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1

INTRODUCTION The Cretaceous-Tertiary (K/T) boundary debate has trig-  

E-print Network

for evidence of possible impact-related mass extinctions in the fossil record. So far, only at the K/T boundaryINTRODUCTION The Cretaceous-Tertiary (K/T) boundary debate has trig- gered intense searches is there significant evidence to support an impact- extinction linkage. The Late Devonian, and more particularly

Claeys, Philippe

2

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

Microsoft Academic Search

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

M. Harting; F. A. Wittler

2006-01-01

3

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

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

4

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

5

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

USGS Publications Warehouse

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

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

2007-01-01

6

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

NASA Astrophysics Data System (ADS)

To assess the environmental perturbation induced by the impact event that marks the Cretaceous-Tertiary (K-T) boundary, concentrations and isotopic compositions of bulk organic carbon were determined in sedimentary rocks that span the terrestrial K-T boundary at Dogie Creek, Montana, and Brownie Butte, Wyoming in the Western Interior of the United States. The boundary clays at both sites are not bounded by coals. Although coals consist mainly of organic matter derived from plant tissue, siliceous sedimentary rocks, such as shale and clay, may contain organic matter derived from microbiota as well as plants. Coals record ?13C values of plant-derived organic matter, reflecting the ?13C value of atmospheric CO 2, whereas siliceous sedimentary rocks record the ?13C values of organic matter derived from plants and microbiota. The microbiota ?13C value reflects not only the ?13C value of atmospheric CO 2, but also biological productivity. Therefore, the siliceous rocks from these sites yields information that differs from that obtained previously from coal beds. Across the freshwater K-T boundary at Brownie Butte, the ?13C values decrease by 2.6‰ (from - 26.15‰ below the boundary clay to - 28.78‰ above the boundary clay), similar to the trend in carbonate at marine K-T sites. This means that the organic ?13C values reflect the variation of ?13C of atmospheric CO 2, which is in equilibrium with carbon isotopes at the ocean surface. Although a decrease in ?13C values is observed across the K-T boundary at Dogie Creek (from - 25.32‰ below the boundary clay to - 26.11‰ above the boundary clay), the degree of ?13C-decrease at Dogie Creek is smaller than that at Brownie Butte and that for marine carbonate. About 2‰ decrease in ?13C of atmospheric CO 2 was expected from the ?13C variation of marine carbonate at the K-T boundary. This ?13C-decrease of atmospheric CO 2 should affect the ?13C values of organic matter derived from plant tissue. As such a decrease in ?13C value was not observed at Dogie Creek, a process that compensates the ?13C-decrease of atmospheric CO 2 should be involved. For example, the enhanced contribution of 13C-enriched organic matter derived from algae in a high-productivity environment could be responsible. The ?13C values of algal organic matter become higher than, and thus distinguishable from, those of plant organic matter in situations with high productivity, where dissolved HCO 3- becomes an important carbon source, as well as dissolved CO 2. As the ?13C-decrease of atmospheric CO 2 reflected a reduction of marine productivity, the compensation of the ?13C decrease by the enhanced activity of the terrestrial microbiota means that the microbiota at freshwater environment recovered more rapidly than those in the marine environment. A distinct positive ?13C excursion of 2‰ in the K-T boundary clays is superimposed on the overall decreasing trend at Dogie Creek; this coincides with an increase in the content of organic carbon. We conclude that the K-T boundary clays include 13C-enriched organic matter derived from highly productive algae. Such a high biological productivity was induced by phenomena resulting from the K-T impact, such as nitrogen fertilization and/or eutrophication induced by enhanced sulfide formation. The high productivity recorded in the K-T boundary clays means that the freshwater environments (in contrast to marine environments) recovered rapidly enough to almost immediately (within 10 yr) respond to the impact-related environmental perturbations.

Maruoka, Teruyuki; Koeberl, Christian; Bohor, Bruce F.

2007-01-01

7

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

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

8

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.

Athro Limited

9

Neoselachian (Chondrichthyes, Elasmobranchii) diversity across the Cretaceous–Tertiary boundary  

Microsoft Academic Search

Fishes are often thought to have passed through mass extinctions, including the Cretaceous–Tertiary (KT) event, relatively unscathed. We show that neoselachian sharks suffered a major extinction at the K\\/T boundary. Out of 41 families, 7 became extinct (17±12%). The proportional measure increases at lower taxic levels: 56±10% loss of genera (loss of 60 out of 107) and 84±5% loss of

Jürgen Kriwet; Michael J. Benton

2004-01-01

10

The CretaceousTertiary (K/T) boundary transition at Coxquihui, state of Veracruz, Mexico: evidence for an early Danian impact event?  

E-print Network

conventional biostratigraphic K/T bound- ary markers (e.g. extinction of tropical and subtropical plankticThe Cretaceous­Tertiary (K/T) boundary transition at Coxquihui, state of Veracruz, Mexico: evidence­Tertiary (K/T) transition at Coxquihui, State of Veracruz, Mexico, differs from all other Mexican sections

Keller, Gerta

11

Fullerenes in the cretaceous-tertiary boundary layer  

SciTech Connect

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

Heymann, D.; Chibante, L.P.F.; Smalley, R.E. (Rice Univ., Houston, TX (United States)); Brooks, R.R. (Massey Univ., Palmerston North (New Zealand)); Wolbach, W.S. (Illinois Wesleyan Univ., Bloomington, IL (United States))

1994-07-29

12

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

NASA Technical Reports Server (NTRS)

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

Koeberl, Christian

1992-01-01

13

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

14

Seawater strontium isotopes at the Cretaceous-Tertiary boundary  

NASA Technical Reports Server (NTRS)

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

Macdougall, J. D.; Martin, E.

1988-01-01

15

Extinction and recovery patterns of scleractinian corals at the Cretaceous-Tertiary boundary  

Microsoft Academic Search

The extinction and recovery of scleractinian corals at the Cretaceous–Tertiary (K–T) boundary was analyzed based on a global database of taxonomically revised late Campanian to Paleocene coral collections. In contrast to earlier statements, our results indicate that extinction rates of corals were only moderate in comparison to other marine invertebrates. We have calculated a 30% extinction rate for Maastrichtian coral

Wolfgang Kiessling; Rosemarie C. Baron-Szabo

2004-01-01

16

The section of the Barranco del Gredero (Caravaca, SE Spain): a crucial section for the Cretaceous/Tertiary boundary impact  

E-print Network

in the future. Keywords: Caravaca, Spain, K/T boundary, extinction, impact. Resumen La sección del Barranco del/Tertiary boundary impact extinction hypothesis La sección del Barranco del Gredero (Caravaca, sureste de España exposed Cretaceous Tertiary (K/T) boundary sections in the world. Therefore, the Gredero section has

Smit, Jan

17

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

NASA Technical Reports Server (NTRS)

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

Izett, G. A.

1988-01-01

18

Palynology and sedimentology across a new marine Cretaceous-Tertiary boundary section on Nuussuaq, West Greenland  

Microsoft Academic Search

A new northern high-latitude Cretaceous-Tertiary (K-T) boundary section has been studied at Annertuneq on the north coast of Nuussuaq, West Greenland. The boundary section is situated in a succession of homogeneous dark mudstone deposited in a marine-slope environment. Identification of the boundary is based on the presence of the latest Maastrichtian palynomorphs Palynodinium grallator, Disphaerogena carposphaeropsis, Manumiella spp., and Wodehouseia

Henrik Nøhr-Hansen; Gregers Dam

1997-01-01

19

Wildfires and animal extinctions at the Cretaceous\\/Tertiary boundary  

Microsoft Academic Search

Persuasive models of the ejection of material at high velocities from the Chicxulub asteroid impact marking the Cretaceous\\/Tertiary boundary have led to the conclusion that upon return, that material, heated in passage through the upper atmosphere, generated a high level of infrared energy density over the Earth's surface. That radiant energy has been considered to be a direct source of

Robert K. Adair

2010-01-01

20

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

USGS Publications Warehouse

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

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

1991-01-01

21

Cathodoluminescence of shocked quartz at the Cretaceous-Tertiary boundary  

NASA Technical Reports Server (NTRS)

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

Owen, Michael R.; Anders, Mark H.

1988-01-01

22

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

23

Extinction and recovery patterns of scleractinian corals at the Cretaceous-Tertiary boundary  

Microsoft Academic Search

Abstract The extinction and recovery of scleractinian corals at the Cretaceous–Tertiary (K–T) boundary,was analyzed based on a global database of taxonomically revised late Campanian to Paleocene coral collections. In contrast to earlier statements, our results indicate that extinction rates of corals were only moderate,in comparison,to other marine invertebrates. We have calculated a 30% extinction rate for Maastrichtian coral genera occurring

Wolfgang Kiessling; Rosemarie C. Baron-Szabo

2004-01-01

24

Extraterrestrial amino acids at the Cretaceous-Tertiary boundary  

SciTech Connect

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

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

1985-01-01

25

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

Microsoft Academic Search

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

Florentin J.-M. Maurrasse; Gautam Sen

1991-01-01

26

Deccan flood basalts and the Cretaceous\\/Tertiary boundary  

Microsoft Academic Search

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

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

1988-01-01

27

Major wildfires at the Cretaceous-Tertiary boundary  

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

28

Ignition of global wildfires at the Cretaceous/Tertiary boundary  

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

29

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

Microsoft Academic Search

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

Alfonso Pardo; Thierry Adatte; Gerta Keller; Hedi Oberhänsli

1999-01-01

30

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

PubMed

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

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

1989-03-01

31

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

Microsoft Academic Search

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

G. Keller; L. Li; N. MacLeod

1996-01-01

32

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

33

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

NASA Astrophysics Data System (ADS)

At most localities where the palynological Cretaceous-Tertiary (K-T) boundary has been located in continuous deposition sequences in nonmarine rocks, an anomalous abundance of fern spores occurs immediately above the boundary. The fern-spore anomaly is characterized by unusually high relative abundance of fern spores and dominance by only one of a few species at each locality; it is independent of lithology. Its presence at the K-T boundary at localities from New Mexico to Saskatchewan is evidence of a regional bioevent in earliest Tertiary time: the overwhelming dominance of the continental flora by pioneer species following catastrophic destruction of existing plant communities by the terminal Cretaceous event.

Fleming, R. F.; Nichols, D. J.

34

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

35

40Ar39Ar Ages of the Large Impact Structures Kara and Manicouagan and their Relevance to the Cretaceous-Tertiary and the Triassic-Jurassic Boundary  

Microsoft Academic Search

Since the discovery of the iridium enrichment in Cretaceous- Tertiary boundary clays by Alvarez et al. (1980) the search for the crater of the K\\/T impactor is in progress. Petrographic evidence at the K\\/T boundary material points towards an impact into an ocean as well as onto the continental crust, multiple K\\/T impacts are now being considered (Alvarez and Asaro,

M. Trieloff; E. K. Jessberger

1992-01-01

36

Wildfires and animal extinctions at the Cretaceous/Tertiary boundary  

NASA Astrophysics Data System (ADS)

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

Adair, Robert K.

2010-06-01

37

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

38

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

PubMed

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

Zhao, M; Bada, J L

1989-06-01

39

Planktonic foraminiferal bioevents and faunal turnover across the Cretaceous Tertiary boundary in north of Iran  

NASA Astrophysics Data System (ADS)

In the north of Iran in the Galanderud area, similar to those known from the eastern Tethys realm, experienced unusually adverse environmental conditions for planktic foraminifera during the last two million years of the terminal Cretaceous to early Danian. This section is studied to determine the foraminiferal biozones of the upper Cretaceous to lower Paleocene and to detect patterns of foraminiferal changes across the Cretaceous-Tertiary (K-T) boundary. All late Maastrichtian planktic foraminiferal biozones CF1 to CF4, and Danian biozones P0 (Parvularugoglobogerina extensa) P1a (Parvularugoglobogerina eugubina) and Parasubbotina pseudobulloides are present. Faunal studies show that all but four of the Cretaceous species identified disappeared at or below the K-T boundary in zone CF1 (P. hantkeninoides). Another four species (Heterohelix globulosa, H. dentata, H. monmouthensis, G. cretacea) appear to have survived in to the early Danian. Early disappearances appear to be environmentally controlled. Coarse ornamented species with small populations disappeared first, where as small species will little or no ornamented and generally large populations tended to survive after the environment changing. This indicates a pattern of gradual and selective faunal turnover in planktonic foraminifera during the latest Maastrichtian and in to the earliest Danian that is similar to that observed at the El kef stratotype of Tunisia, as well as K-T sequences in west of Iran, Egypt, Italy, Spain and Mexico.

Darvishzad, B.; Khaje Tash, R.

2009-04-01

40

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

41

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

42

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

NASA Technical Reports Server (NTRS)

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

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

1983-01-01

43

Deccan volcanism at the Cretaceous-Tertiary boundary  

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

44

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

45

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

46

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

NASA Technical Reports Server (NTRS)

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

Stott, Lowell D.; Kennett, James P.

1988-01-01

47

Palynology and sedimentology across a new marine Cretaceous-Tertiary boundary section on Nuussuaq, West Greenland  

NASA Astrophysics Data System (ADS)

A new northern high-latitude Cretaceous-Tertiary (K-T) boundary section has been studied at Annertuneq on the north coast of Nuussuaq, West Greenland. The boundary section is situated in a succession of homogeneous dark mudstone deposited in a marine-slope environment. Identification of the boundary is based on the presence of the latest Maastrichtian palynomorphs Palynodinium grallator, Disphaerogena carposphaeropsis, Manumiella spp., and Wodehouseia quadrispina below the boundary and on the first occurrence of the earliest Danian species Senoniasphaera inornata above the boundary. Variations in sporomorph and dinoflagellate cyst abundances indicate latest Maastrichtian regression followed by early Danian transgression. The transgressive phase can be subdivided into three high-frequency transgressive-regressive cycles. Each cycle indicates upwelling and transgression, mixing with low-latitudinal water masses, and ocean conditions suggested by the peak occurrences of Senegalinium spp., Trithyrodinium fragile, and Spongodinium delitiense, respectively.

Nøhr-Hansen, Henrik; Dam, Gregers

1997-09-01

48

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

49

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

50

The Cretaceous-Tertiary boundary biotic crisis in the Basque country  

NASA Technical Reports Server (NTRS)

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

Lamolda, M. A.

1988-01-01

51

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

USGS Publications Warehouse

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

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

1992-01-01

52

Major wildfires at the Cretaceous-Tertiary boundary  

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

53

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

NASA Technical Reports Server (NTRS)

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

Maurrasse, Florentin J-M. R.

1988-01-01

54

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

USGS Publications Warehouse

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

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

1989-01-01

55

GEOL 104 Dinosaurs: A Natural History Homework 6: The Cretaceous-Tertiary Extinction  

E-print Network

Name: 1 GEOL 104 Dinosaurs: A Natural History Homework 6: The Cretaceous-Tertiary Extinction DUE) if the taxon: A. Was already extinct by the Cretaceous-Tertiary Boundary X. Died out at the Cretaceous Agents and Physical Evidence There are three environmental changes at or near the K/T boundary that might

Holtz Jr., Thomas R.

56

Ocean alkalinity and the Cretaceous/Tertiary boundary  

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

57

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

Microsoft Academic Search

Recent studies indicate that the bulk (80%) of the Deccan trap eruptions occurred over less than 0.8 m.y. in magnetic polarity C29r spanning the Cretaceous-Tertiary 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

Thierry Adatte; Gerta Keller

2010-01-01

58

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

E-print Network

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

59

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

NASA Astrophysics Data System (ADS)

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

Keller, Gerta

1989-06-01

60

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

SciTech Connect

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

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

1984-09-07

61

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

USGS Publications Warehouse

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

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

1986-01-01

62

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

NASA Technical Reports Server (NTRS)

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

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

1987-01-01

63

Macro-invertebrates and the Cretaceous-Tertiary boundary  

NASA Astrophysics Data System (ADS)

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

Wiedmann, Jost

64

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

NASA Technical Reports Server (NTRS)

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

Pope, Kevin O.

1995-01-01

65

Indication of Global Deforestation at the Cretaceous-Tertiary Boundary by New Zealand Fern Spike  

NASA Astrophysics Data System (ADS)

The devastating effect on terrestrial plant communities of a bolide impact at the Cretaceous-Tertiary boundary is shown in fossil pollen and spore assemblages by a diverse flora being abruptly replaced by one dominated by a few species of fern. Well documented in North America, this fern spike signals widespread deforestation due to an impact winter or massive wildfires. A Southern Hemisphere record of a fern spike, together with a large iridium anomaly, indicates that the devastation was truly global. Recovery of New Zealand plant communities followed a pattern consistent with major climatic perturbations occurring after an impact winter that was possibly preceded by global wildfires.

Vajda, Vivi; Raine, J. Ian; Hollis, Christopher J.

2001-11-01

66

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

NASA Technical Reports Server (NTRS)

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

Pope, Kevin O.

1994-01-01

67

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

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

68

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

PubMed

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

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

1984-10-12

69

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

NASA Astrophysics Data System (ADS)

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

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

1984-10-01

70

The Cretaceous–Tertiary (K–T) mass extinction in planktic foraminifera at Elles I and El Melah, Tunisia  

Microsoft Academic Search

Planktic foraminiferal faunas across the K–T transition at Elles and El Melah in northwestern and northeastern Tunisia, respectively, reveal patterns of species extinctions and species survivorship similar to those found at the El Kef stratotype and the Ain Settara sections. Slightly more than 2\\/3 of the species disappeared at or before the K–T boundary event and slightly less than 1\\/3

Narjess Karoui-Yaakoub; Dalila Zaghbib-Turki; Gerta Keller

2002-01-01

71

Marine and continental K-T boundary clays compared  

NASA Technical Reports Server (NTRS)

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

Schmitz, B.

