

Shocked quartz grains displaying planar features were isolated from Cretaceous- Tertiary boundary clays at five sites in Europe, a core from the north-central Pacific Ocean, and a site in New Zealand. At all of these sites, the planar features in the shocked quartz can be indexed to rational crystallographic planes of the quartz lattice. The grains display streaking indicative of shock in x-ray diffraction photographs and also show reduced refractive indices. These characteristic features of shocked quartz at several sites worldwide confirm that an impact event at the Cretaceous-Tertiary boundary distributed ejecta products in an earth-girdling dust cloud, as postulated by the Alvarez impact hypothesis. PMID:17748309

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

1987-05-01

58

Fractionation of ruthenium from iridium at the Cretaceous-Tertiary boundary  

Microsoft Academic Search

New data on Ru\\/Ir abundance ratios are presented for nonmarine (Hell Creek, Montana; Frenchman River, Saskatchewan) and marine Cretaceous-Tertiary boundary sites (Brazos River, Texas; Beloc, Haiti; DSDP 577 and DSDP 596). The Ru\\/Ir ratio varies from 0.5 to 1 within 4000 km of Chicxulub and increases to 2–3 at paleodistances (65 Ma) of up to 12,000 km from the impact

Noreen Joyce Evans; Thomas J. Ahrens; D. C. Gregoire

1995-01-01

59

Fractionation of ruthenium from iridium at the Cretaceous-Tertiary boundary  

Microsoft Academic Search

New data on Ru\\/Ir abundance ratios are presented for nonmarine (Hell Creek, Montana; Frenchman River, Saskatchewan) and marine Cretaceous-Tertiary boundary sites (Brazos River, Texas; Beloc, Haiti; DSDP 577 and DSDP 596). The Ru\\/Ir ratio varies from 0.5 to 1 within 4000 km of Chicxulub and increases to 2-3 at paleodistances (65 Ma) of up to 12,000 km from the impact

Noreen Joyce Evans; Thomas J. Ahrens; D. C. Gregoire

1995-01-01

60

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

61

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

62

Ru/Ir ratios at the Cretaceous-Tertiary boundary - Implications for PGE source and fractionation within the ejecta cloud  

NASA Astrophysics Data System (ADS)

Ru and Ir are the least mobile platinum group elements (PGEs) within the Cretaceous-Tertiary (K-T) boundary clay. The Ru/Ir ratio is therefore the most useful PGE interelement parameter for distinguishing terrestrial and extraterrestrial contributions to the boundary clay. The Ru/Ir ratio of European marine K-T sections (1.67 +/- 0.38) is statistically different from that of the North American continental sections (0.76 +/- 0.26). It is unlikely that this difference is due to secondary PGE remobilization, PGE input to the boundary clay during multiple impacts, or volcanic emissions. The global difference in Ru/Ir ratios in the boundary clay may therefore be primary. The positive correlation between distance from the Chicxulub impact structure (Yucatan, Mexico) and Ru/Ir ratio and the more than 1000 C difference in the condensation temperatures of these elements lead us to propose that fractionation of Ru from Ir during condensation from the ejecta cloud may have occurred, resulting in the global difference in Ru/Ir ratios.

Evans, Noreen J.; Gregoire, D. C.; Goodfellow, Wayne D.; McInnes, Brent I.; Miles, Norman; Veizer, Jan

1993-07-01

63

Evidence for a small (˜0.000030) but resolvable increase in seawater 87Sr/86Sr ratios across the Cretaceous-Tertiary boundary  

NASA Astrophysics Data System (ADS)

Previous studies of 87Sr/86Sr patterns across the Cretaceous-Tertiary (K-T) boundary have generated inconsistent results. Analyses of samples from Ocean Drilling Program Hole 1049C provide better taphonomic and diagenetic control than has been previously achieved and indicate (1) that there was a rapid increase of ˜0.000030 in seawater 87Sr/ 86Sr ratios across the K-T boundary, (2) that post K-T Cretaceous foraminifera at this site are reworked, and (3) that subtle diagenetic overprinting affects the basal ˜15 cm of the Danian ooze. These conclusions are consistent with the asteroid impact hypothesis. Reworking rather than survivorship confirms nearly complete extinction of Cretaceous Tethyan planktic foraminifera; the 87Sr/86Sr excursion can be explained by enhanced continental weathering, perhaps related to acid rain in the aftermath of the K-T impact.

MacLeod, Kenneth G.; Huber, Brian T.; Fullagar, Paul D.

2001-04-01

64

Catastrophic extinction of Caribbean rudist bivalves at the Cretaceous-Tertiary boundary  

NASA Astrophysics Data System (ADS)

Strontium isotope ratios (87Sr/86Sr) in pristine low-Mg calcite of shells of rudist bivalves from the Titanosarcolites limestones exposed in the Central, Maldon, and Marchmont inliers of Jamaica indicate that species-rich rudist-coral associations persisted into the latest Maastrichtian (66 65 Ma). This finding contradicts the currently accepted hypothesis of stepwise extinction of rudist bivalves in the middle Maastrichtian and argues for a catastrophic, impact-related demise of Caribbean Cretaceous reefal ecosystems at the Cretaceous-Tertiary boundary.

Steuber, Thomas; Mitchell, Simon F.; Buhl, Dieter; Gunter, Gavin; Kasper, Haino U.

2002-11-01

65

Fine-scale structure of the seawater strontium isotope curve at the Cretaceous/Tertiary boundary  

SciTech Connect

The fine-scale structure of the seawater strontium isotope curve near the Cretaceous/Tertiary boundary is of particular interest because it may reflect some of the unusual events that occurred at that time. The authors report an attempt to document that record, emphasizing experimental aspects relevant to strontium isotope stratigraphy. They used very small, well-documented samples of hand-picked foraminifera typically containing about 20 ng Sr. Thus, a fragment of one individual can be analyzed for large specimens, or several individuals for smaller ones. This makes it possible to examine each foram using the scanning electron microscope and reject obviously recrystallized samples. Furthermore, each sample represents a specific point in time rather than an average. However, definition of the curve is limited by age determinations and mechanical reworking. Reproducibility of each data point is well within the precision determined from repeat analyses of NBS 987. This was verified by 10 sets of duplicates and 18 intercore comparisons of samples with similar ages. Also, seven individually analyzed forams from one sample yielded a variation around the mean equivalent to the standard uncertainty. Applying this technique, they have found a statistically significant step function increase in {sup 87}Sr/{sup 86}Sr at the Cretaceous/Tertiary boundary. Recovery from this perturbation was much faster than expected from the residence time of Sr in seawater, suggesting an influx of less radiogenic Sr, possibly from weathering of Cretaceous carbonates.

Martin, E.E.; MacDougall, J.D. (Scripps Institution of Oceanography, La Jolla, CA (USA))

1990-05-01

66

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

67

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

SciTech Connect

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

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

1986-09-01

68

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

PubMed

A review of the scenarios for the Cretaceous/ Tertiary (K/T) boundary event is presented and a coherent hypothesis for the origin of the event is formulated. Many scientists now accept that the event was caused by a meteorite impact at Chicxulub in the Yucatan Peninsula, Mexico. Our investigations show that the oceans were already stressed by the end of the Late Cretaceous as a result of the long-term drop in atmospheric CO2, the long-term drop in sea level and the frequent development of oceanic anoxia. Extinction of some marine species was already occurring several million years prior to the K/T boundary. The biota were therefore susceptible to change. The eruption of the Deccan Traps, which began at 66.2 Ma, coincides with the K/T boundary events. It erupted huge quantities of H2SO4, HCl, CO2, dust and soot into the atmosphere and led to a significant drop in sea level and marked changes in ocean temperature. The result was a major reduction in oceanic productivity and the creation of an almost dead ocean. The volcanism lasted almost 0.7 m.y. Extinction of biological species was graded and appeared to correlate with the main eruptive events. Elements such as Ir were incorporated into the volcanic ash, possibly on soot particles. This horizon accumulated under anoxic conditions in local depressions and became the marker horizon for the K/T boundary. An oxidation front penetrated this horizon leading to the redistribution of elements. The eruption of the Deccan Traps is the largest volcanic event since the Permian-Triassic event at 245 Ma. It followed a period of 36 m.y. in which the earth's magnetic field failed to reverse. Instabilities in the mantle are thought to be responsible for this eruption and therefore for the K/T event. We therefore believe that the K/T event can be explained in terms of the effects of the Deccan volcanism on an already stressed biosphere. The meteorite impact at Chicxulub took place after the onset of Deccan volcanism. It probably played a regional, rather than global, role in the K/T extinction. PMID:11543126

Glasby, G P; Kunzendorf, H

1996-06-01

69

A Major Meteorite Impact on the Earth 65 Million Years Ago: Evidence from the Cretaceous-Tertiary Boundary Clay  

Microsoft Academic Search

Evidence for a major meteorite impact on the earth 65 million years ago is shown by the presence of meteoritic debris in the ``fish clay'' from Denmark representing the Cretaceous-Tertiary boundary Noble metals (iridium, osmium, gold, platinum, rhenium, ruthenium, palladium, nickel, and cobalt), which are sensitive indicators of meteorites and are normally depleted on the terrestrial surface by factors of

R. Ganapathy

1980-01-01

70

A multi-isotopic and trace element investigation of the Cretaceous–Tertiary boundary layer at Stevns Klint, Denmark – inferences for the origin and nature of siderophile and lithophile element geochemical anomalies  

Microsoft Academic Search

Os, Sr, Nd and Pb isotope data were collected from a profile across the Cretaceous–Tertiary (K–T) boundary layer at Stevns Klint, Denmark. ?Nd [T=65 Ma] values from within the boundary layer (Fish Clay) are lower by ?1 ? unit than those of the underlying Maastrichtian limestone and the overlying Danian chalk sequences. Systematic profile-upward changes of Pb, Sr and Os

Robert Frei; Karin M. Frei

2002-01-01

71

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

2004-03-02

72

Fractionation of ruthenium from iridium at the Cretaceous-Tertiary boundary  

NASA Astrophysics Data System (ADS)

New data on Ru/Ir abundance ratios are presented for nonmarine (Hell Creek, Montana; Frenchman River, Saskatchewan) and marine Cretaceous-Tertiary boundary sites (Brazos River, Texas; Beloc, Haiti; DSDP 577 and DSDP 596). The Ru/Ir ratio varies from 0.5 to 1 within 4000 km of Chicxulub and increases to 2-3 at paleodistances (65 Ma) of up to 12,000 km from the impact site. For CI chondrites, Ru/Ir= 1.5. A ballistic model of ejecta cloud cooling and expansion, which employs the available vapor-pressure versus temperature data for Ru and Ir, predicts qualitatively similar global variation in the Ru/Ir ratio but by only a factor of 1.5. We infer that several other factors, such as remobilization of PGE during diagenesis, preferential oxidation of Ru, condensation kinetics and atmospheric chemical and circulation processes, may account for the observed larger Ru/Ir variation.

Evans, Noreen Joyce; Ahrens, Thomas J.; Gregoire, D. C.

1995-08-01

73

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

74

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

75

Cretaceous/Tertiary boundary in the North Pacific: planktonic foraminiferal results from deep sea drilling site 577, Shatsky Rise  

SciTech Connect

A detailed micropalentologic analysis of sediments from DSDP hole 577 from the Shatsky Rise, North Pacific was undertaken to describe extinction and radiation patterns of planktonic foraminifera in an apparently continuous, undisturbed carbonate sequence spanning the Cretaceous/Tertiary boundary. The Cretaceous/Tertiary boundary was placed at the abrupt last appearance of all large Maastrichtian planktonic foraminifera. Coincident with these extinctions was the presence of a large number of sanadine spherules and an improvement in foraminiferal preservation. Diminutive populations of Guembelitria cretacea and Globigerina eugubina first appeared about 30cm below the boundary and survived the boundary event. Globigerina eugubina increase in size and inflatedness through the Danian. In addition, a large population of aberrative G. eugubina and Eoglobigerina was observed in the Danian, with these forms being characterized by the development of secondary apertures, bullae, and abnormal final chambers. These abnormal morphotypes are considered to be ecophenotypic variants, reflecting ecologic stress or instability in the earliest Cenozoic marine environment.

Gerstel, J.; Thunell, R.

1985-01-01

76

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

NASA Astrophysics Data System (ADS)

Three new iridium anomaly sites have been discovered in Cretaceous/Tertiary boundary sequences in New Zealand. These are at Needles Point, Chancet Rocks, and Waipara, where integrated iridium deposition values were 165, 211, and 7 ng/cm2, respectively. In contrast to the previously reported Woodside Creek stratigraphic sequence that had an iridium anomaly of 187 ng/cm2, a ferruginous boundary clay is absent in the three new sites, though the base of the Tertiary is marked by limonite staining. The relatively weak anomaly at the Waipara section is probably due to extensive bioturbation coupled with a high sedimentation rate at the time of deposition. The discovery of these additional boundary rock sequences in New Zealand negates suggestions that the Woodside Creek iridium anomaly was a fortuitous occurrence caused by unusual weathering conditions. The integrated iridium deposition values at these three new sites of somewhat different geology support the previously reported high iridium level for Woodside Creek, which until now was the only iridium anomaly on land in the Southern Hemisphere.

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

1986-09-01

77

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

PubMed

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

Alvarez, W; Asaro, F; Montanari, A

1990-12-21

78

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

NASA Astrophysics Data System (ADS)

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

1990-12-01

79

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

SciTech Connect

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 3,000 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, W.; Montanari, A. (Univ. of California, Berkeley (United States)); Asaro, F. (Lawrence Berkeley Lab., Berkeley, CA (United States))

1990-12-21

80

Meteorite impact as a possible source of soot in the cretaceous-tertiary boundary layer  

SciTech Connect

There is some evidence that a large meteorite may have collided with the earth 65 m.y. ago and deposited a worldwide layer of iridium and other meteorite elements. It is suggested that this event is associated with the mass extinctions that occurred at that time. A recent paper now suggests that in addition to a layer of meteorite and crustal dust, a layer of elemental carbon was deposited worldwide. The mean carbon abundance at the Cretaceous-Tertiary (C-T) boundary was reported to be 0.021 g/cm/sup 2/, and most of it shows the characteristic morphology of carbon deposited from flames, such as soot or carbon black. However, it should be noted that the conclusion rests on only a few data points: three sites are reported, but the background level of soot is given at only one site. It seems clear that more data should be collected before far-reaching conclusions are drawn. To confidently identify the source of the excess C-T carbon (if indeed it turns out to be a worldwide phenomenon) may require considerable analysis. In order to identify the research that would have to be done, this brief report attempts to narrow the range of possible sources for the soot using simple calculations and relying on the limited amount of analysis that has been previously performed. 23 refs.

Speed, R.D.

1986-05-01

81

Evidence from paleosols for ecosystem changes across the Cretaceous/Tertiary boundary in eastern Montana  

NASA Astrophysics Data System (ADS)

Ancient soils (paleosols) of the latest Cretaceous Hell Creek Formation are mildly calcareous, have clayey subsurface (Bt) horizons, and exhibit abundant large root traces, as is typical of forested soils in subhumid climates. The fact that some of the paleosols are capped by thin, impure coals is evidence for seasonally dry swamps. The paleosol evidence thus supports published reconstructions, based on fossil leaves, pollen, and vertebrates, that this area was subtropical, seasonally dry, subhumid, and forested mainly by angiosperms. Paleosols within the earliest Tertiary (Paleocene) Tullock Formation have thicker, coaly, surface (O and A) horizons and are more drab colored and less calcareous than paleosols of the Hell Creek Formation. These features are indications of waterlogging and of a humid climate. Large root traces and clayey subsurface (Bt) horizons are evidence of swamp woodland and forest. Inferred base level and paleoclimate are compatible with evidence from fossil leaves and pollen that indicates more abundant deciduous, early successional angiosperms and swamp conifers compared to those of Late Cretaceous time. Most of the paleosols have drab Munsell hues and can be expected to preserve a reliable fossil record of pollen and other plant remains. The carbonate content of the paleosols declines toward the top of the Hell Creek Formation, and the uppermost 3 m of the formation is noncalcareous. Because of this, the decline in diversity and abundance of bone over this interval is interpreted as a taphonomic artifact. Evidence from paleosols supports paleobotani-cal evidence for catastrophic change in ecosystems at the Cretaceous/Tertiary boundary.

Retallack, Gregory J.; Leahy, Guy D.; Spoon, Michael D.

1987-12-01

82

Dinosaurs, spherules, and the ``magic'' layer: A new K-T boundary clay site in Wyoming  

Microsoft Academic Search

A new Cretaceous-Tertiary (K-T) boundary clay site has been found along Dogie Creek in Wyoming in the drainage of Lance Creek---the type area of the Lance Formation of latest Cretaceous age. The boundary clay was discovered in the uppermost part of the Lance Formation, 4 7 cm beneath the lowest lignite in the Paleocene Fort Union Formation and approximately 1

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

1987-01-01

83

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

NASA Astrophysics Data System (ADS)

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.

1993-03-01

84

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

PubMed

The end-Cretaceous mass extinctions, 65 million years ago, profoundly influenced the course of biotic evolution. These extinctions coincided with a major extraterrestrial impact event and massive volcanism in India. Determining the relative importance of each event as a driver of environmental and biotic change across the Cretaceous-Tertiary boundary (KTB) crucially depends on constraining the mass of CO(2) injected into the atmospheric carbon reservoir. Using the inverse relationship between atmospheric CO(2) and the stomatal index of land plant leaves, we reconstruct Late Cretaceous-Early Tertiary atmospheric CO(2) concentration (pCO(2)) levels with special emphasis on providing a pCO(2) estimate directly above the KTB. Our record shows stable Late Cretaceous/Early Tertiary background pCO(2) levels of 350-500 ppm by volume, but with a marked increase to at least 2,300 ppm by volume within 10,000 years of the KTB. Numerical simulations with a global biogeochemical carbon cycle model indicate that CO(2) outgassing during the eruption of the Deccan Trap basalts fails to fully account for the inferred pCO(2) increase. Instead, we calculate that the postboundary pCO(2) rise is most consistent with the instantaneous transfer of approximately 4,600 Gt C from the lithic to the atmospheric reservoir by a large extraterrestrial bolide impact. A resultant climatic forcing of +12 W.m(-2) would have been sufficient to warm the Earth's surface by approximately 7.5 degrees C, in the absence of counter forcing by sulfate aerosols. This finding reinforces previous evidence for major climatic warming after the KTB impact and implies that severe and abrupt global warming during the earliest Paleocene was an important factor in biotic extinction at the KTB. PMID:12060729

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

2002-06-11

85

Cretaceous-Tertiary Boundary Interval in Badlands National Park, South Dakota.  

National Technical Information Service (NTIS)

A marine K-T boundary interval has been identified throughout the Badlands National Park region of South Dakota. Data from marine sediments suggest that deposits from two asteroid impacts (one close, one far away) may be preserved in the Badlands. These i...

P. W. Stoffer P. Messina J. A. Chamberlain D. O. Terry

2001-01-01

86

Macrofossil Extinction Patterns at Bay of Biscay Cretaceous-Tertiary Boundary Sections.  

National Technical Information Service (NTIS)

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 befo...

P. D. Ward K. MaCleod

1988-01-01

87

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

88

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

NASA Astrophysics Data System (ADS)

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

Trieloff, M.; Jessberger, E. K.

89

The comparison of P\\/Tr and K\\/T boundaries on the basis of cosmic spherules found in Hungary  

Microsoft Academic Search

The major mass extinctions of taxa, enhanced tectonics, sea level changes, and volcanic activity occurred during both the Penno-Triassic (P\\/Tr) and Cretaceous-Tertiary (K\\/T) extinction levels. We give here a brief summary of our analyses of cosmic spherules extracted from geologic samples found in Hungary in the P\\/Tr and close to the K\\/T boundaries. Moreover, we suggest a new stratigraphic method

Cs. H. Detre; I. Toth; Sz. Berczi; Gy. Don; L. Dosztaly; A. Siegl-Garkas; P. Solt

1997-01-01

90

Isotopic Composition and Organic Geochemistry of Nitrogen at the Cretaceous\\/Tertiary Boundary  

Microsoft Academic Search

The boundary clays from several marine K\\/T sites are known to be enriched in nitrogen and to show marked shifts in nitrogen isotopic compositions (1, 2, 3). At Woodside Creek, New Zealand, a 20-fold increase in nitrogen concentration has been observed together with a corresponding shift in delta^15N of +10o\\/oo, (1, 2). Similarly at Caravaca and Bidart, Spain, ^15N enrichments

A. Gardner; A. Hildebrand; I. Gilmour

1992-01-01

91

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

NASA Astrophysics Data System (ADS)

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

Adatte, Thierry; Keller, Gerta

2010-05-01

92

A Major Meteorite Impact on the Earth 65 Million Years Ago: Evidence from the Cretaceous-Tertiary Boundary Clay  

NASA Astrophysics Data System (ADS)

Evidence for a major meteorite impact on the earth 65 million years ago is shown by the presence of meteoritic debris in the ``fish clay'' from Denmark representing the Cretaceous-Tertiary boundary Noble metals (iridium, osmium, gold, platinum, rhenium, ruthenium, palladium, nickel, and cobalt), which are sensitive indicators of meteorites and are normally depleted on the terrestrial surface by factors of 104 to 102 relative to cosmic abundances, are enriched in this boundary clay by factors of 5 to 100 over the expected abundances. With the exception of rhenium, all the enriched noble metals in the clay are present in cosmic proportions, indicating that the impacting celestial body had not undergone gross chemical differentiation. The major extinction of life on the earth at the end of the Cretaceous Period may be related to the meteorite impact.

Ganapathy, R.

1980-08-01

93

Palaeobotanical evidence for a June 'impact winter' at the Cretaceous/Tertiary boundary  

NASA Astrophysics Data System (ADS)

Aquatic leaves in the K/T boundary section near Teapot Dome/Wyoming, preserve structural deformation that can be duplicated experimentally in extant aquatic leaves by freezing. Reproductive stages reached by the fossil aquatic plants at the time of death suggests that freezing took place in approximately early June. Both the existence of the structurally deformed plants and the high abundance of fern spores occur in a horizon containing sparse impact debris, but below the horizon containing abundant impact debris. It is suggested that the lower horizon represents debris and effects from a large, distant bolide impact, and the upper horizon represents a small, nearby bolide impact.

Wolfe, Jack A.

1991-08-01

94

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

USGS Publications Warehouse

A marine K-T boundary interval has been identified throughout the Badlands National Park region of South Dakota. Data from marine sediments suggest that deposits from two asteroid impacts (one close, one far away) may be preserved in the Badlands. These impact-generated deposits may represent late Maestrichtian events or possibly the terminal K-T event. Interpretation is supported by paleontological correlation, sequence stratigraphy, magnetostratigraphy, and strontium isotope geochronology. This research is founded on nearly a decade of NPS approved field work in Badlands National Park and a foundation of previously published data and interpretations. The K-T boundary occurs within or near the base of a stratigraphic interval referred to as the 'Interior Zone.' We interpret the stratigraphy of the Interior Zone as a series of distinct, recognizable lithologic members and units from oldest to youngest, an upper weathered interval of the Elk Butte Member of the Pierre Shale (early late Maestrichtian), a complete (albeit condensed) interval of Fox Hill Formation, a pedogenically altered K-T Boundary 'Disturbed Zone,' and a generally unresolved sequence of marine to marginal marine units ranging in age from possibly latest Maestrichtian to late Paleocene (the 'Yellow Mounds'), that underlie a basal red clay unit (the late Eocene overbank channel facies of the Chamberlain Pass Formation at the base of the White River Group). Within this sequence is a series of unconformities that all display some degree of subaerial weathering and erosion. The dating of marine fossils above and below these unconformities are in line with generally accepted global sea-level changes recognized for the late Campanian through early Eocene. Within the greater framework of regional geology, these findings support that the Western Interior Seaway and subsequent Cannonball Seaway were dependently linked to the changing base-level controlled by sea-level of the global ocean through the Gulf of Mexico and possibly the Arctic Ocean. The variation of facies preserved in Late Cretaceous strata in the Badlands National Park area were in part controlled by local or regional tectonic blocks that were either rising or sinking contemporaneous with deposition.

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

2001-01-01

95

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

NASA Astrophysics Data System (ADS)

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

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

1992-09-01

96

Formation of spinels in cosmic objects during atmospheric entry - A clue to the Cretaceous-Tertiary boundary event  

NASA Astrophysics Data System (ADS)

Magnetic spinels produced by oxidation of extraterrestrial objects in the atmosphere have a composition distinct from terrestrial spinels. They are characterized by a high iron oxidation state, arising from crystallization under high oxygen fugacities, and a high nickel concentration due to the relatively high abundance of this element in extraterrestrial material. The iron oxidation state increased from micrometeorites, to meteoroid ablation material and to impact-generated products. This reflects a progressive increase of the oxygen fugacity, corresponding to decreasing altitudes of crytallization. Spinels found at the Cretaceous-Tertiary boundary are similar to those that crystallized from meteoroid ablation material and impact-generated products, supporting the view that a collisional event did occur at the end of the Cretaceous.

