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

USGS Publications Warehouse

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

1992-01-01

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

Possible Triggering of the Largest Deccan Eruptions by the Chicxulub Impact

NASA Astrophysics Data System (ADS)

Richards, Mark; Alvarez, Walter; Self, Stephen; Karlstrom, Leif; Renne, Paul; Manga, Michael; Sprain, Courtney

2014-05-01

New constraints on the timing of the Cretaceous-Paleogene (K-Pg) mass extinction, the Chicxulub impact, and a particularly voluminous and apparently brief pulse within the "main-stage" eruptions of the Deccan Traps continental flood basalt province suggest that these three events may have occurred within less than several hundred thousand years of each other. Partial melting induced by the Chicxulub event does not provide an energetically-plausible explanation for this coincidence, and both geochronological and magnetic-polarity data show that Deccan volcanism was underway well before Chicxulub/K-Pg time. However, historical evidence for the triggering of distant volcanic and hydrologic events due to earthquakes suggests that surface waves excited by the Chicxulub impact might plausibly have caused a transient increase in the effective permeability of the deep magmatic system beneath the Deccan province ("plume head"), depending upon the efficiency of coupling between the impact energy and seismic waves. Recently published seismic modeling [Meschede et al., 2011] suggests that the Chicxulub impact may have generated seismic energy densities of order 0.1-1.0 J/m3 globally throughout the upper ~200 km of the Earth's mantle, just sufficient to trigger volcanic eruptions worldwide. It therefore seems reasonable to ask whether the Chicxulub impact might have triggered the enormous Poladpur, Ambenali, and Mahabaleshwar (Wai Subgroup) lava flows that account for >50% of the entire Deccan Traps volume. High-precision radioisotopic dating of the main-phase Deccan flood basalt formations should be able to either confirm or reject this hypothesis. In the former case, this singular outburst within the Deccan Traps (and possibly volcanic eruptions worldwide) may have contributed significantly to the K-Pg extinction. In the latter case, a major role for the Deccan Traps in the K-Pg extinction would seem unlikely.

Chicxulub Impact Crater and Yucatan Carbonate Platform - PEMEX Oil Exploratory Wells Revisited

NASA Astrophysics Data System (ADS)

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

2008-12-01

Geophysical oil exploration surveys carried out by PEMEX in the 1940's revealed occurrence of an anomalous pattern of semi-circular concentric gravity anomalies. The Bouguer gravity anomalies covered an extensive area over the flat carbonate platform in the northwestern Yucatan Peninsula; strong density contrasts were suggestive of a buried igneous complex or basement uplift beneath the carbonates, which was referred as the Chicxulub structure. The exploration program carried out afterwards included a drilling program, starting with Chicxulub-1 well in 1952 and comprising eight deep boreholes through the 1970s. An aeromagnetic survey in late 1970's showed high amplitude anomalies in the gravity anomaly central sector. Thus, research showing Chicxulub as a large complex impact crater formed at the K/T boundary was built on the PEMEX decades-long exploration program. Despite frequent reference to PEMEX information and samples, original data and cores have not been openly available for detailed evaluation and integration with results from recent investigations. Core samples largely remain to be analyzed and interpreted in the context of recent marine, aerial and terrestrial geophysical surveys and the drilling/coring projects of UNAM and ICDP. In this presentation we report on the stratigraphy and paleontological data for PEMEX wells: Chicxulub- 1 (1582m), Sacapuc-1 (1530m), Yucatan-6 (1631m), Ticul-1 (3575m) Yucatan-4 (2398m), Yucatan-2 (3474m), Yucatan-5A (3003m) and Yucatan-1 (3221m). These wells remain the deepest drilled in Chicxulub, providing samples of impact lithologies, carbonate sequences and basement, which give information on post- and pre-impact stratigraphy and crystalline basement. We concentrate on stratigraphic columns, lateral correlations and integration with UNAM and ICDP borehole data. Current plans for deep drilling in Chicxulub crater target the peak ring and central sector, with offshore and onshore boreholes proposed to the IODP and ICDP programs.

Chemical Mobility, Variability, and Components of the Yaxcopoil Impact Melt Breccia Matrix as a Function of Depth

NASA Astrophysics Data System (ADS)

Nelson, M. J.; Newsom, H.

2005-05-01

The matrix in the Yaxcopoil 1 drill core produced by the Chicxulub event is semi-amorphous, containing clays and evidence for elemental mobility. We analyzed matrix in impact melt and suevitic breccia samples from the drill hole to detect mineralogical and chemical variability with depth in upper and lower core samples. SEM, microprobe, Cameca 4f ion probe, and XRD were used to determine chemical mobility and variation, and clay structure in several YAX samples, covering the top five units, at a depth range of about 61m. We investigated the possibility of glass, clay, and metastable eutectic dehydroxylates as components in the matrix. Matrix in upper suevite is not optically distinct, but a type of groundmass, with an admixture of calcite, crystallites, and several melt phases with melt texture indicative of simultaneous formation. With an increase in depth, flow tex-ture in the melt matrix is obvious around clasts on all scales, indicating a different temporal relationship than in the upper suevite. Chemically, the matrix is Si and Mg rich in most samples. With an increase in depth, the bulk matrix contains a strong linear increase of Mg, and a decrease of Al. With depth, the increasingly Mg-rich matrix exhibits a stronger flow texture. Aluminum also appears mobile, with enrichments mostly around clasts and veins. In addition, Li and B are strongly correlated, and decrease linearly with depth. The matrix contains materials that appear to be chemically and structurally consistent with smectites at all depths. The compositions range from that of an average montmorillonite in the uppermost units to that of a magnesium rich saponite in the lower units. Aside from the exis-tence of clays, we are considering the possibility that the matrix could contain metastable condensates from the im-pact dust cloud. As an introductory step to test this, matrix compositions were plotted among metastable eutectic dehydroxylate (MED) end members. This produced a remarkably co-linear trend with the join between MED pyro-phyllite and MED serpentine. High resolution equipment will be used to follow up on this idea. The matrix in lower samples had more element mobility, and likely more chemical reactions occurring among phases. An increase in mobility and transport of Mg could help explain this bulk enrichment in lower samples. In addition, variations in the original target material would logically contribute to chemical variations in the matrix. Dolomite and mafic minerals present at greater depth could react with matrix in the melt breccia, while dust and clay may exist in variable amounts within the drill core samples. The linear trend toward metastable dehydroxylate eutec-tic compositions is an encouraging first step to further investigate the possible existence of condensates from the impact cloud within the matrix.

Triggering of the Largest Deccan Eruptions by the Chicxulub Impact

NASA Astrophysics Data System (ADS)

Richards, M. A.; Alvarez, W.; Self, S.; Karlstrom, L.; Renne, P. R.; Manga, M.; Sprain, C. J.; Smit, J.; Vanderkluysen, L.; Gibson, S. A.

2015-12-01

Modern constraints on the timing of the Cretaceous-Paleogene (K-Pg) mass extinction and the Chicxulub impact, together with a particularly voluminous and apparently brief eruptive pulse toward the end of the "main-stage" eruptions of the Deccan continental flood basalt province, suggest that these three events may have occurred within less than about a hundred thousand years of each other. Partial melting induced by the Chicxulub event does not provide an energetically plausible explanation for this remarkable coincidence, and both geochronologic and magnetic-polarity data show that Deccan volcanism was underway well before Chicxulub/K-Pg time. However, historical data show that in some cases eruptions from existing volcanic systems are triggered by earthquakes. Seismic modeling of the ground motion due to the Chicxulub impact suggests that the resulting Mw~11 earthquake could have generated seismic energy densities of at least 0.1-1.0 J/m3 throughout the upper ~200 km of the Earth's mantle, sufficient to trigger volcanic eruptions worldwide based upon comparison with historical examples. Triggering may have been caused by a transient increase in the effective permeability of the existing deep magmatic system beneath the Deccan province, or mantle plume "head." We suggest that the Chicxulub impact triggered the enormous Poladpur, Ambenali, and Mahabaleshwar (Wai sub-group) lava flows that may account for >70% of the Deccan Traps main-stage eruptions. This hypothesis is consistent with independent stratigraphic, geochronologic, geochemical, and tectonic constraints, which combine to indicate that at approximately Chicxulub/K-Pg time a huge pulse of mantle plume-derived magma passed through the crust with little interaction, and erupted to form the most extensive and voluminous lava flows known on Earth. This impact-induced pulse of volcanism may have enhanced the K-Pg extinction event, and/or suppressed post-extinction biotic recovery. High-precision radioisotopic dating of the main-phase Deccan lavas promise a direct test of this hypothesis.

Possible Triggering of the Largest Deccan Traps Eruptions By the Chicxulub Impact

NASA Astrophysics Data System (ADS)

Richards, M. A.; Alvarez, W.; Self, S.; Karlstrom, L.; Renne, P. R.; Manga, M.; Sprain, C. J.; Smit, J.; Vanderkluysen, L.; Gibson, S. A.

2014-12-01

New constraints on the timing of the Cretaceous-Paleogene (K-Pg) mass extinction and the Chicxulub impact, together with a particularly voluminous and apparently brief eruptive pulse toward the end of the "main-stage" eruptions of the Deccan continental flood basalt province, suggest that these three events may have occurred within less than about a hundred thousand years of each other. Partial melting induced by the Chicxulub event does not provide an energetically-plausible explanation for this coincidence, and both geochronologic and magnetic-polarity data show that Deccan volcanism was underway well before Chicxulub/K-Pg time. However, historical data document that eruptions from existing volcanic systems can be triggered by earthquakes. Seismic modeling of the ground motion due to the Chicxulub impact suggests that the impact could have generated seismic energy densities of order 0.1-1.0 J/m3 throughout the upper ~200 km of the Earth's mantle, sufficient to trigger volcanic eruptions worldwide based upon comparison with historical examples. Triggering may have been caused by a transient increase in the effective permeability of the existing deep magmatic system beneath the Deccan province, or mantle plume "head." It is therefore reasonable to hypothesize that the Chicxulub impact might have triggered the enormous Poladpur, Ambenali, and Mahabaleshwar (Wai sub-group) lava flows that account for >70% of the Deccan Traps main-stage eruptions. This hypothesis is consistent with independent stratigraphic, geochronologic, geochemical, and tectonic constraints, which combine to indicate that at approximately Chicxulub/K-Pg time a huge pulse of mantle plume-derived magma passed through the crust with little interaction, and erupted to form the most extensive and voluminous lava flows known on Earth. High-precision radioisotopic dating of the main-phase Deccan flood basalt formations may be able either to confirm or reject this hypothesis, which in turn might help determine whether this singular outburst within the Deccan Traps (and possibly volcanic eruptions worldwide) contributed significantly to the K-Pg extinction.

Is Chicxulub Too Small to be the Source of the K/Pg Boundary Layer and the Cause of the Dinosaur Extinction Event and would the Amazon Basin Considered as an Impact Feature fit the Evidence Better?

NASA Astrophysics Data System (ADS)

Burgener, J. A.

2016-12-01

The Chicxulub impact is well associated with the K/Pg boundary layer and extinction event [Schulte et al., 2010]. However, most agree that Chicxulub is considered to be too small to have caused the extinction in itself [Kring, 2007; Keller, 2014]. Keller [2014] discusses how the K/Pg extinction event may have been due to many factors, of which Chicxulub would be part, but global warming or volcanic fumes or other factors were the main killers. There are several features in the K/Pg layer that require a much higher energy impact than Chicxulub. The worldwide distribution of shocked crystals does not fit Chicxulub - Chicxulub would only send such granules 400 km away [Morgan et al, 2006]. The Fern Spore anomaly extends too far from Chicxulub indicating a much larger fireball and impact [Fleming 1990; Robertson, 2103]. Fireballs falling around the planet have been proposed and dismissed as not possible. [Goldin & Melosh, 2009] and [Adair,2010] rule out a firestorm from ejecta. One of the reasons that Chicxulub is convincingly attributed with the K/Pg boundary layer is the calculation that the size of the impacting asteroid should have been about 10 km in diameter, based on the thickness of the boundary layer and the amount of iridium in the boundary layer [Alvarez, 1980]. Alvarez used the factor from the Krakatoa eruption (0.22) as the amount of asteroid material that would stay in the atmosphere. More recent studies imply that far less than 0.22 of an asteroid would stay in the atmosphere after an impact. When a comet hits at 55 - 72 km/sec, the vast majority of the comet material will be buried deep into the Earth or ejected at speeds in excess of the escape velocity, and very little would remain [Jeffers et al.2001]. Therefore a comet impact should leave a relatively small boundary layer, requiring a much larger impact by a comet to form what Alvaraz calculated for a 10 km asteroid. If a much larger impact occurred at the end of the Cretaceous, it would resolve the challenges of Chicxulub as long as it was near the location of Chicxulub. If the Amazon Basin was considered as an impact, it would be large enough to fit the K/Pg boundary layer details much better than Chicxulub, and it would explain the extinction event without any need to rely on extenuating factors - the impact itself would have been sufficient to cause the extinction.

Chicxulub Ejecta Dynamics

NASA Technical Reports Server (NTRS)

OKeefe, John D.; Stewart, Sarah T.; Ahrens, Thomas J.

2001-01-01

We modeled in detail the ejecta dynamics associated with the Chicxulub impact. We determined: (1) ejecta trajectories, (2) stratigraphic motions, (3) depth of ejecta stages, (4) thermodynamic histories of the ejecta particles, and (5) the final ejecta distribution. Additional information is contained in the original extended abstract.

Large Meteorite Impacts and Planetary Evolution

NASA Technical Reports Server (NTRS)

1997-01-01

Topics considered include: Petrography, geochemistry and geochronology; impact-induced hydrothermal base metal mineralization; nickel-and platinum group element -enriched quartz norite in the latest jurassic morokweng impact structure, south Africa; extraterrestrial helium trapped in fullerenes in the sudbury; synthetic aperture radar characteristics of a glacially modified meltsheet; the chicxulub seismic experiment; chemical compositions of chicxulub impact breccias; experimental investigation of the chemistry of vaporization of targets in relation to the chicxulub impact; artificial ozone hole generation following a large meteoroid impact into an oceanic site; three dimensional modeling of impactite bodies of popigai impact crater, Russia.

Is There any Relationship Between the Santa Elena Depression and Chicxulub Impact Crater, Northwestern Yucatan Peninsula, Mexico?

NASA Astrophysics Data System (ADS)

Lefticariu, L.

2005-05-01

The Terminal Cretaceous Chicxulub Impact Crater had a strong control on the depositional and diagenetic history of the northern Yucatan Platform during most of the Cenozoic Era. The Chicxulub Sedimentary Basin (henceforth Basin), which approximately coincides with the impact crater, is circumscribed by a concentration of karstic sinkholes known as the Ring of Cenotes. Santa Elena Depression (henceforth Depression) is the name proposed for the bowl-shaped buried feature, first contoured by geophysical studies, immediately south of the Basin, in the area where the Ticul 1 and UNAM 5 wells were drilled. Lithologic, petrographic, and biostratigraphic data on PEMEX, UNAM, and ICDP cores show that: 1) Cenozoic deposits are much thicker inside the Basin than inside the Depression, 2) in general, the Cenozoic formations from inside the Depression are the thickest among those outside the Basin, 3) variably dolomitized pelagic or outer-platform wackestone or mudstone occur both inside the Basin and Depression, 4) the age of the deeper-water sedimentary carbonate rocks is Paleocene-Eocene inside the Basin and Paleocene?-Early Eocene inside the Depression, 5) the oldest formations that crop out are of Middle Eocene age at the edge of the Basin and Early-Middle Eocene age inside the Depression, 6) saline lake deposits, that consist chiefly of anhydrite, gypsum, and fine carbonate, and also contain quartz, chert, clay, zeolite, potassium feldspar, pyrite, and fragments of wood, are present in the Cenozoic section of the UNAM 5 core between 282 and 198 m below the present land surface, 7) the dolomite, subaerial exposure features (subaerial crusts, vugs, karst, dedolomite), and vug-filling cement from the Eocene formations are more abundant inside the Depression than inside the Basin. The depositional environments that are proposed for explaining the Cenozoic facies succession within the Santa Elena Depression are: 1) deeper marine water (Paleocene?-Early Eocene), 2) relatively isolated saline lake (Middle Eocene), and 3) shallow marine water (Middle-Late Eocene?). In places, the deeper-water facies are similar to those within the Chicxulub Sedimentary Basin. The shallow-water facies is similar to those occurring outside the Basin. In general, quartz and silicates are rare in the Cenozoic sedimentary carbonate of the northwestern Yucatan Peninsula. Therefore, their presence in the UNAM 5 core could be attributed to either impact breccia reworking or silicic volcanic processes. Quartz, chert, zeolite, and clay also are common in the suevite breccia of both Yax-1 and UNAM 5 cores. The fact that the Santa Elena Depression was a distinct sedimentary basin during much of the Paleogene could be explained by any or a combination of the following hypotheses: 1) In spite of being located outside the cenote ring, the Depression is a sub-basin of the larger and deeper Chicxulub Sedimentary Basin and is therefore located within the Chicxulub Impact Crater, 2) the Depression coincides with an impact crater distinct from the Chicxulub Impact Crater, 3) the Depression formed after the Chicxulub bolide impact due to slumping, crater wall failure, or larger-scale tectonic processes. The lack of conclusive evidence for multiple impact breccia layers in the northwestern Yucatan Peninsula, corroborated with the presence on top of the impact breccia from UNAM 5 core of deeper-water limestone similar to that of Late Paleocene-Early Eocene age from Yax-1 core, would be more consistent with either the first or third hypothesis.

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

NASA Astrophysics Data System (ADS)

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

2004-05-01

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

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

NASA Astrophysics Data System (ADS)

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

2008-12-01

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

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

NASA Technical Reports Server (NTRS)

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

1993-01-01

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

Shock induced reaction in Chicxulub target materials (CaSO4 and SiO2) and their relation to extinctions

NASA Technical Reports Server (NTRS)

Chen, Guangqing; Ahrens, Thomas J.

1993-01-01

The global platinum element rich layer, the presence of shocked quartz grains (in some cases with stishovite), and the observation of a tektite-rich layer, precisely at the K-T boundary, are the three major arguments for the extinction bolide impact hypothesis of Alvarez et al. Tektites (spherules) from Beloc in Haiti and Mimbral in Mexico received particular interest because of their geological proximity to the Chicxulub impact structure, which is a leading candidate for at least one of the K-T impact craters. Although in most localities the original glass has weathered to clay minerals, some shock-induced glass is found in outcrops and drill cores which is used for Ar-38/Ar-39 dating. The glassy tektites were found to be chemically similar and coeval at 65.0 Ma with Chicxulub melt rock. Two kinds of K-T spherules were discovered: (1) a silic black glass; and (2) a yellow glass, enriched in Ca, Mg, and S. The high sulfur content of the glass and the abundance of anhydrite (CaSO4) in the carbonate-evaporite sequence observed in Drill Holes Y-1 and Y-2 at Chicxulub prompted studies of calcium sulfate devolatization. Further discussion of our experiments is presented.

Shock induced reaction in Chicxulub target materials (CaSO4 and SiO2) and their relation to extinctions

NASA Astrophysics Data System (ADS)

Chen, Guangqing; Ahrens, Thomas J.

1993-03-01

The global platinum element rich layer, the presence of shocked quartz grains (in some cases with stishovite), and the observation of a tektite-rich layer, precisely at the K-T boundary, are the three major arguments for the extinction bolide impact hypothesis of Alvarez et al. Tektites (spherules) from Beloc in Haiti and Mimbral in Mexico received particular interest because of their geological proximity to the Chicxulub impact structure, which is a leading candidate for at least one of the K-T impact craters. Although in most localities the original glass has weathered to clay minerals, some shock-induced glass is found in outcrops and drill cores which is used for Ar-38/Ar-39 dating. The glassy tektites were found to be chemically similar and coeval at 65.0 Ma with Chicxulub melt rock. Two kinds of K-T spherules were discovered: (1) a silic black glass; and (2) a yellow glass, enriched in Ca, Mg, and S. The high sulfur content of the glass and the abundance of anhydrite (CaSO4) in the carbonate-evaporite sequence observed in Drill Holes Y-1 and Y-2 at Chicxulub prompted studies of calcium sulfate devolatization. Further discussion of our experiments is presented.

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

NASA Technical Reports Server (NTRS)

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

1992-01-01

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

Chicxulub impact basin: Gravity characteristics and implications for basin morphology and deep structure

NASA Technical Reports Server (NTRS)

Sharpton, Virgil L.; Burke, Kevin; Hall, Stuart A.; Lee, Scott; Marin, Luis E.; Suarez, Gerardo; Quezada-Muneton, Juan Manuel; Urrutia-Fucugauchi, Jaime

1993-01-01

The K-T-aged Chicxulub Impact Structure is buried beneath the Tertiary carbonate rocks of the Northern Yucatan Platform. Consequently its morphology and structure are poorly understood. Reprocessed Bouguer (onshore) and Free Air (offshore) gravity data over Northern Yucatan reveal that Chicxulub may be a 200-km-diameter multi-ring impact basin with at least three concentric basin rings. The positions of these rings follow the square root of 2 spacing rule derived empirically from analysis of multi-ring basins on other planets indicating that these rings probably correspond to now-buried topographic basin rings. A forward model of the gravity data along a radial transect from the southwest margin of the structure indicates that the Chicxulub gravity signature is compatible with this interpretation. We estimate the basin rim diameter to be 204 +/- 16 km and the central peak ring diameter (D) is 104 +/- 6 km.

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

NASA Technical Reports Server (NTRS)

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

1991-01-01

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

Modelling the gravity and magnetic field anomalies of the Chicxulub crater

NASA Technical Reports Server (NTRS)

Aleman, C. Ortiz; Pilkington, M.; Hildebrand, A. R.; Roest, W. R.; Grieve, R. A. F.; Keating, P.

1993-01-01

The approximately 180-km-diameter Chicxulub crater lies buried by approximately 1 km of sediment on the northwestern corner of the Yucatan Peninsula, Mexico. Geophysical, stratigraphic and petrologic evidence support an impact origin for the structure and biostratigraphy suggests that a K/T age is possible for the impact. The crater's location is in agreement with constraints derived from proximal K/T impact-wave and ejecta deposits and its melt-rock is similar in composition to the K/T tektites. Radiometric dating of the melt rock reveals an age identical to that of the K/T tektites. The impact which produced the Chicxulub crater probably produced the K/T extinctions and understanding the now-buried crater will provide constraints on the impact's lethal effects. The outstanding preservation of the crater, the availability of detailed gravity and magnetic data sets, and the two-component target of carbonate/evaporites overlying silicate basement allow application of geophysical modeling techniques to explore the crater under most favorable circumstances. We have found that the main features of the gravity and magnetic field anomalies may be produced by the crater lithologies.

Did the Chicxulub meteorite impact trigger eruptions at mid-ocean ridges globally?

NASA Astrophysics Data System (ADS)

Byrnes, J. S.; Karlstrom, L.

2017-12-01

Are there causal links between the eruption of large igneous provinces, meteorite impacts, and mass extinctions? Recent dating suggests that state shifts in Deccan Traps eruptions, including erupted volumes, feeder dike orientations, and magma chemistry, occurred shortly after the Chicxulub impact. A proposed explanation for this observation is an increase in upper mantle permeability following the Chicxulub impact that accelerated the pace of Deccan volcanism [Richards et al., 2015]. If such triggering occurred, at global distances not associated with the impact antipode, it is reasonable to hypothesize that other reservoirs of stored melt may have been perturbed as well. We present evidence that mid-ocean ridge activity increased globally following the impact. Anomalously concentrated free-air gravity and sea-floor topographic roughness suggest volumes of excess oceanic ridge magmatism in the range of 2 x 105 to 106 km3 within 1 Myrs of the Chicxulub impact. This signal is only clearly observed for half-spreading rates above 35 mm/yr, possibly because crust formed at slower spreading rates is too complex to preserve the signal. Because similar anomalies are observed separately in the Indian and Pacific Oceans, and because the timing of the signal does not clearly align with changes in spreading rates, we do not favor plume activity as an explanation. Widespread mobilization of existing mantle melt by post-impact seismic radiation, and subsequent emplacement of melt as crustal intrusions and eruptions, can explain the volume and distribution of anomalous crust without invoking impact-induced melt production. Although the mechanism for increasing permeability is not clear at either Deccan or mid-ocean ridges, these results support the hypothesis that the causes and consequences of the Deccan Traps, Chicxulub impact, and K-Pg mass extinction should not be considered in isolation. We conclude by discussing several enigmatic observations from K-Pg time that heightened marine volcanism may explain, whether at Deccan or mid-ocean ridges, including the recovery time of carbon isotopes to pre-K-Pg values, a perturbation to the lithium isotopes in seawater, and the hypothesized acidification of the oceans.

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

NASA Technical Reports Server (NTRS)

Pope, Kevin O.

1997-01-01

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

Petrology of Impact-Melt Rocks at the Chicxulub Multiring Basin, Yucatan, Mexico

NASA Technical Reports Server (NTRS)

Schuraytz, Benjamin C.; Sharpton, Virgil L.; Marin, Luis E.

1994-01-01

Compositions and textures of melt rocks from the upper part of the Chicxulub structure are typical of melt rocks at other large terrestrial impact structures. Apart from variably elevated iridium concentrations (less than 1.5 to 13.5 +/- 0.9 ppb) indicating nonuniform dissemination of a meteoritic component, bulk rock and phenocryst compositions imply that these melt rocks were derived exclusively from continental crust and platform-sediment target lithologies. Modest differences in bulk chemistry among samples from wells located approximately 40 km apart suggest minor variations in relative contributions of these target lithologies to the melts. Subtle variations in the compositions of early-formed pyroxene and plagioclase also support minor primary differences in chemistry between the melts. Evidence for pervasive hydrothermal alteration of the porous mesostasis includes albite, K-feldspar, quartz, epidote, chlorite, and other phyllosilicates, as well as siderophile element-enriched sulfides, suggesting the possibility that Chicxulub, like Sudbury, may host important ore deposits.

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

NASA Technical Reports Server (NTRS)

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

1993-01-01

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

Evidence for a Meteoritic Component in Impact Melt Rock from the Chicxulub Structure

NASA Technical Reports Server (NTRS)

Koeberl, Christian; Sharpton, Virgil L.; Schuraytz, Benjamin C.; Shirey, Steven B.; Blum, Joel D.; Marin, Luis E.

1994-01-01

The Chicxulub structure in Yucatan, Mexico, has recently been recognized as a greater then 200-km-diameter multi-ring impact crater of K-T boundary age. Crystalline impact melt rocks and breccias from within the crater, which have compositions similar to those of normal continental crustal rocks and which show shock metamorphic effects, have been studied for trace element and Re-Os isotope compositions. Re-Os isotope systematics allow the sensitive and selective determination of an extraterrestrial component in impact-derived rocks. A melt rock sample shows elevated iridium concentrations, an osmium concentration of 25 ppb, and a low Os-187/Os-188 ratio of 0.113, which are incompatible with derivation from the continental crust. Even though the Os-187/Os-188 ratio is slightly lower than the range so far measured in meteorites, a mantle origin seems unlikely for mass balance reasons and because the cratering event is unlikely to have excavated mantle material. The data support the hypothesis of a heterogeneously distributed meteoritic component in the Chicxulub melt rock. A sample of impact glass from the Haitian K-T boundary at Beloc yielded about 0.1 ppb osmium and an Os-187/0s-188 ratio of 0.251, indicating the presence of a small meteoritic component in the impact ejecta as well.

Distribution of siderophile and other trace elements in melt rock at the Chicxulub impact structure

NASA Technical Reports Server (NTRS)

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

1994-01-01

Recent isotopic and mineralogical studies have demonstrated a temporal and chemical link between the Chicxulub multiring impact basin and ejecta at the Cretaceous-Tertiary boundary. A fundamental problem yet to be resolved, however, is identification of the projectile responsible for this cataclysmic event. Drill core samples of impact melt rock from the Chichxulub structure contain Ir and Os abundances and Re-Os isotopic ratios indicating the presence of up to approx. 3 percent meteoritic material. We have used a technique involving microdrilling and high sensitivity instrumental neutron activation analysis (INAA) in conjunction with electron microprobe analysis to characterize further the distribution of siderophile and other trace elements among phases within the C1-N10 melt rock.

Elements of the Chicxulub Impact Structure as Revealed in SRTM and Surface GPS Topographic Data

NASA Technical Reports Server (NTRS)

Kinsland, Gary L.; Sanchez, Gary; Kobrick, Michael; Cardador, Manuel Hurtado

2003-01-01

Pope et al. [1] utilized the elevations from the Petroleos Mexicanos (PEMEX) gravity data files to show that the main component of the surface expression of the Chicxulub Impact Structure is a roughly semi-circular, lowrelief depression about 90 km in diameter. They also identified other topographic features and the elements of the buried impact, which possibly led to the development of these features. These are summarized in Table 1. Kinsland et al. [2] presented a connection between these topographic anomalies, small gravity anomalies and buried structure of the impact. Very recently we have acquired digital topography data from NASA s Shuttle Radar Topography Mission (SRTM). Our subset covers 6 square degrees from 20deg N 91degW to 22deg N 88degW (corner to corner) with a pixel size of about 90m. This area includes all of the identified portion of the crater on land.

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

NASA Astrophysics Data System (ADS)

Harting, M.; Wittler, F. A.

2006-05-01

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

New Location of Chicxulub's Impact Ejecta in Central Belize.

NASA Astrophysics Data System (ADS)

Ocampo, A.; Ames, D.; Pope, K.; Smit, J.

2003-04-01

Chicxulub ejecta composed of altered glass, accretionary lapilli, and pebble to cobble sized carbonate clasts are found in the Cayo District of central Belize, about 500 km southeast of the Chicxulub impact crater centre. The ejecta layer, found near the town of Armenia, in central Belize, is about 4 m thick, and rests unconformably on a deeply weathered Cretaceous land surface, of the Barton Creek Formation dolomite. There are similarities between these ejecta and the basal bed (spheroid bed) of the continuous ejecta blanket deposits (Albion Formation) found in northern Belize and southern Quintana Roo, Mexico, 340-360 km from Chicxulub. Although, the spheroid bed in the Armenia location exhibits an exceptional state of impact glass preservation, than that found in Northern Belize. Overlying the bed with glass and lapilli is a 5-m-thick layer of limestone pebbles and cobbles, which contain altered glass and shocked quartz in the matrix. The well-rounded limestone pebbles and cobbles show striated and amygdaloidal textures. We interpret the central Belize spheroid bed deposit with accretionary lapilli as ejecta deposited by the rapidly expanding vapour plume, and may contain carbonate condensates. The altered glass component consists of an inter-stratified illite-smectite mixed layer clay dominated by illite. The overlying pebble and cobble bed may be a later deposit containing re-worked ejecta, or a lateral extension of the coarse ejecta beds found in northern Belize. This new impact ejecta deposit, found in central Belize ~500 km from Chicxulub, emphasizes the importance of volatile-rich target rock and the dispersal of ejecta by the expanding vapour plume.

Long-Term Recovery of Life in the Chicxulub Crater

NASA Astrophysics Data System (ADS)

Lowery, C.; Jones, H.; Bralower, T. J.; Smit, J.; Rodriguez-Tovar, F. J.; Whalen, M. T.; Owens, J. D.; Expedition 364 Science Party, I. I.

2017-12-01

The Chicxulub Crater on the Yucatán Peninsula of Mexico was formed by the impact of an asteroid 66 Ma that caused the extinction of 75% of genera on Earth. Immediately following the impact, the decimated ecosystem began the long process of recovery, both in terms of primary productivity and species diversity. This well-documented process was heterogeneous across the world ocean, but until the present time it has been inaccessible at ground zero of the impact. IODP/ICDP Exp. 364 recovered 9.5 m of pelagic limestone spanning the entire Paleocene, including a continuous section spanning the first 5 myr following the impact. The Chicxulub Crater is the largest known marine impact crater on Earth, and the recovery of the ecosystem presented here is the first such record of long-term primary succession in the sterile zone of a large impact crater. Planktic and benthic foraminifera, calcareous nannoplankton, calcispheres, bioturbation, and geochemical proxies all indicate that export productivity in the Chicxulub Crater recovered rapidly (within 30 kyr) following the impact. Recovery in terms of diversity and species abundance took much longer, and varied between groups. Planktic foraminifera quickly diversified, with all common Paleocene tropical/subtropical species appearing roughly when expected. Trace fossils appear rapidly after the event, with a progressive recovery through the lowermost Paleocene. Calcareous nannoplankton took much longer to recover, and disaster taxa like Braarudosphaera dominated the assemblage well into the late Paleocene. Paleoecology and geochemistry relate these trends to oceanographic conditions within the Chicxulub Crater. Planktic foraminifera from known depth habitats, including Morozovellids, Acarininids, Chiloguembelinids, and Subbotinids, track changes in the water column structure and paleoredox conditions within the crater. Diverse and abundant macro- and microbenthic organisms indicate food availability and good oxygen conditions on the seafloor. The latest Paleocene, just prior to the onset of the PETM, is characterized by a typical and diverse assemblage of foraminifera and calcareous nannoplankton; a normal open-marine assemblage with no trace of long-term negative effects from the impact.

IODP-ICDP Expedition 364: Drilling the Chicxulub impact crater to understand planetary evolution and mass extinction

NASA Astrophysics Data System (ADS)

Gulick, S. P. S.; Morgan, J. V.

2017-12-01

The most recent of Earth's five largest mass extinction events occurred 66 Ma, coeval with the impact of a 12 km asteroid, striking at 60 degrees into what is today the Yucatán Peninsula, México, producing the 200 km-wide Chicxulub crater. This impact, by some estimations, drove the extinction of 75% of life on Earth at the genus level. The mass extinction event marks the boundary between the Cretaceous and Paleogene. Proposed kill mechanisms include thermal effects caused by the reentry of fast ejecta into Earth's atmosphere, dust and sulfate aerosols reducing Earth's solar insolation, ocean acidification, and metal toxicity due to the chemical make-up of the impactor. The magnitude and duration of these processes is still debated, and further evaluation of the proposed kill mechanisms requires an understanding of the mechanics of the Chicxulub impact as well as the resulting global environmental perturbations. In April and May 2016, the International Ocean Discovery Program, with co-funding from the International Continental Scientific Drilling Program, successfully cored into the Chicxulub impact crater with nearly 100% recovery. These cores include the first-ever samples of the transition from an intact peak ring through post-impact sediments. A peak ring is a discontinuous ring of mountains observed within the central basin of all large impact craters on rocky planets. Newly drilled cores include the uplifted target rocks, melt-rich impactites, hydrothermal deposits, a possible settling layer, and the resumption of carbonate sedimentation. The discovery that Chicxulub's peak ring consists of largely granitic crust uplifted by 10 km calibrates impact models and allows for observation of impact processes. At the top of the peak ring, the K-Pg boundary deposit includes a impactite sequence 130 m thick deposited by processes that range from minutes to likely years post-impact. This sequence is then overprinted by hydrothermal processes that lasted at least 100s Kyr post-impact and may have fed a subsurface ecosystem within the crater. The full recovery of life within the crater spans from immediately after impact through millions years allowing for a first-order assessment of the environmental consequences of the impact ("kill mechanisms").

Surficial Geology of the Chicxulub Impact Crater, Yucatan, Mexico

NASA Technical Reports Server (NTRS)

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

1993-01-01

The Chicxulub impact crater in northwestern Yucatan, Mexico is the primary candidate for the proposed impact that caused mass extinctions at the end of the Cretaceous Period. The crater is buried by up to a kilometer of Tertiary sediment and the most prominent surface expression is a ring of sink holes, known locally as cenotes, mapped with Landsat imagery. This 165 +/- 5 km diameter Cenote Ring demarcates a boundary between unfractured limestones inside the ring, and fractured limestones outside. The boundary forms a barrier to lateral ground water migration, resulting in increased flows, dissolution, and collapse thus forming the cenotes. The subsurface geology indicates that the fracturing that created the Cenote Ring is related to slumping in the rim of the buried crater, differential thicknesses in the rocks overlying the crater, or solution collapse within porous impact deposits. The Cenote Ring provides the most accurate position of the Chicxulub crater's center, and the associated faults, fractures, and stratigraphy indicate that the crater may be approx. 240 km in diameter.

Surficial geology of the Chicxulub impact crater, Yucatan, Mexico

NASA Technical Reports Server (NTRS)

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

1993-01-01

The Chicxulub impact crater in northwestern Yucatan, Mexico is the primary candidate for the proposed impact that caused mass extinctions at the end of the Cretaceous Period. The crater is buried by up to a kilometer of Tertiary sediment and the most prominent surface expression is a ring of sink holes, known locally as cenotes, mapped with Landsat imagery. This 165 +/- 5 km diameter Cenote Ring demarcates a boundary between unfractured limestones inside the ring, and fractured limestones outside. The boundary forms a barrier to lateral ground water migration, resulting in increased flows, dissolution, and collapse thus forming the cenotes. The subsurface geology indicates that the fracturing that created the Cenote Ring is related to slumping in the rim of the buried crater, differential thicknesses in the rocks overlying the crater, or solution collapse within porous impact deposits. The Cenote Ring provides the most accurate position of the Chicxulub crater's center, and the associated faults, fractures, and stratigraphy indicate that the crater may be approximately 240 km in diameter.

Advanced SEM/EDS Analysis using Stage Control and an annular Silicon Drift Detector: Applications in Impact Studies from Centimetre below Micrometre Scale

NASA Astrophysics Data System (ADS)

Salge, Tobias; Berlin, Jana; Terborg, Ralf; Howard, Kieren; Newsom, Horton; Wozniakiewicz, Penny; Price, Mark; Burchell, Mark; Cole, Mike; Kearsley, Anton

2013-04-01

Introduction: Imaging of ever smaller structures, in situ within large samples, requires low electron beam energy (HV<6 kV) to enhance spatial resolution, and therefore also the use of low energy X-ray lines for element analysis. To separate significantly overlapping peaks e.g. N-K (392 eV) and Ti-Ll (395 eV), the incorporation of line deconvolution algorithms in energy dispersive X-ray software is of crucial importance. Methods: Without adequate X-ray count statistics, deconvolution is unlikely to be effective. We therefore used an annular Silicon Drift Detector (SDD), the Bruker XFlash® 5060F which is placed between the pole piece and sample. High take-off angle and collection of X-rays from four different directions allow data collection across samples with substantial surface topography. Automated stage control and spectrum imaging allow large data sets to be acquired within a short time. Applications: (A) Large area, high resolution images (with tiling or stitching of neighbouring areas) is useful for understanding processes in the formation of tektites [1], revealing flow textures and layering, without destructive section preparation. Coalescence textures formed during the transition from melt to solid, surface pitting produced by micro-impact collisions in the impact plume, and surface etching by chemical attack in the impact plume, or later weathering, can all be revealed. (B) Spectrum imaging of the matrix in the impact melt breccia of the Chicxulub impact crater (Yaxcopoil-1 borehole, Unit 5 861.72 m) reveals secondary mineral formation, such as NaCl (<500 nm) and Fe-Ti-oxides (<150 nm) associated with garnet resorption. It documents the role of multiple episodes of precipitation of Mg-rich phyllosilicates as well as the formation and dissolution of accessory minerals in a relatively high temperature (>300°C) hydrothermal event [2]. (C) In experimental hypervelocity impact craters, spectrum images readily find locations of projectile residue throughout all the complex topography. The very high count rate at even low beam energy and current reveals inhomogeneous compositions and textures below micrometre scale [3]. These results help us understand preservation and modification of structure and composition in the fine-grained cometary dust aggregates which made aluminium foil craters on the Stardust spacecraft during its encounter with comet Wild 2. Acknowledgements: International Continental Scientific Drilling Program and the Museum of Natural History Berlin for providing samples. References: [1] K.T. Howard 2011. Geological Society of London: 573-591. [2] M. Nelson et al. 2012. GCA 86: 1-20. [3] A. T. Kearsley et al. 2013. Submitted to LPSC #1910.

A Tale of Two Swarms: Mapping Of Calderas And 40Ar/39Ar Geochronology Of Rhyolite Ignimbrites Delineate Two Distinct Steens Basalt Fissure Systems

NASA Astrophysics Data System (ADS)

Byrnes, J. S.; Karlstrom, L.

2016-12-01

Are there causal links between the eruption of large igneous provinces, meteorite impacts, and mass extinctions? Recent dating suggests that state shifts in Deccan Traps eruptions, including erupted volumes, feeder dike orientations, and magma chemistry, occurred shortly after the Chicxulub impact. A proposed explanation for this observation is an increase in upper mantle permeability following the Chicxulub impact that accelerated the pace of Deccan volcanism [Richards et al., 2015]. If such triggering occurred, at global distances not associated with the impact antipode, it is reasonable to hypothesize that other reservoirs of stored melt may have been perturbed as well. We present evidence that mid-ocean ridge activity increased globally following the impact. Anomalously concentrated free-air gravity and sea-floor topographic roughness suggest volumes of excess oceanic ridge magmatism in the range of 2 x 105 to 106 km3 within 1 Myrs of the Chicxulub impact. This signal is only clearly observed for half-spreading rates above 35 mm/yr, possibly because crust formed at slower spreading rates is too complex to preserve the signal. Because similar anomalies are observed separately in the Indian and Pacific Oceans, and because the timing of the signal does not clearly align with changes in spreading rates, we do not favor plume activity as an explanation. Widespread mobilization of existing mantle melt by post-impact seismic radiation, and subsequent emplacement of melt as crustal intrusions and eruptions, can explain the volume and distribution of anomalous crust without invoking impact-induced melt production. Although the mechanism for increasing permeability is not clear at either Deccan or mid-ocean ridges, these results support the hypothesis that the causes and consequences of the Deccan Traps, Chicxulub impact, and K-Pg mass extinction should not be considered in isolation. We conclude by discussing several enigmatic observations from K-Pg time that heightened marine volcanism may explain, whether at Deccan or mid-ocean ridges, including the recovery time of carbon isotopes to pre-K-Pg values, a perturbation to the lithium isotopes in seawater, and the hypothesized acidification of the oceans.

IODP/ICDP Expedition 364-Drilling the Cretaceous-Paleogene Chicxulub impact crater: Insights into large craters formation and their effect on life.

NASA Astrophysics Data System (ADS)

Gulick, S. P. S.; Morgan, J. V.; Fucugauchi, J. U.; Bralower, T. J.; Chenot, É.; Christeson, G. L.; Claeys, P.; Cockell, C. S.; Collins, G. S.; Coolen, M.; Gebhardt, C.; Goto, K.; Kring, D. A.; Xiao, L.; Lowery, C.; Mellett, C.; Ocampo-Torres, R.; Osinski, G. R.; Perez-Cruz, L. L.; Pickersgill, A.; Poelchau, M.; Rae, A.; Rasmussen, C.; Rebolledo-Vieyra, M.; Riller, U. P.; Sato, H.; Schmitt, D. R.; Smit, J.; Tikoo, S.; Tomioka, N.; Whalen, M. T.; Zylberman, W.; Jones, H.; Gareth, C.; Wittmann, A.; Lofi, J.; Yamaguchi, K. E.; Ferrière, L.

2016-12-01

An international project to drill the Chicxulub impact crater was conducted in April and May, 2016 as Expedition 364 of the International Ocean Discovery Program (IODP) and International Continental Scientific Drilling Project (ICDP). Site M0077 is located offshore Yucatan in the southern Gulf of Mexico. The target was to core the only pristine terrestrial peak ring and to measure physical properties of the entire borehole. Specific questions included: What rocks comprise a topographic peak ring? How are peak rings formed? How are rocks weakened during large impacts to allow them to collapse and form relatively wide, flat craters? What insights arise from biologic recovery in the Paleogene within a potentially "toxic" ocean basin? Are impact craters (including peak rings) habitats for life? Coring occurred from 503 - 1334.7 mbsf with nearly 100% recovery. Wireline logs were collected from ultra slimline tools to total depth including gamma ray, magnetic susceptibility, sonic, borehole fluid temperature and conductivity, resistivity data, borehole images, and a finely spaced vertical seismic profile. Stratigraphy cored included 110 m of Eocene and Paleocene carbonates, 130 m of allochthonous impactites, and 590 m of crustal basement with dikes. All cores were measured using a shipboard core logger (density, gamma ray, magnetic susceptibility and resistivity) and shorebased dual energy, 0.3 mm resolution CT scanner. These data allow us to: 1) refine numerical models of the formation of the Chicxulub impact structure; 2) place constraints on environmental perturbations that led to the K-Pg mass extinction; 3) improve simulations of impact craters on other planetary bodies; 4) examine deformation mechanisms for insights into how rocks weaken during impacts; 5) study impact generated hydrothermal systems and 6) understand the effects of impacts on the deep biosphere including as a habitat for microbial life with implications for evolution on Earth and astrobiology. Key results are that the Chicxulub peak ring is formed from fractured basement rocks that may host a subsurface biosphere. The impactite layer overlying the peak ring in turn provides insight into resurge and tsunami processes, while the Paleogene sediments contain the record of the recovery of life after the mass extinction event.

Triggering of the Largest Deccan Eruptions and Other Possible Geophysical Effects of the Mw 11 Chicxulub Impact

NASA Astrophysics Data System (ADS)

Richards, M. A.; Renne, P. R.; Alvarez, W.; DePalma, R. A.; Smit, J.; Manga, M.; Karlstrom, L.; Vanderkluysen, L.; Fainstein, R.; Gibson, S. A.

2017-12-01

The Chicxulub impact in Yucatán, México, and the onset of the most voluminous phase of Deccan Traps eruptions in the Western Ghats of India both occurred within <50,000 years of the Cretaceous-Paleogene boundary (KPB), at which time 70% of all species in the fossil record perished, including the non-avian dinosaurs. A broad range of evidence (geochronological, volcanological, geochemical, and tectonic) suggests that the aerially-extensive Wai Sub-group eruptions of the main Deccan sequence may have been triggered by the impact, probably due to a transient increase in the effective permeability of the existing Réunion plume head's mantle magmatic system. Whether similar effects might be observed in the possibly even larger volume of offshore Deccan-equivalent eruptions is not presently well-constrained by geochronological or stratigraphic data. Several lines of evidence suggest that the Chicxulub impact caused an earthquake of magnitude Mw 11, or perhaps 1000 times more energetic than any known tectonic earthquake, and therefore well outside of human historical experience. The consequences of such a large geophysical event remain to be fully explored, but are likely to have involved triggering of volcanism globally (including the mid-ocean ridge system), tsunamis in the open oceans, seiches in confined bodies of water, soft-sediment liquefaction, and mass wasting, with some far-field events most likely responding to longer-period seismic waves. A particularly interesting case is a deposit in the Hell Creek Formation of southwestern North Dakota ("Tanis"), where a remarkable "death assemblage" of marine and terrestrial biota were buried at exactly KPB time in a local surge deposit, most likely due to a seiche on an arm or embayment of the Western Interior Seaway due to seismic waves from the Chicxulub impact. Another KPB unit (Hvar, Croatia) previously identified as a tsunami deposit might also be interpreted as having resulted from a seiche. This presentation will explore a range of possibly observable phenomena associated with the Chicxulub impact, including, of course, the possibility that both impact and triggered volcanism contributed to the mass extinction.

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

NASA Technical Reports Server (NTRS)

Pope, Kevin O.

1994-01-01

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

Environmental Consequences of Big Nasty Impacts on the Early Earth

NASA Astrophysics Data System (ADS)

Zahnle, K. J.

2015-12-01

The geological record of the Archean Earth is spattered with impact spherules from a dozen or so major cosmic collisions involving Earth and asteroids or comets (Lowe, Byerly 1986, 2015). Extrapolation of the documented deposits suggests that most of these impacts were as big or bigger than the Chicxulub event that famously ended the reign of the thunder lizards. As the Archean impacts were greater, the environmental effects were also greater. The number and magnitude of the impacts is bounded by the lunar record. There are no lunar craters bigger than Chicxulub that date to Earth's mid-to-late Archean. Chance dictates that Earth experienced ~10 impacts bigger than Chicxulub between 2.5 Ga and 3.5 Ga, the biggest of which were ~30-100X more energetic than Chicxulub. To quantify the thermal consequences of big impacts on old Earth, we model the global flow of energy from the impact into the environment. The model presumes that a significant fraction of the impact energy goes into ejecta that interact with the atmosphere. Much of this energy is initially in rock vapor, melt, and high speed particles. (i) The upper atmosphere is heated by ejecta as they reenter the atmosphere. The mix of hot air, rock vapor, and hot silicates cools by thermal radiation. Rock raindrops fall out as the upper atmosphere cools. (ii) The energy balance of the lower atmosphere is set by radiative exchange with the upper atmosphere and with the surface, and by evaporation of seawater. Susequent cooling is governed by condensation of water vapor. (iii) The oceans are heated by thermal radiation and rock rain and cooled by evaporation. Surface waters become hot and salty; if a deep ocean remains it is relatively cool. Subsequently water vapor condenses to replenish the oceans with hot fresh water (how fresh depending on continental weathering, which might be rather rapid under the circumstances). (iv) The surface temperature of dry land is presumed to be the same as the lower atmosphere. A thermal wave propagates into the land at a rate set by conduction. Impacts larger than Chicxulub can raise the surface temperature by tens, hundreds, or even thousands of degrees, and evaporate meters to hundreds of meters of water. The biggest should have vitrified exposed dry land. More results - including shock chemistry - are for the talk, as here we have run out of space.

Scientific Drilling of Impact Craters - Well Logging and Core Analyses Using Magnetic Methods (Invited)

NASA Astrophysics Data System (ADS)

Fucugauchi, J. U.; Perez-Cruz, L. L.; Velasco-Villarreal, M.

2013-12-01

Drilling projects of impact structures provide data on the structure and stratigraphy of target, impact and post-impact lithologies, providing insight on the impact dynamics and cratering. Studies have successfully included magnetic well logging and analyses in core and cuttings, directed to characterize the subsurface stratigraphy and structure at depth. There are 170-180 impact craters documented in the terrestrial record, which is a small proportion compared to expectations derived from what is observed on the Moon, Mars and other bodies of the solar system. Knowledge of the internal 3-D deep structure of craters, critical for understanding impacts and crater formation, can best be studied by geophysics and drilling. On Earth, few craters have yet been investigated by drilling. Craters have been drilled as part of industry surveys and/or academic projects, including notably Chicxulub, Sudbury, Ries, Vredefort, Manson and many other craters. As part of the Continental ICDP program, drilling projects have been conducted on the Chicxulub, Bosumtwi, Chesapeake, Ries and El gygytgyn craters. Inclusion of continuous core recovery expanded the range of paleomagnetic and rock magnetic applications, with direct core laboratory measurements, which are part of the tools available in the ocean and continental drilling programs. Drilling studies are here briefly reviewed, with emphasis on the Chicxulub crater formed by an asteroid impact 66 Ma ago at the Cretaceous/Paleogene boundary. Chicxulub crater has no surface expression, covered by a kilometer of Cenozoic sediments, thus making drilling an essential tool. As part of our studies we have drilled eleven wells with continuous core recovery. Magnetic susceptibility logging, magnetostratigraphic, rock magnetic and fabric studies have been carried out and results used for lateral correlation, dating, formation evaluation, azimuthal core orientation and physical property contrasts. Contributions of magnetic studies on impact age, cratering, target-impactite stratigraphy, ejecta, impact dynamics, hydrothermal alterations and post-impact processes are presented. The challenges and perspectives of drilling studies of impact craters are discussed.