1988-01-01

72

Nymphalid butterflies diversify following near demise at the Cretaceous/Tertiary boundary  

PubMed Central

The butterfly family Nymphalidae contains some of the most important non-drosophilid insect model systems for evolutionary and ecological studies, yet the evolutionary history of the group has remained shrouded in mystery. We have inferred a robust phylogenetic hypothesis based on sequences of 10 genes and 235 morphological characters for exemplars of 400 of the 540 valid nymphalid genera representing all major lineages of the family. By dating the branching events, we infer that Nymphalidae originated in the Cretaceous at 90 Ma, but that the ancestors of 10–12 lineages survived the end-Cretaceous catastrophe in the Neotropical and Oriental regions. Patterns of diversification suggest extinction of lineages at the Cretaceous/Tertiary boundary (65 Ma) and subsequent elevated speciation rates in the Tertiary. PMID:19793750

Wahlberg, Niklas; Leneveu, Julien; Kodandaramaiah, Ullasa; Peña, Carlos; Nylin, Sören; Freitas, André V. L.; Brower, Andrew V. Z.

2009-01-01

73

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

74

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

SciTech Connect

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

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

1992-08-21

75

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

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

76

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

SciTech Connect

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

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

1992-02-01

77

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

PubMed

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

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

1992-02-01

78

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

E-print Network

, is generally considered the K/T boundary impact that caused one of the major mass extinctions in the Earth understanding of these events may reconcile the two divergent K/T mass extinction hypotheses. The impact­extinction of the oldest layer at times of sea level changes and tectonic activity. The K/T boundary impact event (65.0 Ma

Keller, Gerta

79

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

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

80

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

NASA Astrophysics Data System (ADS)

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

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

1987-04-01

81

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

82

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

SciTech Connect

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

Chi, W.R.; Keller, G.

1985-01-01

83

45. IRIDIUM AND OTHER ELEMENT DISTRIBUTIONS, MINERALOGY, AND MAGNETOSTRATIGRAPHY NEAR THE CRETACEOUS\\/TERTIARY BOUNDARY IN HOLE 761C1  

Microsoft Academic Search

Samples from Ocean Drilling Program Hole 761C, collected on both sides of the Cretaceous\\/Tertiary boundary have been analyzed for their chemical and mineralogical content. The sediment consists of nannofossil ooze with variable amounts of clay. The boundary is marked by a color change associated with a nearly step-like decrease of the carbonate fraction. Paleomagnetic data and the drop of the

Robert Rocchia; Daniel Boclet; Laurence Froget; Bruno Galbrun; Eric Robin

84

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

85

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

NASA Technical Reports Server (NTRS)

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

Alvarez, Walter; Asaro, Frank; Montanari, Alessandro

1990-01-01

86

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

87

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

88

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

89

The Cretaceous-Tertiary Boundary and the Last of the Dinosaurs  

Microsoft Academic Search

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

A. J. Charig

1989-01-01

90

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

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

91

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

SciTech Connect

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

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

1992-08-01

92

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

PubMed

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

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

1992-08-01

93

The Cretaceous/Tertiary Extinction Controversy Reconsidered.  

ERIC Educational Resources Information Center

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

McCartney, Kevin; Nienstedt, Jeffrey

1986-01-01

94

Chicxulub impact predates the K-T boundary mass extinction  

PubMed Central

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

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

2004-01-01

95

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

96

The Karskiy craters are the probable records of catastrophe at the Cretaceous-Tertiary boundary  

NASA Technical Reports Server (NTRS)

In order to corroborate the hypothesis of Alvarez and others about the connection of mass mortality and meteorite or cometary impact at the Cretaceous-Tertiary boundary, it is necessary to find a meteorite crater which was formed at the same time. Masaitiss suggested that the Karskiy craters (USSR) are suitable, but previous K/Ar data from other laboratories are very different (from 47 to 82 million years). Impact glasses were gathered from the Karskiy and Ust-Karskiy craters K/Ar age analyses were performed. The glasses cooled very rapidly and had the youngest model ages from 65.8 to 67.6 million years. The slower cooling crypto-crystalline aggregates had more ancient model ages, from 70.5 to 73.9 my as had tagamite because they captured excess argon during crystallization. Least squares analysis showed that with probability of 99 percent the findings on crypto-crystalline aggregates, tagamite and quartz glasses from the Karskiy and Ust-Karskiy craters lie on an isochron which has an age of 65.8 + or - 1.1 million years and a content of excess argon. For the two glasses with identical composition which have different quantities of secondary non-potassium minerals, an independent method determined the content of excess argon. Taking into account these data a more exact slope of the first isochron of 66.4 + or - 1.0 million years was observed and the second glass isochron with age 66.5 + or - 1.1 million years was constructed.

Kolesnikov, E. M.; Nazarov, M. A.; Badjukov, D. D.; Shukolyukov, Yu. A.

1988-01-01

97

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

PubMed Central

The end-Cretaceous mass extinctions, 65 million years ago, profoundly influenced the course of biotic evolution. These extinctions coincided with a major extraterrestrial impact event and massive volcanism in India. Determining the relative importance of each event as a driver of environmental and biotic change across the Cretaceous-Tertiary boundary (KTB) crucially depends on constraining the mass of CO2 injected into the atmospheric carbon reservoir. Using the inverse relationship between atmospheric CO2 and the stomatal index of land plant leaves, we reconstruct Late Cretaceous-Early Tertiary atmospheric CO2 concentration (pCO2) levels with special emphasis on providing a pCO2 estimate directly above the KTB. Our record shows stable Late Cretaceous/Early Tertiary background pCO2 levels of 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 CO2 outgassing during the eruption of the Deccan Trap basalts fails to fully account for the inferred pCO2 increase. Instead, we calculate that the postboundary pCO2 rise is most consistent with the instantaneous transfer of ?4,600 Gt C from the lithic to the atmospheric reservoir by a large extraterrestrial bolide impact. A resultant climatic forcing of +12 W?m?2 would have been sufficient to warm the Earth's surface by ?7.5°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.

2002-01-01

98

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

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

99

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

NASA Technical Reports Server (NTRS)

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

Ryder, Graham

1996-01-01

100

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

101

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.

102

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

NASA Technical Reports Server (NTRS)

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.

1992-01-01

103

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

NASA Technical Reports Server (NTRS)

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

Gilmour, Iain; Anders, Edward

1988-01-01

104

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

USGS Publications Warehouse

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

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

1986-01-01

105

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

106

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

NASA Technical Reports Server (NTRS)

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

Ward, Peter D.; Macleod, Kenneth

1988-01-01

107

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

SciTech Connect

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

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

1986-05-01

108

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

SciTech Connect

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

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

1985-01-01

109

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

NASA Technical Reports Server (NTRS)

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.

1992-01-01

110

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

2001-01-01

111

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

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

112

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

113

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

NASA Technical Reports Server (NTRS)

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.

1988-01-01

114

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

NASA Technical Reports Server (NTRS)

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

Bostwick, Jennifer A.; Kyte, Frank T.

1993-01-01

115

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

NASA Astrophysics Data System (ADS)

The palynological Cretaceous/Tertiary boundary is recognized in the northern part of the Western Interior by the abrupt disappearance of a few characteristic Cretaceous pollen genera, principally Proteacidites and Aquilapollenites. In the southern part, the boundary is recognized by the disappearance of a somewhat different group of pollen: Proteacidites, “Tilia” wodehousei, and Trisectoris. The abrupt change in both regions takes place precisely at the stratigraphic horizon at which boundary clay layers containing anomalously high concentrations of iridium (interpreted to be the result of an asteroid impact) are found. Although some characteristic Cretaceous taxa apparently became extinct, others were minimally affected by this boundary event and reappear in strata above. However, all the principal Cretaceous pollen genera (though not species) that disappear regionally have been reported from Tertiary rocks in other parts of North America. Differential apparent extinction and/or survival reflects a pronounced temporary disruption of plant life immediately after the event. Some Cretaceous plants must have persisted in refugia to have provided the propagules for the rapid recovery of the flora. No massive total extinction of plant genera at the end of the Cretaceous can be seen from the palynologic record.

Tschudy, Robert H.; Tschudy, Bernadine D.

1986-08-01

116

PALEOCEANOGRAPHY,VOL. 1, NO. 2, PAGES 97-117, JUNE 1986 THE CRETACEOUS/TERTIARY BOUNDARY  

E-print Network

foraminifera and coccolithophorids underwent rapid and wide- spread extinction at the K/T boundary [Loeblich site 577 from the Shatsky Rise, North Pacific, was undertaken to describe extinction and radiation/ Tertiary (K/T) boundary. A 15-m section containing the boundary was closely sampled and contained

Zachos, James

117

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

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

118

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

USGS Publications Warehouse

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

Izett, G.A.

1991-01-01

119

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

USGS Publications Warehouse

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

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

1986-01-01

120

Ar40 to Ar39 ages of the large impact structures Kara and Manicouagan and their relevance to the Cretaceous-Tertiary and the Triassic-Jurassic boundary  

Microsoft Academic Search

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

M. Trieloff; E. K. Jessberger

1992-01-01

121

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

Microsoft Academic Search

Hypotheses of global wildfires following the Cretaceous-Tertiary (KT) boundary impact are supported by high concentrations of elemental carbon (3.6 mg cm-2) and soot (1.8 mg cm-2) in DSDP Site 465, which was located several thousand kilometers from potential continental sources at 65 Ma. Soot is not preserved at four other central Pacific KT localities, but this is attributed to loss

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

2003-01-01

122

Field guide to Cretaceous-tertiary boundary sections in northeastern Mexico  

NASA Technical Reports Server (NTRS)

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.

1994-01-01

123

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

NASA Astrophysics Data System (ADS)

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

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

2001-10-01

124

Patterns of biodiversity and faunal rebound following the K–T boundary extinction event in Austral Palaeocene molluscan faunas  

Microsoft Academic Search

Palaeocene molluscan faunas are characterised by complex evolutionary histories following the Cretaceous–Tertiary (K–T) boundary extinction event and exhibit dramatic, distinct signatures of composition and biodiversity levels relating to extinction and post-extinction recovery processes. This paper is the first to document and survey the entire Palaeocene record of the Southern Hemisphere, which comprises at least 515 recorded molluscan taxa from Australia,

Jeffrey D. Stilwell

2003-01-01

125

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

NASA Astrophysics Data System (ADS)

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

Trieloff, M.; Jessberger, E. K.

1992-07-01

126

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

NASA Technical Reports Server (NTRS)

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

Keller, G.

1988-01-01

127

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

Microsoft Academic Search

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.

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

1983-01-01

128

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

NASA Astrophysics Data System (ADS)

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

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

2003-01-01

129

A search for soot from global wildfires in central Pacific Cretaceous-Tertiary boundary and other extinction and impact horizon sediments.  

PubMed

Hypotheses of global wildfires following the Cretaceous-Tertiary (KT) boundary impact are supported by high concentrations of elemental carbon (3.6 mg cm(-2)) and soot (1.8 mg cm(-2)) in DSDP Site 465, which was located several thousand kilometers from potential continental sources at 65 Ma. Soot is not preserved at four other central Pacific KT localities, but this is attributed to loss during oxic diagenesis. We find no evidence for wildfires related to major impacts in the late Eocene or to Ir anomalies and extinctions in the late Cenomanian. PMID:12804367

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

2003-01-01

130

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

NASA Technical Reports Server (NTRS)

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

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

2003-01-01

131

Quenched magnetite in cretaceous-tertiary boundary microtekite-like spheroid  

NASA Technical Reports Server (NTRS)

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

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

1984-01-01

132

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

133

The causes for geographical variations in OS187/OS186 at the Cretaceous-Tertiary boundary  

NASA Technical Reports Server (NTRS)

Researchers at Yale has approached the problem of the osmium isotopic composition of marine deposits formed in contact with both oxidized and reduced bottom waters. The measured (187) Os/(186) Os ratios of modern bulk sediment can be explained using mixing equations involving continental detrital, volcaniclastic, cosmogenic and hydrogeneous components. These studies show that sediments deposited under reducing marine conditions contain a hydrogenous component which is enriched in Re and has a radiogenic (187) Os/(186) Os ratio. The presence of such a hydrogenous component in the marine fish clay at Stevns Klint can account for the elevation of its (187) Os/(186) Os ration above the expected meteoritic value. Mass balance considerations require the Re/Os ratio of the phase precipitated from the terminal Cretaceous sea at Stevns Klint to have been about one tenth the value observed in contemporary deposits in the Black Sea, assuming Re has not been lost (or Os gained) subsequent to precipitation. In continental sections, the elevation of the (187) Os/(186) Os ratio in boundary layers may be due to precipitation from continental waters of crustally-derived radiogenic osmium either contemporaneous with the meteoritic (or mantle) osmium deposition or later during diagenesis.

Turekian, K. K.; Esser, B. K.; Ravizza, G. E.

1988-01-01

134

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

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

135

Paleoecology of the Cretaceous^Tertiary mass extinction in planktonic foraminifera  

E-print Network

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

Keller, Gerta

136

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

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

137

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

NASA Technical Reports Server (NTRS)

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

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

2003-01-01

138

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

NASA Technical Reports Server (NTRS)

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

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

1997-01-01

139

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

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

140

Surviving the K-T mass extinction: New perspectives of polyploidization in angiosperms  

E-print Network

Surviving the K-T mass extinction: New perspectives of polyploidization in angiosperms Douglas E lineages survive the Cretaceous-Tertiary (K-T) mass ex- tinction. This intriguing hypothesis illus- trates corresponds with the K-T boundary. Hence, they propose that genome dou- bling was a catalyst for the survival

Gent, Universiteit

141

doi:10.1016/j.gca.2004.11.003 High-resolution geochemical record of Cretaceous-Tertiary boundary sections in Mexico  

E-print Network

; Bohor, 1996) to understanding the causes of the global mass extinction at the K/T boundary and the role sections in Mexico: New constraints on the K/T and Chicxulub events D. ST�BEN,1, * U. KRAMAR,1 M. HARTING,1; accepted in revised form November 3, 2004) Abstract--The investigation of eight Cretaceous­Tertiary (K/T

Keller, Gerta

142

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.

143

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

NASA Technical Reports Server (NTRS)

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.; Oneil, J. R.; Smit, J.

1983-01-01

144

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

PubMed

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

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

1992-08-14

145

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

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

146

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

147

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  

NASA Astrophysics Data System (ADS)

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 isotopic compositions and concentrations in the boundary layer cannot be accounted for by in situ growth of daughter products since the sedimentation of the Fish Clay. While Os, Nd and Pb isotopes indicate the admixing of less radiogenic components to the Fish Clay, Sr isotopes show elevated radiogenic values in the boundary layer, relative to the carbonate sequences beneath and above it. The sudden change in lithophile (e.g., Sr, Pb and Nd) isotope compositions at the base of the Fish Clay and profile-upward trends of 87Sr/ 86Sr and 206Pb/ 204Pb ratios towards those of the overlying Danian chalk are interpreted to reflect recovery from enhanced, acid rain-induced continental (local?) weathering input to the seawater. However, a continental crustal source is invalid for the siderophile element Os. In the light of evidence from chromium isotopes for a cosmic origin of the platinum group elements (PGEs) and certain moderately siderophile elements (Cr, Ni, Co, V) in K-T boundary sediments, including Stevns Klint [Shukolyukov and Lugmair, Science 282 (1998) 927-929], and supported by the finding of projectile debris [Bauluz et al., Earth Planet. Sci. Lett. 182 (2000) 127-136] and the occurrence of abundant Ni-rich spinel at many K-T sites [Robin et al., Nature 363 (1993) 615-617; Kyte, Nature 396 (1998) 237-239], we favor to explain the sudden drop of 187Os/ 188Os ratios from 0.210 to 0.160 at the K-T boundary to derive from global fall-out of extraterrestrial matter. The present 186Os/ 188Os ratio of 0.119836±0.000004 measured in the basal layer of the Fish Clay is within the uncertainty a chondritic value. We therefore exclude the possibility of a major contribution of PGEs to the sediment from iron meteorites. Chondrite-normalized (Ru/Ir) N ratios of ˜0.95±0.14 and (Os/Ir) N ratios of ˜0.93±0.14 in the Fish Clay cannot distinguish between abundance ratios of different types of chondrites, and strongly sub-chondritic (Pt/Ir) N ratios of ˜0.62±0.09 (2?) suggest differential PGE remobilization through the sedimentary column (and consequently the alteration of inter-element ratios). PGEs and the moderately siderophile elements Cr, Ni, V, and Co form an elemental association with systematically upward-decreasing concentrations in the Fish Clay. Low Co/Ni ratios of ˜0.12 in the Fish Clay relative to values of ˜0.35 in the over- and underlying carbonate sequences support mixing of meteorite-derived (Co/Ni ˜0.05) and terrestrial upper mantle/crustal (Co/Ni >˜0.3) sources. While lithophile element isotope data indicate an increased continental crustal input to the Fish Clay at the K-T transition, the uncertainty with respect to possible post-depositional alteration of abundance patterns of siderophile and moderately siderophile elements - though not affecting the chondritic isotopic composition of Os - does not allow confirmation of indications from chromium isotopes for a carbonaceous (CV-type) meteorite as the preferred K-T impactor type by Shukolyukov and Lugmair [Science 282 (1998) 927-929].

Frei, Robert; Frei, Karin M.

2002-10-01

148

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

PubMed

For the past decade, the scientific and popular press have carried frequent articles about a catastrophic mass extinction that supposedly destroyed the majority of the earth's species, including the dinosaurs, approximately 65 million years ago. Since 1980, more than 2000 papers and books have dealt with some aspect of a mass extinction at the Cretaceous-Tertiary (K/T) boundary. One authoritative estimate of the severity of the extinctions is that 60-80% of all the living species became extinct at this boundary (Raup 1988). There appears to be a general acceptance of the fact that such a great catastrophe did occur. Most of the argument among scientists now is devoted to the determination of the cause. In this article, I argue that the species changes at the K/T boundary were neither sudden nor catastrophic. They were most likely caused by a regression of sea level that led to a decrease in primary production. PMID:11538279

Briggs, J C

1991-10-01

149

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

NASA Technical Reports Server (NTRS)

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

Briggs, J. C.

1991-01-01

150

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

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

151

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

NASA Technical Reports Server (NTRS)

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

Pope, Kevin O.