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

1992-02-01

97

The Global Stratigraphy of the Cretaceous-Tertiary Boundary Impact Ejecta  

NASA Astrophysics Data System (ADS)

The Chicxulub crater ejecta stratigraphy is reviewed, in the context of the stratigraphy of underlying and overlying rock sequences. The ejecta sequence is regionally grouped in (a) thick polymict and monomict breccia sequences inside the crater and within 300 km from the rim of the crater known from drill holes in and close to the breater, and exposures near the border of Yucatan and Belize; (b) Gulf of Mexico region, <2500 m from the crater, with up to 9 m thick, complex, tsunami-wave influenced, tektite-bearing sequences in shallow marine (<500 m deep) environments and tektite bearing, decimeter thick gravity-flow deposits in deep water sites; (c) an intermediate region between 2500 and 4000 km from the crater where centimeter thick, tektite-bearing layers occur, and (d) a global distal region with a millimeter thin ejecta layer. The distal ejecta layer is characterized by sub-millimeter sized microkrystites, often rich in Ni-rich spinels and (altered) clinopyroxene. Wherever present, the ejecta layers mark exactly the sudden mass-mortality horizon of the K/T boundary. What exactly caused the mass mortality is still uncertain, but it appears the main event leading to the K/T mass extinctions.

Smit, J.

98

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

NASA Astrophysics Data System (ADS)

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

Gilmour, Iain; Boyd, Stuart R.

99

Biogeochemical and ecological consequences of dissolved organic carbon released from soot particles from global firestorms at the Cretaceous/Tertiary boundary: Was the Strangelove Ocean a blackwater ocean?  

NASA Astrophysics Data System (ADS)

Phytoplankton productivity in the oceans was suppressed for about 200,000 years after the Cretaceous/Tertiary (K/T) boundary event, and many species of marine calcareous plankton became extinct at the boundary. Proposed causes for what has been called the "Strangelove Ocean" include acidification of oceanic surface waters and effects associated with deposition from a global cloud of firestorm ash. We evaluate the potential effects on the marine ecosystem of leaching of dissolved organic carbon (DOC) from firestorm soot particles. Based upon the quantity of soot deposited in the clay layer at the K/T boundary, we estimate that DOC concentrations in oceanic surface waters increased by at least a factor of two. These results are also supported by extrapolations based upon DOC increases in lakes and streams associated with deposition of ash in Rocky Mountain National Park from the Yellowstone fire of 1988. The soluble soot-derived humic substances would have had different chemical properties than marine humic substances, including a more aromatic character, greater absorptivity for visible light and greater quinone content. These humic substances could have acted as stress-inducing xenobiotic compounds and could have changed the physical and chemical characteristics of the marine environment. Cellular uptake of these humic compounds could have also inhibited calcite precipitation by coccolithophorids and foraminifera, contributing to the greater extinction of these species compared to dinoflagellates. Calculations show that the greater light absorption by the firestorm-derived humic substances would have decreased the depth of the mixed zone, limiting the dilution of the DOC pulse, and would have decreased the depth of the photic zone, spatially restructuring marine ecosystems.

McKnight, D. M.; Steinberg, C.; Baron, J. S.

2002-12-01

100

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

NASA Astrophysics Data System (ADS)

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.

1993-03-01

101

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

Microsoft Academic Search

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

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

1997-01-01

102

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

Microsoft Academic Search

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

Kevin O. Pope

1997-01-01

103

Combined osmium and strontium isotopic study of the Cretaceous-Tertiary boundary at Sumbar, Turkmenistan: A test for an impact vs. a volcanic hypothesis  

Microsoft Academic Search

Osmium and strontium isotopic ratios at the Cretaceous-Tertiary boundary at Sumbar, Turkmenistan, display a negative hyperbolic covariation superimposed on the long-term trend, which displays a positive covariation. The minimum ratio for Os and the maximum ratio for Sr occur at the boundary clay. Volcanism with a mantle or crustal source cannot account for the isotopic data. The low 187-Os\\/188-Os and

Thomas Meisel; Urs Krähenbühl; Michael A. Nazarov

1995-01-01

104

Trace and Major Element Chemistry Across the Cretaceous/Tertiary Boundary at Stevns Klint  

NASA Astrophysics Data System (ADS)

INAA measurements of samples obtained by high-resolution stratigraphy on a mm scale reveal considerable variations in element concentrations across the boundary with their respective maxima stratified in distinct sublayers (Graup et al., 1992). These results suggest that measurements of bulk boundary samples a few cm thick may be inappropriate as concentration variations and element ratios would be leveled out pretending a single geochemical signal. Having investigated a sample comprising sublayers B, C, and D (Fig. 1), Alvarez et al.(1980) acknowledge that "no information is available on the chemical variations within the boundary." This kind of information is given below and shown in Fig. 1 (sublayers A and B are drafted in double scale). From the main lithologic characteristics of Maastrichtian to Paleocene sediments (Schmitz, 1988; Graup et al., 1992) it is readily deduced that Eh and pH conditions in the marine environment changed from oxic-mildly alkaline with normal carbonate sedimentation (Q-M) to anoxic-(mildly) acid with deposition of pyrite spherules (A3), organic material, and clay minerals in the Fish Clay (A-D), followed by a restoration of oxic-alkaline conditions depositing the Cerithium limestone (E- I). The element distribution across the boundary obviously mirrors these alternating environmental conditions: compounds soluble under acid and reducing conditions like Ca-carbonate and Mn are strongly depleted in the Fish Clay (Fig. 1A), whereas compounds stable and insoluble under these conditions are highly enriched (Fig. 1B). The opposite holds true for the calcareous sediments. Across the boundary, enhanced element concentrations are not evenly distributed but appear to be stratified with maximum concentrations in three distinct sublayers for the following elements: (1) A1 (hard clay): peak concentrations for REE (La 72 ppm) and U (45.5 ppm) as compared to 13 ppm La and 2 ppm U in sublayer A2 immediately above. (2) A3 (pyrite spherules): peak concentrations for Fe, Co, Ni, Au, and all chalcophiles. The trace elements correlate well with Fe across the boundary. (3) B (organic-rich marl): peak concentrations for Ir (87.6 ppb), Re (96 ppb, but 113 ppb in C), and organic carbon (2.3%). Ir correlates well with organic carbon (data from Schmitz, 1988), to a lesser extent with Re, and, possibly, Os, but is not correlated with Ni, Co or Au (Graup et al., 1992). Despite large variations in absolute concentrations and, therefore, also of ratios for elements with differing chemical behaviour, there are some pairs of chemically closely related elements (siderophiles as well as chalco- and lithophiles), the ratios of which remain fairly constant over the whole boundary range. Examples shown in Fig. 1A: Ni/Co (average 7.6/std.dev. 1.2) and La/Yb (12.9/2.4). Although Eh,pH conditions vary widely, these elements are not fractionated from each other because of their closely similar geochemical behaviour. The high concentrations of Ir, Ni, and chalcophile elements making up the K/T geochemical anomaly should be indicative of an external component added to the marine environment. The elements introduced were subsequently precipitated according to their chemical properties and changing Eh,pH conditions resulting in stratification of peak concentrations. The constancy of certain element ratios indicates an extended period of availability for this external component. REFERENCES: Alvarez L.W., Alvarez W., Asaro F., and Michel H.V. (1980) Science 208, 1095-1108. Graup G., Palme H., and Spettel B. (1992) Lunar Planet. Sci.(abstract) 23, 445. Schmitz B. (1988) Geology 16, 1068-1072.

Graup, G.; Spettel, B.

1992-07-01

105

Isotopic Composition and Organic Geochemistry of Nitrogen at the Cretaceous/Tertiary Boundary  

NASA Astrophysics Data System (ADS)

The boundary clays from several marine K/T sites are known to be enriched in nitrogen and to show marked shifts in nitrogen isotopic compositions (1, 2, 3). At Woodside Creek, New Zealand, a 20-fold increase in nitrogen concentration has been observed together with a corresponding shift in delta^15N of +10o/oo, (1, 2). Similarly at Caravaca and Bidart, Spain, ^15N enrichments of between +12 and +18%o have been found (3) although the same study found no ^15N enrichments at Gubbio, Italy, or Stevns Klint, Denmark. The source of this excess nitrogen, which can result in N/C ratios up to 0.1 is still unknown (typical N/C values for sediments are around 0.01). It has been suggested that it may be a signature of nitric acid rain or reflect a rapid onset of anoxic conditions in the world's oceans. In order to try and distinguish between these possibilities we have measured the abundance and isotopic composition of nitrogen and examined the molecular organic geochemistry of samples from a nonmarine site in the Northwest Territory of Canada, Police Island . A total of 10 samples from across the K/T boundary at Police Island were solvent-extracted using MeOH/CH2Cl2; a kerogen/elemental carbon fraction was isolated by HF/HCl digestion of silicates. Analysis of the nitrogen content and isotopic composition of the kerogen reveals an enrichment in nitrogen in the fireball layer and a corresponding shift in delta^15N. Nitrogen concentrations increase by ca. 8-fold to 11,600 ppm in the 0.3-cm-thick fireball layer over the underlying ejecta layer. The lowermost Tertiary samples show a progressive decrease to 6200 ppm then 1800 ppm over the next 2-3 cm. delta^15N values shift by +3% from 3.3% in the ejecta layer to +6.2% in the fireball layer. Both the abundance and isotopic variations are in the same direction as observed at marine sites, though of lesser magnitude. The total MeOH/CH2Cl2 extract was analyzed by gas chromatography/mass spectrometry. The boundary and lowermost Tertiary samples contain a series of n-alkenes, presumably of bacterial origin. However, the gas chromatogram of the fireball layer sample is dominated (50% of the total ion current signal) by a single compound. The mass spectrum of this compound is distinguished by the presence of strong fragment ions at m/z 59 and 72, characteristic of an aliphatic amide. Using m/z 59 as a marker for amides the ejecta layer and lowermost Tertiary samples were analyzed by selected ion monitoring. Trace quantities of the same amide were found in the ejecta layer but no amides were found in the Tertiary samples. Apparently the amide is restricted to the fireball layer. The enrichment in nitrogen observed at the K/T boundary together with the variable enrichment in ^15N is apparently global but not universal. It is not restricted to marine sediments though the enrichments in ^15N would appear to be greater in marine sediments. The onset of anoxic conditions in the oceans could account for the enrichments observed at marine sites; however, for terrestrial sediments this is clearly not possible. The coincidence of the enrichment in nitrogen in the fireball layer and the presence of significant quantities of a single aliphatic amide in this horizon suggest an association between the two. The shock production of HNO2 and HNO3 (4) from N2 and O2 coinciding with the fireball may result in the enrichment in the fireball layer in nitrogen. The reaction of this "acid rain" with dead or dying organic matter may explain the presence of the amide. References 1. Gilmour et al. (1988) Meteoritics 23, 269. 2. Gilmour et al. (1990) In: Global Catastrophes in Earth History. (Sharpton, V. L. and Ward, P. eds). pp. 383-390. 3. Robert et al. (1990) Meteoritics 25, 401. 4. Prinn and Fegley (1987) Earth Planet. Sci. Lett. 83, 387-396.

Gardner, A.; Hildebrand, A.; Gilmour, I.

1992-07-01

106

Field guide to Cretaceous-tertiary boundary sections in northeastern Mexico  

NASA Astrophysics Data System (ADS)

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

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

107

Search for fullerenes C 60and C 70in Cretaceous–Tertiary boundary sediments from Turkmenistan, Kazakhstan, Georgia, Austria, and Denmark  

Microsoft Academic Search

Fullerenes C60and C70have been found previously in sediments from the Cretaceous-Tertiary boundary (KTB) sites of Woodside Creek and Flaxbourne River (both New Zealand). Additional discoveries from Caravaca (Spain), Sumbar and Malyi Balkhan (Turkmenistan) and Stevns Klint (Denmark) are reported here. Fullerenes were not found in the KTB sediment from Elendgraben (Austria), nor in acid-demineralized sediments from Koshak (Kazakhstan) and Tetri

D. Heymann; A. Korochantsev; M. A. Nazarov; J. Smit

1996-01-01

108

Combined osmium and strontium isotopic study of the Cretaceous-Tertiary boundary at Sumbar, Turkmenistan: A test for an impact vs. a volcanic hypothesis  

NASA Astrophysics Data System (ADS)

Osmium and strontium isotopic ratios at the Cretaceous-Tertiary boundary at Sumbar, Turkmenistan, display a negative hyperbolic covariation superimposed on the long-term trend, which displays a positive covariation. The minimum ratio for Os and the maximum ratio for Sr occur at the boundary clay. Volcanism with a mantle or crustal source cannot account for the isotopic data. The low 187-Os/188-Os and the high 87-Sr/86-Sr ratios can be explained by an impact, whereby Os was derived from the bolide and the 87Sr/86Sr ratio was enhanced by acid rain and/or a tsunami following the event.

Meisel, Thomas; Krähenbühl, Urs; Nazarov, Michael A.

1995-04-01

109

Plants and the K-T Boundary  

NASA Astrophysics Data System (ADS)

In Plants and the K--T Boundary, two of the world's leading experts in palynology and paleobotany provide a comprehensive account of the fate of land plants during the 'great extinction' about 65 million years ago. They describe how the time boundary between the Cretaceous and Paleogene Periods (the K--T boundary) is recognized in the geological record, and how fossil plants can be used to understand global events of that time. There are case studies from over 100 localities around the world, including North America, China, Russia and New Zealand. The book concludes with an evaluation of possible causes of the K--T boundary event and its effects on floras of the past and present. This book is written for researchers and students in paleontology, botany, geology and Earth history, and everyone who has been following the course of the extinction debate and the K--T boundary paradigm shift.

Nichols, Douglas J.; Johnson, Kirk R.

110

Abrupt appearance of shocked quartz at the Cretaceous-Tertiary boundary, Raton Basin, Colorado and New Mexico  

SciTech Connect

Unique quartz grains as large as 0.5 mm and having up to 6 sets of closely spaced microfractures (CSM) occur at the palynological K-T boundary at 9 scattered sites from Trinidad, Colorado, south 50 km to Raton, New Mexico. Similar quartz grains at the K-T boundary in Montana and Europe were ascribed a shock-metamorphic origin by B. Bohor and colleagues in 1984-85. In the Raton Basin, quartz grains with CSM are concentrated at the top and base of a 2.5-cm-tick kaolinite bed in a nonmarine sequence of somber-colored sandstone, siltstone, shale, and coal. No quartz grains with CSM have yet been found below the K-T bed in the Raton Basin, but a few have been found about 25 cm below the K-T bed at Brownie Butte, Montana. Most quartz grains having CSM are single optical units, but some are compound grains showing sutured boundaries (metaquartzite). Nearly all quartz grains with CSM have refractive indices and birefringence normal for quartz which suggests they formed at not more than 100 kb (low shock); however, a few have n/sub 0/ lowered to 1.538, but have normal birefringence. About half of 100 measured CSM in quartz make an angle of 15-25 degrees with the base (0001). The K-T kaolinite bed in the Raton Basin contains anomalously large amounts of Ir and is possibly coeval with marine, Ir-bearing K-T claystone beds in Europe described in 1980 by W. Alvarez and his associated who suggested they formed when a large bolide struck the Earth causing mass extinction of certain animals and plants. The shocked quartz and metaquartzite at the K-T boundary is compelling evidence that a bolide struck an onland-area of quartz-rich crustal rocks--not in an ocean.

Izett, G.A.; Pillmore, C.L.

1985-01-01

111

The Cretaceous-Tertiary biotic transition  

Microsoft Academic Search

Mass extinctions are recognized through the study of fossil groups across event horizons, and from analyses of long-term trends in taxonomic richness and diversity. Both approaches have inherent flaws, and data that once seemed reliable can be readily superseded by the discovery of new fossils and\\/or the application of new analytical techniques. Herein the current state of the Cretaceous-Tertiary (K-T)

N. MACLEOD; P. F. RAWSON; P. L. FOREY; F. T. BANNER; M. K. BOUDAGHER-FADEL; P. R. BOWN; J. A. BURNETT; P. CHAMBERS; S. CULVER; S. E. EVANS; C. JEFFERY; M. A. KAMINSKI; A. R. LORD; A. C. MILNER; N. MORRIS; E. OWEN; B. R. ROSEN; A. B. SMITH; P. D. TAYLOR; E. URQUHART; J. R. YOUNG

1997-01-01

112

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

NASA Astrophysics Data System (ADS)

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

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

1983-09-01

113

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

NASA Astrophysics Data System (ADS)

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

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

1987-10-01

114

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

115

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

USGS Publications Warehouse

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

Bohor, B. F.

1990-01-01

116

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

NASA Astrophysics Data System (ADS)

The event terminating the Cretaceous period and the Mesozoic era caused massive extinctions of flora and fauna worldwide. Theories of the nature of this event can be classed as endogenic (volcanic, climatic, etc.) or exogenic (extraterrestrial causes). All features of the boundary clay are uniquely associated with impact, and cannot have been formed by volcanic or other terrestrial processes.

Bohor, B. F.

1990-01-01

117

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

PubMed

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

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

2007-06-21

118

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

119

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

120

New iridium determinations from mexican K/T boundary localities  

NASA Astrophysics Data System (ADS)

The presence of extraterrestrial material in terrestrial sediments is usually indicated by an enrichment of platinum group elements (PGE) due their concentration in chondrites is about 104-105 times higher than that in the Earth crust. Discovery of anomalously high concentrations of Ir coincident with the K/T boundary, in several stratigraphic sequences worldwide support the hypothesis that a large asteroid ~10 km in diameter impacted the Earth, and it was the source of the Ir. Several studies about Ir concentration in Chicxulub samples and other K/T section in Mexico had been performed. Here we report on the results from samples taken from three Mexican K/T boundary sections, identified as K/T ejecta sites: La Ceiba, Bochil and Guayal. For La Ceiba we found values until 2.82 ppb.

Morton-Bermea, O.; Martinez-Lopez, M.; Rebolledo-Vieyra, M.; Urrutia-Fucugauchi, J.; Hernandez-Alvarez, E.

2002-12-01

121

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

NASA Astrophysics Data System (ADS)

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

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

1991-12-01

122

More evidence that the Chicxulub impact predates the K\\/T mass extinction  

Microsoft Academic Search

Yaxcopoil-1 (Yax-1), drilled within the Chicxulub crater, was expected to yield the final proof that this impact occurred precisely 65 Myr ago and caused the mass extinction at the Cretaceous-Tertiary (K\\/T) boundary. Instead, contrary evidence was discovered based on five independent proxies (sedimentologic, biostratigraphic, magnetostratigraphic, stable isotopic, and iridium) that revealed that the Chicxulub impact predates the K\\/T boundary by

Gerta Keller; Thierry Adatte; Wolfgang Stinnesbeck; Doris Stüben; Zsolt Berner; Utz Kramar; Markus Harting

2004-01-01

123

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

124

Cretaceous-Tertiary (Chicxulub) impact angle and its consequences  

NASA Astrophysics Data System (ADS)

The Chicxulub impact structure exhibits asymmetries in its geophysical signatures that closely resemble asymmetries produced by oblique impacts in laboratory experiments and recognized on planetary surfaces. These asymmetric signatures suggest a trajectory for the Chicxulub bolide from the southeast to the northwest at a 20° 30° angle from the horizontal. As a result, biotic extinctions may have been most severe and catastrophic in the Northern Hemisphere. Geographic variation in the magnitude of the Cretaceous-Tertiary (K-T) “fern spike” and palynofloral extinctions are consistent with the proposed trajectory.

Schultz, Peter H.; D'Hondt, Steven

1996-11-01

125

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

126

Coastal landsliding and catastrophic sedimentation triggered by Cretaceous-Tertiary bolide impact: A Pacific margin example?  

NASA Astrophysics Data System (ADS)

We report here the first-recognized Pacific margin stratigraphic sequence containing evidence for catastrophic landsliding attributed to bolide impact related seismic shocking at the Cretaceous-Tertiary (K-T) boundary. The K-T boundary is not commonly preserved in stratigraphic sequences of the Pacific margin, but we have discovered it within a coastal paleovalley in Baja California, Mexico (near El Rosario). This 5-km-wide, 15-km-long, and 200-m-deep coastal paleovalley formed by massive gravitational collapses and rapidly filled with coastal (shallow marine and lesser fluvial) gravels and sands, as well as slide sheets of marine mudstone that range from meters to kilometers in length. We infer that seismic shocking caused liquefaction and extremely rapid sedimentation of the gravels and sands, simultaneous with unleashing of slide sheets. Laser-heating 40Ar/39Ar data for biotite, hornblende, and plagioclase (single crystal and bulk step heating) on a 20-m-thick pumice lapilli tuff in the middle of the valley fill give an age of 65.5 ± 0.6 Ma; this is indistinguishable from the age of Haitian tektites dated by the same laboratory. Our new Pacific margin sequence, like many K-T boundary sequences in the Gulf of Mexico Caribbean region, provides evidence of giant landslides and catastrophic sedimentation 1800 km from the bolide impact site.

Busby, Cathy J.; Yip, Grant; Blikra, Lars; Renne, Paul

2002-08-01

127

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

128

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

Microsoft Academic Search

A number of alkaline plutons have been recorded at the K-T (Cretaceous-Tertiary) boundary in western Rajasthan, India. Significant magmatism occurred at Mundwara, Barmer, Sarnu-Dandali and Tavider. The evolution of the Cambay-Sanchor-Barmer rift during the K-T period resulted in these alkaline complexes at the rift margins. Sedimentary basins are developed in the Barmer and Jaiselmer regions. The magmatism of Mundwara and

K. Sharma

2004-01-01

129

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

130

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

NASA Astrophysics Data System (ADS)

The search for the Chicxulub crater formed by the impact at the K-T boundary is briefly reviewed. The dating of the crater is described. Arguments that there are other K-T boundary craters are summarized.

Levi, Barbara G.

1992-12-01

131

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

132

Osmium Isotopic Composition of the K/T Boundary Sediments from Sumbar: A Progress Report  

NASA Astrophysics Data System (ADS)

Osmium isotope measurements have been performed on the boundary clay at different Cretaceous-Tertiary boundary (KTB) sites [1-5] since [6] suggested that Os isotopes are an indicator of an extraterrestrial component. The debate over "impact vs. volcanic" could not be resolved, but an isotope ratio close to chondritic could be demonstrated. The study of the distribution of iridium in the stratigraphy of the KTB cannot distinguish the contribution of chondritic and/or terrestrial Ir respectively, whereas the Os isotopes allow us to better constrain a mixing model. The ^187Os/^186Os ratio of the continental crust and chondritic reservoirs differ by at least 10-30 times. Assuming certain parameters, we should be able to calculate the proportion of the reservoirs making up the sediments of the KTB section. We studied a complete section of the KTB of Sumbar, Turkmenistan [7], for its Os isotopic composition. In the section 0-30 cm above the boundary clay, the ^187Os/^186Os ratio increases from 1.15 to 1.47, whereas the Ir concentration decreases from 66 to 1.4 ng/g or 66 to 4.7 ng/g on a carbonate-free basis respectively. Calculations show that the chondritic component makes up 9% at the boundary layer and decreases down to 0.6% at +30 cm. The data cannot be simply explained by varying admixtures of a chondritic component to a sediment of constant Os concentration and isotopic signature. To explain the Os ratios completely it is necessary to consider a mixture of four components (extraterrestrial, ejecta material, local terrigeneous, and carbonacous sediments) with certain assumptions: (1) The extraterrestrial source is chondritic in its Os and Re content and has an initial Os isotope ratio of 1.12 at 65 Ma (time of impact), which is above the average for normal chondrites but is within the range measured so far (e.g., Murray). (2) The ejecta material has a higher Os concentration (0.2 ng/g) than the sediments and is only present in the first 5 cm of the sequence above the basal layer. (3) The local sediments have an Os concentration of 80 pg/g and the ^187Re/^186Os increases with time. Rhenium concentration has not been determined. The Re abundance is a not very sensitive parameter, since the long decay time of ^187Re (42.3 Ga) cannot account for the higher ratios within 65 Ma. It has been observed that Re is highly enriched above the basal layer [9] of the Caravaca section. This might also be true for the Sumbar section, and thus point 3 is plausible. Further analysis of Maastrichtian samples will give additional constraints on the concentration and isotopic composition of the terrigenous source material. References: [1] Luck J. M. and Turekian K. K. (1983) Science, 222, 613-615. [2] Lichte F. E. et al. (1986) Nature, 322, 816-817. [3] Esser B. K. and Turekian K. K. (1989) EOS, 70, 717. [4] Kraehenbuehl U. et al. (1988) Meteoritics, 23, 282. [5] Smitt R. A. (1990) LPS XXI, 1085-1086. [6] Turekian K. K. (1982) Geol. Bull. Am. Spec. Pap., 190, 243-249. [7] Alekseyev A. S. et al. (1988) Int. Geol. Rev., 30, 121-135. [9] Kyte F. T. et al. (1985) EPSL, 73, 183-195. Fig. 1, which appears here in the hard copy, shows the distribution of Ir concentration and Os-isotope ratio over the Sumbar K/T boundary section. Iridium data are from [7].