Environmental consequences of impact cratering events as a function of ambient conditions on Earth.

PubMed

Kring, David A

2003-01-01

The end of the Mesozoic Era is defined by a dramatic floral and faunal turnover that has been linked with the Chicxulub impact event, thus leading to the realization that impact cratering can affect both the geologic and biologic evolution of Earth. However, the environmental consequences of an impact event and any subsequent biological effects rely on several factors, including the ambient environmental conditions and the extant ecosystem structures at the time of impact. Some of the severest environmental perturbations of the Chicxulub impact event would not have been significant in some periods of Earth history. Consequently, the environmental and biological effects of an impact event must be evaluated in the context in which it occurs.

The Cretaceous-Paleogene transition and Chicxulub impact ejecta in the northwestern Gulf of Mexico: Paleoenvironments, sequence stratigraphic setting and target lithologies

NASA Astrophysics Data System (ADS)

Schulte, Peter

2003-07-01

The Cretaceous-Paleogene (K-P) transition is characterized by a period of mass extinctions, the Chicxulub impact event, sea-level changes, and considerable climate changes (e.g., cooling). The Gulf of Mexico region is a key area for addressing these issues, specifically because of the proximity to the large Chicxulub impact structure in southern Mexico, and because of its shallow shelf areas throughout the Maastrichtian to Danian period. This study presents the results of a multidisciplinary investigation of Chicxulub impact ejecta and marine sediments from the K-P transition in the western Gulf of Mexico. Sedimentological, mineralogical, and geochemical aspects of K-P sections and cores from northeastern Mexico, Texas, and Alabama have been by studied with focus on Chicxulub ejecta, long- or short-term facies change, and sequence stratigraphic setting. CHICXULUB EJECTA: The Chicxulub ejecta (or impact spherule) deposits from northeastern Mexico and Texas revealed an unexpected complex and localized ejecta composition. Fe-Mg-rich chlorite- as well as Si-Al-K-rich glass-spherules are the predominant silicic ejecta components in northeastern Mexico, whereas in Texas, spherules of Mg-rich smectite compositions were encountered. Spherules contain Fe-Ti-K-rich schlieren, Fe-Mg-rich globules, and rare µm-sized metallic and sulfidic Ni-Co-(Ir-?) rich inclusions. This composition provides evidence for a distinct range of target rocks of mafic to intermediate composition, presumably situated in the northwestern sector of the Chicxulub impact structure, in addition to the possibility of contamination by meteoritic material. The absence of spinels and the ubiquitous presence of hematite and goethite points to high oxygen fugacity during the impact process. Besides these silicic phases, the most prominent ejecta component is carbonate.! Carbonate is found in ejecta deposits as unshocked clasts, accretionary lapilli-like grains, melt globules (often with quenching textures), and as microspar, suggesting that this area received ejecta mainly from shallow, carbonate-rich lithologies at the impact site on the Yucatán carbonate platform. Albeit the ejecta spherules are mostly altered to clay minerals and iron oxides, the microfacies and internal textures of the ejecta particles show a variety of distinct features, including welding and fusing of components and evidence for liquid immiscibility between silicic-silicic and carbonate-silicic melts. No evidence for binary mixing of ejecta phases was found. Therefore, it is assumed that ejecta in northeastern Mexico derived from less energetic parts of the ejecta curtain. The welding features of ejecta particles suggest an initial ground surge-like ejecta-dispersion mode. The specific morphological features and the compositional range of Chicxulub ejecta, as well as the results of petrological and rock magnetic characteristics reveal similarities to Chicxulub ejecta from K-P sections in the Gulf of Mexico area, the Caribbean, the Atlantic, the Pacific, and Northern America (Western Interior). In addition, Mg-rich smectite, K-feldspar, and iron oxide-rich microspherules are characteristic for the K-P boundary clay layer in sections from the Atlantic and Tethyan realm, suggestive of a relationship between the Chicxulub impact event and the basal K-P boundary clay layer. EJECTA DEPOSITS: The Chicxulub ejecta deposits are commonly associated with an event deposit that shows a complex succession of deposition from high-energetic (channelized) debris flows or turbidity currents derived from multiple source areas, followed by a period of decreasing current energy and intermittent periods of reworking. The uppermost parts of these deposits are often bioturbated, pointing to longer periods of deposition, as also sustained by the complex internal subdivision of the K-P event deposits. In northeastern Mexico, Chicxulub ejecta is also locally embedded within latest Maastrichtian marls, though common soft-sediment deformation opposes a clear age assignation of these deposits. However, individual spherule layers in the slumped and in the channelized spherule deposits are of similar petrological, mineralogical, and geochemical composition with no size-sorting and abrasion of ejecta, hence pointing to an origin from a single impact event (Chicxulub) and providing no evidence for extended periods between reworking of individual spherule layers. In the Brazos core from Texas, a m-thick shale interval, almost devoid of micro- and macrofossils and therefore of unclear stratigraphic age, is sandwiched between Chicxulub impact ejecta and the first appearance of Paleocene microfossils, indicating a period (of enhanced reworking?) between these two events. However, no mm-thick ferruginous layer with Ni-rich spinels, smectite spherules, and shocked quartz that defines the K-P boundary in the Global Stratotype Section and Point (GSSP) at El Kef, Tunisia, and elsewhere has been observed in any of the sections and cores studied. Therefore, an unequivocal positioning of the K-P boundary is difficult for the northwestern Gulf of Mexico region. PALEOCLIMATE RECORD: The long-term record of clay mineral species during the K-P transition of northeastern Mexico, Texas, and Alabama shows remarkably localized compositional patterns, indicating local sediment influx from topographically, petrologically, and probably climatically distinct source regions. Chlorite-illite-dominated clay assemblages in northwestern Mexico indicate mafic source rocks, predominance of physical weathering, and cooler climates, probably associated with the uplift of the Sierra Madre Oriental, whereas a smectite-dominated clay assemblage in Texas indicates semiarid-humid climates. In central Alabama, a distinct trend from tropically humid and warm climates to more seasonal and drier climate that already started in the late Maastrichtian was inferred from a prominent change of a kaolinite- to a smectite-dominated clay mineral assemblage. Hence, no unique climate conditions and distinct climate trends can be inferred for the northwestern Gulf of Mexico area from the data provided by this study. SEQUENCE STRATIGRAPHY: The sequence stratigraphic setting of the Maastrichtian to Danian strata in northeastern Mexico, Texas, and Alabama is also quite complex. The deep-water marls in northeastern Mexico were not amenable to a clear sequence stratigraphic subdivision, though the similar mineralogical (and geochemical) composition of the Maastrichtian to Danian marls provided no evidence for a distinct major facies change during this interval. In Texas, no facies change was observed for the (highstand) shale interval that includes the event bed, though a gradual sea-level lowering took place upon the appearance of the earliest Paleocene microfossils. A sequence boundary is present in the earliest Danian and overlain by transgressive systems tract. In central Alabama, a pronounced sea-level shallowing was recognized during a highstand systems tract in the late Maastrichtian, topped by a sequence boundary and subsequent (strongly) rising sea level throughout the latest Maastrichtian and the early Danian. Rapid and intense water-depth fluctuations are inferred from middle Danian carbonate-rich strata concomitant to a change from a mixed siliciclastic-carbonate depositional system to a more stable carbonate platform in central Alabama during this period. In summary, no universal pattern of facies and related sea-level changes was obtained from the northwestern Gulf of Mexico area, and particularly, no evidence for adverse an- or dysoxic sedimentary conditions were observed for the Maastrichtian to Danian interval governed by this study.

Two astroblems in Ukraine - witnesses of the last days of dinosaurs

NASA Astrophysics Data System (ADS)

Vidmachenko, A. P.

2017-05-01

Moor then 65 million years ago an asteroid with a few kilometers in size with mass of 1 trillion tons created a crater Chicxulub with a diameter of 170 km on the Yucatán Peninsula in Mexico. Then the dinosaurs died out. The largest of Ukrainian astroblems is Manevichska, located in Volyn region. It has a diameter of 45 km and occurred about 65 million years ago too. In the central part of Ukraine on the border of Kirovograd and Cherkassy regions, there is Boltyshka astrobleme. The crater has diameter 25 km and depth of more than 1 km. Boltyshka crater also appeared more than 65 million years ago. These dating of the occurrence of astroblems indicates the close age of these two craters with formation of Chicxulub. If almost coinciding formation time of two or more impact structures, it is significantly increases the effect of impact on the environment and living beings.

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

NASA Astrophysics Data System (ADS)

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

2015-04-01

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

Evidence for a second impactor at the K-Pg Boundary in Baja California, Mexico

NASA Astrophysics Data System (ADS)

Santa Catharina, Amanda; Kneller, Benjamin Charles; Charao Marques, Juliana; McArthur, Adam Daniel; Kane, Ian Antony; Silvestre Cevallos Ferriz, Sergio Rafael

2017-04-01

Controversies remain regarding the trigger, or triggers, of the Cretaceous/Paleogene Mass Extinction. The Chicxulub Impact and the Deccan Volcanism are the main candidates, but discussions about the timing of these events and the magnitude of their effects on the biota are ongoing. Data collected around the globe suggests that profound alterations in the biosphere occurred at this interval, and locations in the Northeastern Atlantic margin and the Gulf of Mexico show evidences of tsunamis and mass waste deposits directly associated with the Chicxulub Impact. Close to El Rosario, Baja California, an enigmatic stratigraphic succession spanning this interval occurs. The succession is distinct from the normal submarine slope deposits in this region and consists of (1) 30 m thick muddy debrites, rich in terrestrial material including fossilized tree trunks up to 2m long and with evidence of exposure to fires, glassy tektites and a horizon rich in gastropods, bivalves, and fragments of corals; (2) an up to 20 m thick coarse grained tuffaceous interval, andesitic in composition, within a channel-like geometry cutting into the debrites, with lapilli (ranging from 1 to 15 cm in size) in discrete sets, fossilized tree trunks close to the base, tektites and shocked quartz; and (3) muddy debrites interbedded with tuffaceous lenses that become less frequent up section. This succession sits between hemipelagic slope deposits, with an abrupt basal contact onto Upper Maastrichtian mudstones and a gradational top, which represents a stabilisation and return to the typical sedimentation environment, with Danian fauna and flora. We believe unit 1 represents material transported onto the slope by the seismic activity caused by the impact of a bolide, which destabilised the coastal region. The tuffaceous channelized unit has been dated (SHRIMP U-Pb in zircons), and its age is indistinguishable from the proposed ages for the K-Pg Boundary. No volcanic activity of this age has been reported in the surrounding areas, either in the Peninsular Ranges or the Sonora Desert, and the presence of shocked quartz and tektites in this unit compels us to believe that its origin is related to ejecta material from an impact. The distance of these thick and coarse grained deposits from the Chicxulub Impact site (c.2000 km) suggests that these deposits are not related to the Chicxulub Impactor, and therefore may have been generated by a different impact of a geologically similar age, but more proximal to this area. The occurrence of multiple impactors is not uncommon, and should be considered a possibility for the K-Pg Boundary.

Time scales of critical events around the Cretaceous-Paleogene boundary.

PubMed

Renne, Paul R; Deino, Alan L; Hilgen, Frederik J; Kuiper, Klaudia F; Mark, Darren F; Mitchell, William S; Morgan, Leah E; Mundil, Roland; Smit, Jan

2013-02-08

Mass extinctions manifest in Earth's geologic record were turning points in biotic evolution. We present (40)Ar/(39)Ar data that establish synchrony between the Cretaceous-Paleogene boundary and associated mass extinctions with the Chicxulub bolide impact to within 32,000 years. Perturbation of the atmospheric carbon cycle at the boundary likely lasted less than 5000 years, exhibiting a recovery time scale two to three orders of magnitude shorter than that of the major ocean basins. Low-diversity mammalian fauna in the western Williston Basin persisted for as little as 20,000 years after the impact. The Chicxulub impact likely triggered a state shift of ecosystems already under near-critical stress.

Environmental Consequences of Big Nasty Impacts on the Early Earth

NASA Technical Reports Server (NTRS)

Zahnle, Kevin

2015-01-01

The geological record of the Archean Earth is spattered with impact spherules from a dozen or so major cosmic collisions involving Earth and asteroids or comets (Lowe, Byerly 1986, 2015). Extrapolation of the documented deposits suggests that most of these impacts were as big or bigger than the Chicxulub event that famously ended the reign of the thunder lizards. As the Archean impacts were greater, the environmental effects were also greater. The number and magnitude of the impacts is bounded by the lunar record. There are no lunar craters bigger than Chicxulub that date to Earth's mid-to-late Archean. Chance dictates that Earth experienced no more than approximately 10 impacts bigger than Chicxulub between 2.5 billion years and 3.5 billion years, the biggest of which were approximately 30-100 times more energetic, comparable to the Orientale impact on the Moon (1x10 (sup 26) joules). To quantify the thermal consequences of big impacts on old Earth, we model the global flow of energy from the impact into the environment. The model presumes that a significant fraction of the impact energy goes into ejecta that interact with the atmosphere. Much of this energy is initially in rock vapor, melt, and high speed particles. (i) The upper atmosphere is heated by ejecta as they reenter the atmosphere. The mix of hot air, rock vapor, and hot silicates cools by thermal radiation. Rock raindrops fall out as the upper atmosphere cools. (ii) The energy balance of the lower atmosphere is set by radiative exchange with the upper atmosphere and with the surface, and by evaporation of seawater. Susequent cooling is governed by condensation of water vapor. (iii) The oceans are heated by thermal radiation and rock rain and cooled by evaporation. Surface waters become hot and salty; if a deep ocean remains it is relatively cool. Subsequently water vapor condenses to replenish the oceans with hot fresh water (how fresh depending on continental weathering, which might be rather rapid under the circumstances). (iv) The surface temperature of dry land is presumed to be the same as the lower atmosphere. A thermal wave propagates into the land at a rate set by conduction. Impacts not greatly larger than Chicxulub can raise the surface temperature by tens, hundreds, or even thousands of degrees, and evaporate meters to hundreds of meters of water. The biggest should have vitrified exposed dry land. More results are for the talk, as here we have run out of space.

Environmental Consequences of Big Nasty Impacts on the Early Earth

NASA Technical Reports Server (NTRS)

Zahnle, Kevin

2015-01-01

The geological record of the Archean Earth is spattered with impact spherules from a dozen or so major cosmic collisions involving Earth and asteroids or comets (Lowe, Byerly 1986, 2015). Extrapolation of the documented deposits suggests that most of these impacts were as big or bigger than the Chicxulub event that famously ended the reign of the thunder lizards. As the Archean impacts were greater, the environmental effects were also greater. The number and magnitude of the impacts is bounded by the lunar record. There are no lunar craters bigger than Chicxulub that date to Earth's mid-to-late Archean. Chance dictates that Earth experienced no more than approximately 10 impacts bigger than Chicxulub between 2.5 billion years and 3.5 2.5 billion years, the biggest of which were approximately30-100 times more energetic, comparable to the Orientale impact on the Moon (1x10 (sup 26) joules). To quantify the thermal consequences of big impacts on old Earth, we model the global flow of energy from the impact into the environment. The model presumes that a significant fraction of the impact energy goes into ejecta that interact with the atmosphere. Much of this energy is initially in rock vapor, melt, and high speed particles. (i) The upper atmosphere is heated by ejecta as they reenter the atmosphere. The mix of hot air, rock vapor, and hot silicates cools by thermal radiation. Rock raindrops fall out as the upper atmosphere cools. (ii) The energy balance of the lower atmosphere is set by radiative exchange with the upper atmosphere and with the surface, and by evaporation of seawater. Susequent cooling is governed by condensation of water vapor. (iii) The oceans are heated by thermal radiation and rock rain and cooled by evaporation. Surface waters become hot and salty; if a deep ocean remains it is relatively cool. Subsequently water vapor condenses to replenish the oceans with hot fresh water (how fresh depending on continental weathering, which might be rather rapid under the circumstances). (iv) The surface temperature of dry land is presumed to be the same as the lower atmosphere. A thermal wave propagates into the land at a rate set by conduction. Impacts not greatly larger than Chicxulub can raise the surface temperature by tens, hundreds, or even thousands of degrees, and evaporate meters to hundreds of meters of water. The biggest should have vitrified exposed dry land. More results are for the talk, as here we have run out of space.

Silicon Carbide Found in K/T Boundary Layer: Implication for Asteroid Collision with Planet Earth

NASA Astrophysics Data System (ADS)

Leung, I. S.; Tsao, C.

2016-12-01

An event at the end of the Cretaceous Period 65.5 m.y. ago produced an impact structure 300 km in diameter designated the Chicxulub Crater, located partly on the Yucatan Peninsula and the Caribbian Sea floor. Mass extinction following that event killed 75% of Earth's living species, including dinosaurs. To this date, the killer space object has not been identified, but it was frequently conjectured to be a comet or an asteroid. The goal of our study was to search for evidence which might implicate the culprit. The Chicxulub impact caused extensive wildfires producing Ir-rich dust fallouts in worldwide localities, among which the least contaminated by land-derived sediments may be situated on deep ocean floors. Our study is based on a sample of pelagic clay from the giant piston core LL44-GPC3 taken from the Pacific Plate, north of the Hawaiian Islands (Woods Hole Oceanographic Institution). The 1-cm thick Ir-rich layer was located at a downcore depth of 1055-1056 cm below sea floor. From a 5 cubic cm sample provided by Jim Broda, we found 29 impact glass spherules and 4 silicon carbide (SiC) crystals. SiC has been reported in carbonaceous meteorites. Our findings of SiC in the K/T boundary layer seem to implicate that an asteroid having composition akin to that of carbonaceous chondrites might have been the killer projectile during the Chicxulub event. However, impact by a comet cannot be ruled out, since the mineralogy of cometary dust is as yet unknown.

Impact ejecta and carbonate sequence in the eastern sector of the Chicxulub crater

NASA Astrophysics Data System (ADS)

Urrutia-Fucugauchi, Jaime; Chavez-Aguirre, Jose Maria; Pérez-Cruz, Ligia; De la Rosa, Jose Luis

2008-12-01

The Chicxulub 200 km diameter crater located in the Yucatan platform of the Gulf of Mexico formed 65 Myr ago and has since been covered by Tertiary post-impact carbonates. The sediment cover and absence of significant volcanic and tectonic activity in the carbonate platform have protected the crater from erosion and deformation, making Chicxulub the only large multi-ring crater in which ejecta is well preserved. Ejecta deposits have been studied by drilling/coring in the southern crater sector and at outcrops in Belize, Quintana Roo and Campeche; little information is available from other sectors. Here, we report on the drilling/coring of a section of ˜34 m of carbonate breccias at 250 m depth in the Valladolid area (120 km away from crater center), which are interpreted as Chicxulub proximal ejecta deposits. The Valladolid breccias correlate with the carbonate breccias cored in the Peto and Tekax boreholes to the south and at similar radial distance. This constitutes the first report of breccias in the eastern sector close to the crater rim. Thickness of the Valladolid breccias is less than that at the other sites, which may indicate erosion of the ejecta deposits before reestablishment of carbonate deposition. The region east of the crater rim appears different from regions to the south and west, characterized by high density and scattered distribution of sinkholes.

Generation, propagation and run-up of tsunamis due to the Chicxulub impact event

NASA Astrophysics Data System (ADS)

Weisz, R.; Wuennenmann, K.; Bahlburg, H.

2003-04-01

The Chicxulub impact event can be investigated in (1) local, (2) regional and in (3) global scales. Our investigations focus on the regional scale, especially on the influence of tsunami waves on the coast around the Gulf of Mexico caused by the impact. During an impact two types of tsunamis are generated. The first wave is known as the "rim wave" and is generated in front of the ejecta curtain. The second one is linked to the late modification stage of the impact and results from the collapsing cavity of water. We designate this wave as "collapse wave". The "rim wave" and "collapse wave" are able to propagate over long distances, without a significant loss of wave amplitude. Corresponding to the amplitudes, the waves have a potentially large influence on the coastal areas. Run-up distance and run-up height can be used as parameters for describing this influence. We are utilizing a multimaterial hydrocode (SALE) to simulate the generation of tsunami waves. The propagation of the waves is based on the non-linear shallow water theory, because tsunami waves are defined to be long waves. The position of the coast line varies according to the tsunami run-up and is implemented with open boundary conditions. We show with our investigations (1) the generation of tsunami waves due to shallow water impacts, (2) wave damping during propagation, and (3) the influence of the "rim wave" and the "collapse wave" on the coastal areas. Here, we present our first results from numerical modeling of tsunami waves owing to a Chicxulub sized impactor. The characteristics of the “rim wave” depend on the size of the bolide and the water depth. However, the amplitude and velocity of the “collapse wave” is only determined by the water depth in the impact area. The numerical modeling of the tsunami propagation and run-up is calculated along a section from the impact point towards to the west and gives the moderate damping of both waves and the run-up on the coastal area. As a first approximation, the bathymetric data, used in the wave propagation and run-up, correspond to a linearized bathymetry of the Recent Gulf of Mexico. The linearized bathymetry allows to study the influence of the bathymetry on wave propagation and run-up. Additionally, we give preliminary results of the implementation of the two-dimensional propagation and run-up model for arbitrary bathymetries. The two-dimensional wave propagation model will enable us to more realistically asses the influence of the impact-related tsunamis on the coasts around the Gulf of Mexico due to the Chicxulub impact event.

UNAM Scientific Drilling Program of Chicxulub Impact Structure-Evidence for a 300 kilometer crater diameter

NASA Astrophysics Data System (ADS)

Urrutia-Fucugauchi, J.; Marin, L.; Trejo-Garcia, A.

As part of the UNAM drilling program at the Chicxulub structure, two 700 m deep continuously cored boreholes were completed between April and July, 1995. The Peto UNAM-6 and Tekax UNAM-7 drilling sites are ˜150 km and 125 km, respectively, SSE of Chicxulub Puerto, near the crater's center. Core samples from both sites show a sequence of post-crater carbonates on top of a thick impact breccia pile covering the disturbed Mesozoic platform rocks. At UNAM-7, two impact breccia units were encountered: (1) an upper breccia, mean magnetic susceptibility is high (˜55 × 10-6 SI units), indicating a large component of silicate basement has been incorporated into this breccia, and (2) an evaporite-rich, low susceptibility impact breccia similar in character to the evaporite-rich breccias observed at the PEMEX drill sites further out. The upper breccia was encountered at ˜226 m below the surface and is ˜125 m thick; the lower breccia is immediately subjacent and is >240 m thick. This two-breccia sequence is typical of the suevite-Bunte breccia sequence found within other well preserved impact craters. The suevitic upper unit is not present at UNAM-6. Instead, a >240 m thick evaporite-rich breccia unit, similar to the lower breccia at UNAM-7, was encountered at a depth of ˜280 m. The absence of an upper breccia equivalent at UNAM-6 suggests some portion of the breccia sequence has been removed by erosion. This is consistent with interpretations that place the high-standing crater rim at 130-150 km from the center. Consequently, the stratigraphic observations and magnetic susceptibiity records on the upper and lower breccias (depth and thickness) support a ˜300 km diameter crater model.

Detection of groundwater conduits in limestones with gravity surveys: data from the area of the Chicxulub Impact crater, Yucatan Peninsula, Mexico.

PubMed

Kinsland, G L; Hurtado, M; Pope, K O

2000-04-15

Small negative gravity anomalies are found in gravity data from along the northwestern shoreline of the Yucatan Peninsula. These anomalies are shown to be due to elongate, shallow anomalous porosity zones in the Tertiary carbonates. These zones are caused primarily by groundwater solution and are presently active conduits for groundwater flow. The association of these small gravity anomalies with known topographic and structural features of the area, which partially overlies the Chicxulub Impact crater, indicates their development was influenced by structures, faults and/or fractures, within the Tertiary and pre-Tertiary carbonates.

Detection of groundwater conduits in limestones with gravity surveys: data from the area of the Chicxulub Impact crater, Yucatan Peninsula, Mexico

NASA Technical Reports Server (NTRS)

Kinsland, G. L.; Hurtado, M.; Pope, K. O.; Ocampo, A. C. (Principal Investigator)

2000-01-01

Small negative gravity anomalies are found in gravity data from along the northwestern shoreline of the Yucatan Peninsula. These anomalies are shown to be due to elongate, shallow anomalous porosity zones in the Tertiary carbonates. These zones are caused primarily by groundwater solution and are presently active conduits for groundwater flow. The association of these small gravity anomalies with known topographic and structural features of the area, which partially overlies the Chicxulub Impact crater, indicates their development was influenced by structures, faults and/or fractures, within the Tertiary and pre-Tertiary carbonates.

The Chicxulub impact at the K-Pg boundary - search for traces of the projectile

NASA Astrophysics Data System (ADS)

Deutsch, A.

2012-04-01

One of the most interesting problems in the context of the end-Cretaceous Chicxulub impact is the question after the whererabouts of the main mass of the projectile. The nature of this >10 km-sized Chicxulub projectile was constrained by an anomaly in the chromium isotope 54 in the K-Pg deposit at Stevens Klint, Denmark, to a carbonaceous chondrite of type CM2 [1]. About 1.5 % of the estimated mass of the projectile has been detected world-wide in the K-Pg boundary layer; mainly in the form of platinum group elements (PGE) as well as other siderophile elements (Ni, Co ... ). A contamination by or even a major contribution of other "projectile" elements to the K-Pg event bed was rarely proposed. The few examples in the literature (cf. compilation in [2, 3]) used rare earth elements (REE) distribution patterns that are slightly inconsistent with REE patterns typical for the upper continental crust (UCC). Ejecta consisting of UCC target rocks is expected to form the overwhelming mass of the ejecta. In most K-Pg layers, however, the ejecta is diluted or even totally masked by a component of more local origin and with features of high-energy deposition mechanisms. Numerical models [4] indicate a deposition of >500km3 projectile material, corresponding to >2 x 10exp9 tons of mainly silica, iron, and magnesium in the K-Pg event bed. Detecting the "meteoritic" origin of these major elements, however, in a matrix of siliceous detritus, is practically impossible. Recent LA-ICP-MS analyses show that siliceous impact spherules - hydrated glass or altered to chlorite - in the Chicxulub event bed at various locations (e.g., Shell Creek, La Lajilla, La Popa) have REE patterns that are flat and un-fractionated, corresponding quite well to a typical CI-pattern. The REE abundances are chondritic to sub-chondritic. Mixing calculations indicate that the maximum REE contribution of UCC material to the REE budget of these spherules is on the order of 2 %, but usually much less. These flat REE patterns cannot originate from any known alteration process; they truly reflect a "meteoritic" component in the spherules. Accepting this fact, a certain amount of the siliceous host material (i.e., the spherules) must consist also of projectile material. Depending on the sampling site, the spherules with the flat REE distribution patterns amount to between 10 and ~70 vol% of the Chicxulub event bed. The widespread occurrence of this projectile matter in the K-Pg event bed reconciles observations with impact models [4]. Ref. [1] Trinquier A. et al. (2006) EPSL 241, 780-788. [2] Smit J. (1999) Ann. Rev. Earth Planet. Sci. 27, 75-113. [3] Schulte P. et al. (2010) Science 327, 1214-1218. [4] Artemieva N. and Morgan J. (2009) Icarus 201, 768-780.

Rapid short-term cooling following the Chicxulub impact at the Cretaceous–Paleogene boundary

PubMed Central

Vellekoop, Johan; Sluijs, Appy; Smit, Jan; Schouten, Stefan; Weijers, Johan W. H.; Sinninghe Damsté, Jaap S.; Brinkhuis, Henk

2014-01-01

The mass extinction at the Cretaceous–Paleogene boundary, ∼66 Ma, is thought to be caused by the impact of an asteroid at Chicxulub, present-day Mexico. Although the precise mechanisms that led to this mass extinction remain enigmatic, most postulated scenarios involve a short-lived global cooling, a so-called “impact winter” phase. Here we document a major decline in sea surface temperature during the first months to decades following the impact event, using TEX86 paleothermometry of sediments from the Brazos River section, Texas. We interpret this cold spell to reflect, to our knowledge, the first direct evidence for the effects of the formation of dust and aerosols by the impact and their injection in the stratosphere, blocking incoming solar radiation. This impact winter was likely a major driver of mass extinction because of the resulting global decimation of marine and continental photosynthesis. PMID:24821785

Self-Shielding of Thermal Radiation by Chicxulub Ejecta: Firestorm or Fizzle?

NASA Astrophysics Data System (ADS)

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

2008-12-01

The discovery of soot within the Chicxulub ejecta sequence and the observed survival patterns of terrestrial organisms across the K/Pg boundary led to the hypothesis that thermal radiation from the atmospheric reentry of hypervelocity impact ejecta was sufficient to ignite global wildfires and cause biological catastrophe. Using a two-dimensional, two-phase fluid flow code, KFIX-LPL, we model the atmospheric reentry of distal Chicxulub ejecta and calculate the fluxes of thermal radiation throughout the atmosphere. The model treatment includes optical opacity, allowing us to examine the effects that greenhouse gases and the spherules themselves have on the transfer of thermal radiation to the ground. We model a simple Chicxulub scenario where 250-µm spherules reenter the atmosphere for an hour with maximum inflow after 10 minutes. Our models predict a pulse of thermal radiation at the ground peaking at ~6 kW/m2, analogous to an oven set on 'broil'. Previous calculations, which did not consider spherule opacity, yielded >10 kW/ m2 sustained over an hour or more and such an extended pulse of high fluxes is thought to be required for wildfire ignition. However, our model suggests a half-hour in which fluxes exceed the solar norm and only a few minutes >5 kW/m2. Large fluxes are not sustained in our models due to the increasingly opaque cloud of settling spherules, which increasingly blocks the transmission of thermal radiation from the decelerating spherules above. Hence, the spherules themselves limit the magnitude and duration of thermal radiation at the ground. Such self-shielding may have prevented the ignition of global wildfires following Chicxulub and limited other environmental effects. Keeping the impact wildfire hypothesis will require a mechanism to override this effect. A nonuniform distribution of spherule reentry may produce gaps in the opaque spherule layer through which the downward thermal radiation may be concentrated. Additionally, an opaque cloud of dust, injected into the upper atmosphere from the impact plume, would act to reflect some of the space-bound thermal radiation downwards.

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

NASA Technical Reports Server (NTRS)

Sharpton, Virgil L.; Marin, Luis E.

1997-01-01

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

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

PubMed

Sharpton, V L; Marin, L E

1997-05-30

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

The formation of peak rings in large impact craters.

PubMed

Morgan, Joanna V; Gulick, Sean P S; Bralower, Timothy; Chenot, Elise; Christeson, Gail; Claeys, Philippe; Cockell, Charles; Collins, Gareth S; Coolen, Marco J L; Ferrière, Ludovic; Gebhardt, Catalina; Goto, Kazuhisa; Jones, Heather; Kring, David A; Le Ber, Erwan; Lofi, Johanna; Long, Xiao; Lowery, Christopher; Mellett, Claire; Ocampo-Torres, Rubén; Osinski, Gordon R; Perez-Cruz, Ligia; Pickersgill, Annemarie; Poelchau, Michael; Rae, Auriol; Rasmussen, Cornelia; Rebolledo-Vieyra, Mario; Riller, Ulrich; Sato, Honami; Schmitt, Douglas R; Smit, Jan; Tikoo, Sonia; Tomioka, Naotaka; Urrutia-Fucugauchi, Jaime; Whalen, Michael; Wittmann, Axel; Yamaguchi, Kosei E; Zylberman, William

2016-11-18

Large impacts provide a mechanism for resurfacing planets through mixing near-surface rocks with deeper material. Central peaks are formed from the dynamic uplift of rocks during crater formation. As crater size increases, central peaks transition to peak rings. Without samples, debate surrounds the mechanics of peak-ring formation and their depth of origin. Chicxulub is the only known impact structure on Earth with an unequivocal peak ring, but it is buried and only accessible through drilling. Expedition 364 sampled the Chicxulub peak ring, which we found was formed from uplifted, fractured, shocked, felsic basement rocks. The peak-ring rocks are cross-cut by dikes and shear zones and have an unusually low density and seismic velocity. Large impacts therefore generate vertical fluxes and increase porosity in planetary crust. Copyright © 2016, American Association for the Advancement of Science.

Chicxulub ejecta at the Cretaceous-Paleogene (K-P) boundary in Northeastern Mexico

NASA Astrophysics Data System (ADS)

Schulte, Peter; Kontny, Agnes

2005-04-01

The combined petrological and rock magnetic study of the Cretaceous-Paleogene (K-P) boundary in northeastern Mexico revealed compositionally and texturally complex Chicxulub ejecta deposits. The predominant silicic ejecta components are Fe-Mg-rich chlorite and Si-Al-K-rich glass spherules with carbonate inclusions and schlieren. Besides these silica phases, the most prominent ejecta component is carbonate. Carbonate occurs as lithic clasts, accretionary lapilli, melt globules (often with quench textures), and as microspar. The composition of the spherules provides evidence for a range of target rocks of mafic to intermediate composition, presumably situated in the northwestern sector of the Chicxulub impact structure. The abundance of carbonate ejecta suggests that this area received ejecta mainly from shallow, carbonate-rich lithologies. Rare µm-sized metallic and sulfidic Ni-Co-rich inclusions in the spherules indicate a possible contamination by meteoritic material. This complex composition underlines the similarities of ejecta in NE Mexico to Chicxulub ejecta from K-P sections worldwide. Although the ejecta display a great variability, the magnetic susceptibility, remanence, and hysteresis properties of the ejecta deposits are fairly homogeneous, with dominantly paramagnetic susceptibilities and a weak ferromagnetic contribution from hematite and goethite. The absence of spinels and the ubiquitous presence of hematite and goethite points to high oxygen fugacity during the impact process. The microfacies and internal texture of the ejecta deposits show welding and fusing of components, as well as evidence for liquid immiscibility between silicic and carbonate melts. No evidence for binary mixing of ejecta phases was found. Therefore, Chicxulub ejecta in NE Mexico probably derived from less energetic parts of the ejecta curtain. However, welding features of ejecta particles and enclosed marl clasts and/or benthic foraminifera from a siliciclastic environment suggest interaction of the - still hot - ! ejecta curtain with northern Mexican shelf sediments. In addition, an initial ground surge-like ejecta-dispersion mode seems possible.

Shaded Relief with Height as Color, Yucatan Peninsula, Mexico

NASA Image and Video Library

2003-03-06

This shaded relief image of Mexico Yucatan Peninsula show a subtle, but unmistakable, indication of the Chicxulub impact crater. Most scientists now agree that this impact was the cause of the Cretatious-Tertiary Extinction.

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

NASA Technical Reports Server (NTRS)

Pope, Kevin O.

1996-01-01

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

Anomalous K-Pg-aged seafloor attributed to impact-induced mid-ocean ridge magmatism.

PubMed

Byrnes, Joseph S; Karlstrom, Leif

2018-02-01

Eruptive phenomena at all scales, from hydrothermal geysers to flood basalts, can potentially be initiated or modulated by external mechanical perturbations. We present evidence for the triggering of magmatism on a global scale by the Chicxulub meteorite impact at the Cretaceous-Paleogene (K-Pg) boundary, recorded by transiently increased crustal production at mid-ocean ridges. Concentrated positive free-air gravity and coincident seafloor topographic anomalies, associated with seafloor created at fast-spreading rates, suggest volumes of excess magmatism in the range of ~10 5 to 10 6 km 3 . Widespread mobilization of existing mantle melt by post-impact seismic radiation can explain the volume and distribution of the anomalous crust. This massive but short-lived pulse of marine magmatism should be considered alongside the Chicxulub impact and Deccan Traps as a contributor to geochemical anomalies and environmental changes at K-Pg time.

Anomalous K-Pg–aged seafloor attributed to impact-induced mid-ocean ridge magmatism

PubMed Central

Byrnes, Joseph S.; Karlstrom, Leif

2018-01-01

Eruptive phenomena at all scales, from hydrothermal geysers to flood basalts, can potentially be initiated or modulated by external mechanical perturbations. We present evidence for the triggering of magmatism on a global scale by the Chicxulub meteorite impact at the Cretaceous-Paleogene (K-Pg) boundary, recorded by transiently increased crustal production at mid-ocean ridges. Concentrated positive free-air gravity and coincident seafloor topographic anomalies, associated with seafloor created at fast-spreading rates, suggest volumes of excess magmatism in the range of ~105 to 106 km3. Widespread mobilization of existing mantle melt by post-impact seismic radiation can explain the volume and distribution of the anomalous crust. This massive but short-lived pulse of marine magmatism should be considered alongside the Chicxulub impact and Deccan Traps as a contributor to geochemical anomalies and environmental changes at K-Pg time. PMID:29441360

High Resolution Vertical Seismic Profile from the Chicxulub IODP/ICDP Expedition 364 Borehole: Wave Speeds and Seismic Reflectivity.

NASA Astrophysics Data System (ADS)

Nixon, C.; Kofman, R.; Schmitt, D. R.; Lofi, J.; Gulick, S. P. S.; Christeson, G. L.; Saustrup, S., Sr.; Morgan, J. V.

2017-12-01

We acquired a closely-spaced vertical seismic profile (VSP) in the Chicxulub K-Pg Impact Crater drilling program borehole to calibrate the existing surface seismic profiles and provide complementary measurements of in situ seismic wave speeds. Downhole seismic records were obtained at spacings ranging from 1.25 m to 5 m along the borehole from 47.5 m to 1325 mwsf (meters wireline below sea floor) (Fig 1a) using a Sercel SlimwaveTM geophone chain (University of Alberta). The seismic source was a 30/30ci Sercel Mini GI airgun (University of Texas), fired a minimum of 5 times per station. Seismic data processing used a combination of a commercial processing package (Schlumberger's VISTA) and MatlabTM codes. The VSP displays detailed reflectivity (Fig. 1a) with the strongest reflection seen at 600 mwsf (280 ms one-way time), geologically corresponding to the sharp contact between the post-impact sediments and the target peak ring rock, thus confirming the pre-drilling interpretations of the seismic profiles. A two-way time trace extracted from the separated up-going wavefield matches the major reflection both in travel time and character. In the granitic rocks that form the peak ring of the Chicxulub impact crater, we observe P-wave velocities of 4000-4500 m/s which are significantly less than the expected values of granitoids ( 6000 m/s) (Fig. 1b). The VSP measured wave speeds are confirmed against downhole sonic logging and in laboratory velocimetry measurements; these data provide additional evidence that the crustal material displaced by the impact experienced a significant amount of damage. Samples and data provided by IODP. Samples can be requested at http://web.iodp.tamu.edu/sdrm after 19 October 2017. Expedition 364 was jointly funded by ECORD, ICDP, and IODP with contributions and logistical support from the Yucatan State Government and UNAM. The downhole seismic chain and wireline system is funded by grants to DRS from the Canada Foundation for Innovation and the Alberta Enterprise and Advanced Education Grants Program.

Anhydrite EOS and Phase Diagram in Relation to Shock Decomposition

NASA Technical Reports Server (NTRS)

Ivanov, B. A.; Langenhorst, F.; Deutsch, A.; Hornemann, U.

2004-01-01

In the context of the Chicxulub impact, it became recently obvious that experimental and theoretical research on the shock behavior of sulfates is essential for an assessment of the role of shock-released gases in the K/T mass extinction. The Chicxulub crater is the most important large impact structure where the bolide penetrated a sedimentary layer with large amounts of interbedded anhydrite (Haughton has also significant anhydrite in the target). The sulfuric gas production by shock compression/decompression of anhydrite is an important issue, even if the size of Chicxulub crater is only half of the so far assumed size. The comparison of experimental data for anhydrite, shocked with different techniques at various laboratories, reveals large differences in the threshold pressures for melting and decomposition. To gain insight into this issue, we have made a theoretical investigation of the thermodynamic properties of anhydrite. The project includes the review of data published in the last 40 years - reasons to study anhydrite cover a wide field of interests: from industrial problems of cement and ceramic production to the analysis of nuclear underground explosions in salt domes, conducted in the USA and USSR in the 1970th.

Chicxulub: testing for post-impact hydrothermal inputs into the Tertiary ocean

NASA Astrophysics Data System (ADS)

Rowe, A.; Wilkinson, J.; Morgan, J.

2003-04-01

Large terrestrial impacts produce intense fracturing of the crust and large melt sheets, providing ideal conditions for extensive hydrothermal circulation. In marine settings, such as Chicxulub, there is the potential for downward penetration of cold seawater, heating by the thermal anomaly at the impact site and leaching of metals, prior to buoyancy driven flow back to the surface. There, fluids may undergo venting into the water column. A large proportion of the metals in such vent fluids precipitate close to the site of discharge; however, a proportion of the fluid is dispersed as a hydrothermal plume. Dissolved and particulate materials (in particular manganese and iron oxyhydroxides) can be carried for several hundreds of kilometers, before falling out to form metal-rich sediments. A series of Tertiary core samples has been obtained from the International Continental Drilling Program at Chicxulub (CSDP). These comprise fine-grained cream coloured carbonate sediments with fine laminations. Transmitted light and cathodoluminescence petrography have been used to carry out a preliminary characterization of the samples. Multi-element analysis has also been undertaken by ICP-AES. Samples were reduced to powder and digested using a nitric-perchloric-hydrofluoric acid attack. Rare earth elements (REE) have been analysed by ICP-MS and solutions were prepared using a modified nitric-perchloric-hydrofluoric acid attack. Geochemical analyses have been carried out to test for characteristic signals of hydrothermal input, such as enrichments in Mn, Fe, Cu, Zn, Pb, Mg, Ba, Co, Cr and Ni. The REE are scavenged from seawater onto iron oxide surfaces in the plume; hence anomalous REE concentrations are also indicative of hydrothermal addition. Furthermore, the type of anomaly can differentiate between sediments proximal (+ve Eu) distal (-ve Ce) to the vent site. The stratigraphic extent of any anomalies can be used to constrain the duration of any post-impact circulation. The wider significance of such hydrothermal circulation, if identified, include the potential formation of hydrothermal mineralization and vent-related ecosystems in the Chicxulub crater. The results will also have implications for the exploration of impact-related hydrothermal ecosystems on other planets.

High-Resolution Aeromagnetic Survey over the Yucatan Peninsula - Implications for Chicxulub Impact, Secondary Craters and Regional Crustal Structures

NASA Astrophysics Data System (ADS)

Fucugauchi, J. U.; Lopez-Loera, H.; Rebolledo-Vieyra, M.

2011-12-01

We present the initial results of a low-altitude high-resolution aeromagnetic study over the Yucatan peninsula. Area surveyed extends from 86W to 91W and 18N to 21N, covering the peninsula and adjacent continental margin of Gulf of Mexico and Caribbean Sea. Aeromagnetic surveys are integrated into a regional map, and regional and residual anomalies are separated using spectral and least-squares methods. For the study, aeromagnetic field was reduced to the pole and several data filtering techniques were used, including first and second vertical derivatives, analytical signal, and upward and downward analytical continuations. The region is characterized by large amplitude broad elongated magnetic anomalies oriented north-south in the northern sector of the continental shelf, and northwest-southeast and northeast-southwest over the western and eastern sides of the peninsula, respectively. Major regional anomalies extend from the continental shelf into the peninsula, whereas other anomaly trends in the central northern sector, at northeast limit of Chicxulub crater, are restricted to the shelf. Largest anomaly on the east extends over the Holbox fracture zone. At its southern end, south of Chetumal a parallel trend extends over the Rio Hondo fault zone between Quintana Roo and Belize. On the western peninsula the anomaly is characterized by two parallel trends offset between Yucatan and Campeche. The central zone of Chicxulub is characterized by a semi-circular anomaly pattern, surrounded by long wavelength small amplitude anomalies extending to the east on the peninsula and shelf, isolated from the regional broad anomalies. To the south of Chicxulub anomaly, there is an elongated low with a central high extending southward from the terrace zone inside the crater rim. The elongated magnetic anomaly correlates with a broad gravity low, which is apparent south of the concentric zone of anomalies. To the north of Chicxulub anomaly, a magnetic high inside the crater is followed by a low outside, which extend to the north and northwest. The regional broad anomalies crossing the peninsula and shelf are interpreted as crustal structures on the Yucatan block related to pre- and rifting deformation, which include basement uplift. The southward elongated magnetic anomaly and gravity low may correspond to a pre-impact structure. From analysis of residual anomalies, we found no clear indication of secondary craters or multiple impacts.

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

NASA Technical Reports Server (NTRS)

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

1997-01-01

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

Geophysical characterization of the Chicxulub impact structure

NASA Astrophysics Data System (ADS)

Gulick, S. P.; Christeson, G. L.; Barton, P. J.; Grieve, R. A.; Morgan, J. V.; Fucugauchi, J. U.

2013-05-01

The Chicxulub impact structure, conclusively linked to the 65.5 Ma mass extinction, includes three sets of inward dipping, ring faults, between 70 and 130 km radially with a topographically elevated inner rim, at the inner edge of these faults except in the northeast where such a rim is absent. Slump blocks offset by large faults result in a terrace zone, that steps down from the inner rim into the annular trough. The inner blocks underlie the peak ring --an internal topographic ring of topography that exhibits variable relief due to target asymmetries and bounds the coherent melt sheet within the central basin. Impact breccias lie within the annular trough above the slump blocks and proximal ejecta and within the central basin above the melt sheet. Beneath the melt sheet is the top of the central uplift, displaced by >10 km vertically, and an upwarped Moho, displaced by 1-2 km. These interpretations and hydrocode models support the following working hypothesis for the formation of Chicxulub: a 50 km radius transient cavity, lined with melt and impact breccia, formed within 10s of seconds of the 65.5 Ma impact and within minutes, weakened rebounding crust rose above kilometers above the surface, the transient crater rim underwent localized, brittle deformation and collapsed into large slump blocks resulting in a inner rim being preserved 70-85 km from crater center, and ring faults forming farther outwards. The overheightened central uplift of weakened crust collapsed outwards forming the peak ring, and buried the inner slump blocks. Most impact melt that lined the transient cavity was transported on top of the central uplift, ultimately emplaced as a coherent <3-km thick melt sheet that shallows within the inner regions of the peak ring. Smaller pockets of melt flowed into the annular trough. During and likely for sometime after these events, slope collapse, proximal ejecta, ground surge, and tsunami waves infilled the annular trough with sediments up to 3 km thick and the central basin with sediments up to 900 m thick. Testing this working hypothesis requires direct observation and measurements on the impact materials, especially within and adjacent to the peak ring and central basin.

Exploring the Hydrothermal System in the Chicxulub Crater and Implications for the Early Evolution of Life on Earth

NASA Astrophysics Data System (ADS)

Kring, D. A.; Schmieder, M.; Tikoo, S.; Riller, U. P.; Simpson, S. L.; Osinski, G.; Cockell, C. S.; Coolen, M.; Gulick, S. P. S.; Morgan, J. V.

2017-12-01

Impact cratering, particularly large basin-size craters with diameters >100 km, have the potential to generate vast subsurface hydrothermal systems. There were dozens of such impacts during the Hadean and early Archean, some of which vaporized seas for brief periods of time, during which the safest niches for early life may have been in those subsurface hydrothermal systems. The Chicxulub crater can serve as a proxy for those events. New IODP-ICDP core recovered by Expedition 364 reveals a high-temperature (>300 degree C) system that may have persisted for more than 100,000 years. Of order 105 to 106 km3 of crust was structurally deformed, melted, and vaporized within about 10 minutes of the impact. The crust had to endure immense strain rates of 104/s to 106/s, up to 12 orders of magnitude greater than those associated with igneous and metamorphic processes. The outcome is a porous, permeable region that is a perfect host for hydrothermal circulation across the entire diameter of the crater to depths up to 5 or 6 km. The target rocks at Chicxulub are composed of an 3 km-thick carbonate platform sequence over a crystalline basement composed of igneous granite, granodiorite, and a few other intrusive components, such as dolerite, and metamorphic assemblages composed, in part, of gneiss and mica schist. Post-impact hydrothermal alteration includes Ca-Na- and K-metasomatism, pervasive hydration to produce layered silicates, and lower-temperature vug-filling zeolites as the system cycled from high temperatures to low temperatures. While the extent of granitic crust on early Earth is still debated and, thus, the direct application of those mineral reactions to the Hadean and early Archean can be debated, the thermal evolution of the system should be applicable to diverse crustal compositions. It is important to point out that pre-impact thermal conditions of Hadean and early Archean crust can affect the size of an impact basin and, in turn, the proportion of that basin that may experience hydrothermal conditions. The Chicxulub crater - as sampled by Expedition 364 - will provide the baseline needed to assess the spatial and temporal extent of Hadean and early Archean hydrothermal systems and their potential as crucibles for pre-biotic chemistry and the early evolution of microbial life.

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

NASA Technical Reports Server (NTRS)

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

1993-01-01

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

Anaglyph, Yucatan Peninsula, Mexico

NASA Image and Video Library

2003-03-06

This anaglyph of Mexico Yucatan Peninsula was generated from NASA Shuttle Radar Topography Mission data, and shows a subtle but distinctive indication of the Chicxulub impact crater. 3D glasses are necessary to view this image.

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

USGS Publications Warehouse

Brett, R.

1992-01-01

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

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

NASA Astrophysics Data System (ADS)

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

2003-12-01

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

Paleomagnetic and Magnetostratigraphic Studies in Drilling Projects of Impact Craters - Recent Studies, Challenges and Perspectives

NASA Astrophysics Data System (ADS)

Fucugauchi, J. U.; Velasco-Villarreal, M.; Perez-Cruz, L. L.