1997-01-01

152

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

153

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

USGS Publications Warehouse

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

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

1987-01-01

154

Deccan volcanism and K-T boundary signatures  

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

155

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

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

156

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

USGS Publications Warehouse

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

Brett, R.

1992-01-01

157

Geochemistry of K/T boundaries in India and contributions of Deccan volcanism  

NASA Technical Reports Server (NTRS)

Three possible Cretaceous/Tertiary (K/T) boundary sections in the Indian subcontinent were studied for their geochemical and fossil characteristics. These include two marine sections of Meghalaya and Zanskar and one continental section of Nagpur. The Um Sohryngkew river section of Meghalaya shows a high iridium, osmium, iron, cobalt, nickel and chromium concentration in a 1.5 cm thick limonitic layer about 30 cm below the planktonic Cretaceous-Palaeocene boundary identified by the characteristic fossils. The Bottaccione and Contessa sections at Gubbio were also analyzed for these elements. The geochemical pattern at the boundary at the Um Sohryngkew river and Gubbio sections are similar but the peak concentrations and the enrichment factors are different. The biological boundary is not as sharp as the geochemical boundary and the extinction appears to be a prolonged process. The Zanskar section shows, in general, similar concentration of the siderophile, lithophile and rare earth elements but no evidence of enrichment of siderophiles has so far been observed. The Takli section is a shallow inter-trappean deposit within the Deccan province, sandwiched between flow 1 and flow 2. The geochemical stratigraphy of the inter-trappeans is presented. The various horizons of ash, clay and marl show concentration of Fe and Co, generally lower than the adjacent basalts. Two horizons of slight enrichment of iridium are found within the ash layers, one near the contact of flow 1 and other near the contact of flow 2, where iridium occurs at 170 and 260 pg/g. These levels are lower by a factor of 30 compared to Ir concentration in the K/T boundary in Meghalaya section. If the enhanced level of some elements in a few horizons of the ash layer are considered as volcanic contribution by some fractionation processes than the only elements for which it occurs are REE, Ir and possibly Cr.

Bhandari, N.; Gupta, M.; Pandey, J.; Shukla, P. N.

1988-01-01

158

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

NASA Technical Reports Server (NTRS)

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

Rampino, Michael R.; Volk, Tyler

1988-01-01

159

ELSEVIER Marine Micropaleontology 3I (1997) 97-133 The CretaceousD'ertiary boundary event in Ecuador  

E-print Network

A multidisciplinary study of a new Cretaceous-Tertiary (K/T) boundary section near Guayaquil, Ecuador, reveals similar to those found in southern high-latitude K/T sequences despite the fact that this section was deposited near the Cretaceous equator. The K/T boundary is located by planktic foraminifera within a narrow

Keller, Gerta

160

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

161

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

NASA Technical Reports Server (NTRS)

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

Fastovsky, D. E.

1988-01-01

162

Guembelitria irregularis Bloom at the K-T Boundary: Morphological Abnormalities Induced by Impact-related Extreme Environmental Stress?  

Microsoft Academic Search

The planktonic foraminiferal species Guembelitria irregularis displays an aberrant test due to the irregular disposition and growth of the chambers which suggest a morphological malformation.\\u000a Available data across the Cretaceous-Tertiary (K-T) transition from three Tunisian sections (El Kef II, Elles II, Ain Settara)\\u000a and Kazakhstan (Koshak) and new data from Spain (Caravaca), and Italy (Erto), show a dramatic and remarkable

Rodolfo Coccioni; Valeria Luciani

163

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

164

Nanodiamonds and Carbon Spherules from Tunguska, the K/T Boundary, and the Younger Dryas Boundary Layer  

NASA Astrophysics Data System (ADS)

More than a dozen markers, including nanodiamonds (NDs) and carbon spherules (CS), occur in a sedimentary layer marking the onset of the Younger Dryas (YD) cooling episode at ~12.9 ka. This boundary layer, called the YDB, has been found at nearly forty locations across North America, Europe, and Asia, although not all markers are present at any given site. Firestone et al. (2007) and Kennett et al. (2008, 2009) proposed that these markers resulted from a cosmic impact/airburst and impact-related biomass burning. Here we report features common to the YDB event, the Cretaceous-Tertiary (K/T) impact, and the Tunguska airburst of 1908. In sediments attributed to each event, we and other researchers have recovered NDs either inside or closely associated with CS, which appear to be the high-temperature by-products of biomass burning. CS range in diameter from about 500 nanometers to 4 millimeters with a mean of ~100 microns, and they typically contain NDs, including lonsdaleite (hexagonal diamonds), in the interior matrix and in the crust. To date, CS and NDs have been found in the K/T layer in the United States, Spain, and New Zealand. Similarly, CS and NDs have been found in the YDB layer in the United States, Canada, United Kingdom, Belgium, the Netherlands, Germany, and France. Thus far, every site examined contains NDs and/or CS in the K/T and YDB layers; conversely, we have yet to detect CS associated with NDs in any non-YDB sediments tested. Five allotropes of NDs have been identified in association with CS: cubic diamonds, lonsdaleite, n-diamonds, p-diamonds, and i-carbon, which are differentiated by slight variations in their crystalline structure. All allotropes have been identified using scanning electron microscopy (SEM), high-resolution electron microscopy (HREM), and transmission electron microscopy (TEM) with confirmation by selected area diffraction (SAED). Lonsdaleite is found on Earth only in three instances: (1) in the laboratory, where it is produced by shock synthesis under a high-temperature-high-pressure regime (~1000°C to 1700°C at 15 GPa) or by carbon vapor deposition (CVD) under a very-high-temperature-low-pressure regime (~13,000°C at 300 Torr) (Maruyama et al., 1993); (2) after arrival on Earth inside extraterrestrial material; and (3) as a result of high-temperature cosmic impact/airbursts. Lonsdaleite associated with CS has been found in sediments only at the K/T, the YDB, and Tunguska, consistent with the hypothesis that all three events have cosmic origins, although the nature of the impactors may have been different.

Wittke, J. H.; Bunch, T. E.; West, A.; Kennett, J.; Kennett, D. J.; Howard, G. A.

2009-12-01

165

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

166

Explosive volcanism, shock metamorphism and the K-T boundary  

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

167

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

E-print Network

. These data show that Chicxulub was not the K­T impact that caused the end-Cretaceous mass extinction scenario for the end-Cretaceous mass extinction. Keywords: Belize, Guatemala, K­T boundary, Chicxulub and the Caribbean. Most spherule deposits and breccias with spherules are stratigraphically at or near the K­T

Keller, Gerta

168

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

NASA Technical Reports Server (NTRS)

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

Loper, D. E.; Mccartney, K.

1988-01-01

169

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

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

170

Cretaceous-Tertiary findings, paradigms and problems  

NASA Astrophysics Data System (ADS)

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

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

171

Cretaceous-Tertiary findings, paradigms and problems  

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

172

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

NASA Technical Reports Server (NTRS)

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

Sweet, A. R.

1988-01-01

173

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

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

174

Large meteorite impacts: The K/T model  

NASA Technical Reports Server (NTRS)

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

Bohor, B. F.

1992-01-01

175

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

NASA Technical Reports Server (NTRS)

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.

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

1997-01-01

176

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

177

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

NASA Technical Reports Server (NTRS)

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

Sharpton, Virgil L.; Marin, Luis E.

1997-01-01

178

Terrestrial Acidification at the K/T Boundary James R. Lyons*  

E-print Network

1 Terrestrial Acidification at the K/T Boundary James R. Lyons* and Thomas J. Ahrens Lindhurst acidification of the mixed-layer of the oceans, an implication not consistent with the record of marine, it is clear significant continental acidification occurred at the K/T boundary. 1. Introduction We focus here

Stewart, Sarah T.

179

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

180

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

181

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

NASA Technical Reports Server (NTRS)

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

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

1983-01-01

182

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

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

183

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. PMID:19251660

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

2009-01-01

184

Benthic extinction and recovery patterns at the K\\/T boundary in shallow water carbonates, Denmark  

Microsoft Academic Search

Benthic extinction at the K\\/T boundary in the Danish Basin is abrupt and indistinguishable from the termination of Maastrichtian White Chalk deposition. The Danian benthic fauna — already fully established in the earliest Danian nannoplankton zone NP1 — is essentially an impoverished Maastrichtian fauna established through direct survival or limited evolution within well-established clades, already present in the Maastrichtian of

Eckart Håkansson; Erik Thomsen

1999-01-01

185

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

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

186

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

187

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

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

188

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

NASA Technical Reports Server (NTRS)

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.

1993-01-01

189

Environmental effects of Deccan volcanism across the Cretaceous-Tertiary transition in Meghalaya, India  

NASA Astrophysics Data System (ADS)

The Um Sohryngkew section of Meghalaya, NE India, located 800-1000 km from the Deccan volcanic province, is one of the most complete Cretaceous-Tertiary boundary (KTB) transitions worldwide with all defining and supporting criteria present: mass extinction of planktic foraminifera, first appearance of Danian species, ? 13C shift, Ir anomaly (12 ppb) and KTB red layer. The geochemical signature of the KTB layer indicates not only an extraterrestrial signal (Ni and all Platinum Group Elements (PGEs)) of a second impact that postdates Chicxulub, but also a significant component resulting from condensed sedimentation (P), redox fluctuations (As, Co, Fe, Pb, Zn, and to a lesser extent Ni and Cu) and volcanism. From the late Maastrichtian C29r into the early Danian, a humid climate prevailed (kaolinite: 40-60%, detrital minerals: 50-80%). During the latest Maastrichtian, periodic acid rains (carbonate dissolution; CIA index: 70-80) associated with pulsed Deccan eruptions and strong continental weathering resulted in mesotrophic waters. The resulting super-stressed environmental conditions led to the demise of nearly all planktic foraminiferal species and blooms (> 95%) of the disaster opportunist Guembelitria cretacea. These data reveal that detrimental marine conditions prevailed surrounding the Deccan volcanic province during the main phase of eruptions in C29r below the KTB. Ultimately these environmental conditions led to regionally early extinctions followed by global extinctions at the KTB.

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

2011-10-01

190

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

191

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

192

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

193

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

194

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. PMID:11296857

Cracraft, J.

2001-01-01

195

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

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

196

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

197

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

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

198

The cretaceous-tertiary transition on the shallow Saharan Platform of southern tunisia  

Microsoft Academic Search

A multidisciplinary approach to the study of a K\\/T boundary section on the Saharan Platform based on planktic and benthic foraminifera, calcareous nannofossils, lithology, stable isotopes, mineralogy and geochemistry reveals a biota stressed by fluctuating hyposaline, hypoxic littoral and nearshore environments, productivity changes, and a paleoclimate altering between seasonal warm to temperate and warm\\/humid conditions. Benthic formaminifera indicate that during

Gerta Keller; Thierry Adatte; Wolfgang Stinnesbeck; Doris Stüben; Utz Kramar; Zsolt Berner; Liangquan Li; Katharina von Salis Perch-Nielsen

1997-01-01

199

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

NASA Technical Reports Server (NTRS)

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

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

2003-01-01

200

Stratigraphy of the Cretaceous-Tertiary and Paleocene-Eocene transition rocks of Big Bend National Park, Texas  

SciTech Connect

The marine to terrestrial transition in the Big Bend area falls within the Late Cretaceous Aguja Formation, and, in light of new biostratigraphic data resulting from screening for small vertebrates and magneto-stratigraphic data, the Cretaceous-Tertiary boundary falls within the Javelina Formation, which includes the first red banding produced by oxidation of overbank fluvial mudstones. No record of a catastrophic event is apparent in the Javelina Formation. The Javelina, Black Peaks, and Hannold Hill Formations and the Big Yellow Sandstone Member of the Canoe Formation record increasing uplift in the region, culminating in uplift and volcanism in the Chisos mountains, the source for upper Canoe Formation sediments. The sequence of changes produced by this trend and by unroofing in source highlands to the west is sufficiently gradual that the Javelina through Black Peaks units are not lithostratigraphically distinct at the formation level and therefore are reduced to member status, and placed, along with the Big Yellow Sandstone Member, within the redefined Tornillo Formation. The Aguja Formation and the Tornillo Formation are united in the Chilicotal Group (new), which spans the deposits from the first significant influxes of terrestrial sediments, formed as the Cretaceous sea retreated, up to the beginning of local volcanism in the Chisos. The volcanic strata of the upper Canoe Formation are reassigned to the Chisos Formation. 46 references.

Schiebout, J.A.; Rigsby, C.A.; Rapp, S.D.; Hartnell, J.A.; Standhardt, B.R.

1987-05-01

201

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

PubMed

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

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

2009-04-01

202

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. PMID:19325131

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

2009-01-01

203

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

204

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

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

205

Trace elements, stable isotopes, and clay mineralogy of the Elles II K–T boundary section in Tunisia: indications for sea level fluctuations and primary productivity  

Microsoft Academic Search

Trace elements and stable isotopes in bulk rocks and foraminifera, bulk rock and clay mineral compositions, are used as palaeoproxies to evaluate sea level fluctuations, climatic changes and variations in primary productivity across the K–T transition at Elles II in Tunisia from 1 m (?33 kyr) below to 1 m (?70 kyr) above the K–T boundary. Results on clay minerals,

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

2002-01-01

206

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

207

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

NASA Technical Reports Server (NTRS)

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

Kring, David A.; Boynton, William V.

1991-01-01

208

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

SciTech Connect

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

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

1991-06-01

209

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

NASA Astrophysics Data System (ADS)

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

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

2009-01-01

210

The K-T Transition in Meghalaya, NE India  

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

211

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

NASA Astrophysics Data System (ADS)

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

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

2012-08-01

212

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

Microsoft Academic Search

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

Song Zhichen; Zheng Yahui; Liu Jinling

1995-01-01

213

Planktonic foraminiferal bioevents and faunal turnover across the Cretaceous Tertiary boundary in north of Iran  

Microsoft Academic Search

In the north of Iran in the Galanderud area, similar to those known from the eastern Tethys realm, experienced unusually adverse environmental conditions for planktic foraminifera during the last two million years of the terminal Cretaceous to early Danian. This section is studied to determine the foraminiferal biozones of the upper Cretaceous to lower Paleocene and to detect patterns of

B. Darvishzad; R. Khaje Tash

2009-01-01

214

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

NASA Technical Reports Server (NTRS)

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.

1987-01-01

215

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

NASA Technical Reports Server (NTRS)

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

Macdougall, J. D.

1988-01-01

216

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

217

Iridium abundance anomaly at the palynological Cretaceous-tertiary boundary in northern New Mexico  

SciTech Connect

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

Orth, C.J. (Los Alamos National Lab., NM); Gilmore, J.S.; Knight, J.D.; Pillmore, C.L.; Tschudy, R.H.; Fassett, J.E.

1981-12-18

218

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

USGS Publications Warehouse

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

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

1981-01-01

219

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

Microsoft Academic Search

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

Lee Nordt; Stacy Atchley; S. I. Dworkin

2002-01-01

220

vol. 165, no. 3 the american naturalist march 2005 Explosive Radiation of Malpighiales Supports a Mid-Cretaceous  

E-print Network

, following the mass extinction event at the Cretaceous- Tertiary (K/T) boundary (65 Ma [Tiffney 1984; Wing not originate until after the Cretaceous-Tertiary (K/T) boundary. However, some mid-Cretaceous leaf floras have that closed-canopy tropical rain forests existed well before the K/T boundary. This case illustrates

221

Marine Micropaleontology, 20 (1992) 77-88 77 Elsevier Science Publishers B.V., Amsterdam  

E-print Network

that the Cretaceous/Tertiary (K/T) mass extinction was a consequence of a large meteorite collid- ing with the earth to elucidate the causes of these mass extinctions. For many years a hiatus across the K/T boundary has been acrossthe Cretaceous/Tertiary boundary (K/T boundary). The stratigraphic rangeofthe samplesis from

Grossman, Ethan L.

222

Meteoritics & Planetary Science 39, Nr 7, 11271144 (2004) Abstract available online at http://meteoritics.org  

E-print Network

the K/T mass extinction Gerta KELLER,1* Thierry ADATTE,2 Wolfgang STINNESBECK,3 Doris STÃ?BEN,4 Zsolt and caused the mass extinction at the Cretaceous-Tertiary (K/T) boundary. Instead, contrary evidence the dinosaurs and caused the mass extinction of many other organisms at the Cretaceous-Tertiary (K/T) boundary

Keller, Gerta

223

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

224

Norris, R.D., Kroon, D., Klaus, A., et al., 1998 Proceedings of the Ocean Drilling Program, Initial Reports, Vol. 171B  

E-print Network

's biota. Some of these events, such as the Cretaceous/Tertiary (K/T) extinction and the late Eocene tek, the Cretaceous/Tertiary (K/T) extinction, the mid-Maastrichtian event, and several episodes of or- ganic extinction occurs within an expanded interval of calcare- ous sediments. The K/T boundary was recovered

225

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

USGS Publications Warehouse

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

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

1986-01-01

226

Strangelove ocean at era boundaries, terrestrial or extraterrestrial cause  

NASA Technical Reports Server (NTRS)

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.

1988-01-01

227

The K-T Extinction  

NSDL National Science Digital Library

This chapter from the book History of Life describes the results of the K-T extinction and looks at the Impact theory and a giant volcanic eruption as possible causes. The essay covers the catastrophic scenarios for extinction that could result from these events. After reviewing the paleontological record across the K-T boundary, the author concludes that it is not clear that the catastrophes themselves can explain the extinction patterns that we see in the fossil record.