Meisel, T.; Krahenbuhl, U.; Nazarov, M. A.

1993-07-01

133

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

PubMed Central

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.

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

2009-01-01

134

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

Microsoft Academic Search

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

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

2007-01-01

135

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

136

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

137

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

NASA Astrophysics Data System (ADS)

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 108 and 4 x 109 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.

Sharpton, Virgil L.; Marín, Luis E.

1997-05-01

138

Extraterrestrial cause for the Cretaceous-Tertiary extinction  

SciTech Connect

Platinum metals are depleted in the earth's crust relative to their cosmic abundance; concentrations of these elements in deep-sea sediments may thus indicate influxes of extraterrestrial material. Deep-sea limestones exposed in Italy, Denmark, and New Zealand show iridium increases of about 30, 160, and 20 times, respectively, above the background level at precisely the time of the Cretaceous-Tertiary extinctions, 65 million years ago. Reasons are given to indicate that this iridium is of extraterrestrial origin, but did not come from a nearby supernova. A hypothesis is suggested which accounts for the extinctions and the iridium observations. Impact of a large earth-crossing asteroid would inject about 60 times the object's mass into the atmosphere as pulverized rock; a fraction of this dust would stay in the stratosphere for several years and be distributed worldwide. The resulting darkness would suppress photosynthesis, and the expected biological consequences match quite closely the extinctions observed in the paleontological record. One prediction of this hypothesis has been verified: the chemical composition of the boundary clay, which is thought to come from the stratospheric dust, is markedly different from that of clay mixed with the Cretaceous and Tertiary limestones, which are chemically similar to each other. Four different independent estimates of the diameter of the asteroid give values that lie in the range 10 +- 4 kilometers.

Alvarez, L.W. (Univ. of California, Berkeley); Alvarez, W.; Asaro, F.; Michel, H.V.

1980-06-06

139

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

NASA Astrophysics Data System (ADS)

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

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

2005-05-01

140

Chicxulub Impact Predates K-T Boundary: new evidence from Texas  

NASA Astrophysics Data System (ADS)

In March 2005 NSF-EAR supported the drilling of three holes by DOSECC, along the Brazos River, Falls County, Texas, about 1000 km from the impact crater in order to test earlier observations in NE Mexico and the Chicxulub crater that this impact predates the K-T boundary by about 300,000 years. The new Texas Mullinax cores and new outcrops recovered the most complete K-T sequences known in this area and a stratigraphic record which revealed: (1) the K-T boundary 90 cm above the event deposit that is commonly interpreted as impact tsunami, and (2) the discovery of the original Chicxulub impact ejecta layer 40 cm below the event deposit. Multidisciplinary biostratigraphic, sedimentological, geochemical and mineralogical analyses reveal that in the new Mullinax-1 core and the outcrop the K-T boundary is marked by the global K-T negative /?13C excursion, a major faunal turnover from Cretaceous to Tertiary dominated assemblages and the first appearances of Tertiary species in all microfossil groups (planktic foraminifera, nannofossils, palynomorphs). A major iridium anomaly was earlier reported coincident with these K-T characteristics at the classic Brazos-1 outcrop only 150 m to the east. The underlying 45 cm thick event deposit, interbedded in late Maastrichtian sediments, contains multiple depositional events with burrows, and near the base reworked and altered Chicxulub impact glass spherules in a clast-rich, shelly, glauconitic sandstone. The event deposits infill a channel and overlie an erosional surface. The original impact ejecta layer is in a claystone 40 cm below the event deposit and consists of a 3 cm thick layer of altered impact glass in the lower part of chron 29R and near the base of biozone CF1, which marks the last 300,000 years of the Cretaceous. The new Brazos results confirm the earlier results from NE Mexico and the crater core Yaxcopoil-1 that the Chicxulub impact predates the K-T boundary by about 300,000 years.

Keller, G.; Adatte, T.; Harting, M.; Berner, Z.; Baum, G. R.; Stueben, D.

2006-05-01

141

Impact did not trigger Deccan volcanism: Evidence from Anjar K/T boundary intertrappean sediments  

NASA Astrophysics Data System (ADS)

Many hypotheses including asteroidal and cometary impacts, Deccan volcanism, impact induced volcanism and coincidental impact and volcanism have been put forth to explain the observed enhancement of iridium and mass extinction at the K/T boundary (KTB). The identification of KTB layer within the Deccan intertrappean sediments at Anjar, about half way between Flow 3 and Flow 4 provides new constraints on some of these hypotheses. The chemical characteristics of this layer show high concentrations of Ir, Os and other siderophiles accompanied by enrichment of chalcophiles and depletion of lithophiles. The Os/Ir tilde-1.1, close to the meteoritic value and other chemical and stratigraphic criteria indicate that it may by the ejecta fallout layer, resulting from a bolide impact at the KTB. Presence of three basalt flows below this layer implies that the volcanism was already active when this layer was deposited and impact of the K/T bolide did not trigger Deccan volcanism.

Bhandari, N.; Shukla, P. N.; Ghevariya, Z. G.; Sundaram, S. M.

1995-02-01

142

The Deposition of the K/T Boundary Layer: Atmospheric Chaos and the Double Layer  

NASA Astrophysics Data System (ADS)

The mechanics of impact ejecta deposition are not well understood, especially for planets with atmospheres where complex interactions occur between the ejected particles and the surrounding atmosphere. The K/T boundary ejecta layer is found world-wide and is thought to represent material from the vapor plume produced by the Chicxulub impact. We modeled a simplified Chicxulub scenario using KFIX-LPL, a two-phase fluid flow code which allows us to simulate deposition of the K/T boundary layer through the atmosphere. Air is modeled as a perfect gas and the spherules (condensed from the vapor plume), which are injected into the atmosphere, are modeled as a simple incompressible fluid with the properties of basaltic glass. The particles fall through the thin upper atmosphere, pushing the atmosphere downwards until the particles decelerate due to drag and increasing atmospheric pressure. The particles accumulate at ~50-km altitude and the deceleration heats the atmosphere around the particles (>700 K), causing expansion of the atmosphere and creating a sharp transition between hot dense atmosphere below the deceleration boundary and cool thin atmosphere above. Surface deposition of the global K/T boundary layer occurs on the scale of a few hours. Our models also shed light on the mysterious dual layer observed in several North American localities. Adding an initial injection of terrestrial ejecta (from the ejecta curtain) into our model atmosphere, as would occur at such intermediate distances from the impact, produces two distinct layers due to the alteration of the atmosphere's structure. Deposition of the lower terrestrial layer on the ground begins at ~80 minutes and that of the upper fireball layer begins at ~130 minutes. Our models show dramatic changes to the atmosphere, which have important environmental implications and provide the starting conditions and timeframes for chemical models examining the environmental consequences of Chicxulub. Our models, which include an accurate treatment of thermal radiation, also provide support for the delivery of significant thermal radiation to the Earth's surface.

Goldin, T. J.; Melosh, H. J.

2006-12-01

143

Extraterrestrial Cause for the Cretaceous-Tertiary Extinction  

Microsoft Academic Search

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

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

1980-01-01

144

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

NASA Astrophysics Data System (ADS)

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

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

1993-03-01

145

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

NASA Astrophysics Data System (ADS)

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

Martínez-López, M.; Urrutia-Fucugauchi, J.

2007-05-01

146

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

147

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

148

More evidence that the Chicxulub impact predates the K/T mass extinction  

NASA Astrophysics Data System (ADS)

Yaxcopoil-1 (Yax-1), drilled within the Chicxulub crater, was expected to yield the final proof that this impact occurred precisely 65 Myr ago and caused the mass extinction at the Cretaceous-Tertiary (K/T) boundary. Instead, contrary evidence was discovered based on five independent proxies (sedimentologic, biostratigraphic, magnetostratigraphic, stable isotopic, and iridium) that revealed that the Chicxulub impact predates the K/T boundary by about 300,000 years and could not have caused the mass extinction. This is demonstrated by the presence of five bioturbated glauconite layers and planktic foraminiferal assemblages of the latest Maastrichtian zone CF1 and is corroborated by magnetostratigraphic chron 29r and characteristic late Maastrichtian stable isotope signals. These results were first presented in Keller et al. (2004). In this study, we present more detailed evidence of the presence of late Maastrichtian planktic foraminifera, sedimentologic, and mineralogic analyses that demonstrate that the Chicxulub impact breccia predates the K/T boundary and that the sediments between the breccia and the K/T boundary were deposited in a normal marine environment during the last 300,000 years of the Cretaceous.

Keller, Gerta; Adatte, Thierry; Stinnesbeck, Wolfgang; Stüben, Doris; Berner, Zsolt; Kramar, Utz; Harting, Markus

2004-07-01

149

Ocean Alkalinity and the Cretaceous/Tertiary Boundary. (Abstract Only).  

National Technical Information Service (NTIS)

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 valu...

K. G. Caldeira M. R. Rampino

1988-01-01

150

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

151

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

152

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

153

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

Microsoft Academic Search

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.,

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

2005-01-01

154

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

Microsoft Academic Search

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

D. E. Fastovsky; P. M. Sheehan

1992-01-01

155

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

156

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

NASA Astrophysics Data System (ADS)

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

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

1997-11-01

157

Cretaceous-Tertiary Growth of the Tibetan Orogen  

NASA Astrophysics Data System (ADS)

Knowledge of the Cretaceous-Tertiary geologic evolution of Tibet has increased dramatically during the past decade, and is summarized here along with our tectonic interpretations. The Qiangtang terrane of central Tibet was uplifted above sea level before or during Early Cretaceous continental collision with the Lhasa terrane to the south. This collision resulted in (1) major shortening and exhumation along the intervening Bangong suture zone, (2) growth of a regional east-plunging culmination in the Qiangtang hinterland, (3) peripheral foreland basin development in the Lhasa terrane, and (4) far-field tectonism in central Asia. Driving the Lhasa- Qiangtang collision was the northward subducting Neo-Tethys oceanic slab to the south, which was shallowing in dip throughout the Early Cretaceous based on a northward sweep in magmatism. Magmatism swept southward at ~105 Ma, marking rollback of the Neo-Tethys slab. Between 105 Ma and 50 Ma, thrusting in response to continued Lhasa-Qiangtang convergence propagated southward into the northern Lhasa terrane and a northward-directed retroarc thrust belt was active in the southern Lhasa terrane. The Lhasa terrane is estimated to have been shortened by ~50% during this time interval. Given evidence for minimal denudation in large parts of Tibet since the Early Cretaceous, the pre-50 Ma shortening must have resulted in substantial crustal thickening and elevation gain. During the Indo-Asian collision, the upper crust of the Lhasa terrane underwent minimal shortening. Syncollisional thrusting is more prevalent in the Qiangtang terrane than in the Lhasa terrane, but accommodated only ~25% shortening. In contrast, thrust belts in north-central Tibet accommodated 40- 50% shortening from ~50 Ma to 30 Ma. We speculate that the gravitational potential energy associated with a preexisting thick crust in southern and central Tibet was sufficient to inhibit upper crustal shortening in this area and to transmit collisional stresses to lower elevation regions in the north and south (to form the Himalayan thrust belt) during the early Tertiary. Following cessation of thrusting in north-central Tibet, the Bangong and Indus-Yarlung sutures underwent simultaneous thrust reactivation during the Oligo-Miocene, which in turn was followed by southward emplacement/extrusion of the Main Central Thrust sheet in the Himalaya. These timing relationships suggest that Tertiary shortening in Tibet and the Himalaya may have been mechanically linked and that the Himalayan thrust belt is merely the southern part of a much larger, composite orogenic wedge system. Given that the magnitude of Tibetan shortening is sufficient to explain present-day crustal thickness, the Cenozoic insertion of >670 km of Indian crust must have driven lower Tibetan crust into the mantle and/or away from the collision zone.

Kapp, P.; Decelles, P. G.; Ding, L.

2006-12-01

158

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

NASA Astrophysics Data System (ADS)

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

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

2003-12-01

159

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

160

History and controls of subsidence in the Late Cretaceous: Tertiary Great Valley forearc basin, California  

Microsoft Academic Search

Analysis of the Upper Cretaceous-Tertiary fill of the Great Valley forearc basin of California reveals a complicated history of subsidence partitioned in time and space. Western, oceanward parts of the basin record subsidence, then uplift, in apparent response to the angle and rate of descent of the underlying subducting plate. Specifically, uplift in the forearc basin corresponds to the onset

Ian W. Moxon; Stephan A. Graham

1987-01-01

161

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

162

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

163

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

164

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

SciTech Connect

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

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

1980-09-01

165

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

PubMed Central

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

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

2009-01-01

166

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

167

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

168

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

169

History and controls of subsidence in the Late Cretaceous: Tertiary Great Valley forearc basin, California  

SciTech Connect

Analysis of the Upper Cretaceous-Tertiary fill of the Great Valley forearc basin of California reveals a complicated history of subsidence partitioned in time and space. Western, oceanward parts of the basin record subsidence, then uplift, in apparent response to the angle and rate of descent of the underlying subducting plate. Specifically, uplift in the forearc basin corresponds to the onset of the Laramide orogeny and inferred low angles of subduction. In contrast, eastern, arcward parts of the basin display subsidence histories suggestive of thermal contraction and compatible with continentward migration of Sierran are magmatism in the Late Cretaceous. These results imply that subsidence histories of forearc basins are likely to be much more complicated and less predictable than those of rifted continental margins and foreland basins, where single subsidence mechanisms predominate and time-varying subduction is not an underlying controlling factor.

Moxon, I.W.; Graham, S.A.

1987-07-01

170

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

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

171

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.

172

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

Microsoft Academic Search

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

Ronald G. Prinn; Bruce Fegley Jr.

1987-01-01

173

Evidence from paleosols for ecosystem changes across the Cretaceous\\/Tertiary boundary in eastern Montana  

Microsoft Academic Search

Ancient soils (paleosols) of the latest Cretaceous Hell Creek Formation are mildly calcareous, have clayey subsurface (Bt) horizons, and exhibit abundant large root traces, as is typical of forested soils in subhumid climates. The fact that some of the paleosols are capped by thin, impure coals is evidence for seasonally dry swamps. The paleosol evidence thus supports published reconstructions, based

Gregory J. Retallack; Guy D. Leahy; Michael D. Spoon

1987-01-01

174

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

NASA Astrophysics Data System (ADS)

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

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

2007-12-01

175

Strangelove ocean at era boundaries, terrestrial or extraterrestrial cause  

NASA Astrophysics Data System (ADS)

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

Hsue, Kenneth J.

176

Toward understanding the post-collisional evolution of an orogen influenced by convergence at adjacent plate margins: Late Cretaceous-Tertiary thermotectonic history of the Apuseni Mountains  

NASA Astrophysics Data System (ADS)

The relationship between syn- to post-collisional orogenic shortening and stresses transmitted from other neighboring plate boundaries is important for understanding the kinematics of mountain belts, but has received little attention so far. The Apuseni Mountains are an example of an orogen in the interference zone between two other subduction systems located in the external Carpathians and Dinarides. This interference is demonstrated by the results of a combined thermochronological and structural field study that quantifies the post-collisional latest Cretaceous-Tertiary evolution. The exhumation history derived from apatite fission track and (U-Th)/He thermochronology indicates that the present-day topography of the Apuseni Mountains originates mainly from latest Cretaceous times, modified by two tectonic pulses during the Paleogene. The latter are suggested by cooling ages clustering around ˜45 Ma and ˜30 Ma and the associated shortening recorded along deep-seated fault systems. Paleogene exhumation pulses are similar in magnitude (˜3.5 km) and are coeval with the final collisional phases recorded in the Dinarides and with part of the Carpathian rotation around the Moesian promontory. These newly quantified Paleogene exhumation and shortening pulses contradict the general view of tectonic quiescence, subsidence and overall sedimentation for this time interval. The Miocene collapse of the Pannonian Basin did not induce significant regional exhumation along the western Apuseni flank, nor did the subsequent Carpathian collision. This is surprising in the overall context of Pannonian Basin formation and its subsequent inversion, in which the Apuseni Mountains were previously interpreted as being significantly uplifted in both deformation stages.

Merten, S.; Matenco, L.; Foeken, J. P. T.; Andriessen, P. A. M.

2011-12-01

177

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

178

The oldest African crocodylian: phylogeny, paleobiogeography, and differential survivorship of marine reptiles through the Cretaceous-Tertiary boundary  

Microsoft Academic Search

A gavialoid crocodylian from the Maastrichtian of the Oulad Abdoun phosphatic Basin (Morocco) is described, representing the oldest known crocodylian from Africa. The specimen consists of a skull that exhibits several features not found in other gavialoids, and a new genus and species is erected, Ocepesuchus eoafricanus. A phylogenetic analysis has been conducted including 201 characters and 71 taxa, where

Stéphane Jouve; Nathalie Bardet; Nour-Eddine Jalil; Xabier Pereda Suberbiola; Baâdi Bouya; Mbarek Amaghzaz

2008-01-01

179

Improved k t BLAST and k t SENSE using FOCUSS  

NASA Astrophysics Data System (ADS)

The dynamic MR imaging of time-varying objects, such as beating hearts or brain hemodynamics, requires a significant reduction of the data acquisition time without sacrificing spatial resolution. The classical approaches for this goal include parallel imaging, temporal filtering and their combinations. Recently, model-based reconstruction methods called k-t BLAST and k-t SENSE have been proposed which largely overcome the drawbacks of the conventional dynamic imaging methods without a priori knowledge of the spectral support. Another recent approach called k-t SPARSE also does not require exact knowledge of the spectral support. However, unlike k-t BLAST/SENSE, k-t SPARSE employs the so-called compressed sensing (CS) theory rather than using training. The main contribution of this paper is a new theory and algorithm that unifies the abovementioned approaches while overcoming their drawbacks. Specifically, we show that the celebrated k-t BLAST/SENSE are the special cases of our algorithm, which is asymptotically optimal from the CS theory perspective. Experimental results show that the new algorithm can successfully reconstruct a high resolution cardiac sequence and functional MRI data even from severely limited k-t samples, without incurring aliasing artifacts often observed in conventional methods.

Jung, Hong; Ye, Jong Chul; Yeop Kim, Eung

2007-06-01

180

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

SciTech Connect

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

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

1981-10-01

181

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

SciTech Connect

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

Molinaroli, E.; Basu, A. (Indiana Univ., Bloomington (United States))

1991-03-01

182

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

183

Shocked minerals and the K/T controversy  

NASA Astrophysics Data System (ADS)

The initial discoveries of elevated Ir and other siderophile element concentrations at the K/T boundary by Alvarez et al. [1980] and Ganapathy [1980] and their interpretation as the signature of a major impact event on Earth has prompted vigorous debate over the nature and cause of the K/T mass extinction event. The wide spectrum of scientists interested in this fundamental problem of Earth-evolution gathered at the conference, Global Catastrophes in Earth History, held in late October 1988 at Snowbird, Utah. Cosponsors were the Lunar and Planetary Institute, Houston, Tex., and the National Academy of Sciences, Washington, D. C.

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

184

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

185

Evidence for a Widespread Disruption Layer Associated With the Cretaceous-Tertiary Boundary in the Upper Fox Hills Formation Throughout the Badland National Park Region of South Dakota  

NASA Astrophysics Data System (ADS)

A widespread zone of disrupted bedding (0.5 to 3.0 m thick) is preserved in the upper Fox Hills Formation throughout the Badlands National Park region. This unit, the Disturbed Zone (DZ), is recognizable in park outcrops extending for twelve miles (east to west) along the crest of the Sage Creek Arch. It also extends at least 20 miles north of the park along the Cheyenne River valley. The DZ features an abundance of soft-sediment liquefaction characteristics including rolled-up sandy beds (now mostly concretions) with an east-to-west axis orientation. The current mapped extent of the DZ covers about 3,000 square kilometers in central South Dakota, but may be much greater. In the park, the DZ unit rest on top of richly fossiliferous marine marls bearing marine mollusks (mostly ammonites and belemnites) of Late Maestrichtian age. After many seasons of searching, the sandstone and shale units overlying the DZ have not yielded any Cretaceous fossils. However, the overlying beds do preserve an abundance of small traces fossils, arthropod and fish remains, and plant material. In the park, this uppermost unit above the DZ ranges up to 16 meters thick, and the upper part preserves a series of paleosols known locally as the Yellow Mounds. The Fox Hills Formation in the park preserves the same biozonation sequence as the Type Fox Hills in the Missouri Valley region. In both regions the thickness of the formation varies, but the measurable maximum thickness is about the same (50 meters). In the Badlands National Park area, structural patterns preserved in the underlying Pierre Shale seem to have influenced sedimentation characteristics (including sand content and fossil distribution) in the overlying Fox Hills Formation. In addition, the thickness of the Fox Hills Formation is controlled by the distribution and pattern of ancient stream valleys preserved beneath the overlying Tertiary White River Group.

Stoffer, P. W.

2002-12-01

186

Evidence for a Widespread Disruption Layer Associated With the Cretaceous-Tertiary Boundary in the Upper Fox Hills Formation Throughout the Badland National Park Region of South Dakota  

Microsoft Academic Search

A widespread zone of disrupted bedding (0.5 to 3.0 m thick) is preserved in the upper Fox Hills Formation throughout the Badlands National Park region. This unit, the Disturbed Zone (DZ), is recognizable in park outcrops extending for twelve miles (east to west) along the crest of the Sage Creek Arch. It also extends at least 20 miles north of

P. W. Stoffer

2002-01-01

187

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

NASA Astrophysics Data System (ADS)

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

Chenet, Anne-Lise; Fluteau, FréDéRic; Courtillot, Vincent; GéRard, Martine; Subbarao, K. V.

2008-04-01

188

Shock-synthesized hexagonal diamonds in Younger Dryas boundary sediments  

PubMed Central

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

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

2009-01-01

189

Deccan Volcanism likely cause for K-T Mass Extinction  

NASA Astrophysics Data System (ADS)

Recent advances in Deccan volcanic studies suggest that the main phase of eruptions occurred rapidly over tens of thousands of years near the end of the Maastrichtian (Chenet et al. 2007, 2008) and may have caused the mass extinction as initially discovered in intertrappean sediments exposed in quarries of Rajahmundry, SE India. In these shallow marine sediments early Danian zone P1a planktic foraminifera were deposited in C29r immediately above the last mega eruption of the main volcanic phase (Keller et al. (2008). At Jhilmili in central India (Madhya Pradesh), early Danian zone P1a assemblages were also discovered in intertrappean sediments, which mark a marine incursion in a predominantly terrestrial sequence which signals a major seaway existed at K-T time. In Meghalaya, NE India, about 600 km from the Deccan volcanic province the K-T boundary and mass extinction identified from planktic foraminifera, calcareous nannofossils and palynomorphs is marked by very large Ir (11.8 ppb), Ru, Rh and Pd anomalies. High biotic stress conditions precede the KTB. Critical new data linking Deccan volcanism to the K-T mass extinction comes also from investigations of subsurface cores drilled in the Krishna-Godavari Basin, eastern India, by the Oil and Natural Gas Corporation of India (ONGC). In eight subsurface cores examined, a total of 4 volcanic megaflows have been identified as occurring in very rapid succession near the end of the Maastrichtian. These megaflows span a 1000 km across India and out to the Gulf of Bengal. They are the longest lava flows known in Earth's history. Preliminary evaluation of the biotic effects of these megaflows on planktic foraminifera indicate that after the first megaflow up to 50% of the species disappeared and with each new megaflow more species died out culminating in near total mass extinction coincident with the last megaflow by K-T boundary time. After the mass extinction, no megaflows reached the Krishna-Godavari Basin for about 250-280 ky during which time a low diversity early Danian assemblage of small new species evolved globally. The last major Deccan volcanic pulses began at the C29R/C29N boundary and may have been the cause for the long delay in the full biotic recovery. These studies suggest that the real cause for the K-T mass extinction may have been the main phase of Deccan volcanic eruptions at the end of the Maastrichtian. In particular, the rapid succession of megaflows and the massive SO2 emissions estimated at least 10 to 30 times those from the Chicxulub impact may have caused a deadly runaway effect that lead to the K-T mass extinction. Chenet, A-L. et al. (2007) EPSL 263, 1-15; Chenet et al. (2008) JGR, 113, B04101; Keller, G. et al. (2008) EPSL 268, 293-311.