2013-05-01

Paleomagnetic studies have long been successfully carried out in drilling projects, to characterize the borehole columns and to investigate the subsurface structure and stratigraphy. Magnetic susceptibility logging and magnetostratigraphic studies provide data for lateral correlation, formation evaluation, azimuthal core orientation, physical properties, etc., and are part of the tools available in the ocean and continental drilling programs. The inclusion of continuous core recovery in scientific drilling projects have greatly expanded the range of potential applications of paleomagnetic and rock magnetic studies, by allowing laboratory measurements on core samples. For this presentation, we concentrate on drilling studies of impact structures and their usefulness for documenting the structure, stratigraphy and physical properties at depth. There are about 170-180 impact craters documented in the terrestrial record, which is a small number compared to what is observed in the Moon, Mars, Venus and other bodies of the solar system. Of the terrestrial impact craters, only a few have been studied by drilling. Some craters have been drilled as part of industry exploration surveys and/or academic projects, including notably the Sudbury, Ries, Vredefort, Manson and many other craters. As part of the Continental ICDP program, drilling projects have been conducted on the Chicxulub, Bosumtwi, Chesapeake and El gygytgyn craters. Drilling of terrestrial craters has proved important in documenting the shallow stratigraphy and structure, providing insight on the cratering and impact dynamics. Questions include several that can only be addressed by retrieving core samples and laboratory analyses. Paleomagnetic, rock magnetic and fabric studies have been conducted in the various craters, which are here summarized with emphasis on the Chicxulub crater and Yucatan carbonate platform. Chicxulub is buried under a kilometer of younger sediments, making drilling an essential tool. Oil exploration included several boreholes, and additionally we have drilled 11 boreholes with continuous core recovery. Contributions and limitations of paleomagnetism for investigating the impact age, crater stratigraphy, cratering, ejecta emplacement, impact dynamics, hydrothermal system and post-impact processes are discussed.

The Cretaceous-Paleogene boundary unit in the Gulf of Mexico: Large-scale oceanic basin response to the Chicxulub impact

NASA Astrophysics Data System (ADS)

Sanford, J. C.; Gulick, S. P.; Snedden, J.

2013-12-01

The prevailing theory for the Cretaceous-Paleogene (K-Pg) extinction event cites the Chicxulub asteroid impact on the Yucatán Peninsula as the catalyst for the global climatologic and ecologic crisis. This theory has been corroborated by a multitude of K-Pg boundary deposits observed globally in both boreholes and outcrops. The change in character of these deposits with proximity to the crater, from a millimeter-scale clay layer to a hectometer-scale carbonate sequence, supports a causal link between the boundary unit and the asteroid impact. Due to its passive marine setting and proximity to the Chicxulub crater, the Gulf of Mexico is the premier locale in which to study the near-field geologic effect of a massive bolide impact. Until recently, investigation of the K-Pg boundary deposit within the Gulf has been largely confined to outcrops and boreholes on the periphery of the basin due to the difficulty of observation of the boundary unit in the deep water. However, hydrocarbon exploration in the past decade has yielded significant borehole and seismic data that can be used to better understand the deep-water response to the impact and to gain a comprehensive regional understanding impact-related processes in the Gulf. Based on roughly 100 offshore and 300 onshore Cretaceous well penetrations, the K-Pg boundary is interpreted to range from a strictly erosional surface in shallow-water and coastal regimes to a mass transport deposit up to ~400 meters thick. Depth-converted seismic data throughout the Gulf corroborate such thicknesses and reveal that the deposit is virtually ubiquitous throughout the deep water. For the first time, the K-Pg boundary deposit has been tied from the central Gulf to the Chicxulub crater, further establishing a causative link between the two. Biostratigraphic data in wells confirm the age of the deposit and document the presence of the 'K-Pg boundary cocktail.' Seismic data reveals areas of extensive debris flows and slump deposits on the lower slope of the Florida Platform, providing further evidence of massive sediment redistribution. Log character of the boundary deposit varies significantly, suggesting changes in both depositional style (e.g, mass flow deposit, collapsed platform block, etc.) and sediment source (e.g., Yucatán Platform, Florida Platform, Texas coast, etc.). Reinvestigation of the classic K-Pg boundary deposits in DSDP Leg 77 cores reveals evidence of several sequences of debris flows and/or turbidites with possibly unique sediment sources, furthering our understanding of small-scale sedimentary processes of impact-related deposition. Generally, evidence supports the theory that the Chicxulub impact was a source of extreme allogenic energy that drastically altered the Gulf Mexico at the start of the Cenozoic. Seismogenic ground roll and multiple episodes of tsunami, erosion, platform collapse, and remobilized sediment effectively overwhelmed and resurfaced the basin's existing depositional systems within a matter of weeks to months. Such processes resulted in the nearly ubiquitous and often extremely thick K-Pg boundary unit in the Gulf. These results yield insight into the near-field effects of a massive bolide impact in a passive marine setting and the ability of such an impact to instantaneously restructure an oceanic basin and its depositional systems.

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

NASA Technical Reports Server (NTRS)

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

1997-01-01

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

Hydrocode simulation of the Chicxulub impact event and the production of climatically active gases

NASA Astrophysics Data System (ADS)

Pierazzo, Elisabetta; Kring, David A.; Melosh, H. Jay

1998-12-01

We constructed a numerical model of the Chicxulub impact event using the Chart-D Squared (CSQ) code coupled with the ANalytic Equation Of State (ANEOS) package. In the simulations we utilized a target stratigraphy based on borehole data and employed newly developed equations of state for the materials that are believed to play a crucial role in the impact-related extinction hypothesis: carbonates (calcite) and evaporites (anhydrite). Simulations explored the effects of different projectile sizes (10 to 30 km in diameter) and porosity (0 to 50%). The effect of impact speed is addressed by doing simulations of asteroid impacts (vi=20km/s) and comet impacts (vi=50km/s). The masses of climatically important species injected into the upper atmosphere by the impact increase with the energy of the impact event, ranging from 350 to 3500 Gt for CO2, from 40 to 560 Gt for S, and from 200 to 1400 Gt for water vapor. While our results are in good agreement with those of Ivanov et al. [1996], our estimated CO2 production is 1 to 2 orders of magnitude lower than the results of Takata and Ahrens [1994], indicating that the impact event enhanced the end-Cretaceous atmospheric CO2 inventory by, at most, 40%. Consequently, sulfur may have been the most important climatically active gas injected into the stratosphere. The amount of S released by the impact is several orders of magnitude higher than any known volcanic eruption and, with H2O, is high enough to produce a sudden and significant perturbation of Earth's climate.

Yucatán subsurface stratigraphy: Implications and constraints for the Chicxulub impact

NASA Astrophysics Data System (ADS)

Ward, W. C.; Keller, G.; Stinnesbeck, W.; Adatte, T.

1995-10-01

Much of the discussion about the effects of an end-of-Cretaceous impact by a large extraterrestrial body in northwestern Yucatán has been done in the context of limited and partly erroneous published data on the Mesozoic stratigraphy of that area. Reexamination of cores and geophysical logs taken in several Pemex wells has produced improved lithologic and biostratigraphic correlation of the Jurassic to Maastrichtian section across the northern Yucatán peninsula. These data suggest that major disturbance of strata by an impact would have been confined to within about 100 km of the proposed impact center near Chicxulub. The only unusual lithologic unit is polymict breccia, which apparently was penetrated at or near the top of the Cretaceous section in all the deep wells of northern Yucatán. This breccia in Pemex wells Yucatán 1, 2, 4, 5A, and 6 is composed predominantly of detrital dolomite, limestone, and anhydrite clasts set in dolomitized carbonate mud matrix, which contains upper Maastrichtian foraminifers. These constituents, mixed with fragments of altered glass or melt rock, shocked quartz and feldspar, and basement rock, suggest an impact as the most likely origin for the breccia. The timing of brecciation is poorly constrained by biostratigraphic data. There is some evidence, however, that the breccia unit is overlain by about 18 m of uppermost Maastrichtian marls, suggesting an impact before the Cretaceous-Tertiary boundary. In addition, there may have been more than one episode of breccia deposition.

Impacts and Ophiolites: A Way to Recognize Large Terrestrial Impact Basins?

NASA Astrophysics Data System (ADS)

Olds, E. P.

2015-12-01

That Chicxulub Crater is located on ~35 km thick continental crust is apparently inconsistent with oceanic crustal/upper mantle geochemical signatures detected globally in the KT boundary impact layer [1-5 and unpublished Cr isotope data from the Yin lab at UC Davis] since introduction of the Alvarez hypothesis [6]. Apparent excavation and ejection of mafic/ultramafic target rock by the KT boundary impact might imply an additional KT impact site involving oceanic lithosphere. We speculate: 1) The Greater Antilles island chain ophiolite belt marks the rim of a ~700 km diameter impact basin, deformed and dismembered from an originally circular form by at least 50 million years of left lateral shear on the North American-Caribbean transform plate boundary; 2) Other ophiolite segments may similarly mark rims of large impact basins deformed to greater or lesser extent by, and serving as strain markers for, relative plate motions over geologic time; 3) The Greater Antilles/Chicxulub and Sulu Sea Basin/Spratly Island cases may constitute doublet craters of similar size ratio and separation distance; 4) Plate boundaries may be formed or modified by such impacts. Problems include: 1) The KT fireball layer should be tens of cm thick rather than a few mm thick [8-9]; 2) Impact basins of this size/scale are not expected in the Phanerozoic/Proterozoic [10]; References: [1] DePaolo D. J. et al. 1983. EPSL 64:356-373. [2] Hildebrand A. R. and Boynton W. V. 1988, LPI Contributions 673:78-79. [3] Hildebrand A. R. and Boynton W. V.. 1990. Science 248:843-847. [4] Montanari A. et al. 1983. Geology 11:668. [5] Bohor B. F. et al. 1989. Meteoritics 24:253. [6] Alvarez L. W. et al. 1980 Science 208:1095-1108. [7][8] Grieve R.A.F. and Cintala M.J. 1992 Meteoritics 27: 526-538. [9] Pierazzo E. et al. 1997 Icarus 127/2:408-423. [10] Ivanov B.A. et al. 2002 Asteroids III 89-101

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

NASA Astrophysics Data System (ADS)

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

2010-05-01

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

Large Meteorite Impacts and Planetary Evolution

NASA Technical Reports Server (NTRS)

1997-01-01

The present volume of abstracts of conference papers discusses topics associated with the role of meteorite impacts on the Earth, the moon, and Titan. Particular attention is given to the description of the impact damage and the description of the actual craters. Attention is also given to the Sudbury structure, and the Chicxulub crater. Mineralogical, geophysical, petrographic, seismic and image data are described and discussed.

Run-up of Tsunamis in the Gulf of Mexico caused by the Chicxulub Impact Event

NASA Astrophysics Data System (ADS)

Weisz, R.; Wünnenmann, K.; Bahlburg, H.

2003-04-01

The Chicxulub impact event can be investigated on (1) local, (2) regional and in (3) global scales. Our investigations focus on the regional scale, especially on the run-up of tsunami waves on the coast around the Gulf of Mexico caused by the impact. An impact produces two types of tsunami waves: (1) the rim wave, (2) the collapse wave. Both waves propagate over long distances and reach coastal areas. Depending on the tsunami wave characteristics, they have a potentionally large influence on the coastal areas. Run-up distance and run-up height can be used as parameters for assessing this influence. To calculate these parameters, we are using a multi-material hydrocode (SALE) to simulate the generation of the tsunami wave, a non-linear shallow water approach for the propagation, and we implemented a special open boundary for considering the run-up of tsunami waves. With the help of the one-dimensional shallow water approach, we will give run-up heights and distances for the coastal area around the Gulf of Mexico. The calculations are done along several sections from the impact site towards the coast. These are a first approximation to run-up calculations for the entire coast of the Gulf of Mexico. The bathymetric data along the sections, used in the wave propagation and run-up, correspond to a linearized bathymetry of the recent Gulf of Mexico. Additionally, we will present preliminary results from our first two-dimensional experiments of propagation and run-up. These results will be compared with the one-dimensional approach.

The Chicxulub crater - impact metamorphism of sulfate and carbonate lithologies

NASA Astrophysics Data System (ADS)

Deutsch, A.; Langenhorst, F.; Hornemann, U.; Ivanov, B. A.

2003-04-01

It is discussed whether in the aftermath of the Chicxulub event, impact-released CO_2 and SO_x have changed the Earth's climate, acting also as lethal thread for life. Undoubtedly, vaporization of carbonates and sulfates, which are major target lithologies at the Chicxulub impact site, occurred in the footprint of the projectile. What happened to these lithologies outside this very restricted zone was so far unconstrained. Petrologic observations on PEMEX and UNAM as well as on the CSDP cores allow to set up a general classification for shock-related pro-grade effects on sulfate and carbonate sedimentary rocks. Shock effects in lithic breccias are restricted to brecciation and formation of twins in calcite. Suevites mostly lack melted carbonate clasts; annealing effects in anhydrite fragments are absent. The underlying melt breccias contain anhydrite fragments still displaying a sedimentary texture, and limestone clasts, whose texture reflect crystallization from melt. Impact melt breccias from deeper levels frequently contain partially resorbed anhydrite clasts and a melt matrix with the Ca-rich mineral assemblage quartz + plagioclase + clinopyroxene; this mineral assemblage provides evidence for partial dissociation of CaSO_4. Large clasts of anhydrite consist of equant crystals with 120^o triple junctions, a feature indicative for re-crystallization in the solid state. Tagamites (impact melt rocks) are virtually free of clasts from sedimentary lithologies. These rocks have an extremely high formation temperature, which caused total dissociation of CaSO_4 and CaCO_3. Finally, up to 100 μm wide veins of anhydrite + calcite + quartz cut the matrix of all lithologies except the tagamites. They probably represent "degassing vents". The given scheme is in qualitative accordance with data of shock recovery and annealing experiments as well as with modeling results. In addition, it substantiates that annealing plays a fundamental role in the impact metamorphism of sedimentary rocks.

Shaded Relief with Height as Color and Landsat, Yucatan Peninsula, Mexico

NASA Image and Video Library

2003-03-06

The top picture is a shaded relief image of the northwest corner of Mexico Yucatan Peninsula generated from NASA Shuttle Radar Topography Mission SRTM data, and shows a subtle, but unmistakable, indication of the Chicxulub impact crater.

Journey to the end of the dinosaur era: A society expedition to Belize

NASA Technical Reports Server (NTRS)

Ocampo, Adriana

1995-01-01

The impact of the extraterrestrial object that formed the Chicxulub crater in the northwestern Yucatan peninsula of Mexico is the leading suspect for the extinction of the dinosaurs. This article reports on a Planetary Society expedition to Albion Island in the Rio Hondo region of Belize to investigate evidence supporting the impact theory.

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

NASA Technical Reports Server (NTRS)

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

1996-01-01

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

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Levi, B.G.

1992-12-01

In 1980, scientists at the University of California, Berkeley proposed that a massive comet or asteroid might have struck the earth about 65 million years ago, changing the earth's climate so drastically that dinosaurs and other creatures could no longer survive. This article describes the evidence for the elusive crater required to support this theory. The structure in question is 180 km in diameter and is submeged beneath the Yucatan peninsula and centered on the Mexican village of Chicxulub. Material drilled from this crater has been linked chemically and geologically to pellets found in Northeast Mexico and Haiti. The linkmore » 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.« less

Connectivity among sinkholes and complex networks: The case of Ring of Cenotes in northwest Yucatan, Mexico

NASA Astrophysics Data System (ADS)

Gomez-Nicolas, Mariana; Rebolledo-Vieyra, Mario; Huerta-Quintanilla, Rodrigo; Canto-Lugo, Efrain

2014-05-01

A 180-km-diameter semicircular alignment of abundant karst sinkholes (locally known as cenotes) in northwestern Yucatán, México, coincides approximately with a concentric ring of the buried Chicxulub structure, a circular feature manifested in Cretaceous and older rocks, that has been identified as the product of the impact of a meteorite. The secondary permeability generated by the fracturing and faulting of the sedimentary sequence in the Chicxulub impact, has favored the karstification process and hence the development of genuine underground rivers that carry water from the continent to the sea. The study of the structure and morphology of the crater has allowed researchers to understand the key role of the crater in the Yucatán hydrogeology. It is generally accepted that the Ring of Cenotes, produced by the gravitational deformation of the Tertiary sedimentary sequence within the crater, controls the groundwater in northern Yucatán. However, today there is not solid evidence about the connectivity among cenotes, which is important because if established, public policies could be designed to manage sanitary infrastructure, septic control, regulation of agricultural and industrial activities and the protection of water that has not been compromised by anthropogenic pollution. All these directly affect more than half a million people whose main source of drinking water lies in the aquifer. In this contribution we investigated a set of 16 cenotes located in the vicinity of a gravimetric anomaly of Chicxulub crater ring, using complex networks to model the interconnectivity among them. Data from a geoelectrical tomography survey, collected with SuperSting R1/IP equipment, with multi-electrodes (72 electrodes), in a dipole-dipole configuration was used as input of our model. Since the total number of cenotes on the ring structure amounts to about 2000, the application of graph theoretic algorithms and Monte Carlo simulation to efficiently investigate network properties is proposed. We created a digital network model representing the observation network topology.

Yucatan Subsurface Stratigraphy from Geophysical Data, Well Logs and Core Analyses in the Chicxulub Impact Crater and Implications for Target Heterogeneities

NASA Astrophysics Data System (ADS)

Canales, I.; Fucugauchi, J. U.; Perez-Cruz, L. L.; Camargo, A. Z.; Perez-Cruz, G.

2011-12-01

Asymmetries in the geophysical signature of Chicxulub crater are being evaluated to investigate on effects of impact angle and trajectory and pre-existing target structural controls for final crater form. Early studies interpreted asymmetries in the gravity anomaly in the offshore sector to propose oblique either northwest- and northeast-directed trajectories. An oblique impact was correlated to the global ejecta distribution and enhanced environmental disturbance. In contrast, recent studies using marine seismic data and computer modeling have shown that crater asymmetries correlate with pre-existing undulations of the Cretaceous continental shelf, suggesting a structural control of target heterogeneities. Documentation of Yucatan subsurface stratigraphy has been limited by lack of outcrops of pre-Paleogene rocks. The extensive cover of platform carbonate rocks has not been affected by faulting or deformation and with no rivers cutting the carbonates, information comes mainly from the drilling programs and geophysical surveys. Here we revisit the subsurface stratigraphy in the crater area from the well log data and cores retrieved in the drilling projects and marine seismic reflection profiles. Other source of information being exploited comes from the impact breccias, which contain a sampling of disrupted target sequences, including crystalline basement and Mesozoic sediments. We analyze gravity and seismic data from the various exploration surveys, including multiple Pemex profiles in the platform and the Chicxulub experiments. Analyses of well log data and seismic profiles identify contacts for Lower Cretaceous, Cretaceous/Jurassic and K/Pg boundaries. Results show that the Cretaceous continental shelf was shallower on the south and southwest than on the east, with emerged areas in Quintana Roo and Belize. Mesozoic and upper Paleozoic sediments show variable thickness, possibly reflecting the crystalline basement regional structure. Paleozoic and Precambrian basement outcrops are located farther to the southeast in Belize and northern Guatemala. Inferred shelf paleo-bathymetry supports existence of a sedimentary basin extending to the northeast, where crater rim and terrace zones are subdued in the seismic images.

An Archaean heavy bombardment from a destabilized extension of the asteroid belt.

PubMed

Bottke, William F; Vokrouhlický, David; Minton, David; Nesvorný, David; Morbidelli, Alessandro; Brasser, Ramon; Simonson, Bruce; Levison, Harold F

2012-05-03

The barrage of comets and asteroids that produced many young lunar basins (craters over 300 kilometres in diameter) has frequently been called the Late Heavy Bombardment (LHB). Many assume the LHB ended about 3.7 to 3.8 billion years (Gyr) ago with the formation of Orientale basin. Evidence for LHB-sized blasts on Earth, however, extend into the Archaean and early Proterozoic eons, in the form of impact spherule beds: globally distributed ejecta layers created by Chicxulub-sized or larger cratering events4. At least seven spherule beds have been found that formed between 3.23 and 3.47 Gyr ago, four between 2.49 and 2.63 Gyr ago, and one between 1.7 and 2.1 Gyr ago. Here we report that the LHB lasted much longer than previously thought, with most late impactors coming from the E belt, an extended and now largely extinct portion of the asteroid belt between 1.7 and 2.1 astronomical units from Earth. This region was destabilized by late giant planet migration. E-belt survivors now make up the high-inclination Hungaria asteroids. Scaling from the observed Hungaria asteroids, we find that E-belt projectiles made about ten lunar basins between 3.7 and 4.1 Gyr ago. They also produced about 15 terrestrial basins between 2.5 and 3.7 Gyr ago, as well as around 70 and four Chicxulub-sized or larger craters on the Earth and Moon, respectively, between 1.7 and 3.7 Gyr ago. These rates reproduce impact spherule bed and lunar crater constraints.

Search for Impact Craters in the Volcanic and Volcano-Sedimentary Terrains of Mexico

NASA Astrophysics Data System (ADS)

Bartali, R.; Fucugauchi, J. U.

2011-12-01

It has long been recognized that the numbers of impact craters documented in the terrestrial record are small compared to those of the Moon and other planets and satellites. Processes acting on the Earth surface including tectonics, volcanism and erosion contribute to erase, modify and cover evidence of crater-forming impacts that have occurred through Earth's history. Even evidence on large impact structures is limited to few examples, with only three complex multi-ring structures so far recognized. Chicxulub is a ~200 km diameter multi-ring crater formed by an impact in the southern Gulf of Mexico about 65.5 Ma ago at the Cretaceous/Paleogene boundary. Chicxulub is the only impact structure documented in Mexico, Central and northern South America (http:www.unb.ca/passc/ImpactDatabase). Chicxulub, located in the Yucatan platform buried under a kilometer of carbonate rocks, was initially identified from its concentric semi-circular gravity and magnetic anomaly patterns. Yucatan peninsula has a low-relief topography and high contrasts in physical properties between carbonate rocks, impact lithologies and deformed target rocks. In contrast, most of the country has an abrupt topography with limited outcrops of Paleozoic and Precambrian terrains. The extensive igneous cover of the Sierra Madre Occidental, Trans-Mexican volcanic belt and Sierra Madre del Sur makes search for impact craters a difficult task. Early attempts were limited by the numerous volcanic craters and lack of high-resolution geophysical data. As part of a new country-wide search program, we have been conducting studies in northern Mexico using remote sensing and geophysical data to document circular and semi-circular crater-like features. The search has identified several structures, some well exposed and characterized by simple crater morphologies and topographic rims. These landforms have been mapped, estimating their dimensions, distribution and characterizing the surrounding terrains. Aeromagnetic anomaly data from low-altitude surveys have been used to characterize the structures, together with geological and topographic maps. For the promising sites, low altitude aerial images and on-site reconnaissance surveys and sampling are completed. Sites studied include isolated structures built on low relief terrains as well as multiple crater-like structures on volcanic terrains. Here we present initial results of the project in the Chihuahua region and discuss the methods, findings and difficulties in identification of impact structures.

Tectonic escape of the Caribbean plate since the Paleocene: a consequence of the Chicxulub meteor impact?

NASA Astrophysics Data System (ADS)

Rangin, C.; Martinez-Reyes, J.; Crespy, A.; Zitter, T. A. C.

2012-04-01

The debate for Pacific exotic origin versus in situ inter American plate Atlantic origin of the Caribbean plate is active in the scientific community since decades. Independently of the origin of this plate, its fast motion towards the east at a present rate of 2cm/yr is accepted to have been initiated during the early-most Cenozoic. The Paleocene is a key period in the global evolution of Central America mainly marked also by the Chicxulub multiring meteor impact in Yucatan. We question here the genetic relationship between this impact event and the incipient tectonic escape of the Caribbean plate. The mostly recent published models suggest this impact has affected the whole crust down to the Moho, the upper mantle being rapidly and considerably uplifted. The crust was then fragmented 600km at least from the point of impact, and large circular depressions were rapidly filled by clastic sediments from Cantarell to Western Cuba via Chiapas and Belize. North of the impact, the whole Gulf of Mexico was affected by mass gravity sliding, initiated also during the Paleocene in Texas, remaining active in this basin up to present time. South of the impact, in the Caribbean plate, the Yucatan basin was rapidly opened, indicating a fast escape of the crustal material towards the unique free boundary, the paleo-Antilles subduction zone. Shear waves velocity data below the Caribbean plate suggest this crustal tectonic escape was enhanced by the fast eastward flowing mantle supporting a fragmented and stretched crust. The proposed model suggests Chicxulub impact (but also the hypothetic Beata impact) have fragmented brittle crust, then easily drifted towards the east. This could explain the Paleogene evolution of the Caribbean plate largely stretched during its early evolution. Geologically, this evolution could explain the absence of evident Paleogene oblique subduction along the Caribbean plate northern and southern margins, marked only by Mid Cretaceous dragged volcanic complexes, but also the relatively recent motion along the Cayman Fault zone (Miocene instead of Eocene). These results are part of a cooperative research-industry programm conducted by CEREGE/EGERIE, Aix-en-Provence and GeoAzur, Nice, with Frontier Basin study group, TOTAL S.A., Paris.

Severe environmental effects of Chicxulub impact imply key role in end-Cretaceous mass extinction

NASA Astrophysics Data System (ADS)

Brugger, Julia; Feulner, Georg; Petri, Stefan

2017-04-01

66 million years ago, during the most recent of the five severe mass extinctions in Earth's history, non-avian dinosaurs and many other organisms became extinct. The cause of this end-Cretaceous mass extinction is seen in either flood-basalt eruptions or an asteroid impact. Modeling the climatic changes after the Chicxulub asteroid impact allow to assess its contribution to the extinction event and to analyze the short-term and long-term response of the climate and the biosphere to the impact. Existing studies either investigated the effect of dust, which is now believed to play a minor role, or used one-dimensional, non-coupled models. In contrast, we use a coupled climate model to explore the longer lasting cooling due to sulfate aerosols. Based on data from geophysical impact modeling, we set up simulations with different stratospheric residence times for sulfate aerosols. Depending on this residence time, global surface air temperature decreased by at least 26°C, with 3 to 16 years subfreezing temperatures and a recovery time larger than 30 years. Vigorous ocean mixing, caused by the fast cooling of the surface ocean, might have perturbed marine ecosystems by the upwelling of nutrients. The dramatic climatic changes seen in our simulations imply severe environmental effects and therefore a significant contribution of the impact in the end-Cretaceous mass extinction.

Hydrogeothermal Convective Circulation Model for the Formation of the Chicxulub Ring of Cenotes in the Yucatan Peninsula, Mexico.

NASA Astrophysics Data System (ADS)

Monroy-Rios, E.; Beddows, P. A.

2015-12-01

Despite being deeply buried, the topography and geophysical characteristics of the multi-ring Chicxulub impact structure are reflected on the now subaerial Yucatan Peninsula with aligned arcs of cenotes (sinkholes), forming the "Ring of Cenotes". A pending question is the determination of the geological, geochemical, structural features and associated processes that have led to void development, and the upwards propagation of the voids, cross cutting over 1000 m of super-deposited carbonate sequences. Drawing from the published literature on drill core and geophysical surveys undertaken by Pemex, UNAM, and IODP/ICDP, numerical modeling, and general carbonate platform hydrothermal reactive transport models, we provide a conceptual model for the genesis of the Ring of Cenotes. In horizontally bedded carbonate platforms, geothermal gradients will drive convective flow, with strong vertical components specifically in the platform center. In the Yucatan Platform, a high occurrence of anhydrite and dolomite at depth evokes early burial dolomitization and anhydritization, sourcing Mg from seawater. The Chicxulub impact near the center of the platform produced a low permeability and high thermal conductivity melt rock that arguably extends to the basement rock at 3.5 km below surface. Heat of impact enforced the pre-existing geothermal circulation pattern, and even with depletion of the heat of impact, the high thermal conductivity of the crystalline melt would lead to enhanced geothermal gradients in the center of the platform. The cenotes overlying the crater are deep (150+ m) vertical shafts with most (but not all) breaching the surface. The pit geomorphology suggests a bottom-up formation. Excess Si in the shallow groundwater points to a convective circulation with strong vertical components geochemically linking the granodioritic basement rock to the surface. Water temperature and conductivity profiles support ongoing vertical flux in some deep pit cenotes. Within this framework, we argue for the formation of the Ring of Cenotes by hydrogeothermal convective circulation in the post-impact carbonate sequences, leading to spatially focused dissolution at depth, with voids initiated along the crater edge effectively propagating upwards, often breaching the surface.

Geology of Southern Quintana Roo (Mexico) and the Chicxulub Ejecta Blanket

NASA Astrophysics Data System (ADS)

Schönian, F.; Tagle, R.; Stöffler, D.; Kenkmann, T.

2005-03-01

In southern Quintana Roo (Mexico) the Chicxulub ejecta blanket is discontinuously filling a karstified pre-KT land surface. This suggests a completely new scenario for the geological evolution of the southern Yucatán Peninsula.

Preliminary Results From the Chicxulub Post-Impact Sediments: XRF and Physical Properties Data

NASA Astrophysics Data System (ADS)

Gebhardt, C.; Perez-Cruz, L. L.; Chenot, É.; Christeson, G. L.; Le Ber, E.; Lofi, J.; Nixon, C.; Rae, A.; Expedition 364 Science Party, I. I.

2017-12-01

In spring 2016, joint IODP/ICDP Expedition 364 drilled into the peak ring of the Chicxulub crater, offshore the Yucatan Peninsula, Mexico. A continuous core was drilled (Hole M0077A) and recovered a sequence of Paleogene post-impact rocks, suevites, impact-melt rocks and granitic basement between 505.7 m and 1334.7 m below sea floor (bsf). The Chicxulub crater was formed 66 million years ago by an impact. This catastrophic event was directly linked to a major mass extinction. For this study, we concentrate on the post-impact sediments (505.7 to 617.3 m bsf; 48 to 66 Ma). The main goal of drilling the post-impact section was to study the pace and mode of recovery of life in the ocean after the impact, and to analyze the paleoenvironmental changes across the Paleocene and Eocene. The late Paleocene and Eocene are characterized by a series of transient warming events, so-called hyperthermals that were associated with increased atmospheric pCO2. Here, we present preliminary geochemical and physical properties data from the 112 m of Paleogene sediments. XRF data show high log (Ca/Ti) values between 617 and 598 m bsf (Paleocene and early Eocene), and lower values between 598 and 505 m bsf. In particular the upper part is characterized by high-frequency fluctuations in log (Ca/Ti) reflecting repeated changes in lithology. These were presumably caused by Milankovitch cycles. Low log (Ba/Ti) values characterize the lowermost part of the record between 617 and 610, followed by a gradual increase to higher values, presumably indicating an increase in primary productivity towards the end of the Paleocene. Values remain at this higher level between 605 and 540 m bsf. Hyperthermals are characterized by strong positive log (Ba/Ti) peaks, likely pointing at highly elevated primary productivity levels during these short-lived events. Between 540 and 505 m bsf, log (Ba/Ti) values are more variable and drop occasionally to values as low as were encountered in the lowermost part. Similar to the log Ca/Ti curve, the log Ba/Ti curve is superimposed by high-frequency fluctuations. These fluctuations are also strongly visible in color reflectance measurements.

The Mechanics of Peak-Ring Impact Crater Formation from the IODP-ICDP Expedition 364

NASA Astrophysics Data System (ADS)

Melosh, H.; Collins, G. S.; Morgan, J. V.; Gulick, S. P. S.

2017-12-01

The Chicxulub impact crater is one of very few peak-ring impact craters on Earth. While small (less than 3 km on Earth) impact craters are typically bowl-shaped, larger craters exhibit central peaks, which in still larger (more than about 100 km on Earth) craters expand into mountainous rings with diameters close to half that of the crater rim. The origin of these peak rings has been contentious: Such craters are far too large to create in laboratory experiments and remote sensing of extraterrestrial examples has not clarified the mechanics of their formation. Two principal models of peak ring formation are currently in vogue, the "nested crater" model, in which the peak ring originates at shallow depths in the target, and the "dynamic collapse" model in which the peak ring is uplifted at the base of a collapsing, over-steepened central peak and its rocks originate at mid-crustal depths. IODP-ICDP Expedition 364 sought to elucidate, among other important goals, the mechanics of peak ring formation in the young (66 Myr), fresh, but completely buried Chicxulub impact crater. The cores from this borehole now show unambiguously that the rocks in the Chicxulub peak ring originated at mid-crustal depths, apparently ruling out the nested crater model. These rocks were shocked to pressures on the order of 10-35 GPa and were so shattered that their densities and seismic velocities now resemble those of sedimentary rocks. The morphology of the final crater, its structure as revealed in previous seismic imaging, and the results from the cores are completely consistent with modern numerical models of impact crater excavation and collapse that incorporate a model for post-impact weakening. Subsequent to the opening of a ca. 100 km diameter and 30 km deep transient crater, this enormous hole in the crust collapsed over a period of about 10 minutes. Collapse was enabled by movement of the underlying rocks, which briefly behaved in the manner of a high-viscosity fluid, a brittle deformation state described by the process of "acoustic" fluidization initiated by strong elastic vibrations accompanying the opening and collapse of the crater. The shattered core, cut by both melt rock and clastic dikes, is consistent with the block model of acoustic fluidization supporting its application to crater collapse both on the Earth and on other planets.

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

NASA Technical Reports Server (NTRS)

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

1993-01-01

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

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

NASA Technical Reports Server (NTRS)

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

1994-01-01

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

Abrupt Climate Change Caused by Global Fires from a Large Meteor Impact

NASA Astrophysics Data System (ADS)

Bardeen, C.; Toon, O. B.; Garcia, R. R.; Otto-Bliesner, B. L.; Wolf, E. T.

2015-12-01

Global or near-global fires like those that are thought to have occurred after the Chicxulub asteroid impact are associated with abrupt climate change and the K-Pg mass extinction event. Using the Community Earth System Model (CESM), a three-dimensional coupled climate model with interactive chemistry, we have simulated the climate response to global fires assuming a burden of 70,000 Tg, as estimated from the K-Pg layer sediments by Wolbach et al. (1988). Soot aerosols are lofted by solar heating and remain in the atmosphere for about 6 years, warming the stratosphere by more than 240 K and suppressing completely solar radiation at the surface for 2 years. Global average land surface temperatures cool by -28 K after 3 years and ocean temperatures by -11 K after 4 years. Precipitation is reduced by 80 % for 5 years, and the ozone column is reduced by 80 % for 4 years. The tropical tropopause cold point disappears for a few years, leading to water vapor mixing ratios of > 1000 ppmv in the stratosphere. There is a rapid recovery around year 6, when the soot is removed by wet deposition as stratospheric water condenses and precipitates, but this is followed by a peak in the UV Index in the tropics of over 40 before stratospheric ozone recovers. Ocean temperature cools by more than -2 K to a depth of 300 m, and sea ice develops in the Black Sea, Caspian Sea, and Baltic Sea. Global fires, two years of darkness, extreme surface cooling, significant ocean cooling, increases in sea ice extent and a large short-term increase in UV Index would have been catastrophic for many life forms. This work is the first step in an effort to simulate the climatic effects of all of the aerosols and gases that may have been generated by the Chicxulub impact in a model that has been configured for late-Cretaceous conditions to help assess the role of the Chicxulub impact in the K-Pg extinction.

Terrestrial Palynology of Paleocene and Eocene Sediments Above the Chicxulub Impact Crater

NASA Astrophysics Data System (ADS)

Smith, V.; Warny, S.; Bralower, T. J.; Jones, H.; Lowery, C. M.; Smit, J.; Vajda, V.; Vellekoop, J.; 364 Scientists, E.

2017-12-01

International Ocean Discovery Program (IODP) Expedition 364, with support from the International Continental Scientific Drilling Program, cored through Paleocene and Eocene sediments and into the impact structure of the Chicxulub impact crater. Three palynological studies of the post-impact section are currently underway. The two other studies are investigating the dinoflagellate palynology and terrestrial palynology of the K/Pg boundary section, while this study focuses on the early Eocene terrestrial palynology of the IODP 364 core, which has yielded a diverse and well preserved pollen assemblage. A few samples from the Early Paleocene have also been examined but organic microfossil preservation is quite poor. Samples from this core are the oldest palynological record from the Yucatan peninsula. Sample preparation and detailed abundance counts of sixty samples throughout the post-impact section are in progress, with a particular focus on the Paleocene-Eocene Thermal Maximum (PETM) and the Early Eocene Climatic Optimum (EECO). Terrestrial palynomorph assemblages will be used to reconstruct paleoclimatological conditions throughout this time period. Floral response to hyperthermal events in the IODP 364 core will be compared with records from other Gulf of Mexico and Caribbean sections. In addition to the biological and paleoclimatological implications of this research, age control from foraminiferal and nannofossil biostratigraphy, paleomagnetism, and radiometric dating will provide a chronological framework for the terrestrial pollen biostratigraphy, with applications to hydrocarbon exploration in the Wilcox Formation and age equivalent sections in the Gulf of Mexico.

Cosmic Genes in the Cretaceous-Tertiary transition

NASA Astrophysics Data System (ADS)

Wallis, M. K.

2003-07-01

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

On Kill Curves and Sampling Protocols: Studying the Relationships between Impact and Extinction

NASA Astrophysics Data System (ADS)

Ward, Peter D.

1997-05-01

The pioneering efforts of Raup (1990) have suggested that a relationship exists between crater diameter and percentage of organisms killed as a result of meteor or comet impact with the Earth. The new data (coming from study of the Manson and Chicxulub craters) suggest that the nature of target rock may be a factor nearly as important as impacter size, and that other aspects of the target, including its latitude, the atmospheric and climate conditions characterizing the Earth, as well as the stage of biological evolution and community development at the time of impact are factors which all must be factored into any new kill curve. It may be that no single 'curve' is appropriate, but that a family of curves may be necessary to model the biological effects of large impacts. We propose that a new protocol be developed to better constrain and understand the relationship between impact and extinction. Rather than searching known mass extinction boundaries for evidence of impact (an exercise which up to now has demonstrated that only the Chicxulub crater can be unambiguously related to a mass extinction of planetary scale), we propose that four known craters be investigated to see if they are temporally correlated with extinction at any detectable level. We suggest that Kara, Popigai, Manson, and Manicouagan Craters be investigated in the following way. First, what is their age? The Manson lesson is that the first step in understanding the relationship between impact and extinction is through reliable age dating. Second, can distal components of the impact ejecta (spherules, shocked quartz, and mineral signatures) be located from sedimentary record? Third, once identified, do these signatures coincide with paleontological or geochemical markers of extinction in either the synoptic literature, or from actual outcrops (or deep sea cores).

The Geology of Haiti: An Annotated Bibliography of Haiti’s Geology, Geography and Earth Science

DTIC Science & Technology

2010-07-01

Yucatan Peninsula. Abstract: The stratigraphy and age of breccia containing Chicxulub impact glass spherules is documented in late Maastrichtian-early...Tertiary; tsunamis; turbidite; turbidity current structures; Upper Cretaceous; West Indies; Yucatan Peninsula. Notes: SP: USGSOP, Non-USGS...Chichancanab, and Coba, Yucatan Peninsula, Bibliography of Haitian Earth Science Army Geospatial Center June 2010 70 Mexico; Lake Peten-Itza, Peten

Connectivity in a Karst System Using Electrical Resistivity Tomography and Network Theory.

PubMed

Gómez-Nicolás, Mariana; Rebolledo-Vieyra, Mario; Canto-Lugo, Efrain; Huerta-Quintanilla, Rodrigo; Ochoa-Sandoval, Pablo

2017-11-29

The Ring of Cenotes (RC) is an alignment of numerous cenotes (sinkholes) in a semicircular form (with a radius of 100 km) located in northwestern Yucatán, México. The formation roughly coincides with a concentric ring that corresponds to a buried structure, which has been identified as the product of a meteor impact, known as the Chicxulub crater. Secondary permeability generated by the fracturing and faulting of the sedimentary sequence in the Chicxulub crater has favored the karstification process and therefore the development of underground rivers that transport water from the mainland to the sea. This study implements the network theory to study the hydrological connectivity between a group of 11 cenotes within the RC. Eight electrical resistivity tomography transects were used as an empirical basis. Each transect was acquired directly in the field using the SuperSting R1/IP equipment with a dipole-dipole configuration. An adapted version of the reliability algorithm for communication networks was used as a theoretical model. We found evidence of the existence of water cavities in the study area. We made a network from the data and assigned connection probabilities among cenotes as a function of the separation length and the number of water cavities, as well as their size. © 2017, National Ground Water Association.

Impact melting of carbonates from the Chicxulub crater

NASA Astrophysics Data System (ADS)

Jones, A. P.; Claeys, P.; Heuschkel, S.

We have recently interpreted distinctive feathery-textured spinifex carbonate in the upper part of the Chicxulub suevite breccia as quenched carbonate melts (Jones et al. 1998); these distinctive fragments make up to 10 vol% of the breccia. Carbonate clasts and spherules occurring in the ejecta-rich basal part of the coarse clastic sequence, which marks the K/T boundary all around the Gulf of Mexico, may represent distal quenched droplets of carbonate liquids. In seeking to explain this widespread carbonate impact-melting phenomenon, we have re-examined the available experimental evidence. The important decarbonation reaction for calcite CaCO3=CaO+CO2 is inhibited by very small pressures up to temperatures >2000 K. We conclude that massive decarbonation by direct shock pressure is unlikely without attainment of temperatures >4000 K. Therefore, decarbonation generally can only occur during post-shock cooling for carbonates at low pressure (< 10 bars). We assume that post-shock cooling is quasi-thermodynamic, and provide a general P-T model for carbonate spanning 11 orders of magnitude in pressure (atmosphere to core). Subtle differences in sample preconditioning can probably explain the wildly divergent experimental shock data. A major planetary implication for the formation of the Earth's early atmosphere is that impacts on limestone would be less likely to have contributed substantial CO2 than has previously been assumed. Lastly, we note that carbonate melts at high pressures serve as excellent catalysts for diamond growth, and may have contributed to the widespread formation of some impact diamond.

Highly siderophile elements and Os isotope signatures in the K-Pg transition of the Chicxulub peak-ring rocks

NASA Astrophysics Data System (ADS)

Sato, H.; Ishikawa, A.; Ferrière, L.; Morgan, J. V.; Gulick, S. P. S.

2017-12-01

The Chicxulub impact structure, located in the northern Yucatan Peninsula, Mexico, formed 66 My ago, was drilled by IODP-ICDP 364 expedition in April-May, 2016. A continuous core was successfully recovered from the peak ring from depth between 505.7 and 1334.7 mbsf. In order to determine the distribution and abundance of the projectile component in the Chicxulub peak-ring rocks, we determined highly siderophile elements (HSE: Os, Ir, Ru, Pt, Pd, and Re) concentrations and Os isotope ratio (187Os/188Os) in five samples of Unit 1G from a 75 cm-thick transitional layer between the impactites and early Paleogene rocks (616.59-617.34 mbsf interval). HSE concentrations and 187Os/188Os ratios show systematic variations across the transitional layer. The upper part (616.59-616.63 mbsf) is characterized by about one order of magnitude higher Os, Ir, and Ru contents compared to the average continental crust abundances, but much lower than for the typical Ir-enriched Cretaceous-Paleogene boundary sites (e.g., Gubbio and Caravaca). Relatively flat CI chondrite-normalized HSE patterns are observed in the upper part of the layer. Meanwhile, the HSE concentrations in the lower part of the transitional layer (617.315-617.34 mbsf) are almost equivalent to those of upper continental crust showing pronounced step CI chondrite-normalized HSE patterns (low Ir, and high Pt and Pd). 187Os/188Os and Re/Os ratios in the transitional layer gradually decrease from 0.33 to 0.25 and 35.45 to 1.14, respectively, from bottom to top. These results suggest that the projectile component, with chondritic composition, is enriched in the uppermost part of the transitional layer just below carbonate rocks that are early Paleogene in age, but could be distributed over a thicker interval than for the typical Ir-enriched sites. Further detailed studies of HSE and Os isotope compositions through the stratigraphic sequence will reveal the distribution and dilution effect of the projectile component.

Quantitative Characterization of Chicxulub Impact Basin Peak Ring Materials

NASA Astrophysics Data System (ADS)

King, B.; Nixon, C.; Kofman, R.; Schmitt, D. R.

2017-12-01

The exceptionally low seismic wave speeds determined by tomographic image models of the upper portions of the peak ring of the Chicxulub Impact Structure were largely confirmed by sonic and seismic borehole measurements from the IODP/ICDP Expedition 364 scientific drilling campaign. These low wave speeds result from the extensive damage to the peak ring rocks that, based on the results of numerical modelling, were likely displaced 20 km outwards and 10 km upwards after being subject to initial shock pressures as high as 60 GPa. Here, we describe a series of detailed petrophysical and wave speed measurements on select `granite' and `impact melt' cores from the borehole in order to better understand the nature of this damage To date, two granite and two impact melt samples have been studied. X-ray CT scans (30 mm voxel) reveal extensive micro-fracturing between and within the mineral grains in the granites (Fig. 1a) while highlighting the existence of relatively large, 1000 mm3, occluded pores (Fig. 1b). The porosities, as determined using a Hg-injection porosimeter, were also remarkably high with values of <10% and <25% observed in the granites and the melts, respectively. Grain densities, measured using a helium pycnometer, were similar between both samples ranging between 2.581-2.654 g/cc. Both VP and VS were determined under hydrostatic confining pressures between 3 MPa and 200 MPa by ultrasonic transit time measurements (Fig. 1c). The velocities increase linearly with pressure in the impact melt rock suggesting this material lacks microcrack porosity. In contrast, the velocities in the granites depend strongly on pressure further indicating the existence of pervasive microcracking. Even at the highest confining pressure of 200 MPa available to us, the observed VP is 4.5 km/s, a value much below the 6.0 km/s expected for the same nonporous rock. These observations suggest that the low wave speeds and densities within the peak ring differ based on whether the material is the original displaced granite or the intruded impact melt. Samples and data provided by IODP. Samples can be requested at http://web.iodp.tamu.edu/sdrm after 19 October 2017. Expedition 364 was funded by ECORD, IODP and ICDP with contributions and logistical support from the Yucatan State Government and Universidad Nacional Autónoma de México (UNAM).

Some implications of large impact craters and basins on Venus for terrestrial ringed craters and planetary evolution

NASA Technical Reports Server (NTRS)

Mckinnon, W. B.; Alexopoulos, J. S.

1994-01-01

Approximately 950 impact craters have been identified on the surface of Venus, mainly in Magellan radar images. From a combination of Earth-based Arecibo, Venera 15/1, and Magellan radar images, we have interpreted 72 as unequivocal peak-ring craters and four as multiringed basins. The morphological and structural preservation of these craters is high owing to the low level of geologic activity on the venusian surface (which is in some ways similar to the terrestrial benthic environment). Thus these craters should prove crucial to understanding the mechanics of ringed crater formation. They are also the most direct analogs for craters formed on the Earth in Phanerozoic time, such as Chicxulub. We summarize our findings to date concerning these structures.

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

NASA Technical Reports Server (NTRS)

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

1994-01-01

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

Erice International Seminars on Planetary Emergencies, 17th Workshop: The Collision of an Asteroid or Comet with the Earth Held in Erice, Italy on 28 April-4 May 1993

DTIC Science & Technology

1993-05-04

biomass and decrease in ocean productivity, and a climate warming of -80 C in the first few thousand years of the Tertiary. Productivity seems to have... Oligocene transition, and Chicxulub (-200 km) at the K/T boundary. Newly proposed impact structures on the Falkland Plateau (-350 km and 200 Km) apparently

Earth history. U-Pb geochronology of the Deccan Traps and relation to the end-Cretaceous mass extinction.

PubMed

Schoene, Blair; Samperton, Kyle M; Eddy, Michael P; Keller, Gerta; Adatte, Thierry; Bowring, Samuel A; Khadri, Syed F R; Gertsch, Brian

2015-01-09

The Chicxulub asteroid impact (Mexico) and the eruption of the massive Deccan volcanic province (India) are two proposed causes of the end-Cretaceous mass extinction, which includes the demise of nonavian dinosaurs. Despite widespread acceptance of the impact hypothesis, the lack of a high-resolution eruption timeline for the Deccan basalts has prevented full assessment of their relationship to the mass extinction. Here we apply uranium-lead (U-Pb) zircon geochronology to Deccan rocks and show that the main phase of eruptions initiated ~250,000 years before the Cretaceous-Paleogene boundary and that >1.1 million cubic kilometers of basalt erupted in ~750,000 years. Our results are consistent with the hypothesis that the Deccan Traps contributed to the latest Cretaceous environmental change and biologic turnover that culminated in the marine and terrestrial mass extinctions. Copyright © 2015, American Association for the Advancement of Science.

Deep Subsurface Microbial Communities Shaped by the Chicxulub Impactor

NASA Astrophysics Data System (ADS)

Cockell, C. S.; Coolen, M.; Schaefer, B.; Grice, K.; Gulick, S. P. S.; Morgan, J. V.; Kring, D. A.; Osinski, G.

2017-12-01

Fresh core material was obtained by drilling of the Chicxulub impact crater during IODP-ICDP Expedition 364 to assess the present-day biosphere in the crater structure. Cell enumerations through the core show that beneath the post-impact sedimentary rock there is a region of enhanced cell abundance that corresponds to the upper impact suevite layer (Units 1G/2A). We also observed a peak in cell numbers in samples at the bottom of suevite Unit 2C and between the suevitic and grainitoid interface (Unit 3/4). These patterns may reflect preferential movement of fluid and/or availability of nutrients and energy at interfaces. 16S rDNA analysis allows us to rule out contamination of the suevite material since no taxa associated with the drilling mud were observed. Two hundred and fifty microbial enrichments were established using diverse culture media for heterotrophs, autotrophs and chemolithotrophs at temperatures consistent with measured core temperatures. Six yielded growth in the breccia, lower breccia and upper granitoid layer and they affiliated with Acidiphilium, Thermoanaerobacteracea and Desulfohalbiaceae. The latter exhibited visible microbial sulfate-reduction. By contrast, the granitoid material exhibited low cell abundances, most samples were below direct cell detection. DNA extraction revealed pervasive low level contamination by drilling mud taxa, consistent with the highly fractured, high porosity of the impact-shocked granitoids. Few taxa can be attributed to an indigenous biota and no enrichments (at 60 and 70°C) yielded growth. These data show that even with a porosity approximately an order of magnitude greater than most unshocked granites, the uplifted granites have not experienced sufficient fluid flow to establish a significant deep biosphere. Paleosterilisation of the material during impact may have re-set colonisation and the material may have originally been below the depth at which temperatures exceeded the upper temperature limit for life. These data show that the deep biosphere can preserve the imprint of catastrophe long after these events. In this case, the distribution of deep subsurface microbial communities reflects the lithological sequence established during the substantial impact-induced geological rearrangements that occurred in the first hours of the Cenozoic.