Richard Cowen

228

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

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

229

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

Microsoft Academic Search

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

Ryunosuke Kikuchi; Maarten Vanneste

2010-01-01

230

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

USGS Publications Warehouse

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

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

2013-01-01

231

Stratigraphy and tectono-sedimentary evolution of the Upper Cretaceous–Tertiary sequence in the southern part of the Malatya Basin, East Anatolia, Turkey  

Microsoft Academic Search

The Malatya Basin is situated on the southern Taurus-Anatolian Platform. The southern part of the basin contains a sedimentary sequence which can be divided into four main units, each separated by an unconformity. From base to top, these are: (1) Permo-Carboniferous; (2) Upper Cretaceous–Lower Paleocene, (3) Middle-Upper Eocene and (4) Upper Miocene. The Upper Cretaceous–Tertiary sedimentary sequence resting on basement

Mehmet Önal; Meral Kaya

2007-01-01

232

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

Microsoft Academic Search

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

M. S. Barash

2011-01-01

233

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

E-print Network

and propagation of several plant lineages during or following the KT extinction event. Due to advantages­Tertiary extinction event Jeffrey A. Fawcetta,b,1 , Steven Maerea,b,1 , and Yves Van de Peera,b,2 aDepartment of Plant duplications are clustered in time and seem to coincide with the Cretaceous­Tertiary (KT) boundary. The KT

Gent, Universiteit

234

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

PubMed

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

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

2001-04-01

235

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

236

Iridium abundance patterns across extinction boundaries  

SciTech Connect

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

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

1985-01-01

237

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

E-print Network

of weathered chert boulders resting unconformably atop the Hell Creek strata (Fig. 1.4). Ranches to the immediate north of Bone Butte have abundant intact Paleocene exposures conformably overlying the Hell Creek strata, and preserved at elevations just... an area approximately 15 m long (north to south) by 12 m wide (east to west) and with an average depth of 6 m. Laminated sandstone and clay-pebble conglomerates containing abundant vertebrate remains represent a paleo stream channel (Fastovsky, 1987...

DePalma, Robert Anthony

2010-04-27

238

A track of the giant theropod dinosaur Tyrannosaurus from close to the Cretaceous\\/Tertiary Boundary, northern New Mexico  

Microsoft Academic Search

The first unequivocal example of a large tyrannosaur track attributable to the species Tyrannosaurus rex is an 86 cm long tetradactyl pedal impression assigned to Tyrannosauripus pillmorei ichnogen. et ichnosp. nov. The ichnospecies Tyrannosauropus petersoni Haubold is a nomen dubium. The only other example of a possible track of Tyrannosaurus is from the Laramie Formation of Colorado.

Martin G. Lockley; Adrian P. Hunt

1994-01-01

239

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

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

240

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

NASA Technical Reports Server (NTRS)

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

Johnson, Kirk R.; Hickey, Leo J.

1988-01-01

241

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

242

Independent Mammalian Genome Contractions Following the KT Boundary  

Microsoft Academic Search

Although it is generally accepted that major changes in the earth's history are significant drivers of phylogenetic diversification and extinction, such episodes may also have long-lasting effects on genomic architecture. Here we show that widespread reductions in genome size have occurred in multiple lineages of mammals subsequent to the Cretaceous- Tertiary (KT) boundary, whereas there is no evidence for such

Mina Rho; Mo Zhou; Xiang Gao; Sun Kim; Haixu Tang; Michael Lynch

2009-01-01

243

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

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

244

U-Pb Isotopic Ages of the K/T Impact Event and its Target Rocks from Shocked Zircons  

NASA Astrophysics Data System (ADS)

U-Pb isotopic results for individual zircon grains from the fire- ball ejecta layer of the Cretaceous/Tertiary (K/T) boundary claystone, Raton Basin, Colorado, lie on a Pb loss line between 550 +- 10 Ma and 65.5 +- 3 Ma. This implies that the target area is dominated by rocks of the older age, and that grains plotting near the younger end of the Pb-loss line record a high degree of shock-related isotopic resetting. Intersection of the Pb loss line with the younger end of the concordia curve at 65.5 +- 3 Ma defines the age of the impact event. Zircon grains that record increasing degrees of shock metamorphism in K/T ejecta can be classified into three textural types: 1) grains that show only shock lamellae or planar deformation features (PDF), 2) grains that show both PDF and granular (polycrystalline) texture, and 3) grains that show only well-developed granular texture. The degree of isotopic resetting correlates closely to the three textural types of zircons that represent increasing intensities of shock. PDF in zircons were originally discovered in K/T ejecta [1], and granular textures were also first observed in K/T zircons. Both granular textures and PDF have been reported recently in zircons from Onaping Fm. fall-back ejecta at the Sudbury impact structure [2]. Granular texture in zircons indicates exposure to a very high level of shock, resulting in diaplectic transformation and subsequent recrystallization--all below the fusion temperature. In our concordia diagram, an unshocked zircon grain showed the least discordant point (3%), while a second grain displaying PDF was displaced down the Pb loss line by 12%. A third grain with both PDF and granular texture plotted with a displacement intermediate to those with PDF only and the completely granular grains. Five completely polycrystalline zircon grains represent the greatest degree of isotopic resetting and show the largest displacements along the Pb loss line (49%, 58%, 62%, 82%, and 90%), approaching the ca. 65 Ma age of the resetting event. Twelve of the fourteen analyzed zircons plotted on or close to a discordant linear array that indicates an original age of ~550 Ma. However, two other grains gave primary ages of ~300 and ~350 Ma from poorer quality data, suggesting a possible bimodal source of zircons. The quality of data often varies from grain to grain, but not because of a high laboratory Pb background (ours is one of the lowest ever recorded). Instead, the variation in quality is due to the low radiogenic Pb content of these small (3 to <1 microgram) and geologically young zircons grains, often barely exceeding our detection limits. The refractory nature of zircon allows it to record shock-induced textural features without any annealing by later thermal events. A volcanic origin for the K/T ejecta is ruled out by the presence of PDF and polycrystalline textures in these zircons, as well as by their older isotopic ages. The analytical data show that the source of the fireball layer ejecta is dominated by target rock with zircons having a U-Pb isotopic age of about 550 +- 10 Ma. This adds another constraint to possible impact sites. References: [1] Bohor, B.F. et al. (1990) Meteoritics 25, 350; [2] Bohor, B.F. and Betterton, W.J. (1992) Inter. Conf. on Large Meteor. Impacts (Sudbury), in press.

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

1992-07-01

245

A unique geochemical record at the Permian/Triassic boundary  

NASA Astrophysics Data System (ADS)

A 330-m core drilled through the marine Permian/Triassic boundary in the Austrian Carnic Alps has been used to make closely correlated studies of geochemistry, petrography, and paleontology across that boundary. The isotope shifts and metal concentrations are found to be extended, multiple, and complex, and do not resemble those seen at the Cretaceous/Tertiary boundary. Both the carbon isotope shifts and the chemical events, including an iridium anomaly, may have causes related to a major regression of the sea.

Holser, William T.; Schoenlaub, Hans-Peter; Klein, Peter; Attrep, Moses, Jr.; Boeckelmann, Klaus

1989-01-01

246

Examination of 10 K/T boundary sections in northeastern and east-central Mexico, and new data presented from 7 sections, permit the fol-  

E-print Network

/T boundary and siliciclastic or breccia deposits is ob- served at Brazos River in Texas, Beloc in Haiti/T boundary and is marked by glass and siliciclastic or breccia deposits. INTRODUCTION Yucatan The subsurface (breccia sample N19) and C1 (sample N10) reported by Sharpton et al. (1992), although these results could

Keller, Gerta

247

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

248

Palaeogeography, Palaeoclimatology, Palaeoecology, 69 (1989):245-266 245 Elsevier Science Publishers B.V., Amsterdam --Printed in The Netherlands  

E-print Network

in this shallow-marine setting at the time ofthe K/T boundary extinctions. Although extensive diagenesis has., Palaeoclimatol., Palaeoecol., 69:245 266. The Cretaceous/Tertiary (K/T) boundary in southern Alabama occurs into the Danian. The characteristicdepletion in 513Cacross the K/T boundary displayed by planktonic microfossils

Zachos, James

249

High stress late Maastrichtian paleoenvironment: inference from planktonic foraminifera in Tunisia  

E-print Network

that aimed to describe the nature of the Cretaceous^Tertiary (K^T) boundary mass extinction focused in extra experienced a further decline at the climax of a rapid warm event about 300 kyr before the K^T boundary Maastrichtian, and particularly at the K^T boundary, are indicated by low species diversity and blooms

Keller, Gerta

250

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

251

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

252

Geochemistry of the sedimentary rocks from the Nanxiong Basin, South China and implications for provenance, paleoenvironment and paleoclimate at the K/T boundary  

NASA Astrophysics Data System (ADS)

Cretaceous and Tertiary clastic sedimentary rocks from the Nanxiong Basin, South China have been analyzed to constrain their provenance, depositional climate and environment. Evidence from discrimination diagrams for sedimentary provenance and tectonic setting show that the Nanxiong Basin sediments were derived from typical continental sources. Geochemical signatures (e.g. Eu/Eu *, Th/Ti, La/Ti, Ta/Ti, Yb/Ti and Y/Ti ratios of the claystone) are nearly constant, suggesting the provenance of the Nanxiong Basin remained similar throughout the Late Cretaceous to Early Paleocene (83-56 Ma). In contrast Rb/Ti, Cs/Ti ratios and TOC and CaCO 3 concentrations require an obvious change in climate across the Late Cretaceous and Early Paleocene boundary. Singularly higher CaCO 3 contents and lower TOC values and Rb/Ti, Cs/Ti ratios in the Late Cretaceous indicate that a long period extreme dry climate occurred at that time in South China. Rb/Ti, Cs/Ti ratios and TOC values escalated and CaCO 3 contents decreased in the Early Paleocene suggesting that the climate became relatively wet, which resulted in greater vegetation cover. The lasting extreme dry climate in the Late Cretaceous may provide a clue to the extinction of the dinosaurs in the Nanxiong Basin.

Yan, Yi; Xia, Bin; Lin, Ge; Cui, Xuejun; Hu, Xiaoqiong; Yan, Pin; Zhang, Faqiang

2007-04-01

253

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

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

254

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

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

255

Geological Society of America Special Paper 356  

E-print Network

Tertiary sec- tions, thanks to their close association with the K-T boundary mass extinction information in a large database on the Cretaceous-Tertiary (K-T) boundary is used to document the distri. The database will be available in part on the internet in the near future, and contains data from 345 K-T

Claeys, Philippe

256

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

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

257

Stratigraphy and tectono-sedimentary evolution of the Upper Cretaceous Tertiary sequence in the southern part of the Malatya Basin, East Anatolia, Turkey  

NASA Astrophysics Data System (ADS)

The Malatya Basin is situated on the southern Taurus-Anatolian Platform. The southern part of the basin contains a sedimentary sequence which can be divided into four main units, each separated by an unconformity. From base to top, these are: (1) Permo-Carboniferous; (2) Upper Cretaceous-Lower Paleocene, (3) Middle-Upper Eocene and (4) Upper Miocene. The Upper Cretaceous-Tertiary sedimentary sequence resting on basement rocks is up to 700 m thick. The Permo-Carboniferous basement consist of dolomites and recrystallized limestones. The Upper Cretaceous-Lower Paleocene transgressive-regressive sequence shows a transition from terrestrial environments, via lagoonal to shallow-marine limestones to deep marine turbiditic sediments, followed upwards by shallow marine cherty limestones. The marine sediments contain planktic and benthic foraminifers indicating an upper Campanian, Maastrichtian and Danian age. The Middle-Upper Eocene is a transgressive-regressive sequence represented by terrestrial and lagoonal clastics, shallow-marine limestones and deep marine turbidites. The planktic and benthic foraminifers in the marine sediments indicate a Middle-Upper Eocene age. The upper Miocene sequence consists of a reddish-brown conglomerate-sandstone-mudstone alternation of alluvial and fluvial facies. During Late Cretaceous-Early Paleocene times, the Gündüzbey Group was deposited in the southern part of a fore-arc basin, simultaneously with volcanics belonging to the Yüksekova Group. During Middle-Late Eocene times, the Ye?ilyurt Group was deposited in the northern part of the Maden Basin and the Helete volcanic arc. The Middle-Upper Eocene Malatya Basin was formed due to block faulting at the beginning of the Middle Eocene time. During the Late Paleocene-Early Eocene, and at the end of the Eocene, the study areas became continental due to the southward advance of nappe structures. The rock sequences in the southern part of the Malatya Basin may be divided into four tectonic units, from base to top: the lower allochthon, the upper allochthon, the parautochthon and autochthonous rock units.

Önal, Mehmet; Kaya, Meral

2007-03-01

258

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

E-print Network

at the K/T boundary. This major extinction appears now to be related to the impact on the Earth of a largeShock-induced vaporization of anhydrite and global cooling from the K/T impact Satish C. Gupta 1 of the target rock at the K/T impact site has prompted research on these minerals. Evaluation of the severity

Stewart, Sarah T.

259

2001 Geological Society of America. For permission to copy, contact Copyright Clearance Center at www.copyright.com or (978) 750-8400. Geology; October 2001; v. 29; no. 10; p. 891894; 3 figures. 891  

E-print Network

-day faunas, as documented by the lack of significant extinction at the K-T collapse of surface productivity, New Haven, Connecticut 06520-8109, USA ABSTRACT Cretaceous-Tertiary (K-T) boundary sections, indicating redeposition in the deep basin by mass-wasting processes resulting from the K-T bolide impact

Royer, Dana

260

The disappearance of nonavian dinosaurs is probably the most notorious extinction event of all time, yet it is only a small part  

E-print Network

),theTriassic-Jurassicextinction(208mya), and the Cretaceous-Tertiary (K/T) extinction (65 mya). Surpris- ingly, little is known about) are estimated to have become extinct at that time (Erwin 1993). By this standard, the K/T extinction Events at or Near the K/T Boundary Our search for a cause or causes of the extinctions requires us

Archibald, J. David

261

Geological Society of America Special Paper 356  

E-print Network

the sandstone-siltstone complex and Cretaceous-Tertiary (K-T) boundary in the La Sierrita area of northeastern Mexico reveals a more complex K-T scenario than pre- viously imagined. These spherule layers were deposited within pelagic marls of the Mendez Formation; the oldest layer is as much as 10 m below the K-T

Keller, Gerta

262

To determine the geomagnetic polarity stratigraphy and the duration and age of  

E-print Network

, and it can be used as an important tool for interpreting rates of biotic recovery after the K-T extinction the Cretaceous-Tertiary (K-T) boundary extinctions (e.g., Belt et al., 1984; Hicks et al., 2003; Hunter and- mating speciation rates and changes in biodi- versity of plants and mammals following the K-T extinctions

263

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

NASA Astrophysics Data System (ADS)

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

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

264

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

Microsoft Academic Search

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

DOUGLAS H. ERWIN

265

West-northwest directed obduction of the Batain Group on the eastern Oman continental margin at the Cretaceous-Tertiary boundary  

NASA Astrophysics Data System (ADS)

The Batain coast area in eastern Oman is dominated by allochthonous Permian to Late Maastrichtian sedimentary and volcanic rocks (Batain Group), unconformably overlain by neoautochthonous Tertiary sediments. The allochthonous rocks of the Batain coast were previously attributed to the Hawasina complex, the Permian to Coniacian/Santonian sedimentary infill of the neo-Tethyan Hawasina basin off northern Oman. Previous structural interpretations suggested that the Batain Group, along with the Hawasina complex and the Semail ophiolite, was obducted in the Coniacian to Campanian from NE to SW onto the northern Oman continental margin. Results of our work in the Batain area differ from previous interpretations, with most significant differences concerning timing and direction of obduction. Our results show that WNW directed tectonic movements formed a fold-and-thrust belt and led to the obduction of allochthonous rocks onto the east Oman continental margin during latest Maastrichtian/earliest Paleocene times. This is coeval with emplacement of ophiolitic fragments along the eastern coast of Oman (eastern ophiolite belt) but is about 15-20 Myr later than emplacement of Hawasina complex and Semail ophiolite in northern Oman. Postemplacement structural evolution during the Tertiary involved intraplate extension, possibly reflecting the Red Sea/Gulf of Aden opening, and late Tertiary shortening related to convergence between Arabia and Eurasia. Late Tertiary contractional deformation resulted in refolding of the Batain nappes and in folding of the overlying Tertiary sediments. A palinspastic reconstruction of the Batain area indicates that the Permian to Upper Cretaceous sediments were formerly deposited in the Batain basin, a part of the proto-Indian Ocean, along the present-day eastern Oman margin. This leads us to propose that Permian breakup of Gondwanaland created both continental margins of Oman and led to the opening of two major basins: the neo-Tethyan Hawasina basin in the north and the proto-Indian Ocean Batain basin in the east, the latter separating Arabia from greater India.

Schreurs, Guido; Immenhauser, Adrian

1999-02-01

266

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

Microsoft Academic Search

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

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

1992-01-01

267

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

SciTech Connect

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

Heymann, D.; Chibante, L.P.F.; Smalley, R.E. (Rice Univ., Houston, TX (United States)); Wolbach, W.S. (Wesleyan Univ., Bloomington, IL (United States)); Brooks, R.R. (Massey Univ., Palmerston North (New Zealand))

1994-08-01

268

The succession of Vertebratesand Plants across the Cretaceous-Tertiary boundary in the Tremp Formation, Ager valley (South-central Pyrenees, Spain)  

Microsoft Academic Search

The Tremp Formation red beds in the Ager valley (Fontllonga section, Lleida, Spain) have yieldedplants (macrorests, palynomorphs) and vertebrates (teeth, bones, eggshells and footprints) at different levels from Early Maastrichtian to Early Palaeocene. A decrease in diversity affected both, plants and vertebrates, but not synchronously. Plant diversity decreases early in the Maastrichtian, while the change in vertebrate assemblages (sudden extinction

Nieves López-Martínez; M Fernández-Marrón; Maria F. Valle

1999-01-01

269

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

Microsoft Academic Search

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

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

2003-01-01

270

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. PMID:19620728

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

2009-01-01

271

Geological Society of America Special Paper 361  

E-print Network

evolutionary radiation following the extinction of dinosaurs at the K-T boundary (McKenna and Bell, 1997 dinosaur extinction and an early Paleocene mam- malian radiation is documented primarily in stratigraphic investigation of this Cretaceous-Tertiary (K-T) transition to new areas. Studies in southwestern North Dakota

Archibald, J. David

272

Divergence Times of Eutherian In the continuing debate about the timing of  

E-print Network

of major extant placental clades, both proponents of a divergence after the Cretaceous-Tertiary (K-T-called condylarths) that in turn are ancestral to a number of extinct and extant placental orders (4). Conversely not appear until shortly after the K-T boundary. Neither of these studies, however, contain data regarding

Hedges, Blair

273

``Ultraviolet spring'' and the ecological consequences of catastrophic impacts  

E-print Network

for exacerbating the demise of land animals at the Cretaceous-Tertiary (K/T) boundary, e.g. dinosaurs, our in this case. If the K/T impact event had occurred in any other region on Earth, the stress to the biosphere would probably have been considerably greater. Keywords Asteroid, comet, extinction, global change

Blaustein, Andrew R.