Keller, G.; Reddy, A. N.; Jaiprakash, B. C.; Adatte, T.; Gertsch, B.; Bajpai, S.; Garg, R.; Prasad, V.; Upadhyay, H.; Bhowmick, P. K.

2009-04-01

190

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

191

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

192

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

Microsoft Academic Search

Terrestrial palynomorphs from the Hokkaido marime sedimentary sequence spanning the Cretaceous\\/Tertiary (K\\/T) boundary record sudden changes in the floristic composition at the exact base of the boundary claystone layer; pollen abundance declines that are accompanied by an abrupt rise in the proportion of fern spores are noted to resemble the palynologically defined K\\/T boundary in the western interior of North

Tsunemasa Saito; Tohru Yamanoi; Kunio Kaiho

1986-01-01

193

Shock Deformation and Volcanism across the Cretaceous - Transition  

Microsoft Academic Search

The cause of the Cretaceous-Tertiary (K\\/T) transition remains one of the most controversial scientific topics in the geosciences. Geological and geophysical evidence associated with the K\\/T boundary have been used to argue that the extinctions were caused by meteor impact or volcanism. The goal of this study was to assess the viability of a volcanic model for the K\\/T transition.

Alan Royce Huffman

1990-01-01

194

Lepton K t spectrum from W production at collider energies  

NASA Astrophysics Data System (ADS)

The effect of subleading corrections to multiple soft gluon emission is shown to be very relevant for the determination of the k T -spectrum of the decay charged lepton from W produced inbar p p collisions. We study the k T distributions atsqrt s =540 GeV andsqrt s =2000 GeV and comment on various aspects of these predictions.

Chiappetta, P.; Soffer, J.; Greco, M.

1985-12-01

195

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

Microsoft Academic Search

The Phanerozoic paleontological record is marked by several biological extinction events. One of them, at the Cretaceous\\/Tertiary (K\\/T) boundary, was responsible for the demise of about 5% of genera and 75% of species, including the dinosaurs. These drastic and abrupt changes in the development of life on Earth puzzled paleontologists in the past. Many a cause was put forward to

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

2003-01-01

196

Iridium in Sediments Containing Large Abundances of Australasian Microtektites from DSDP Hole 758B in the Eastern Indian Ocean and from DSDP Hole 769A in the Sulu Sea.  

National Technical Information Service (NTIS)

Excess Ir found in sediments at the Cretaceous/Tertiary (K/T) boundary and in other (e.g., Pliocene) sediments from deep sea drilling cores is widely interpreted as evidence of major impact events. The Australasian tektites originated in an impact event a...

G. Schmidt L. Zhou J. T. Wasson

1993-01-01

197

Projectile-Target Mixing in Melted Ejecta Formed During a Hypervelocity Impact Cratering Event.  

National Technical Information Service (NTIS)

Tektites contain little to no projectile contamination while, in contrast, some distal ejecta deposits can be relatively projectile-rich (e.g. the Cretaceous-Tertiary (K-T) boundary clay). This compositional difference motivated an experimental study of h...

N. J. Evans T. J. Ahrens M. Shahinpoor W. W. Anderson

1993-01-01

198

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

199

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

200

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

Microsoft Academic Search

Coarse, spherule-bearing, elastic units have been discovered at 10 marine sites that span the K\\/T boundary in northeastern Mexico. We examined one of the best exposed sites in Arroyo el Mimbral, northwest of Tampico. The Mimbral outcrop displays a layered elastic unit up to 3 m thick enclosed by marly limestones of the Mendez (Latest Maastrichian) and Velasco (Earliest Danian)

Bruce F. Bohor; William J. Betterton

1993-01-01

201

Radial k-t FOCUSS using motion estimation and compensation  

NASA Astrophysics Data System (ADS)

Recently, a model based dynamic imaging algorithm called k-t BLAST/SENSE has drawn significant attentions from MR imaging community due to its improved spatio-temporal resolution for dynamic MR imaging. In our previous work, we proved that k-t BLAST/SENSE can be derived as the first step of FOCal Underdetermined System Solver (FOCUSS) that exploits the sparsity of x-f support. Furthermore, the newly derived algorithm called k-t FOCUSS can be shown optimal from compressed sensing perspective. In this paper, the k-t FOCUSS algorithm is extended to radial trajectory. More specifically, the radial data are transformed to Cartesian domain implicitly during the FOCUSS iterations without explicit gridding to prevent error propagation. Thanks to the implicit gridding that allows fast Fourier transform, we can reduce the computational burden significantly. Additionally, a novel concept of motion estimation and compensation (ME/MC) is proposed to improve the performance of the algorithm significantly. In our ME/MC framework, we additionally obtain one reference sinogram with the full view, then the reference signogram is subtracted from all the radial data. Then, we can apply motion estimation/ motion compensation (ME/MC) to improve the final reconstruction. The experimental results show that our new method can provide very high resolution even from very limited radial data set.

Jung, Hong; Yoo, Jaeheung; Ye, Jong Chul

2008-08-01

202

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

203

B meson wave function in kT factorization  

NASA Astrophysics Data System (ADS)

We study the asymptotic behavior of the B meson wave function in the framework of kT factorization theorem. We first construct a definition of the kT-dependent B meson wave function, which is free of light-cone divergences. Next-to-leading-order corrections are then calculated based on this definition. The treatment of different types of logarithms in the above corrections, including the Sudakov logarithms, and those depending on a renormalization scale and on an infrared regulator, is summarized. The criticism raised in the literature on our resummation formalism and Sudakov effect is responded. We show that the B meson wave function remains normalizable after taking into account renormalization-group evolution effects, contrary to the observation derived in the collinear factorization theorem.

Li, Hsiang-Nan; Liao, Huei-Shih

2004-10-01

204

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

205

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

206

K-t sparse GROWL: sequential combination of partially parallel imaging and compressed sensing in k-t space using flexible virtual coil.  

PubMed

Because dynamic MR images are often sparse in x-f domain, k-t space compressed sensing (k-t CS) has been proposed for highly accelerated dynamic MRI. When a multichannel coil is used for acquisition, the combination of partially parallel imaging and k-t CS can improve the accuracy of reconstruction. In this work, an efficient combination method is presented, which is called k-t sparse Generalized GRAPPA fOr Wider readout Line. One fundamental aspect of this work is to apply partially parallel imaging and k-t CS sequentially. A partially parallel imaging technique using a Generalized GRAPPA fOr Wider readout Line operator is adopted before k-t CS reconstruction to decrease the reduction factor in a computationally efficient way while preserving temporal resolution. Channel combination and relative sensitivity maps are used in the flexible virtual coil scheme to alleviate the k-t CS computational load with increasing number of channels. Using k-t FOCUSS as a specific example of k-t CS, the experiments with Cartesian and radial data sets demonstrate that k-t sparse Generalized GRAPPA fOr Wider readout Line can produce results with two times lower root-mean-square error than conventional channel-by-channel k-t CS while consuming up to seven times less computational cost. PMID:22162191

Huang, Feng; Lin, Wei; Duensing, George R; Reykowski, Arne

2011-12-09

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

Shock pressures in igneous processes: Implications for K/T events  

NASA Astrophysics Data System (ADS)

The seismicity initiating the May 18, 1980 catastrophic eruption at Mt. St. Helens indicates an explosion occurred at depth generating an average pressure of about 500 kbar. Such pressures fall off with distance from the magma chamber although jointing, fractures, etc. may act as stress concentrators to extend the radius of formation of shocked minerals as far as a kilometer. Shocked minerals are not to be expected from the magma itself as high temperatures would anneal such features but temperatures fall away rapidly enough from the chamber wall to allow retention even of such possible exotics as stishovite. The subsequent kinetics of the failure of the north slope support these pressures as do thermodynamic considerations and nucleation kinetics of CO2 exsolution from magmatic melt. Confining pressures (e.g., overburden head) are not a limiting factor. Unconfined detonations in open air yield pressures to several megabars although some recent arguments asserted to be volcanological would indicate open air bursts greater than one bar to be impossible. Further, it has been indicated that pressure estimates from ballistic considerations have been too high and large phenocryst content in the discharge material argues against high pressure explosions. In the first instance, sonic choking and volatile diffusion time constraints make these assessments implausible and in the second instance, both theoretical and geological considerations provide for the phenocryst distributions under explosive situations. These results and recent discoveries of high levels of iridium in volcanic ash in the Antarctic blue ice have implication for K/T boundary events, mass extinctions and endoexplosions. The geographical breadth of volcanic activity attending the K-T transition (e.g., Antarctic volcanism as well as the Deccan Traps) indicates a global mechanism and suggests a large portion of the mantle experienced convective surge as occurs at high Rayleigh number flow. Scaling to mantle conditions yields episodicities of the same order as the 30 my intervals.

Rice, Alan

209

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

210

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)

211

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

212

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

PubMed

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

Marshall; Ward

1996-11-22

213

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

NASA Astrophysics Data System (ADS)

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

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

1986-09-01

214

Radial k-t FOCUSS for High-Resolution Cardiac Cine MRI  

Microsoft Academic Search

A compressed sensing dynamic MR technique called k-t FOCUSS (k-t FOCal Underdetermined System Solver) has been recently proposed. It outperforms the conventional k-t BLAST\\/SENSE (Broad-use Linear Acquisition Speed-up Tech- nique\\/SENSitivity Encoding) technique by exploiting the sparsity of x-f signals. This paper applies this idea to radial trajectories for high-resolution cardiac cine imaging. Radial trajectories are more suitable for high-resolution dynamic

Hong Jung; Jaeheung Yoo; Jong Chul Ye

2010-01-01

215

Boundaries. Boundaries...Boundaries???  

PubMed

One way to modulate transcription is by partitioning the chromatin fiber within the nucleus into the active or inactive domains through the establishment of higher-order chromatin structure. Such subdivision of chromatin implies the existence of insulators and boundaries that delimit differentially regulated chromosomal loci. Recently published data on transcriptional interference from the repeated component of the genome fits the classic definition of insulator/boundary activity. This review discusses the phenomena of transcriptional interference and raises the question about functionality of genomic "junk" along with the need to stimulate a dialogue on how we would define the insulators and boundaries in the light of contemporary data. Rule 19 (a) (Boundaries)"Before the toss, the umpires shall agree the boundary of the field of play with both captains. The boundary shall, if possible, be marked along its whole length" Rules of Cricket. PMID:18524562

Lunyak, Victoria V

2008-06-02

216

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

217

First Look at kT Measurements Using di-jet Correlations  

SciTech Connect

The intrinsic parton transverse momentum kT is associated to Fermi motion of the confined partons within a nucleon. In this work we concentrate effort to investigate this phenomena in di-jets simulated in the ALICE framework, for p+p collisions. The goal of this analysis is to determine the sensitivity of the observed parameters, such as, momentum imbalance and acoplanarity, on the magnitude of kT.

Dominguez, Isabel; Cuautle, Eleazar; Paic, Guy [Departamento de Fisica de Altas Energias, Instituto de Ciencias Nucleares, Universidad Nacional Autonoma de Mexico (Mexico); Diaz, Rafael [Helsinki Institute of Physics, University of Jyvaeskylae, FI-40014 Jyvaeskylae (Finland); Morsch, Andreas [CERN, PH-Division, 1211 Geneva (Switzerland)

2008-07-02

218

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

219

Accelerating k-t sparse using k-space aliasing for dynamic MRI imaging.  

PubMed

Dynamic imaging is challenging in MRI and acceleration techniques are usually needed to acquire dynamic scene. K-t sparse is an acceleration technique based on compressed sensing, it acquires fewer amounts of data in k-t space by pseudo random ordering of phase encodes and reconstructs dynamic scene by exploiting sparsity of k-t space in transform domain. Another recently introduced technique accelerates dynamic MRI scans by acquiring k-space data in aliased form. K-space aliasing technique uses multiple RF excitation pulses to deliberately acquire aliased k-space data. During reconstruction a simple Fourier transformation along time frames can unaliase the acquired aliased data. This paper presents a novel method to combine k-t sparse and k-space aliasing to achieve higher acceleration than each of the individual technique alone. In this particular combination, a very critical factor of compressed sensing, the ratio of the number of acquired phase encodes to the number of total phase encode (n/N) increases therefore compressed sensing component of reconstruction performs exceptionally well. Comparison of k-t sparse and the proposed technique for acceleration factors of 4, 6 and 8 is demonstrated in simulation on cardiac data. PMID:24110264

Pawar, Kamlesh; Egan, Gary F; Zhang, Jingxin

2013-07-01

220

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

PubMed

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. PMID:24077063

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

2013-09-27

221

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

222

Deep inelastic beauty production at HERA in the kT-factorization approach  

Microsoft Academic Search

We calculate the cross section of beauty production in ep deep inelastic scattering at HERA collider in the framework of the kT-factorization approach. The unintegrated gluon distributions in a proton are obtained from the full CCFM, from unified BFKL-DGLAP evolution equations as well as from the Kimber-Martin-Ryskin prescription. We investigate different production rates and study the b-quark contribution to the

Artem V. Lipatov; Nikolai P. Zotov

2006-01-01

223

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

224

Associated photon and heavy quark production at high energy within kT-factorization  

NASA Astrophysics Data System (ADS)

In the framework of the kT-factorization approach, the production of prompt photons in association with a heavy (charm or beauty) quarks at high energies is studied. The consideration is based on the O(??2s) off-shell amplitudes of gluon-gluon fusion and quark-(anti)quark interaction subprocesses. The unintegrated parton densities in a proton are determined using the Kimber-Martin-Ryskin prescription. Our numerical predictions are compared with the D0 and CDF experimental data. Also we extend our results to LHC energies.

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

2013-04-01

225

Improved k-t BLAST for fast fMR imaging  

NASA Astrophysics Data System (ADS)

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

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

2010-06-01

226

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

2012-08-06

227

Terminal Cretaceous Extinctions in the Hell Creek Area, Montana: Compatible with Catastrophic Extinction  

Microsoft Academic Search

Inaccurate stratigraphic correlations in the Hell Creek area, Montana, have led to the assumption that transitional vertebrate faunas (Bug Creek Anthills) exist in the latest Cretaceous, refuting a catastrophic turnover at the Cretaceous-Tertiary boundary. Establishment of the transitional faunas in Paleocene channels that cut down through the Cretaceous-Tertiary boundary renders the terrestrial faunal record compatible with the marine record and

J. Smit; S. van der Kaars

1984-01-01

228

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

NASA Astrophysics Data System (ADS)

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

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

2012-05-01

229

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

230

Charmonium production at high energy in the kT-factorization approach  

NASA Astrophysics Data System (ADS)

We study charmonium production at high-energy colliders (Tevatron, HERA, and LEP2) in the framework of the kT-factorization approach and the factorization formalism of nonrelativistic quantum chromodynamics at leading order in the strong-coupling constant ?s and the relative velocity v. The transverse-momentum distributions of direct and prompt J/?-meson production measured at the Fermilab Tevatron are fitted to obtain the nonperturbative long-distance matrix elements for different choices of unintegrated gluon distribution functions in the proton. Using the matrix elements thus obtained, we predict charmonium production rates in ??, ?p, and deep-inelastic ep collisions including the contributions from both direct and resolved photons. The results are compared with the known ones obtained in the conventional parton model and with recent experimental data from HERA and LEP2.

Kniehl, B. A.; Vasin, D. V.; Saleev, V. A.

2006-04-01

231

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

232

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

233

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

234

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

235

Mass Mortality and Extraterrestrial Impacts.  

National Technical Information Service (NTIS)

The discovery of iridium enrichment at the Cretaceous/Tertiary boundary resulted in formulation of hypothesis of a cometary or asteroid impact as the cause of the biological extinctions at this boundary. Subsequent discoveries of geochemical anomalies at ...

L. F. Jansa F. M. Gradstein M. Pierre-Aubry

1988-01-01

236

SHIVA STRUCTURE: A POSSIBLE KT BOUNDARY IMPACT CRATER ON THE WESTERN SHELF OF INDIA  

Microsoft Academic Search

Evidence is accumulating for multiple impacts across the Cretaceous-Tertiary transition, such as the Chicxulub crater in Yucatan Peninsula, Mexico, the Shiva crater offshore western India, and the much smaller Boltysh crater in Ukraine. Among these, the submerged Shiva crater on the Mumbai Offshore Basin on the western shelf of India is the largest (~500 km diameter), which is covered by

SANKAR CHATTERJEE; NECIP G UVEN; AARON YOSHINOBU; RICHARD D ONOFRIO

237

Europe's last Mesozoic bird  

NASA Astrophysics Data System (ADS)

Birds known from more than isolated skeletal elements are rare in the fossil record, especially from the European Mesozoic. This paucity has hindered interpretations of avian evolution immediately prior to, and in the aftermath of, the Cretaceous-Tertiary (K-T) extinction event. We report on a specimen of a large ornithurine bird (closely related to Ichthyornis) from the uppermost Cretaceous (Maastricht Formation) of Belgium. This is the first record of a bird from these historic strata and the only phylogenetically informative ornithurine to be recovered from the Mesozoic of Europe. Because this new specimen was collected from 40 m below the K-T boundary (approximate age of 65.8 Ma), it is also the youngest non-neornithine (=non-modern) bird known from anywhere in the world.

Dyke, Gareth; Dortangs, Rudi; Jagt, John; Mulder, Eric; Schulp, Anne; Chiappe, Luis

2002-08-01

238

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

NASA Astrophysics Data System (ADS)

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

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

239

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

240

kT -points: short three-dimensional tailored RF pulses for flip-angle homogenization over an extended volume.  

PubMed

With Transmit SENSE, we demonstrate the feasibility of uniformly exciting a volume such as the human brain at 7T through the use of an original minimalist transmit k-space coverage, referred to as "k(T) -points." Radio-frequency energy is deposited only at a limited number of k-space locations in the vicinity of the center to counteract transmit sensitivity inhomogeneities. The resulting nonselective pulses are short and need little energy compared to adiabatic or other B?1+-robust pulses available in the literature, making them good candidates for short-repetition time 3D sequences at high field. Experimental verification was performed on three human volunteers at 7T by means of an 8-channel transmit array system. On average, whereas the standard circularly polarized excitation resulted in a 33%-flip angle spread (standard deviation over mean) throughout the brain, and a static radio-frequency shim showed flip angle variations of 17% and up, application of k(T) -point-based excitations demonstrated excellent flip angle uniformity (8%) for a small target flip angle and with sub-millisecond durations. PMID:21590724

Cloos, M A; Boulant, N; Luong, M; Ferrand, G; Giacomini, E; Le Bihan, D; Amadon, A

2011-05-16

241

62 FR 44748 - Coach USA, Inc. and K-T Contract Services, Inc.Control and Merger ExemptionGray Line Tours of...  

Federal Register 2010, 2011, 2012, 2013

...STB Finance Docket No. 33431] Coach USA, Inc. and K-T Contract Services, Inc...SUMMARY: Coach USA, Inc. (Coach), a noncarrier that controls...Notre Capital Ventures II, LLC and Coach USA, Inc.-- Control...

1997-08-22

242

Cretaceous–Tertiary diversification among select Scolopendrid centipedes of South India  

Microsoft Academic Search

Given that peninsular India was part of the Gondwanan super continent, part of its current biota has Gondwanan origin. To determine the Gondwanan component of the peninsular Indian biota, a large number of species spanning diverse taxonomic groups need to be sampled from multiple, if not all, of the former Gondwanan fragments. Such a large scale phylogenetic approach will be

Jahnavi Joshi; K. Praveen Karanth

2011-01-01

243

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

244

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

245

Cretaceous-Tertiary diversification among select Scolopendrid centipedes of South India.  

PubMed

Given that peninsular India was part of the Gondwanan super continent, part of its current biota has Gondwanan origin. To determine the Gondwanan component of the peninsular Indian biota, a large number of species spanning diverse taxonomic groups need to be sampled from multiple, if not all, of the former Gondwanan fragments. Such a large scale phylogenetic approach will be time consuming and resource intensive. Here, we explore the utility of a limited sampling approach, wherein sampling is confined to one of the Gondwanan fragments (peninsular India), in identifying putative Gondwanan elements. To this end, samples of Scolopendrid centipedes from Western Ghats region of peninsular India were subjected to molecular phylogenetic and dating analyses. The resulting phylogenetic tree supported monophyly of the family Scolopendridae which was in turn split into two clades constituting tribes Otostigmini and Scolopendrini-Asanadini. Bayesian divergence date estimates suggested that the earliest diversifications within various genera were between 86 and 73mya, indicating that these genera might have Gondwanan origin. In particular, at least four genera of Scolopendrid centipedes, Scolopendra, Cormocephalus, Rhysida and Digitipes, might have undergone diversification on the drifting peninsular India during the Late Cretaceous. These putative Gondwanan taxa can be subjected to more extensive sampling to confirm their Gondwanan origin. PMID:21575731

Joshi, Jahnavi; Karanth, K Praveen

2011-05-06

246

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

NASA Astrophysics Data System (ADS)

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

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

2009-07-01

247

Terminal cretaceous extinctions in the hell creek area, montana: compatible with catastrophic extinction.  

PubMed

Inaccurate stratigraphic correlations in the Hell Creek area, Montana, have led to the assumption that transitional vertebrate faunas (Bug Creek Anthills) exist in the latest Cretaceous, refuting a catastrophic turnover at the Cretaceous-Tertiary boundary. Establishment of the transitional faunas in Paleocene channels that cut down through the Cretaceous-Tertiary boundary renders the terrestrial faunal record compatible with the marine record and with catastrophic extinction. PMID:17742932

Smit, J; VAN DER Kaars, S

1984-03-16

248

Terminal Cretaceous Extinctions in the Hell Creek Area, Montana: Compatible with Catastrophic Extinction  

NASA Astrophysics Data System (ADS)

Inaccurate stratigraphic correlations in the Hell Creek area, Montana, have led to the assumption that transitional vertebrate faunas (Bug Creek Anthills) exist in the latest Cretaceous, refuting a catastrophic turnover at the Cretaceous-Tertiary boundary. Establishment of the transitional faunas in Paleocene channels that cut down through the Cretaceous-Tertiary boundary renders the terrestrial faunal record compatible with the marine record and with catastrophic extinction.

Smit, J.; van der Kaars, S.

1984-03-01

249

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

PubMed

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

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

2012-03-19

250

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

251

Mapping lithospheric boundaries using Os isotopes of mantle xenoliths: An example from the North China Craton  

Microsoft Academic Search

The petrology, mineral compositions, whole rock major\\/trace element concentrations, including highly siderophile elements, and Re–Os isotopes of 99 peridotite xenoliths from the central North China Craton were determined in order to constrain the structure and evolution of the deep lithosphere. Samples from seven Early Cretaceous–Tertiary volcanic centers display distinct geochemical characteristics from north to south. Peridotites from the northern section

Jingao Liu; Roberta L. Rudnick; Richard J. Walker; Shan Gao; Fu-yuan Wu; Philip M. Piccoli; Honglin Yuan; Wen-liang Xu; Yi-Gang Xu

2011-01-01

252

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

253

Drilling Probes Past Carbon Cycle Perturbations on the Demerara Rise  

NASA Astrophysics Data System (ADS)

Ocean Drilling Program (ODP) Leg 207 recently cored sediments on the Demerara Rise at ~9°N in the tropical Atlantic and successfully recovered continuous records of the Paleocene/Eocene Thermal Maximum (PETM), the Cretaceous/Tertiary boundary (K/T), and Cretaceous Ocean Anoxic Events (OAEs). The Demerara Rise, north of Suriname and French Guyana, South America, is an ideal drilling target because expanded sections of Cretaceous- and Paleogene-age deep-sea sediments are shallowly buried and exist with good stratigraphic control in expanded sections. Furthermore, the northwestern escarpment of the Demerara Rise offered the possibility of recovering sediments along a paleo-depth transect. The paleogeographic position of the Demerara Rise lies within the core of the tropics in a location near the Equatorial Atlantic Gateway between South America and Africa, which is believed to have played an important role in controlling changes in global climate during the Cretaceous.