Elements of the Chicxulub Impact Structure as revealed in SRTM and surface GPS topographic data

NASA Astrophysics Data System (ADS)

Kobrick, M.; Kinsland, G. L.; Sanchez, G.; Cardador, M. H.

2003-04-01

Pope et al have utilized elevations from the Petroleos Mexicanos (PEMEX) gravity data files to show that the main component of the surface expression of the Chicxu-lub Impact Structure is a roughly semi-circular, low-relief depression about 90 km in diameter. They also identified other topographic features and the elements of the buried impact which possibly led to the development of these features. Kinsland et al presented a connection between these topographic anomalies, small gravity anomalies and buried structure of the impact. Shaded relief images from recently acquired SRTM elevation data clearly show the circular depression of the crater and the moat/cenote ring. In addition we can readily identify Inner trough 1, Inner trough 2 and Outer trough as defined by Pope et al. The agreement between the topographic maps of Pope et al, Kinsland et al and SRTM data are remarkable considering that the distribution and types of data in the sets are so different. We also have ground topographic data collected with a special "autonomous differ-ential GPS" system during summer 2002. Profiles from these data generally agree with both the gravity data based topographic maps and profiles extracted from the SRTM data. Preliminary analyses of our new data, SRTM and GPS, have uncovered features not previously recognized: 1) as shown by the GPS data the moat/cenote ring consists of two distinct depressions separated by about 10 km...perhaps separate ring faults, 2) in the SRTM data over the southern part of the crater and on southward for perhaps 20 km beyond the moat/ cenote ring there exists a pattern, as yet unexplained, of roughly concentric topographic features whose center lies at about 21deg 40min N and 89deg 25min W, about 50km NNE of the moat/cenote ring center. The corroboration and better definition of the previously recognized topographic features yielded by the two new forms of data strengthens the cases for these fea-tures and for their relevance to the underlying collapsed crater structure.

State shift in Deccan volcanism at the Cretaceous-Paleogene boundary, possibly induced by impact

NASA Astrophysics Data System (ADS)

Renne, Paul R.; Sprain, Courtney J.; Richards, Mark A.; Self, Stephen; Vanderkluysen, Loÿc; Pande, Kanchan

2015-10-01

Bolide impact and flood volcanism compete as leading candidates for the cause of terminal-Cretaceous mass extinctions. High-precision 40Ar/39Ar data indicate that these two mechanisms may be genetically related, and neither can be considered in isolation. The existing Deccan Traps magmatic system underwent a state shift approximately coincident with the Chicxulub impact and the terminal-Cretaceous mass extinctions, after which ~70% of the Traps' total volume was extruded in more massive and more episodic eruptions. Initiation of this new regime occurred within ~50,000 years of the impact, which is consistent with transient effects of impact-induced seismic energy. Postextinction recovery of marine ecosystems was probably suppressed until after the accelerated volcanism waned.

Ichnofabrics and Facies in the Paleocene of Chicxulub: A Record of the Recovery of Life Post-Impact

NASA Astrophysics Data System (ADS)

Whalen, M. T.; O'Malley, K.; Lowery, C. M.; Rodriguez-Tovar, F. J.; Gulick, S. P. S.; Morgan, J. V.

2017-12-01

IODP/ICDP Expedition 364 recovered 829 m of core at Site M0077 including 110 m of post-impact, (hemi)pelagic Paleogene sedimentary rocks overlying the Chicxulub impact crater peak ring formed from suevite, melt rock, and granitic basement. The transition between suevite and Paleocene limestone (Unit 1F) is a remarkable fining upward package of gravel to sand-sized suevite (Unit 2A) overlain by the laminated carbonate-rich Unit 1G that records deposition of fine-grained material post-impact and contains a mix of Late Cretaceous and earliest Danian taxa. This study concentrates on the overlying Unit 1F. The ichnofabric index (ii, 1-6 indicating no bioturbation to complete homogenization), provides a semiquantitative estimate of burrow density to help assess the return of life to the crater. Unit 1F is 10 m thick with a sharp contact at the base of a green claystone (ii 2) that overlies Unit 1G. It consists of cm-dm interbedded blue-gray marlstone (ii 2) grading upward into gray to blue-gray wacke/packstone (ii 3-5). Contacts between facies are mostly gradational due to burrowing. The upper 3 m of the unit is a yellow-brown burrowed packstone (ii 4) intercalated with gray marlstone (ii 2). The uppermost 7.5 cm is calcite cemented with 1 cm wide burrows (ii 3-4) and fine to coarse sand size clasts including foraminifera. The upper surface of the unit is a hardground with an 2 Myr unconformity overlain by Eocene rocks. The first well-defined burrows occur in the upper 30 cm of Unit 1G. Unequivocal burrows (ii 2) that disturb sedimentary facies occur in overlying Unit 1F with values of 3-5 recorded in the overlying 10 cm indicating significant disruption of primary sedimentary structures. The iis in Unit 1F vary between 2 and 5 with rare laminated intervals without bioturbation (ii 1). Values of ii correlate well with facies changes, i.e. marlstones display lower iis than more carbonate-rich facies, implying a depth and/or redox control on burrower distribution. The ii data indicate that burrowers were re-established in the crater before the end of deposition of Unit 1G. The lowest Danian zone Pα is documented in the lowermost part of Unit 1F. Trace makers were thus active by the earliest Danian with an increase in abundance and diversity during the lower Danian, indicating a rapid and continuous return of benthic life to the crater.

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

NASA Technical Reports Server (NTRS)

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

2003-01-01

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

Unusual Physical Properties of the Chicxulub Crater Peak Ring: Results from IODP/ICDP Expedition 364

NASA Astrophysics Data System (ADS)

Christeson, G. L.; Gebhardt, C.; Gulick, S. P. S.; Le Ber, E.; Lofi, J.; Morgan, J. V.; Nixon, C.; Rae, A.; Schmitt, D. R.

2017-12-01

IODP/ICDP Expedition 364 Hole M0077A drilled into the peak ring of the Chicxulub impact crater, recovering core between 505.7 and 1334.7 m below the seafloor (mbsf). Physical property measurements include wireline logging data, a vertical seismic profile (VSP), Multi-Sensor Core Logger (MSCL) measurements, and discrete sample measurements. The Hole M0077A peak ring rocks have unusual physical properties. Across the boundary between post-impact sediment and crater breccia we measure a sharp decrease in velocities and densities, and an increase in porosity. Mean crater breccia values are 3000-3300 m/s, 2.14-2.15 g/cm3, and 31% for velocity, density, and porosity, respectively. This zone is also associated with a low-frequency reflector package on MCS profiles and a low-velocity layer in FWI images, both confirmed from the VSP dataset. The thin (24 m) crater melt unit has mean velocity measurements of 3800-4150 m/s, density measurements of 2.32-2.34 g/cm3, and porosity measurements of 20%; density and porosity values are intermediate between the overlying impact breccia and underlying granitic basement, while the velocity values are similar to those for the underlying basement. The Hole M0077A crater melt unit velocities and densities are considerably less than values of 5800 m/s and 2.68 g/cm3 measured at an onshore well located in the annular trough. The uplifted granitic peak ring materials have mean values of 4100-4200 m/s, 2.39-2.44 g/cm3, and 11% for compressional wave velocity, density, and porosity, respectively; these values differ significantly from typical granite which has higher velocities (5400-6000 m/s) and densities (2.62-2.67 g/cm3), and lower porosities (<1%). All Hole M0077A peak-ring velocity, density, and porosity measurements indicate considerable fracturing, and are consistent with numerical models for peak-ring formation.

Plant Ecological Strategies Shift Across the Cretaceous–Paleogene Boundary

PubMed Central

Blonder, Benjamin; Royer, Dana L.; Johnson, Kirk R.; Miller, Ian; Enquist, Brian J.

2014-01-01

The Chicxulub bolide impact caused the end-Cretaceous mass extinction of plants, but the associated selectivity and ecological effects are poorly known. Using a unique set of North Dakota leaf fossil assemblages spanning 2.2 Myr across the event, we show among angiosperms a reduction of ecological strategies and selection for fast-growth strategies consistent with a hypothesized recovery from an impact winter. Leaf mass per area (carbon investment) decreased in both mean and variance, while vein density (carbon assimilation rate) increased in mean, consistent with a shift towards “fast” growth strategies. Plant extinction from the bolide impact resulted in a shift in functional trait space that likely had broad consequences for ecosystem functioning. PMID:25225914

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

NASA Technical Reports Server (NTRS)

Koeberl, Christian

1992-01-01

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

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

NASA Astrophysics Data System (ADS)

Koeberl, Christian

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.

State shift in Deccan volcanism at the Cretaceous-Paleogene boundary, possibly induced by impact.

PubMed

Renne, Paul R; Sprain, Courtney J; Richards, Mark A; Self, Stephen; Vanderkluysen, Loÿc; Pande, Kanchan

2015-10-02

Bolide impact and flood volcanism compete as leading candidates for the cause of terminal-Cretaceous mass extinctions. High-precision (40)Ar/(39)Ar data indicate that these two mechanisms may be genetically related, and neither can be considered in isolation. The existing Deccan Traps magmatic system underwent a state shift approximately coincident with the Chicxulub impact and the terminal-Cretaceous mass extinctions, after which ~70% of the Traps' total volume was extruded in more massive and more episodic eruptions. Initiation of this new regime occurred within ~50,000 years of the impact, which is consistent with transient effects of impact-induced seismic energy. Postextinction recovery of marine ecosystems was probably suppressed until after the accelerated volcanism waned. Copyright © 2015, American Association for the Advancement of Science.

Exploring the KT source crater: Progress and future prospects

NASA Astrophysics Data System (ADS)

Sharpton, Virgil L.

It has been 15 years since an iridium-enriched clay layer at the Cretaceous-Tertiary (KT) boundary was discovered, providing the first hard evidence linking the most recent mass extinction event to a comet or asteroid strike [Alvarez et al., 1980]. Now it is widely accepted that the site of this collision is on the Yucatan platform, centered near Progreso, Mexico. The 200-300-km-wide crater lies buried beneath 300-1000 m of limestone laid down in the intervening 65 million years, and few clues of its presence remain at the surface, save an arcuate arrangement of water-filled sinkholes centered approximately on the structure (Figure 1). Yet prominent circular anomalies in gravity and magnetic anomaly maps gained the interest of Petroleos Mexicanos (Pemex), and in the early 1950s they began an exploration campaign that included deep drilling to recover samples of the subsurface rocks. The buried feature became known as the Chicxulub structure. Pemex drilling continued throughout the early 1970s and by that time, three wells near the center had recovered silicate rocks with igneous textures, initially mistaken for volcanic rocks. Other wells, located between 130 km and 210 km from ground zero recovered breccia deposits hundreds of meters thick that showed evidence of catastropic or explosive conditions. By 1980, Antonio Camargo, a geophysicist at Pemex, felt the evidence pointed to impact, although a volcanic origin for the Chicxulub structure could not be ruled out.

GRACE Gravity Data Target Possible Mega-impact in North Central Wilkes Land, Antarctica

NASA Technical Reports Server (NTRS)

vonFrese, Ralph R. B.; Wells, Stuart B.; Potts. Laramie V.; Gaya-Pique, Luis R.; Golynsky, Alexander V.; Hernandez, Orlando; Kim, Jeong Woo; Kim, Hyung Rae; Hwang, Jong Sun; Taylor, Patrick T.

2005-01-01

A prominent positive GRACE satellite-measured free-air gravity anomaly over regionally depressed subglacial topography may identify a mascon centered on (70 deg S, 120 deg E) between the Gamburtsev and Transantarctic Mountains of East Antarctica. Being more than twice the size of the Chicxulub crater, the inferred Wilkes Land impact crater is a strong candidate for a Gondwana source of the greatest extinction of life at the end of the Permian. Its ring structure intersects the coastline and thus may have strongly influenced the Cenozoic rifting of East Antarctica from Australia that resulted in the enigmatic lack of crustal thinning on the conjugate Australian block.

Surface expression of the Chicxulub crater

PubMed

Pope, K O; Ocampo, A C; Kinsland, G L; Smith, R

1996-06-01

Analyses of geomorphic, soil, and topographic data from the northern Yucatan Peninsula, Mexico, confirm that the buried Chicxulub impact crater has a distinct surface expression and that carbonate sedimentation throughout the Cenozoic has been influenced by the crater. Late Tertiary sedimentation was mostly restricted to the region within the buried crater, and a semicircular moat existed until at least Pliocene time. The topographic expression of the crater is a series of features concentric with the crater. The most prominent is an approximately 83-km-radius trough or moat containing sinkholes (the Cenote ring). Early Tertiary surfaces rise abruptly outside the moat and form a stepped topography with an outer trough and ridge crest at radii of approximately 103 and approximately 129 km, respectively. Two discontinuous troughs lie within the moat at radii of approximately 41 and approximately 62 km. The low ridge between the inner troughs corresponds to the buried peak ring. The moat corresponds to the outer edge of the crater floor demarcated by a major ring fault. The outer trough and the approximately 62-km-radius inner trough also mark buried ring faults. The ridge crest corresponds to the topographic rim of the crater as modified by postimpact processes. These interpretations support previous findings that the principal impact basin has a diameter of approximately 180 km, but concentric, low-relief slumping extends well beyond this diameter and the eroded crater rim may extend to a diameter of approximately 260 km.

Faunal evidence for reduced productivity and uncoordinated recovery in Southern Hemisphere Cretaceous-Paleogene boundary sections

NASA Astrophysics Data System (ADS)

Aberhan, Martin; Weidemeyer, Sven; Kiessling, Wolfgang; Scasso, Roberto A.; Medina, Francisco A.

2007-03-01

The mass extinction at the Cretaceous-Paleogene boundary is generally explained by a severe crisis in primary productivity, following a catastrophic bolide impact. Consistent with this scenario, Danian mollusk-dominated benthic shelf ecosystems of southern middle paleolatitudes (Neuquén Basin, Argentina) are characterized by (1) a stratigraphically limited low in macrofossil abundances; (2) an increase in starvation-resistant, nonplanktotrophic deposit feeders and chemosymbionts; (3) a reduction in the average body size of individuals; and (4) individuals with inactive lifestyles being more common than in the late Maastrichtian. Return to pre-extinction conditions of the various synecological attributes occurred over unequal time spans, indicating that recovery was uncoordinated with respect to ecological traits. Global comparison of ecological patterns suggests that reduced food supply (1) was a controlling factor in both hemispheres; (2) affected macrobenthic marine faunas at various distances from the Chicxulub impact site; and (3) was more effective in siliciclastic environments as compared to oligotrophic carbonate settings.

Extraordinary rocks from the peak ring of the Chicxulub impact crater: P-wave velocity, density, and porosity measurements from IODP/ICDP Expedition 364

NASA Astrophysics Data System (ADS)

Christeson, G. L.; Gulick, S. P. S.; Morgan, J. V.; Gebhardt, C.; Kring, D. A.; Le Ber, E.; Lofi, J.; Nixon, C.; Poelchau, M.; Rae, A. S. P.; Rebolledo-Vieyra, M.; Riller, U.; Schmitt, D. R.; Wittmann, A.; Bralower, T. J.; Chenot, E.; Claeys, P.; Cockell, C. S.; Coolen, M. J. L.; Ferrière, L.; Green, S.; Goto, K.; Jones, H.; Lowery, C. M.; Mellett, C.; Ocampo-Torres, R.; Perez-Cruz, L.; Pickersgill, A. E.; Rasmussen, C.; Sato, H.; Smit, J.; Tikoo, S. M.; Tomioka, N.; Urrutia-Fucugauchi, J.; Whalen, M. T.; Xiao, L.; Yamaguchi, K. E.

2018-08-01

Joint International Ocean Discovery Program and International Continental Scientific Drilling Program Expedition 364 drilled into the peak ring of the Chicxulub impact crater. We present P-wave velocity, density, and porosity measurements from Hole M0077A that reveal unusual physical properties of the peak-ring rocks. Across the boundary between post-impact sedimentary rock and suevite (impact melt-bearing breccia) we measure a sharp decrease in velocity and density, and an increase in porosity. Velocity, density, and porosity values for the suevite are 2900-3700 m/s, 2.06-2.37 g/cm3, and 20-35%, respectively. The thin (25 m) impact melt rock unit below the suevite has velocity measurements of 3650-4350 m/s, density measurements of 2.26-2.37 g/cm3, and porosity measurements of 19-22%. We associate the low velocity, low density, and high porosity of suevite and impact melt rock with rapid emplacement, hydrothermal alteration products, and observations of pore space, vugs, and vesicles. The uplifted granitic peak ring materials have values of 4000-4200 m/s, 2.39-2.44 g/cm3, and 8-13% for velocity, density, and porosity, respectively; these values differ significantly from typical unaltered granite which has higher velocity and density, and lower porosity. The majority of Hole M0077A peak-ring velocity, density, and porosity measurements indicate considerable rock damage, and are consistent with numerical model predictions for peak-ring formation where the lithologies present within the peak ring represent some of the most shocked and damaged rocks in an impact basin. We integrate our results with previous seismic datasets to map the suevite near the borehole. We map suevite below the Paleogene sedimentary rock in the annular trough, on the peak ring, and in the central basin, implying that, post impact, suevite covered the entire floor of the impact basin. Suevite thickness is 100-165 m on the top of the peak ring but 200 m in the central basin, suggesting that suevite flowed downslope from the collapsing central uplift during and after peak-ring formation, accumulating preferentially within the central basin.

Return to the Strangelove Ocean?: Preliminary results of carbon and oxygenisotope compositions of post-impact sediments, IODP Expedition 364 "Chicxulub Impact Crater"

NASA Astrophysics Data System (ADS)

Yamaguchi, K. E.; Ikehara, M.; Hayama, H.; Takiguchi, S.; Masuda, S.; Ogura, C.; Fujita, S.; Kurihara, E.; Matsumoto, T.; Oshio, S.; Ishihata, K.; Fuchizawa, Y.; Noda, H.; Sakurai, U.; Yamane, T.; Morgan, J. V.; Gulick, S. P. S.

2017-12-01

The Chicxulub crater in the northern Yucatan Peninsula, Mexico was formed by the asteroid impact at the Cretaceous-Paleogene boundary (66.0 Ma). In early 2016 the IODP Exp. 364 successfully drilled the materials from the topographic peak ring within the crater that was previously identified by seismological observations. A continuous core was recovered. The 112m-thick uppermost part of the continuous core (505.7-1334.7 mbsf) is post-impact sediments, including the PETM, that are mainly composed of carbonate with intercalation of siliciclastics and variable contents of organic carbon. More than 300 samples from the post-impact section were finely powdered for a variety of geochemical analysis. Here we report their carbon and oxygen isotope compositions of the carbonate fraction (mostly in the lower part of the analyzed section) and carbon and nitrogen isotope compositions of organic matter (mostly in the middle-upper part of the analyzed section). Isotope mass spectrometer Isoprime was used for the former analysis, and EA-irMS (elemental analyzer - isotope ratio mass spectrometer) was used for the latter analysis, both at CMCR, Kochi Univ. Depth profile of oxygen isotope compositions of carbonate fraction is variable and somewhat similar to those of Zachos et al. (2001; Science). Carbon isotope compositions of carbonate and organic carbon in the lower part of the analyzed section exhibit some excursions that could correspond to the hyperthemals in the early Paleogene. Their variable nitrogen isotope compositions reflect temporal changes in the style of biogeochemical cycles involving denitrification and nitrogen fixation. Coupled temporal changes in the carbon isotope compositions of organic and carbonate carbon immediately after the K-Pg boundary might support a Strangelove ocean (Kump, 1991; Geology), however high export production (Ba/Ti, nannoplankton and calcisphere blooms, high planktic foram richness, and diverse and abundant micro- and macrobenthic organisms) at the base of the Danian limestone cored during Exp. 364 contradict a Strangelove Ocean.

The K-PG boundary: how geological events lead to collapse of marine primary producers

NASA Astrophysics Data System (ADS)

Hir guillaume, Le; frederic, Fluteau; yves, Goddéris

2017-04-01

The cause(s) of Cretaceous/Paleogene (K-Pg) mass extinction event is a matter of debate since three decades. A first scenario connects the K-Pg crisis with the Chicxulub impact while the second scenario evokes the emplacement of the Deccan traps in India as the cause for the K-Pg biodiversity collapse. Pierazzo et al. (1998) estimated that the extraterrestrial bolide lead to an instantaneously CO2 degassing ranging from 880 Gt to 2,960 Gt into the atmosphere, together with a massive release of SO2 ranging from 150 to 460 Gt.. Self et al. (2006, 2008) and Chenet et al. (2009) suggested that the emplacement of the Deccan traps released 15,000 Gt to 35,000 Gt of CO2 and 6,800 Gt to 17,000 Gt of SO2 over a 250 kyr-long period (Schoene et al., 2015). To decipher and quantify the long term environmental consequences of both events, we tested different scenarios: a pulse-like magmatic degassing, a bolide impact, and a combination of both. To understand the environmental changes and quantify biodiversity responses, we improve GEOCLIM, a coupled climate-carbon numerical model, by implementing a biodiversity model in which marine species are described by specific death/born rates, sensitivity to abiotic factors (temperature, pH, dissolved O2, calcite saturation state) and feeding relationships, each of these characteristics is assigned randomly. Preliminary simulations accounting for the eruption of the Deccan traps show that successive cooling events (S-aerosols effect) combined with a progressive acidification of surface water (caused by CO2 and SO2 injections) cause a major collapse of the marine biomass. Additional simulations in which Chicxulub impact, different community structures of primary producers will be discussed.

Summary of impact markers and potential impact mechanisms for the YDB impact event at 12.9 ka

NASA Astrophysics Data System (ADS)

Bunch, T. E.; Schultz, P. H.; Wittke, J. H.; West, A.; Kennett, J.; Kennett, D. J.

2009-12-01

Until the announcements of a possible impact event (Firestone et al. 2007; Kennett et al., 2009a; 2009b) at the beginning of the Younger Dryas (YD) around 12.9 ka, the KT impact layer (KTB) that resulted from the Chicxulub impact at 65 mya was the only geological boundary layer known to contain coeval peaks in various impact markers, including diamonds. Here, we compare impact markers from the KTB, YD boundary layer (YDB), and the 1908 Tunguska airburst layer (TAL). First order markers, related to impact and biomass burning, include: magnetic spherules, carbon spherules, nanodiamonds (cubic and lonsdaleite), iridium anomalies, charcoal, fullerenes (with high 3He to 4He ratio), grape-like soot, and widespread extinctions. Observations and analytical data for the YDB are consistent with all of the KTB markers, while the last three markers are unknown or inconclusive for the Tunguska layer. Selected markers for cratering events, e.g, Chicxulub, are: a visible crater, shocked minerals, impact breccia, and microtektites. None of these are known for the YD event or Tunguska. The discussion here is limited to possible origins of the impact markers and not with impact consequences (climate change, extinctions, etc.). Several origins may account for impact materials in the YDB: (1) An extraordinary accretion of micrometeorites (Pinter and Ishman, 2008). However, this is inconsistent with YDB carbon spherule compositions, including the large concentrations of nanodiamonds found embedded in those carbon spherules. (2) Oblique impact(s) into the Laurentide Ice Sheet. This model is consistent with the lack of a visible crater and apparent lack of cratering markers (above), and yet also provides for shock production of the many cubic nanodiamonds and lonsdaleite found in the YDB. (3) Impact-induced aerial burst. e.g, Boslough and Crawford (2007); Shuvalov (2008). The lack of high shock pressures in an aerial detonation does not necessarily preclude the formation of cubic and hexagonal diamonds, as shown by Maruyama et al. (1993), who made hexagonal and cubic diamonds by a CVD process from a high-temperature plasma atmosphere (13,000°C) under pressure conditions similar to those in an aerial burst. The Tunguska event is commonly accepted as the result of a near-surface aerial burst and has many similarities to the YD event. (4) Comet grazing of the atmosphere (Drobysheski, 2009), involving nearly tangential entry of a comet into the Earth’s atmosphere with partial detonation and melting followed by escape of the unexploded nucleus into space. This has the net effect of an atmosphere-penetrating aerial burst followed by global fallout of detonation products. Three of the four above scenarios are plausible.

Shock pressure estimation in basement rocks of the Chicxulub impact crater using cathodoluminescence spectroscopy of quartz

NASA Astrophysics Data System (ADS)

Tomioka, N.; Tani, R.; Kayama, M.; Chang, Y.; Nishido, H.; Kaushik, D.; Rae, A.; Ferrière, L.; Gulick, S. P. S.; Morgan, J. V.

2017-12-01

The Chicxulub impact structure, located in the northern Yucatan Peninsula, Mexico, was drilled by the joint IODP-ICDP Expedition 364 in April-May 2016. This expedition is the first attempt to obtain materials from the topographic peak ring within the crater previously identified by seismic imaging. A continuous core was successfully recovered from the peak ring at depths between 505.7 and 1334.7 mbsf. Uplifted, fractured, and shocked granitic basement rocks forming the peak ring were found below, in the impact breccia and impact melt rock unit (747.0-1334.7 mbsf; Morgan et al. 2016). In order to constrain impact crater formation, we investigated shock pressure distribution in the peak-ring basement rocks. Thin sections of the granitic rocks were prepared at intervals of 60 m. All the samples contains shocked minerals, with quartz grains frequently showing planar deformation features (PDFs). We determined shock pressures based on the cathodoluminescence (CL) spectroscopy of quartz. The strong advantage of the CL method is its applicability to shock pressure estimation for individual grains for both quartz and diaplectic SiO2 glass with high-spatial resolution ( 1 μm) (Chang et al. 2016). CL spectra of quartz shows a blue emission band caused by shock-induced defect centers, where its intensity increases with shock pressure. A total of 108 quartz grains in ten thin sections were analyzed using a scanning electron microscope with a CL spectrometer attached (an acceleration voltage of 15 kV and a beam current of 2 nA were used). Natural quartz single crystals, which were experimentally shocked at 0-30 GPa, were used for pressure calibration. CL spectra of all the quartz grains in the basement rocks showed broad blue emission band at the wavelength range of 300-500 nm and estimated shock pressures were in the range of 15-20 GPa. The result is consistent with values obtained from PDFs analysis in quartz using the universal stage (Ferrière et al. 2017; Rae et al. 2017). Although shock pressure gradient in the drilled section is small, the pressure slightly increases at depths of 1113.7 and 1167.0 m. The shock pressure variation could be due to dynamic perturbation of the basement rock during peak ring formation.

Characterization of Fractures in the Chicxulub Peak Ring: Preliminary Results from IODP/ICDP Expedition 364

NASA Astrophysics Data System (ADS)

McCall, N.; Gulick, S. P. S.; Morgan, J. V.; Hall, B. J.; Jones, L.; Expedition 364 Science Party, I. I.

2017-12-01

During Expedition 364, IODP/ICDP drilled the peak ring of the Chicxulub impact crater at Site M0077, recovering core from 505.7 to 1334.7 mbsf. The core has been imaged via X-ray Computer Tomography (CT) as a noninvasive method to create a 3-dimensional model of the core, providing information on the density and internal structure at a 0.3 mm resolution. Results from the expedition show that from 748 mbsf and deeper the peak ring is largely composed of uplifted and fractured granitic basement rocks originally sourced from approximately 8-10 km depth. Impact crater modeling suggests the peak ring was formed through dynamic collapse of a rebounding central peak within 10 minutes of impact, requiring the target rocks to temporarily behave as a viscous fluid. The newly recovered core provides a rare opportunity to investigate the cratering process, specifically how the granite was weakened, as well as the extent of the hydrothermal system created after the impact. Based on the CT data, we identify four classes of fractures based on their CT facies deforming the granitoids: pervasive fine fractures, discrete fine fractures, discrete filled fractures, and discrete open fractures. Pervasive fine fractures were most commonly found proximal to dikes and impact melt rock. Discrete filled fractures often displayed a cataclastic texture. We present density trends for the different facies and compare these to petrophysical properties (density, NGR, P-wave seismic velocity). Fractured areas have a lower density than the surrounding granite, as do most filled fractures. This reduction suggests that fluid migrating through the peak ring in the wake of the impact either deposited lower density minerals within the fractures and/or altered the original fracture fill. The extent and duration of fluid flow recorded in these fractures will assist in the characterization of the post-impact hydrothermal system. Future work includes combining information from CT images with thin sections and plug samples at similar depths, refinement of CT facies characterization, examining cross-cutting relationships to determine timing constraints of deformation processes, and measurement of the orientation of the fractures.

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

NASA Technical Reports Server (NTRS)

Pope, Kevin O.

1995-01-01

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

Petrological, Magnetic and Geochemical Characterization of Cretaceous-Paleogene Boundary El Mimbral and La Lajilla Sections, Northeastern Mexico

NASA Astrophysics Data System (ADS)

Ortega Nieto, A.; Fucugauchi, J. U.; Perez-Cruz, L. L.

2009-12-01

We present initial results of a petrological, magnetic and geochemical study of El Mimbral and La Lajilla sections that span the Cretaceous-Paleogene (K-Pg) boundary. K-Pg sections in northeastern Mexico have been intensively studied in past years, mainly because of their relationship to the Chicxulub crater in the Yucatan platform and for investigating the nature, origin, stratigraphic relations and age of the impact ejecta deposits. The K-Pg boundary is preserved in between hemipelagic marls and limestones of the Mendez (Maastrichtian) and Velasco (Paleocene) formations. The two sections are situated about 1000 km away from Chicxulub and K-Pg deposits are part of the proximal ejecta and the complex channelized siliciclastic units. We had separated the siliciclastic units into two parts, with a basal coarse poorly graded spherulitic bed some 0.2 to 1 m thick and a second part with several sandstone siltstone beds that have been grouped in various ways in previous studies. In the field, samples were collected across stratigraphic profiles for rock magnetic, petrological and geochemical analyses. Using field observations and analytical data, detailed columns for the two localities are prepared. Rock magnetic measurements include susceptibility, remanent and isothermal magnetization and remanent coercivity. Magnetic hysteresis loops and IRM and back-field demagnetization were measured for samples of spherulitic bed. X-ray fluorescence analyses on whole rock were complemented with previous data obtained for the Mimbral section by atomic absorption spectrometry and inductively coupled plasma mass spectrometry (including platinum group elements). Further detailed analysis concentrated in the ejecta material. The spherulitic bed is characterized by Fe-Mg rich chlorite and Si-Al-K rich glass spherules and carbonate accretionary lapilli spherules. The silicic component spherules are altered to calcite or chlorite-smectite, with some retaining glass cores. Spherules have been shown to contain Fe-Mg bubbly spherules, Fe-Ti-K schlieren and micrometer size metallic inclusions documenting a compositional range of mafic to intermediate rocks, which relate to the target stratigraphy in Yucatan with the thick surface carbonate platform sediments and the granitic and metamorphic basement. To further characterize the spherules and analyze the within- and between-sites diversity, some 60 individual spherules were separated from the two section beds. The spherules display different morphologies, surface colors and sizes, with vesiculated globular spherules, tear drop-like and ribbon and angular fragments. They show varying degrees of alteration and spherules often form aggregates, with welding and amalgamation. Fractured and deformed spherules appear almost altered. Results are discussed in terms of the K-Pg stratigraphy, nature and emplacement mechanism of ejecta deposits, alteration processes and implications/relationship with the Chicxulub impact.

Biomarkers and their stable isotopes in Cenozoic sediments above the Chicxulub impact crater

NASA Astrophysics Data System (ADS)

Grice, K.; Schaefer, B.; Coolen, M.; Greenwood, P. F.; Scarlett, A. G.; Freeman, K.; Lyons, S. L.

2017-12-01

The most widely accepted hypothesis for the cause of the End-Cretaceous mass extinction (K/Pg event) 66 Ma ago is the impact of an extra-terrestrial body, which produced the 200 km wide Chicxulub impact structure. This event led to an extinction of 75% of all species on Earth. The massive extinction in the terrestrial realm is partly attributed to the intense heat pulse, the widespread wild fires caused by the impact and the ensuing darkness, as dust and sulfate aerosols blocked out the sun leading to photosynthesis shut off and productivity collapse in both the terrestrial and marine realms. The marine realm may additionally have experienced ocean acidification resulting in mass extinction of plankton (foraminifera and coccolithophorids) and marine reptiles. Samples from the Cenozoic marine sediments including the Paleocene-Eocene Thermal Maximum (PETM) have been extracted for hydrocarbons and analysed to investigate the molecular and isotopic organic record of biotic and environmental change after the K/Pg boundary event. Specific biomarker-precursor relationship has been established by the direct correlation of sedimentary biomarkers with the biochemicals (e.g. lipids) of extant biological systems. The structural characterisation of biomarkers as well as their stable isotopic compositions (C, H and N) are used to evaluate the source(s) of organic matter (OM) and to reconstruct paleoenvironmental depositional conditions. Throughout the Cenozoic sediments (including the PETM) the biomarker distribution suggests a variation in the source of organic matter from terrestrial to marine. Furthermore, the presence of sulfurised biomarkers indicates euxinic environmental conditions at the time of deposition. Biomarker distributions indicative of green sulfur bacteria reveal persistent photic zone euxinic conditions at several intervals in the Cenozoic. Further compound specific isotope analyses will provide insights into the long-term biogeochemical cycling of C, H and S after the K/Pg extinction including the PETM.

Consequences of Chixculub Impact for the Tectonic and Geodynamic Evolution of the Gulf of Mexico North Carribean Region

NASA Astrophysics Data System (ADS)

Rangin, C.; Crespy, A.; Martinez-Reyes, J.

2013-05-01

The debate for Pacific exotic origin versus in situ inter American plate Atlantic origin of the Caribbean plate is active in the scientific community since decades. Independently of the origin of this plate, its fast motion towards the east at a present rate of 2cm/yr is accepted to have been initiated during the early-most Cenozoic. The Paleocene is a key period in the global evolution of Central America mainly marked also by the Chicxulub multiring meteor impact in Yucatan. We question here the genetic relationship between this impact event and the incipient tectonic escape of the Caribbean plate. The mostly recent published models suggest this impact has affected the whole crust down to the Moho, the upper mantle being rapidly and considerably uplifted. The crust was then fragmented 600km at least from the point of impact, and large circular depressions were rapidly filled by clastic sediments from Cantarell to Western Cuba via Chiapas and Belize. North of the impact, the whole Gulf of Mexico was affected by mass gravity sliding, initiated also during the Paleocene in Texas, remaining active in this basin up to present time. South of the impact, in the Caribbean plate, the Yucatan basin was rapidly opened, indicating a fast escape of the crustal material towards the unique free boundary, the paleo-Antilles subduction zone. Shear waves velocity data below the Caribbean plate suggest this crustal tectonic escape was enhanced by the fast eastward flowing mantle supporting a fragmented and stretched crust. The proposed model suggests Chicxulub impact (but also the hypothetic Beata impact) have fragmented brittle crust, then easily drifted towards the east. This could explain the Paleogene evolution of the Caribbean plate largely stretched during its early evolution. Geologically, this evolution could explain the absence of evident Paleogene oblique subduction along the Caribbean plate northern and southern margins, marked only by Mid Cretaceous dragged volcanic complexes, but also the relatively recent motion along the Cayman Fault zone (Miocene instead of Eocene). These results are part of a cooperative research-industry programm conducted by CEREGE/EGERIE, Aix-en-Provence and GeoAzur, Nice, with Frontier Basin study group TOTAL S.A., Paris.

A lost generation of impact structures: Imaging the Arctic and Antarctic in magnetics and gravity

NASA Astrophysics Data System (ADS)

Purucker, M. E.

2017-12-01

The process of convection that drives plate tectonics has fragmented the early record on the continents, and subducted it in the oceans. Erosion blurs the upper surfaces of impact structures exposed to the atmosphere beyond recognition after a few million years. The largest confirmed impact structures on the Earth are Vredefort, Chicxulub, and Sudbury, with crater diameters averaging 150 km, and maximum ages of about 2 Ga. Contrast this with the situation at Mars or the Moon, where the largest confirmed impact structures have diameters of 2000 km, and ages of 4 Ga. The giant impact basins that form the most ancient, and most prominent, visible structures on the other terrestrial planets and moons have vanished on the Earth. Only with the use of techniques like magnetics and gravity is it possible to see deeper within the crust. We identify possible impact structure(s) in the Arctic and Antarctic in this way, and discuss techniques that can be used to confirm or refute these identifications.

On the Magnitude and Orientation of Stress during Shock Metamorphism: Understanding Peak Ring Formation by Combining Observations and Models.

NASA Astrophysics Data System (ADS)

Rae, A.; Poelchau, M.; Collins, G. S.; Timms, N.; Cavosie, A. J.; Lofi, J.; Salge, T.; Riller, U. P.; Ferrière, L.; Grieve, R. A. F.; Osinski, G.; Morgan, J. V.; Expedition 364 Science Party, I. I.

2017-12-01

Shock metamorphism occurs during the earliest moments after impact. The magnitude and orientation of shock leaves recordable signatures in rocks, which spatially vary across an impact structure. Consequently, observations of shock metamorphism can be used to understand deformation and its history within a shock wave, and to examine subsequent deformation during crater modification. IODP-ICDP Expedition 364 recovered nearly 600 m of shocked target rocks from the peak ring of the Chicxulub Crater. Samples from the expedition were used to measure the magnitude and orientation of shock in peak ring materials, and to determine the mechanism of peak-ring emplacement. Here, we present the results of petrographic analyses of the shocked granitic target rocks of the Chicxulub peak ring; using universal-stage optical microscopy, back-scattered electron images, and electron back-scatter diffraction. Deformation microstructures in quartz include planar deformation features (PDFs), feather features (FFs), which are unique to shock conditions, as well as planar fractures and crystal-plastic deformation bands. The assemblage of PDFs in quartz suggest that the peak-ring rocks experienced shock pressures of 15 GPa throughout the recovered drill core, and that the orientation of FFs are consistent with the present-day orientation of the maximum principal stress direction during shock is close to vertical. Numerical impact simulations of the impact event were run to determine the magnitude and orientation of principal stresses during shock and track those orientations throughout crater formation. Our results are remarkably consistent with the geological data, and accurately predict both the shock-pressure magnitudes, and the final near-vertical orientation of the direction of maximum principal stress in the shock wave. Furthermore, analysis of the state of stress throughout the impact event can be used to constrain the timing of fracture and fault orientations observed in the core. Our results quantitatively describe the deviatoric stress conditions of rocks in shock, which are consistent with observations of shock deformation. Our integrated analysis provides further support for the dynamic collapse model of peak-ring formation, and places dynamic constraints on the conditions of peak-ring formation.

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

NASA Technical Reports Server (NTRS)

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

1992-01-01

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

The hazard of near-Earth asteroid impacts on earth

NASA Astrophysics Data System (ADS)

Chapman, Clark R.

2004-05-01

Near-Earth asteroids (NEAs) have struck the Earth throughout its existence. During epochs when life was gaining a foothold ˜4 Ga, the impact rate was thousands of times what it is today. Even during the Phanerozoic, the numbers of NEAs guarantee that there were other impacts, possibly larger than the Chicxulub event, which was responsible for the Cretaceous-Tertiary extinctions. Astronomers have found over 2500 NEAs of all sizes, including well over half of the estimated 1100 NEAs >1 km diameter. NEAs are mostly collisional fragments from the inner half of the asteroid belt and range in composition from porous, carbonaceous-chondrite-like to metallic. Nearly one-fifth of them have satellites or are double bodies. When the international telescopic Spaceguard Survey, which has a goal of discovering 90% of NEAs >1 km diameter, is completed, perhaps as early as 2008, nearly half of the remaining impact hazard will be from land or ocean impacts by bodies 70-600 m diameter. (Comets are expected to contribute only about 1% of the total risk.) The consequences of impacts for civilization are potentially enormous, but impacts are so rare that worldwide mortality from impacts will have dropped to only about 150 per year (averaged over very long durations) after the Spaceguard goal has, presumably, ruled out near-term impacts by 90% of the most dangerous ones; that is, in the mid-range between very serious causes of death (disease, auto accidents) and minor but frightening ones (like shark attacks). Differences in perception concerning this rather newly recognized hazard dominate evaluation of its significance. The most likely type of impact events we face are hyped or misinterpreted predicted impacts or near-misses involving small NEAs.

The Vichada Impact Crater in Northwestern South America and its Potential for Economic Deposits

NASA Astrophysics Data System (ADS)

Hernandez, O.; von Frese, R. R.

2008-05-01

A prominent positive free-air gravity anomaly mapped over a roughly 50-km diameter basin is consistent with a mascon centered on (4o30`N, -69o15`W) in the Vichada Department, Colombia, South America. The inferred large impact crater is nearly one third the size of the Chicxulub crater. It must have formed recently, in the last 30 m.a. because it controls the partially eroded and jungle-covered path of the Vichada River. No antipodal relationship has been detected. Thick sedimentary cover, erosional processes and dense vegetation greatly limit direct geological testing of the inferred impact basin. However, EGM-96 gravity data together with ground gravity and magnetic profiles support the interpretation of the impact crater structure. The impact extensively thinned and disrupted the Precambrian cratonic crust and may be associated with mineral and hydrocarbon deposits. A combined EM and magnetic airborne program is being developed to resolve additional crustal properties of the inferred Vichada impact basin Keywords: Impact crater, economic deposits, free-air gravity anomalies

Baby, it's cold outside: Climate model simulations of the effects of the asteroid impact at the end of the Cretaceous

NASA Astrophysics Data System (ADS)

Brugger, Julia; Feulner, Georg; Petri, Stefan

2017-01-01

Sixty-six million years ago, the end-Cretaceous mass extinction ended the reign of the dinosaurs. Flood basalt eruptions and an asteroid impact are widely discussed causes, yet their contributions remain debated. Modeling the environmental changes after the Chicxulub impact can shed light on this question. Existing studies, however, focused on the effect of dust or used one-dimensional, noncoupled atmosphere models. Here we explore the longer-lasting cooling due to sulfate aerosols using a coupled climate model. Depending on aerosol stratospheric residence time, global annual mean surface air temperature decreased by at least 26°C, with 3 to 16 years subfreezing temperatures and a recovery time larger than 30 years. The surface cooling triggered vigorous ocean mixing which could have resulted in a plankton bloom due to upwelling of nutrients. These dramatic environmental changes suggest a pivotal role of the impact in the end-Cretaceous extinction.

Noril'sk/Siberian plateau basalts and Bahama hot spot: Impact triggered?

NASA Technical Reports Server (NTRS)

Deitz, R. S.; Mchone, J. F.

1992-01-01

Twenty-eight years after one of us argued that Sudbury was an astrobleme, this interpretation has only recently attained wide acceptance; not so for the view that the Sudbury Cu/Ni sulfide ores are cosmogenic. Other research has provided the triggering of plateau basalts by super-large impacts a modicum of respectability. The recent apparent successful tying in of the K/T extinctions to the Chicxulub astrobleme in the Yucatan encourages the search for an impact event that may have caused the other two major post-Paleozoic extinctions (P/Tr, Tr/J). This gives us heart to offer two further outrageous hypotheses. The cosmogenic concept for the Sudbury ore deposite remains viable because it is giant, nonultramafic, and unique (except for Noril'sk). The Triassic/Jurassic boundary catastrophic extinctions have been attributed to the Manicouagan asteroidal impact, but recent radiometric dating indicates these events are diachronous (Manicouagan astrobleme 212 +/- 2 Ma and Tr/J boundary 200 Ma).

Peak-ring structure and kinematics from a multi-disciplinary study of the Schrödinger impact basin

PubMed Central

Kring, David A.; Kramer, Georgiana Y.; Collins, Gareth S.; Potter, Ross W. K.; Chandnani, Mitali

2016-01-01

The Schrödinger basin on the lunar farside is ∼320 km in diameter and the best-preserved peak-ring basin of its size in the Earth–Moon system. Here we present spectral and photogeologic analyses of data from the Moon Mineralogy Mapper instrument on the Chandrayaan-1 spacecraft and the Lunar Reconnaissance Orbiter Camera (LROC) on the LRO spacecraft, which indicates the peak ring is composed of anorthositic, noritic and troctolitic lithologies that were juxtaposed by several cross-cutting faults during peak-ring formation. Hydrocode simulations indicate the lithologies were uplifted from depths up to 30 km, representing the crust of the lunar farside. Through combining geological and remote-sensing observations with numerical modelling, we show that a Displaced Structural Uplift model is best for peak rings, including that in the K–T Chicxulub impact crater on Earth. These results may help guide sample selection in lunar sample return missions that are being studied for the multi-agency International Space Exploration Coordination Group. PMID:27762265

Lunar and Planetary Science XXXV: Impacts: Modeling and Observations

NASA Technical Reports Server (NTRS)

2004-01-01

This document covers the following topics: Cratering on Titan: Projectiles, Craters and Impact Melt; The Cratering Database: Making Code Jockeys Honest; Popigai Impact Structure Modeling: Morphology and Worldwide Ejecta; Anhydrite EOS and Phase Diagram in Relation to Shock Decomposition; Computational Investigations of the Chesapeake Bay Impact Structure; Hydrocode Simulations of the Chesapeake Bay Impact; Lockne Crater as a Result of Oblique Impact; The Influence of a Deep Shelf Sea on the Excavation and Modification of a Marine-Target Crater, the Lockne Crater, Central Sweden; Pre-Drilling Investigation of the Lake Bosumtwi Impact Crater: Constraints from Geophysics and Numerical Modelling; Central Uplift Formation at the Middlesboro Impact Structure, Kentucky, USA; A SRTM Investigation of Serra da Cangalho Impact Structure, Brazil; Brazilian Impact Craters: A Review; Flynn Creek Impact Structure: New Insights from Breccias, Melt Features, Shatter Cones, and Remote Sensing; The Howell Structure, Lincoln County, Tennessee: A Review of Past and Current Research; After the Chicxulub Impact: Control on Depositional and Diagenetic History of the Cenozoic Carbonate Formations of the Northwestern Yucatan Peninsula, Mexico; Ni Contents by Non-Destructive In-Situ XRF Method of Takamatsu-Kagawa Crater District in Japan; and Akiyoshi Limestone Blocks Transported by the P/T Boundary Event to Japan Islands.

Imaging the Chicxulub central crater zone from large scale seismic acoustic wave propagation and gravity modeling

NASA Astrophysics Data System (ADS)

Fucugauchi, J. U.; Ortiz-Aleman, C.; Martin, R.

2017-12-01

Large complex craters are characterized by central uplifts that represent large-scale differential movement of deep basement from the transient cavity. Here we investigate the central sector of the large multiring Chicxulub crater, which has been surveyed by an array of marine, aerial and land-borne geophysical methods. Despite high contrasts in physical properties,contrasting results for the central uplift have been obtained, with seismic reflection surveys showing lack of resolution in the central zone. We develop an integrated seismic and gravity model for the main structural elements, imaging the central basement uplift and melt and breccia units. The 3-D velocity model built from interpolation of seismic data is validated using perfectly matched layer seismic acoustic wave propagation modeling, optimized at grazing incidence using shift in the frequency domain. Modeling shows significant lack of illumination in the central sector, masking presence of the central uplift. Seismic energy remains trapped in an upper low velocity zone corresponding to the sedimentary infill, melt/breccias and surrounding faulted blocks. After conversion of seismic velocities into a volume of density values, we use massive parallel forward gravity modeling to constrain the size and shape of the central uplift that lies at 4.5 km depth, providing a high-resolution image of crater structure.The Bouguer anomaly and gravity response of modeled units show asymmetries, corresponding to the crater structure and distribution of post-impact carbonates, breccias, melt and target sediments

Imaging the Buried Chicxulub Crater with Gravity Gradients and Cenotes

NASA Astrophysics Data System (ADS)

Hildebrand, A. R.; Pilkington, M.; Halpenny, J. F.; Ortiz-Aleman, C.; Chavez, R. E.; Urrutia-Fucugauchi, J.; Connors, M.; Graniel-Castro, E.; Camara-Zi, A.; Vasquez, J.

1995-09-01

Differing interpretations of the Bouguer gravity anomaly over the Chicxulub crater, Yucatan Peninsula, Mexico, have yielded diameter estimates of 170 to 320 km. Knowing the crater's size is necessary to quantify the lethal perturbations to the Cretaceous environment associated with its formation. The crater's size (and internal structure) is revealed by the horizontal gradient of the Bouguer gravity anomaly over the structure, and by mapping the karst features of the Yucatan region. To improve our resolution of the crater's gravity signature we collected additional gravity measurements primarily along radial profiles, but also to fill in previously unsurveyed areas. Horizontal gradient analysis of Bouguer gravity data objectively highlights the lateral density contrasts of the impact lithologies and suppresses regional anomalies which may obscure the gravity signature of the Chicxulub crater lithologies. This gradient technique yields a striking circular structure with at least 6 concentric gradient features between 25 and 85 km radius. These features are most distinct in the southwest probably because of denser sampling of the gravity field. Our detailed profiles detected an additional feature and steeper gradients (up to 5 mGal/km) than the original survey. We interpret the outer four gradient maxima to represent concentric faults in the crater's zone of slumping as is also revealed by seismic reflection data. The inner two probably represent the margin of the central uplift and the peak ring and or collapsed transient cavity. Radial gradients in the SW quadrant over the inferred ~40 km-diameter central uplift (4) may represent structural "puckering" as revealed at eroded terrestrial craters. Gradient features related to regional gravity highs and lows are visible outside the crater, but no concentric gradient features are apparent at distances > 90 km radius. The marginal gradient features may be modelled by slump faults as observed in large complex craters on the other terrestrial planets. A modeled fault of 1.5 km displacement (slightly slumped block exterior and impact breccia interior) reproduces the steepest gradient feature. This model is incompatible with models that place these gradient features inside the collapsed transient cavity. Locations of the karst features of the northern Yucatan region were digitized from 1:50,000 topographic maps, which show most but not all the water-filled sinkholes (locally known as cenotes). A prominent ring of cenotes is visible over the crater that is spatially correlated to the outer steep gravity gradient feature. The mapped cenotes constitute an unbiased sampling of the region's karst surface features of >50 m diameter. The gradient maximum and the cenote ring both meander with amplitudes of up to 2 km. The wiggles in the gradient feature and the cenote distribution probably correspond to the "scalloping" observed at the headwall of terraces in large complex craters. A second partial cenote ring exterior to the southwest side of the main ring corresponds to a less-prominent gravity gradient feature. No concentric structure is observable in the distribution of karst features at radii >90 km. The cenote ring is bounded by the outer peripheral steep gradient feature and must be related to it; the slump faults must have been reactivated sufficiently to create fracturing in the overlying and much younger sediment. Long term subsidence, as found at other terrestrial craters is a possible mechanism for the reactivation. Such long term subsidence may be caused by differential compaction or thermal relaxation. Elevations acquired during gravity surveys show that the cenote ring also corresponds to a topographic low along some of its length that probably reflects preferential erosion.