274

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

PubMed

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

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

2011-09-13

275

The K\\/T stratotype section of El Kef (Tunisia): Events and biotic turnovers  

Microsoft Academic Search

At El Kef (NW Tunisia), the absence of bioturbation and the high sedimentation rate preserve a high resolution record of the Cretaceous-Tertiary transition. In the upper part of the Maastrichtian (Mayaroensis zone) planktonic foraminifer assemblages show a clear marine regression while the variations of spore-pollen contents show a trend related to a climatic cooling. In addition to these gradual changes,

Omrane Ben Abdelkader; Habib Ben Salem; Pierre Donze; Anne-Louise Maamouri; Henriette Méon; Éric Robin; Robert Rocchia; Laurence Froget

1997-01-01

276

Palinspastic reconstructions of southeastern Marlborough, New Zealand, for mid?Cretaceous?Eocene times  

Microsoft Academic Search

Southeastern Marlborough, New Zealand, preserves many complete sections through the Cretaceous\\/ Tertiary (K\\/T) boundary. Attempts to understand the paleogeography of these sections are hampered by the pervasive, Neogene deformation of the area associated with the propagation of the modern Pacific\\/Australian plate boundary through New Zealand. In this paper, we produce palinspastic maps of southeastern Marlborough for five intervals of Cretaceous

James Crampton; Malcolm Laird; Andrew Nicol; Dougal Townsend; Russell Van Dissen

2003-01-01

277

Darkness after the K-T impact: Effects of soot  

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

278

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

E-print Network

1 #12;2 The Chicxulub Impact and K-T Mass Extinction in Texas *Gerta Keller, Department spherule ejecta layer, a sea-level lowstand sandstone complex, and the K-T mass extinction. The newly from the original impact spherule layer. The third event is the K-T boundary mass extinction, which

Keller, Gerta

279

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

280

ORIGINAL PAPER Protungulatum, Confirmed Cretaceous Occurrence  

E-print Network

early Tertiary mammals appeared in North America a minimum of 300 k years before the extinction of non after the Cretaceous/Tertiary (K/T) boundary and also suggests that other reports of North American Late et al. 1986). This work argued that there were gradual rather than catastrophic extinctions

Archibald, J. David

281

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

NASA Technical Reports Server (NTRS)

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

Cisowski, Stanley M.

1988-01-01

282

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

283

Eventoestratigrafía del límite Cretácico\\/Terciario en Aïn Settara, Tunicia: ¿disminución de la productividad y\\/o de la oxigenación oceánicas?  

Microsoft Academic Search

The qualitative and quantitative study on benthic foraminifera from Aïn Setara (Tunisia) al- lows us to recognize qualitative and quantitative changes just at the Cretaceous\\/Tertiary boundary (K\\/T). Benthic foraminiferal extinction rate at Aïn Settara (21.5% of the species) is lower than plank- tic foraminiferal rate. Nevertheless, there is an important turnover in benthic foraminiferal assem- blages across the K\\/T boundary,

Laia Alegret; Ignacio Arenillas; José A. Arz; Eustoquio Molina

2002-01-01

284

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

285

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

Microsoft Academic Search

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

Susan M. Bush

1990-01-01

286

Chicxulub impact predates the K-T boundary mass extinction  

E-print Network

, a 100- m-thick impact (suevite) breccia overlies a 617-m-thick sequence of horizontally layered shallow (suevite) breccia consist primarily of clasts from these underlying shallow-water lithologies, some and spherules. The upper 15 m of the breccia are stratified with alternating layers of upward fining clasts (3

Keller, Gerta

287

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

USGS Publications Warehouse

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

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

1999-01-01

288

Independent Mammalian Genome Contractions Following the KT Boundary  

PubMed Central

Although it is generally accepted that major changes in the earth's history are significant drivers of phylogenetic diversification and extinction, such episodes may also have long-lasting effects on genomic architecture. Here we show that widespread reductions in genome size have occurred in multiple lineages of mammals subsequent to the Cretaceous–Tertiary (KT) boundary, whereas there is no evidence for such changes in other vertebrate, invertebrate, or land plant lineages. Although the mechanisms remain unclear, such shifts in mammalian genome evolution may be a consequence of an increase in the efficiency of selection against excess DNA resulting from post-KT population size expansions. Independent historical changes in genome architecture in diverse lineages raise a significant challenge to the idea that genome size is finely tuned to achieve adaptive phenotypic modifications and suggest that attempts to use phylogenetic analysis to infer ancestral genome sizes may be problematical. PMID:20333172

Rho, Mina; Zhou, Mo; Gao, Xiang; Kim, Sun; Tang, Haixu

2009-01-01

289

Independent mammalian genome contractions following the KT boundary.  

PubMed

Although it is generally accepted that major changes in the earth's history are significant drivers of phylogenetic diversification and extinction, such episodes may also have long-lasting effects on genomic architecture. Here we show that widespread reductions in genome size have occurred in multiple lineages of mammals subsequent to the Cretaceous-Tertiary (KT) boundary, whereas there is no evidence for such changes in other vertebrate, invertebrate, or land plant lineages. Although the mechanisms remain unclear, such shifts in mammalian genome evolution may be a consequence of an increase in the efficiency of selection against excess DNA resulting from post-KT population size expansions. Independent historical changes in genome architecture in diverse lineages raise a significant challenge to the idea that genome size is finely tuned to achieve adaptive phenotypic modifications and suggest that attempts to use phylogenetic analysis to infer ancestral genome sizes may be problematical. PMID:20333172

Rho, Mina; Zhou, Mo; Gao, Xiang; Kim, Sun; Tang, Haixu; Lynch, Michael

2009-01-01

290

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

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

291

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

NASA Technical Reports Server (NTRS)

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

Carpenter, Kenneth

1988-01-01

292

Chicxulub Impact and the Stratigraphy, Nature and Origin of Near-K-T Breccia  

NASA Astrophysics Data System (ADS)

Breccias with altered impact glass and located at or near the K-T boundary in Texas (USA), northern and southern Mexico, Belize, Guatemala, Haiti and Brazil are investigated to determine their age, stratigraphy and origin. Ages are variable. The oldest breccia deposit is within the uppermost Maastrichtian in the southern USA (Brazos, Texas), NE Mexico (e.g., Loma Cerca, El Penon) and in the Chicxulub impact crater cores on Yucatan (e.g., cores Yaxcopoil-1, Y6, C1). In all these sections, the geochemistry of glass within the breccias is identical and consistent with Chicxulub impact ejecta. The K-T boundary, Ir anomaly and mass extinction is located well above these impact breccia layers. This strongly supports a pre-K-T age for the Chicxulub impact, as also determined based on sedimentology, stratigraphy and paleontology. In NE Mexico and Texas the oldest Chicxulub impact spherule ejecta layer is interbedded in normal marine sedimentation in the upper Maastrichtian (base of CF1 Zone), about 300'000 year prior to the K-T boundary. All stratigraphically younger spherule ejecta layers represent repeated episodes of reworking and transport of the original layer during a sea-level regression and re- deposition in incised valleys in shallow environments (e.g., Brazos, Texas, La Popa Basin NE Mexico) and submarine canyons in deeper environments via mass flows and turbidites (e.g. Mimbral, Penon, Loma Cerca and many other section throughout NE Mexico). In southern Mexico, Belize and eastern Guatemala, the widespread thick microspherule and larger spheroid deposits are interbedded with breccia, microbreccias and conglomerates in the early Danian as a result of erosion in shallow carbonate platform sediments. The presence of early Danian planktic foraminifera in the matrix of the breccia, as well as within spherule clasts, indicate that redeposition occurred during the early Danian Parvularugoglobigerina eugubina (P1a) zone. In Haiti (Beloc sections), spherule deposits and microbreccias are also reworked together with late Maastrichtian microfossils and redeposited during the early Danian zone P1a. In NE Brazil (Poty Quarry) and Argentina (Neuquen Basin), the breccia layers identified as K-T age are also younger and deposited in the early Danian P1a and P1c zones, respectively. No extraterrestrial markers, such as glass, glass spherules or shocked quartz are present. These breccia and sandstone deposits thus represent normal sedimentary processes with deposition primarily linked to sea-level changes. However, an Ir anomaly is detected in the Early Danian P1a(1) subzone (100-200ky after the KT boundary) in southern Mexico (Coxquihui, Bochil), Guatemala (Actela), Haiti (Beloc) and Brasil (Poty). This suggests that the K-T transition was a time comet showers with current evidence of two large impacts, the pre-K-T Chicxulub impact and K-T impact, and smaller impacts in the early Danian and late Maastrichtian (Boltysh crater). The distribution of the K-T impact breccia is consistent with a multi-impact scenario.

Adatte, T.; Keller, G.; Berner, Z.; Stüben, D.

2007-05-01

293

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

294

Explosive Radiation of Malpighiales Supports a Mid?Cretaceous Origin of Modern Tropical Rain Forests  

Microsoft Academic Search

Fossil data have been interpreted as indicating that Late Cretaceous tropical forests were open and dry adapted and that mod- ern closed-canopy rain forest did not originate until after the Cretaceous-Tertiary (K\\/T) boundary. However, some mid-Cretaceous leaf floras have been interpreted as rain forest. Molecular divergence- time estimates within the clade Malpighiales, which constitute a large percentage of species in

2005-01-01

295

Sediments and Impact Rocks Filling the Boltysh Impact Crater  

Microsoft Academic Search

Ar-Ar dating of impact melts extracted from boreholes into the crater floor indicate that the Boltysh impact crater formed\\u000a on the Ukrainian Shield at 65.17±0.64 Ma, an age that is indistinguishable from that of the Cretaceous-Tertiary (K\\/T) boundary\\u000a and formation time of the giant Chicxulub impact crater. Unfortunately almost all information relating to the drilling along\\u000a with much of the

Eugene P. Gurov; Simon P. Kelley; Christian Koeberl; Natalia I. Dykan

296

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

NASA Technical Reports Server (NTRS)

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

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

2003-01-01

297

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

298

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

299

Princeton//9817 K.T. McDonald  

E-print Network

Princeton/µµ/98­17 K.T. McDonald November 5, 1998 Updated Feb. 5, 2000 Comments on Ionization Cooling 1 Introduction This note began in Oct. 1998 as a commentary on Sec. V of the Status Report [1 remarks, and corrects as error in Sec. 5. Section 2 presents a series of general comments on ionization

McDonald, Kirk

300

Princeton//98-17 K.T. McDonald  

E-print Network

Princeton//98-17 K.T. McDonald November 5, 1998 Updated Feb. 5, 2000 Comments on Ionization Cooling 1 Introduction This note began in Oct. 1998 as a commentary on Sec. V of the Status Report [1 remarks, and corrects as error in Sec. 5. Section 2 presents a series of general comments on ionization

McDonald, Kirk

301

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

USGS Publications Warehouse

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

Wingard, G. Lynn

1993-01-01

302

Inferring snow types from , SSA and kT (transform SSA and kT from diagnostic to prognostic variables of the model).  

E-print Network

· Inferring snow types from , SSA and kT (transform SSA and kT from diagnostic to prognostic on mesurable state variables. · Specific surface area (SSA): - quantifies the surface/mass ratio of snow-CT) · Thermal conductivity (kT): - related to snow type, grain size and bonds between grains - effective value

Ribes, Aurélien

303

The CretaceousTertiary Mass Extinction, Chicxulub Impact,  

E-print Network

-held belief in the Chicxulub impact as the sole or even major contributor to the KT mass extinction. The KT mass extinction may have been caused by these rapid and massive Deccan lava and gas eruptions studies on the Cretaceous­Tertiary (KT) mass extinction in the marine realm concentrated almost

Keller, Gerta

304

Late Maastrichtian and K\\/T paleoenvironment of the eastern Tethys (Israel): mineralogy, trace and platinum group elements, biostratigraphy and faunal turnovers  

Microsoft Academic Search

The late Maastrichtian to early Danian at Mishor Rotem, Israel, was examined based on geochemistry, bulk rock and clay mineralogies, biostratigraphy and lithology. This section contains four red clay layers of suspect impact or volcanic origin interbedded in chalk and marly chalks. PGE anomalies indicate that only the K\\/T boundary red layer has an Ir dominated PGE anomaly indicative of

THIERRY ADATTE; G ERTA KELLER; D ORIS STÜBEN; M ARKUS HARTING; U TZ KRAMAR; WOLFGANG STINNESBECK; S IGAL ABRAMOVICH

2005-01-01

305

Impact at the Permo-Triassic boundary: a critical evaluation.  

PubMed

The recognition in 1980 of a signature of an extraterrestrial impact at the Cretaceous-Tertiary boundary and its apparent involvement with the mass extinction generated considerable enthusiasm for impacts at other mass extinctions. Numerous claims of impact evidence for the Permo-Triassic mass extinction (251.6 Ma), the largest of the Phanerozoic mass extinctions, have generally been rejected, found wanting, or been difficult to reproduce. Despite this lack of repeatable support, considerable available evidence is consistent with an impact, including the rapidity of extinction, coincident carbon shift, and evident correlation between terrestrial and marine extinctions. However attractive the hypothesis, the coincidence with the Siberian flood basalts and the complex nature of the carbon shift are in conflict with an impact. The most intriguing possibility is that the greatest mass extinction of the Phanerozoic left signals very similar to the end-Cretaceous mass extinction but was produced by entirely Earth-bound processes. If true, this would tell us far more about the nature of ecosystems and how they fail than would identification of another impact. PMID:12804365

Erwin, Douglas H

2003-01-01

306

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

Microsoft Academic Search

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

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

2007-01-01

307

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

NASA Technical Reports Server (NTRS)

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

Caldeira, Ken; Rampino, Michael R.

1990-01-01

308

Radiation of Extant Marsupials After the K\\/T Boundary: Evidence from Complete Mitochondrial Genomes  

Microsoft Academic Search

The complete mitochondrial (mt) genomes of five marsupial species have been sequenced. The species represent all three South American orders (Didelphimorphia, Paucituberculata, and Microbiotheria). Phylogenetic analysis of this data set indicates that Didelphimorphia is a basal marsupial lineage followed by Paucituberculata. The South American microbiotherid Dromiciops gliroides (monito del monte) groups with Australian marsupials, suggesting a marsupial colonization of Australia

Maria A. Nilsson; Anette Gullberg; Angel E. Spotorno; Ulfur Arnason; Axel Janke

2003-01-01

309

Accelerated parallel imaging by transform coding data compression with k-t SENSE.  

PubMed

The theory and implementation of the k-t approach (k-t BLAST and k-t SENSE) are reviewed in the context of transform coding. The k-t approach exploits the information redundancy in typical time series of magnetic resonance images that depict anatomy and/or functional parameters. By utilizing this redundancy, it opens up the opportunity for significant acceleration, which in turn allows for scan time reduction, improvements in spatial or temporal resolution, or extended volume coverage for a given acquisition time. PMID:17946824

Tsao, Jeffrey; Hansen, Michael S; Kozerke, Sebastian

2006-01-01

310

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

USGS Publications Warehouse

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

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

1988-01-01

311

The Cometary Hypothesis of the K\\/t Mass Extinctions  

Microsoft Academic Search

The correlation of the extended period of biological mass extinctions around the KIT boundary with extraterrestrial amino acids in the sediment record constitutes strong evidence of a cometary cause. While the fact that the dinosaurs' extinction coincided with the Chixculub cratering event and iridium-rich sediments suggests a chance asteroidal or cometary impact, the enhanced input of extraterrestrial matter over 1

N. C. Wickramasinghe; M. K. Wallis

1994-01-01

312

The structure of the group G(k[t]): Variations on a theme of Soule  

E-print Network

The structure of the group G(k[t]): Variations on a theme of Soulâ??e Benedictus Margaux Abstract. Following Soulâ??e's ideas [14] we give a presentation of the abstract group G(k[t]) for any semisimple absolutely almost simple k--group. For G split, Soulâ??e [14] has given a presentation of the group G

313

ORIGINAL PAPER A. L. Huber M. Heuer K. T. Fehr K. Bente  

E-print Network

ORIGINAL PAPER A. L. Huber Æ M. Heuer Æ K. T. Fehr Æ K. Bente E. Schmidbauer Æ G. D. Bromiley. (1982), Haselton et al. (1987), Moe- cher and Chou (1990), Raudsepp et al. (1990), Perkins and Vielzeuf, Salzburg, on occasion of his 60th birthday A. L. Huber Æ K. T. Fehr (&) Æ E. Schmidbauer Department

Cambridge, University of

314

LTHOUGH EVOLUTIONARY SUCCESS IS A difficult if not im-possible concept to define, we believe we know it when we see it. This is the  

E-print Network

and possibly Antarctica by the time dinosaurs be- came extinct some 65 million years ago. Thus, they were (Kirchner and Weil, 2001). But even by about 10­15 million years after the Cretaceous/Tertiary (K/T

Archibald, J. David

315

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

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

316

The structure of the group G(k[t]): Variations on a theme of Soule  

E-print Network

The structure of the group G(k[t]): Variations on a theme of Soul´e Benedictus Margaux Abstract. Following Soul´e's ideas [14] we give a presentation of the abstract group G(k[t]) for any semisimple absolutely almost simple k­group. For G split, Soul´e [14] has given a presentation of the group G

317

T H I N K T A N K O N Enhancing Obesity  

E-print Network

T H I N K T A N K O N Enhancing Obesity Research at the National Heart,Lung, andBlood Institute U Institute #12;#12;T H I N K T A N K O N Enhancing Obesity Research at the National Heart,Lung, and with an unprecedented obesity epidemic--the solu- tion to which will be as complex in its nature as the epidemic itself

Bandettini, Peter A.