Erbacher, Jochen; Mosher, David; Malone, Mitchell

2004-02-01

254

Drilling probes past carbon cycle perturbations on the Demerara Rise  

NASA Astrophysics Data System (ADS)

Ocean Drilling Program (ODP) Leg 207 recently cored sediments on the Demerara Rise at ˜9°N in the tropical Atlantic and successfully recovered continuous records of the Paleocene/Eocene Thermal Maximum (PETM), the Cretaceous/Tertiary boundary (K/T), and Cretaceous Ocean Anoxic Events (OAEs). The Demerara Rise, north of Suriname and French Guyana, South America, is an ideal drilling target because expanded sections of Cretaceous- and Paleogene-age deep-sea sediments are shallowly buried and exist with good stratigraphic control in expanded sections. Furthermore, the northwestern escarpment of the Demerara Rise offered the possibility of recovering sediments along a paleo-depth transect. The paleogeographic position of the Demerara Rise lies within the core of the tropics in a location near the Equatorial Atlantic Gateway between South America and Africa, which is believed to have played an important role in controlling changes in global climate during the Cretaceous.

ODP Leg 207 Scientific Party; Erbacher, Jochen; Mosher, David; Malone, Mitchell

2004-02-01

255

Plate Boundaries  

NSDL National Science Digital Library

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

256

Dinosaur extinction: closing the '3 m gap'  

PubMed Central

Modern debate regarding the extinction of non-avian dinosaurs was ignited by the publication of the Cretaceous–Tertiary (K–T) asteroid impact theory and has seen 30 years of dispute over the position of the stratigraphically youngest in situ dinosaur. A zone devoid of dinosaur fossils reported from the last 3 m of the Upper Cretaceous, coined the ‘3 m gap’, has helped drive controversy. Here, we report the discovery of the stratigraphically youngest in situ dinosaur specimen: a ceratopsian brow horn found in a poorly rooted, silty, mudstone floodplain deposit located no more than 13 cm below the palynologically defined boundary. The K–T boundary is identified using three criteria: (i) decrease in Cretaceous palynomorphs without subsequent recovery, (ii) the existence of a ‘fern spike’, and (iii) correlation to a nearby stratigraphic section where primary extraterrestrial impact markers are present (e.g. iridium anomaly, spherules, shocked quartz). The in situ specimen demonstrates that a gap devoid of non-avian dinosaur fossils does not exist and is inconsistent with the hypothesis that non-avian dinosaurs were extinct prior to the K–T boundary impact event.

Lyson, Tyler R.; Bercovici, Antoine; Chester, Stephen G. B.; Sargis, Eric J.; Pearson, Dean; Joyce, Walter G.

2011-01-01

257

Measurement of the MACS of Ta181(n,?) at kT=30 keV as a test of a method for Maxwellian neutron spectra generation  

NASA Astrophysics Data System (ADS)

Measurement of the Maxwellian-Averaged Cross-Section (MACS) of the Ta(n,?)181 reaction at kT=30 keV by the activation technique using an innovative method for the generation of Maxwellian neutron spectra is presented. The method is based on the shaping of the proton beam to produce a desired neutron spectrum using the 7Li(p,n) reaction as a neutron source. The characterization of neutron spectra has been performed by combining measured proton distributions, an analytical description of the differential neutron yield in angle and energy of the 7Li(p,n) reaction, and with Monte Carlo simulations of the neutron transport. A measured value equal to 815±73 mbarn is reported for the MACS of the reaction Ta(n,?)181 at kT=30 keV. The MACS of the reaction Au(n,?)197 provided by KADoNiS has been used as a reference.

Praena, J.; Mastinu, P. F.; Pignatari, M.; Quesada, J. M.; García-López, J.; Lozano, M.; Dzysiuk, N.; Capote, R.; Martín-Hernández, G.

2013-11-01

258

Compilation of Information and Data on the Manson Impact Structure.  

National Technical Information Service (NTIS)

A problem for the impact hypothesis for the Cretaceous-Tertiary (K-T) mass extinction is the apparent absence of an identifiable impact site. The Manson Impact Structure is a candidate because it is the largest recognized in the U.S.; it is relatively clo...

J. B. Hartung R. R. Anderson

1988-01-01

259

Evolutionary Catastrophes: The Science of Mass Extinction  

NASA Astrophysics Data System (ADS)

The stories behind the greatest scientific controversies are more than entertaining. They provide windows into the evolution of scientific thought, scientific method, technological achievements and their research applications, and the influence of individuals and personalities on a community's acceptance of a theory Epic controversies surround the theories for Earth's mass extinction events, and none is more spectacular than the continuing polemic over the Cretaceous-Tertiary (K/T) mass extinctions and ultimate demise of the dinosaurs.In contrast to other great scientific debates, we tend to view the K/T event in the context of a crime scene, where the spectacularly diverse flora and fauna of a primordial Eden were unwittingly slain by one or more ruthless and efficient killers. A “foreign” suspect has been fingered; an intruder that killed suddenly and randomly has become the principal suspect. The main clues uncovered in the case include a global K/T iridium anomaly; shock-deformed minerals in K/T boundary sediments; the ˜6 5 m.y-old Deccan flood-basalt province, which covered an area roughly the size of France; and the ˜6 5 m.y-old Chicxulub impact crater in the Yucatan peninsula, which seems to be among the largest to have formed in the inner solar system over the past billion years.

Hames, Willis

260

Complete mitochondrial DNA genome sequences show that modern birds are not descended from transitional shorebirds.  

PubMed Central

To test the hypothesis put forward by Feduccia of the origin of modern birds from transitional birds, we sequenced the first two complete mitochondrial genomes of shorebirds (ruddy turnstone and blackish oystercatcher) and compared their sequences with those of already published avian genomes. When corrected for rate heterogeneity across sites and non-homogeneous nucleotide compositions among lineages in maximum likelihood (ML), the optimal tree places palaeognath birds as sister to the neognaths including shorebirds. This optimal topology is a re-rooting of recently published ordinal-level avian trees derived from mitochondrial sequences. Using a penalized likelihood (PL) rate-smoothing process in conjunction with dates estimated from fossils, we show that the basal splits in the bird tree are much older than the Cretaceous-Tertiary (K-T) boundary, reinforcing previous molecular studies that rejected the derivation of modern birds from transitional shorebirds. Our mean estimate for the origin of modern birds at about 123 million years ago (Myr ago) is quite close to recent estimates using both nuclear and mitochondrial genes, and supports theories of continental break-up as a driving force in avian diversification. Not only did many modern orders of birds originate well before the K-T boundary, but the radiation of major clades occurred over an extended period of at least 40 Myr ago, thus also falsifying Feduccia's rapid radiation scenario following a K-T bottleneck.

Paton, Tara; Haddrath, Oliver; Baker, Allan J

2002-01-01

261

Fingerprinting the K/T impact site and determining the time of impact by UPb dating of single shocked zircons from distal ejecta  

USGS Publications Warehouse

UPb isotopic dating of single 1-3 ??g zircons from K/T distal ejecta from a site in the Raton Basin, Colorado provides a powerful new tool with which to determine both the time of the impact event and the age of the basement at the impact site. Data for the least shocked zircons are slightly displaced from the 544 ?? 5 Ma primary age for a component of the target site, white those for highly shocked and granular grains are strongly displaced towards the time of impact at 65.5 ?? 3.0 Ma. Such shocked and granular zircons have never been reported from any source, including explosive volcanic rocks. Zircon is refractory and has one of the highest thermal blocking temperatures; hence, it can record both shock features and primary and secondary ages without modification by post-crystallization processes. Unlike shocked quartz, which can come from almost anywhere on the Earth's crust, shocked zircons can be shown to come from a specific site because basement ages vary on the scale of meters to kilometers. With UPb zircon dating, it is now possible to correlate ejecta layers derived from the same target site, test the single versus multiple impact hypothesis, and identify the target source of impact ejecta. The ages obtained in this study indicate that the Manson impact site, Iowa, which has basement rocks that are mid-Proterozoic in age, cannot be the source of K/T distal ejecta. The K/T distal ejecta probably originated from a single impact site because most grains have the same primary age. ?? 1993.

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

1993-01-01

262

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

263

Comet impacts and chemical evolution on the bombarded Earth  

NASA Astrophysics Data System (ADS)

Amino acids yields for previously published shock tube experiments are used with minimum Cretaceous-Tertiary (K/T) impactor mass and comet composition to predict AIB amino acid K/T boundary sediment column density. The inferred initial concentration of all amino acids in the K/T sea and in similar primordial seas just after 10 km comet impacts would have been at least 10-7 M. However, sinks for amino acids must also be considered in calculating amino acid concentrations after comet impacts and in assessing the contribution of comets to the origin of life. The changing concentration of cometary amino acids due to ultraviolet light is compared with the equilibrium concentration of amino acids produced in the sea from corona discharge in the atmosphere, deposition in water, and degradation by ultraviolet light. Comets could have been more important than endogenous agents for initial evolution of amino acids. Sites favorable for chemical evolution of amino acids are examined and it is concluded that chemical evolution could have occurred at or above the surface even during periods of intense bombardment of Earth before 3.8 billion years ago.

Oberbeck, Verne R.; Aggarwal, Hans

1991-09-01

264

Thermochronology and tectonics of the Central and Western Cordilleras of Colombia: Early Cretaceous-Tertiary evolution of the Northern Andes  

NASA Astrophysics Data System (ADS)

New thermochronological data record a complex cooling history in the Central and Western Cordilleras of Colombia that is a function of Early Cretaceous to late Miocene tectonic events. Alkali-feldspar 40Ar/39Ar cooling ages of ~ 138-130 Ma immediately post-date the cessation of Jurassic arc-magmatism and a major unconformity within the retro-foreland region of the northern Andes. We interpret these ages as cooling driven by exhumation in response to either compression driven by subduction of a seamount, or extension and oceanward migration of the slab during the earliest Cretaceous, giving rise to the Lower Cretaceous Quebradagrande arc sequence. Biotite and alkali-feldspar 40Ar/39Ar data from the palaeocontinental margin reveal the presence of a younger cooling event at 117-107 Ma, which was contemporaneous with hornblende 40Ar/39Ar cooling ages obtained from medium-high P-T metamorphic relicts of a Late Jurassic-Early Cretaceous subduction channel. This cooling event is attributed to exhumation driven by the collision and accretion of a fringing arc against the continental margin, and obduction of the subduction channel onto the forearc. Inverse modelling of zircon and apatite fission track and (U-Th)/He data from throughout the Central and Western Cordilleras reveals three periods of rapid cooling since the Late Cretaceous. The earliest phase is recorded by Jurassic and Cretaceous granitoids that cooled rapidly during 75-65 Ma. We attribute cooling to exhumation of the continental margin during ~ 75-70 Ma (~ 1.6 km/My), which was forced by the collision and accretion of the Caribbean Large Igneous Province in the Campanian. The Central Cordillera exhumed at moderate rates of ~ 0.3 km/My during ~ 45-30 Ma, which are also observed over widely dispersed regions along the Andean chain, and were probably caused by an increase in continent-ocean plate convergence rates. Exhumation rates drastically increased in the middle-late Miocene, with the greatest amount occurring in southern Colombia as a consequence of the collision and subduction of the buoyant Carnegie Ridge at 15 Ma.

Villagómez, Diego; Spikings, Richard

2013-02-01

265

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

266

Petrology of Tullock Member, Fort Union Formation, Wyoming and Montana: Evidence for early Paleocene uplift of Bighorn Mountains  

SciTech Connect

New petrologic data collected from sandstones in the Paleocene Tullock Member of the Fort Union Formation above the Cretaceous/Tertiary boundary in the Powder River basin (PRB) and from the lowermost Paleocene in the Bighorn basin, Wyoming and Montana, compel reevaluation of the timing of the bighorn uplift, formerly thought to be middle Paleocene. The Cretaceous/Tertiary boundary is identified by regionally valid palynological and trace element geochemical criteria. Basin-wide outcrop and subsurface studies of the Tullock Member indicate deposition on a low-gradient alluvial plain extending toward the retreating Cannonball sea. Eastward-flowing, low-sinuosity paleostreams containing small, sandy, stable channels characterized the fluvial systems.

Brown, J.L.; Hansley, P.L. (Geological Survey, Denver, CO (USA))

1989-09-01

267

A method to obtain a Maxwell-Boltzmann neutron spectrum at kT=30 keV for nuclear astrophysics studies  

NASA Astrophysics Data System (ADS)

A method based on shaping the proton beam energy in order to shape the neutron beam energy to a desired form for accelerator-based neutron sources is proposed. An application to a superconductive RFQ proton accelerator of 5 MeV and 50 mA for the production of a stellar neutron spectrum at thermal energy equal to 30 keV using the 7Li(p,n)7Be reaction is investigated. The chosen energy beam shaper is a carbon foil which shapes the quasi-monochromatic proton beam to a quasi-Gaussian distribution: after the carbon foil, the beam is still shaped by chopping the Gaussian distribution at the reaction energy threshold. The obtained proton beam is impinged in a metallic lithium target. The concepts of the energy shaper, the proposed lithium target and the calculations performed to remove their power load are presented. Calculations show that a power density of 3 kW/cm2 can be sustained by the target which produces a forward-directed neutron source of 7.3×1010 neutrons/s. The obtained neutron spectrum resembles a Maxwell-Boltzmann distribution at kT=30 keV with a coefficient of determination of 0.997. The method is intended to be applied in activation analysis for measuring the Maxwellian-averaged neutron capture cross-section of elements of interest for astrophysics and validation of integral neutron data in the epithermal energy range.

Mastinu, P. F.; Martín Hernández, G.; Praena, J.

2009-04-01

268

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

269

Boundary Layer Simulator Improvement.  

National Technical Information Service (NTIS)

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 p...

S. C. Praharaj C. P. Schmitz J. A. Nouri

1989-01-01

270

Decline of the Maastrichtian pelagic ecosystem based on planktic foraminifera assemblage change: Implication for the terminal Cretaceous faunal crisis  

NASA Astrophysics Data System (ADS)

An outer shelf upper slope tropical Tethyan pelagic environment existed over southern Israel during Maastrichtian time. Planktic foraminifera in the >63 and >149 ?m size fractions from four sections in this area were studied quantitatively for a high-resolution ecostratigraphic analysis of the pre Cretaceous-Tertiary (K-T) paleoenvironment. During the Maastrichtian, 41% of the planktic foraminifera species became extinct, mostly keeled Globotruncanidae, which also became quantitatively reduced near the end of the Maastrichtian from as much as 35% to only 5% of the planktic foraminifera population. Evolutionary replacement of extinct species by new forms nearly ceased in that interval. Two major opportunistic blooms of Guembelitria took place, associated with reduced abundances of keeled forms and the dominant species Heterohelix globulosa. The first bloom occurred within the upper Gansserina gansseri to lower Abathomphalus mayaroensis Zones and the second within the Plummerita hantkeninoides Zone. The extinctions, concomitant changes in faunal dominance, and opportunist blooms indicate that the pelagic ecosystem in the Negev area experienced multiple stresses during the Maastrichtian. The planktic foraminiferal assemblages were taxonomically impoverished and in decline prior to the K-T boundary crisis.

Abramovich, Sigal; Almogi-Labin, Ahuva; Benjamini, Chaim

1998-01-01

271

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

PubMed Central

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.

Codron, Daryl; Carbone, Chris; Muller, Dennis W. H.; Clauss, Marcus

2012-01-01

272

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

2012-04-18

273

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

2008-09-08

274

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

275

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

PubMed Central

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.

Sengor, A. M. Celal; Atayman, Saniye; Ozeren, Sinan

2008-01-01

276

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

277

Textural Boundary Analysis  

Microsoft Academic Search

A procedure is demonstrated for locating textural boundaries in the digital image representation of a natural scene. The technique involves development of an edge operator capable of integrating multiple textural features into a single boundary determination. The process is designed to simulate actual perception of textural discontinuities. Success of the system is demonstrated on pictures with prominent perceived boundaries not

William B. Thompson; WILLIAM B. THOMPSON

1977-01-01

278

Symmetry boundary conditions  

SciTech Connect

A simple approach to energy conserving boundary conditions using exact symmetries is described which is especially useful for numerical simulations using the finite difference method. Each field in the simulation is normally either symmetric (even) or antisymmetric (odd) with respect to the simulation boundary. Another possible boundary condition is an antisymmetric perturbation about a nonzero value. One of the most powerful aspects of this approach is that it can be easily implemented in curvilinear coordinates by making the scale factors of the coordinate transformation symmetric about the boundaries. The method is demonstrated for magnetohydrodynamics (MHD), reduced MHD, and a hybrid code with particle ions and fluid electrons. These boundary conditions yield exact energy conservation in the limit of infinite time and space resolution. Also discussed is the interpretation that the particle charge reverses sign at a conducting boundary with boundary normal perpendicular to the background magnetic field.

Denton, R.E. [Dartmouth College, Department of Physics and Astronomy, 6127 Wilder Lab, Hanover, NH 03755 (United States)], E-mail: rdjcp@rdenton.fastem.com; Hu, Y. [Dartmouth College, Department of Physics and Astronomy, 6127 Wilder Lab, Hanover, NH 03755 (United States)

2009-07-20

279

Fe-rich and K-rich mafic spherules from slumped and channelized Chicxulub ejecta deposits in the northern La Sierrita area, NE Mexico  

Microsoft Academic Search

Spherule deposits, commonly interpreted as ejecta from the Chicxulub impact at Yucatán, Mexico, are present in many K-T (Cretaceous-Tertiary) sections. Geological mapping of the northern La Sierrita area, NE Mexico, revealed the presence of (1) multiple spherule deposits embedded in late Maastrichtian marls, which are folded or disaggregated (breccia-like). They are up to 6 m thick, locally present in two

P. Schulte; W. Stinnesbeck; D. Stüben; U. Kramar; Z. Berner; G. Keller; T. Adatte

2003-01-01

280

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

281

Fullerenes, Noble Gases and the Flux of Extraterrestrial Debris to  

NASA Astrophysics Data System (ADS)

The discovery of fullerenes in deposits associated with two separate impact events involving a large bolide with the Earth suggests that these carbon (C) molecules may also be an indicator of extraterrestrial (ET) events over geologic time. Fullerenes were detected in carbon-rich breccias (Onaping Fm.) associated with the 1.85 byr Sudbury Crater (Becker et al., Science 265, 1994) and in clay sediments within the 65 myr old Cretaceous/Tertiary (K/T) boundary (Heymann et al., Science 265, 1994). To determine the origin of the Sudbury fullerenes, we searched for noble gases trapped inside the fullerene molecules (Saunders et al., Science 259, 1993). The Sudbury fullerenes contain trapped 3He/4He ratios (~5.5 times 10^{-4}) similar to those found in meteorites and some interplanetary dust particles (Becker et al., Science 272, 1996). Preliminary measurements of He in a continental K/T fullerene residue from Raton Basin (Colorado) revealed ^3He/^4He ratios some 100 times above air. A marine K/T residue from Stevns Klint, (Denmark) revealed ^3He/^4He ratios several thousand times above air in the high temperature fraction! We attribute the anomalously high ^3He/^4He ratios and high ^3He concentration in Stevns Klint to the abundance of higher fullerenes in the residue. The high ^3He/^4He ratio in the K/T fullerenes suggests that they were present in the bolide and somehow survived the impact event. Confirmation of these results could have broad implications concerning the importance of exogenous delivery in providing carbon, volatiles and perhaps other organics to the early Earth's crustal reservoir.

Becker, Luann; Poreda, Robert; Bunch, Ted

282

Maxwellian-averaged neutron-induced reaction cross sections and astrophysical reaction rates for kT = 1 keV to 1 MeV calculated from microscopic neutron cross section library JENDL-3.3  

Microsoft Academic Search

Maxwellian-averaged cross sections and astrophysical reaction rates were calculated for neutron capture, fission, (n,p), (n,?), and some threshold reactions based on a microscopic neutron cross section data library, the Japanese Evaluated Nuclear Data Library Version 3.3 (JENDL-3.3). The calculation was made for temperatures (kT) from 1keV to 1MeV including the most important range in astrophysical nucleosynthesis. Results are presented in

T.. Nakagawa; S.. Chiba; T. Hayakawa; T. Kajino

2005-01-01

283

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

284

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

285

Alvarez, Luis Walter (1911-88)  

Microsoft Academic Search

Physicist and astronomer, born in San Francisco, CA, professor at the University of California, Nobel prizewinner (1968) for his discoveries in particle physics. Used cosmic rays to `x-ray' the pyramids of Egypt, finding in particular that the tombs in the Great Pyramid at Giza had no hidden rooms. Alvarez (and his son) discovered globally distributed iridium at the Cretaceous\\/Tertiary boundary

P. Murdin

2000-01-01

286

Gallery: Asteroid and Comet Impact Hazards  

NSDL National Science Digital Library

This site consists of a gallery of artists' conceptions of catastrophic strikes on Earth by asteroids or comets, including the impact which occurred at the Cretaceous-Tertiary boundary and is suspected of causing mass extinction of the dinosaurs. Links to other related sites and a short movie of the Peekskill, New York meteorite, which fell in 1993, are also included.

287

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

288

Proceedings of the SEPM annual midyear meeting. Volume 3  

SciTech Connect

These proceedings collect papers on economic geology. Topics include: controls on framework composition of sandstones, stylolitic porosity as a critical factor for deep gas production, use of clastic wedges to interpret water depth during deposition of black shales, sandstone diagenesis, petrology and reservoir rock potential of Mississippi fan sands, zinc and petroleum resources in dolomites, chemical tracers, and the cretaceous-tertiary boundary event.

Not Available

1986-01-01

289

The dimensions of the Chicxulub impact crater and impact melt sheet  

Microsoft Academic Search

The Chicxulub impact crater, which is the principal source of impact debris in Cretaceous-Tertiary boundary sediments, is currently buried by a ~1 km thick sequence of carbonate sediments. Because the crater is not exposed for direct scrutiny, its size has remained uncertain, and in particular, estimates ranging from ~100 to ~300 km have been made on the basis of gravity

David A. Kring

1995-01-01

290

Fluid Inclusions from Anhydrite Related to the Chicxulub Crater Impact Breccias, Yucatan, Mexico: Preliminary Report  

Microsoft Academic Search

Abstract, Results of a study of fluid inclusions in anhydrite from drill hole Y-6 in the Chicxulub crater, of northwestern Yucatan, Mexico, are reported in this work. The Chicxulub crater was formed at the Cretaceous-Tertiary boundary by a meteorite impact. The resulting ejection breccias are composed mostly of hydrothermally altered crystalline basement material. The mineral assemblage pyroxene + anhydrite +

Eduardo Gonzalez-Partida; Alejandro Carillo-Chavez; Ricardo Martinez-Ibarra

2000-01-01

291

Water and Carbon Dioxide Preserved in Crystals of the Deccan Basalts  

Microsoft Academic Search

The Cretaceous-Tertiary boundary event (~66 Ma) is approximately contemporaneous with the Chicxulub impact and with the eruption of the Deccan traps. Phipps Morgan and others (2004) suggested that volatile-rich mantle plumes could generate extraordinarily explosive events that result in excavation and transport of large masses of shocked crust and mantle, the impacts of which would be indistinguishable from those of

S. J. Seaman

2009-01-01

292

Is the KTB Iridium Anomaly a Unique Cosmic Marker?  