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

NASA Astrophysics Data System (ADS)

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

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

Space Radar Image of the Yucatan Impact Crater Site

NASA Technical Reports Server (NTRS)

1999-01-01

This is a radar image of the southwest portion of the buried Chicxulub impact crater in the Yucatan Peninsula, Mexico. The radar image was acquired on orbit 81 of space shuttle Endeavour on April 14, 1994 by the Spaceborne Imaging Radar C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR). The image is centered at 20 degrees north latitude and 90 degrees west longitude. Scientists believe the crater was formed by an asteroid or comet which slammed into the Earth more than 65 million years ago. It is this impact crater that has been linked to a major biological catastrophe where more than 50 percent of the Earth's species, including the dinosaurs, became extinct. The 180-to 300-kilometer-diameter (110- to 180-mile)crater is buried by 300 to 1,000 meters (1,000 to 3,000 feet) of limestone. The exact size of the crater is currently being debated by scientists. This is a total power radar image with L-band in red, C-band in green, and the difference between C-band L-band in blue. The 10-kilometer-wide (6-mile) band of yellow and pink with blue patches along the top left (northwestern side) of the image is a mangrove swamp. The blue patches are islands of tropical forests created by freshwater springs that emerge through fractures in the limestone bedrock and are most abundant in the vicinity of the buried crater rim. The fracture patterns and wetland hydrology in this region are controlled by the structure of the buried crater. Scientists are using the SIR-C/X-SAR imagery to study wetland ecology and help determine the exact size of the impact crater. Spaceborne Imaging Radar-C and X-band Synthetic Aperture Radar (SIR-C/X-SAR) is part of NASA's Mission to Planet Earth. The radars illuminate Earth with microwaves allowing detailed observations at any time, regardless of weather or sunlight conditions. SIR-C/X-SAR uses three microwave wavelengths: L-band (24 cm), C-band (6 cm) and X-band (3 cm). The multi-frequency data will be used by the international scientific community to better understand the global environment and how it is changing. The SIR-C/X-SAR data, complemented by aircraft and ground studies, will give scientists clearer insights into those environmental changes which are caused by nature and those changes which are induced by human activity. SIR-C was developed by NASA's Jet Propulsion Laboratory. X-SAR was developed by the Dornier and Alenia Spazio companies for the German space agency, Deutsche Agentur fuer Raumfahrtange-legenheiten (DARA), and the Italian space agency, Agenzia Spaziale Italiana (ASI), with the Deutsche Forschungsanstalt fuer Luft und Raumfahrt e.v.(DLR), the major partner in science, operations, and data processing of X-SAR. Research on the biological effects of the Chicxulub impact is supported by the NASA Exobiology Program.

End-Cretaceous extinction in Antarctica linked to both Deccan volcanism and meteorite impact via climate change

PubMed Central

Petersen, Sierra V.; Dutton, Andrea; Lohmann, Kyger C.

2016-01-01

The cause of the end-Cretaceous (KPg) mass extinction is still debated due to difficulty separating the influences of two closely timed potential causal events: eruption of the Deccan Traps volcanic province and impact of the Chicxulub meteorite. Here we combine published extinction patterns with a new clumped isotope temperature record from a hiatus-free, expanded KPg boundary section from Seymour Island, Antarctica. We document a 7.8±3.3 °C warming synchronous with the onset of Deccan Traps volcanism and a second, smaller warming at the time of meteorite impact. Local warming may have been amplified due to simultaneous disappearance of continental or sea ice. Intra-shell variability indicates a possible reduction in seasonality after Deccan eruptions began, continuing through the meteorite event. Species extinction at Seymour Island occurred in two pulses that coincide with the two observed warming events, directly linking the end-Cretaceous extinction at this site to both volcanic and meteorite events via climate change. PMID:27377632

End-Cretaceous extinction in Antarctica linked to both Deccan volcanism and meteorite impact via climate change.

PubMed

Petersen, Sierra V; Dutton, Andrea; Lohmann, Kyger C

2016-07-05

The cause of the end-Cretaceous (KPg) mass extinction is still debated due to difficulty separating the influences of two closely timed potential causal events: eruption of the Deccan Traps volcanic province and impact of the Chicxulub meteorite. Here we combine published extinction patterns with a new clumped isotope temperature record from a hiatus-free, expanded KPg boundary section from Seymour Island, Antarctica. We document a 7.8±3.3 °C warming synchronous with the onset of Deccan Traps volcanism and a second, smaller warming at the time of meteorite impact. Local warming may have been amplified due to simultaneous disappearance of continental or sea ice. Intra-shell variability indicates a possible reduction in seasonality after Deccan eruptions began, continuing through the meteorite event. Species extinction at Seymour Island occurred in two pulses that coincide with the two observed warming events, directly linking the end-Cretaceous extinction at this site to both volcanic and meteorite events via climate change.

End-Cretaceous extinction in Antarctica linked to both Deccan volcanism and meteorite impact via climate change

NASA Astrophysics Data System (ADS)

Petersen, Sierra V.; Dutton, Andrea; Lohmann, Kyger C.

2016-07-01

The cause of the end-Cretaceous (KPg) mass extinction is still debated due to difficulty separating the influences of two closely timed potential causal events: eruption of the Deccan Traps volcanic province and impact of the Chicxulub meteorite. Here we combine published extinction patterns with a new clumped isotope temperature record from a hiatus-free, expanded KPg boundary section from Seymour Island, Antarctica. We document a 7.8+/-3.3 °C warming synchronous with the onset of Deccan Traps volcanism and a second, smaller warming at the time of meteorite impact. Local warming may have been amplified due to simultaneous disappearance of continental or sea ice. Intra-shell variability indicates a possible reduction in seasonality after Deccan eruptions began, continuing through the meteorite event. Species extinction at Seymour Island occurred in two pulses that coincide with the two observed warming events, directly linking the end-Cretaceous extinction at this site to both volcanic and meteorite events via climate change.

Seawater Chemistry Across Cretaceous-Tertiary Boundary

NASA Astrophysics Data System (ADS)

Misra, S.; Turchyn, A. V.

2016-12-01

Continental weathering is recognized as one of the primary mechanisms moderating the concentration of CO2 in the atmosphere. Past carbon cycle perturbations, often associated with mass extinction events, recovered on a timescale of hundreds of thousands of years, broadly consistent with enhanced chemical weathering being the key moderating process. Since chemical weathering of continental rocks controls the delivery of cations to the oceans, records of seawater cation chemistry provide a powerful archive of this interplay and feedback between climate and weathering.The Cretaceous-Paleogene (K-Pg) boundary at 65.6 Ma is the last major mass extinction event. The two accepted drivers of K-Pg events were the geologically coeval eruption of Deccan Trap continental flood basalts and the meteorite impact at Chicxulub. The Chicxulub impact happened during a second pulse of Deccan traps volcanism. Thus, teasing apart the timing and dominant driver of the mass extinction and the recovery remains enigmatic. A key feature of the K-Pg event is the transient acidification of the global surface ocean that drove the collapse of the oceanic ecosystem. This surface ocean acidification was caused by `geologically instantaneous' influx of large quantities of acidic gases (viz. CO2, SO2) to the ocean-atmosphere system. We will present high-resolution records of Li, B, Mg, and Ca isotope (δ7Li, δ11B, δ26Mg, and δ44Ca, respectively) measured in single species foraminifera across the K-Pg boundary to assess the perturbation and the subsequent continental weathering feedback. The unique aspect of the proposed research is in the first direct reconstruction of seawater isotopic composition of elements intimately linked to the continental weathering cycle (Li, Mg, and Ca), and the carbon budget of the ocean-atmosphere system (Boron) across an event of rapid climate transition and recovery. Moreover, this will allow to fingerprint the timing of the acidic gas input to the atmosphere and to test the `impact hypothesis'. Benthic foraminifera are faithful recorders of the seawater composition and pH of their growth habitat. A continuous array of chemically cleaned benthic foraminifera (Nuttallides sp. & Stensioina sp.) across the K-Pg section from deep-sea sites (DSDP 490; IODP 1210, 1262, & 1267) will be presented.

Experimental alteration of artificial and natural impact melt rock from the Chesapeake Bay impact structure

USGS Publications Warehouse

Declercq, J.; Dypvik, H.; Aagaard, Per; Jahren, J.; Ferrell, R.E.; Horton, J. Wright

2009-01-01

The alteration or transformation of impact melt rock to clay minerals, particularly smectite, has been recognized in several impact structures (e.g., Ries, Chicxulub, Mj??lnir). We studied the experimental alteration of two natural impact melt rocks from suevite clasts that were recovered from drill cores into the Chesapeake Bay impact structure and two synthetic glasses. These experiments were conducted at hydrothermal temperature (265 ??C) in order to reproduce conditions found in meltbearing deposits in the first thousand years after deposition. The experimental results were compared to geochemical modeling (PHREEQC) of the same alteration and to original mineral assemblages in the natural melt rock samples. In the alteration experiments, clay minerals formed on the surfaces of the melt particles and as fine-grained suspended material. Authigenic expanding clay minerals (saponite and Ca-smectite) and vermiculite/chlorite (clinochlore) were identified in addition to analcime. Ferripyrophyllite was formed in three of four experiments. Comparable minerals were predicted in the PHREEQC modeling. A comparison between the phases formed in our experiments and those in the cores suggests that the natural alteration occurred under hydrothermal conditions similar to those reproduced in the experiment. ?? 2009 The Geological Society of America.

Wildfires Caused by Formation of Small Impact Craters: A Kaali Crater Case

NASA Astrophysics Data System (ADS)

Losiak, Anna; Belcher, Claire; Hudspith, Victoria; Zhu, Menghua; Bronikowska, Malgorzata; Jõeleht, Argo; Plado, Juri

2016-04-01

Formation of ~200-km Chicxulub 65 Ma ago was associated with release of significant amount of thermal energy [1,2,3] which was sufficient to start wildfires that had either regional [4] or global [5] range. The evidence for wildfires caused by impacts smaller than Chicxulub is inconclusive. On one hand, no signs of fires are associated with the formation of 24-km Ries crater [6]. On the other hand, the Tunguska site was burned after the impact and the numerical models of the bolide-produced thermal radiation suggest that the Tunguska-like event would produce a thermal flux to the surface that is sufficient to ignite pine needles [7]. However, in case of Tunguska the only proof for the bolide starting the fire comes from an eyewitness description collected many years after the event. Some authors [8] suggest that this fire might have been caused "normaly" later during the same year, induced on dead trees killed by the Tunguska fall. More recently it was observed that the Chelyabinsk meteor [9] - smaller than Tunguska event - did not produced a fire. In order to explore this apparent relationship in more detail, we have studied the proximal ejecta from a 100-m in diameter, ~3500 years old [10] Kaali crater (Estonia) within which we find pieces of charred organic material. Those pieces appear to have been produced during the impact, according to their stratigraphic location and following 14C analysis [19] as opposed to pre- or post-impact forest fires. In order to determine the most probable formation mechanism of the charred organic material found within Kaali proximal ejecta blanket, we: 1) Analyzed charcoal under SEM to identify the charred plants and determine properties of the charcoal related to the temperature of its formation [11]. Detected homogenization of cell walls suggests that at least some pieces of charcoal were formed at >300 °C [11]. 2) Analyzed the reflectance properties of the charred particles in order to determine the intensity with which pyrolysis occurred [12,13]. Initial mesurements suggest some particles are partially charred. This may be consistent with a short thermal exposure. 3) Numerically estimated entry parameters and thermal radiation from the bolide that reaches the surface of the impact site. 4) Performed numerical modeling using iSALE of the Kaali crater formation and ejecta distribution, especially in terms of the temperature of the ejected particles [14]. References: [1] Melosh et al. 1990. Nature 343:251-254. [2] Shuvalov and Artemieva 2002. Geol. Soc. Am. Special Papers 356:695-703. [3] Goldin and Melosh 2009. Geology 37:1135-1138. [4] Belcher et al. 2015. J. Geolog. Soc. doi:10.1144/jgs2014-082. [5] Robertson et al. 2013. J. Geoph. Res. Biogeosc. 118:329-336. [6] Jones and Lim 2000. Paleogeog. Paleoclim.Paleoecol. 164:57-66. [7] Svetsov 2008. Catastrophic Events Caused by Cosmic Objects 207-226. [8] Jones. 2002. Paleogeog. Paleoclim.Paleoecol. 185:407-408. [9] Popowa et al. 2013. Science 342:1069-1073. [10] Losiak et al. 2016. MAPS (in press). [11] Scott 2000. Palaeoecol. 164:281-329. [12] Hudspith et al. 2014. Front Plant Sci. 5:714. [13] Hudspith et al. 2015. PloS One 10.1371/journal.pone.0120835. [14] Zhu et al. 2015. JGR:Planets 10.1002/2015JE004827.

Characterization of Shock Effects in Calcite by Raman Spectroscopy: Results of Experiments

NASA Technical Reports Server (NTRS)

Bell, M. S.

2016-01-01

Carbonates comprise approx. 20% by volume of present day Earth's sedimentary rocks and store most of the terrestrial CO2 inventory. Some of the oldest meta-sedimentary rocks found on Earth contain abundant carbonate from which impact-induced release of CO2 could have played a role in the formation and evolution of the atmosphere. Carbonates are also present in the target materials for approx. 30% of all terrestrial impact structures including large impacts such as Chicxulub which happened to occur at a location with extraordinarily thick platform carbonate 3-6 km deep. The impact release of CO2 from carbonates can cause global warming as a result of the well-known greenhouse effect and have subsequent effects on climate and biota. Therefore, the shock behavior of calcite is important in understanding the Cretaceous-Paleogene event and other impacts with carbonate-bearing sediments in their target(s) such as Mars and some asteroids. A comprehensive survey utilizing a variety of techniques to characterize the effects manifest in Calcite (Iceland Spar) experimentally shocked to 60.8 GPa has been completed. Results of analysis by Raman Spectroscopy are reported here.

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

NASA Technical Reports Server (NTRS)

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

1994-01-01

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

Petrography and geochemistry of distal spherules from the K-Pg boundary in the Umbria-Marche region (Italy) and their origin as fractional condensates and melts in the Chicxulub impact plume

NASA Astrophysics Data System (ADS)

Belza, J.; Goderis, S.; Montanari, A.; Vanhaecke, F.; Claeys, P.

2017-04-01

The impact spherules from the distal K-Pg boundary sections are considered to represent silicate droplets condensed and solidified from a laterally expanding, cooling vapor plume formed upon hypervelocity impact. In the present-day Cretaceous-Paleogene boundary (K-Pg) spherule population of the Umbria-Marche region in Italy, three texturally and compositionally distinct types of impact spherules can be identified that are dominantly composed of (1) goethite, (2) K-feldspar or (3) glauconite. Although these phases represent the products of diagenetic alteration, the remnant textural characteristics of the spherules and the type of alteration product are indicative of the spherules' original compositions, which are important to constrain the physicochemical conditions prevalent throughout the impact vapor plume. The presence of relict ghost crystals and the identification of 'iddingsite' indicate that goethite likely represents pseudomorphic replacement after olivine. Goethite spherules contain numerous dendritic, euhedral and skeletal spinel crystals variably dispersed in the groundmass. In terms of textures, five types of goethite spherules can be distinguished, showing striking similarities to chondrules: (I) skeletal, (II) barred, (III) radial/barred, (IV) porphyritic and (V) relict/granular. The morphology of both spinel and olivine (pseudomorphs) is consistent with established formation conditions (peak temperature Tmax, degree of supercooling ΔT, cooling rate, presence of nucleation sites) for different chondrule textural types. As goethite spherules are anomalously enriched in moderately to highly refractory lithophile (Sc, V, Y, Zr, Nb, REE, Hf, Ta, Th) and siderophile (Cr, Co, Ni, W, Ir, Pt) elements, they are interpreted to represent (diagenetically altered) refractory (high-T) condensation products from a well-homogenized plume consisting of both vaporized target and projectile matter. Different from goethite spherules, K-feldspar spherules exhibit pseudomorphic textures after lower-liquidus silicates such as Ca-rich pyroxene and plagioclase. Furthermore, the K-feldspar spherules yield systematically lower abundances of the most refractory trace elements. This suggests that the pre-altered K-feldspar spherules are part of the same fractional condensation sequence of the target-impactor vapor plume, cooled during lateral expansion. Glauconite spherules are cryptocrystalline, exhibiting hemispherical lamellae that resemble the palagonite/smectite alteration layers of basaltic glasses and the K-Pg spherules (microtektites) found at proximal sites around the Gulf of Mexico region. Their trace element contents and REE patterns are strikingly similarity to those of (altered) K-Pg microtektites, suggesting that glauconite spherules represent former glass spherules without crystallites/microlites. Glauconite spherules are interpreted not to be part of the fractional condensation sequence of the impact vapor plume that led to the formation of the replaced goethite and K-felspar spherules. They were likely formed by entrainment of melt, expelled at the steepest angles and highest ejection velocities from the central melt sheet, within the edges of the vapor plume. This work is the first to create a geochemical foundation for vapor plume models, both at the major and trace element scale. In addition, it highlights the unique characteristics of the Chicxulub impact event and emphasizes the importance of its unusual target lithologies. The heterogeneous, layered, and volatile-rich target contributed significantly to the formation of a dust-rich environment, high oxygen fugacities and the preservation of some degree of heterogeneity in the vapor plume. In addition, striking similarities between distal (goethite-type) K-Pg spherules and chondrules may argue for a reevaluation of the impact model as a possible origin for the formation of certain types of cosmic chondrules.

The last polar dinosaurs: high diversity of latest Cretaceous arctic dinosaurs in Russia

NASA Astrophysics Data System (ADS)

Godefroit, Pascal; Golovneva, Lina; Shchepetov, Sergei; Garcia, Géraldine; Alekseev, Pavel

2009-04-01

A latest Cretaceous (68 to 65 million years ago) vertebrate microfossil assemblage discovered at Kakanaut in northeastern Russia reveals that dinosaurs were still highly diversified in Arctic regions just before the Cretaceous-Tertiary mass extinction event. Dinosaur eggshell fragments, belonging to hadrosaurids and non-avian theropods, indicate that at least several latest Cretaceous dinosaur taxa could reproduce in polar region and were probably year-round residents of high latitudes. Palaeobotanical data suggest that these polar dinosaurs lived in a temperate climate (mean annual temperature about 10°C), but the climate was apparently too cold for amphibians and ectothermic reptiles. The high diversity of Late Maastrichtian dinosaurs in high latitudes, where ectotherms are absent, strongly questions hypotheses according to which dinosaur extinction was a result of temperature decline, caused or not by the Chicxulub impact.

Space Radar Image of the Yucatan Impact Crater Site

NASA Image and Video Library

1999-01-27

This is a radar image of the southwest portion of the buried Chicxulub impact crater in the Yucatan Peninsula, Mexico. The radar image was acquired on orbit 81 of space shuttle Endeavour on April 14, 1994 by the Spaceborne Imaging Radar C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR). The image is centered at 20 degrees north latitude and 90 degrees west longitude. Scientists believe the crater was formed by an asteroid or comet which slammed into the Earth more than 65 million years ago. It is this impact crater that has been linked to a major biological catastrophe where more than 50 percent of the Earth's species, including the dinosaurs, became extinct. The 180-to 300-kilometer-diameter (110- to 180-mile) crater is buried by 300 to 1,000 meters (1,000 to 3,000 feet) of limestone. The exact size of the crater is currently being debated by scientists. This is a total power radar image with L-band in red, C-band in green, and the difference between C-band L-band in blue. The 10-kilometer-wide (6-mile) band of yellow and pink with blue patches along the top left (northwestern side) of the image is a mangrove swamp. The blue patches are islands of tropical forests created by freshwater springs that emerge through fractures in the limestone bedrock and are most abundant in the vicinity of the buried crater rim. The fracture patterns and wetland hydrology in this region are controlled by the structure of the buried crater. Scientists are using the SIR-C/X-SAR imagery to study wetland ecology and help determine the exact size of the impact crater. http://photojournal.jpl.nasa.gov/catalog/PIA01723

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

NASA Technical Reports Server (NTRS)

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

1993-01-01

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

Hyperspectral Imaging at the Micro- and Nanoscale using Energy-dispersive Spectroscopy (EDS) with Silicon Drift Detector (SDD) and EBSD Analysis

NASA Astrophysics Data System (ADS)

Salge, T.; Goran, D.

2010-12-01

SDD systems have become state of the art technology in the field of EDS. The main characteristic of the SDDs is their extremely high pulse load capacity of up to 750,000 counts per second at good energy resolution (<123 eV Mn-Kα, <46 eV C-Kα at 100,000 counts per seconds). These properties in conjunction with electron backscatter diffraction (EBSD) technique and modern data processing allows not only high speed mapping but also hyperspectral analysis. Here, a database is created that contains an EDS spectrum and/or EBSD pattern for each pixel of the SEM image setting the stage for innovative analysis options: The Maximum Pixel Spectrum function [1] synthesizes a spectrum out of the EDS database, consisting of the highest count level found in each spectrum channel. Here, (trace) elements which occur in only one pixel can be detected qualitatively. Areas of similar EDS composition can be made visible with Autophase, a spectroscopic phase detection system. In cases where the crystallographic phase assessment by EBSD is problematic due to pattern similarity, the EDS signal can be used as additional information for phase separation. This paper presents geoscience applications with the QUANTAX system with EDS SDD and EBSD detector using the options described above: (1) Drill core analysis of a Chicxulub impact ejecta sequence from the K/Pg boundary at ODP leg 207 [2] using fast, high resolution element maps. (2) Detection of monazite in granite by the Maximum Pixel Spectrum function. (3) Distribution of elements with overlapping peaks by deconvolution at the example of rare earth elements in zoned monazite. (4) Spectroscopic phase analysis of a sulfate-carbonate-dominated impact matrix at borehole UNAM-7 from the Chicxulub impact crater [3]. (5) EBSD studies with examples of iron meteorites and impact-induced, recrystallized carbonate melts [4]. In addition, continuing technological advances require the elemental analysis of increasingly smaller structures in many fields, including geosciences. It will be demonstrated that using low accelerating voltages, the element distribution of structures at the nanoscale in bulk samples can be displayed in a short time due to optimized signal processing and solid angle. Peaks composed of contributions from several overlapping elements e.g. N-K (392 eV) and Ti-Ll (395 eV) can be deconvolved [6] using an improved atomic database with 250 additional L, M and N lines below 4 keV. Improved light element quantification allows the standardless quantification of features at the nanoscale such as rutile grains 200-500 nm in size. References: [1] Bright D S. & Newbury D. E. (2004) Journal of Microscopy 216:186-193. [2] Schulte P. et al. (2010) Science 327: 1214-1218. [3] Salge T. (2007) PhD thesis: 130p. http://edoc.huberlin.de/docviews/abstract.php?lang=ger&id=27753. [4] Deutsch A. et al. MAPS 45: A45. [6] Tunckan O. (2010) Joining ceramics using capacitor discharge technique and determination of metal ceramic interface reactions, PhD thesis, Anadolu University, Eskisehir, Turkey. Acknowledgements: We thank P. Schulte, A. Deutsch, ODP, L. Hecht, A. Kearsley, J. Urrutria-Fucugauchi, O. Tunckan and S. Turan for generously providing the samples.

Designing global climate and atmospheric chemistry simulations for 1 and 10 km diameter asteroid impacts using the properties of ejecta from the K-Pg impact

NASA Astrophysics Data System (ADS)

Toon, Owen B.; Bardeen, Charles; Garcia, Rolando

2016-10-01

About 66 million years ago, an asteroid about 10 km in diameter struck the Yucatan Peninsula creating the Chicxulub crater. The crater has been dated and found to be coincident with the Cretaceous-Paleogene (K-Pg) mass extinction event, one of six great mass extinctions in the last 600 million years. This event precipitated one of the largest episodes of rapid climate change in Earth's history, yet no modern three-dimensional climate calculations have simulated the event. Similarly, while there is an ongoing effort to detect asteroids that might hit Earth and to develop methods to stop them, there have been no modern calculations of the sizes of asteroids whose impacts on land would cause devastating effects on Earth. Here, we provide the information needed to initialize such calculations for the K-Pg impactor and for a 1 km diameter impactor. There is considerable controversy about the details of the events that followed the Chicxulub impact. We proceed through the data record in the order of confidence that a climatically important material was present in the atmosphere. The climatic importance is roughly proportional to the optical depth of the material. Spherules with diameters of several hundred microns are found globally in an abundance that would have produced an atmospheric layer with an optical depth around 20, yet their large sizes would only allow them to stay airborne for a few days. They were likely important for triggering global wildfires. Soot, probably from global or near-global wildfires, is found globally in an abundance that would have produced an optical depth near 100, which would effectively prevent sunlight from reaching the surface. Nanometer-sized iron particles are also present globally. Theory suggests these particles might be remnants of the vaporized asteroid and target that initially remained as vapor rather than condensing on the hundred-micron spherules when they entered the atmosphere. If present in the greatest abundance allowed by theory, their optical depth would have exceeded 1000. Clastics may be present globally, but only the quartz fraction can be quantified since shock features can identify it. However, it is very difficult to determine the total abundance of clastics. We reconcile previous widely disparate estimates and suggest the clastics may have had an optical depth near 100. Sulfur is predicted to originate about equally from the impactor and from the Yucatan surface materials. By mass, sulfur is less than 10 % of the observed mass of the spheres and estimated mass of nanoparticles. Since the sulfur probably reacted on the surfaces of the soot, nanoparticles, clastics, and spheres, it is likely a minor component of the climate forcing; however, detailed studies of the conversion of sulfur gases to particles are needed to determine if sulfuric acid aerosols dominated in late stages of the evolution of the atmospheric debris. Numerous gases, including CO2, SO2 (or SO3), H2O, CO2, Cl, Br, and I, were likely injected into the upper atmosphere by the impact or the immediate effects of the impact such as fires across the planet. Their abundance might have increased relative to current ambient values by a significant fraction for CO2, and by factors of 100 to 1000 for the other gases. For the 1 km impactor, nanoparticles might have had an optical depth of 1.5 if the impact occurred on land. If the impactor struck a densely forested region, soot from the forest fires might have had an optical depth of 0.1. Only S and I would be expected to be perturbed significantly relative to ambient gas-phase values. One kilometer asteroids impacting the ocean may inject seawater into the stratosphere as well as halogens that are dissolved in the seawater. For each of the materials mentioned, we provide initial abundances and injection altitudes. For particles, we suggest initial size distributions and optical constants. We also suggest new observations that could be made to narrow the uncertainties about the particles and gases generated by large impacts.

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

USGS Publications Warehouse

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

1999-01-01

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

Slumping and a sandbar deposit at the Cretaceous-Tertiary boundary in the El Tecolote section (northeastern Mexico): An impact-induced sediment gravity flow

NASA Astrophysics Data System (ADS)

Soria, Ana R.; Liesa, Carlos L.; Mata, Maria Pilar; Arz, José A.; Alegret, Laia; Arenillas, Ignacio; Meléndez, Alfonso

2001-03-01

Slumps affecting uppermost Méndez Formation marls, as well as the spherulitic layer and basal part of the sandy deposits of the Cretaceous-Tertiary (K-T) boundary clastic unit, are described at the new K-T El Tecolote section (northeastern Mexico). These K-T clastic deposits represent sedimentation at middle-bathyal water depths in channel and nonchannel or levee areas of reworked materials coming from environments ranging from outer shelf to shallower slope via a unidirectional, high- to low-density turbidite flow. We emphasize the development and accretion of a lateral bar in a channel area from a surging low-density turbidity current and under a high-flow regime. The slumps discovered on land and the sedimentary processes of the K-T clastic unit reflect destabilization and collapse of the continental margin, support the mechanism of gravity flows in the deep sea, and represent important and extensive evidence for the impact effects in the Gulf of México triggered by the Chicxulub event.

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

PubMed

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

2007-09-06

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

Reverse polarity magnetized melt rocks from the Chicxulub impact structure, Yucatan Peninsula, Mexico

NASA Astrophysics Data System (ADS)

Urrutia-Fucugauchi, Jaime; Marin, Luis E.; Sharpton, Virgil L.; Quezada, Juan Manuel

1993-03-01

Further paleomagnetic data for core samples of melt rock recovered in the Petroleos Mexicanos (PEMEX) exploratory wells within the Chicxulub structure, northern Yucatan peninsula, Mexico are reported. A previous report by Sharpton showed that the rocks studied contain high iridium levels and shocked breccia clasts, and an Ar-40/Ar-39 age of 65.2 plus or minus 0.4 Ma. The geomagnetic polarity determined for two samples is reverse (R) and was correlated with chron 29R that includes the K/T boundary. Our present analysis is based on two samples from each of three clasts of the melt rock from PEMEX well Y6-N17 (1295 to 1299 m b.s.l.). This study concentrates on the vectorial nature and stability of the remanence (NRM), the magnetic mineralogy and remanence carriers (i.e., the reliability and origin of the record), and on the implications (correlation with expected paleolatitude and polarity). The relative orientation of the drill core samples with respect to the horizontal is known. Samples were stable under alternating field (AF) and thermal treatments, and after removal of a small component they exhibited single-vectorial behavior. The characteristic remanence inclinations show small dispersion and a mean value (-43 deg) in close agreement with the expected inclination and paleolatitude (derived from the North American apparent polar wander path). Isothermal remenence (IRM) acquisition experiments, Lowrie-Fuller tests, coercivity and unblocking temperature spectra of NRM and saturation IRM, susceptibility and Q-coefficient analyses, and the single-component nature indicate a dominant mineralogy of iron-rich titanomagnetites with single or pseduo-single domain states. The stable characteristic magnetization may be interpreted as a result of shock heating of the rock at the time of formation of the inpact structure and its polarity, age, and paleolatitude are consistent with a time about the K/T boundary.

Reverse polarity magnetized melt rocks from the Chicxulub impact structure, Yucatan Peninsula, Mexico

NASA Technical Reports Server (NTRS)

Urrutia-Fucugauchi, Jaime; Marin, Luis E.; Sharpton, Virgil L.; Quezada, Juan Manuel

1993-01-01

Further paleomagnetic data for core samples of melt rock recovered in the Petroleos Mexicanos (PEMEX) exploratory wells within the Chicxulub structure, northern Yucatan peninsula, Mexico are reported. A previous report by Sharpton showed that the rocks studied contain high iridium levels and shocked breccia clasts, and an Ar-40/Ar-39 age of 65.2 plus or minus 0.4 Ma. The geomagnetic polarity determined for two samples is reverse (R) and was correlated with chron 29R that includes the K/T boundary. Our present analysis is based on two samples from each of three clasts of the melt rock from PEMEX well Y6-N17 (1295 to 1299 m b.s.l.). This study concentrates on the vectorial nature and stability of the remanence (NRM), the magnetic mineralogy and remanence carriers (i.e., the reliability and origin of the record), and on the implications (correlation with expected paleolatitude and polarity). The relative orientation of the drill core samples with respect to the horizontal is known. Samples were stable under alternating field (AF) and thermal treatments, and after removal of a small component they exhibited single-vectorial behavior. The characteristic remanence inclinations show small dispersion and a mean value (-43 deg) in close agreement with the expected inclination and paleolatitude (derived from the North American apparent polar wander path). Isothermal remenence (IRM) acquisition experiments, Lowrie-Fuller tests, coercivity and unblocking temperature spectra of NRM and saturation IRM, susceptibility and Q-coefficient analyses, and the single-component nature indicate a dominant mineralogy of iron-rich titanomagnetites with single or pseduo-single domain states. The stable characteristic magnetization may be interpreted as a result of shock heating of the rock at the time of formation of the inpact structure and its polarity, age, and paleolatitude are consistent with a time about the K/T boundary.

Lunar and Planetary Science XXXV: Impact-Related Deposits

NASA Technical Reports Server (NTRS)

2004-01-01

The session "Impact-Related Deposits" included:Evidence for a Lightning-Strike Origin of the Edeowie Glass; 57Fe M ssbauer Spectroscopy of Fulgurites: Implications for Chemical Reduction; Ca-Metasomatism in Crystalline Target Rocks from the Charlevoix Structure, Quebec, Canada: Evidence for Impact-related Hydrothermal Activity; Magnetic Investigations of Breccia Veins and Basement Rocks from Roter Kamm Crater and Surrounding Region, Namibia; Petrologic Complexities of the Manicouagan Melt Sheet: Implications for 40Ar-39Ar Geochronology; Laser Argon Dating of Melt Breccias from the Siljan Impact Structure, Sweden: Implications for Possible Relationship to Late Devonian Extinction Events; Lunar Impact Crater, India: Occurrence of a Basaltic Suevite?; Age of the Lunar Impact Crater, India: First Results from Fission Track Dating; The Fluidized Chicxulub Ejecta Blanket, Mexico: Implications for Mars; Low Velocity Ejection of Boulders from Small Lunar Craters: Ground Truth for Asteroid Surfaces; Ejecta and Secondary Crater Distributions of Tycho Crater: Effects of an Oblique Impact; Potassium Isotope Systematics of Crystalline Lunar Spherules from Apollo 16; Late Paleocene Spherules from the North Sea: Probable Sea Floor Precipitates: A Silverpit Provenance Unproven; A Lithological Investigation of Marine Strata from the Triassic-Jurassic Boundary Interval, Queen Charlotte Islands, British Columbia, Including a Search for Shocked Quartz; Triassic Cratered Cobbles: Shock Effects or Tectonic Pressure?; Regional Variations of Trace Element Composition Within the Australasian Tektite Strewn Field; Cretaceous-Tertiary Boundary Microtektite-bearing Sands and Tsunami Beds, Alabama Gulf Coastal Plain; Sand Lobes on Stewart Island as Probable Impact-Tsunami Deposits; Distal Impact Ejecta, Uppermost Eocene, Texas Coastal Plain; and Continental Impact Debris in the Eltanin Impact Layer.

The impact of the Cretaceous-Paleogene (K-Pg) mass extinction event on the global sulfur cycle: Evidence from Seymour Island, Antarctica

NASA Astrophysics Data System (ADS)

Witts, James D.; Newton, Robert J.; Mills, Benjamin J. W.; Wignall, Paul B.; Bottrell, Simon H.; Hall, Joanna L. O.; Francis, Jane E.; Alistair Crame, J.

2018-06-01

The Cretaceous-Paleogene (K-Pg) mass extinction event 66 million years ago led to large changes to the global carbon cycle, primarily via a decrease in primary or export productivity of the oceans. However, the effects of this event and longer-term environmental changes during the Late Cretaceous on the global sulfur cycle are not well understood. We report new carbonate associated sulfate (CAS) sulfur isotope data derived from marine macrofossil shell material from a highly expanded high latitude Maastrichtian to Danian (69-65.5 Ma) succession located on Seymour Island, Antarctica. These data represent the highest resolution seawater sulfate record ever generated for this time interval, and are broadly in agreement with previous low-resolution estimates for the latest Cretaceous and Paleocene. A vigorous assessment of CAS preservation using sulfate oxygen, carbonate carbon and oxygen isotopes and trace element data, suggests factors affecting preservation of primary seawater CAS isotopes in ancient biogenic samples are complex, and not necessarily linked to the preservation of original carbonate mineralogy or chemistry. Primary data indicate a generally stable sulfur cycle in the early-mid Maastrichtian (69 Ma), with some fluctuations that could be related to increased pyrite burial during the 'mid-Maastrichtian Event'. This is followed by an enigmatic +4‰ increase in δ34SCAS during the late Maastrichtian (68-66 Ma), culminating in a peak in values in the immediate aftermath of the K-Pg extinction which may be related to temporary development of oceanic anoxia in the aftermath of the Chicxulub bolide impact. There is no evidence of the direct influence of Deccan volcanism on the seawater sulfate isotopic record during the late Maastrichtian, nor of a direct influence by the Chicxulub impact itself. During the early Paleocene (magnetochron C29R) a prominent negative excursion in seawater δ34S of 3-4‰ suggests that a global decline in organic carbon burial related to collapse in export productivity, also impacted the sulfur cycle via a significant drop in pyrite burial. Box modelling suggests that to achieve an excursion of this magnitude, pyrite burial must be reduced by >15%, with a possible role for a short term increase in global weathering rates. Recovery of the sulfur cycle to pre-extinction values occurs at the same time (∼320 kyrs) as initial carbon cycle recovery globally. These recoveries are also contemporaneous with an initial increase in local alpha diversity of marine macrofossil faunas, suggesting biosphere-geosphere links during recovery from the mass extinction. Modelling further indicates that concentrations of sulfate in the oceans must have been 2 mM, lower than previous estimates for the Late Cretaceous and Paleocene and an order of magnitude lower than today.

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

PubMed

Glasby, G P; Kunzendorf, H

1996-06-01

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

Multiple (immiscible) melt phases of mafic composition in Chicxulub impact ejecta from northeastern Mexico: New constraints on target lithologies

NASA Astrophysics Data System (ADS)

Schulte, P.; Stinnesbeck, W.; Kontny, A.; Stüben, D.; Kramar, U.; Harting, M.

2002-12-01

Proximal ejecta deposits in sections from NE Mexico (Rancho Nuevo, La Sierrita, El Peñon, El Mimbral) have been investigated by backscattered electron imaging, wave-length dispersive electron microprobe analyses, and cathodoluminiscence, in order to characterize target lithologies, and ejecta mixing, fractionation, and distribution mechanisms. Additional investigations included magnetic properties (Kontny et al, this meeting) and trace element analyses (Harting et al, this meeting). Petrological features of these ejecta deposits are extraordinarily well preserved. They consist of mm-cm sized vesiculated spherical to drop-shaped spherules and angular to filamentous (ejecta-) fragments, as well as carbonate clasts, marl clasts, and rare benthic foraminifera floating in a carbonaceous matrix. Occasionally, spherules and fragments show welding-amalgamation features and enclose other components, thus resulting in a foam-like texture. An origin from the Chicxulub impact is suggested by geographical proximity and morphologically similarity to spherules found in other K-T sites in North to Central America and the Atlantic. The far distribution of such coarse-grained, foamy, and fragile ejecta-clasts as well as welding features suggest ignimbrite-like transport mechanisms or nearby secondary impacts. Several silicic ejecta phases have been observed that occur as distinct phases, even within one ejecta particle with textures indicative of liquid immiscibility: (1) Fe- (25-35 wt%), Mg- (10-15 wt%) rich phases with <25 wt% SiO2, altered to chlorite, (2) K- (5-8 wt.%) and Al- (25-30 wt%) rich hydrated glass with 45-50 wt% SiO2, and (3) rare SiO2- (>60 wt%) rich andesitic glasses. In addition to these silicic phases, abundant carbonate characterizes all studied ejecta deposits. It occurs within spherules and fragments and as clasts and globules, and shows textures indicative of either liquid immiscibility and/or quenching (`feathery calcite'). Quenched carbonates are enriched in Fe and Mg (up to one wt%) and are characterized by dark red-brown luminescence, in contrast to the carbonaceous matrix, which shows bright luminescence colors. Within all phases, but mainly in (1), various inclusions have been observed: (a) Globules enriched in Fe and Mg, (b) schlieren, rich in Ti, K, Fe, (c) garland-shaped Ti-rich lamellae, (d) dendritic and skeletal crystals of Ti-Fe oxides, (e) hematite crystals with a Ni-content up to 0.4 wt%, as well as goethite and rutile crystals, (f) rare μm-sized Co-, Ni-, Fe-rich metallic or sulfidic particles. These compositional phases are present in all studied outcrops, but their individual amount varies with prevailing Fe-rich phases at Rancho Nuevo and La Sierrita and Fe-, K-rich and silicic phases at El Peñon and El Mimbral. These characteristics imply an origin of the ejecta from mafic lithologies and carbonaceous sediments, in addition to contribution from felsic rocks. The occurrence of different compositional phases in single ejecta layers and even within individual ejecta particles suggests strong fractionation effects and/or negligible mixing of different melt phases. The presence of metallic Fe, Ni and Co may indicate that additional contamination by meteoritic material occurred.

Impacts and environmental catastrophes: A study of the effects of impact events on the climate system

NASA Technical Reports Server (NTRS)

Pierazzo, E.

2005-01-01

The goal of this work is to investigate the perturbation of the climate system due to large impact events. Impacts are among the most important mechanisms for the evolution, distribution, and destruction of life in the universe. However, the possible climatic effects of an impact were not seriously considered until 1980, when Louis and Walter Alvarez suggested that the profound end-Cretaceous extinction might have been caused by the impact of an asteroid or comet about 10 km in diameter. Since then, the climatic change associated with the end-Cretaceous impact has become one of the most interesting and still unresolved questions in linking the well-known Chicxulub impact event and the end- Cretaceous mass extinction. While the end-Cretaceous impact offers the best-documented case of an impact affecting the Earth's climate and biota, even smaller (and more frequent in time) impacts could introduce significant perturbations of the climate comparable, if not larger, to the largest known volcanic perturbations. We propose to study the mechanical and thermal state of the atmosphere following an impact event. This will be done by using both one-dimensional and three-dimensional climate models. When necessary, modifications of the state-of-the-art general circulation models will b e carried out. We want to use the end-Cretaceous impact event as a case study. This allows us to take advantage of the extensive modeling of this impact event that has already been carried out through a previous Exobiology grant. Furthermore, a large experimental dataset, that can be used to constrain and test our models, is associated with the end-Cretaceous mass extinction (one of the largest of the Phanerozoic) and impact event.

Impact-driven ocean acidification as a mechanism of the Cretaceous-Palaeogene mass extinction

NASA Astrophysics Data System (ADS)

Ohno, S.; Kadono, T.; Kurosawa, K.; Hamura, T.; Sakaiya, T.; Shigemori, K.; Hironaka, Y.; Sano, T.; Watari, T.; Otani, K.; Matsui, T.; Sugita, S.

2014-12-01

The Cretaceous-Paleogene (K-Pg) mass extinction event at 66 Ma triggered by a meteorite impact is one of the most drastic events in the history of life on the Earth. Many hypotheses have been proposed as killing mechanisms induced by the impact, including global darkness due to high concentrations of atmospheric silicate dust particles, global wildfires, greenhouse warming due to CO2 release, and global acid rain. However, the actual mechanism of extinction remains highly controversial. One of the most important clues for understanding the extinction mechanism is the marine plankton record, which indicates that plankton foraminifera, living in the near-surface ocean, suffered very severe extinction in contrast to the high survival ratio of benthic foraminifera. No proposed extinction mechanism can account for this globally observed marine extinction pattern. Here, we show that SO3-rich impact vapor was released in the K-Pg impact and resulted in the occurrence of global acid rain and sudden severe ocean acidification at the end of the Cretaceous, based on the new results of impact experiments at velocities much higher than previous works (> 10 km/s) and theoretical calculations on aerosol coagulation processes. Sudden severe ocean acidification can account for many of the features of various geologic records at the K?Pg boundary, including severe extinction of plankton foraminifera. This extinction mechanism requires impact degassing of SO3-rich vapor, which is not necessarily found at impact sites other than Chicxulub, suggesting that the degree of mass extinction was controlled greatly by target lithology.

Shock vaporization of carbonate and sulfate minerals

NASA Astrophysics Data System (ADS)

Shen, A. H.; Ahrens, T. J.; O'Keefe, J. D.

2001-12-01

Strong shock waves induced by impacts can cause vaporization of rocks and minerals. The products of such process play important roles in planetary differentiation (Yakovlev et al., Geochem. International, 38, 1027, 2000) and in effecting the planetary climate. Many experiments and computer simulations have been performed to simulate the Chicxulub impact at Cretaceous/Tertiary boundary (see, for example, Pierazzo et al., J. Geophys. Res., 103, 28607, 1998 and Pope et al., J. Geophys. Res., 102, 21645, 1997). However, the pressure range for incipient and complete vaporization of carbonates and sulfates are not well constrained, especially, for minerals with various initial porosities. Furthermore, evidence for chemical species in the products of vaporized carbonate and sulfate minerals is almost non-existing. In this study, we employed published Hugoniot data for carbonate and sulfate minerals. By using the methods described in Ahrens (J. Appl. Phys., 43, 2443, 1972) and Ahrens and O'Keefe (The Moon, 4, 214, 1972), we calculated the entropy associated with the thermodynamic states produced by hypervelocity impacts at various velocities for carbonate and sulfate minerals with different initial porosities. The results were compared with the entropy of incipient vaporization and complete vaporization of these minerals to determine the degree of vaporization due to impacts. Moreover, these results are utilized to guide our experimental study in speciation reactions in shock-induced vaporization of carbonates and sulfates.

Importance and Perspectives of the Earth Sciences Popularization in Mexico

NASA Astrophysics Data System (ADS)

Flores-Estrella, H.; Yussim, S.

2007-05-01

In our days the scientific popularization in Mexico has not a promising future and with the earth sciences is not better; most of the papers in the popularization magazines deal with subjects as earthquakes, volcanoes, plate tectonics, meteorite impacts and the massive extensions associated with them (e.g. Chicxulub). However, these subjects have not been enough to create conscience about the importance of earth sciences in the society and it has even motivated the idea of a community distant scientific with no social obligation, the idea that the earth scientists are responsible for all the problems in the planet (global warming, catastrophes) is wide spread. In these days that we need a change in our consumption, mainly in the energetic one, it's compulsory to change the relation between the subject and its environment; then, as we can not take care of something that we don't know, the scientific popularization has a fundamental role that we must start to pay attention to.

Wildfires and animal extinctions at the Cretaceous/Tertiary boundary

NASA Astrophysics Data System (ADS)

Adair, Robert K.

2010-06-01

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

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

NASA Technical Reports Server (NTRS)

Kyte, Frank T.

2004-01-01

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

Resolving the Timing of Events Around the Cretaceous-Paleogene Boundary

NASA Astrophysics Data System (ADS)

Sprain, Courtney Jean

Despite decades of study, the exact cause of the Cretaceous-Paleogene boundary (KPB) mass extinction remains contentious. Hypothesized scenarios center around two main environmental perturbations: voluminous (>10 6 km3) volcanic eruptions from the Deccan Traps in modern-day India, and the large impact recorded by the Chicxulub crater. The impact hypothesis has gained broad support, bolstered by the discoveries of iridium anomalies, shocked quartz, and spherules at the KPB worldwide, which are contemporaneous with the Chicxulub impact structure. However, evidence for protracted extinctions, particularly in non-marine settings, and paleoenvironmental change associated with climatic swings before the KPB, challenge the notion that the impact was the sole cause of the KPB mass extinction. Despite forty years of study, the relative importance of each of these events is unclear, and one key inhibitor is insufficient resolution of existing geochronology. In this dissertation, I present work developing a high-precision global chronologic framework for the KPB that outlines the temporal sequence of biotic changes (both within the terrestrial and marine realms), climatic changes, and proposed perturbations (i.e. impact, volcanic eruptions) using 40Ar/39Ar geochronology and paleomagnetism. This work is focused on two major areas of study: 1) refining the timing and tempo of terrestrial ecosystem change around the KPB, and 2) calibrating the geomagnetic polarity timescale, and particularly the timing and duration of magnetic polarity chron C29r (the KPB falls about halfway into C29r). First I develop a high-precision chronostratigraphic framework for fluvial sediments within the Hell Creek region, in NE Montana, which is one of the best-studied terrestrial KPB sections worldwide. For this work I dated 15 tephra deposits with +/- 30 ka precision using 40Ar/ 39Ar geochronology, ranging in time from 300 ka before the KPB to 1 Ma after. By tying these results to paleontological records, this work is able to constrain the timing of terrestrial faunal decline and recovery in addition to calibrating late Cretaceous and early Paleocene North American Land Mammal Ages biostratigraphy. To aid in global correlation, I next sought to calibrate the timing and duration of C29r. However, based on discrepancies noticed between a calculated duration for C29r, from new dates collected as part of this dissertation and previously published magnetostratigraphy for the Hell Creek region, and the duration provided within the Geologic Time Scale 2012, it became clear that reliability of sediments from the Hell Creek as paleomagnetic recorders was suspect. To test this claim, a complete characterization of the rock magnetic properties of sediments from the Hell Creek region was undertaken. To aid characterization, a new test to determine the presence of intermediate composition titanohematite (Fe2-yTiyO3; 0.5 ≤ y ≤ 0.7) was developed. Results from rock magnetic characterization show that sediments from the Hell Creek should be reliable paleomagnetic recorders, so long as care is taken to remove goethite (a secondary mineral that previous magnetostratigraphic studies in the Hell Creek did not remove), and to avoid samples that have been heated above 200ºC. With the knowledge that sediments from the Hell Creek region are reliable magnetic recorders, I collected 14 new magnetostratigraphic sections, and 18 new high-precision 40Ar/39Ar dates which together provide constraints on the timing and duration of chron C29r, at unprecedented precision. This work enables correlation of our record in the Hell Creek to other KPB records around the globe, in addition to providing a test of the Paleocene astrochronologic timescale.

Meteorite Impacts and Planetary Habitability: The Good, the Bad, and the Ugly

NASA Astrophysics Data System (ADS)

Osinski, G. R.

2012-12-01

It is now widely accepted that meteorite impacts negatively affect life on a planet, as evidenced by the deleterious effects associated with the formation of the Chicxulub impact structure, Mexico, 65 Myr. ago and its link to the Cretaceous-Paleogene mass extinction event. This impact event had a profound affect on the evolution of life on Earth by ending the age of the dinosaurs and paving the way for mammals to ascend to dominance. In terms of the origin of life, despite the controversy over when exactly life appeared on Earth, it is likely that it did so during one of the harshest, most inhospitable times in Earth history: the Late Heavy Bombardment Period ~4.0-3.8 Ga. During this time, asteroid and comet impacts were ~10-20 times as frequent as they are at the present day. This may seem counterintuitive until one considers that these cataclysmic, initially destructive impact events may also have had beneficial effects with respect to life. This contribution will present a synthesis of information concerning the role that meteorite impacts may have played in the origin and evolution of life on Earth and, by analogy, with other planetary bodies throughout the Universe. It will hopefully be demonstrated that impact events do not just frustrate life, but that impact craters, once formed, may represent protected niches where life can survive and evolve and, potentially, where life may have originated. It is proposed that the geological, biological, and environmental changes known to be caused by an impact allow for the formulation of key cross-cutting hypotheses concerning the potential deleterious and beneficial effects of meteorite impact events. Most notably, it is proposed that impact events produce new, unique habitats for life and, therefore, can have an overall positive effect on planetary habitability. Habitats include: 1) impact-generated hydrothermal systems, which could provide habitats for thermophilic and hyperthermophilic microorganisms, 2) impact-processed crystalline rocks, which have increased porosity and translucence compared to unshocked materials, improving microbial colonization, 3) impact glasses, which, similar to volcanic glasses, provide an excellent readily available source of bioessential elements, and 4) impact crater lakes, which form protected sedimentary basins with various niches and that increase the preservation potential of fossils and organic material.