318

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

NASA Technical Reports Server (NTRS)

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

Boston, P. J.

1988-01-01

319

Inclusive-jet cross sections in NC DIS at HERA and a comparison of the kT, anti-kT and SIScone jet algorithms  

NASA Astrophysics Data System (ADS)

For the first time, differential inclusive-jet cross sections have been measured in neutral current deep inelastic ep scattering using the anti-kT and SIScone algorithms. The measurements were made for boson virtualities Q2 > 125GeV2 with the ZEUS detector at HERA using an integrated luminosity of 82 pb-1 and the jets were identified in the Breit frame. The performance and suitability of the jet algorithms for their use in hadron-like reactions were investigated by comparing the measurements to those performed with the kT algorithm. Next-to-leading-order QCD calculations give a good description of the measurements. Measurements of the ratios of cross sections using different jet algorithms are also presented; the measured ratios are well described by calculations including up to O (?s3) terms. Values of ?s (MZ) were extracted from the data; the results are compatible with and have similar precision to the value extracted from the kT analysis.

Abramowicz, H.; Abt, I.; Adamczyk, L.; Adamus, M.; Aggarwal, R.; Antonelli, S.; Antonioli, P.; Antonov, A.; Arneodo, M.; Aushev, V.; Aushev, Y.; Bachynska, O.; Bamberger, A.; Barakbaev, A. N.; Barbagli, G.; Bari, G.; Barreiro, F.; Bartsch, D.; Basile, M.; Behnke, O.; Behr, J.; Behrens, U.; Bellagamba, L.; Bertolin, A.; Bhadra, S.; Bindi, M.; Blohm, C.; Bo?d, T.; Boos, E. G.; Borodin, M.; Borras, K.; Boscherini, D.; Bot, D.; Boutle, S. K.; Brock, I.; Brownson, E.; Brugnera, R.; Brümmer, N.; Bruni, A.; Bruni, G.; Brzozowska, B.; Bussey, P. J.; Butterworth, J. M.; Bylsma, B.; Caldwell, A.; Capua, M.; Carlin, R.; Catterall, C. D.; Chekanov, S.; Chwastowski, J.; Ciborowski, J.; Ciesielski, R.; Cifarelli, L.; Cindolo, F.; Contin, A.; Cooper-Sarkar, A. M.; Coppola, N.; Corradi, M.; Corriveau, F.; Costa, M.; D'Agostini, G.; Corso, F. Dal; de Favereau, J.; del Peso, J.; Dementiev, R. K.; De Pasquale, S.; Derrick, M.; Devenish, R. C. E.; Dobur, D.; Dolgoshein, B. A.; Doyle, A. T.; Drugakov, V.; Durkin, L. S.; Dusini, S.; Eisenberg, Y.; Ermolov, P. F.; Eskreys, A.; Fang, S.; Fazio, S.; Ferrando, J.; Ferrero, M. I.; Figiel, J.; Forrest, M.; Foster, B.; Fourletov, S.; Gach, G.; Galas, A.; Gallo, E.; Garfagnini, A.; Geiser, A.; Gialas, I.; Gladilin, L. K.; Gladkov, D.; Glasman, C.; Gogota, O.; Golubkov, Yu. A.; Göttlicher, P.; Grabowska-Bo?d, I.; Grebenyuk, J.; Gregor, I.; Grigorescu, G.; Grzelak, G.; Gwenlan, C.; Haas, T.; Hain, W.; Hamatsu, R.; Hart, J. C.; Hartmann, H.; Hartner, G.; Hilger, E.; Hochman, D.; Holm, U.; Hori, R.; Horton, K.; Hüttmann, A.; Iacobucci, G.; Ibrahim, Z. A.; Iga, Y.; Ingbir, R.; Ishitsuka, M.; Jakob, H.-P.; Januschek, F.; Jimenez, M.; Jones, T. W.; Jüngst, M.; Kadenko, I.; Kahle, B.; Kamaluddin, B.; Kananov, S.; Kanno, T.; Karshon, U.; Karstens, F.; Katkov, I. I.; Kaur, M.; Kaur, P.; Keramidas, A.; Khein, L. A.; Kim, J. Y.; Kisielewska, D.; Kitamura, S.; Klanner, R.; Klein, U.; Koffeman, E.; Kollar, D.; Kooijman, P.; Korol, Ie.; Korzhavina, I. A.; Kota?ski, A.; Kötz, U.; Kowalski, H.; Kulinski, P.; Kuprash, O.; Kuze, M.; Kuzmin, V. A.; Lee, A.; Levchenko, B. B.; Levy, A.; Libov, V.; Limentani, S.; Ling, T. Y.; Lisovyi, M.; Lobodzinska, E.; Lohmann, W.; Löhr, B.; Lohrmann, E.; Loizides, J. H.; Long, K. R.; Longhin, A.; Lontkovskyi, D.; Lukina, O. Yu.; ?u?niak, P.; Maeda, J.; Magill, S.; Makarenko, I.; Malka, J.; Mankel, R.; Margotti, A.; Marini, G.; Martin, J. F.; Mastroberardino, A.; Matsumoto, T.; Mattingly, M. C. K.; Melzer-Pellmann, I.-A.; Miglioranzi, S.; Idris, F. Mohamad; Monaco, V.; Montanari, A.; Morris, J. D.; Musgrave, B.; Nagano, K.; Namsoo, T.; Nania, R.; Nicholass, D.; Nigro, A.; Ning, Y.; Noor, U.; Notz, D.; Nowak, R. J.; Nuncio-Quiroz, A. E.; Oh, B. Y.; Okazaki, N.; Oliver, K.; Olkiewicz, K.; Onishchuk, Yu.; Ota, O.; Papageorgiu, K.; Parenti, A.; Paul, E.; Pawlak, J. M.; Pawlik, B.; Pelfer, P. G.; Pellegrino, A.; Perlanski, W.; Perrey, H.; Piotrzkowski, K.; Plucinski, P.; Pokrovskiy, N. S.; Polini, A.; Proskuryakov, A. S.; Przybycie?, M.; Raval, A.; Reeder, D. D.; Reisert, B.; Ren, Z.; Repond, J.; Ri, Y. D.; Robertson, A.; Roloff, P.; Ron, E.; Rubinsky, I.; Ruspa, M.; Sacchi, R.; Salii, A.; Samson, U.; Sartorelli, G.; Savin, A. A.; Saxon, D. H.; Schioppa, M.; Schlenstedt, S.; Schleper, P.; Schmidke, W. B.; Schneekloth, U.; Schönberg, V.; Schörner-Sadenius, T.; Schwartz, J.; Sciulli, F.; Shcheglova, L. M.; Shehzadi, R.; Shimizu, S.; Singh, I.; Skillicorn, I. O.; S?omi?ski, W.; Smith, W. H.; Sola, V.; Solano, A.; Son, D.; Sosnovtsev, V.; Spiridonov, A.; Stadie, H.; Stanco, L.; Stern, A.; Stewart, T. P.; Stifutkin, A.; Stopa, P.; Suchkov, S.; Susinno, G.; Suszycki, L.; Sztuk, J.; Szuba, D.; Szuba, J.; Tapper, A. D.; Tassi, E.; Terrón, J.; Theedt, T.; Tiecke, H.; Tokushuku, K.; Tomalak, O.; Tomaszewska, J.; Tsurugai, T.; Turcato, M.; Tymieniecka, T.; Uribe-Estrada, C.; Vázquez, M.; Verbytskyi, A.; Viazlo, V.; Vlasov, N. N.; Volynets, O.; Walczak, R.; Wan Abdullah, W. A. T.; Whitmore, J. J.; Whyte, J.; Wiggers, L.; Wing, M.; Wlasenko, M.; Wolf, G.; Wolfe, H.; Wrona, K.; Yagües-Molina, A. G.; Yamada, S.; Yamazaki, Y.; Yoshida, R.; Youngman, C.; ?arnecki, A. F.; Zawiejski, L.; Zenaiev, O.; Zeuner, W.; Zhautykov, B. O.; Zhmak, N.; Zhou, C.; Zichichi, A.; Zolko, M.; Zotkin, D. S.; Zulkapli, Z.; ZEUS Collaboration

2010-07-01

320

Nuclear k_T in d+Au Collisions from Multiparticle Jet Reconstruction at STAR  

E-print Network

This paper presents the most recent nuclear k_T measurements from STAR derived from multiparticle jet reconstruction of d+Au and p+p collisions at sqrt(s)=200 GeV. Since jets reconstructed from multiple particles are relatively free of fragmentation biases, nuclear k_T can be measured with greater certainty in this way than with traditional di-hadron correlations. Multi-particle jet reconstruction can also be used for a direct measurement of the fragmentation function.

Thomas Henry

2005-11-01

321

Paleontological and Mineralogical Evidence for a Single K/T Extinction Impact at Chicxulub  

NASA Astrophysics Data System (ADS)

We integrate the Chicxulub impact, global Ir radiation, condensate mineralogy, and the N.J. coastal plain (USA) record of post-K/T life at ~25 m water depth: ~50 yr delayed Cretaceous filter-feeder death; no life; and life's return in the Paleogene.

Ebel, D. S.; Mac Low, M.-M.; Landman, N. H.

2008-03-01

322

RESEARCH Open Access Acceleration of tissue phase mapping by k-t  

E-print Network

and quantitative motion information in three directions. Today, whole volume coverage of the heart by TPM encoding of the heart. Different k-t factors were evaluated with respect to their impact on the quantitative assessment detailed assessment of cer- tain myocardial diseases such as cardiac insufficiency. A major limitation

Boyer, Edmond

323

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

324

Constraining mass accumulation rates across the Cretaceous-Paleogene boundary clay layer using extraterrestrial helium-3  

NASA Astrophysics Data System (ADS)

The extended duration of the negative ?13C excursion observed in marine carbonates spanning the Cretaceous-Paleogene (K-Pg) mass extinction event has lead to two main hypothesized post-extinction models ("Strangelove" and "Living Ocean";[1, 2]) for the status of marine primary productivity and the global carbon cycle. However, these models are largely inconsistent with recent paleontological and geochemical evidence suggesting heterogeneous changes in marine productivity and carbon export [3, 4]. While the analysis of lipid biomarkers in the cosmopolitan boundary clay layer allows us to assess changes in primary production by non-calcifying organisms in the immediate aftermath of the mass extinction [4], our poor understanding of the deposition of the clay layer precludes a more detailed reconstruction of short-term variations in marine ecosystem resilience. Here, we present data on extraterrestrial 3He derived from interplanetary dust particles used as a constant flux proxy to constrain fluctuations in mass accumulation rates (MARs) [5] and the duration of the boundary clay deposition in three classic and expanded K-Pg boundary sections: El Kef (Tunisia), Caravaca (Spain), and Kulstirenden (Denmark). Our results from different depositional environments indicate average durations for the sedimentation of the clay layer that are comparable (~10 kyr) to other localities [5], thus confirming its globally brief deposition. Early Paleogene MARs vary among locations when compared to background Late Cretaceous values and do not strictly follow carbonate content as traditionally assumed, thus suggesting variable depositional conditions at different locations. Changes in sediment MARs across the K-Pg will be used to calculate MARs of algal- and bacterial-derived biomarkers, as well as benthic foraminifera, in order to assess the timing and global nature of the recovery of marine primary production and carbon export. 1. Hsu, K.J., He, Q., Mckenzie, J.A., Weissert, H., Perchnielsen, K., Oberhansli, H., Kelts, K., Labrecque, J., Tauxe, L., Krahenbuhl, U., et al. (1982). Mass Mortality and Its Environmental and Evolutionary Consequences. Science 216, 249-256. 2. D'hondt, S. (1998). Organic carbon fluxes and ecological recovery from the Cretaceous-Tertiary mass extinction (vol 282, pg 276, 1998). Science 282, 1051-1051. 3. Alegret, L., Thomas, E., and Lohmann, K.C. (2012). End-Cretaceous marine mass extinction not caused by productivity collapse. P Natl Acad Sci USA 109, 728-732. 4. Sepulveda, J., Wendler, J.E., Summons, R.E., and Hinrichs, K.U. (2009). Rapid Resurgence of Marine Productivity After the Cretaceous-Paleogene Mass Extinction. Science 326, 129-132. 5. Mukhopadhyay, S., Farley, K.A., and Montanari, A. (2001). A short duration of the Cretaceous-Tertiary boundary event: Evidence from extraterrestrial helium-3. Science 291, 1952-1955.

Giron, M.; Sepulveda, J.; Mukhopadhyay, S.; Alegret, L.; Summons, R. E.

2012-12-01

325

Pressure contact probe for resistivity measurements in the temperature range 77 K<200 K  

Microsoft Academic Search

We have designed and built a sample probe that is particularly well suited for measuring the resistivity and superconducting transition temperature Tc of bulk high-Tc materials of nonuniform shape, in the temperature range 77 K<200 K. The probe uses spring-loaded indium pressure contacts and allows electrical contact to be made without altering or contaminating the sample. The probe is relatively

T. M. Tritt; A. C. Ehrlich; H. S. Davis

1989-01-01

326

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

NASA Technical Reports Server (NTRS)

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

Bohor, Bruce F.; Betterton, William J.

1993-01-01

327

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

NASA Astrophysics Data System (ADS)

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

Bohor, Bruce F.; Betterton, William J.

1993-03-01

328

Correction to "Parametric Resonance in Immersed Elastic Boundaries"  

E-print Network

to polar coordinates. This led to an error in the perturbation expansion of the immersed boundary forcing equation in Claim 1 to (^z · � f(1) ) = K(t)(X ss + Xr s ) r(r - 1) r - K(t)(Xr sss - X ss) (r - 1) r) of the circular fiber. The blue points denote harmonic modes and 2 #12;Figure A: Original stability contours

Stockie, John

329

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

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

330

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

331

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.

332

Discovery and focused study of the Chicxulub impact crater  

NASA Astrophysics Data System (ADS)

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

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

2011-06-01

333

Modeling study of infrasonic detection of 1 kT atmospheric blast  

SciTech Connect

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

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

1998-12-31

334

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

335

Bio-events in the continental realm during the Cretaceous/Tertiary transition: a multidisciplinary approach  

NASA Astrophysics Data System (ADS)

This study is a short progress report of a multidisciplinary cooperation. It deals with animal and plant biotas found in five nonmarine Maastrichtian-Paleocene sequences in southern Europe (southern France, north-east Spain). In addition, contributions on North America charophyte floras are taken into account.

Feist, Monique

336

Early Cretaceous &Tertiary metamorphic events of the Pelagonian Zone in the E. Thessaly area, Greece  

NASA Astrophysics Data System (ADS)

The area occupied by what is known as the Pelagonian Zone is composed of several tectonic units showing different Alpine tectonometamorphic evolution. The lowermost unit is exposed as tectonic window in the Olympos and Ossa area and has been affected by a low grade metamorphism of post-Eocene age. Two main tectonometamorphic units are exposed as nappes over the Olympos window: the Makrynitsa-Ambelakia Unit (relevant to the Cyclades Blueschist Unit), and the Pelagonian Nappe. They show dominant differences on their mineral parageneses and, consequently, the P-T path during their metamorphic evolution. The Ambelakia-Makrynitsa Unit has experienced a Late Cretaceous/Early Tertiary HP/LT metamorphism. In glaucophane-bearing rocks glaucophane is in equilibrium with lawsonite, phengite (Si=3.55), chlorite and sphene defining a lawsonite blueschist facies metamorphism at T~280 0C and P~9 kbar. This HP/LT metamorphism had been terminated by 54 Ma (Lips et al., 1998). On the contrary, the Pelagonian Nappe provides evidence of two main Alpine metamorphic events. The first one of albite-epidote-amphibolite facies at T~ 500-550 0C and P~10-11 kbar led to the formation of garnet with prograde zoning pattern, coexisting with phengite, barroisite/Na-rich hornblende, epidote and albite. Rb-Sr phengite-whole rock dating on phengite biotite gneisses from the Ossa area yielded Early Cretaceous ages (114-110 Ma) for this metamorphic event. It is related to the obduction of the Axios ophiolites over the Pelagonian microcontinent. Riebeckite/glaucophane, stilpnomelane, chlorite and phengite neoblasts characterize the second metamorphic event at HP/LT conditions that is contemporaneous with the HP/LT metamorphism of the Makrynitsa-Ambelakia Unit. It is related to underthrusting of the Makrynitsa-Ambelakia Unit under the Pelagonian microcontinent. A retrograde greenschist facies overprinting affected both units during exhumation. Lips, A.L.W., White, S.H., Wijbrans, J.R., 1998: Tectonophysics, 298, 133-153.

Perraki, M.; Hoinkes, G.; Mposkos, E.; Thoeni, M.

2003-04-01

337

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

338

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

SciTech Connect

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

Genik, G.J. (Exxon Exploration Co., Houston, TX (United States))

1993-08-01

339

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

2011-09-01

340

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

NASA Technical Reports Server (NTRS)

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

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

1981-01-01

341

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

NASA Technical Reports Server (NTRS)

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

Pope, Kevin O.

1996-01-01

342

Accelerated dynamic cardiac MRI exploiting sparse-Kalman-smoother self-calibration and reconstruction (k??-??t SPARKS).  