Microsoft Academic Search

Historically, the major breaks in the Phanerozoic stratigraphic record were defined by palaeontological hiatuses. Since the seminal work on the Cretaceous-Tertiary boundary (KTB) by Alvarez et al. (1980), however, the idea that a layer of anomalous chemistry (especially the highly siderophile elements (HSEs), typified by Ir), is exactly coincident with the end-Cretaceous mass extinction event has become deeply rooted. In

M. Tredoux; G. Keller

2008-01-01

293

The atmospheric boundary layer  

Microsoft Academic Search

In this book, the author successfully reviews the current state of affairs in boundary-layer meteorology research. The book is organized into nine chapters. The first chapter is an introduction to the topic of the atmospheric boundary layer. The second chapter is a survey of turbulence theory. The third chapter reviews the similarity relationships that have been formulated for the various

J. R. Garratt

1992-01-01

294

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

295

Rethinking the Boundaries  

ERIC Educational Resources Information Center

The splintering of the public domain makes the development of a coherent lifelong learning system less likely. But while people might want to resist plans to dissolve the boundaries between the public, private and voluntary sectors, debate about the relationship between professionals and volunteers in adult education suggests those boundaries

Schuller, Tom

2011-01-01

296

Rethinking the Boundaries  

ERIC Educational Resources Information Center

|The splintering of the public domain makes the development of a coherent lifelong learning system less likely. But while people might want to resist plans to dissolve the boundaries between the public, private and voluntary sectors, debate about the relationship between professionals and volunteers in adult education suggests those boundaries

Schuller, Tom

2011-01-01

297

Boundary layer transition studies  

Microsoft Academic Search

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 &

Jonathan H. Watmuff

1995-01-01

298

Boundary layer transition  

Microsoft Academic Search

The boundary layer stability, its active control by sound and surface heating and the effect of curvature are studied numerically and experimentally for subsonic flow. In addition, the experimental and flight test data are correlated using the stability theory for supersonic Mach numbers. Active transition fixing and feedback control of boundary layer by sound interactions are experimentally investigated at low

L. Maestrello; A. Bayliss; S. M. Mangalam; M. R. Malik

1986-01-01

299

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

300

Discovering Plate Boundaries  

NSDL National Science Digital Library

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

Henning, Alison

301

Boundary Element Method  

Microsoft Academic Search

\\u000a In Chapter 2 Green’s functions in piezoelectric materials were described. Applications of these Green’s functions to the boundary\\u000a element method (BEM) are discussed in this chapter. In contrast to the finite element method (FEM), BEM involves only discretization\\u000a of the boundary of the structure due to the governing differential equation being satisfied exactly inside the domain leading\\u000a to a relatively

Qing-Hua Qin

302

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

303

CÁC Y?U T? ?NH H??NG ??N QUÁ TRÌNH K?T T?A PHOTPHAT TRONG N??C TH?I CÓ ?? KI?M TH?P FACTORS AFFECTING PHOSPHORUS PRECIPITATION IN LOW ALKANILITY WASTEWATER  

Microsoft Academic Search

???c th?c hi?n b?ng thi?t b? Jar-test. K?t qu? thu ???c hàm l??ng c?a nhôm sunphat b? sung và hi?u qu? x? lý photpho ph? thu?c vào pH c?a n??c th?i sau khi b? sung ch?t k?t t?a. pH t?i ?u cho quá trình k ?t t?a photphat ??t hi?u qu? n?m trong kho?ng 5,7 - 5,9. Th?i gian t?i

Rajesh Banu; Ick-tae Yeom

2009-01-01

304

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

305

Characterizing Plate Boundaries  

NSDL National Science Digital Library

To prepare for this exercise students read about the processes that operate at plate boundaries and how they are related to the distinct patterns of seismicity, volcanism, surface elevations (e.g., ridges versus trenches), and seafloor ages characteristic of different boundary types. During the week the assignment is available online, students have access to: (1) an index map that locates three boundaries they are to study; and (2) four maps from Sawyer's Discovering Plate Boundaries website that provide the data mentioned above. Student tasks are to: (1) document patterns in each type of data along the three targeted boundaries; and (2) use these observations in conjunction with their understandings of the processes that operate along different types of boundaries to decide whether each of the targeted sites is most likely to be a divergent, convergent, or shear boundary. This activity gives students practice in map reading, interpreting the likely tectonic setting of a boundary by pulling together constraints from several types of data, and collaborating with their classmates in an online environment. The activity also provides a foundation for understanding a wide range of phenomena that are discussed later in the semester in the context of plate tectonic processes. Teaching Tips Adaptations that allow this activity to be successful in an online environment Sawyer's Discovering Plate Boundaries is a jigsaw exercise in which students collaboratively develop an empirical classification of plate boundaries by first studying an individual data set (e.g., seismicity) and then working as part of a multidisciplinary team to develop a composite classification for the boundaries of a single plate using several types of data. In order for the classification to be truly empirical, students are not introduced to the "traditional" classification of plate boundaries till the end of the exercise. In adapting this assignment to the online environment I have: (1) asked students to prepare by becoming familiar with the standard classification of plate boundaries and the processes that operate at them; (2) limited their work to three targeted boundaries of different types; and (3) provided guidance about which features to look for in the each data set. I have found that these modifications help online students, who often work alone "on their own schedules", to avoid getting "lost" and frustrated with the assignment and to compensate for the lack of collaborative input they would receive in a classroom setting. Elements of this activity that are most effective The success of this exercise is really seems to depend on how well a student follows the directions. If a student learns about the geologic differences among plate boundaries, makes careful observations, and thoughtfully compares his or her observations to the expected patterns he or she typically does quite well based on answers to the follow-up questions. If, on the other hand, a student simply looks up the types of the targeted boundaries on a map and then attempts to "back out" the observations that he or she thinks should fit, the result is often inconsistency and a poor score on the questions. (I can often tell which approach a student is taking based on the queries they post to the discussion board, but rarely seem to be able to get those who are trying to work backwards through the assignment to change direction.) Recommendations for other faculty adapting this activity to their own course: To date my experience developing an engaging online exercise to help students learn the principles of plate tectonics has only been partly successful. I think that having such an exercise is critical, however, because this topic provides the framework for so much of what we learn in the geosciences. Based on my efforts to adapt elements of Discovering Plate Boundaries to an online environment I would offer three recommendations. (1) Provide examples. Confronted with an unfamiliar map students are sometimes confused when asked to decide if seafloor age, for example, is uniform or variable along the length of a boundary. Showing them what you mean using snapshots from a map can often clear questions like this up quickly. Similarly, for written work a single example that gives them a clear sense of "what you're looking for" and can often head off a lot of questions. (2) Choose the boundaries you ask students to study carefully. The scarcity of documented volcanism along a mid-ocean ridge or the burial of seafloor age belts by sediment along a trench can result in student observations that are correct, but problematic for correctly assessing the nature of a boundary. (3) Stay on top of student questions and comments, and be prepared to make well-publicized "mid-course corrections" if something you thought was clear turns out to be misunderstood. These minor corrections happen naturally in face-to-face classes but can require real diligence to catch and correct in the online environment.

Hirt, Bill

306

The educational boundary.  

PubMed

In this contribution, the authors define and discuss the educational boundary in analytic training, which they believe is an often neglected and useful concept in psychoanalytic education. The framework on which their discussion rests includes the recent attention of psychoanalysts to issues of boundaries and ethics. Their understanding of how clinical work affects the mind of the analyst educator, as well as the ways the personalities of various analysts affect their dealings with faculty peers and students, are the other cornerstones of their discussion. The authors contend that many of the institutional problems encountered in the training of analysts can be better understood when viewed through the prism of the educational boundary. They present examples which illustrate several of the ways psychoanalytic educators complicate the training experience of candidates, offer specific explanations as to why analysts struggle as they try to manage their educational interventions, and indicate in a discussion of potential remedies that those behaviors might be avoided if the educational boundary is in focus. They also provide an example of how the educational boundary can be more effectively managed. PMID:17244575

Sonnenberg, Stephen M; Myerson, William A

2007-02-01

307

Learning with boundary conditions.  

PubMed

Kernel machines traditionally arise from an elegant formulation based on measuring the smoothness of the admissible solutions by the norm in the reproducing kernel Hilbert space (RKHS) generated by the chosen kernel. It was pointed out that they can be formulated in a related functional framework, in which the Green's function of suitable differential operators is thought of as a kernel. In this letter, our own picture of this intriguing connection is given by emphasizing some relevant distinctions between these different ways of measuring the smoothness of admissible solutions. In particular, we show that for some kernels, there is no associated differential operator. The crucial relevance of boundary conditions is especially emphasized, which is in fact the truly distinguishing feature of the approach based on differential operators. We provide a general solution to the problem of learning from data and boundary conditions and illustrate the significant role played by boundary conditions with examples. It turns out that the degree of freedom that arises in the traditional formulation of kernel machines is indeed a limitation, which is partly overcome when incorporating the boundary conditions. This likely holds true in many real-world applications in which there is prior knowledge about the expected behavior of classifiers and regressors on the boundary. PMID:23339616

Gnecco, Giorgio; Gori, Marco; Sanguineti, Marcello

2013-01-22

308

Shock Deformation and Volcanism across the Cretaceous - Transition.  

NASA Astrophysics Data System (ADS)

The cause of the Cretaceous-Tertiary (K/T) transition remains one of the most controversial scientific topics in the geosciences. Geological and geophysical evidence associated with the K/T boundary have been used to argue that the extinctions were caused by meteor impact or volcanism. The goal of this study was to assess the viability of a volcanic model for the K/T transition. Comparison of natural and experimentally-shocked quartz and feldspar using optical and transmission electron microscopy (TEM) revealed that the optical and statistical character of shock-induced microstructures in volcanic rocks are different from both classic impact microstructures, and from the Raton K/T samples. A series of 31 high-explosive (HE) shock-recovery experiments at pressures to 25 GPa and temperatures to 750^circC were completed on samples of granite and quartzite. TEM and optical microscopy reveal that pre-shock temperature and pulse duration have a first-order effect on the development of shock-induced microstructures in quartz and feldspar. Application of the experimental results to natural shock-induced microstructures indicates that the volcanic microstructures are probably produced at elevated temperatures and shock pressures that do not exceed 15 GPa. The results also suggest that the Raton K/T deposits were produced at pressures below about 25 GPa. Analysis of samples from the K/T transition at DSDP Site 527 and correlations between biostratigraphy, isotopes, and the data from this study suggest that the decline in marine productivity over an extended period of time may be due to climate changes induced by basaltic volcanism. The eruption of the Deccan Traps is a viable mechanism for the K/T extinctions, and the correlation of flood basalts with every major biotic crisis in the last 250 Ma supports the link between these two phenomena. Eruption of flood basalts enriched in F, Cl, CO_2 , and SO_2, could disrupt the terrestrial ecosystem, and could produce effects including elevated pCO_2, acid rain, ozone depletion, lower ocean alkalinity, and climatic change, which can explain the observation of stepped or gradual extinction.

Huffman, Alan Royce

1990-01-01

309

Grain boundary cracking  

SciTech Connect

A chronological summary is given of the various types of grain boundary fracture found in metals. In each case, there is an impurity that adsorbs at the new (fracture) surface being formed. For the case of De-P alloys, a quantitative argument can show that adsorption of phosphorus on the free surface greatly reduces the barrier to void nucleation compared to that in the absence of phosphorus. The same or larger reduction would appear for any other element, which adsorbs more strongly than phosphorus and displaces it at the surface. Such an argument is shown to explain a great many cases of dimpled grain boundary fracture in strong alloys undergoing creep or hydrogen attack. The reduction in surface energy can also lead to a smooth grain boundary fracture (no void nucleation), in which diffusion of solute to the new surface limits crack growth. Numerous examples of this are also discussed.

Shewmon, P.G.

1998-06-01

310

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

311

Boundary layer receptivity - Theory  

NASA Astrophysics Data System (ADS)

The receptivity mechanisms by which free-stream disturbances generate instability waves in laminar boundary layers are discussed. Free-stream disturbances have wavelengths which are generally much longer than those of instability waves. Hence, the transfer of energy from the free-stream disturbance to the instability wave requires a wavelength conversion mechanism. Recent analyses using asymptotic methods have shown that the wavelength conversion takes place in regions of the boundary layer where the mean flow adjusts on a short streamwise length scale. This paper reviews recent progress in the theoretical understanding of these phenomena.

Kerschen, E. J.

312

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

313

Lithologic and diagenetic attributes of the Sharwayn (Maastrichtian) and Umm Er Radhuma (late Paleocene–Eocene) formations and their significance to the K-T unconformity, Jabal Samhan area, Dhofar, Sultanate of Oman  

Microsoft Academic Search

The boundary separating Maastrichtian Sharwayn Formation from late Paleocene Eocene Umm Er Radhuma (UER) Formation in Dhofar,\\u000a southern Oman, is characterized by a regionally extensive unconformity. The Jabal Samhan escarpment, north of Marbat-Sadh\\u000a transect, preserves this unconformable boundary. This paper addresses the lithologic and diagenetic differences of the strata\\u000a across the boundary and discusses their significance and link to the

Osman Salad Hersi

2011-01-01

314

The Moving Boundary Problems.  

National Technical Information Service (NTIS)

The problem of a phase boundary that moves via diffusion in a binary solid is presented in a tutorial format. Particular attention is given to an internally consistent definition of the reference frames in which diffusive fluxes in each phase, the velocit...

R. F. Sekerka C. L. Jeanfils R. W. Heckel

1975-01-01

315

Dialogic Bonds and Boundaries.  

ERIC Educational Resources Information Center

|A study of literature cannot be divorced from cultural contexts, nor can it ignore the humanist vision in interpreting literary texts. To discover dialogic bonds and boundaries between the reader and the text, or the writer and the audience, English classes should have two objectives: (1) to explore the diversity of perspectives, and (2) to…

Khawaja, Mabel

316

Boundary superstring field theory  

Microsoft Academic Search

Using the Batalin–Vilkovisky formalism we provide a detailed analysis of the NS sector of boundary superstring field theory. We construct explicitly the relevant BV structure and derive the master action. Furthermore, we show that this action is exactly equal to the superdisk worldsheet partition function as was recently conjectured.

Vasilis Niarchos; Nikolaos Prezas

2001-01-01

317

Eddies along western boundaries  

Microsoft Academic Search

The Ulleung eddy owes its existence to beta and nonlinearities . A nonlinear theory for the Ulleung Warm Eddy (UWE) in the Japan\\/East Sea is proposed. Using the nonlinear reduced gravity (shallow water) equations, it is shown analytically and numerically that the eddy is established in order to balance the northward momentum flux exerted by the separating western boundary current

Wilton Zumpichiatti Arruda

2002-01-01

318

Plasma sheet boundary layer  

Microsoft Academic Search

The plasma sheet boundary layer is a temporally variable transition region located between the magnetotail lobes and the central plasma sheet. We have made a survey of these regions by using particle spectra and three-dimensional velocity-space distributions sampled by the ISEE 1 LEPEDEA. Ion composition measurements obtained by the Lockhead ion mass spectrometers indicate that ionospheric ions play a crucial

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

1984-01-01

319

Plasma boundaries and shocks  

Microsoft Academic Search

The quadrennium has seen an explosive growth in our knowledge and understanding of the various plasma and magnetic field boundaries in the terrestrial magnetosphere. Nowhere is that more evident than at the magneto pause and bow shock. In the 1975 and 1979 quadrennial reports, the magnetopause was covered in a single paragraph each year. The bow shock received one paragraph

C. T. Russell; E. W. Greenstadt

1983-01-01

320

Zircon U–Pb and Hf isotopic constraints on petrogenesis of the Cretaceous–Tertiary granites in eastern Karakoram and Ladakh, India  

Microsoft Academic Search

Multiple subduction events occurred preceding the collision of Greater India with the Karakoram terrane that consumed the Neotethyan Ocean between Early Cretaceous and Eocene time. Zircon U–Pb dating and Hf isotope analyses of granitic rocks collected from the Karakoram terrane and Ladakh batholith have been conducted to constrain these geological processes. Undeformed Ladakh batholith granodiorite yielded zircon U–Pb ages of

Vadlamani Ravikant; Fu-Yuan Wu; Wei-Qiang Ji

2009-01-01

321

Cretaceous–Tertiary structures and kinematics of the Serbomacedonian metamorphic rocks and their relation to the exhumation of the Hellenic hinterland (Macedonia, Greece)  

Microsoft Academic Search

The kinematic pattern and associated metamorphism of the predominant ductile deformation and the subsequent deformational\\u000a stages of the Serbomacedonian metamorphic rocks and granitoids are presented in terms of peri-Tethyan tectonics. A systematic\\u000a record of structural and metamorphic data gives evidence of a main top-to-ENE to ESE ductile flow of Cretaceous age (120–90?Ma)\\u000a associated with a crustal stretching and unroofing. A

A. Kilias; G. Falalakis; D. Mountrakis

1999-01-01

322

Lamellar diblock copolymer grain boundary morphology. 1. Twist boundary characterization  

Microsoft Academic Search

Grain boundary morphologies in poly(styrene-b-butadiene) lamellar diblock copolymers were characterized using transmission electron microscopy (TEM). Two types of twist grain boundaries were observed in which microphase separation of the two blocks was maintained in the grain boundary region by intermaterial dividing surfaces that approximate classically known minimal surfaces. The geometry of these interfaces was demonstrated by comparing experimental TEM images

Samuel P. Gido; Janelle Gunther; Edwin L. Thomas; David Hoffman

1993-01-01

323

Boundary condition effects on turbulent boundary layer wall pressure fluctuations  

Microsoft Academic Search

To better understand the flow and pressure field associated with automobile underbodies, laboratory experiments were conducted to map the velocity and pressure fluctuation statistics on two simulated underbodies operating next to a moving ground plane. The effect of boundary condition changes on the statistics for underbodies subject to equilibrium turbulent boundary layer flow and turbulent boundary layer flow perturbed by

Timothy Allen Brungart

1997-01-01

324

Florida's Seaward Boundaries - a Dilemma.  

National Technical Information Service (NTIS)

A pending lawsuit should determine precisely the extent of seaward boundaries. The financial future of this state appears to rest on the outcome of this litigation. Offshore petroleum deposits have been confirmed. Criteria for ocean boundaries are reviewe...

M. S. Scott

1972-01-01

325

SOLE SOURCE AQUIFER BOUNDARY DATA  

EPA Science Inventory

There are 7 polygons representing 6 individual sole source aquifer boundaries and one streamflow source area in California, Arizona, and Nevada. Various efforts were combined to create the final product, which represents the Federal Register boundary description. Sole source aqu...

326

Maritime boundaries and ocean resources  

SciTech Connect

International maritime boundaries have become a major issue in international politics with the increasing exploitation of maritime resources, including mineral extraction from the sea bed, and the associated exstention of territorial waters and zones of exclusive economic activity. This book examines this important international problem. It considers the growth in the exploration of marine resources. It examines particular boundary disputes in different parts of the world and discusses the implications for international law, international politics and maritime activity and management. Contents. Antarctic maritime boundary problems; the law of the sea and the mediterranean; historical geography and the world court line of delimitation across the Gulf of Maine; maritime boundary delimitation worldwide: the current state of play; technical delimitation problems in the Mediterranean Sea; offshore boundaries and mineral resources; maritime boundaries and the emerging regional bases of world ocean management; recent delimitation decisions and trends in international law; maritime boundary problems in the Barents Sea; local government boundaries in U.K. coastal areas.

Blake, G.

1987-01-01

327

Generalized Boundary Condition in SEMP.  

National Technical Information Service (NTIS)

A generalized boundary condition, to be used for modeling structures which are not compatible with the finite differencing mesh of Maxwell's equations, is proposed. The boundary condition is tested for a long thin conducting cylinder which is separated in...

R. Stettner

1975-01-01

328

Laminar vortex boundary layers  

NASA Astrophysics Data System (ADS)

The interaction of a Burgers--Rott vortex with a rigid no-slip normal wall is investigated via direct numerical simulations of the unsteady axisymmetric Navier--Stokes equations. The flows in the boundary layer and away from the vortex core have a self-similar structure, i.e. the solutions at time t, radius r, height z, and Reynolds number Re can be reduced to single profiles for the angular momentum and the azimuthal vorticity dependent on a single similarity variable. The similarity variable is the direction normal to the wall scaled by Re^1/2 and a function of r and t. The boundary layer flow near the axis for low-Re consists of a matching between a Bödewadt-like flow near r=0, where the vortex flow is near solid-body rotation, and a potential vortex boundary layer flow. For medium Re, waves form within the core radius resulting from the inflection points in the Bödewadt-like profiles. At large Re, there are also waves that travel vertically along the interface between the rotational core and the irrotational flow outside the core at r? 1.

Arrese, Juan C.; Lopez, John M.

1996-11-01

329

Minimalist turbulent boundary layer model  

Microsoft Academic Search

We discuss an elementary model of a turbulent boundary layer over a flat surface given as a vertical random distribution of spanwise Lamb-Oseen vortex configurations placed over a nonslip boundary-condition line. We are able to reproduce several important features of realistic flows, such as the viscous and logarithmic boundary sublayers, and the general behavior of the first statistical moments (turbulent

L. Moriconi

2009-01-01

330

Magnetohydrodynamic boundary layer control system  

NASA Astrophysics Data System (ADS)

An active boundary layer control system for marine vehicles is disclosed. The boundary layer control system comprises a plurality of magnets and seawater electrodes placed in circumferential rows around the beam of the hull. The magnets and electrodes are positioned so that a Lorentz force generated by the interacting magnetic and electric fields will drive the boundary layer flow in an axial direction toward the aft end of the bull. The boundary control system reduces turbulence and may relaminarize boundary layer flow, thereby reducing radiated noise.

Meng, James C.

1993-12-01

331

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

332

Boundary localization in texture segmentation.  

PubMed

Localizing boundaries between textured image regions without sacrificing the labeling accuracy of interior regions remains a problem in segmentation. Difficulties arise because of the conflicting requirements of localization and labeling. Boundary localization usually demands observing the features over small neighborhoods, whereas labeling accuracy increases with the size of the observation neighborhood. This problem is further exacerbated in texture segmentation by the spatially distributed nature of texture features. In this correspondence, we develop a multiresolution approach that combines localized and distributed features to directly address boundary localization in texture segmentation. Maximum localization is achieved by using the gray-level discontinuities at the boundary between textures to define the boundary. The properties that characterize the gray-level discontinuity at texture boundaries are developed and an algorithm is designed to localize the boundary using these discontinuities. This segmentation algorithm is implemented and successfully tested on a set of Brodatz texture mosaics and AVHRR satellite imagery. PMID:18290036

Yhann, S R; Young, T Y

1995-01-01

333

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.

334

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

335

Structure and properties of grain boundaries  

Microsoft Academic Search

Results were obtained in the following areas: determination of relative grain boundary energies by the rotating crystallite method; simple structural unit model for core dependent properties of tilt boundaries; twist boundary energies for metals with long ranged pairwise interatomic potentials; structural unit\\/grain boundary dislocation model for grain boundary structure; detection of expansion of boundaries using diffraction; effect of secondary relaxations

R. W. Balluffi; P. D. Bristowe

1984-01-01

336

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

337

[Surgery without boundaries].  

PubMed

Surgery at the turn of the century and at the millennium is characterised by an extremely rapid development. There are no boundaries anymore among the different branches of medicine, in different anatomical regions of the human body, between the living human and the artificial tissues, between the reality and the virtual reality. Nanotechnology and robotics offer new possibilities for minimally invasive procedures. By the introduction of telepresence surgery there are no more surgical limits among countries and continents, between Earth and Space as well. A new chapter in history of medicine is the Cyber Surgery. The future has already arrived. Even in this new world we have to follow the ethical requirements summarised in the Hyppocrates Oath. PMID:11723733

Sándor, J; Máté, M; Irtó, I; Záborszky, A; Benedek, G; Sterlik, G; Regöly-Mérei, J

2001-10-01

338

Boundary layer transition studies  

NASA Astrophysics Data System (ADS)

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.

Watmuff, Jonathan H.

1995-02-01

339

Boundary Chromatic Polynomial  

NASA Astrophysics Data System (ADS)

We consider proper colorings of planar graphs embedded in the annulus, such that vertices on one rim can take Q s colors, while all remaining vertices can take Q colors. The corresponding chromatic polynomial is related to the partition function of a boundary loop model. Using results for the latter, the phase diagram of the coloring problem (with real Q and Q s) is inferred, in the limits of two-dimensional or quasi one-dimensional infinite graphs. We find in particular that the special role played by Beraha numbers Q=4\\cos2{?over n} for the usual chromatic polynomial does not extend to the case Q? Q s. The agreement with (scarce) existing numerical results is perfect; further numerical checks are presented here.

Jacobsen, Jesper Lykke; Saleur, Hubert

2008-08-01

340

Minimalist turbulent boundary layer model.  

PubMed

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

Moriconi, L

2009-04-06

341

Minimalist turbulent boundary layer model  

NASA Astrophysics Data System (ADS)

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

Moriconi, L.