Solution pans and linear sand bedforms on the bare-rock limestone shelf of the Campeche Bank, Yucatán Peninsula, Mexico

NASA Astrophysics Data System (ADS)

Goff, John A.; Gulick, Sean P. S.; Cruz, Ligia Perez; Stewart, Heather A.; Davis, Marcy; Duncan, Dan; Saustrup, Steffen; Sanford, Jason; Fucugauchi, Jaime Urrutia

2016-04-01

A high-resolution, near-surface geophysical survey was conducted in 2013 on the Campeche Bank, a carbonate platform offshore of Yucatán, Mexico, to provide a hazard assessment for future scientific drilling into the Chicxulub impact crater. It also provided an opportunity to obtain detailed information on the seafloor morphology and shallow stratigraphy of this understudied region. The seafloor exhibited two morphologies: (1) small-scale (<2 m) bare-rock karstic features, and (2) thin (<1 m) linear sand accumulations overlying the bedrock. Solution pans, circular to oblong depressions featured flat bottoms and steep sides, were the dominant karstic features; they are known to form subaerially by the pooling of rainwater and dissolution of carbonate. Observed pans were 10-50 cm deep and generally 1-8 m wide, but occasionally reach 15 m, significantly larger than any solution pan observed on land (maximum 6 m). These features likely grew over the course of many 10's of thousands of years in an arid environment while subaerially exposed during lowered sea levels. Surface sands are organized into linear bedforms oriented NE-SW, 10's to 100's meters wide, and kilometers long. These features are identified as sand ribbons (longitudinal bedforms), and contained asymmetric secondary transverse bedforms that indicate NE-directed flow. This orientation is incompatible with the prevalent westward current direction; we hypothesize that these features are storm-generated.

Balancing Mitigation Against Impact: A Case Study From the 2005 Chicxulub Seismic Survey

NASA Astrophysics Data System (ADS)

Barton, P.; Diebold, J.; Gulick, S.

2006-05-01

In early 2005 the R/V Maurice Ewing conducted a large-scale deep seismic reflection-refraction survey offshore Yucatan, Mexico, to investigate the internal structure of the Chicxulub impact crater, centred on the coastline. Shots from a tuned 20 airgun, 6970 cu in array were recorded on a 6 km streamer and 25 ocean bottom seismometers (OBS). The water is exceptionally shallow to large distances offshore, reaching 30 m about 60 km from the land, making it unattractive to the larger marine mammals, although there are small populations of Atlantic and spotted dolphins living in the area, as well as several turtle breeding and feeding grounds on the Yucatan peninsula. In the light of calibrated tests of the Ewing's array (Tolstoy et al., 2004, Geophysical Research Letters 31, L14310), a 180 dB safety radius of 3.5 km around the gun array was adopted. An energetic campaign was organised by environmentalists opposing the work. In addition to the usual precautions of visual and listening watches by independent observers, gradual ramp-ups of the gun arrays, and power-downs or shut-downs for sightings, constraints were also placed to limit the survey to daylight hours and weather conditions not exceeding Beaufort 4. The operations were subject to several on-board inspections by the Mexican environmental authorities, causing logistical difficulties. Although less than 1% of the total working time was lost to shutdowns due to actual observation of dolphins or turtles, approximately 60% of the cruise time was taken up in precautionary inactivity. A diver in the water 3.5 km from the profiling ship reported that the sound in the water was barely noticeable, leading us to examine the actual sound levels recorded by both the 6 km streamer and the OBS hydrophones. The datasets are highly self-consistent, and give the same pattern of decay with distance past about 2 km offset, but with different overall levels: this may be due to geometry or calibration differences under investigation. Both datasets indicate significantly lower levels than reported by Tolstoy et al. (2004). There was no evidence of environmental damage created by this survey. It can be concluded that the mitigation measures were extremely successful, but there is also a concern that the overhead cost of the environmental protection made this one of the most costly academic surveys ever undertaken, and that not all of this protection was necessary. In particular, the predicted 180 dB safety radius appeared to be overly conservative, even though based on calibrated measurements in very similar physical circumstances, and we suggest that these differences were a result of local seismic velocity structure in the water column and/or shallow seabed, which resulted in different partitioning of the energy. These results suggest that real time monitoring of hydrophone array data may provide a method of determining the safety radius dynamically, in response to local conditions.

Earth's Archean Impact Record In The ICDP Drilling "Barberton Mountain Land".

NASA Astrophysics Data System (ADS)

Fritz, Jörg; Schmitt, Ralf-Thomas; Reimold, Uwe; Koeberl, Christian; Mc Donald, Ian; Hofmann, Axel; Luais, Beatrice

2013-04-01

The marine meta-sedimentary successions in the "Barberton Mountain Land" are formed by Archean volcanic and sedimentary rocks including the oldest known impact ejecta layers on Earth. The chemical signature (high iridium concentrations, chromium isotopic ratios) of some of these up to tens of cm thick Archean spherule layers advocate that these ejecta deposits represent mainly extraterrestrial material [1]. These ejecta layers contain millimetre sized spherules that are larger and accumulated thicker layers compared to any impact ejecta layer known from Phanerozoic sediments, including the global ejecta layer of the Chicxulub impact catering event terminating the Mesozoic era of Earth's history [2]. The Archean spherule layers are interpreted as products of large impacts by 20 to >100 km diameter objects [3, 4]. Identifying traces of mega-impacts in Earth's ancient history could be of relevance for the evolution of atmosphere, biosphere, and parts of the Earth's crust during that time. In addition, recognizing global stratigraphic marker horizons is highly valuable for inter-correlating sedimentary successions between Archean cratons [5]. However estimates regarding size of the impact event and correlations between the different outcrops in the Barberton mountain land are complicated by post depositional alterations of the tectonically deformed sediments [6, 7]. The relatively fresh samples recovered from below the water table during the 2011-2012 ICDP drilling "Barberton Mountain Land" are promising samples to investigate and to discriminate primary and secondary features of these rare rocks. We plan to conduct 1) petrographic, micro-chemical and mineralogical characterization of the impact ejecta layers, 2) bulk chemical analyses of major and trace elements, and 3) LAICP- MS elemental mapping of platinum group element (PGE) distributions. and elemental analyses of moderately siderophile elements. This aims at 1) characterization of the ejecta layers, 2) identification of the phases hosting the extraterrestrial PGE signature, 3) discrimination of the primary geological evidence of the impact event from those characteristics that resulted from syn- and post-sedimentary alteration. Acknowledgement: Financial support by the DFG - RE 528/14-1. References: [1] Lowe D. R. et al. (2003) Astrobiology 3, 7-47. [2] Simonson B. M. and Harnik P. (2000) Geology 28, 975-978. [3] Lowe D. R. and Byerly G. R. (1986) Geology 14, 83-86. [4] Melosh H. J. and Vickery A. M. (1991) Nature 350, 494-497. [5] Byerly G. R. et al. (2002) Science 297, 1325-1327. [6] Reimold W. U. et al. (2000) Impacts and the Early Earth. Eds.: Gilmour I., Koeberl C. Lecture Notes in Earth Sciences 91, Springer-Verlag, Berlin, pp.117-180. [7] Hofmann A. et al. (2006) GSA Special Paper 405, 33 - 56.

Numerical Simulations of Silverpit Crater Collapse

NASA Technical Reports Server (NTRS)

Collins, G. S.; Turtle, E. P.; Melosh, H. J.

2003-01-01

The Silverpit crater is a recently discovered, 60-65 Myr old complex crater, which lies buried beneath the North Sea, about 150 km east of Britain. High-resolution images of Silverpit's subsurface structure, provided by three-dimensional seismic reflection data, reveal an inner-crater morphology similar to that expected for a 5-8 km diameter terrestrial crater. The crater walls show evidence of terracestyle slumping and there is a distinct central uplift, which may have produced a central peak in the pristine crater morphology. However, Silverpit is not a typical 5-km diameter terrestrial crater, because it exhibits multiple, concentric rings outside the main cavity. External concentric rings are normally associated with much larger impact structures, for example Chicxulub on Earth, or Orientale on the Moon. Furthermore, external rings associated with large impacts on the terrestrial planets and moons are widely-spaced, predominantly inwardly-facing, asymmetric scarps. However, the seismic data show that the external rings at Silverpit represent closely-spaced, concentric fault-bound graben, with both inwardly and outwardly facing faults-carps. This type of multi-ring structure is directly analogous to the Valhalla-type multi-ring basins found on the icy satellites. Thus, the presence and style of the multiple rings at Silverpit is surprising given both the size of the crater and its planetary setting.

Cretaceous/Paleogene floral turnover in Patagonia: drop in diversity, low extinction, and a Classopollis spike.

PubMed

Barreda, Viviana D; Cúneo, Nestor R; Wilf, Peter; Currano, Ellen D; Scasso, Roberto A; Brinkhuis, Henk

2012-01-01

Nearly all data regarding land-plant turnover across the Cretaceous/Paleogene boundary come from western North America, relatively close to the Chicxulub, Mexico impact site. Here, we present a palynological analysis of a section in Patagonia that shows a marked fall in diversity and abundance of nearly all plant groups across the K/Pg interval. Minimum diversity occurs during the earliest Danian, but only a few palynomorphs show true extinctions. The low extinction rate is similar to previous observations from New Zealand. The differing responses between the Southern and Northern hemispheres could be related to the attenuation of damage with increased distance from the impact site, to hemispheric differences in extinction severity, or to both effects. Legacy effects of the terminal Cretaceous event also provide a plausible, partial explanation for the fact that Paleocene and Eocene macrofloras from Patagonia are among the most diverse known globally. Also of great interest, earliest Danian assemblages are dominated by the gymnosperm palynomorphs Classopollis of the extinct Mesozoic conifer family Cheirolepidiaceae. The expansion of Classopollis after the boundary in Patagonia is another example of typically Mesozoic plant lineages surviving into the Cenozoic in southern Gondwanan areas, and this greatly supports previous hypotheses of high latitude southern regions as biodiversity refugia during the end-Cretaceous global crisis.

Impact craters at falling of large asteroids in Ukraine

NASA Astrophysics Data System (ADS)

Vidmachenko, A. P.

2016-05-01

Catastrophes of different scale that are associated with the fall of celestial bodies to the Earth - occurred repeatedly in its history. But direct evidence of such catastrophes has been discovered recently. Thus, in the late 1970s studies of terrestrial rocks showed that in layers of the earth's crust that corresponded to the period of 65 million years before the present, marked by the mass extinction of some species of living creatures, and the beginning of the rapid development of others. It was then - a large body crashed to Earth in the Gulf of Mexico in Central America. The consequence of this is the Chicxulub crater with a diameter of ~170 km on Yucatan Peninsula. Modern Earth's surface retains many traces of collisions with large cosmic bodies. To indicate the craters with a diameter of more than 2 km using the name "astrobleme". Today, it found more than 230. The largest astroblems sizes exceeding 200 km. Ukraine also has some own astroblems. In Ukraine, been found nine large impact craters. Ukrainian crystalline shield, because of its stability for a long time (more than 1.5 billion years), has the highest density of large astroblems on the Earth's surface. The largest of the Ukrainian astroblems is Manevytska. It has a diameter of 45 km. There are also Ilyinetskyi (7 km), Boltysh (25 km), Obolon' (20 km), Ternivka (12-15 km), Bilylivskyi (6 km), Rotmystrivka (3 km) craters. Zelenohayska astrobleme founded near the village Zelenyi Gay in Kirovograd region and consists of two craters: larger with diameter 2.5-3.5 km and smaller - with diameter of 800 m. The presence of graphite, which was the basis for the research of the impact diamond in astroblems of this region. As a result, the diamonds have been found in rocks of Ilyinetskyi crater; later it have been found in rocks in the Bilylivska, Obolon' and other impact structures. The most detailed was studied the geological structure and the presence of diamonds in Bilylivska astrobleme

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

NASA Technical Reports Server (NTRS)

Skala, R.; Hoerz, F.

2003-01-01

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

The lacustrine record of the Dan-C2 hyperthermal event of the Boltysh Impact Crater, Ukraine

NASA Astrophysics Data System (ADS)

Ebinghaus, Alena; Jolley, David W.

2015-04-01

Vegetation response to rapid climate change in the geological record is a fundamental element in our understanding of ancient environments; however, the relationships between climate change, plant ecosystems and geological processes are still not fully understood. The filling of the K/Pg Boltysh meteorite crater, Ukraine, comprise a complete terrestrial sedimentological, palynological and δ13C record of the negative carbon isotope excursion of the early Danian hyperthermal episode. The meteorite impact formed a crater of c. 24 km in diameter at c. 65.2 Ma, which was filled with more than 500 m of organic- and fossil-rich claystones, siltstones and marls, interbedded with sandstones and less frequently gravelly sandstones. The sedimentary succession indicates a deep lake setting that was characterised by fluvial input of reworked basement material via a marginal delta system. Palynological investigations indicate a post-impact early- to mid-successional flora followed by a barren zone which coincides with the age of the Chicxulub impact and therefore argues for a series of impact events at the K/Pg boundary. This barren zone was succeeded by a fern spike marking an initial plant re-colonization. The following palynoflora suggests moisture availability oscillations (MAOs) reflecting 41 k.y. obliquity cycles, which can be correlated with lithological fluctuations during lake evolution. The aim is to conduct a detailed, complete facies analysis, and to correlate lake evolutionary aspects with climatic oscillations and vegetation change within the catchment area. This study will be compared with records of similar hyperthermal events, such as the Paleocene-Eocene Thermal Maximum (PETM) in the Western Interior in North America. This integrated approach will help to better understand the controlling factors of global warming events, and their effects on ancient sedimentary environments and ecosystems.

Distal Impact Ejecta Material in Marine Sediments in the North-Central Pacific Ocean

NASA Astrophysics Data System (ADS)

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

2006-12-01

We studied a sample of red clay weighing 1.4 grams, derived from a deep sea core (GPC3) located at Latitude 30 degrees N, Longitude 158 degrees W, provided by Jim Broda at the core lab of Woods Hole Oceanographic Institution (supported by NSF). The 65 Ma K/T boundary layer was identified by magnetic susceptibility measurements and Ir anomaly which peaked at a down-hole depth of 2055-2056 cm. We dissolved calcium carbonate in the red clay with dilute HCl to facilitate wet sieving for the size fraction greater than 38 microns. This process yielded 0.0l gram of clean grains from which we hand-picked materials under a binocular microscope. We picked out 40 microtektites (glass spherules, now devitrified), 12 olive- green aggregates composed of talc (probably from alteration of olivine), pyroxene, and magnetite, 6 crystals of biotite, a few magnetic oxide minerals and spherules, and 3 green and 1 blue crystals of silicon carbide (SiC). We are studying the SiC by X-rays. Also, there are abundant quartz grains. Six of the grains we picked out show two sets of shock lamellae decorated by a black substance. Some quartz crystals show mosaic structures. One other grain has a foreign particle embedded in it, while another has two penetrating hollow tubes. These two grains might have been impacted upon by high-velocity "bullets". Because the olive-green aggregates we found have both their mineralogy and texture similar to those often observed in chondrules, in addition to the presence of SiC, which is typically associated with carbonaceous chondrites, we recognize that there seems to be a strong implication that the impactor at Chicxulub which caused extinction of dinosaurs might have been a carbonaceous chondrite which sent the distal ejecta to our core site.

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

NASA Technical Reports Server (NTRS)

Bohor, Bruce F.; Betterton, William J.

1993-01-01

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

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

NASA Astrophysics Data System (ADS)

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

2008-04-01

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

A fossiliferous spherule-rich bed at the Cretaceous–Paleogene (K–Pg) boundary in Mississippi, USA: Implications for the K–Pg mass extinction event in the Mississippi Embayment and Eastern Gulf Coastal Plain

USGS Publications Warehouse

Witts, James D.; Landman, Neil H.; Garb, Matthew P.; Boas, Caitlin; Larina, Ekaterina; Rovelli, Remy; Edwards, Lucy E.; Sherrell, Robert; Cochran, J. Kirk

2018-01-01

We describe an outcrop of the Cretaceous–Paleogene (K–Pg) boundary exposed due to construction near New Albany, Union County, Mississippi. It consists of the Owl Creek Formation and overlying Clayton Formation. The Owl Creek Formation is rich in the ammonites Discoscaphites iris and Eubaculites carinatus, which, along with biostratigraphically important dinoflagellate cysts and calcareous nannofossils, indicate deposition occurred within the last 1 million years, most likely last 500 kyrs, of the Cretaceous. The base of the overlying Clayton Formation marks the K–Pg boundary, and consists of a 15-30 cm thick muddy, poorly sorted quartz sand containing abundant spherules representing ejecta derived from the Chicxulub impact event. Impact spherules range in size from 0.5 mm to 1 mm in diameter and are hollow and well preserved, with details such as smaller vesicular spherules enclosed within. The spherules are altered to clay minerals such as smectite and are typical of those found at K–Pg boundary sites in the Gulf of Mexico and beyond. Spherules are scattered throughout the bed, and surface counts suggest an average of 4 spherules per cm2. Macrofossils within the spherule bed represent a rich fauna of ammonites, benthic molluscs (bivalves and gastropods), echinoids, as well as crabs and sharks. Macrofossil preservation ranges from whole to fragmentary, with most fossils preserved as internal moulds. The infill of the fossils is lithologically identical to the matrix of the spherule bed, including impact ejecta preserved within phagmocones and body chambers of ammonites, and differs from the underlying Owl Creek Formation. This suggests that the animals were either alive or loosely scattered on the sea floor at the time of deposition. Grain size changes indicate multiple events were responsible for deposition, and together with taphonomic evidence are consistent with dynamic high energy post-impact processes. Later sea level change during the Paleocene is responsible for a sharp contact at the top of the spherule bed. Geochemical evidence from the Owl Creek and Clayton Formations at this locality indicate numerous local palaeoenvironmental changes affected the Mississippi Embayment at the time of the K–Pg boundary and mass extinction event.

Impact Cratering Processes as Understood Through Martian and Terrestrial Analog Studies

NASA Astrophysics Data System (ADS)

Caudill, C. M.; Osinski, G. R.; Tornabene, L. L.

2016-12-01

Impact ejecta deposits allow an understanding of subsurface lithologies, volatile content, and other compositional and physical properties of a planetary crust, yet development and emplacement of these deposits on terrestrial bodies throughout the solar system is still widely debated. Relating relatively well-preserved Martian ejecta to terrestrial impact deposits is an area of active research. In this study, we report on the mapping and geologic interpretation of 150-km diameter Bakhuysen Crater, Mars, which is likely large enough to have produced a significant volume of melt, and has uniquely preserved ejecta deposits. Our mapping supports the current formation hypothesis for Martian crater-related pitted material, where pits are likened to collapsed degassing features identified at the Ries and Haughton terrestrial impact structures. As hot impact melt-bearing ejecta deposits are emplaced over volatile-saturated material during crater formation, a rapid degassing of the underlying layer results in lapilli-like fluid and gas flow pipes which may eventually lead to collapse features on the surface. At the Haughton impact structure, degassing pipes are related to crater fracture and fault systems; this is analogous to structure and collapse pits mapped in Bakhuysen Crater. Based on stratigraphic superposition, surface and flow texture, and morphological and thermophysical mapping of Bakhuysen, we interpret the top-most ejecta unit to be likely melt-bearing and analogous to terrestrial impact deposits (e.g., Ries suevites). Furthermore, we suggest that Chicxulub is an apt terrestrial comparison based on its final diameter and the evidence of a ballistically-emplaced and volatile-entrained initial ejecta. This is significant as Bakhuysen ejecta deposits may provide insight into larger impact structures where limited exposures make studies difficult. This supports previous work which suggests that given similarities in volatile content and subsurface stratigraphy, mechanisms of multi-unit ejecta emplacement extend to impact cratering processes on comparable rocky bodies. The widespread pitted material, ejecta rampart and lobe formations, and distal debris flows associated with Bakhuysen impactite emplacement further indicates a volatile-rich Martian crust during its formation.

Striations, Polish, and Related Features from Clasts in Impact-Ejecta Deposits and the "Tillite Problem"

NASA Technical Reports Server (NTRS)

Rampino, M. R.; Ernstson, K.; Anguita, F.; Claudin F.

1997-01-01

Proximal ejecta deposits related to three large terrestrial impacts, the 14.8-Ma Ries impact structure in Germany (the Bunte Breccia), the 65-Ma Chicxulub impact structure in the Yucatan (the Albion and Pook's Hill Diamictites in Belize) and the mid-Tertiary Azuara impact structure in Spain (the Pelarda Fm.) occur in the form of widespread debris-flow deposits most likely originating from ballistic processes. These impact-related diamictites typically are poorly sorted, containing grain sizes from clay to large boulders and blocks, and commonly display evidence of mass flow, including preferred orientation of long axes of clasts, class imbrication, flow noses, plugs and pods of coarse debris, and internal shear planes. Clasts of various lithologies show faceting, various degrees of rounding, striations (including nailhead striae), crescentic chattermarks, mirror-like polish, percussion marks, pitting, and penetration features. Considering the impact history of the Earth, it is surprising that so few ballistic ejecta, deposits have been discovered, unless the preservation potential is extremely low, or such materials exist but have been overlooked or misidentified as other types of geologic deposits . Debris-flow diamictites of various kinds have been reported in the geologic record, but these are commonly attributed to glaciation based on the coarse and poorly sorted nature of the deposits and, in many cases, on the presence of clasts showing features considered diagnostic of glacial action, including striations of various kinds, polish, and pitting. These diamictites are the primary evidence for ancient ice ages. We present evidence of the surface features on clasts from known proximal ejecta debris-flow deposits and compare these features with those reported in diamictites. interpreted as ancient glacial deposits (tillites). Our purpose is to document the types of features seen on clasts in diamictites of ejecta origin in order to help in the interpretation of the origin of ancient diamictites. The recognition of characteristic features in clast populations in ancient diamictites may allow identification and discrimination of debris-flow deposits of various origins (e.g., impact glacial, tectonic) and may shed light on some climatic paradoxes, such as inferred Proterozoic glaciations at low paleolatitudes.

Lost Impacts (Invited)

NASA Astrophysics Data System (ADS)

Schultz, P. H.; Stickle, A. M.

2009-12-01

The absence of a clearly identified crater (or craters) for the proposed YDB impact has raised questions concerning the reality of such an event. Geologic studies have identified impact deposits well before recognizing a causative crater (e.g., Chicxulub and Chesapeake Bay); some have yet to be discovered (e.g., Australasian tektite strewnfields). The absence of a crater, therefore, cannot be used as an argument against the reality of the YDB impact (and its possible consequences). The study here addresses how a large on-land impact during the late Pleistocene or early Holocene could avoid easy detection today. It does not argue the case for a YDB impact, since such evidence must come from the rock record. During the late Pleistocene, the receding Laurentide ice sheet still covered a significant portion of Canada. While a large (1km) body impacting vertically (90°) would penetrate such a low-impedance ice layer and excavate the substrate, an oblique impact couples more of its energy into the surface layer, thereby partially shielding the substrate. Three approaches address the effectiveness of this flak-jacket effect. First, hypervelocity impact experiments at the NASA Ames Vertical Gun Range investigated the effectiveness of low-impedance layers of different thicknesses for mitigating substrate damage. Second, selected experiments were compared with hydrocode models (see Stickle and Schultz, this volume) and extended to large scales. Third, comparisons were made with relict craters found in eroding sediment and ice covers on Mars. Oblique impacts (30 degrees) into soft particulates (no. 24 sand) covering a solid substrate (aluminum) have no effect on the final crater diameter for layer thicknesses exceeding a projectile diameter and result in only plastic deformation in the substrate. In contrast, a vertical impact requires a surface layer at least 3 times the projectile diameter to achieve the same diameter (with significant substrate damage). Oblique impacts into ice and plasticene layers over clear acrylic blocks allow assessing internal damage. These experiments reveal that low-impedance surface layers approaching 1 to 2 projectile diameters effectively shield the substrate from shock damage for impact angles less than 30 degrees. Missing craters (and relict crater roots) within ice-rich deposits on Mars illustrate the rapid erasure the impact record. Numerous small pedestal craters (crater diameter < 5km) occur at high latitudes and reflect the cyclic expansion and disappearance of polar ice/dust deposits up to 0.5 km thick. Much larger examples (> 50km), however, occur at low latitudes but are localized in certain regions where even thicker deposits (locally >2km) have been removed, uncovering a preserved Noachian landscape. Crater statistics further document this missing cratering record. Thick Pleistocene ice sheets on Earth would have played a similar role for the removal of terrestrial cratering record. We calculate that a crater as large as 15km in diameter formed by an oblique impact could have been effectively erased, except for dispersed ejecta containing shocked impactor relicts and a disturbed substrate. While plausible, evidence for specific missing events (e.g., the proposed YB impact) must be found in still-preserved ice layers and sediments.

Magnetic properties of the ejecta blanket from the Chicxulub impact crater: Analog for robotic exploration of similar deposits on Mars

NASA Astrophysics Data System (ADS)

Kletetschka, G.; Wasilewski, P. J.; Ocampo, A.; Pope, K.

2001-05-01

A major focus in the search for fossil life on Mars is on recognition of the proper material on the surface. Heavily cratered surface suggests high concentration of fluidized ejecta deposits. Because magnetism of rocks is an easy measure for remote robotic tools we collected samples of ejecta blanket deposits in southern Mexico and throughout Belize as a Martian analog. The ejecta layer (spheroid bed) that blankets the preexisting Cretaceous dolomite units consists of green glassy fragments, pink and white spheroids (accretionary lapilli) and darker fragments of limestone. The spheroid bed is overlain by a coarse unit of pebbles, cobbles, and boulders, which in more distal locations is composed of a pebble conglomerate. Clasts in the conglomerate (Pooks Pebbles) have striated features consistent with hypervelocity collisions during impact. We examined the magnetic properties of individual fragments within the spheroid bed. Green glassy fragments are highly paramagnetic (0.2 to 0.3 Am2kg-1 at 2 Tesla field) with no ferromagnetic component detected. Pink spheroids are slightly paramagnetic (0.001 to 0.04 Am2kg-1 at 2 Tesla field) and commonly contain soft ferromagnetic component (saturation magnetization (Ms) = 0.02 to 0.03 Am2kg-1). White spheroids have more or less equal amount of paramagnetic and diamagnetic components (-0.08 to 0.03 Am2kg-1 at 2 Tesla field) and no apparent ferromagnetism. Darker fragments are diamagnetic (-0.05 to -0.02 Am2kg-1 at 2 Tesla field) with absence of ferromagnetism. Intense paramagnetic properties of the glass allow easy distinction of glass containing samples. Pink spheroids appear to contain the largest amount of ferromagnetic particles. Diamagnetic dark grains are most likely fragments of limestone. Pebbles from the conglomerate unit are dolomite and consequently diamagnetic. The diamagnetism was established with field magnetic susceptibility measurements. Pebbles have very small natural remanent magnetization (NRM). Thermal remanent magnetization (TRM) acquisition in laboratory field (0.04 mT) does, however, indicate that carriers capable of acquiring TRM are present. Absence of TRM in these pebbles indicates that they were not heated above the Currie point of hematite and/or magnetite (680 C and 570 C respectively) after they were deposited.

Numerical Simulations of Silverpit Crater Collapse

NASA Technical Reports Server (NTRS)

Collins, G. S.; Ivanov, B. A.; Turtle, E. P.; Melosh, H. J.

2003-01-01

The Silverpit crater is a recently discovered, 60-65 Myr old complex crater, which lies buried beneath the North Sea, about 150 km east of Britain. High-resolution images of Silverpit's subsurface structure, provided by three-dimensional seismic reflection data, reveal an inner-crater morphology similar to that expected for a 5-8 km diameter terrestrial crater. The crater walls show evidence of terrace-style slumping and there is a distinct central uplift, which may have produced a central peak in the pristine crater morphology. However, Silverpit is not a typical 5-km diameter terrestrial crater, because it exhibits multiple, concentric rings outside the main cavity. External concentric rings are normally associated with much larger impact structures, for example Chicxulub on Earth, or Orientale on the Moon. Furthermore, external rings associated with large impacts on the terrestrial planets and moons are widely-spaced, predominantly inwardly-facing, asymmetric scarps. However, the seismic data show that the external rings at Silverpit represent closely-spaced, concentric faultbound graben, with both inwardly and outwardly facing fault-scarps. This type of multi-ring structure directly analogous to the Valhalla-type multi-ring basins found on the icy satellites. Thus, the presence and style of the multiple rings at Silverpit is surprising given both the size of the crater and its planetary setting. A further curiosity of the Silverpit structure is that the external concentric rings appear to be extensional features on the West side of the crater and compressional features on the East side. The crater also lies in a local depression, thought to be created by postimpact movement of a salt layer buried beneath the crater.

What Really Happened to Earth's Older Craters?

NASA Astrophysics Data System (ADS)

Bottke, William; Mazrouei, Sara; Ghent, Rebecca; Parker, Alex

2017-10-01

Most assume the Earth’s crater record is heavily biased, with erosion/tectonics destroying older craters. This matches expectations, but is it actually true? To test this idea, we compared Earth’s crater record, where nearly all D ≥ 20 km craters are < 650 Myr old, to the Moon’s. Here lunar crater ages were computed using a new method employing LRO-Diviner temperature data. Large lunar rocks have high thermal inertia and remain warm through the night relative to the regolith. Analysis shows young craters with numerous meter-sized fragments are easy to pick out from older craters with eroded fragments. Moreover, an inverse relationship between rock abundance (RA) and crater age exists. Using measured RA values, we computed ages for 111 rocky craters with D ≥ 10 km that formed between 80°N and 80°S over the last 1 Gyr.We found several surprising results. First, the production rate of D ≥ 10 km lunar craters increased by a factor of 2.2 [-0.9, +4.4; 95% confidence limits] over the past 250 Myr compared to the previous 750 Myr. Thus, the NEO population is higher now than it has been for the last billion years. Second, the size and age distributions of lunar and terrestrial craters for D ≥ 20 km over the last 650 Myr have similar shapes. This implies that crater erasure must be limited on stable terrestrial terrains; in an average sense, for a given region, the Earth either keeps all or loses all of its D ≥ 20 craters at the same rate, independent of size. It also implies the observed deficit of large terrestrial craters between 250-650 Myr is not preservation bias but rather reflects a distinctly lower impact flux. We predict 355 ± 86 D ≥ 20 km craters formed on Earth over the last 650 Myr. Only 38 ± 6 are known, so the ratio, 10.7 ± 3.1%, is a measure of the Earth’s surface that is reasonably stable to large crater formation over 650 Myr. If erosion had dominated, the age distribution of terrestrial craters would be strongly skewed toward younger ages, which is not observed. We predict Chicxulub-type impacts were rare over the last Gyr, with the event 66 Ma a probable byproduct of the current high terrestrial impact flux.

High-Precision 40Ar/39Ar dating of the Deccan Traps

NASA Astrophysics Data System (ADS)

Sprain, C. J.; Renne, P. R.; Richards, M. A.; Self, S.; Vanderkluysen, L.; Pande, K.; Morgan, L. E.; Cosca, M. A.

2015-12-01

The Deccan Traps (DT) have been strongly implicated over the past thirty years as a potential cause of the mass extinctions at the Cretaceous-Paleogene boundary (KPB). While a broad coincidence between the DT eruptions and the KPB is increasingly clear, variables such as tempo, volume of eruptions, and amount of associated climate-modifying volatiles, are too poorly constrained to properly assess causality. In order to appropriately test whether the DT played a role in the mass extinctions a high-precision geochronologic framework defining the timing and tempo of volcanic eruptions is needed. Recent high-precision U/Pb dating of zircons from inferred paleosols (red boles) and melt segregation horizons is the only available geochronology of the DT that is sufficiently precise to resolve age differences of less than 100 ka (Schoene et al., 2015). While this technique can achieve high-precision dates for individual zircon crystals, protracted age distributions may not include the actual eruption age. Moreover, the applicability of U/Pb dating in the DT is limited as suitable material is only sporadically present and therefore the technique is unlikely to achieve the resolution necessary to assess the tempo of DT eruptions. To mediate these limitations, we present new high-precision 40Ar/39Ar ages for plagioclase separated from the lava flows sampled from each of ten chemostratigraphically-defined formations within the Western Ghats. Multiple (N = 1-4) plateau ages from each sample and detailed neutron fluence monitoring during irradiation yield ages with precision commonly better than 100 ka (1 sigma). Results provide the first precise location of the KPB within the DT eruption sequence, which approximately coincides with major changes in eruption frequency, flow-field volumes, extent of crustal contamination, and degree of fractionation. Collectively, these results suggest that a state shift occurred in the DT magma system within ~50 ka of the Chicxulub impact, consistent with transient effects of seismic energy associated with the impact. Further, our new data invalidate the concept of three discrete eruption pulses in the Western Ghats (Chenet et al., 2007, 2009; Keller et al., 2008) and rather indicate only a sharp increase in mean volumetric eruption rates near the KPB.

EARTHTIME: Teaching geochronology to high school students

NASA Astrophysics Data System (ADS)

Bookhagen, Britta; Buchwaldt, Robert; McLean, Noah; Rioux, Matthew; Bowring, Samuel

2010-05-01

The authors taught an educational module developed as part of the EARTHTIME (www.earth-time.org) outreach initiative to 215 high school students from a Massachusetts (USA) High School as part of an "out-of-school" field trip. The workshop focuses on uranium-lead (U-Pb) dating of zircons and its application to solving a geological problem. The theme of our 2.5-hour module is the timing of the K-T boundary and a discussion of how geochronology can be used to evaluate the two main hypotheses for the cause of the concurrent extinction—the Chicxlub impact and the massive eruption of the Deccan Traps. Activities are divided into three parts: In the first part, the instructors lead hands-on activities demonstrating how rock samples are processed to isolate minerals by their physical properties. Students use different techniques, such as magnetic separation, density separation using non-toxic heavy liquids, and mineral identification with a microscope. We cover all the steps from sampling an outcrop to determining a final age. Students also discuss geologic features relevant to the K-T boundary problem and get the chance to examine basalts, impact melts and meteorites. In the second part, we use a curriculum developed for and available on the EARTHTIME website (http://www.earth-time.org/Lesson_Plan.pdf). The curriculum teaches the science behind uranium-lead dating using tables, graphs, and a geochronology kit. In this module, the students start by exploring the concepts of half-life and exponential decay and graphically solving the isotopic decay equation. Manipulating groups of double-sided chips labeled with U and Pb isotopes reinforces the concept that an age determination depends on the Pb/U ratio, not the absolute number of atoms present. Next, the technique's accuracy despite loss of parent and daughter atoms during analysis, as well as the use of isotopic ratios rather than absolute abundances, is explained with an activity on isotope dilution. Here the students determine the number of beads in a large bucket without counting them all by adding a precisely known number of "tracer" beads and averaging ratios from several small samples of the mixture. The (pre-counted) unknown quantity of beads represents the isotopic composition of zircon from four samples—the Deccan Trap basalts, the Chicxulub impact melt, and ash layers above and below the K-T boundary —and the students' measurements are used in the final part of the module. An introduction to statistical inference from small samples can also be added to this exercise. After this, the chemistry and physics behind geochemical laboratory techniques, ion exchange chromatography and isotope ratio measurements using a mass spectrometer, are explained using models, movies, posters, and analogies to familiar physics. In the final part, students engage in a summary exercise where they apply what they have learned to test the two competing hypotheses. Using the dates they calculated with isotope dilution and a graphical solution to the decay equation, they determine if the Chicxulub impact or the Deccan Trap volcanic eruption can explain the K/T boundary mass extinction. They learn the importance of measurement uncertainty in interpreting data and brainstorm how best to resolve this outstanding scientific problem. Feedback from written evaluations shows that teachers valued the interdisciplinary association of concepts from physics, chemistry and mathematics. Students enjoyed the hands-on exercises that gave them the opportunity to see how rocks can be broken down into mineral separates and individual zircons selected for analysis. The K/T-boundary exercise at the end was appreciated because it demonstrates an exciting application of geochronological methods to popular science.

The Formation of Lunar Impact Basins: Observational Constraints from LRO Datasets and Comparisons with Models

NASA Astrophysics Data System (ADS)

Baker, D. M. H.; Head, J. W., III

2016-12-01

Impact basins provide windows into the subsurface and through time on a planetary body. However, meaningful geologic interpretations rely on a detailed understanding of their formation and the origin of basin materials. Data from the Lunar Reconnaissance Orbiter (LRO) have been critical to advancing our understanding of the formation of impact basins. We present a number of recent observations, including measurements of basin morphometry, mineralogy, and gravity anomalies, which provide a framework for constraining current formation models. Image data from the LRO Wide Angle Camera (WAC) and altimetry data from the Lunar Orbiter Laser Altimeter (LOLA) were used to refine the recognition of both fresh and degraded impact basins, including their ring structures. Analyses of gravity anomalies from the GRAIL mission show that mantle uplifts confined within the inner basin rings are characteristics that basins acquire from the onset. We used LOLA data to also make new measurements of basin morphometry. Small basins possessing two concentric rings ("peak-ring basins") have unique topographic signatures, consisting of inner depressions bounded by a peak ring and a higher annulus that grades to steeper wall material. LRO Narrow Angle Camera (NAC) images and Diviner rock abundance maps were used to identify boulder-rich outcrops in basin rings, which focused mineralogical analyses using Moon Mineralogy Mapper hyperspectral data. Crystalline plagioclase and candidate shock plagioclase outcrops were found to be abundant within basins of all sizes. These observations combined with crater scaling laws and lunar crustal thickness constrain the depth of origin of basin peak rings to be near the maximum depth of excavation. Comparisons between iSALE numerical models and observations show important consistencies and inconsistencies that can help to refine current models. In particular, improvements in the match between observed and modeled morphometry of craters transitional between complex craters with central peaks and peak-ring basins are needed. Models of the predicted gravity signature for a range of basin sizes could also benefit from additional comparisons with those observed. This work also provides a framework for understanding the degraded impact-basin record on Earth, including the Chicxulub basin.

Early Evolution of Modern Birds Structured by Global Forest Collapse at the End-Cretaceous Mass Extinction.

PubMed

Field, Daniel J; Bercovici, Antoine; Berv, Jacob S; Dunn, Regan; Fastovsky, David E; Lyson, Tyler R; Vajda, Vivi; Gauthier, Jacques A

2018-06-04

The fossil record and recent molecular phylogenies support an extraordinary early-Cenozoic radiation of crown birds (Neornithes) after the Cretaceous-Paleogene (K-Pg) mass extinction [1-3]. However, questions remain regarding the mechanisms underlying the survival of the deepest lineages within crown birds across the K-Pg boundary, particularly since this global catastrophe eliminated even the closest stem-group relatives of Neornithes [4]. Here, ancestral state reconstructions of neornithine ecology reveal a strong bias toward taxa exhibiting predominantly non-arboreal lifestyles across the K-Pg, with multiple convergent transitions toward predominantly arboreal ecologies later in the Paleocene and Eocene. By contrast, ecomorphological inferences indicate predominantly arboreal lifestyles among enantiornithines, the most diverse and widespread Mesozoic avialans [5-7]. Global paleobotanical and palynological data show that the K-Pg Chicxulub impact triggered widespread destruction of forests [8, 9]. We suggest that ecological filtering due to the temporary loss of significant plant cover across the K-Pg boundary selected against any flying dinosaurs (Avialae [10]) committed to arboreal ecologies, resulting in a predominantly non-arboreal post-extinction neornithine avifauna composed of total-clade Palaeognathae, Galloanserae, and terrestrial total-clade Neoaves that rapidly diversified into the broad range of avian ecologies familiar today. The explanation proposed here provides a unifying hypothesis for the K-Pg-associated mass extinction of arboreal stem birds, as well as for the post-K-Pg radiation of arboreal crown birds. It also provides a baseline hypothesis to be further refined pending the discovery of additional neornithine fossils from the Latest Cretaceous and earliest Paleogene. Copyright © 2018 Elsevier Ltd. All rights reserved.

Tying Extinction Events to Comet Impacts Large Enough to Cause an Extinction in Themselves.

NASA Astrophysics Data System (ADS)

Burgener, J. A.

2017-12-01

Comets over 35 km in size impacting Earth will create vast fireballs, and will boil large parts of the oceans, causing extinction events in themselves. They will likely provide enough energy to shatter the crust and eject large masses of molten rock from the mantle, forming traps. Traps are clearly associated with extinction events, but are not expected to cause extinctions. While Chicxulub is recognized to have occurred at the time of the K/Pg boundary layer, it is recognized as being too small in itself to cause an extinction. Are large comet impacts likely? The Kuiper belt has more than 100,000 objects over 100 km in diameter and millions over 10 km. Typically their orbits are less stable than asteroid orbits due to large bodies such as Pluto moving through the belt. The asteroid belt has only 10,000 objects over 10 km diameter. Comet impacts should be more common than asteroid impacts, yet none of the recognized craters are expected to be due to comets. There are many features on Earth that are poorly explained by Plate Tectonics that would be well explained if they were considered to be comet impact craters. A consideration of the Black Sea and the Tarim Basin will show that impact interpretations are a better fit than the present Plate Tectonics' explanations. Both basins are in the midst of mountain building from plate collisions, but are themselves not being disturbed by the plate collisions. Both are ellipses angled at 23.4 degrees to the equator, matching the angle expected for a low angle impact from a comet traveling in the ecliptic. Both are too deep at 15 km depths to be standard oceans (typically 5 km deep). Both are filled with horizontal layers of sediments, undisturbed by the mountain building occurring at the edges. Both have thin crusts and high Moho boundaries. Both have thin lithosphere. Yet both show GPS movement of the land around them moving away from them, as though they were much thicker and stronger than the surrounding land. The Tarim Basin is 1000 km X 380 km, and the Black Sea is in two sections each 600 km X 350 km. They would require impactors in the range of 35 - 40 km diameter, hitting at impact angles of 20 - 30 degrees. The fireballs from such impacts would cover nearly half the planet, which would be large enough in themselves to cause extinctions.

Rock magnetic properties of iron-rich Chicxulub impact ejecta from La Sierrita, northeastern Mexico

NASA Astrophysics Data System (ADS)

Kontny, A.; Schulte, P.; Stinnesbeck, W.

2002-12-01

Chicxulub ejecta deposits from La Sierrita, NE Mexico, are composed mainly of mm-cm sized vesicular spherules and (ejecta-) fragments that consist of Fe- and Mg-rich chlorite, opaque phases, and calcite infillings. Their Fe-rich and Si-poor composition may be indicative of contribution to the ejecta from mafic target rocks (Schulte et al., this meeting). This study addresses the magnetic mineralogy and properties of these ejecta deposits, since they could provide clues to target lithologies, physical conditions during the impact (quenching, crystallization, oxidation), and diagenetic processes. Optical microscopy, backscattered electron images, and electron microprobe (EMP) analyses show that opaque phases within spherules and fragments (even in calcite infillings) are hematite, goethite, rutile, and Ti-Fe oxides. Cubic and hexagonal hematite crystals are up to 20 μm in size and show a zonar composition with elevated Si (4-8 wt%) and Ni (up to 0.4 wt%) concentrations in the cores of crystals. Hematite formed either primary from melt or as replacement product of cubic minerals such as magnetite or pyrite during diagenesis. Garland-shaped, Ti- and Fe-rich lamellae are present with grain sizes of the opaque minerals below the resolution of the EMP; rutile and Ti-Fe oxide phases within these lamellae show crystal sizes growing towards the interior of grains. Some Ti-Fe oxides also show dendritic or skeletal crystals with spinifex textures that may be indicative of quenching. The volume magnetic susceptibility (MS) of ejecta deposits show relatively homogeneous paramagnetic values between 6 and 30 x 10-6 SI/g that correlate well with the bulk Fe-content and are enhanced as compared to the surrounding marls and sandstones. In the range from -192 to 700°C, temperature-dependent MS shows a dominant exponential decrease, thus confirming the paramagnetic behavior. However, a small peak at about -80°C is superimposed on the paramagnetic curve. This peak either indicates a Curie or Néel temperature or reflects a grain-size effect of a ferromagnetic phase. The heating leg of the MS(T) curve generally displays constant low MS values. However, heating and cooling runs are irreversible and the cooling leg displays two Curie temperatures (TC) at 570 and 480°C, thus indicating transformation during heating of iron-bearing minerals into magnetite or magnetite-near phases. No characteristic TC related either to hematite or to goethite has been detected; this absence could be related to impurities (Si, Ni) or cation deficiency. Intensity of the natural remanent magnetization (NRM) of the ejecta deposits is very small (0.3-0.7 mA/m). In fields below 10 mT, alternating field-demagnetization of NRM shows initial rapid decrease of about 50 % of the original intensity, whereas in fields of 160 mT no further demagnetization occurs. Induced remanent magnetization (IRM) acquisition curves reveal that some studied samples are nearly saturated in fields of 1000 mT while others are not. Furthermore, the IRM data confirm the presence of a single dominant high coercive mineral such as hematite and goethite; these are the main iron-bearing magnetic phases, in addition to chlorite. The occurrence of hematite and goethite in the La Sierrita ejecta points to highly oxidizing conditions during or after ejecta formation. Such conditions may have prevented the origination of stronger (ferro-) magnetic phases (e.g. magnetite) or destroyed them.

Linking downhole logging data with geology and drilling /coring operations - Example from Chicxulub Expedition 364.

NASA Astrophysics Data System (ADS)

Lofi, Johanna; Smith, Dave; Delahunty, Chris; Le Ber, Erwan; Mellet, Claire; Brun, Laurent; Henry, Gilles; Paris, Jehanne

2017-04-01

Expedition 364 was a joint IODP/ICDP mission specific platform expedition to explore the Chicxulub impact crater buried below the Yucatán continental shelf. In April and May 2016, our Expedition drilled a single borehole at Site M0077A into the crater's peak ring. It allowed recovering 303 excellent quality cores from 505.7 to 1334.7 meters below sea floor and acquiring more than 5.8 km of high resolution open hole logs. Downhole logs are rapidly collected, continuous with depth, and measured in situ; these data are classically interpreted in terms of stratigraphy, lithology, porosity, fluid content, geochemical composition and structure of the formation drilled. Downhole logs also allow assessing borehole quality (eg. shape and trajectory), and can provide assistance for decision support during drilling operations. In this work, Expedition 364 downhole logs are used to improve our understanding of the drilling/coring operation history. Differentiating between natural geological features and borehole artifacts are also critical for data quality assessment. The set of downhole geophysical tools used during Expedition 364 was constrained by the scientific objectives, drilling/coring technique, hole conditions and temperature at the drill site. Wireline logging data were acquired with slimline tools in three logging phases at intervals 0-503, 506-699 and 700-1334 mbsf. Logs were recorded either with standalone logging tools or, for the first time in IODP, with stackable slimline tools. Log data included total gamma radiation, sonic velocity, acoustic and optical borehole images, resistivity, conductivity, magnetic susceptibility, caliper and borehole fluid parameters. The majority of measurements were performed in open borehole conditions. During the drilling operations some problems were encountered directly linked to the geology of the drilled formation. For example, two zones of mud circulation losses correlate in depth with the presence of karst cavities or open faults, as evidenced from borehole wall images. Both form conduits probably open at a large scale as suggested by associated anomalies in the borehole fluid temperature profiles. When coring the basement, pieces of metal trapped outside the drill bit apparently led to an increase of the borehole tilt as well as to an enlargement of the hole, although this later remained sub-circular. In the post impact carbonates, 6-7 m long apparent cyclic oscillations in the magnetic field coupled to a spiral shape trajectory of the same wavelength suggest drilling induced artifacts and formation re-magnetization. Acknowledgements: Expedition 364 was funded by IODP with co-funding from ICDP and implemented by ECORD, with contributions and logistical support from the Yucatán state government and Universidad Nacional Autónoma de México. Drilling Services were provided by DOSECC Exploration Services. The downhole logging program was coordinated by EPC, as part of ESO. Expedition 364 Scientists: S. Gulick, J.V. Morgan, E. Chenot, G. Christeson, P. Claeys, C. Cockell, M.J. L. Coolen, L. Ferrière, C. Gebhardt, K. Goto, H. Jones, D.A. Kring, J. Lofi, X. Long, C. Lowery, C. Mellett, R. Ocampo-Torres, L. Perez-Cruz, A. Pickersgill, M. Poelchau, A. Rae, C. Rasmussen, M. Rebolledo-Vieyra, U. Riller, H. Sato, J. Smit, S. Tikoo, N. Tomioka, M. Whalen, A. Wittmann, J. Urrutia-Fucugauchi, K.E. Yamaguchi, W. Zylberman.

The variability of meteoroid falling

NASA Astrophysics Data System (ADS)

Velasco Herrera, V. M.; Cordero, G.

2016-10-01

We analysed a historical catalogue of meteoroid falling during the last 400 years. We report here for the first time the synchronization between observed meteors and solar barycentric parameters in 19.6 and 13.2 years periodicities using a new multiple cross wavelet. The group of moderated number of meteors is distributed around the positive phase of the solar barycentric periodicity of 13.2 years. While the group of severe number of meteors are distributed on the positive phase of the solar barycentric periodicity of 19.6 years. These periodicities could be associated with Jupiter periodicities. So understanding the modulation of meteoroid falling is important for determining the falling patterns of these objects and for knowing when it is more likely to expect the entry of one of these objects into the Earth's atmosphere, because bodies falling onto the Earth can cause damage from minor impacts to mass-extinctions events. One of the most extreme events was the formation of the Chicxulub impact crater 65,000,000 years ago that caused one of the five major mass extinctions in the last 500,000,000 years. During the 20th and 21st centuries, a series of events demonstrated the importance of collisions between planets and small bodies (comets and asteroids), which included our own planet. In the case of the Earth, we can cite three examples: Tunguska, Curuça and Chelyabinsk. These events invite us to think that perhaps the occurrence of this phenomenon might be more common than we realize, but the lack of communication or people in the area where they happened prevents us from having a complete record. Modern man has not witnessed the impact of large asteroids or comets on our planet, but it has been observed on other planetary bodies. The most spectacular of these events was the collision of fragments of the comet Shoemaker-Levy 9 with Jupiter in 1994. The total energy of the 21 impacts on Jupiter's atmosphere was estimated as the equivalent of tens of millions of megatons of TNT.