PubMed

Accelerated dynamic MRI, which exploits spatiotemporal redundancies in k??-??t space and coil dimension, has been widely used to reduce the number of signal encoding and thus increase imaging efficiency with minimal loss of image quality. Nonetheless, particularly in cardiac MRI it still suffers from artifacts and amplified noise in the presence of time-drifting coil sensitivity due to relative motion between coil and subject (e.g. free breathing). Furthermore, a substantial number of additional calibrating signals is to be acquired to warrant accurate calibration of coil sensitivity. In this work, we propose a novel, accelerated dynamic cardiac MRI with sparse-Kalman-smoother self-calibration and reconstruction (k??-??t SPARKS), which is robust to time-varying coil sensitivity even with a small number of calibrating signals. The proposed k??-??t SPARKS incorporates Kalman-smoother self-calibration in k??-??t space and sparse signal recovery in x??-???f space into a single optimization problem, leading to iterative, joint estimation of time-varying convolution kernels and missing signals in k??-??t space. In the Kalman-smoother calibration, motion-induced uncertainties over the entire time frames were included in modeling state transition while a coil-dependent noise statistic in describing measurement process. The sparse signal recovery iteratively alternates with the self-calibration to tackle the ill-conditioning problem potentially resulting from insufficient calibrating signals. Simulations and experiments were performed using both the proposed and conventional methods for comparison, revealing that the proposed k??-??t SPARKS yields higher signal-to-error ratio and superior temporal fidelity in both breath-hold and free-breathing cardiac applications over all reduction factors. PMID:25884383

Park, Suhyung; Park, Jaeseok

2015-05-01

343

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

344

Pulse-tube dilution refrigeration below 10 mK T. Prouve, H. Godfrin, C. Gian`ese,  

E-print Network

Pulse-tube dilution refrigeration below 10 mK T. Prouv´e, H. Godfrin, C. Gian`ese, S. Triqueneaux´emenci`ere, 38360 Sassenage, France We report the design, realization and performance of dilution refrigerators makes this new type of refrigerators particularly versatile. The system provides relatively high cooling

Paris-Sud XI, Université de

345

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

E-print Network

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

Paris-Sud XI, Université de

346

Temperature dependence of the Raman spectra of single-wall carbon H. D. Li, K. T. Yue,a)  

E-print Network

of carbonaceous materials including carbon fiber,4 highly ori- ented pyrolytic graphite HOPG ,5 disordered carbonTemperature dependence of the Raman spectra of single-wall carbon nanotubes H. D. Li, K. T. Yue-wall carbon nanotubes SWCNTs were measured at different temperatures by varying the incident laser power

Wang, Zhong L.

347

K.T. McDonald June 18, 2009 DUSEL Workshop @ FNAL 1 Strategies for Liquid Argon Detectors at DUSEL  

E-print Network

K.T. McDonald June 18, 2009 DUSEL Workshop @ FNAL 1 Strategies for Liquid Argon Detectors at DUSEL proposal is to build a 5 kton liquid argon detector for use at that time. However, that size is too small desire a giant liquid argon detector in its first round of accelerator neutrino physics. We should rise

McDonald, Kirk

348

Plastic flow localization in bulk tungsten with ultrafine microstructure Q. Wei, K. T. Ramesh, and E. Maa  

E-print Network

Plastic flow localization in bulk tungsten with ultrafine microstructure Q. Wei, K. T. Ramesh localization is demonstrated in bulk tungsten W of commercial purity under dynamic uniaxial compression energy penetrators.2­4 However, pure body-centered cubic metals and especially tungsten W are notoriously

Wei, Qiuming

349

The structure of the group G (k[t]): Variations on a theme of Soul'e  

E-print Network

of Soul'e Benedictus Margaux Abstract. Following Soul'e's ideas [14] we almost s* *imple k-group. For G split, Soul'e [14] has given a presentation of the group G (k is to provide a presentation of G (k[t]) in the general case. We will follow Soul'e's original ideas

350

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

E-print Network

and TechnologyNuclear Science and Technology (FNST). 4 #12;FNST is the science, engineering, technology and materials Fusion Nuclear Science & Technology (FNST) FNST is the science, engineering, technologyBl k t T h l F l C l dBlanket Technology, Fuel Cycle and Tritium Self Sufficiency M h d Abd

Abdou, Mohamed

351

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

E-print Network

Fluid acceleration effects on suspended sediment transport in the swash zone J. A. Puleo, K. T. [1] Suspended sediment concentrations and fluid velocities measured in the swash zone of a high transport. Swash flow acceleration was nearly constant at about one-half downslope gravitational

Slinn, Donald

352

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

E-print Network

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

Laughlin, David E.

353

Blast From the Past  

NSDL National Science Digital Library

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

354

Kaon Electromagnetic Form Factor within the $k_T$ Factorization Formalism and It's Light-Cone Wave Function  

E-print Network

We present a systematical study on the kaon electromagnetic form factors $F_{K^{\\pm},K^0,\\bar{K}^0}(Q^2)$ within the $k_T$ factorization formalism, where the transverse momentum effects, the contributions from the different helicity components and different twist structures of the kaon light-cone (LC) wave function are carefully analyzed for giving a well understanding of the hard contributions at the energy region where pQCD is applicable. The right power behavior of the hard contribution from the higher helicity components and from the higher twist structures can be obtained by keeping the $k_T$ dependence in the hard amplitude. Our results show that the $k_T$ dependence in LC wave function affects the hard and soft contributions substantially and the power-suppressed terms (twist-3 and higher helicity components) make an important contribution below $Q^2\\sim several GeV^2$ although they drop fast as $Q^2$ increasing. The parameters of the proposed model wave function can be fixed by the first two moments of its distribution amplitude and other conditions. By varying the first two moments $a^K_1(1GeV)$ and $a^K_2(1GeV)$ with the region of $0.05\\pm0.02$ and $0.10\\pm 0.05$ respectively, we find that the uncertainty of the kaon electromagnetic form factor is rather small.

Xing-Gang Wu; Tao Huang

2008-04-11

355

Mass extinctions in the deep sea  

NASA Technical Reports Server (NTRS)

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

Thomas, E.

1988-01-01

356

Geologic Time Scale 2010 1 Minority Science Programs School of Biological Sciences University of California, Irvine  

E-print Network

Cretaceous Cretaceous-Tertiary (K-T) extinction 65 0.65 Cenozoic Tertiary First primates (monkeys) 55 0? Fishes, amphibians, reptiles. 5. What major event marked the end of the Paleozoic Era? A mass extinction.43 Paleozoic Ordovician First fishes (jawless) 455 4.55 Paleozoic Silurian Ordivician extinction (2nd most

Rose, Michael R.

357

What's news about the Deccan traps emplacement ? An attempt to estimate the eruptive sequence of lava emplacement  

Microsoft Academic Search

Synchronism between Large Igneous Provinces formations and mass extinctions along the Phanerozoic is clearly evidenced and suggests that LIPs could be deeply involved in such environmental crisis. As example, the Cretaceous-Tertiary (K-T) mass extinction coincides with the emplacement of the Deccan continental flood basalts. However the climatic and environmental impact of the traps emplacement is not well known. One reason

A. Chenet; V. Courtillot; F. Fluteau; J. Besse; K. Subbarao; S. Khadri

2005-01-01

358

Definitive fossil evidence for the extant avian radiation in the Cretaceous.  

PubMed

Long-standing controversy surrounds the question of whether living bird lineages emerged after non-avian dinosaur extinction at the Cretaceous/Tertiary (K/T) boundary or whether these lineages coexisted with other dinosaurs and passed through this mass extinction event. Inferences from biogeography and molecular sequence data (but see ref. 10) project major avian lineages deep into the Cretaceous period, implying their 'mass survival' at the K/T boundary. By contrast, it has been argued that the fossil record refutes this hypothesis, placing a 'big bang' of avian radiation only after the end of the Cretaceous. However, other fossil data--fragmentary bones referred to extant bird lineages--have been considered inconclusive. These data have never been subjected to phylogenetic analysis. Here we identify a rare, partial skeleton from the Maastrichtian of Antarctica as the first Cretaceous fossil definitively placed within the extant bird radiation. Several phylogenetic analyses supported by independent histological data indicate that a new species, Vegavis iaai, is a part of Anseriformes (waterfowl) and is most closely related to Anatidae, which includes true ducks. A minimum of five divergences within Aves before the K/T boundary are inferred from the placement of Vegavis; at least duck, chicken and ratite bird relatives were coextant with non-avian dinosaurs. PMID:15662422

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

2005-01-20

359

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. PMID:21752814

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

2011-01-01

360

Production of $c \\bar c$ pairs at LHC: $k_t$-factorization and double-parton scattering  

E-print Network

We discuss charm production at LHC. The production of single $c \\bar c$ pairs is calculated in the $k_t$-factorization approach. We use several unintegrated gluon distributions from the literature. Differential distributions for several charmed mesons are presented and compared to recent results of the ALICE and LHCb collaborations. Some missing strength can be observed. Furthermore we discuss production of two $c \\bar c$ pairs within a simple formalism of double-parton scattering (DPS). Surprisingly large cross sections, comparable to single-parton scattering (SPS) contribution to $c \\bar c$ production, are predicted for LHC energies.

Antoni Szczurek

2012-06-01

361

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

362

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

PubMed

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

Xiao, Dan; Balcom, Bruce J

2014-06-01

363

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

NASA Astrophysics Data System (ADS)

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

Xiao, Dan; Balcom, Bruce J.

2014-06-01

364

On the undersampling strategies to accelerate time-resolved 3D imaging using k-t-GRAPPA.  

PubMed

The purpose of this study was to explore how to optimally undersample and reconstruct time-resolved 3D data using a k-t-space-based GRAPPA technique. The performance of different reconstruction strategies was evaluated using data sets with different ratios of phase (N(y)) and partition (N(z)) encoding lines (N(y) × N(z) = 64-128 × 40-64) acquired in a moving phantom. Image reconstruction was performed for different kernel configurations and different reduction factors (R = 5, 6, 8, and 10) and was evaluated using regional error quantification and SNR analysis. To analyze the temporal fidelity of the different kernel configurations in vivo, time-resolved 3D phase contrast data were acquired in the thoracic aorta of two healthy volunteers. Results demonstrated that kernel configurations with a small kernel extension yielded superior results especially for more asymmetric data matrices as typically used in clinical applications. The application of k-t-GRAPPA to in vivo data demonstrated the feasibility of undersampling of time-resolved 3D phase contrast data set with a nominal reduction factors of up to R(net) = 8, while maintaining the temporal fidelity of the measured velocity field. Extended GRAPPA-based parallel imaging with optimized multidimensional reconstruction kernels has the potential to substantially accelerate data acquisitions in time-resolved 3D MRI. PMID:21437975

Jung, Bernd; Stalder, Aurélien F; Bauer, Simon; Markl, Michael

2011-10-01

365

Effect of environmental variables on body size evolution of crinoids between periods of mass extinctions  

NASA Astrophysics Data System (ADS)

Body size plays a major role in determining whether or not an organism can sustain in its local environment. The ecosystem of an animal has a major effect on the fitness of organisms, and it would be interesting to note the degree to which various environmental factors alter body size. In my project, I identify three environmental factors that seem to affect body size of crinoids, marine invertebrates from phylum Echinodermata, and explore how these variables play out in the intervals between the five mass extinctions. The particular factors I study include atmospheric CO2 concentration (proxy for temperature), O2 concentration, and sea level. Although the r and p values for all of these factors were statistically insignificant to definitively make any correlation, there was a visual correlation. For O2, I noted a generally positive correlation with body size over time. CO2 trends suggested a negative correlation until the K-T boundary, but a positive correlation afterwards. Correlation with sea level was a little more complicated: correlation was positive from the start of the Phanerozoic to the Permian extinction; it turned negative until the Cretaceous-Tertiary boundary; afterwards, it again became positive. However, for all three variables, statistical values are too low to say definitively mark any correlation. Out of all three factors, CO2 levels had the highest correlation and lowest p-values in the most time intervals: from the start of the Phanerozoic to Ordovician-Silurian Extinction, from the Late Devonian to the Permian Extinction, and from the Cretaceous-Tertiary boundary to the present. When considering first differences, CO2 levels also had the highest correlation from the Permian Extinction to Triassic-Jurassic Extinction and from the Triassic-Jurassic Extinction to Cretaceous-Tertiary Extinction. Using PaleoTS, I found that body size evolution patterns either seemed to follow either an unbiased random walk (URW) or stasis in the intervals between mass extinctions. Put together, these results suggest that environmental factors may have an effect of body size, but it may be the consequence of several environmental factors in conjunction. That is a correlation between body size and an individual environmental factor is hard to determine, but several biotic and abiotic factors may work interdependently to alter body size of crinoids.

Jani, T.; Heim, N. A.; Payne, J.

2013-12-01

366

Iridium abundance measurements across bio-event horizons in the geological record  

NASA Technical Reports Server (NTRS)

Geochemical studies have been performed on thousands of rock samples collected across bio-event horizons in the fossil record using INAA for about 40 common and trace elements and radiochemical isolation procedures for Os, Ir, Pt, and Au on selected samples. These studies were begun soon after the Alvarez team announced their discovery of the Cretaceous-Tertiary (K-T) Ir anomaly in marine rock sequences in Europe. With their encouragement the Authors searched for the anomaly in nearby continental (freshwater coal swamp) deposits. In collaboration with scientists from the U.S.G.S. in Denver, the anomaly was located and it was observed that a floral crisis occurred at the same stratigraphic position as the Ir spike. Further work in the Raton Basin has turned up numerous well-preserved K-T boundary sections. Although the Authors have continued to study the K-T boundary and provide geochemical measurements for other groups trying to precisely locate it, the primary effort was turned to examining the other bio-events in the Phanerozoic, especially to those that are older than the terminal Cretaceous. A list of horizons that were examined in collaboration with paleontologists and geologists is given. Results are also given and discussed.

Orth, C. J.; Attrep, M., Jr.

1988-01-01

367

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. PMID:11958716

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

2002-01-01

368

k_T factorization is violated in production of high-transverse-momentum particles in hadron-hadron collisions  

E-print Network

We show that hard-scattering factorization is violated in the production of high-p_T hadrons in hadron-hadron collisions, in the case that the hadrons are back-to-back, so that k_T factorization is to be used. The explicit counterexample that we construct is for the single-spin asymmetry with one beam transversely polarized. The Sivers function needed here has particular sensitivity to the Wilson lines in the parton densities. We use a greatly simplified model theory to make the breakdown of factorization easy to check explicitly. But the counterexample implies that standard arguments for factorization fail not just for the single-spin asymmetry but for the unpolarized cross section for back-to-back hadron production in QCD in hadron-hadron collisions. This is unlike corresponding cases in e^+e^- annihilation, Drell-Yan, and deeply inelastic scattering. Moreover, the result endangers factorization for more general hadroproduction processes.

John Collins; Jian-Wei Qiu

2007-06-28

369

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

E-print Network

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

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

2008-11-02

370

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

PubMed Central

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

2012-01-01

371

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

372

Comet impacts and chemical evolution on the bombarded earth  

NASA Technical Reports Server (NTRS)

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

Oberbeck, Verne R.; Aggarwal, Hans

1992-01-01

373

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

Microsoft Academic Search

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

Dimitris Nikolos; Alexandros Krokos

1992-01-01

374

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

NASA Astrophysics Data System (ADS)

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

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

2006-06-01

375

Rock-magnetic properties of the Cretaceous\\/Tertiary Micara Formation in the Guantánamo area, eastern Cuba  

Microsoft Academic Search

SI. Las intensidades de NRM e IRM son de cerca de 7 mA\\/m y 7 A\\/m. El horizonte de 12 m se caracteriza por intensidades de NRM e IRM de 14 mA\\/m y 22 A\\/m, respectivamente, mientras que el horizonte de 20 m presenta valores del orden de 16 mA\\/m y 3 A\\/m, respectivamente. La anomalía magnética a los 4

J. Urrutia-Fucugauchi; J. Pérez-Lazo; M. Fundora; J. M. Espíndola

1998-01-01

376

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

E-print Network

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

Rogers, John A.

377

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

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

378

Projectile-target mixing in melted ejecta formed during a hypervelocity impact cratering event  

NASA Technical Reports Server (NTRS)

Tektites contain little to no projectile contamination while, in contrast, some distal ejecta deposits can be relatively projectile-rich (e.g. the Cretaceous-Tertiary (K-T) boundary clay). This compositional difference motivated an experimental study of hypervelocity target-projectile mixing processes. We hope to scale up the results from these experiments and apply them to terrestrial impact structures like the Chicxulub Crater, Yucutan, Mexico, the leading contender as the site for the impact that caused the mass extinction that marks the K-T boundary. Shock decomposition of the approximately 500m thickness of anhydrite, or greater thickness of limestone, in the target rocks at Chicxulub may have been a critical mechanism for either global cooling via SO3, and subsequently H2SO4, formation, or possibly, global warming via increased CO2 formation. Understanding target-projectile mixing processes during hypervelocity impact may permit more accurate estimates of the amount of potentially toxic, target-derived material reaching stratospheric heights.

Evans, Noreen Joyce; Ahrens, Thomas J.; Shahinpoor, M.; Anderson, W. W.