2009-04-01

342

Boundary elements and nuclear organization  

Microsoft Academic Search

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

Maya Capelson; Victor G. Corces

2004-01-01

343

Expansive Learning across Workplace Boundaries  

ERIC Educational Resources Information Center

|The article analyses a collaborative effort of learning across workplace boundaries in a regional learning network of South Savo, Finland. The focus is on the "Forum of In-house Development" in the network. Our objective is to highlight a dialectical approach to boundaries that draws from the ideas of cultural-historical activity theory.…

Kerosuo, Hannele; Toiviainen, Hanna

2011-01-01

344

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

345

Marshak boundary condition recurrence formulae  

Microsoft Academic Search

The Marshak boundary condition is applied in the one-dimensional case of thermal radiative heat transport solved by the spherical harmonics method. Recurrence formulae for the Marshak boundary condition are derived for the cases where the absorbing, emitting and scattering material is limited by diffusely emitting, partly diffusely and partly specularly reflecting walls. The recurrence formulae are applied to an example

F. M. B. Andersen

1997-01-01

346

Magnetic clouds at sector boundaries  

Microsoft Academic Search

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

N. U. Crooker; J. T. Gosling; S. W. Kahler

1998-01-01

347

Probability of marine invasion into the chicxulub crater and consequent generation of large tsunamis  

NASA Astrophysics Data System (ADS)

A great number of Cretaceous/Tertiary (K/T) boundary tsunami deposits around the Gulf of Mexico have been reported (e. g., Smit, 1999). However, the origin, propagation process and magnitude of tsunamis have been poorly understood. Although Matsui et al. (2002) suggested that the movement of water rushing into and receding from the Chicxulub crater have a potential to generate the largest tsunamis, no strong evidence to support this mechanism has been presented. In this study, samples from the YAX-1 site drilled by the Chicxulub Scientific Drilling Program (CSDP), were investigated to test the probability of the marine invasion into the crater and consequent generation of tsunamis. The impactite in the YAX-1 occurred between 794.60 (?) m and 894.94 m depth and is divided into two lithologic units: impact melt rock unit (822.86 m to 894.94 m) and suevite unit (794.60 (?) m to 822.86 m). The impact melt rock unit is mainly composed of infinite form of melt fragments with small amount of basement and carbonate rock fragments. The suevite unit overlies the impact melt breccia unit with irregular contact. The suevite unit is composed of fragments of rocks and minerals together with melt in a clastic matrix. Poorly-sorted, grain-supported fabric and intraclast-like nature suggest lower part of the suevite unit was re-deposited as a debris flow from the crater rim. On the other hand, normal grading, relatively well-sorting and “K/T boundary cocktail (Bralower et al., 1998)” nature of nannofossil assemblage in the upper part of the suevite unit suggest that this part was deposited from a dense sediment suspended cloud. Furthermore, compositional oscillations repeated by >5 times are observed in this part, similar compositional oscillations are observed in the K/T boundary deep-sea tsunami deposit in Cuba (Goto et al., 2002). The uppermost several tens centimeter of the suevite unit is composed of medium to coarse, greenish sandstone with parallel lamination, suggesting the influence of strong current during its deposition. The boundary cocktail nature of nannofossil assemblage, compositional oscillations and existence of parallel lamination in the upper part of the suevite unit is suggestive of the marine invasion into the crater cavity and potential generation of tsunamis. Further research is needed to confirm the timing of marine invasion, based on identification of iridium anomaly and the first appearance of Danian fossils.

Goto, K.; Tada, R.; Bralower, T.; Tajika, E.; Matsui, T.

2003-04-01

348

Delineating anatomical boundaries using the boundary fragment model.  

PubMed

In this paper we present a method to automatically isolate relevant anatomical boundary positions in an image using only the structure of edges. The purpose of this method is to facilitate model-based segmentation algorithms which rely on accurate initialisation and assume that the correct anatomical boundary positions are close to the current model surface. The method is built around a weak parts-based shape model - the Boundary Fragment Model (BFM) - which represents an object by sections of its boundary. Following previous literature, we use the BFM in a boosted classifier framework to first automatically detect the object of interest. Extending previous work, we use the BFM to drive a classifier which isolates boundary candidates from spurious and irrelevant edge responses. The application of our algorithm leads to a labelled edge map which encodes the positions of (multiple) object boundaries. By way of illustrating what is a general solution, the task of identifying the endocardium and epicardium in three-dimensional ultrasound images is completely examined, including a detailed analysis of the parameters which impact on the model construction, the structure of the learned edge response classifier, and implementation concerns. For completeness, we also demonstrate how the output boundary positions can be used in a full model-based segmentation framework. PMID:23941869

Stebbing, Richard V; Noble, J Alison

2013-07-23

349

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

NASA Astrophysics Data System (ADS)

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

Henriquez, Ricardo; Moraga, Luis; Kremer, German; Flores, Marcos; Espinosa, Andres; Munoz, Raul C.

2013-02-01

350

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

351

Alvarez, Luis Walter (1911-88)  

NASA Astrophysics Data System (ADS)

Physicist and astronomer, born in San Francisco, CA, professor at the University of California, Nobel prizewinner (1968) for his discoveries in particle physics. Used cosmic rays to `x-ray' the pyramids of Egypt, finding in particular that the tombs in the Great Pyramid at Giza had no hidden rooms. Alvarez (and his son) discovered globally distributed iridium at the Cretaceous/Tertiary boundary i...

Murdin, P.

2000-11-01

352

40K– 40Ar dating of the Main Deccan large igneous province: Further evidence of KTB age and short duration  

Microsoft Academic Search

Most mass extinctions coincide in time with outpourings of continental flood basalts (CFB). Some 20 years ago, it was shown [Courtillot, V., Besse, J., Vandamme, D., Montigny, R., Jaeger, J.-J., Cappetta, H., 1986. Deccan flood basalts at the Cretaceous\\/Tertiary boundary? Earth Planet. Sci. Lett. 80, 361–374; Courtillot, V., Feraud, G., Maluski, H., Vandamme, D., Moreau, M.G., Besse, J., 1988. Deccan flood

Anne-Lise Chenet; Xavier Quidelleur; Frédéric Fluteau; Vincent Courtillot; Sunil Bajpai

2007-01-01

353

Late Cretaceous\\/early Tertiary convergence between the Indian and Arabian plates recorded in ophiolites and related sediments  

Microsoft Academic Search

Remnants of ocean floor forming the Eastern Ophiolite Belt in Oman and the Western Ophiolite Belt in Pakistan have a common plate-tectonic history culminating in emplacement at the Cretaceous\\/Tertiary boundary. Fragments of ocean floor in these two belts have ages between 150 and 65 Ma and recorded tectonic events in the early Indian Ocean at 150 Ma, 130-120 Ma, 110-100

E. Gnos; A. Immenhauser; Tj. Peters

1997-01-01

354

Combined Paleomagnetic and Petromagnetic Study of the Upper Cretaceous Volcanic Sequence in Western Mexico: Implications for Tectonics and Magnetostratigraphy of the Jalisco Block  

Microsoft Academic Search

Results of detailed paleomagnetic studies of the Upper Cretaceous Autlan volcanic sequence from the Sierra Cacoma area (Jalisco block, western Mexico) are reported. The 67.4 ± 1.2 Ma whole-rock K-Ar date for these lavas and the magnetic polarity stratigraphy indicate that flows were emplaced after the Cretaceous Normal Superchron and just prior to the Cretaceous-Tertiary boundary. Fifteen sites (~150 oriented

Avto Goguitchaichvili; Luis M. Alva-Valdivia; José Rosas-Elguera; Jaime Urrutia-Fucugauchi; Ana-Maria Soler; Cecilia Caballero

2003-01-01

355

Reception of the asteroid hypothesis of terminal Cretaceous extinctions  

NASA Astrophysics Data System (ADS)

A random sampling of North American, British, and German paleontologists, North American geophysicists, and Polish geoscientists was made in mid-1984 to determine attitudes toward the hypothesis that an extraterrestrial impact caused mass extinctions at the Cretaceous/Tertiary boundary. The attitudes differ widely not only within but also between these scientific communities, thus raising the question of significance of the cultural and educational background in development of scientific opinions.

Hoffman, Antoni; Nitecki, Matthew H.

1985-12-01

356

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.

357

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

Microsoft Academic Search

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

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

2004-01-01

358

Casimir effect for soft boundaries  

NASA Astrophysics Data System (ADS)

In quantum field theory with confining ``hard'' (e.g., Dirichlet) boundaries, the latter are represented in the Schrödinger equation defining spatial quantum modes by infinite step-function potentials. One can instead introduce confining ``soft'' boundaries, represented in the mode equation by some smoothly increasing potential function. Here the global Casimir energy is calculated for a scalar field confined by harmonic-oscillator (HO) potentials in 1, 2, and 3 dimensions. Combinations of HO and Dirichlet boundaries are also considered. Some results differ in sign from comparable hard-wall ones.

Actor, A. A.; Bender, I.

1995-09-01

359

Lamellar diblock copolymer grain boundary morphology. 1. Twist boundary characterization  

SciTech Connect

Grain boundary morphologies in poly(styrene-b-butadiene) lamellar diblock copolymers were characterized using transmission electron microscopy (TEM). Two types of twist grain boundaries were observed in which microphase separation of the two blocks was maintained in the grain boundary region by intermaterial dividing surfaces that approximate classically known minimal surfaces. The geometry of these interfaces was demonstrated by comparing experimental TEM images with ray tracing computer simulations of the model surfaces as the projection direction was systematically varied in both the experimental and simulated images. The two morphologies observed were found to have intermaterial dividing surfaces that approximate either Scherk's first (doubly periodic) surface or a section of the right helicoid. The helicoid section boundary was observed at low twist angles, less than or equal to about 15. The Scherk surface family of boundary morphologies, which consists of a doubly periodic array of saddle surfaces, was found over the entire twist range from 0 to 90[degree]. As the twist angle approaches 0[degree] the Scherk surface grain boundary morphology is transformed into a single screw dislocation that has an intermaterial dividing surface with the geometry of a single helicoid. Direct TEM imaging of the detailed core structure of this screw dislocation is presented. These images demonstrate that in the lamellar diblock copolymer the screw dislocation core is nonsingular. This nonsingular core structure represents a radical departure from the singular core structures observed in classical studies of dislocations in atomic crystals.

Gido, S.P.; Gunther, J.; Thomas, E.L. (Massachusetts Inst. of Technology, Cambridge, MA (United States). Dept. of Materials Science and Engineering); Hoffman, D. (Univ. of Massachusetts, Amherst, MA (United States). Dept. of Mathematics and Statistics)

1993-08-16

360

Boundary Layer Control on Airfoils.  

ERIC Educational Resources Information Center

|A phenomena, boundary layer control (BLC), produced when visualizing the fluidlike flow of air is described. The use of BLC in modifying aerodynamic characteristics of airfoils, race cars, and boats is discussed. (KR)|

Gerhab, George; Eastlake, Charles

1991-01-01

361

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); Gosling, J.T. [Los Alamos National Laboratory, Los Alamos, New Mexico (United States); Kahler, S.W. [Phillips Laboratory, Hanscom Air Force Base, Massachusetts (United States)

1998-01-01

362

Boundary Disputes in Latin America.  

National Technical Information Service (NTIS)

Since the start of 2000, five Latin American boundary disputes between neighboring states have resulted in the use of force, and two others in its deployment. These incidents involved ten of the nineteen independent countries of South and Central America....

J. I. Dominguez D. Mares M. Orozco D. S. Palmer F. R. Aravena A. Serbin

2002-01-01

363

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 ...

364

Changing the Structure Boundary Geometry  

NASA Astrophysics Data System (ADS)

Analysis of previously obtained results shows that hexagonal crystal lattice is the dominant type of ordering, in particular, in striated glow discharges. We explore the possibility for changing the dust distribution in horizontal cross sections of relatively highly ordered structures in a glow-discharge. Presuming that boundary geometry can affect dust distribution, we used cylindrical coolers held at 0 °C and placed against a striation containing a structure, to change the geometry of its outer boundary. By varying the number of coolers, their positions, and their separations from the tube wall, azimuthally asymmetric thermophoretic forces can be used to form polygonal boundaries and vary the angles between their segments (in a horizontal cross section). The corner in the structure's boundary of 60° stimulates formation of hexagonal cells. The structure between the supported parallel boundaries is also characterized by stable hexagonal ordering. We found that a single linear boundary segment does not give rise to any sizable domain, but generates a lattice extending from the boundary (without edge defects). A square lattice can be formed by setting the angle equal to 90°. However, angles of 45° and 135° turned out easier to form. Square lattice was created by forming a near-135° corner with four coolers. It was noted that no grain ordering is observed in the region adjacent to corners of angles smaller than 30°, which do not promote ordering into cells of any shape. Thus, manipulation of a structure boundary can be used to change dust distribution, create structures free of the ubiquitous edge defects that destroy orientation order, and probably change the crystal lattice type.

Karasev, Viktor; Dzlieva, Elena; Ivanov, Artyom

2008-09-01

365

WebSite Boundary Detection  

Microsoft Academic Search

Defining the boundaries of a web-site, for (say) archiving or information retrieval purposes, is an important but complicated task. In this paper a web-page clustering approach to boundary detection is sug- gested. The principal issue is feature selection, hampered by the observa- tion that there is no clear understanding of what a web-site is. This paper proposes a definition of

Ayesh Alshukri; Frans Coenen; Michele Zito

2010-01-01

366

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

367

Marshak boundary condition recurrence formulae  

NASA Astrophysics Data System (ADS)

The Marshak boundary condition is applied in the one-dimensional case of thermal radiative heat transport solved by the spherical harmonics method. Recurrence formulae for the Marshak boundary condition are derived for the cases where the absorbing, emitting and scattering material is limited by diffusely emitting, partly diffusely and partly specularly reflecting walls. The recurrence formulae are applied to an example with good results.

Andersen, F. M. B.

368

Boundary characterization experiment series overview  

Microsoft Academic Search

Ocean acoustic propagation and reverberation in continental shelf regions is often controlled by the seabed and sea surface boundaries. A series of three multi-national and multi-disciplinary experiments was conducted between 2000-2002 to identify and measure key ocean boundary characteristics. The frequency range of interest was nominally 500-5000 Hz with the main focus on the seabed, which is generally considered as

Charles W. Holland; Roger C. Gauss; Paul C. Hines; Peter Nielsen; John R. Preston; Chris H. Harrison; Dale D. Ellis; Kevin D. LePage; John Osler; Redwood W. Nero; Dan Hutt; Altan Turgut

2005-01-01

369

The Chicxulub event - sulfur-bearing minerals and lithologies  

NASA Astrophysics Data System (ADS)

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

Strauss, H.; Deutsch, A.

2003-04-01

370

Tidal boundary conditions in SEAWAT.  

PubMed

SEAWAT, a U.S. Geological Survey groundwater flow and transport code, is increasingly used to model the effects of tidal motion on coastal aquifers. Different options are available to simulate tidal boundaries but no guidelines exist nor have comparisons been made to identify the most effective approach. We test seven methods to simulate a sloping beach and a tidal flat. The ocean is represented in one of the three ways: directly using a high hydraulic conductivity (high-K) zone and indirect simulation via specified head boundaries using either the General Head Boundary (GHB) or the new Periodic Boundary Condition (PBC) package. All beach models simulate similar water fluxes across the upland boundary and across the sediment-water interface although the ratio of intertidal to subtidal flow is different at low tide. Simulating a seepage face results in larger intertidal fluxes and influences near-shore heads and salinity. Major differences in flow occur in the tidal flat simulations. Because SEAWAT does not simulate unsaturated flow the water table only rises via flow through the saturated zone. This results in delayed propagation of the rising tidal signal inland. Inundation of the tidal flat is delayed as is flow into the aquifer across the flat. This is severe in the high-K and PBC models but mild in the GHB models. Results indicate that any of the tidal boundary options are fine if the ocean-aquifer interface is steep. However, as the slope of that interface decreases, the high-K and PBC approaches perform poorly and the GHB boundary is preferable. PMID:21275984

Mulligan, Ann E; Langevin, Christian; Post, Vincent E A

2011-01-28

371

Ego Boundary Disturbance in Juvenile Anorexia Nervosa.  

ERIC Educational Resources Information Center

|Anorexics were compared to female depressed controls to measure boundary impairment. Anorexics scored higher on inner-outer and conceptual boundary disturbance and produced significantly more responses that emphasized the solidity of object boundaries. Boundary scores were unrelated to degree of weight loss and global symptom severity. (Author)|

Strober, Michael; Goldenberg, Irene

1981-01-01

372

A Correction to QED at Boundaries  

Microsoft Academic Search

The author would like to point out a minor correction to QED at spherical boundaries, that may be of some use in Cosmology and interestingly enough in QCD calculations. It seems that at boundaries that are not fixed, but rely on relative positioning of the observer and the boundary (when the boundary moves with the observer on a long road

Richard Kriske

2010-01-01

373

Boundaries and the Exploration of Self  

ERIC Educational Resources Information Center

Boundaries and the exploration of self are conceptualized within the agency-structure problem first articulated in social theory during the 1970s. Constructing boundaries as a professional issue within the discipline has to take account the agency embedded within boundaries. Multiple boundary dilemmas are discussed within the framework of the…

Gharabaghi, Kiaras

2008-01-01

374

Ego Boundary Disturbance in Juvenile Anorexia Nervosa.  

ERIC Educational Resources Information Center

Anorexics were compared to female depressed controls to measure boundary impairment. Anorexics scored higher on inner-outer and conceptual boundary disturbance and produced significantly more responses that emphasized the solidity of object boundaries. Boundary scores were unrelated to degree of weight loss and global symptom severity. (Author)

Strober, Michael; Goldenberg, Irene

1981-01-01

375

The FZZ duality with boundary  

NASA Astrophysics Data System (ADS)

The Fateev-Zamolodchikov-Zamolodchikov (FZZ) duality relates Witten's cigar model to sine-Liouville theory. This duality was proven in the path integral formulation and extended to the case of higher genus closed Riemann surfaces by Schomerus and one of the authors. In this note we further extend the duality to the case with boundary. Specifically, we relate D1-branes in the cigar model to D2-branes in the sine-Liouville theory. In particular, the boundary action for D2-branes in the sine-Liouville theory is constructed. We also consider the fermionic version of the FZZ duality. This duality was proven as a mirror symmetry by Hori and Kapustin, but we give an alternative proof in the path integral formulation which directly relates correlation functions. Also here the case with boundary is investigated and the results are consistent with those for branes in mathcal{N} = 2 super Liouville field theory obtained by Hosomichi.

Creutzig, Thomas; Hikida, Yasuaki; Rønne, Peter B.

2011-09-01

376

Free boundary ballooning mode representation  

NASA Astrophysics Data System (ADS)

Considerable efforts have been made in this field to develop a free boundary ballooning mode representation, which can incorporate the peeling mode stability criterion. Those efforts have not succeeded, simply because the so-called ballooning mode invariance is broken toward plasma edge. This makes 1D description of high n modes at plasma edge become impossible, where n is toroidal mode number. Nevertheless, we prove that the existence of ``half" ballooning mode invariance toward plasma core enables an 1.?-dimentional representation of the modes, where ?˜O(1/n). This considerably reduces the complicity in investigating high n modes at plasma edge and can be used to study peeling-ballooning modes. This technique can also be useful to extend the 1D calculation of fixed boundary ballooning modes for free boundary ballooning modes. Numerical example will also be presented together with the topological symmetry analysis.

Zheng, Linjin

2012-03-01

377

Watershed Boundary Dataset for Mississippi  

USGS Publications Warehouse

The U.S. Geological Survey, in cooperation with the Mississippi Department of Environmental Quality, U.S. Department of Agriculture-Natural Resources Conservation Service, Mississippi Department of Transportation, U.S. Department of Agriculture-Forest Service, and the Mississippi Automated Resource Information System developed a 1:24,000-scale Watershed Boundary Dataset for Mississippi including watershed and subwatershed boundaries, codes, names, and areas. The Watershed Boundary Dataset for Mississippi provides a standard geographical framework for water-resources and selected land-resources planning. The original 8-digit subbasins (Hydrologic Unit Codes) were further subdivided into 10-digit watersheds (62.5 to 391 square miles (mi2)) and 12-digit subwatersheds (15.6 to 62.5 mi2) - the exceptions being the Delta part of Mississippi and the Mississippi River inside levees, which were subdivided into 10-digit watersheds only. Also, large water bodies in the Mississippi Sound along the coast were not delineated as small as a typical 12-digit subwatershed. All of the data - including watershed and subwatershed boundaries, subdivision codes and names, and drainage-area data - are stored in a Geographic Information System database, which are available at: http://ms.water.usgs.gov/. This map shows information on drainage and hydrography in the form of U.S. Geological Survey hydrologic unit boundaries for water-resource 2-digit regions, 4-digit subregions, 6-digit basins (formerly called accounting units), 8-digit subbasins (formerly called cataloging units), 10-digit watershed, and 12-digit subwatersheds in Mississippi. A description of the project study area, methods used in the development of watershed and subwatershed boundaries for Mississippi, and results are presented in Wilson and others (2008). The data presented in this map and by Wilson and others (2008) supersede the data presented for Mississippi by Seaber and others (1987) and U.S. Geological Survey (1977).

Wilson, K. Van, Jr.; Clair, Michael G., II; Turnipseed, D. Phil; Rebich, Richard A.

2009-01-01

378

Grain boundary structure in alumina  

SciTech Connect

In liquid phase sintered aluminas, basal twins and glass phase at boundary regions are very common. The microstructures of a very glassy alumina show that coarse ledges (up to several hundred angstroms in height) are usually present at the Al/sub 2/O/sub 3//glass interface and the preferred ledge plane is (0001). This result suggests that the basal plane is the most stable plane at Al/sub 2/O/sub 3//glass interfaces while ((1 bar)012) plane is the most stable surface in Al/sub 2/O/sub 3/. The hot-pressed high purity material contains a small number of basal twins, rhombohedral twins, ((1 bar)011) twins and (10(1 bar)1) twins. This material also shows no detectable glass film at boundary regions. Both basal and rhombohedral twins have been shown to occur in alumina ceramics while the ((1 bar)011) and (10(1 bar)1) twins have never been reported in Al/sub 2/O/sub 3/. The four are well described by the conventional CSL/DSCL models as ..sigma.. = 3, 7, 11 and 11 boundaries, respectively. Basal twins sometimes, and rhombohedral twins always, contain SGBDs whose Burgers vectors lie on the relevant DSCL. The ((1 bar)011) and (10(1 bar)1) twins show stacking-fault like fringes at the (1(2 bar)10) common reflections. It is concluded that these boundaries contain rigid body displacement vectors to relieve atomic overcrowding at boundary regions. The magnitudes of displacement vectors at the ((1 bar)011) twin boundary can be measured indirectly by comparing the experimental image contrast with image simulation in computer.

Shiue, Y.R.

1985-01-01

379

Nested and Dynamic Contract Boundaries  

NASA Astrophysics Data System (ADS)

Previous work on software contracts assumes fixed and statically known boundaries between the parties to a contract. Implementations of contract monitoring systems rely on this assumption to explain the nature of contract violations and to assign blame to violators. In this paper, we explain how to implement arbitrary, nested, and dynamic contract boundaries with two examples. First, we add nestable contract regions to a static, first-order module system. Second, we show that even a dynamic, higher-order, and hierarchical module system can be equipped with software contracts that support precise blame assignment.

Strickland, T. Stephen; Felleisen, Matthias

380

Chromosomal boundaries in S. cerevisiae.  

PubMed

Chromatin boundary elements or insulators in metazoans delimit distinct chromosomal domains of gene expression. Recently, DNA sequences with properties similar to boundary elements were also discovered in Saccharomyces cerevisiae. These sequences block the spread of transcriptionally silent chromatin, the yeast equivalent of metazoan heterochromatin, and are referred to as 'heterochromatin barriers'. These barriers share no sequence homology but all consist of multiple binding sites for various regulatory proteins. Current data suggest that barriers may function in yeast by recruiting a protein complex that precludes nucleosome assembly and thereby disrupts a contiguous array of nucleosomes required for the spread of silent chromatin. PMID:11250144

Bi, X; Broach, J R

2001-04-01

381

Boundary effect in electrorheological fluids.  

PubMed

The effect of the boundary friction coefficient on the rheological properties of the electrorheological (ER) fluids in quasistatic and dynamic states is investigated by computer simulation. The relation between the shear stress and the boundary friction coefficient in quasistatic and dynamic states is discussed qualitatively and quantitatively, and the trend matches the previously reported experimental results well. The flow curves of ER fluids, under different friction coefficients, are calculated, and it is found that the friction coefficient affects the flow curves. In two dimensions, the transitions in structure corresponding to the shear stress variations are presented to understand the mechanism of ER fluids. PMID:22304095

Gong, X L; Yang, F; Xuan, S H; Zong, L H; Zhu, W; Jiang, W Q

2011-12-20

382

Microphysics of Low-Frequency Attenuation: Grain Boundaries, Heterophase Boundaries, Subgrain Boundaries, Spatiotemporal Scaling (Invited)  

NASA Astrophysics Data System (ADS)

The dynamical mechanical response of polycrystalline materials is effected by lattice defects: point defects, dislocations, subgrain boundaries, grain and heterophase boundaries—and larger-length-scale structures (e.g., groups or “rafts” of grains or of subgrains). That the response is temperature- and frequency-dependent indicates that an understanding of spatial scaling of these defects is critical in interpreting—and extrapolating—experimental results. We have engaged in an experimental effort to tease apart the effects of various defects on low-frequency attenuation. The power-law attenuation response (QG-1~f -m; m~0.3-0.5), described as the “high-temperature background” and characteristic, e.g., of Earth’s upper mantle, need not represent a distribution of grain sizes, as is often taught, but can represent different spatiotemporal scales of relaxation within a uniform microstructure. This presentation outlines various experimental studies we and others have undertaken—grain and heterophase boundary effects in peridotite and in ice/salt-hydrate eutectics; grain boundary and dislocation effects in ice; subgrain boundary effects in an intermetallic—and scrutinizes them relative to non-equilibrium thermodynamics and to Edward Hart’s state-variable model of inelastic deformation.