Ancient impact structures on modern continental shelves: The Chesapeake Bay, Montagnais, and Toms Canyon craters, Atlantic margin of North America

USGS Publications Warehouse

Poag, C. Wylie; Plescia, J.B.; Molzer, P.C.

2002-01-01

Three ancient impact craters (Chesapeake Bay - 35.7 Ma; Toms Canyon - 35.7 Ma; Montagnais - 51 Ma) and one multiring impact basin (Chicxulub - 65 Ma) are currently known to be buried beneath modern continental shelves. All occur on the passive Atlantic margin of North America in regions extensively explored by seismic reflection surveys in the search for oil and gas reserves. We limit our discussion herein to the three youngest structures. These craters were created by submarine impacts, which produced many structural and morphological features similar in construction, composition, and variability to those documented in well-preserved subaerial and planetary impact craters. The subcircular Chesapeake Bay (diameter 85 km) and ovate Montagnais (diameter 45-50 km) structures display outer-rim scarps, annular troughs, peak rings, inner basins, and central peaks similar to those incorporated in the widely cited conceptual model of complex impact craters. These craters differ in several respects from the model, however. For example, the Montagnais crater lacks a raised lip on the outer rim, the Chesapeake Bay crater displays only small remnants of a raised lip, and both craters contain an unusually thick body of impact breccia. The subtriangular Toms Canyon crater (diameter 20-22 km), on the other hand, contains none of the internal features of a complex crater, nor is it typical of a simple crater. It displays a prominent raised lip on the outer rim, but the lip is present only on the western side of the crater. In addition, each of these craters contains some distinct features, which are not present in one or both of the others. For example, the central peak at Montagnais rises well above the elevation of the outer rim, whereas at Chesapeake Bay, the outer rim is higher than the central peak. The floor of the Toms Canyon crater is marked by parallel deep troughs and linear ridges formed of sedimentary rocks, whereas at Chesapeake Bay, the crater floor contains concentric faults and compression ridges formed in rocks of the crystalline basement. The Chesapeake Bay crater is distinguished further by its cluster of at least 23 adjacent secondary craters. The North American tektite strewn field, a widespread deposit of distal ejecta, is thought to be derived from the Chesapeake Bay impact, perhaps with a small contribution from the Toms Canyon impact. No ejecta field is known to be associated with the Montagnais impact. No immediate major extinction event is directly linked to any of these three impacts. There is evidence, however, that the Chesapeake Bay and Toms Canyon impacts helped initiate a long-term pulse of warm global climate, whose eventual dissipation coincided with an early Oligocene mass extinction event, 2 Ma after the impacts.

Hybrid Guidance Control for a Hypervelocity Small Size Asteroid Interceptor Vehicle

NASA Technical Reports Server (NTRS)

Zebenay, Melak M.; Lyzhoft, Joshua R.; Barbee, Brent W.

2017-01-01

Near-Earth Objects (NEOs) are comets and/or asteroids that have orbits in proximity with Earth's own orbit. NEOs have collided with the Earth in the past, which can be seen at such places as Chicxulub crater, Barringer crater, and Manson crater, and will continue in the future with potentially significant and devastating results. Fortunately such NEO collisions with Earth are infrequent, but can happen at any time. Therefore it is necessary to develop and validate techniques as well as technologies necessary to prevent them. One approach to mitigate future NEO impacts is the concept of high-speed interceptor. This concept is to alter the NEO's trajectory via momentum exchange by using kinetic impactors as well as nuclear penetration devices. The interceptor has to hit a target NEO at relative velocity which imparts a sufficient change in NEO velocity. NASA's Deep Impact mission has demonstrated this scenario by intercepting Comet Temple 1, 5 km in diameter, with an impact relative speed of approximately 10 km/s. This paper focuses on the development of hybrid guidance navigation and control (GNC) algorithms for precision hypervelocity intercept of small sized NEOs. The spacecraft's hypervelocity and the NEO's small size are critical challenges for a successful mission as the NEO will not fill the field of view until a few seconds before intercept. The investigation needs to consider the error sources modeled in the navigation simulation such as spacecraft initial state uncertainties in position and velocity. Furthermore, the paper presents three selected spacecraft guidance algorithms for asteroid intercept and rendezvous missions. The selected algorithms are classical Proportional Navigation (PN) based guidance that use a first order difference to compute the derivatives, Three Plane Proportional Navigation (TPPN), and the Kinematic Impulse (KI). A manipulated Bennu orbit that has been changed to impact Earth will be used as a demonstrative example to compare the three methods. In addition, a hybrid approach that is a combination between proportional navigation and kinematic impulse will be investigated to find an effective, error tolerant, and power saving approach. A 3-dimension mission scenario for both the asteroid and the interceptor spacecraft software simulator is developed for testing of the controllers. The current result demonstrates that a miss distance magnitude of less than 10m is found using the PN and TPPN guidance laws for small asteroid in the presence of error in the spacecraft states. Moreover, the paper presents these results and also the hybrid control approach simulation results.

A Paleocene lowland macroflora from Patagonia reveals significantly greater richness than North American analogs

NASA Astrophysics Data System (ADS)

Iglesias, Ari; Wilf, Peter; Johnson, Kirk R.; Zamuner, Alba B.; Rubén Cúneo, N.; Matheos, Sergio D.; Singer, Bradley S.

2007-10-01

Few South American macrofloras of Paleocene age are known, and this limits our knowledge of diversity and composition between the end-Cretaceous event and the Eocene appearance of high floral diversity. We report new, unbiased collections of 2516 compression specimens from the Paleocene Salamanca Formation (ca. 61.7 Ma) from two localities in the Palacio de los Loros exposures in southern Chubut, Patagonia, Argentina. Our samples reveal considerably greater richness than was previously known from the Paleocene of Patagonia, including 36 species of angiosperm leaves as well as angiosperm fruits, flowers, and seeds; ferns; and conifer leaves, cones, and seeds. The floras, which are from siltstone and sandstone channel-fills deposited on low-relief floodplain landscapes in a humid, warm temperate climate, are climatically and paleoenvironmentally comparable to many quantitatively collected Paleocene floras from the Western Interior of North America. Adjusted for sample size, there are >50% more species at each Palacio de los Loros quarry than in any comparable U.S. Paleocene sample. These results indicate more vibrant terrestrial ecosystems in Patagonian than in North American floodplain environments ˜4 m.y. after the end-Cretaceous extinction, and they push back the time line 10 m.y. for the evolution of high floral diversity in South America. The cause of the dis parity is unknown but could involve reduced impact effects because of greater distance from the Chicxulub site, higher latest Cretaceous diversity, or faster recovery or immigration rates.

Lunar and Planetary Science XXXVI, Part 22

NASA Technical Reports Server (NTRS)

2005-01-01

The Lunar and Planetary Science XXXVI, Part 22 is presented. The topics include: 1) Pressure Histories from Thin and Thick Shock-induced Melt Veins in Meteorites; 2) Nano-structured Minerals as Signature of Microbial Activity; 3) The Insoluble Carbonaceous Material of CM Chondrites as Possible Source of Discrete Organics During the Asteroidal Aqueous Phase; 4) Discovery of Abundant Presolar Silicates in Subgroups of Antarctic Micrometeorites; 5) Characteristics of a Seismometer for the LUNAR-A Penetrator; 6) Heating Experiments of the HaH 262 Eucrite and Implication for the Metamorphic History of Highly Metamorphosed Eucrites; 7) Measurements of Ejecta Velocity Distribution by a High-Speed Video Camera; 8) Petrological Comparison of Mongolian Jalanash Ureilite and Twelve Antarctic Ureilites; 9) Metallographic Cooling Rate of IVA Irons Revisited; 10) Inhomogeneous Temperature Distribution in Chondrules in Shock-Wave Heating Model; 11) Subsurface Weathering of Rocks and Soils at Gusev Crater; 12) Extinct Radioactivities in the Early Solar System and the Mean Age of the Galaxy; 13) Correlation of Rock Spectra with Quantitative Morphologic Indices: Evidence for a Single Rock Type at the Mars Pathfinder Landing Site; 14) Silicon Isotopic Ratios of Presolar Grains from Supernovae; 15) Current Status and Readiness on In-Situ Exploration of Asteroid Surface by MINERVA Rover in Hayabusa Mission; 16) Long Formation Period of Single CAI: Combination of O and Mg Isotope Distribution; 17) Supra-Canonical Initial 26Al/27Al Indicate a 105 Year Residence Time for CAIs in the Solar Proto-Planetary Disk; 18) Evolution of Mercury's Obliquity; 19) First Results from the Huygens Surface Science Package; 20) Polyhedral Serpentine Grains in CM Chondrites; 21) Mountainous Units in the Martian Gusev Highland Region: Volcanic, Tectonic, or Impact Related? 22) Petrography of Lunar Meteorite MET 01210, A New Basaltic Regolith Breccia; 23) Earth-Moon Impacts at 300 Ma and 500 Ma Ago; 24) Chemical and Isotopic Analyses of Apollo 16 Glasses: An Integrated Approach; 25) Measuring the Surfaces on Mars; 26) Melting in Martian Snowbanks; 27) The Effect of Ni on Fe-FeS Phase Relations: Implications for the Chemistry of the Martian Core; 28) Shorelines in the Western United States as Analogs for Hypothesized Shoreline Features on Mars; 29) Al and Ti Isotopic Ratios of Presolar SiC Grains of Type Z; 30) Physicochemical Conditions of Clinopyroxene Crystallization in the Parental Bodies of Ordinary Chondrites; 31) Metamorphosed CM and CI Carbonaceous Chondrites Could be from the Breakup of the Same Earth-crossing Asteroid; 32) Aqueous Alteration and Hydrogen Generation on Parent Bodies of Unequilibrated Ordinary Chondrites: Thermodynamic Modeling for the Semarkona Composition; and 33) Preliminary Analysis of Relative Abundances of Hydrothermal Alteration Products in the C1-N10, Y6-N19, and Yax-1_863.51 Impact Melt Samples, Chicxulub Structure, Mexico

Multibeam Mapping of Cretaceous-Paleogene Meteorite Impact Deposits on the Campeche Escarpment, YUCATÁN , MÉXICO

NASA Astrophysics Data System (ADS)

Gwiazda, R.; Paull, C. K.; Caress, D. W.; Rebolledo-Vieyra, M.; Fucugauchi, J. U.; Canales, I.; Sumner, E. J.; Tubau Carbonell, X.; Lundsten, E. M.; Anderson, K.

2013-12-01

The Chicxulub crater in the Yucatán Peninsula, México, at the Cretaceous-Paleogene (K-Pg) boundary, is believed to have been created by the impact of a meteorite ~65 million years ago. Ejecta from the impact were deposited beyond the crater site and are now buried under >1 km of Cenozoic carbonate sediments. Outcrops of the ejecta are believed to be exposed on the Campeche escarpment, which is the dramatically steep northern edge of the Yucatán Peninsula. A seafloor-mapping cruise aboard the R/V Falkor, equipped with Kongsberg EM302 30 kHz and EM710 70-100 kHz multibeam sonars, was conducted in March 2013 to produce a detailed map of the escarpment. Surveys were conducted along the escarpment face for 612 km, targeting the water depth range between 400 m and the escarpment base at ≤ 3,700 m. Segments with two distinctive reliefs are observed in the escarpment face: The first type of relief is a continuous slope over the entire surveyed depth, with numerous v-shaped gullies and intervening ridges. In contrast, the second type of relief is characterized by slopes of 5° above ~2-2.5 km depth with an abrupt change to 25° slopes below. As many as 80 submarine canyons are present along this relief. The canyons are topped with semicircular amphitheaters of gentler slopes above ~2-2.5 km but rimmed with 500 m high cliffs on the steep slope section below. The steep cliffs appear free from sediment drape and can be traced laterally for large segments of the escarpment, suggesting that these are horizontal units with outcropping strata. The location of the K-Pg boundary on the escarpment can be inferred from its identification on DSDP Leg 17 Site 86, drilled on a terrace at 1,462 m depth, and 200 m from the edge of the escarpment, and on DSDP Leg 17 Site 94, drilled in 1,793 m depth, 5.5 km from the edge of the platform. Based on the biostratigraphy of core cuttings recovered from both boreholes the base of the Tertiary in Site 86 is placed at between 2,016 and 2,081 m, and in Site 94 between 2,427 and 2,436 m depth. Lateral projection of these depths to the face of the escarpment correspond with the abrupt change from the 5° slope to the 25° slope associated with the 500 m high cliff which can be followed laterally for hundreds of kilometers. How much of this 500 m cliff is composed of meteorite impact ejecta or in-place Cretaceous sediments is unknown. Nevertheless, the data from this cruise constrains the location of the ejecta and boundary along most of the horizontal extent of the Campeche escarpment to within a 25 m depth interval, thus providing attractive sampling targets for future expeditions utilizing robotic vehicles.

Volcanic eruptions, global change and evolution of species

NASA Astrophysics Data System (ADS)

Courtillot, V.

2007-12-01

Our group proposed in 1986 that the Deccan traps of India had been co-eval with the Cretaceous-Tertiary mass extinction, had lasted less than 800 kyears, straddling the KT. In 1995, Bhandari and colleagues showed that the iridium level marking the Chicxulub impact could be found in the Deccan and was sandwiched between flows, demonstrating that they were co-eval events but that volcanism had started first and could not be a consequence of impact. Since then, many groups have contributed to dating more precisely continental flood basalts around the world and found that there was almost a one to one correspondance between flood basalts and mass extinctions (but not impacts, except for the KT) : for a recent review see Courtillot and Renne (2003). In recent years, a number of significant advances have been made. It has been shown in the case of the historically large but geologically very small Icelandic Laki eruption of 1783 that such eruptions could inject large amounts of sulfate aerosols all the way to the stratosphere and have a global impact on climate : therefore, effusive basaltic volcanism on a large scale could alter climate (our group with Frédéric Fluteau and Anne-Lise Chenet and Steve Self with Thor Thordarson). Petrologic, volcanological, paleomagnetic, paleontological and geochronologic studies of the entire 3000m thick Deccan pile have been resumed (mainly our group, that of Self with Mike Widdowson and Anne Jay, and that of Gerta Keller). The result is that the thick lava pile actually erupted in a relatively small number of gigantic pulses (with mega-flows up to 10000 km3 in volume having erupted in decades !). Field evidence has been given that flows could extend over almost 1000km, and paleontological and K-Ar dating now reveals a history of mainly two mega-pulses having occurred, one just prior to the KT the second somewhat afterwards explaining the long delay of recovery of species from the catastrophe. There is little doubt now that the KT catastrophe would have occurred even if the impact (which did have a significant additionnal effect) had not struck, and that the impact could not have generated a mass extinction if volcanism had not already been going on. Finally, global change during these periods of anomalous volcanism may provide interesting benchmarks for modelling of more current potential global change, and geologists be a major help to climate modelers.

Field guide to Cretaceous-tertiary boundary sections in northeastern Mexico

NASA Technical Reports Server (NTRS)

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

1994-01-01

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

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

NASA Astrophysics Data System (ADS)

Gupta, Satish C.; Ahrens, Thomas J.; Yang, Wenbo

2001-06-01

Discovery of abundant anhydrite (CaSO 4) and gypsum (CaSO 4·2H 2O) in the otherwise carbonate sediment comprising the upper 3 km thick layer of the target rock at the K/T impact site has prompted research on these minerals. Evaluation of the severity of the proposed extinction mechanism involving injection of impact-generated SO 2 and SO 3 into the stratosphere entails determination of criteria for shock-induced vaporization of these minerals. In the present work we present new data on the vaporization criteria of anhydrite. These are based on the reanalysis of the shock wave experiments of Yang and Ahrens [Earth Planet. Sci. Lett. 156 (1998) 125-140], conducted on material with 30% porosity, in which the shock- (fully or partially) vaporized sample interacts with an overlying LiF window. The velocity histories, monitored using a velocity interferometer, are compared with numerical simulations employing an improved equation of state for porous anhydrite and its vaporization products. We also employ the 'entropy criterion' for vaporization of material under shock compression. The values of the entropies of incipient and complete vaporization for anhydrite are determined to be 1.65±0.12 and 3.17±0.12 kJ (kg K) -1, respectively, and the corresponding pressures for incipient and the complete vaporization along the Hugoniot for the solid material are 32.5±2.5 and 122±13 GPa, respectively as compared with 81±7 and 155±13 GPa previously reported by Yang and Ahrens. Along with these criteria, the use of the recent estimate of diameter (100 km) for the Chicxulub transient crater [O'Keefe and Ahrens, J. Geophys. Res. 104 (E11) (1999) 27091-27104; Morgan et al., Nature 390 (1997) 472-476] that is smaller than previously assumed, along with Ivanov et al.'s [Geol. Soc. Am. Spec. Pap. 307 (1996) 125-142] 2-D hydrodynamic simulation to determine the shock attenuation and Pope et al.'s [J. Geophys. Res., 102 (E9) (1997) 21645-21664] radiative transfer model, yields the maximum decrease in the average global surface temperature of 12-19 K for 9.0-9.5 years at the K/T boundary. Thus, the global cooling is inferred to have been less severe than that indicated by the upper limit of the range of 5-31 K decrease lasting for ˜12 years calculated by Pope et al. Because ambient global surface temperatures at K/T time were ˜18-20°C warmer than present values, this cooling event produced cold, but not freezing conditions at the Earth's surface.

Groundwater geochemistry of the Yucatan Peninsula, Mexico: Constraints on stratigraphy and hydrogeology

NASA Astrophysics Data System (ADS)

Perry, Eugene; Paytan, Adina; Pedersen, Bianca; Velazquez-Oliman, Guadalupe

2009-03-01

SummaryWe report 87Sr/ 86Sr and ion concentrations of sulfate, chloride, and strontium in the groundwater of the northern and central Yucatan Peninsula, Mexico. Correlation between these data indicates that ejecta from the 65.95 m.y. old Chicxulub impact crater have an important effect on hydrogeology, geomorphology, and soil development of the region. Ejecta are present at relatively shallow subsurface depths in north-central Yucatan and at the surface along the Rio Hondo escarpment in southeast Quintana Roo, where they are referred to as the Albion Formation. Anhydrite/gypsum (and by inference celestite) are common in impact ejecta clasts and in beds and cements of overlying Paleocene and Lower Eocene rocks cored around the margin of the crater. The sulfate-rich minerals that are found in rocks immediately overlying the impact ejecta blanket, may either be partially mobilized from the ejecta layer itself or may have been deposited after the K/T impact event in an extensive pre-Oligocene shallow sea. These deposits form a distinctive sedimentary package that can be easily traced by the Eocene-Cretaceous 87Sr/ 86Sr signal. A distinct Sr isotopic signature and high SO 4/Cl ratios are observed in groundwater of northwestern and north-central Yucatan that interacts with these rocks. Moreover, the distribution of the gypsum-rich stratigraphic unit provides a solution-enhanced subsurface drainage pathway for a broad region characterized by dissolution features (poljes) extending from Chetumal, Quintana Roo to Campeche, Campeche. The presence of gypsum quarries in the area is also consistent with a sulfate-rich stratigraphic "package" that includes ejecta. The distinctive chemistry of groundwater that has been in contact with evaporite/ejecta can be used to trace flow directions and confirms a groundwater divide in the northern Peninsula. Information about groundwater flow directions and about deep subsurface zones of high permeability is useful for groundwater and liquid waste management in the area. Where it discharges at the coast, the unique chemistry of the groundwater that has interacted with the evaporite/ejecta strata may also have significant geomorphologic implications. While groundwater-seawater mixing at the coast has been shown to dissolve and erode limestone, PHREEQC modeling shows that mixing of water nearly saturated in CaSO 4 with seawater has a less vigorous dissolution effect due to its high Ca content.

Impact Cratering Calculations

NASA Technical Reports Server (NTRS)

Ahrens, Thomas J.

1997-01-01

Understanding the physical processes of impact cratering on planetary surfaces and atmospheres as well as collisions of finite-size self-gravitating objects is vitally important to planetary science. The observation has often been made that craters are the most ubiquitous landform on the solid planets and the satellites. The density of craters is used to date surfaces on planets and satellites. For large ringed basin craters (e.g. Chicxulub), the issue of identification of exactly what 'diameter' transient crater is associated with this structure is exemplified by the arguments of Sharpton et al. (1993) versus those of Hildebrand et al. (1995). The size of a transient crater, such as the K/T extinction crater at Yucatan, Mexico, which is thought to be the source of SO,-induced sulfuric acid aerosol that globally acidified surface waters as the result of massive vaporization of CASO, in the target rock, is addressed by our present project. The impact process excavates samples of planetary interiors. The degree to which this occurs (e.g. how deeply does excavation occur for a given crater diameter) has been of interest, both with regard to exposing mantle rocks in crater floors, as well as launching samples into space which become part of the terrestrial meteorite collection (e.g. lunar meteorites, SNC's from Mars). Only in the case of the Earth can we test calculations in the laboratory and field. Previous calculations predict, independent of diameter, that the depth of excavation, normalized by crater diameter, is d(sub ex)/D = 0.085 (O'Keefe and Ahrens, 1993). For Comet Shoemaker-Levy 9 (SL9) fragments impacting Jupiter, predicted excavation depths of different gas-rich layers in the atmosphere, were much larger. The trajectory and fate of highly shocked material from a large impact on the Earth, such as the K/T bolide is of interest. Melosh et al. (1990) proposed that the condensed material from the impact upon reentering the Earth's atmosphere induced. radiative heating, and producing global firestorms. The observed reentry splash of the SL-9 impact-induced plumes that reimpact Jupiter (Boslough et al., 1994) supported Melosh's K/T model. The fate of early primitive planetary atmospheres during the latter stages of planetary accretion, resulting from impactors in the 100 to 103 km diameter require modeling, e.g. Newman et al. (1997). Ahrens (1990; 1993) and Chen and Ahrens (1997) found that upon delivery of most of the impact energy to the solid planet, very large ground motions arise, which couple sufficient kinetic energy to the atmosphere to cause substantial atmospheric escape. The trade-off of this model with that of Cameron (1997) who suggests that atmospheric blow-off occurs as a result of the massive impact-induced heating of the atmosphere and Pepin (1997) who uses this heating event to model differential hydrodynamic loss of lighter atmospheric gases, requires further research.

The role of impact cratering in planetary environmental change and implications for the search for life in the solar system (Invited)

NASA Astrophysics Data System (ADS)

Osinski, G. R.

2013-12-01

Beginning in the late 18th century with the work of James Hutton, uniformitarianism emerged as a central tenet of the natural sciences and remained so well into the 20th century. Central to the idea of uniformitarianism is the concept of gradualism whereby processes throughout time occur at the same, or similar rates. In the 20th century, the idea that asteroids and comets have struck, and continue to strike, planetary bodies throughout geological time, has revolutionized our understanding of Solar System history and evolution. Indeed, it is now widely recognized that impact cratering is one of the most important and fundamental geological process in the Solar System. It is also now apparent that impact events have profoundly affected the origin and evolution of Earth, its environment, and the habitability of our planet. The extreme physical conditions (e.g., 10's of thousands of K and 100's of GPa), the concentrated nature of the energy release at a single point on a planetary surface, and the virtually instantaneous nature of the impact process sets apart impact events from all other geological processes. It should not be surprising then that such a rapid geological process can cause rapid environmental change. The destructive geological, environmental, and biological effects of meteorite impact events are well studied and well known. This is largely due to the discovery of the ~180 km diameter Chicxulub impact structure, Mexico, and its link to the mass extinction event that marks the end of the Cretaceous Period 65 Myr. ago. While the main driver for this mass extinction event remains debated, a long list of possible causes of environmental change have been proposed, including: heat from the impact explosion, tsunamis, earthquakes, global forest fires, dust injection in the upper atmosphere, production of vast quantities of N2O, and release of CO2 and sulfur species from the target rocks. Any one of these effects could potentially cause the annihilation of a particular planetary habitat. But the news is not all bad. Impact events can redistribute viable planetary habitats instantly - and regionally to globally depending on the size of the impact event. They can bring material from depths of many km in the form of ejecta deposits and central uplifts in so-called complex impact structures. Importantly, much of the material excavated and/or redistributed by impact events is shocked to such low pressures and temperatures that habitats, bioessential elements (e.g., C, N, O), and even organisms can remain intact. In recent years, it has also become apparent that impact events can also create new planetary habitats where none previously existed, including hydrothermal systems, endolithic habitats in shocked rocks and impact glasses, and impact crater lakes. Finally, impact events can also generate conditions conducive for the origin of life (e.g., clays, which form catalysts for organic reactions, and hot spring environments). Thus, far from being the agents of destruction that they were once thought to be, impact events can also be viewed as a favourable agent of rapid environmental change. This may have important implications for our understanding of the origin and evolution of early life on Earth, and possibly other planets such as Mars.

Cataclysms and Catastrophes: A Case Study of Improving K-12 Science Education Through a University Partnership

NASA Astrophysics Data System (ADS)

Fennell, T.; Ellins, K. K.; Morris, M.; Christeson, G.

2003-12-01

The K-12 science teacher is always seeking ways of improving and updating their curriculum by integrating the latest research into their most effective classroom activities. However, the daily demands of delivering instruction to large numbers of students coupled with the rapid advances in some fields of science can often overwhelm this effort. The NSF-sponsored Cataclysms and Catastrophes curriculum, developed by scientists from the The University of Texas at Austin Institute for Geophysics (UTIG) and Bureau of Economic Geology (BEG), middle and high school teachers, and UT graduate students (NSF GK-12 fellows) working together through the GK-12 program, is a textbook example of how universities can facilitate this quest, benefiting education at both K-12 and university levels. In 1992, "The Great K-T Extinction Debate" was developed as an activity in the Planet Earth class at the Liberal Arts and Science Academy of Austin as an interdisciplinary approach to science. Taking advantage of the media attention generated by the impact scenario for the K-T extinction, the activity consists of students participating in a simulated senate hearing on the potential causes of the K-T extinction and their implications for society today. This activity not only exposes students to the wide range of science involved in understanding mass extinctions, but also to the social, political and economic implications when this science is brought into the public arena and the corresponding use of data in decision making and disaster preparedness. While "The Great K-T Extinction Debate" was always a popular and effective activity with students, it was in desperate need of updating to keep pace with the evolving scientific debate over the cause of the K-T extinction and the growing body of impact evidence discovered over the past decade. By adding two inquiry-based learning activities that use real geophysical data collected by scientists studying the buried Chicxulub feature as a culmination to the classroom debate, we developed a curriculum module on Asteroids Impacts for the Cataclysms and Catastrophes project. This approach proved to be the ideal way to update the existing Planet Earth curriculum and to provide students with opportunities to use cutting-edge, hands-on geophysical and computer techniques to understand the most up-to-date science concerning the K-T extinction event.

High-Precision 40Ar/39Ar dating of the Deccan Traps

NASA Astrophysics Data System (ADS)

Sprain, C. J.; Renne, P. R.; Fendley, I.; Pande, K.; Self, S.; Vanderkluysen, L.; Richards, M. A.

2017-12-01

Almost forty years ago it was first hypothesized that greenhouse gases emitted from the Deccan Traps (DT) played a role in the Cretaceous-Paleogene boundary (KPB) mass extinction (McLean 1979, 1980, 1985). At that time, this hypothesis was dismissed due to insufficient geochronology and new evidence that a bolide impact coincided with the KPB. Since then, evidence such as records of protracted extinction and climate change in the Late Cretaceous, in addition to new high-precision geochronology of the DT, has bolstered the Deccan hypothesis. Recently, many models have been produced to simulate how DT volcanism may have perturbed global ecosystems. However, modeled outcomes are largely dependent upon variables such as the amount and species of gas released and the tempo of eruptions, which are not well constrained (Self et al., 2014). To better constrain climatic models and better understand the role DT volcanism played in the KPB extinction, we developed a high-precision geochronologic framework defining the timing and tempo of DT eruptions within the Western Ghats using high-precision 40Ar/39Ar geochronology. Our new results show that the DT erupted relatively continuously starting 66.4 Ma and extending to at least 65.3 Ma with no hiatuses longer than 50 ka, invalidating the concept of three discrete eruption pulses in the Western Ghats (Chenet et al., 2007, 2009; Keller et al., 2008). Our new data further provide the first precise location of the KPB within the DT sequence and place this boundary at or near the Lonavala-Wai subgroup transition, roughly coincident with major changes in eruption frequency, flow-field volumes, and extent of crustal magma contamination. Taken together, these results suggest that a state shift occurred in the DT magmatic system around the time of the Chicxulub impact, consistent with the impact triggering hypothesis of Richards et al. (2015). Our work further shows that over 80% of the estimated volume of the DT within the Western Ghats erupted in 600 ka; however, 70% of this volume, erupted after the KPB calling for a reassessment of the role of DT volcanism played in the KPB mass extinction and subsequent recovery. It is important to note that current volume estimates are likely to change as we work to improve understanding of the distribution of chemical formations, both on and offshore.

Stability of Basalt plus Anhydrite plus Calcite at HP-HT: Implications for Venus, the Earth and Mars

NASA Technical Reports Server (NTRS)

Martin, A. M.; Righter, K.; Treiman, A. H.

2010-01-01

"Canali" observed at Venus surface by Magellan are evidence for very long melt flows, but their composition and origin remain uncertain. The hypothesis of water-rich flow is not reasonable regarding the temperature at Venus surface. The length of these channels could not be explained by a silicate melt composition but more likely, by a carbonate-sulfate melt which has a much lower viscosity (Kargel et al 1994). One hypothesis is that calcite CaCO3 and anhydrite CaSO4 which are alteration products of basalts melted during meteorite impacts. A famous example recorded on the Earth (Chicxulub) produced melt and gas rich in carbon and sulfur. Calcite and sulfate evaporites are also present on Mars surface, associated with basalts. An impact on these materials might release C- and S-rich melt or fluid. Another type of planetary phenomenon (affecting only the Earth) might provoke a high pressure destabilization of basalt+anhydrite+calcite. Very high contents of C and S are measured in some Earth s magmas, either dissolved or in the form of crystals (Luhr 2008). As shown by the high H content and high fO2 of primary igneous anhydrite-bearing lavas, the high S content in their source may be explained by subduction of an anhydrite-bearing oceanic crust, either directly (by melting followed by eruption) or indirectly (by release of S-rich melt or fluid that metasomatize the mantle) . Calcite is a major product of oceanic sedimentation and alteration of the crust. Therefore, sulfate- and calcite-rich material may be subducted to high pressures and high temperatures (HP-HT) and release S- and C-rich melts or fluids which could influence the composition of subduction zone lavas or gases. Both phenomena - meteorite impact and subduction - imply HP-HT conditions - although the P-T-time paths are different. Some HP experimental/theoretical studies have been performed on basalt/eclogite, calcite and anhydrite separately or on a combination of two. In this study we performed piston-cylinder experiments at 1 GPa between 950 and 1700 C using a mixture of 70wt% tholeiitic basalt + 15wt% anhydrite + 15wt% calcite. Up to 1440 C, an ultracalcic (CaO>13.5 wt%; CaO/Al2O3>1 wt%) picrobasaltic (SiO240-45 wt%; Na2O+K2O<2 wt%) melt containing up to 5 wt% SO3 and up to 5.3 wt% CO2+H2O (calculated by difference) is present in equilibrium with clinopyroxene, anhydrite, spinel-chromite, a CAS-phase and a gas composed mainly of CO and an aliphatic thiol (CH2)4SH. Hydrogen was incorporated either by contact between the starting material and air or by diffusion through the capsule during the experiments. The S content in the gas increases with temperature and run duration, implying that gases with various C/S ratios might be released during an impact or at subduction zones, depending on the P-T-t path and on the H content. Above approx.1440 C, a Ca-rich carbonate-sulfate melt forms (in equilibrium with the picrobasaltic melt) which contains a few percents of Na and K. Such melt is not expected to form at Earth s subduction temperatures. If it forms by meteorite impact, it might crystallize too fast to explain long flows like Venus canali. A different basalt/anhydrite/calcite ratio might, however, decrease its formation temperature.

Anaglyph, Yucatan Peninsula, Mexico

NASA Technical Reports Server (NTRS)

2003-01-01

This anaglyph (stereoscopic view) of Mexico's Yucatan Peninsula was generated entirely from Shuttle Radar Topography Mission (SRTM) data, and shows a subtle but distinctive indication of the Chicxulub impact crater. Most scientists now agree that this impact was the cause of the Cretatious-Tertiary extinction, the event 65 million years ago that marked the demise of the dinosaurs as well as the majority of life then on Earth. The crater's rim is marked by a shallow semicircular depression arcing about an offshore center point in the upper left of the picture. (The arcing depression is just above the blue line, when viewed with the naked eye.) This depression, or trough, only about 3 to 5 meters (10 - 15 feet) deep and about 5 kilometers (3 miles) wide, was likely caused by collapse of limestone caverns preferentially above the crater rim, resulting in an arcing chain of sinkholes. The limestone that covers most of the Yucatan Peninsula post-dates the impact crater. However, the crater pattern apparently controls the subsidence pattern just enough to show through.

This anaglyph was created by deriving a shaded relief image from the SRTM data, draping it back over the SRTM elevation model, and then generating two differing perspectives, one for each eye. Illumination is from the north (top). When viewed through special glasses, the anaglyph is a vertically exaggerated view of the Earth's surface in its full three dimensions. Anaglyph glasses cover the left eye with a red filter and cover the right eye with a blue filter. The total relief (range of elevations) across this entire image is less than 300 meters (1000 feet).

Elevation data used in this image were acquired by the Shuttle Radar Topography Mission (SRTM) aboard the Space Shuttle Endeavour, launched on Feb. 11, 2000. SRTM used the same radar instrument that comprised the Spaceborne Imaging Radar-C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR) that flew twice on the Space Shuttle Endeavour in 1994. SRTM was designed to collect 3-D measurements of the Earth's surface. To collect the 3-D data, engineers added a 60-meter (approximately 200-foot) mast, installed additional C-band and X-band antennas, and improved tracking and navigation devices. The mission is a cooperative project between NASA, the National Imagery and Mapping Agency (NIMA) of the U.S. Department of Defense and the German and Italian space agencies. It is managed by NASA's Jet Propulsion Laboratory, Pasadena, Calif., for NASA's Earth Science Enterprise, Washington, D.C.

Size: 465 by 334 kilometers (288 by 207 miles) Location: 20 degrees North latitude, 89 degrees West longitude Orientation: North toward the top Image Data: Shaded SRTM elevation model Original Data Resolution: SRTM 1 arcsecond (about 30 meters or 98 feet) Date Acquired: February 2000

Diagnostic Clast-Texture Criteria for Recognition of Impact Deposits

NASA Technical Reports Server (NTRS)

Marshall, J. R.; Bratton, C.; Pope, K. O.; Ocampo, A. C.

1999-01-01

It is difficult to find definitive evidence for impact in the geological record because there are many endogenous geological processes that can produce diamictites similar to those generated by impact ejecta. The classic impact criteria of shock fabrics in certain minerals, and iridium layers, for example, may be either difficult to find, or long-since erased from the impact site (shock fabrics also anneal with time). It is important to be able to recognize impact-generated materials in order to understand earth's crustal development and biological evolution. In future exploration of Mars and other solar-system bodies, recognition of impact materials will be important for elucidating planetary evolution, planetary volatile inventories, and exobiological issues. The cobble depicted is typical of many that have been found in diamictite deposits in Belize generated by the Chicxulub K-T impact event. The pebbles are roughly-hewn in general shape with smoothed corners and edges. Surfaces are almost uniformly frosted (on both protuberances and hollows), but some asperities are glazed. Optical microscopy and thin-section petrographic microscopy reveal the frosting to be only a few microns thick, with a well-defined granular structure; grains are the same size as those composing the bulk of the limestone, but their clearer appearance may represent annealing. One or two adjacent pebble faces are often decorated with striated gouges and closely-spaced hemispherical depressions representing indentation hollows produced by well-rounded impacting clasts of up to 0.5 cm in diameter. Some of the impactors are still embedded in the cobble surface. Non-destructive x-ray diffraction techniques showed the impactors to be of the same mineralogy as the target cobble. We believe this unusual glazing and frosting to be related to the impact event, but this must be reconciled with its survival for over 60 my. since it is composed of one of the most alterable substances, CaCO3. We focus, however, on the non-fractured rounded pebbles that appear to have impacted the larger cobble as a swarm of clasts, probably encountered during ballistic flight. It cannot be defined whether the cobble swept through the pebble cloud, or the pebbles rained upon a slowermoving cobble. Two interesting questions arise: (1) Where did large numbers of such well rounded pebbles come from in the ejecta curtain?, and (2) How did they embed themselves in a nominally brittle rock without suffering damage? Are the well-rounded pebbles crystalline (devitrified) melt spherules? Further investigations are in progress. If the cobble was cold and brittle, impact of well-rounded pebbles would have produced Hertzian fracture patterns (a) in the virtually elastically isotropic cobble target. For penetration depths of about 0.5 of the impactor diameter, the pebbles would require a relative impact velocity sufficient to cause pebble fragmentation and crushing, and the development of a complex Hertzian-Boussinesq fracture field (b) involving deep fracturing and lateral surface spalling (impact velocities > 50 m/s). The existing relationship could only evolve by the impact of cold, hard pebbles into a soft, plastic cobble surface (c). For limestone to have been plastic, it must have been at elevated temperature, but to prevent calcification of the material, the ambient pressure must also have been elevated. This would be possible either in the impact's gas plume, or within the confines of a thin aerodynamically-produced shock bow generated by supersonic ballistic motion of the cobble. In the latter case, it is implied that the cobble swept through the pebbles rather than vice-versa. Although there are high T-P conditions associated with volcanism, such textures have not been reported on volcaniclastic materials, nor from other high T-P environments; e.g., metamorphic (as far as the authors are aware). We propose that this very easily recognizable embedding and indentation surface texture can be used as a diagnostic criterion for the recognition of impact ejecta. The term "peening texture" is suggested, because it is absolutely analogous to the plastic-deformation induced, metal-surface textures generated by ball-bearing bombardment used in engineering metallurgy to work-harden metal surfaces. Additional information is contained in the original (Figures).

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

NASA Astrophysics Data System (ADS)

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

2004-05-01

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

Shaded Relief with Height as Color, Yucatan Peninsula, Mexico

NASA Technical Reports Server (NTRS)

2003-01-01

This shaded relief image of Mexico's Yucatan Peninsula show a subtle, but unmistakable, indication of the Chicxulub impact crater. Most scientists now agree that this impact was the cause of the Cretatious-Tertiary Extinction, the event 65 million years ago that marked the sudden extinction of the dinosaurs as well as the majority of life then on Earth.

Most of the peninsula is visible here, along with the island of Cozumel off the east coast. The Yucatan is a plateau composed mostly of limestone and is an area of very low relief with elevations varying by less than a few hundred meters (about 500 feet.) In this computer-enhanced image the topography has been greatly exaggerated to highlight a semicircular trough, the darker green arcing line at the upper left corner of the peninsula. This trough is only about 3 to 5 meters (10 to 15 feet) deep and is about 5 km. wide (3 miles), so subtle that if you walked across it you probably would not notice it, and is a surface expression of the crater's outer boundary. Scientists believe the impact, which was centered just off the coast in the Caribbean, altered the subsurface rocks such that the overlying limestone sediments, which formed later and erode very easily, would preferentially erode on the vicinity of the crater rim. This formed the trough as well as numerous sinkholes (called cenotes) which are visible as small circular depressions.

Two visualization methods were combined to produce the image: shading and color coding of topographic height. The shade image was derived by computing topographic slope in the northwest-southeast direction, so that northwestern slopes appear bright and southeastern slopes appear dark. Color coding is directly related to topographic height, with green at the lower elevations, rising through yellow and tan, to white at the highest elevations.

For a smaller, annotated version of this image, please select Figure 1, below: [figure removed for brevity, see original site] (Large image: 1.5 mB jpeg)

Elevation data used in this image were acquired by the Shuttle Radar Topography Mission (SRTM) aboard the Space Shuttle Endeavour, launched on Feb. 11, 2000. SRTM used the same radar instrument that comprised the Spaceborne Imaging Radar-C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR) that flew twice on the Space Shuttle Endeavour in 1994. SRTM was designed to collect 3-D measurements of the Earth's surface. To collect the 3-D data, engineers added a 60-meter (approximately 200-foot) mast, installed additional C-band and X-band antennas, and improved tracking and navigation devices. The mission is a cooperative project between NASA, the National Imagery and Mapping Agency (NIMA) of the U.S. Department of Defense and the German and Italian space agencies. It is managed by NASA's Jet Propulsion Laboratory, Pasadena, Calif., for NASA's Earth Science Enterprise, Washington, D.C.

Size: 261 by 162 kilometers (162 by 100 miles) Location: 20.8 degrees North latitude, 89.3 degrees West longitude Orientation: North toward the top, Mercator projection Image Data: shaded and colored SRTM elevation model Original Data Resolution: SRTM 1 arcsecond (about 30 meters or 98 feet) Date Acquired: February 2000

Latest Cretaceous Climatic and Environmental Change in the South Atlantic Region

NASA Astrophysics Data System (ADS)

Woelders, L.; Vellekoop, J.; Smit, J.; Kroon, D.; Casadío, S.; Prámparo, M.; Dinarès-turell, J.; Peterse, F.; Sluijs, A.; Speijer, R. P.

2016-12-01

It is generally assumed that the Chicxulub impact resulted in the Cretaceous-Paleogene (K-Pg) boundary mass extinction ( 66 Ma). However, there is continuing debate about the contribution of latest Maastrichtian climate changes, possibly caused by Deccan volcanism, to this mass extinction event. This debate is complicated because of the lack of high quality latest Maastrichtian climatological and ecological reconstructions. Here we present an astronomically tuned late Maastrichtian - early Danian record of bulk carbonate δ18O, a proxy record of sea surface temperature (SST), from Southern Atlantic Ocean Drilling Program Site 1262 (Walvis Ridge) and a late Maastrichtian TEX86 sea surface temperature record from the Bajada del Jagüel site in the Neuquén Basin (Argentina). The combination of these inferred temperature records with foraminiferal and organic-walled dinoflagellate cyst (dinocyst) data from Bajada del Jagüel allows to reconstruct environmental changes across this time interval in a mid-latitude, Southern Atlantic setting. Our results show that latest Maastrichtian warming of 2.5-4°C started gradually around 66.7 Ma, culminating in the interval between 450 to 150 kyr before the K-Pg boundary. Highest temperatures occurred 200 kyr before the K-Pg boundary. During the last 150 kyr of the Maastrichtian, the temperature trend reversed again at both sites. Benthic foraminiferal and dinocyst assemblage changes indicate that late Maastrichtian warming resulted in more humid climate conditions in the Neuquén basin, causing enhanced runoff and stratification of the water column. Vice versa, the subsequent cooling induced again a drier climate in the basin, resulting in reduced salinity stratification and better ventilation of the basin. We conclude that late Maastrichtian climate and sea level change caused distinct environmental perturbations in the Neuquén basin, although it remains uncertain to which extent late Maastrichtian climatological changes contributed directly to the K-Pg boundary mass extinction.

Recent Developments and Adaptations in Diamond Wireline Core Drilling Technology

NASA Astrophysics Data System (ADS)

Thomas, D. M.; Nielson, D. L.; Howell, B. B.; Pardey, M.

2001-05-01

Scientific drilling using diamond wireline technology is presently undergoing a significant expansion and extension of activities that has allowed us to recover geologic samples that have heretofore been technically or financially unattainable. Under the direction and management of DOSECC, a high-capacity hybrid core drilling system was designed and fabricated for the Hawaii Scientific Drilling Project (HSDP) in 1998. This system, the DOSECC Hybrid Coring System (DHCS), has the capacity to recover H-sized core from depths of more than 6 km. In 1999, the DHCS completed the first phase of the HSDP to a depth of 3100 m at a substantially lower cost per foot than any previous scientific borehole to comparable depths and, in the process, established a new depth record for recovery of H-sized wireline core. This system has been offered for use in the Unzen Scientific Drilling Project, the Chicxulub (impact crater) Scientific Drilling Project, and the Geysers Deep Geothermal Reservoir Project. More recently, DOSECC has developed a smaller barge-mounted wireline core drilling system, the GLAD800, that is capable of recovering P-sized sediment core to depths of up to 800 m. The GLAD800 has been successfully deployed on Great Salt Lake and Bear Lake in Utah and is presently being mobilized to Lake Titicaca in South America for an extensive core recovery effort there. The coring capabilities of the GLAD800 system will be available to the global lakes drilling community for acquisition of sediment cores from many of the world's deep lakes for use in calibrating and refining global climate models. Presently under development by DOSECC is a heave-compensation system that will allow us to expand the capabilities of the moderate depth coring system to allow us to collect sediment and bottom core from the shallow marine environment. The design and capabilities of these coring systems will be presented along with a discussion of their potential applications for addressing a range of earth sciences questions.

Extinction Risk of Phytoplankton Species to Potential Killing Mechanisms at the Cretaceous-Paleogene Boundary

NASA Astrophysics Data System (ADS)

Bralower, T. J.; Schueth, J.; Jiang, S.

2013-05-01

The impact at Chicxulub caused catastrophic changes in marine habitats including extended darkness, ocean acidification and eutrophication. These changes were devastating to some groups of phytoplankton at the base of the marine food chain while others escaped virtually unscathed. For example, diatoms had ~85% survival across the boundary and dinoflagellates actually increased in diversity. These non-calcareous plankton most likely survived due to their adaptation to high-stress environments and their ability to form spores and resting cysts. The calcareous nannoplankton, however, were decimated with approximately 85% of genera and 93% of species going extinct. Nannoplankton generally lack the ability to encyst and thus, as a group, would have been susceptible to darkness, ocean acidification and eutrophication. However, we still do not fully understand why certain nannofossil taxa survived while others went extinct. Extinction risk, the projected susceptibility of a taxon to extinction based on its ecology and ability to adapt, is a concept that is widely applied to extant species and higher order fossil groups, but not to phytoplankton. This concept is a useful for probing the selectivity of ancient species to mass extinction. Determining the extinction risk of latest Maastrichtian nannoplankton species would be a step towards understanding the selection of survivors. The deep-sea record contains a remarkable archive of nannoplankton extinction and recovery across the Cretaceous-Paleogene boundary. The recovery was geologically extended, enabling detailed comparisons between the ocean basins. A large, global database of assemblages had led to the discovery that the Northern Hemisphere oceans suffered higher nannoplankton extinction rates than the Southern Hemisphere with an ecological "crisis" that lasted for approximately 350 thousand years after the impact. In addition, incumbency played a major role in the origination of new species. Since extinction almost certainly occurred over durations far shorter than can be resolved in the stratigraphic record, determining their ultimate causes is challenging and far more speculative. In our presentation, we discuss the extinction risk of latest Maastrichtian nannoplankton species by comparing our understanding of their ecology with the biological effects of each potential killing mechanism. Our results show that no one mechanism can explain the extinction of nannoplankton as a group, while also explaining the selection of survivors. We show how acidification and eutrophication amplified extinction risk of species to cessation of photosynthesis caused by darkness.

Provenance and depositional conditions of Cretaceous-Paleogene boundary sandstones from northeastern Mexico

NASA Astrophysics Data System (ADS)

Rehrmann, Stephanie; Augustsson, Carita; Izaguirre Valdez, Rocio Nereyda; Jenchen, Uwe; Schulte, Peter

2012-12-01

We compare Late Maastrichtian siliciclastic sandstone in northeastern Mexico with those representing the Cretaceous-Paleogene (K-Pg) boundary to reveal differences in provenance and depositional conditions between background sedimentation and K-Pg sand. Lithology and compositional variations are presented for the deep-water Burgos Basin and the shallow-water La Popa Basin. The Late Maastrichtian sandstones in the Burgos Basin have sharp lower contacts, contain abundant trace fossils and are separated by meter-thick marl layers. They represent sporadic mass flows from coastal areas separated by long phases of hemipelagic sedimentation. The K-Pg sandstone layers are amalgamated, contain thin marl intercalations only in the uppermost part and trace fossils are present in the top sandstone layer only. Also this succession represents mass-flow deposits, but the sand may have been deposited during a very short period. The La Popa Basin sandstones represent deltaic sedimentation interrupted by submarine channel deposition during the K-Pg boundary transition with abundant rip-up clasts and bioclasts at the base. The sandstones of the Burgos Basin are quartz to akosic wacke dominated by quartz (> 90%) and some feldspar (< 10%) in calcite cement and matrix. Lithic fragments are rare and dominated by chert and bioclasts. Ultra-stable heavy minerals (ZTR = 50-80) and plutonic quartz grains (ca. 40% of the total quartz population) are particularly common in the K-Pg sandstones. In the Maastrichtian sandstones, metamorphic heavy minerals, particularly chlorite, clinozoisite, and tourmaline (20-50% of the heavy mineral population), and metamorphic quartz (80% of the quartz population) have higher abundances. The La Popa sandstones are subarkose to arkose and arkosic wacke and have a high abundance of feldspar (15-30%) and lithic fragments (5-20%), mainly of siltstone and carbonate. The sandstones from both basins have chemical compositions typical for recycling (Zr/Sc = 12-27 and 17-140 in the Burgos and La Popa Basin, respectively) and influences from mafic source rocks (Th/Sc = 0.4-1.1; Ti/Nb = 350-510). Therefore we suggest that all studied successions share a common provenance with transport of recycled orogenic metasedimentary components from northwestern Mexico and magmatic arc material from western Mexico. Subsequently, longshore currents mixed the detritus with limestone clasts derived from the tectonically active Sierra Madre Oriental, which probably is the cause for compositional changes in the sandstones. Due to increased sediment input from western Mexico at the K-Pg boundary, provenance changes cannot be related to the Chicxulub impact.

Storm-generated bedforms and relict dissolution pits and channels on the Yucatan carbonate platform

NASA Astrophysics Data System (ADS)

Gulick, S. P.; Goff, J. A.; Stewart, H. A.; Perez-Cruz, L. L.; Davis, M. B.; Duncan, D.; Saustrup, S.; Sanford, J. C.; Fucugauchi, J. U.