1993-01-01

379

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

NASA Technical Reports Server (NTRS)

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

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

1996-01-01

380

Boundary issues  

NASA Astrophysics Data System (ADS)

What is our point of no return? Caesar proclaimed 'the die is cast' while crossing the Rubicon, but rarely does modern society find so visible a threshold in our continued degradation of ecosystems and the services they provide. Humans have always used their surroundings to make a living— sometimes successfully, sometimes not (Diamond 2005)—and we intuitively know that there are boundaries to our exploitation. But defining these boundaries has been a challenge since Malthus first prophesied that nature would limit the human population (Malthus 1798). In 2009, Rockström and colleagues tried to quantify what the 6.8 billion (and counting) of us could continue to get away with, and what we couldn't (Rockström et al 2009). In selecting ten 'planetary boundaries', the authors contend that a sustainable human enterprise requires treating a number of environmental thresholds as points of no return. They suggest we breach these Rubicons at our own peril, and that we've already crossed three: biodiversity loss, atmospheric CO2, and disruption of the global nitrogen (N) cycle. As they clearly hoped, the very act of setting targets has provoked scientific inquiry about their accuracy, and about the value of hard targets in the first place (Schlesinger 2009). Such debate is a good thing. Despite recent emphasis on the science of human-ecosystem interactions, understanding of our planetary boundaries is still in its infancy, and controversy can speed scientific progress (Engelhardt and Caplan 1987). A few weeks ago in this journal, Carpenter and Bennett (2011) took aim at one of the more controversial boundaries in the Rockström analysis: that for human alteration of the global phosphorus (P) cycle. Rockström's group chose riverine P export as the key indicator, suggesting that humans should not exceed a value that could trigger widespread marine anoxic events—and asserting that we have not yet crossed this threshold. There are defensible reasons for a marine-centric boundary (Filippelli 2008, Handoh and Lenton 2003). However, human alteration of the P cycle has multiple potential boundaries (figure 1), including P-driven freshwater eutrophication (Smith and Schindler 2009), the potential for world P supply to place an ultimate limit on food production (Smil 2000, Childers et al 2011), and depletion of soil P stocks in some world regions (MacDonald et al 2011). Carpenter and Bennett revisit the P boundary from the freshwater eutrophication perspective. Given the extraordinary variation in freshwater ecosystems across the globe, this is a challenging task, but the authors strengthen their analysis by using three different boundaries with relevance to eutrophication, along with two water quality targets and a range of estimates of P flow to the sea. In doing so, they make a compelling case that if freshwater eutrophication is indeed a Rubicon, we have already crossed it. Importantly, Carpenter and Bennett go beyond the calculation of new boundaries to make broader points about humanity's relationship with the P cycle. Disruptions of both the P and N cycles are mostly about our need for food (Galloway et al 2008, Cordell et al 2009), but unlike N, P supplies are finite and irreplaceable. Environmental concerns aside, we can fix all the N2 from the atmosphere we want—but deplete our economically viable P reserves and we're in trouble. Figure 1 Figure 1. Human alteration of the global P cycle has multiple possible boundaries. These include the environmental risks posed by freshwater eutrophication and marine anoxic events, and the food security risks that come from depletion of soil P stocks in some world regions, as well as finite global supplies of high-value mineral P reserves. Photo credits beyond authors: upper left, Shelby Riskin; upper right, Pedro Sanchez. In effect, Carpenter and Bennett argue that among P's multiple boundaries, the one for freshwaters is less forgiving of our current activities (but no less important) than is the one for oceans. Encouragingly, while they argue that we've already crossed one key bound

Townsend, Alan R.; Porder, Stephen

2011-03-01

381

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

382

A. T. Motta, 1 K. T. Erwin, 10. Delaire, 1 R. C. Birtcher, 2 Y Chu,3 J. Maser, 3 D. C. Mancini, 3 and B. LaP  

E-print Network

A. T. Motta, 1 K. T. Erwin, 10. Delaire, 1 R. C. Birtcher, 2 Y Chu,3 J. Maser, 3 D. C. Mancini, 3 in REFERENCE: Motta, A. T., Erwin, K. T., Delaire, O., Birtcher, R. C., Chu, Y., Maser, J., Mancini, D. C

Motta, Arthur T.

383

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. PMID:18779562

?engör, A. M. Celâl; Atayman, Saniye; Özeren, Sinan

2008-01-01

384

Large Deep-Ocean Impacts, Sea-Floor Hiatuses, and Apparent Short Term Sea-Level Changes  

NASA Astrophysics Data System (ADS)

Widespread discontinuities and unconformities in deep-sea sedimentary records (hiatuses) often correspond to rapid fluctuations in eustatic sea level. Such global paleoceanographic events have been attributed to vertical tectonic movements, to changes in ocean basin configuration and volume, and to glacial versus non-glacial climates. Alternatively, megatsunami waves generated by large deep-ocean impacts cause widespread erosion of the sea floor centered on the impact site. At the shoreline, run-up heights can exceed 1 km on a global scale. These high-energy events might be the source of some sea-floor hiatuses as well as stratigraphic intervals currently interpreted as short-term regression and transgression (r-t) pulses in sea level. A widespread hiatus, probable impact ejecta, ocean chemistry and sediment changes, and r-t pulse occurring at ~68-67 Ma indicate that a large oceanic impact might have preceded the Chicxulub impact by a few million years. The hiatus proximal to the Cretaceous-Tertiary (K-T) boundary is most pronounced in the northern Pacific basin and, because tsunami amplitude is proportional to water depth, could not have been caused by the shallow-water (<=100 m) Chicxulub impact at ~65 Ma. Thus K-T time likely experienced two large bolide impacts, one of which occurred in the deep ocean.

Hagstrum, J. T.

2001-12-01

385

Evolutionary and Ecological Sequelae of Mass Extinctions: Examples From the Continental Triassic-Jurassic Boundary  

Microsoft Academic Search

The Triassic-Jurassic boundary at ˜200 Ma marks one of the five major mass-extinctions of the Phanerozoic and, depending on the metrics used, was similar in magnitude to the K-T mass extinction. In continental environments about 50% of all tetrapod families are eliminated and although floral diversity change is difficult to gauge, a similar proportion of palynomorph taxa disappear at the

P. E. Olsen; J. H. Whiteside

2003-01-01

386

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

387

Geological Society of America Special Paper 307  

E-print Network

Geological Society of America Special Paper 307 1996 A model ofthe Chicxulub impact basin based sought-after source of the ejecta found world- wide at the Cretaceous-Tertiary (K!f) boundary terrestrial craters. This assemblage comprises suevite breccias, ejecta deposit breccias (Bunte Breccia

Spudis, Paul D.

388

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

389

Diachronism between extinction time of terrestrial and marine dinosaurs  

NASA Technical Reports Server (NTRS)

The dinosaur eggs of southern France occur in continental, fine-grained red-beds, rich in carbonate. The last eggs in the region occur in the magnetic polarity interval 30 normal. Estimates of the accumulation rate of these sediments on the basis of the magneto-stratigraphy leads to placement of the time of disappearance of the dinosaurs in this region of 200,000 to 400,000 years earlier than the Cretaceous-Tertiary boundary. In the Red Deer Valley, Canada, estimates of average accumulation rate lead to a time of disappearance of the dinosaurs of 135,000 to 157,000 years earlier than the Cretaceous-Tertiary boundary. In the central part of Poland, in the Nasilow Quarry, the paleomagnetic pattern shows 7 m of chalk of reversed polarity containing in its upper part the marine Cretaceous-Tertiary biostratigraphic boundary. A greensand deposit contains numerous re-deposited Maastrichtian fossils. The fossils show no signs of wear and are of very different sizes including 1 mm thick juvenile belemnites. The deposit was described as a lag-sediment. Among the various fossils are teeth of mosasaurs. Thus there is coincidence in time between the extinction of mosasaurs and other Cretaceous organisms. This leads to the conclusion, that extinction of terrestrial dinosaurs took place earlier than extinction of marine dinosaurs at the Cretaceous-Tertiary boundary.

Hansen, H. J.

1988-01-01

390

Volcanism and related Environmental changes linked to Late Maastrichtian High Stress and KT Mass Extinction  

Microsoft Academic Search

Near the end of the Maastrichtian Earth was hit by a confluence of catastrophes ranging from impacts to some of the most devastating volcanic eruptions coupled with major changes in climate, sea level and ocean chemistry that ultimately led to the Cretaceous-Tertiary boundary (KTB) mass extinction. For three decades this mass extinction has been commonly attributed to the sole kill-effect

Gerta Keller; Thierry Adatte

2010-01-01

391

A Systematic Study of the Correlations Between Meteorite Impacts and Soot Formation  

Microsoft Academic Search

A massive extinction of more than 50 percent of existing life forms on Earth occurred 65 million years (Ma) ago. This event is marked in the geological record by the Cretaceous-Tertiary (KT) boundary and corresponds to the Chicxulub meteorite impact in the Yucatan Peninsula. Since 1985, large quantities ofreduced elemental carbon in the form of characteristic spheroidal clusters of soot

Susanna L. Widicus

2000-01-01

392

Biotic eects of impacts and volcanism Gerta Keller  

E-print Network

Ridge and Deccan volcanism mirror those of the Cretaceous^Tertiary (KT) mass extinction and impact event the KT mass extinction worldwide. Similar high stress late Maastrichtian assemblages have recently been, this is not the case with every impact. The most catastrophic biotic effects occurred at the KT boundary (65.0 Ma) when

Keller, Gerta

393

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

394

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

395

Boundary streaming with Navier boundary condition  

NASA Astrophysics Data System (ADS)

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

Xie, Jin-Han; Vanneste, Jacques

2014-06-01

396

Boundary streaming with Navier boundary condition.  

PubMed

In microfluidic applications involving high-frequency acoustic waves over a solid boundary, the Stokes boundary-layer thickness ? is so small that some non-negligible slip may occur at the fluid-solid interface. This paper assesses the impact of this slip by revisiting the classical problem of steady acoustic streaming over a flat boundary, replacing the no-slip boundary condition with the Navier condition u|_{y=0}=L_{s}?_{y}u|_{y=0}, where u is the velocity tangent to the boundary y=0, and the parameter L_{s} is the slip length. A general expression is obtained for the streaming velocity across the boundary layer as a function of the dimensionless parameter L_{s}/?. The limit outside the boundary layer provides an effective slip velocity satisfied by the interior mean flow. Particularizing to traveling and standing waves shows that the boundary slip respectively increases and decreases the streaming velocity. PMID:25019882

Xie, Jin-Han; Vanneste, Jacques

2014-06-01

397

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

398

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

NASA Astrophysics Data System (ADS)

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

Darrah, Thomas H.; Poreda, Robert J.

2012-05-01

399

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

NASA Technical Reports Server (NTRS)

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

Skala, R.; Hoerz, F.

2003-01-01

400

Subgroups of Mod(S) generated by $X \\in \\{(T_aT_b)^k,(T_bT_a)^k\\}$ and $Y \\in \\{T_a,T_b\\}$  

E-print Network

Suppose a and b are distinct isotopy classes of essential simple closed curves in an orientable surface S. Let T_a and T_b represent the respective Dehn twists along a and b. In this paper, we study the subgroups of Mod(S) generated by X and Y, where X belongs to {(T_aT_b)^k,(T_bT_a)^k}, k an integer, and Y belongs to {T_a,T_b}. For a large class of examples, we show that the subgroups and are isomorphic. Moreover, we prove that = whenever i(a,b) = 1 and k is not a multiple of three or i(a,b) bigger or equal to two and k equals plus or minus one. Further, we compute the index in when is a proper subgroup.

Mortada, Jamil

2011-01-01

401

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. PMID:21242529

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

2011-01-01

402

Boundary Conditions Copenhagen University  

E-print Network

Boundary Conditions Gerd Grubb Copenhagen University Lecture in memory of Lars H¨ormander 26th Nordic and 1st Nordic-European Congress of Mathematicians June 2013 Gerd Grubb Copenhagen University, and the people involved. Gerd Grubb Copenhagen University Boundary Conditions #12;On boundary conditions

Grubb, Gerd

403

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

404

Numerical Boundary Condition Procedures  

NASA Technical Reports Server (NTRS)

Topics include numerical procedures for treating inflow and outflow boundaries, steady and unsteady discontinuous surfaces, far field boundaries, and multiblock grids. In addition, the effects of numerical boundary approximations on stability, accuracy, and convergence rate of the numerical solution are discussed.

1981-01-01

405

Iridium in sediments containing large abundances of Australasian microtektites from DSDP hole 758B in the Eastern Indian Ocean and from DSDP hole 769A in the Sulu Sea  

NASA Technical Reports Server (NTRS)

Excess Ir found in sediments at the Cretaceous/Tertiary (K/T) boundary and in other (e.g., Pliocene) sediments from deep sea drilling cores is widely interpreted as evidence of major impact events. The Australasian tektites originated in an impact event approximately 0.77 Ma ago; microtektites have been found in deep-sea sediment cores from throughout the Indian Ocean, the Philippine Sea, and western Pacific Ocean, but Ir has not been previously reported in these horizons. The deep-sea record of tektites is of particular interest, because in contrast to most continental occurrences, the stratigraphy preserves the original depositional position. Recently several cores having exceptionally high contents of Australasian microtektites have been investigated, Glass and Wu found shocked quartz associated with the microtektites. We used neutron activation to determine concentrations of Ir and other elements in two cores bearing microtektites, one from Deep Sea Drilling Project (DSDP) hole 758B in the Eastern Indian Ocean and one from DSDP hole 769A in the Sulu Sea (near Mindanao, Philippines). The sedimentation age for the microtektite layers in core 758B lies between 0.73 - 0.78 Ma and agrees well with the mean laser-fusion Ar-40/Ar-39 age of Australasian tektites of 0.77 +/- 0.02 Ma by Izett et al. We are able to resolve a small positive Ir enhancement in 758B. Core 769A shows too much scatter to allow resolution of an Ir peak.

Schmidt, Gerhard; Zhou, Lei; Wasson, John T.

1993-01-01

406

Placenta-Specific Protein 1 Is Conserved throughout the Placentalia under Purifying Selection  

PubMed Central

Placental mammals (Placentalia) are a very successful group that, today, comprise 94% of all mammalian species. Recent phylogenetic analyses, coupled with new, quite complete fossils, suggest that the crown orders were all established rapidly from a common ancestor just after the Cretaceous/Tertiary (K/T) boundary 65 million years ago. Extensive molecular and morphologic evidence has led to a description of the common ancestor of all Placentalia in which a two-horned uterus and a hemochorial placenta are present. Thus, the process of placentation in which the placenta invades and anchors to the uterine epithelium was already established. One factor that has been suggested as a crucial component of this process is placenta-specific protein 1 (PLAC1). A phylogenetic analysis of the PLAC1 protein in 25 placental mammal species, representing nine of the sixteen crown orders of the Placentalia, suggests that this protein was present in the placental common ancestor in the form we see it today, that it evolved in the Placentalia and has been subject to the effects of purifying selection since its appearance. PMID:25180201

Devor, Eric J.

2014-01-01

407

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

408

Accretion rate of extraterrestrial matter: Iridium deposited over the last 70 million years  

NASA Technical Reports Server (NTRS)

In order to quantify the accretion rate of extraterrestrial matter during the Cenozoic, Ir concentrations were measured in a continuous series of 450 samples across most of the length of piston core LL44-GPC3. LL44-GPC3 is a 25-meter-long, large-diameter piston core of abyssal clay from the central North Pacific. This core contains a nearly continuous record of sedimentation over the last 70 Ma, as this site migrated from a region near the Equator in the late Cretaceous to its present position north of Hawaii. The first-cut survey across the core is nearing completion, and all of the conclusions of the earlier study, in which was reported the concentrations of Ir, Co, and Sb across 9 meters of this core, remain unchanged. The only strongly enhanced Ir concentrations occur at the Cretaceous-Tertiary (K-T) boundary and outside the K-T boundary Ir correlates well with Co, a terrestrial element which is largely present in hydrogenous ferromanganese oxide precipitates from seawater. Concentrations of both elements appear to be inversely correlated with the sedimentation rate. Although the K-T Ir anomaly is unique in magnitude in this core, there are several small bumps in the Ir profile which may reflect smaller accretionary events. The most promising Ir enhancement was observed in a 30 cm section approximately 1 m below the K-T boundary. Preliminary data suggest deposition of an excess across this interval at a time estimate to be approximate 1 Ma before the K-T impact event, but there is insufficient evidence at present to prove that this reflects enhanced accretion of extraterrestrial matter. A detailed model is being prepared of the chemical record of sedimentation in this core using a combined database of 39 elements in approximately 450 samples across the Cenozoic. Preliminary working model indicates that the only sedimentary sources which contribute significantly to the Ir budget in this core are the hydrogenous precipitates and extraterrestrial particulates.

Kyte, Frank T.

1988-01-01

409

Nature and timing of extinctions in Cretaceous-Tertiary planktic foraminifera preserved in Deccan intertrappean sediments of the KrishnaGodavari  

E-print Network

, Chennai, India a r t i c l e i n f o Article history: Accepted 11 June 2012 Communicated by P. De of Deccan volcanism and its potential cause-and-effect relationship with the demise of the dinosaurs

Keller, Gerta

410

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

411

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

Microsoft Academic Search

Mostflowering 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

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

2009-01-01

412

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

Microsoft Academic Search

Most flowering plants have been shown to be ancient polyploids that have undergone one or more whole genome duplications early in their evolution. Furthermore, many different plant lineages seem to have experienced an additional, more recent genome duplication. Starting from paralogous genes lying in duplicated segments or identified in large expressed sequence tag collections, we dated these youngest duplication events

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

2009-01-01

413

Two-Gluon Correlations in Heavy-Light Ion Collisions: Energy and Geometry Dependence, IR Divergences, and $k_T$-Factorization  

E-print Network

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

Yuri V. Kovchegov; Douglas E. Wertepny

2014-03-11

414

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

USGS Publications Warehouse

Palynology has great potential for providing comparative data and interpretations about changes in biodiversity during the Cretaceous Period. This is especially true for both eastern Asia and western North America because of strong floristic similarities that existed between these regions during Cretaceous time. Also, because palynomorphs of terrestrial origin can be deposited in offshore as well as terrestrial environments, significant potential exists for marine-to-continental palynostratigraphic correlations in both regions. Palynological biostratigraphy can improve the geologic dating of changes in biodiversity. During the Early Cretaceous, eastern Asia and western North America lay within the Cerebropollenites palynofloral province, a circumpolar phytogeographic zone characterized by distinctive palynological assemblages. During most of the Late Cretaceous, these regions lay within the palynofloristically unique Aquilapollenites Province, which was more restricted geographically than the Cerebropollenites Province. The most important development during Cretaceous time that is reflected in palynological assemblages was the rise of the angiosperms as the numerically and ecologically dominant forms of vegetation. The most striking short-term palynofloral event in the two regions was the sudden disappearance of species of Aquilapollenites and associated genera at the Cretaceous-Tertiary (K/T) boundary. Both of these occurrences produced major changes in biodiversity in the terrestrial realm. Geologic research in International Geological Correlation Program Project 434 can benefit from applications of palynostratigraphy. Palynologic research within Project 434 could include development of a comprehensive palynostratigraphic zonation for the Cretaceous, the definition of regional palynostratigraphic datums, and investigation of the record of floral change at the K/T boundary. ?? 2002 Elsevier Science Ltd. All rights reserved.

Nichols, D.J.

2003-01-01

415

Boundary lubrication: Revisited  

NASA Technical Reports Server (NTRS)

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

Jones, W. R., Jr.