Cooper, R. F.; Sundberg, M. I.; McCarthy, C.

2009-12-01

383

Extended smoothed boundary method for solving partial differential equations with general boundary conditions on complex boundaries  

NASA Astrophysics Data System (ADS)

In this paper, we describe an approach for solving partial differential equations with general boundary conditions imposed on arbitrarily shaped boundaries. A continuous function, the domain parameter, is used to modify the original differential equations such that the equations are solved in the region where a domain parameter takes a specified value while boundary conditions are imposed on the region where the value of the domain parameter varies smoothly across a short distance. The mathematical derivations are straightforward and applicable to a wide variety of partial differential equations. To demonstrate the general applicability of the approach, we provide four examples herein: (1) the diffusion equation with both Neumann and Dirichlet boundary conditions; (2) the diffusion equation with both surface diffusion and reaction; (3) the mechanical equilibrium equation; and (4) the equation for phase transformation with the presence of additional boundaries. The solutions for several of these cases are validated against numerical solutions of the corresponding sharp-interface equations. The potential of the approach is demonstrated with five applications: surface-reaction-diffusion kinetics with a complex geometry, Kirkendall-effect-induced deformation, thermal stress in a complex geometry, phase transformations affected by substrate surfaces and relaxation of a droplet on irregular surfaces.

Yu, Hui-Chia; Chen, Hsun-Yi; Thornton, K.

2012-10-01

384

Stability of Compressible Boundary Layers.  

National Technical Information Service (NTIS)

The stability of compressible 2-D and 3-D boundary layers is reviewed. The stability of 2-D compressible flows differs from that of incompressible flows in two important features: There is more than one mode of instability contributing to the growth of di...

A. H. Nayfeh

1989-01-01

385

Atlas of Historical County Boundaries  

NSDL National Science Digital Library

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

386

Science beyond the Classroom Boundaries  

ERIC Educational Resources Information Center

|There have been many years of innovation in primary science education. Surprisingly, however, most of this has taken place within the confines of the classroom. What primary science has not yet done with universal success is step outside the classroom boundaries to use the school grounds for teaching and learning across all aspects of the science…

Feasey, Rosemary; Bianchi, Lynne

2011-01-01

387

Patients, friends, and relationship boundaries.  

PubMed Central

When patient and physician are close friends, both professional and personal relationships can suffer. Jointly exploring and setting explicit boundaries can help avoid conflict and maintain these valuable relationships. This is particularly important when the physician practises in a small community where such concurrent relationships are unavoidable.

Rourke, J. T.; Smith, L. F.; Brown, J. B.

1993-01-01

388

On deep western boundary currents  

NASA Astrophysics Data System (ADS)

The Stommel and Arons [1960a, b] theory of the deep circulation of the world ocean does not directly address the physics of deep boundary currents. In the present paper a maximally simple steady state physics for deep western boundary currents is developed and integrated into the Stommel-Arons model. This is accomplished by modifying the assumptions of the latter to include effective horizontal eddy viscous terms everywhere in the deep water, including in the interior. The resulting solution for the meridional velocity in a rectangular ocean on a beta plane is mathematically analogous to that of Munk [1950] for the wind-driven circulation. In the interior the meridional velocity reduces identically to that of Stommel and Arons. Among other benefits, the solution eliminates the theoretical difficulties associated with the crossing of the equator by the deep western boundary current. As an initial test of the theory's consistency with observation, theoretical plots of pressure and meridional velocity as a function of longitude are qualitatively compared with hydrographic sections and inferred meridional velocity fields in the eastern and western basins of the abyssal North Atlantic. Also, the theoretical profile for the meridional velocity as a function of longitude is qualitatively compared with observations of longshore velocity as a function of offshore distance in the deep western boundary current of the North Atlantic Deep Water.

Cember, Richard P.

1998-03-01

389

Boundary Layer Over Uniform Roughness.  

National Technical Information Service (NTIS)

The boundary-layer survey is conducted of a rough plate consisting of uniform spherical particles arranged in a random and in highly compact fashion. Strong turbulent mixing is observed in a region within a quarter of the particle size from the top of the...

J. Wu

1970-01-01

390

Boundary conditions in quantum cosmology  

Microsoft Academic Search

The problem of boundary conditions for the cosmological wave function psi is analyzed using a simple model as an example. The model has two degrees of freedom: the scale factor and a homogeneous scalar field. A tunneling wave function is found for this model which describes an ensemble of universes tunneling from ``nothing'' to a de Sitter space, then evolving

Alexander Vilenkin

1986-01-01

391

Prosodic Boundaries in Adjunct Attachment  

Microsoft Academic Search

Five studies explored the processing of ambiguous sentences like Martin maintained that the CEO lied when the investigation started\\/at the start of the investigation. The central question was why particular prosodic boundaries have the effects they do. A written questionnaire provided baseline preferences and suggested that clausal adjuncts (when the investigation started) receive more high attachments than nonclausal adjuncts (at

Katy Carlson; Charles Clifton; Lyn Frazier

2001-01-01

392

HAWAII RCRA TSD FACILITY BOUNDARIES  

EPA Science Inventory

Polygon coverage of RCRA TSD facility boundaries in Hawaii. These are derived from original maps and descriptions located in the US EPA Region 9 Records Center files. Current TSD facility designations were extracted from the ARIS (RCRIS) database in June 1998. Auxiliary tables i...

393

Laminar boundary layer over riblets  

Microsoft Academic Search

Laser doppler anemometry (LDA) measurements and numerical calculations have been made for a laminar boundary layer on triangular riblets. Calculated mean velocity distributions along the riblet contour are in good agreement with the measured ones. The results show that no transversal motion exists above and within the riblet valleys (e.g., no secondary motion). It is found that despite the large

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

1994-01-01

394

Transgressing Boundaries through Learning Communities.  

ERIC Educational Resources Information Center

|Cooperative education should adopt the learning communities model because (1) it situates learning in communities of inquirers who share meanings and ideas; (2) it related learning to experiences and the larger cultural context; and (3) it enables learning that has value and meaning. In co-op, learning communities help cross the boundaries

Howard, Adam; England-Kennedy, Elizabeth S.

2001-01-01

395

Quasiperiodic Ordering in Grain Boundaries.  

National Technical Information Service (NTIS)

The authors show that a general grain boundary consists of a quasiperiodic grid of topological dislocation lines, with the same golden or noble inflation coefficient in all directions. In some particular cases, the grid may be periodic in one or more dire...

N. Rivier A. J. A. Lawrence

1988-01-01

396

CALIFORNIA RCRA TSD FACILITY BOUNDARIES  

EPA Science Inventory

Polygon coverage of RCRA TSD facility boundaries in California. These are derived from original maps and descriptions located in the US EPA Region 9 Records Center files. Current TSD facility designations were extracted from the ARIS (RCRIS) database in June 1998. Auxiliary tabl...

397

ARIZONA RCRA TSD FACILITY BOUNDARIES  

EPA Science Inventory

Polygon coverage of RCRA TSD facility boundaries in Arizona. These are derived from original maps and descriptions located in the US EPA Region 9 Records Center files. Current TSD facility designations were extracted from the ARIS (RCRIS) database in June 1998. Auxiliary tables ...

398

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

PubMed

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

Brenner, H; Ganesan, V

2000-06-01

399

Postapocalypse stratigraphy: Some considerations and proposals  

NASA Astrophysics Data System (ADS)

An imminent nuclear apocalypse will be a geologically significant event characterized by widespread extinction and marked by a highly radioactive lower boundary layer. The concept of a fallout-enriched Cenozoic/postapocalypse boundary layer is significant in that such a horizon would constitute an ideal, global isochron that is both readily detectable and correlatable; the only other systemic boundary that appears to be analogous is the Cretaceous/Tertiary boundary. New terminology consistent with the established stratigraphic nomenclature is herein proposed for the major anticipated postapocalypse geochronologic units.

Prosh, E. C.; McCracken, A. D.

1985-01-01

400

FLARING SOLAR HALE SECTOR BOUNDARIES  

SciTech Connect

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

Svalgaard, L. [HEPL, Stanford University, Stanford, CA 94304 (United States); Hannah, I. G.; Hudson, H. S., E-mail: leif@leif.org [School of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ (United Kingdom)

2011-05-20

401

Is boundary extension emotionally selective?  

PubMed

When they have to memorize a picture, people usually build a memory trace including more extensive boundaries than the original picture, a phenomenon known as boundary extension or BE. This article looks at whether the emotion category expressed (i.e., happiness, pleasure, irritation, or anger) by actors in short films could have an influence on the BE effect. The results showed that positively valenced emotions (happiness, pleasure) led to an extension effect, while the negatively valenced ones (anger, irritation) did not produce any significant memory distortion. The arousal dimension of emotions had no significant effect on BE. The current results were discussed in the light of previous studies on the links between BE and emotions. PMID:23445174

Ménétrier, Emmanuelle; Didierjean, André; Vieillard, Sandrine

2013-02-28

402

Boundary layer sensitivity and receptivity  

NASA Astrophysics Data System (ADS)

The relation between the receptivity and the sensitivity of the incompressible flow in the boundary layer over a flat plate to harmonic perturbations is determined. Receptivity describes the birth of a disturbance, whereas sensitivity is a concept of larger breath, describing the modification incurred by the state of a system as a response to parametric variations. The governing equations ruling the system's state are the non-local stability equations. Receptivity and sensitivity functions can be obtained from the solution of the adjoint system of equations. An application to the case of Tollmien-Schlichting waves spatially developing in a flat plate boundary layer is studied. To cite this article: C. Airiau et al., C. R. Mecanique 330 (2002) 259-265.

Airiau, Christophe; Walther, Steeve; Bottaro, Alessandro

403

Casimir energy for spherical boundaries  

SciTech Connect

Calculations of the Casimir energy for spherical geometries which are based on integrations of the stress tensor are critically examined. It is shown that despite their apparent agreement with numerical results obtained from mode summation methods, they are subject to criticism on several points. Specifically, these include (1) an improper application of the stress tensor to spherical boundaries, (2) the neglect of pole terms in contour integrations, and (3) the imposition of inappropriate boundary conditions upon the relevant propagators. A calculation which is based on the stress tensor and which avoids such problems is shown to be possible. It is, however, equivalent to the mode summation method and does not therefore constitute an independent calculation of the Casimir energy. (c) 2000 The American Physical Society.

Hagen, C. R. [Department of Physics and Astronomy, University of Rochester, Rochester, New York 14627 (United States)

2000-03-15

404

Tectonic Plates and Plate Boundaries  

NSDL National Science Digital Library

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

2011-05-09

405

Tectonic Plates and Plate Boundaries  

NSDL National Science Digital Library

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

406

Topography of inner core boundary  

NASA Astrophysics Data System (ADS)

Precise determination of the topography of a major internal boundary of the Earth is difficult because of the trade-off with the unknown velocity structure above it. However, the discoveries of the inner core (IC) rotation and high-quality teleseismic waveform doublets make the precise mapping of the topography of the inner core boundary (ICB) possible, as demonstrated in recent studies. Here we examine IC refracted (PKP-DF) and reflected (PKP-CD) waves recorded at the Yellowknife Array and global stations from 13 high-quality doublets, among a large collection of doublets in S. Sandwich Islands that we have assembled. Our results show clear evidence for spatial and temporal variations of IC reflections in travel times and in waveforms. If the time separation (dT) between the two members of the doublet is less than 3 years, the IC arrivals show little temporal change in travel times or waveforms. If dT is greater than about 6 years, some doublets show large variations but some others do not. The ICB regions beneath Atlantic Ocean and Indian Ocean show little temporal change. The regions show large variations are beneath Africa and the Central America, which coincide with large seismic anomalies at the core-mantle boundary (CMB). Inside these two ICB regions, there are fine-scale (km scale) variations. The largest temporal changes of IC reflections are about 0.10 to 0.15 s, corresponding to a topographic variation of up to 3.7 to 5.6 km. The results suggest ICB topography of a few kms on fine to regional scales. Dynamical models include a bumpy ICB rotating with the IC itself or a transient slurry boundary sloshing about in the turbulence at the base of the convecting outer core. The geographical coincidence of the ICB and CMB anomalies may suggest strong thermal coupling of the mantle and the core.

Song, X.; Dai, W.

2007-12-01

407

Momentum transfer in boundary layers  

Microsoft Academic Search

The continuity and momentum equations of fluid flow are considered along with thin-shear-layer equations, the analysis of laminar shear layers, the analysis of turbulent shear layers, numerical methods for thin shear layers, numerical solutions of laminar and turbulent boundary layers, aspects of stability and transition, and complex shear layers and viscous\\/inviscid interactions. Three-dimensional and unsteady flows are discussed, taking into

T. Cebeci; P. Bradshaw

1977-01-01

408

15 CFR 922.190 - Boundary.  

Code of Federal Regulations, 2010 CFR

...MARINE SANCTUARY PROGRAM REGULATIONS Thunder Bay National Marine Sanctuary and Underwater...Preserve § 922.190 Boundary. The Thunder Bay National Marine Sanctuary and...under the underwater cultural resources in Thunder Bay. The boundary forms an...

2010-01-01

409

Boundary Layer Transport of Small Particles.  

National Technical Information Service (NTIS)

The transport of small particles across the aerodynamic boundary layer that developed over a smooth, flat, acrylic plate and their subsequent deposition was investigated. The velocity boundary layer over the flat plate was characterized for a wind tunnel ...

D. McCready

1984-01-01

410

Enhancement of Perfluoropolyether Boundary Lubrication Performance.  

National Technical Information Service (NTIS)

A ball bearing simulator operating under starved conditions was used to perform screening tests to evaluate the boundary lubrication performance of a branched perfluoropolyether (PFPE), K-143 AB. Several approaches to enhance boundary lubrication were stu...

W. R. Jones O. O. Ajayi L. D. Wedeven

1996-01-01

411

Nonequilibrium Chemistry Boundary Layer Integral Matrix Procedure.  

National Technical Information Service (NTIS)

The development of an analytic procedure for the calculation of nonequilibrium boundary layer flows over surfaces of arbitrary catalycities is described. An existing equilibrium boundary layer integral matrix code was extended to include nonequilibrium ch...

A. C. Buckingham H. Tong H. L. Morse

1973-01-01

412

Microscopic filter feeders near boundaries  

NASA Astrophysics Data System (ADS)

We show through calculations, simulations, and experiments that the eddies often observed near sessile filter feeders are due to the presence of nearby boundaries. We model the common filter feeder Vorticella, which is approx 50 ?m across and which feeds by removing bacteria from ocean or pond water that it draws towards itself. We use an analytic stokeslet model and a Brinkman flow approximation with the organism modeled as a cylinder with two different boundary conditions to predict the size of the eddy caused by two parallel no-slip boundaries that represent the slides between which experimental observations are often made. We also use three-dimensional finite-element simulations to fully solve for the flow around a model Vorticella. Additionally, we track particles around live feeding Vorticella in order to determine the experimental flow field. Our models are in good agreement both with each other and with the experiments. We also show through calculations that filter feeders such as Vorticella can greatly enhance their nutrient uptake by feeding at an angle rather than perpendicular to a substrate.

Pepper, Rachel; Roper, Marcus; Ryu, Sangjin; Matsudiara, Paul; Stone, Howard

2009-11-01

413

Voting based object boundary reconstruction  

NASA Astrophysics Data System (ADS)

A voting-based object boundary reconstruction approach is proposed in this paper. Morphological technique was adopted in many applications for video object extraction to reconstruct the missing pixels. However, when the missing areas become large, the morphological processing cannot bring us good results. Recently, Tensor voting has attracted people"s attention, and it can be used for boundary estimation on curves or irregular trajectories. However, the complexity of saliency tensor creation limits its applications in real-time systems. An alternative approach based on tensor voting is introduced in this paper. Rather than creating saliency tensors, we use a "2-pass" method for orientation estimation. For the first pass, Sobel d*etector is applied on a coarse boundary image to get the gradient map. In the second pass, each pixel puts decreasing weights based on its gradient information, and the direction with maximum weights sum is selected as the correct orientation of the pixel. After the orientation map is obtained, pixels begin linking edges or intersections along their direction. The approach is applied to various video surveillance clips under different conditions, and the experimental results demonstrate significant improvement on the final extracted objects accuracy.

Tian, Qi; Zhang, Like; Ma, Jingsheng

2005-07-01

414

Integral Equation Solution for the Boundary Condition  

Microsoft Academic Search

In this letter, we develop a surface integral equation solution for analyzing scattering by objects with D'B' boundary conditions. The D'B' boundary conditions require that the normal derivatives of the electric and magnetic flux density field components normal to the boundary are zero. We show that the D'B' boundary conditions can be enforced to the standard electromagnetic (EM) surface integral

Sami P. Kiminki; Johannes Markkanen; Pasi Ylä-Oijala

2010-01-01

415

Photoacoustic speckles: boundary dependence and experimental validation  

NASA Astrophysics Data System (ADS)

Photoacoustic tomography (PAT) suppresses speckles by prominent boundary buildups. We theoretically study the dependence of PAT speckles on the boundary roughness, which is quantified by the root-mean-squared (RMS) value and the correlation length of the height. The speckle visibility and the correlation coefficient between the reconstructed and actual boundaries are quantified as a function of the boundary roughness. The statistics of PAT speckles is studied experimentally.

Guo, Zijian; Xu, Zhun; Wang, Lihong V.

2012-02-01

416

Boundary layer receptivity and control  

NASA Astrophysics Data System (ADS)

Receptivity processes initiate natural instabilities in a boundary layer. The instabilities grow and eventually break down to turbulence. Consequently, receptivity questions are a critical element of the analysis of the transition process. Success in modeling the physics of receptivity processes thus has a direct bearing on technological issues of drag reduction. The means by which transitional flows can be controlled is also a major concern: questions of control are tied inevitably to those of receptivity. Adjoint systems provide a highly effective mathematical method for approaching many of the questions associated with both receptivity and control. The long term objective is to develop adjoint methods to handle increasingly complex receptivity questions, and to find systematic procedures for deducing effective control strategies. The most elementary receptivity problem is that in which a parallel boundary layer is forced by time-harmonic sources of various types. The characteristics of the response to such forcing form the building blocks for more complex receptivity mechanisms. The first objective of this year's research effort was to investigate how a parallel Blasius boundary layer responds to general direct forcing. Acoustic disturbances in the freestream can be scattered by flow non-uniformities to produce Tollmien-Schlichting waves. For example, scattering by surface roughness is known to provide an efficient receptivity path. The present effort is directed towards finding a solution by a simple adjoint analysis, because adjoint methods can be extended to more complex problems. In practice, flows are non-parallel and often three-dimensional. Compressibility may also be significant in some cases. Recent developments in the use of Parabolized Stability Equations (PSE) offer a promising possibility. By formulating and solving a set of adjoint parabolized equations, a method for mapping the efficiency with which external forcing excites the three-dimensional motions of a non-parallel boundary layer was developed. The method makes use of the same computationally efficient formulation that makes the PSE currently so appealing. boundary layers involves the application of localized mean wall suction.

Hill, D. C.

1993-12-01

417

Compressible Ekman–Hartmann boundary layers  

Microsoft Academic Search

We consider the effect of compressibility on mixed Ekman–Hartmann boundary layers on an infinite plane (z = 0), in the presence of an external magnetic field oblique to the boundary. The aim is to investigate the influence of the magnetic pressure on the fluid density, and hence, via mass conservation, on the mass flow into or out of the boundary

Krzysztof A. Mizerski; David W. Hughes

2010-01-01

418

The Arabia-India plate boundary unveiled  

Microsoft Academic Search

Since the advent of Plate Tectonics, tectonic plate boundaries were explored on land as at sea for search of active faults where the destructive energy of earthquakes is released. Yet, some plate boundaries, less active or considered as less dangerous to humankind, escaped general attention and remained unknown to a large extent. Among them, the boundary between two major tectonic

M. Fournier; N. R. Chamot-Rooke; M. Rodriguez; C. Petit; P. Huchon; M. Beslier; B. Hazard

2009-01-01

419

Synoptic Controls on Boundary-Layer Characteristics  

Microsoft Academic Search

We report the characteristics of the three-dimensional, time evolving, atmospheric boundary layer that develops beneath an idealised, dry, baroclinic weather system. The boundary-layer structure is forced by thermal advection associated with the weather system. Large positive heat fluxes behind the cold front drive a vigorous convective boundary layer, whereas moderate negative heat fluxes in the warm sector between the cold

Victoria A. Sinclair; Stephen E. Belcher; Suzanne L. Gray

2010-01-01

420

Grain boundaries in high-Tc superconductors  

Microsoft Academic Search

Since the first days of high-Tc superconductivity, the materials science and the physics of grain boundaries in superconducting compounds have developed into fascinating fields of research. Unique electronic properties, different from those of the grain boundaries in conventional metallic superconductors, have made grain boundaries formed by high-Tc cuprates important tools for basic science. They are moreover a key issue for

H. Hilgenkamp; J. Mannhart

2002-01-01

421

Grain boundary damping in substitutional alloys  

Microsoft Academic Search

A study was made of the grain boundary damping characteristics of twelve Cu-Ni alloys, chosen to cover the entire range of solid solutions. The height, temperature, and activation energy of the solute peak was used to investigate solute segregation to grain boundaries. A criterion was developed to determine solute build up in the grain boundaries, and when applied to other

J. T. A. Roberts

1970-01-01

422

Exceptional boundary states at \\/c=1  

Microsoft Academic Search

We consider the CFT of a free boson compactified on a circle, such that the compactification radius \\/R is an irrational multiple of Rselfdual. Apart from the standard Dirichlet and Neumann boundary states, Friedan suggested [D. Friedan, The space of conformal boundary conditions for the \\/c=1 Gaussian model, unpublished note, 1999] that an additional 1-parameter family of boundary states exists.

Romuald A. Janik

2001-01-01

423

Exceptional boundary states at c=1  

Microsoft Academic Search

We consider the CFT of a free boson compactified on a circle, such that the compactification radius R is an irrational multiple of Rselfdual. Apart from the standard Dirichlet and Neumann boundary states, Friedan suggested [D. Friedan, The space of conformal boundary conditions for the c=1 Gaussian model, unpublished note, 1999] that an additional 1-parameter family of boundary states exists. These

Romuald A. Janik; M. Smoluchowski

2001-01-01

424

BOUNDARY CONDITION IDENTIFICATION BY SOLVING CHARACTERISTIC EQUATIONS  

Microsoft Academic Search

The behaviour of a mechanical structure in the lower frequencies is dominated by constraints at the boundaries. Most structures have elastic supports and specifying the boundary conditions requires knowledge of the support parameters. In this paper, a new method is developed to determine the boundary parameters based on the solution of reduced order characteristic equations. The order of these non-linear

H. Ahmadian; J. E. MOTTERSHEAD; M. I. Friswell

2001-01-01

425

Boundaries in the Practice of Humanistic Counselling.  

ERIC Educational Resources Information Center

|Uses the concept of boundary to describe the ground rules, quality, and type of therapeutic relationships in a humanistic form of counseling--a form that blends Rogerian principles with ideas taken from psychodynamic practice. Discusses the work of Robert Langs, boundaries in person-centered work, and the limits of boundaries. (RJM)|

Owen, Ian R.

1997-01-01

426

Ecotone or Ecocline: Ecological Boundaries in Estuaries  

Microsoft Academic Search

Two main ecological boundaries, ecotone and ecocline, have been defined in landscape ecology. At this scale, the estuary represents a boundary between rivers and the sea, but there has been no attempt to fit empirical data for estuaries to these boundary models. An extensive data set from the Thames estuary was analysed using multivariate techniques and species-range analysis, in order

M. J Attrill; S. D Rundle

2002-01-01

427

Implementation of boundary conditions for meshless methods  

Microsoft Academic Search

Boundaries and boundary conditions are an aspect of the numerical solution of partial differential equations where meshless methods have had to surmount many initial difficulties due to the lack of a finite-element-like Kronecker delta condition. Furthermore, it is frequently desirable, especially in fluid mechanics, to impose general, nonlinear boundary and interface constraints. This paper describes a computationally efficient algorithm based

Frank C. Günther

1998-01-01

428

Boundary Homogenization for Periodic Arrays of Absorbers  

Microsoft Academic Search

We introduce a homogenization procedure for reaction-diffusion equations in domains whose boundary consists of small alternating regions with prescribed Dirichlet and Neumann data of comparable areas. The homogenized problem is shown to satisfy an effective Dirichlet boundary condition which depends on the geometry of the small-scale boundary structure. This problem is also related to finding the effective trapping rate for

Cyrill B. Muratov; Stanislav Y. Shvartsman

2008-01-01

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