2013-12-01

The Yucatan 2013 (cruise number 2013/4_ECORD) geophysical and geotechnical hazard site survey took place aboard the R/V Justo Sierra in April 2013. Our study was conducted within the Chicxulub impact crater, encompassing three potential IODP drilling sites. The survey was located ~32 km northwest of Progreso, Mexico; data acquired included ~15.6 km2 of complete multibeam bathymetry coverage, ~435 line km of side scan sonar and CHIRP data, 204 line kilometers of magnetometer data, and 194 line kilometers of surface tow boomer profiles. Based on these data, this portion of the Yucatan Shelf consists of flat-lying, hard limestone rock overlain by isolated ribbons of carbonate sand <1.0 m thick. These ribbons are oriented along NE-SW trends and have smaller scale orthogonal sand-waves (~20-100 m wavelengths and relief of ~0.2-0.6 m) on them. The sand waves are anisotropic with steeper slopes facing the NE. The larger scale morphology can be classified as longitudinal bedforms (ribbons), and the smaller scale transverse bedforms formed in response to a NE-directed flow. This flow direction is inconsistent with the ambient west-directed current conditions, and may therefore be indicative of storm-driven currents. Numerous dissolution pits, ~5-50m in diameter, ~0.2-0.5 m deep with steep (0.1-0.5 gradient) walls, are present in the bare rock regions of most of the study area. These occasionally are floored by rippled, highly reflective (coarse) sediments. We interpret these pits as representing karstic morphology formed during the last sub-aerial exposure of the study area interpreted to have occurred during Holocene times given the present day ~17 m average water depth. A sub-surface reflector imaged on the surface tow boomer data lies 1-3 m below the hard seafloor reflection (sand ribbons are below the vertical resolution of the surface tow boomer), which we interpret as a layer within the limestone bedrock. This reflector is flat-lying and undisturbed throughout the survey area. Therefore, none of these dissolution pits appear to be underlain by a cenote or sink hole. The NW sector of the survey area exhibits a more complex morphology than the alternating ribbon/bare rock morphology elsewhere, including linear scarps (up to ~1 m relief), deeper pitting (up to ~1 m relief), and sinuous, dendritic channeling (up to ~2 m relief). The geologic origin of these features will require further investigation. Sand drifts are present in this region, but are thinner and cover less area. These observations show the dominant modern sediment formation and transport processes on this starved platform are from large storms and hurricanes that place large regions of the platform at wave base. Remaining observed features were generated during times of lower sea level.

Shaded Relief with Height as Color and Landsat, Yucatan Peninsula, Mexico

NASA Technical Reports Server (NTRS)

2003-01-01

The top picture is a shaded relief image of the northwest corner of Mexico's Yucatan Peninsula generated from Shuttle Radar Topography Mission (SRTM) data, and shows a subtle, but unmistakable, indication of the Chicxulub impact crater. Most scientists now agree that this impact was the cause of the Cretatious-Tertiary Extinction, the event 65 million years ago that marked the sudden extinction of the dinosaurs as well as the majority of life on Earth. The pattern of the crater's rim is marked by a trough, the darker green semicircular line near the center of the picture. This trough is only about 3 to 5 meters (10 - 15 feet) deep and is about 5 km (3 miles) wide; so subtle that if you walked across it you probably would not notice it. It is the surface expression of the buried crater's outer boundary. Scientists believe the impact, which was centered just off the coast in the Caribbean, altered the subsurface rocks such that the overlying limestone sediments, which formed later and erode very easily, would preferentially erode along the crater rim. This formed the trough as well as numerous sinkholes (called cenotes) which are visible as small circular depressions.

The bottom picture is the same area viewed by the Landsat satellite, and was made by displaying the Thematic Mapper's Band 7 (mid-infrared), Band 4 (near-infrared) and Band 2 (green) as red, green and blue. These colors were chosen to maximize the contrast between different vegetation and land cover types, with native vegetation and cultivated land showing as green, yellow and magenta, and urban areas as white. The circular white area near the center of the image is Merida, a city of about 720,000 population. Notice that in the SRTM image, which shows only topography, the city is not visible, while in the Landsat image, which does not show elevations, the trough is not visible.

Two visualization methods were combined to produce the SRTM image: shading and color coding of topographic height. The shade image was derived by computing topographic slope in the northwest-southeast direction, so that northwest slopes appear bright and southeast slopes appear dark. Color coding is directly related to topographic height, with green at the lower elevations, rising through yellow and tan, to white at the highest elevations.

Elevation data used in this image were acquired by the Shuttle Radar Topography Mission (SRTM) aboard the Space Shuttle Endeavour, launched on Feb. 11, 2000. SRTM used the same radar instrument that comprised the Spaceborne Imaging Radar-C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR) that flew twice on the Space Shuttle Endeavour in 1994. SRTM was designed to collect 3-D measurements of the Earth's surface. To collect the 3-D data, engineers added a 60-meter (approximately 200-foot) mast, installed additional C-band and X-band antennas, and improved tracking and navigation devices. The mission is a cooperative project between NASA, the National Imagery and Mapping Agency (NIMA) of the U.S. Department of Defense and the German and Italian space agencies. It is managed by NASA's Jet Propulsion Laboratory, Pasadena, Calif., for NASA's Earth Science Enterprise, Washington, D.C.

Size: 261 by 162 kilometers (162 by 100 miles) Location: 20.8 degrees North latitude, 89.3 degrees West longitude Orientation: North toward the top, Mercator projection Image Data: shaded and colored SRTM elevation model Original Data Resolution: SRTM 1 arcsecond (about 30 meters or 98 feet) Date Acquired: February 2000

Advanced light element and low energy X-ray line analysis using Energy Dispersive Spectrometry (EDS) with Silicon Drift Detectors (SDD)

NASA Astrophysics Data System (ADS)

Salge, T.; Palasse, L.; Berlin, J.; Hansen, B.; Terborg, R.; Falke, M.

2013-12-01

Introduction: Characterization at the micro- to nano-scale is crucial for understanding many processes in earth, planetary, material and biological sciences. The composition of thin electron transparent samples can be analyzed in the nm-range using transmission electron microscopes (TEM) or, specific sample holders provided, in the field emission scanning electron microscope (FE-SEM). Nevertheless both methods often require complex sample preparation. An alternative method is to analyze bulk samples with a FE-SEM. In order to decrease the excitation volume for generated X-rays, low accelerating voltages (HV<10) are required. Consequently, only low to intermediate energy X-ray lines can be evaluated and many peak overlaps have to be deconvoluted since the high energy range is not available. Methods: A BRUKER Quantax EDS system with an XFlash Silicon Drift Detector acquired EDS spectra in spectrum images. To separate overlapping peaks, an extended atomic database [1] was used. For single channel EDS the electron beam current, solid angle, take-off angle and exposure time can be optimized to investigate the element composition. Multiple SDD setups ensure an even higher efficiency and larger collection angles for the X-ray analysis than single channel detectors. Shadowing effects are minimized in element distribution maps so that samples can be investigated quickly and sometimes in a close to natural state, with little preparation. A new type of EDS detector, the annular four channel SDD (XFlash 5060F), is placed between the pole piece and sample. It covers a very large solid angle (1.1 sr) and allows sufficient data collection at low beam currents on beam sensitive samples with substantial surface topography. Examples of applications: Results demonstrate that SDD-based EDS analysis contributes essential information on the structure at the micro- to nano scale of the investigated sample types. These include stardust analogue impact experiments [2], Chicxulub asteroid impactites [3,4], ore characterization of the Sudbury igneous complex [5], biomineralization in bacteria and insects [6], and characterization of ceramics [7] and ceramic metal joints [8]. We conclude that improvements in SDD and pulse processor technology including multi-detector and multi-segment options provide new insights because a vast amount of detailed information can be collected in a short period of time. Using the XFlash QUAD 5060F, samples can be analyzed rapidly at low beam current without carbon coating. [1] A. Assmann, A. and M. Wendt 2003. Spectrochim. Acta Part B, 58: 711-716. [2] A.T. Kearsley et al. 2013. 44th LPSC, 18-22.03.2013, The Woodlands, USA: #1910. [3] P. Schulte et al. 2010. Science 327: 1214-1218. [4] M. Nelson et al. 2012. GCA 86: 1-20. [5] Salge et al. 2013. LPI Contrib .No. 1737: 89. [6] M. Falke et al. 2013. EURO BioMat. 23-24.04.2013, Weimar, Germany. [7] H. Yurdakul et al. 2013.accepted for MC 2013, 25-30.08.2013, Regensburg, Germany [8] O. Tunckan 2010. PhD thesis. Anadolu University, Eskisehir, Turkey.

Obituary: Elisabetta (Betty) Pierazzo (1963-2011)

NASA Astrophysics Data System (ADS)

Sykes, Mark

2011-12-01

Elisabetta Pierazzo, Senior Scientist at the Planetary Science Institute, died at her home in Tucson, Arizona, on May 15. She was 47. Betty was an expert in the area of impact modeling throughout the solar system, as well as an expert on the astrobiological and environmental effects of impacts on Earth and Mars. Her work ranged widely, from providing detailed insights into the Chicxulub impact that caused the extinction of the dinosaurs to putting constraints on the thickness of the ice shell of Jupiter's moon Europa. She was interested in the rise of life and explored the delivery of organics to planets and Europa by comets as well as the creation of subsurface hydrothermal systems by impacts that may have been favorable sites for life on Mars. She was also an expert on Meteor Crater in Arizona and made several appearances on national and international broadcasts of programs including National Geographic specials, explaining the formation of this well-known structure. Betty was innovative, rigorous and systematic in her approach to science. She recognized the need for benchmarking and validating the different complex numerical codes to model impact and explosion cratering, organizing and leading a community effort to accomplish this major task. In addition to her science, Betty passionately promoted science education and public outreach. She took time away from her successful research career to teach undergraduates at the University of Arizona, she developed interactive websites and impact rock and meteorite kits for classroom use, as well as created professional development workshops for elementary and middle school science teachers. Betty arrived in the United States in 1989 from Italy and the following year attended graduate school at the Department of Planetary Sciences at the University of Arizona. She handled the difficulties of living in a foreign country by opening her house and her kitchen to others. She received her Ph.D. in 1997. The quality of her graduate work was recognized by the University of Arizona with the Gerard P. Kuiper Memorial Award. She continued at the University of Arizona as a Research Associate, and in 2002 joined the Planetary Science Institute as a Research Scientist. She was promoted to Senior Scientist in 2007. Betty was an active member of the planetary community. She served on numerous NASA review panels, was an associate editor of Meteoritics and Planetary Sciences, reviewed papers for numerous scientific journals, served as organizer of workshops and meetings on impact cratering held around the world, and was an organizer of the 2007 Meteoritical Society Meeting held in Tucson, Arizona. Betty was noted for the intensity with which she approached both life and work. Whether it was in the office, the classroom, on the volleyball court, the soccer field, or dance floor, her enthusiasm and joy in the activity was irresistible. She was cherished by very many people for her staunch friendship and support. She inspired countless people as a colleague, teacher, mentor and friend. Her life was even more brightened with her marriage to Keith Powell in 2007. Over the past six months, Betty battled a rare form of cancer. She dealt with it aggressively, and never let it overwhelm her. She was always looking towards the future. In the last week of her life, in the midst of chemotherapy, she was grading class papers, working on research papers, writing reviews and preparing education proposals with her colleagues, all the while finding time to spend precious moments with her family and friends. She was ultimately and suddenly struck down by a pulmonary embolism. Her loss is great to all those who knew her and worked with her. Hers is a great loss to the Planetary Science Institute and to our profession. We are grateful to her husband, Keith, and to her family for the time she did have with us.

Ecosystems response and restitution time across the K/Pg boundary transition at high-latitudes, Southern Hemisphere, New Zealand - a palynological approach

NASA Astrophysics Data System (ADS)

Willumsen, Pi; Vajda, Vivi

2010-05-01

Several major groups of biota/fauna disappeared globally across the Cretaceous-Paleogene boundary (K/Pg boundary) and several other important groups suffered considerable, but not complete, species-level extinction. For marine phytoplankton - a major driver of ocean productivity - darkness and suppression of photosynthesis, in the aftermath of the asteroid impact, was likely a major killing mechanism. Thus, in the marine realm there is a separation in extinction rate between strongly affected groups with calcareous shells and groups that had organic cysts or siliceous tests. Detailed regional records of the long-term post-K/Pg boundary therefore still need to be undertaken to enhance the understanding of how each of the major microfossil groups recovered to elucidate recovery in different ecosystem types following this unique event. Throughout the New Zealand region, widespread deposition of siliceous sediments occurred during the Late Cretaceous to early Paleocene indicating the existence of a south Pacific upwelling regime (Hollis 1993, 1995; Strong et al. 1995). Silica concentration in the oceans increased after the K/Pg event and remained high for 1-2 millions years during the early Paleogene, reflecting high bio-siliceous productivity in the aftermath of the K/Pg boundary event (Hollis et al. 1995, 2003). The geological archives of New Zealand includes outcrops from several basins which provide a unique possibility for examining ecosystem response and restitution time from latest Cretaceous to early Paleogene in a suite of depositional environments spanning from terrestrial to bathyal (Willumsen 2000, Vajda et al. 2001, Vajda and Raine 2003). High-resolution palynological comparative studies of organic-walled microfossils such as dinoflagellate assemblages (dinocysts), spores and pollen are currently carried out on New Zealand sediments. The recovery period in the marine realm is much extended compared with the much shorter recovery time reflected by the terrestrial record e.g. "Fern-spike" interval (Vajda et al. 2001; Vajda and Raine 2003; Vajda and McLoughlin 2004). Interestingly, the dinocyst Trithyrodinium evittii has first occurrence immediately above the K/Pg boundary horizon in the southwest Pacific (Helby et al., 1987; Wilson 1987, 1988; Williams et al. 2004; Willumsen 2000, 2006). This dinocyst pattern is interpreted to reflect an invasion of this species into the southwest Pacific, in the aftermath of the Chicxulub impact. In the New Zealand sections, two earliest Paleocene intervals with dominance of T. evittii are separated by an acme interval of Paleoperidinium pyrophorum (Willumsen 2000, 2006; Willumsen et al., 2004a; 2004b). The sudden acme of P. pyrophorum ca. 0.5 Ma after the K/Pg boundary event is interpreted to reflect a regional cold water pulse taking place after a period with relatively warmer sea-surface e.g. T. evittii dominated dinocyst assemblages. A second period with warm-surface water is observed c. 0.8-1.5 Ma after the event. The end of the main marine recovery period is marked by a gradual arrival of new suite of dinocyst species and oligotrophic conditions. The timing of these early Paleocene events in New Zealand aligns well with D'Hondt et al. (1998, 2005) who propose that the marine ecosystem was radically altered due to the K/Pg boundary event and that the post-K/Pg boundary is divided into several recovery steps before the open-ocean ecosystem was fully recovered c. 3 Ma after the event.

Paleozoic Orogens of Mexico and the Laurentia-Gondwana Connections: an Update

NASA Astrophysics Data System (ADS)

Ortega-Gutierrez, F.

2009-05-01

The present position of Mexico in North America and the fixist tectonic models that prevailed prior to the seventies of the past century, have considered the main Paleozoic tectonic systems of Mexico as natural extensions of the orogens that fringed the eastern and southern sides of the Laurentian craton. Well known examples of pre-Mesozoic orogens in Mexico are the Oaxacan, Acatlan, and Chiapas polymetamorphic terranes, which have been correlated respectively with the Grenville and Appalachian-Ouachitan orogens of eastern North America. Nonetheless, several studies conducted during the last decade in these Mexican orogenic belts, have questioned their Laurentian connections, regarding northwestern Gondwana instead as the most plausible place for their birth and further tectonic evolution. This work pretends to approach the problem by briefly integrating the massive amount of new geological information, commonly generated through powerful dating methods such as LA-ICPM-MS on detrital zircon of sedimentary and metasedimentary units in the Paleozoic crustal blocks, which are widely exposed in southern and southeastern Mexico. The Acatlan Complex bears the closest relationships to the Appalachian orogenic system because it shows thermotectonic evidence for opening and closure of the two main oceans involved in building the Appalachian mountains in eastern Laurentia, whereas two other Paleozoic terranes in NW and SE Mexico, until recently rather geologically unknown, may constitute fundamental links between the Americas for the last-stage suturing and consolidation of western Pangea. The buried basement of the Yucatan platform (400,000 squared km) on the other hand, remains as one of the most relevant problems of tectonostratigraphic correlations across the Americas, because basement clasts from the Chicxulub impact ejecta reveal absolute and Nd-model ages that suggest close Gondwanan affinities. Major changes in the comprehension of the Paleozoic orogens in Mexico include the swift of the Acatlan Complex from Iapetus to Rheic scenarios, and the apparent continuation of the Ouachita belt across northern Mexico into south central Sonora, rather than displaced eastwards along the legendary Mojave-Sonora megashear. And yet, poorly known suture-related lithotectonic associations of Paleozoic metamorphic rocks and arc granitoids that underlie the eastern margin of Mexico, have not been explained by existing models dealing with the Appalachian-Mexico-Gondwanan connections.

Tempo of the Deccan Traps eruptions in relation to events at the Cretaceous-Paleogene boundary

NASA Astrophysics Data System (ADS)

Renne, Paul; Sprain, Courtney; Pande, Kanchan; Richards, Mark; Vanderkluysen, Loyc; Self, Stephen

2016-04-01

It has been known for decades that the Deccan Traps (DT) continental flood basalts were erupted over an interval spanning the Cretaceous-Paleogene boundary (KPB). Paleomagnetic data clearly show that the volumetric majority of preserved DT lavas were erupted during geomagnetic polarity chron 29r, hence over an interval <1 Ma. Until recently, radioisotope geochronology has failed to clarify the tempo of the eruptions or to delineate where the KPB age-equivalent horizon occurs within the eruptive sequence. An ongoing high-precision 40Ar/39Ar geochronologic study is providing the first indications of variable time-averaged eruption rates in the important Western Ghats region, in addition to providing the first precise location of the KPB within the Deccan pile. One to three samples from each of the ten geochemically-defined Jawhar through Mahabaleshwar Formations [Beane et al., 1986], sampled in seven stratigraphic sections, have been analyzed. Replicate analyses of plagioclase separates were conducted in as many as five incremental-heating experiments for each sample, yielding weighted mean plateau ages as precise as ±0.035 Ma with fully propagated systematic uncertainties as low as ±0.055 Ma. The accumulating data require abandoning several misconceptions about Deccan magmatism. Most importantly, the notion of several temporally discrete pulses of volcanism in the Western Ghats is unsupported by our data and should be abandoned. Despite changes in mean extrusion rates, volcanism was essentially continuous for 0.91 ±0.1 Ma, from 66.38 ±0.05 to 65.47 ±0.1 Ma, with no regional hiatuses >100 ka. A sharp increase in mean volumetric eruption rate commencing within the Poladpur or uppermost Bushe Fm., near the base of the laterally extensive Wai Subgroup, is now well-documented. Based on recent area-weighted volume estimates [Richards et al., 2015], the eruption rate tripled from 0.2 to 0.6 km^3/year at this transition. The transition coincided with increased mantle relative to crustal melt contributions and much larger volume, albeit seemingly more episodic, individual eruptive events. Prior to the transition, lavas were erupted dominantly as compound flows, whereas afterwards fields of inflated sheet flows are more abundant. These changes in magma chemistry, eruptive style, and tempo imply a fundamental change in the DT magma plumbing system, which is consistent with enlargement and/or consolidation of magma chambers. The timing and abruptness of the transition occurred within ~50 ka of the KPB, supporting a causal relationship to the Chicxulub impact whose synchrony with the KPB at 66.04 ±0.01 Ma [Sprain et al., 2015] is unambiguous. Further 40Ar/39Ar dating (in progress) will refine the tempo of DT eruptions and will test for synchrony of geochemically-defined formations on a regional scale. Improving volume estimates for each formation remains a significant challenge. Quantifying volatile release as a function of time is also challenging but critical to providing realistic constraints on the role of DT volcanism in ecosystem stress around the KPB. New high-precision geochronological and geochemical constraints on large "outlying" regions such as the Malwa Plateau, Mandla Lobe, and Kutch Peninsula will be crucial to a more complete understanding of the evolution of Deccan volcanism and its relation to the KPB.

Environmental Assessment Report: Geotechnical Field Investigations.

DTIC Science & Technology

1975-06-30

ENVIRONMENTAL IMPACT OF THE PROPOSED ACTION...................148 4.1 SOCIOECONOMIC IMPACT ...................148 4.2 IMPACT ON CLIMATE.......................149...4.3 IMPACT ON AIR QUALITY.................150 4.3.1 VEHICULAR EMISSIONS....................150 4.3.2 DUST.............................150 4.4 NOISE... IMPACT .............................151 4.5 AESTHETIC IMPACT .......................152 4.6 IMPACT ON ECOLOGY...................153 4.6.1 GENERAL

13 CFR 310.1 - Special Impact Area.

Code of Federal Regulations, 2010 CFR

2010-01-01

... 13 Business Credit and Assistance 1 2010-01-01 2010-01-01 false Special Impact Area. 310.1 Section... SPECIAL IMPACT AREAS § 310.1 Special Impact Area. Upon the application of an Eligible Recipient, and with... the Project will serve as a Special Impact Area if the Eligible Recipient demonstrates that its...

47 CFR 1.1305 - Actions which normally will have a significant impact upon the environment, for which...

Code of Federal Regulations, 2012 CFR

2012-10-01

... impact upon the environment, for which Environmental Impact Statements must be prepared. 1.1305 Section 1... which normally will have a significant impact upon the environment, for which Environmental Impact... the human environment requires the preparation of a Draft Environmental Impact Statement (DEIS) and...

47 CFR 1.1305 - Actions which normally will have a significant impact upon the environment, for which...

Code of Federal Regulations, 2014 CFR

2014-10-01

... impact upon the environment, for which Environmental Impact Statements must be prepared. 1.1305 Section 1... which normally will have a significant impact upon the environment, for which Environmental Impact... the human environment requires the preparation of a Draft Environmental Impact Statement (DEIS) and...

47 CFR 1.1305 - Actions which normally will have a significant impact upon the environment, for which...

Code of Federal Regulations, 2013 CFR

2013-10-01

... impact upon the environment, for which Environmental Impact Statements must be prepared. 1.1305 Section 1... which normally will have a significant impact upon the environment, for which Environmental Impact... the human environment requires the preparation of a Draft Environmental Impact Statement (DEIS) and...

Hypervelocity Impact (HVI). Volume 8; Tile Small Targets A-1, Ag-1, B-1, and Bg-1

NASA Technical Reports Server (NTRS)

Gorman, Michael R.; Ziola, Steven M.

2007-01-01

During 2003 and 2004, the Johnson Space Center's White Sands Testing Facility in Las Cruces, New Mexico conducted hypervelocity impact tests on the space shuttle wing leading edge. Hypervelocity impact tests were conducted to determine if Micro-Meteoroid/Orbital Debris impacts could be reliably detected and located using simple passive ultrasonic methods. The objective of Targets A-1, Ag-1, B-1, and Bg-1 was to study hypervelocity impacts on the reinforced Shuttle Heat Shield Tiles of the Wing. Impact damage was detected using lightweight, low power instrumentation capable of being used in flight.

Mobile Sensors Environmental Assessment

DTIC Science & Technology

2005-09-26

4-1 4.1 Impacts of Land-Based Sensors.........................................................................4-1 4.1.1 Air Quality...4-27 4.3 Impacts of the Proposed Action...4-38 4.6 Cumulative Impacts

Risk of osteoradionecrosis after extraction of impacted third molars in irradiated head and neck cancer patients.

PubMed

Oh, Hee-Kyun; Chambers, Mark S; Garden, Adam S; Wong, Pei-Fong; Martin, Jack W

2004-02-01

This study was performed to compare the risk of osteoradionecrosis (ORN) in head and neck cancer patients in whom 1 or more impacted third molars were extracted before radiotherapy with patients whose impacted third molars were left intact. Eighty-one patients were selected from the medical records from 1989 to 1998. Patients had at least 1 impacted third molar and received radiotherapy for a head and neck cancer. These patients were divided into 2 groups on the basis of preirradiation extraction: group 1, patients who had impacted third molars extracted before radiotherapy (n = 55), and group 2, patients whose impacted third molars were left intact before radiotherapy (n = 38). In 12 patients of combined groups 1 and 2, at least 1 but not all of the impacted third molars were extracted before radiotherapy. Before radiotherapy, a total of 99 impacted third molars were extracted from the 55 patients in group 1 and a total of 55 impacted third molars were left intact in the 38 patients in group 2. After radiotherapy, a total of 7 impacted third molars were removed from 5 patients as treatment for infection (5 lower molars) or discomfort (2 upper molars). A total of 4 patients (2 from group 1 and 2 from group 2) developed ORN in the mandible. Of these 4 cases of ORN, 1 from group 1 appeared to be related to a dry socket that developed after preirradiation extraction of a lower impacted third molar, 1 from group 2 seemed to be related to infection of a lower impacted third molar after radiotherapy, and the remaining 2 cases appeared to be unrelated to an impacted third molar. Because few patients in this study developed ORN, the study failed to demonstrate whether preirradiation extraction versus retention of impacted third molars affects the risk for ORN.

47 CFR 1.1305 - Actions which normally will have a significant impact upon the environment, for which...

Code of Federal Regulations, 2011 CFR

2011-10-01

... impact upon the environment, for which Environmental Impact Statements must be prepared. 1.1305 Section 1... significant impact upon the environment, for which Environmental Impact Statements must be prepared. Any Commission action deemed to have a significant effect upon the quality of the human environment requires the...

46 CFR 504.7 - Environmental impact statements.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 46 Shipping 9 2010-10-01 2010-10-01 false Environmental impact statements. 504.7 Section 504.7... POLICY ANALYSIS § 504.7 Environmental impact statements. (a) General. (1) An environmental impact... environmental impact statements. (1) A draft environmental impact statement (DEIS) will initially be prepared in...

Quantifying Head Impacts in Collegiate Lacrosse.

PubMed

Reynolds, Bryson B; Patrie, James; Henry, Erich J; Goodkin, Howard P; Broshek, Donna K; Wintermark, Max; Druzgal, T Jason

2016-11-01

Concussion and repetitive head impact in sports has increased interest and concern for clinicians, scientists, and athletes. Lacrosse is the fastest growing sport in the United States, but the burden of head impact in lacrosse is unknown. The goal of this pilot study was to quantify head impact associated with practicing and playing collegiate lacrosse while subjects were fitted with wearable accelerometers. Descriptive epidemiology study. In a single year, a collegiate cohort of 14 women's and 15 men's lacrosse players wore mastoid-patch accelerometers to measure the frequency and severity of head impacts during official practices and games. Average impact severity, mean number of impacts, and cumulative acceleration were evaluated, stratified by sport and event type. Men's and women's collegiate lacrosse players did not significantly differ in the number of head impacts received during games (11.5 for men vs 9.2 for women) or practices (3.1 vs 3.1). Men's lacrosse players had significantly higher average head acceleration per impact during games compared with women (21.1g vs 14.7g) but not during practices (21.3g vs 18.1g). For both men and women, more impacts occurred during games than during practices (men, 11.5 vs 3.1; women, 9.2 vs 3.1), but impact severity did not significantly differ between events for either sport (men, 21.1g vs 21.3g; women, 14.7g vs 18.1g). The study data suggest a higher impact burden during games compared with practices, but this effect is driven by the quantity rather than severity of impacts. In contrast, sex-based effects in impact burden are driven by average impact severity rather than quantity. Data collected from larger multisite trials and/or different age groups could be used to inform ongoing debates, including headgear and practice regulations, that might appreciably affect the burden of head impacts in lacrosse. While most head impacts do not result in a clinical diagnosis of concussion, evidence indicates that subconcussive head impacts may increase susceptibility to concussion and contribute to long-term neurodegeneration. © 2016 The Author(s).

23 CFR 771.125 - Final environmental impact statements.

Code of Federal Regulations, 2010 CFR

2010-04-01

... 23 Highways 1 2010-04-01 2010-04-01 false Final environmental impact statements. 771.125 Section... ENVIRONMENT ENVIRONMENTAL IMPACT AND RELATED PROCEDURES § 771.125 Final environmental impact statements. (a)(1..., economic, or environmental impacts of the action may need to be more fully explored; (iii) the impacts of...

Failure Wave in DEDF and Soda-Lime Glass During Rod Impact

NASA Astrophysics Data System (ADS)

Orphal, Dennis; Behner, Thilo; Anderson, Charles; Templeton, Douglas

2005-07-01

Investigations of glass by planar, and classical and symmetric Taylor impact experiments reveal that failure wave velocity U/F depends on impact velocity, geometry, and the type of glass. U/F typically increases with impact velocity to between ˜ 1.4 C/S and C/L (shear and longitudinal wave velocities, respectively). This paper reports the results of direct high-speed photographic measurements of the failure wave for gold rod impact from 1.2 and 2.0 km/s on DEDF glass (C/S = 2.0, C/L =3.5 km/s). The average rod penetration velocity, u, was measured using flash X-rays. Gold rods eliminated penetrator strength effects. U/F for gold rod impact on DEDF is ˜ 1.0-1.2 km/s, which is considerably less than C/S. The increase of u with impact velocity is greater than that of U/F. These results are confirmed by soda-lime glass impact on a gold rod at an impact velocity of 1300 m/s. Similar results are found in``edge-on-impact'' tests; U/F values of 1.4 km/s and 2.4-2.6 km/s in soda-lime glass are reported for W-alloy rod impact, considerably less than C/S (3.2 km/s) [1,2]. [1] Bless, et. al.(1990) AIP Proc. Shock Comp. Cond. Matter---1989, pp. 939-942 (1990) [2] E. L. Zilberbrand, et. al. (1999) Int. J. Impact Engng., 23, 995-1001 (1999).

Characterizing Verified Head Impacts in High School Girls' Lacrosse.

PubMed

Caswell, Shane V; Lincoln, Andrew E; Stone, Hannah; Kelshaw, Patricia; Putukian, Margot; Hepburn, Lisa; Higgins, Michael; Cortes, Nelson

2017-12-01

Girls' high school lacrosse players have higher rates of head and facial injuries than boys. Research indicates that these injuries are caused by stick, player, and ball contacts. Yet, no studies have characterized head impacts in girls' high school lacrosse. To characterize girls' high school lacrosse game-related impacts by frequency, magnitude, mechanism, player position, and game situation. Descriptive epidemiology study. Thirty-five female participants (mean age, 16.2 ± 1.2 years; mean height, 1.66 ± 0.05 m; mean weight, 61.2 ± 6.4 kg) volunteered during 28 games in the 2014 and 2015 lacrosse seasons. Participants wore impact sensors affixed to the right mastoid process before each game. All game-related impacts recorded by the sensors were verified using game video. Data were summarized for all verified impacts in terms of frequency, peak linear acceleration (PLA), and peak rotational acceleration (PRA). Descriptive statistics and impact rates were calculated. Fifty-eight verified game-related impacts ≥20 g were recorded (median PLA, 33.8 g; median PRA, 6151.1 rad/s 2 ) during 467 player-games. The impact rate for all game-related verified impacts was 0.12 per athlete-exposure (AE) (95% CI, 0.09-0.16), equivalent to 2.1 impacts per team game, indicating that each athlete suffered fewer than 2 head impacts per season ≥20 g. Of these impacts, 28 (48.3%) were confirmed to directly strike the head, corresponding with an impact rate of 0.05 per AE (95% CI, 0.00-0.10). Overall, midfielders (n = 28, 48.3%) sustained the most impacts, followed by defenders (n = 12, 20.7%), attackers (n = 11, 19.0%), and goalies (n = 7, 12.1%). Goalies demonstrated the highest median PLA and PRA (38.8 g and 8535.0 rad/s 2 , respectively). The most common impact mechanisms were contact with a stick (n = 25, 43.1%) and a player (n = 17, 29.3%), followed by the ball (n = 7, 12.1%) and the ground (n = 7, 12.1%). One hundred percent of ball impacts occurred to goalies. Most impacts occurred to field players within the attack area of the field (n = 32, 55.2%) or the midfield (n = 18, 31.0%). Most (95%) impacts did not result in a penalty. The incidence of verified head impacts in girls' high school lacrosse was quite low. Ball to head impacts were associated with the highest impact magnitudes. While stick and body contacts are illegal in girls' high school lacrosse, rarely did such impacts to the head result in a penalty. The verification of impact mechanisms using video review is critical to collect impact sensor data.

An Investigation of Community Attitudes Toward Blast Noise. General Community Survey, Study Site 1

DTIC Science & Technology

2012-04-01

1 1.1.1 Blast noise and community impact ...P. Holland. ERDC/CERL TR-12-9 1 1 Introduction 1.1 Background 1.1.1 Blast noise and community impact In the United States, the number of...decade, has heightened the potential for noise generated by US military installations to negatively impact surrounding communities. For many years

16 CFR 1.85 - Final environmental impact statements.

Code of Federal Regulations, 2010 CFR

2010-01-01

... 16 Commercial Practices 1 2010-01-01 2010-01-01 false Final environmental impact statements. 1.85... Final environmental impact statements. (a) After the close of the comment period, the Bureau responsible for the matter will consider the comments received on the draft environmental impact statement and...

16 CFR 1.84 - Draft environmental impact statements: Availability and comment.

Code of Federal Regulations, 2011 CFR

2011-01-01

... 16 Commercial Practices 1 2011-01-01 2011-01-01 false Draft environmental impact statements... Environmental Policy Act of 1969 § 1.84 Draft environmental impact statements: Availability and comment. Except for proposals for legislation, environmental impact statements shall be prepared in two stages: Draft...

16 CFR 1.84 - Draft environmental impact statements: Availability and comment.

Code of Federal Regulations, 2013 CFR

2013-01-01

... 16 Commercial Practices 1 2013-01-01 2013-01-01 false Draft environmental impact statements... Environmental Policy Act of 1969 § 1.84 Draft environmental impact statements: Availability and comment. Except for proposals for legislation, environmental impact statements shall be prepared in two stages: Draft...

16 CFR 1.84 - Draft environmental impact statements: Availability and comment.

Code of Federal Regulations, 2014 CFR

2014-01-01

... 16 Commercial Practices 1 2014-01-01 2014-01-01 false Draft environmental impact statements... Environmental Policy Act of 1969 § 1.84 Draft environmental impact statements: Availability and comment. Except for proposals for legislation, environmental impact statements shall be prepared in two stages: Draft...

16 CFR 1.84 - Draft environmental impact statements: Availability and comment.

Code of Federal Regulations, 2012 CFR

2012-01-01

... 16 Commercial Practices 1 2012-01-01 2012-01-01 false Draft environmental impact statements... Environmental Policy Act of 1969 § 1.84 Draft environmental impact statements: Availability and comment. Except for proposals for legislation, environmental impact statements shall be prepared in two stages: Draft...

16 CFR 1.84 - Draft environmental impact statements: Availability and comment.

Code of Federal Regulations, 2010 CFR

2010-01-01

... 16 Commercial Practices 1 2010-01-01 2010-01-01 false Draft environmental impact statements... Environmental Policy Act of 1969 § 1.84 Draft environmental impact statements: Availability and comment. Except for proposals for legislation, environmental impact statements shall be prepared in two stages: Draft...

47 CFR 1.1315 - The Draft Environmental Impact Statement (DEIS); Comments.

Code of Federal Regulations, 2014 CFR

2014-10-01

... 47 Telecommunication 1 2014-10-01 2014-10-01 false The Draft Environmental Impact Statement (DEIS); Comments. 1.1315 Section 1.1315 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL PRACTICE AND... § 1.1315 The Draft Environmental Impact Statement (DEIS); Comments. (a) The DEIS shall include: (1) A...

47 CFR 1.1315 - The Draft Environmental Impact Statement (DEIS); Comments.

Code of Federal Regulations, 2013 CFR

2013-10-01

... 47 Telecommunication 1 2013-10-01 2013-10-01 false The Draft Environmental Impact Statement (DEIS); Comments. 1.1315 Section 1.1315 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL PRACTICE AND... § 1.1315 The Draft Environmental Impact Statement (DEIS); Comments. (a) The DEIS shall include: (1) A...

47 CFR 1.1315 - The Draft Environmental Impact Statement (DEIS); Comments.

Code of Federal Regulations, 2012 CFR

2012-10-01

... 47 Telecommunication 1 2012-10-01 2012-10-01 false The Draft Environmental Impact Statement (DEIS); Comments. 1.1315 Section 1.1315 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL PRACTICE AND... § 1.1315 The Draft Environmental Impact Statement (DEIS); Comments. (a) The DEIS shall include: (1) A...

47 CFR 1.1315 - The Draft Environmental Impact Statement (DEIS); Comments.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 47 Telecommunication 1 2010-10-01 2010-10-01 false The Draft Environmental Impact Statement (DEIS... Environmental Impact Statement (DEIS); Comments. (a) The DEIS shall include: (1) A concise description of the... way to comment on the environmental impact of the facilities, a statement of his or her qualifications...

47 CFR 1.1308 - Consideration of environmental assessments (EAs); findings of no significant impact.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 1969 § 1.1308 Consideration of environmental assessments (EAs); findings of no significant impact. (a) Applicants shall prepare EAs for actions that may have a significant environmental impact (see § 1.1307). An...), that the proposal will have a significant environmental impact upon the quality of the human...

Preoperative immunonutrition suppresses perioperative inflammatory response in patients with major abdominal surgery-a randomized controlled pilot study.

PubMed

Giger, Urs; Büchler, Markus; Farhadi, Jian; Berger, Dieter; Hüsler, Jürg; Schneider, Heinz; Krähenbühl, Stephan; Krähenbühl, Lukas

2007-10-01

Perioperative administration of immunoenriched diets attenuates the perioperative inflammatory response and reduces postoperative infection complications. However, many questions still remain unresolved in this area, such as the length of diet administration, diet composition, and the mechanisms involved. We performed an open, randomized, triple-arm study comparing the effect of two perioperative feeding regimens with a postoperative one. 46 candidates for major elective surgery for malignancy in the upper gastrointestinal tract were randomized to drink preoperatively either 1 L of an immunoenriched formula (Impact) for 5 days (IEF group) or 1 L of Impact plus (Impact enriched with glycine) for 2 days (IEF plus group). The same product as the patient received preoperatively was given to both groups for 7 days postoperatively. In the control group (CON group), patients only received Impact for 7 days postoperatively; there was no preoperative treatment. The main outcome measures were postoperative C-reactive protein (CRP) serum levels. In the two preoperatively supplemented groups (treatment groups), perioperative endotoxin levels, CRP (postoperative day 7), and TNF-alpha (postoperative days 1 and 3) levels were significantly lower compared to the CON group (p < .01). Furthermore, the length of postoperative IMU/ICU stay (Impact 1.9 +/- 1.3 days; Impact plus 2.2 +/- 1.1 days; control group 5.9 +/- 0.8 days) and length of hospital stay (Impact 19.7 +/- 2.3 days; Impact plus 20.1 +/- 1.3 days; control group 29.1 +/- 3.6 days) were both reduced in the treatment groups compared to the control group. Infectious complications (Impact 2/14 (14%); Impact plus 5/17 (29%); control group 10/15 (67%)) also showed a trend toward reduction in the treatment groups. Perioperative administration of an immunoenriched diet significantly reduces systemic perioperative inflammation and postoperative complications in patients undergoing major abdominal cancer surgery, when compared with postoperative diet administration alone. A shortened preoperative feeding regimen of 2 days with Impact enriched with glycine (Impact plus) was as effective as Impact administered for 5 days preoperatively.

48 CFR 30.606 - Resolving cost impacts.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 48 Federal Acquisition Regulations System 1 2010-10-01 2010-10-01 false Resolving cost impacts. 30... impacts. (a) General. (1) The CFAO shall coordinate with the affected contracting officers before negotiating and resolving the cost impact when the estimated cost impact on any of their contracts is at least...

Severe injury in multiple impacts: Analysis of 1997-2015 NASS-CDS.

PubMed

Viano, David C; Parenteau, Chantal S

2018-07-04

This is a descriptive study of the incidence and risk for severe injury in single-impact and multi-impact crashes by belt use and crash type using NASS-CDS. 1997-2015 NASS-CDS data were used to determine the distribution of crashes by the number of impacts and severe injury (Maximum Abbreviated Injury Score [MAIS] 4+F) to >15-year-old nonejected drivers by seat belt use in 1997+ MY vehicles. It compares the risk for severe injury in a single impact and in crashes involving 2, 3, or 4+ impacts in the collision with a focus on a frontal crash followed by other impacts. Most vehicle crashes involve a single impact (75.4% of 44,889,518 vehicles), followed by 2-impact crashes (19.6%), 3-impact crashes (5.0%) and 4+ impacts (2.6%). For lap-shoulder-belted drivers, the distribution of severe injury was 42.1% in a single impact, 29.3% in 2 impacts, 13.4% in 3 impacts, and 15.1% in 4+ impact crashes. The risk for a belted driver was 0.256 ± 0.031% in a single impact, 0.564 ± 0.079% in 2 impacts, 0.880 ± 0.125% in 3 impacts, and 2.121 ± 0.646% in 4+ impact. The increase in risk from a single crash to multi-impact collisions was statistically significant (P < .001). In a single impact, 53.8% of belted drivers were in a frontal crashes, 22.4% in side crashes, 20% in rear crashes, and 1.7% in rollover crashes. The risk for severe injury was highest in a rollover at 0.677 ± 0.250%, followed by near-side impact at 0.467 ± 0.084% and far-side impact at 0.237 ± 0.071%. Seat belt use was 82.4% effective in preventing severe injury (MAIS 4+F) in a rollover, 47.9% in a near-side impact, and 74.8% in a far-side impact. In 2-impact crashes with a belted driver, the most common sequence was a rear impact followed by a frontal crash at 1,843,506 (21.5%) with a risk for severe injury of 0.100 ± 0.058%. The second most common was a frontal impact followed by another frontal crash at 1,257,264 (14.7%) with a risk of 0.401 ± 0.057%. The risk was 0.658 ± 0.271% in a frontal impact followed by a rear impact. A near-side impact followed by a rear crash had the highest risk for severe injury at 2.073 ± 1.322%. Restraint systems are generally developed for a single crash or sled test. The risk for severe injury was significantly higher in 2-, 3-, and 4+-impact crashes than a single impact. The majority (57.9%) of severe injuries occurred in multi-impact crashes with belted drivers. The evaluation of restraint performance warrants additional study in multi-impact crashes.

An Investigation of the Ecological and Social Impacts Caused by Rock Climbers.

ERIC Educational Resources Information Center

Attarian, Aram

This study examined the ecological and social impacts of rock climbing. The survey included climbing sites in 10 federal areas, 2 state parks, 1 private area, and 1 city park. Resource managers provided information on the observed impacts of rock climbing and current management practices to minimize impacts. Survey results indicate: (1) 71 percent…

Impact strength of small icy bodies that experienced multiple collisions

NASA Astrophysics Data System (ADS)

Yasui, Minami; Hayama, Ryo; Arakawa, Masahiko

2014-05-01

Frequent collisions are common for small bodies in the Solar System, and the cumulative damage to these bodies is thought to significantly affect their evolution. It is important to study the effects of multiple impacts such as the number of impacts on the impact strength and the ejection velocity of impact fragments. Here we conducted multiple-impact experiments using a polycrystalline water ice target, varying the number of impacts from 1 to 10 times. An ice cylindrical projectile was impacted at 84-502 m s-1 by using a single-stage gas gun in a cold room between -10 and -15 °C. The impact strength of the ice target that experienced a single impact and multiple impacts is expressed by the total energy density applied to the same target, ΣQ, and this value was observed to be 77.6 J kg-1. The number of fine impact fragments at a fragment mass normalized by an initial target mass, m/Mt0 ∼ 10-6, nm, had a good correlation with the single energy density at each shot, Qj, and the relationship was shown to be nm=10·Qj1.31±0.12. We also estimated the cumulative damage of icy bodies as a total energy density accumulated by past impacts, according to the crater scaling laws proposed by Housen et al. (Housen, K.R., Schmidt, R.M., Holsapple, K.A. [1983]. J. Geophys. Res. 88, 2485-2499) of ice and the crater size distributions observed on Phoebe, a saturnian icy satellite. We found that the cumulative damage of Phoebe depended significantly on the impact speed of the impactor that formed the craters on Phoebe; and the cumulative damage was about one-third of the impact strength ΣQ* at 500 m s-1 whereas it was almost zero at 3.2 km s-1.

Impact of type 1 diabetes mellitus on the family is reduced with the medical home, care coordination, and family-centered care.

PubMed

Katz, Michelle L; Laffel, Lori M; Perrin, James M; Kuhlthau, Karen

2012-05-01

To examine whether the medical home, care coordination, or family-centered care was associated with less impact of type 1 diabetes mellitus (T1D) on families' work, finances, time, and school attendance. With the 2005 to 2006 National Survey of Children with Special Health Care Needs, we compared impact in children with T1D (n = 583) with that in children with other special health care needs (n = 39 944) and children without special health care needs (n = 4945). We modeled the associations of the medical home, care coordination, and family-centered care with family impact in T1D. Seventy-five percent of families of children with T1D reported a major impact compared with 45% of families of children with special health care needs (P < .0001) and 17% of families of children without special health care needs (P < .0001). In families of children with T1D, 35% reported restricting work, 38% reported financial impact, 41% reported medical expenses >$1000/year, 24% reported spending ≥11 hours/week caring or coordination care, and 20% reported ≥11 school absences/year. The medical home, care coordination, and family-centered care were associated with less work and financial impact. In childhood T1D, most families experience major impact. Better systems of health care delivery may help families reduce some of this impact. Copyright © 2012 Mosby, Inc. All rights reserved.

General Reevaluation Report for Flood Control Project: Raccoon River and Walnut Creek, West Des Moines-Des Moines, Iowa with Final Supplement Number 1 to the Final Environmental Impact Statement

DTIC Science & Technology

1989-07-01

to the FINAL ENVIRONMENTAL IMPACT STATEMENT D T C EIECTE SMAR 1 41990 US Army Corps of Engineers Rock Island District JULY 1989 S03� 1601...SUPPLEMENT NO. 1 TO THE FINAL ENVIRONMENTAL IMPACT STATEMENT NTIS z ITIC Av’, < , r Dist JULY 1989 TECHNICAL CONTRIBUTORS Primary study team personnel who are...AND COMMENTS 45 SECTION 6 - RECOMMENDATIONS 46 List of Tables No. Title Page 1 Impacts of Levee on Raccoon River Profiles 20 2 Impacts of Levee on

47 CFR 1.1319 - Consideration of the environmental impact statements.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 47 Telecommunication 1 2010-10-01 2010-10-01 false Consideration of the environmental impact... PROCEDURE Procedures Implementing the National Environmental Policy Act of 1969 § 1.1319 Consideration of the environmental impact statements. (a) If the action is subject to a hearing: (1) In rendering his...

Food impaction after expandable metal stent placement: experience in 1,360 patients with esophageal and upper gastrointestinal tract obstruction.

PubMed

Song, Min; Song, Ho-Young; Kim, Jin Hyoung; Park, Jung-Hoon; Jung, Hwoon-Yong; Kim, Jong-Hoon; Kim, Sung-Bae

2011-09-01

To retrospectively evaluate the incidence, predictive factors, and interventional management of food impaction after expandable metallic stent placement in patients with obstruction of the esophagus or upper gastrointestinal tract caused by benign or malignant disease. Between March 1993 and March 2010, 1,360 patients (1,029 men, 331 women; age range, 21-89 y; mean age, 61 y) underwent fluoroscopically guided stent placement for dysphagia caused by esophageal or gastrointestinal tract strictures. Five types of covered expandable metal stents were used, including four types of esophageal stents (types A-D) and one type of gastroduodenal stent (type E), with types A, B, C, D, and E stents used in 180, 60, 90, 432, and 598 patients, respectively. Multivariate analysis was performed to evaluate factors predictive of food impaction. Food impaction occurred in 41 of 1,360 patients (3.0%). The food impaction rates for types A, B, C, D, and E stents were 0.6%, 1.7%, 1.1%, 3.2%, and 4.0%, respectively. Multivariate analysis showed that stent length was an independent predictor of food impaction (odds ratio, 0.839; P = .012). Of the 41 patients with food impaction, 23 underwent endoscopic management, 12 underwent fluoroscopically guided management, and six did not require management because impacted food spontaneously passed through the stent. The overall food impaction rate was 3.0%, with multiple logistic regression analysis showing that shorter stent length was the only significant predictor of food impaction. Food impaction can be managed by endoscopic or fluoroscopically guided removal or placement of a second stent. Copyright © 2011 SIR. Published by Elsevier Inc. All rights reserved.

Draft Environmental Impact Statement: Peacekeeper Rail Garrison Program

DTIC Science & Technology

1988-06-01

2-13 3.0 ENVIRONMENTAL ANALYSIS METHODS ................................ 3-1 3.1 Methods for Assessing Nationwide Impacts...3-2 3.1.1 Methods for Assessing National Economic Impacts ........... 3-2 3.1.2 Methods for Assessing Railroad Network...3.2.4 Methods for Assessing Existing and Future Baseline Conditions .......................................... 3-6 3.2.5 Methods for Assessing

Defining the impaction frequency and threshold force required for femoral impaction grafting in revision hip arthroplasty

PubMed Central

2011-01-01

Background and purpose The two most common complications of femoral impaction bone grafting are femoral fracture and massive implant subsidence. We investigated fracture forces and implant subsidence rates in embalmed human femurs undergoing impaction grafting. The study consisted of two arms, the first examining the force at which femoral fracture occurs in the embalmed human femur, and the second examining whether significant graft implant/subsidence occurs following impaction at a set force at two different impaction frequencies. Methods Using a standardized impaction grafting technique with modifications, an initial group of 17 femurs underwent complete destructive impaction testing, allowing sequentially increased, controlled impaction forces to be applied until femoral fracture occurred. A second group of 8 femurs underwent impaction bone grafting at constant force, at an impaction frequency of 1 Hz or 10 Hz. An Exeter stem was cemented into the neomedullary canals. These constructs underwent subsidence testing simulating the first 2 months of postoperative weight bearing. Results No femurs fractured below an impaction force of 0.5 kN. 15/17 of the femurs fractured at or above 1.6 kN of applied force. In the second group of 8 femurs, all of which underwent femoral impaction grafting at 1.6 kN, there was no correlation between implant subsidence and frequency of impaction. Average subsidence was 3.2 (1–9) mm. Interpretation It is possible to calculate a force below which no fracture occurs in the embalmed human femur undergoing impaction grafting. Higher impaction frequency at constant force did not reduce rates of implant subsidence in this experiment. PMID:21689068

Evaluating impact level of different factors in environmental impact assessment for incinerator plants using GM (1, N) model.

PubMed

Pai, T Y; Chiou, R J; Wen, H H

2008-01-01

In this study, the impact levels in environmental impact assessment (EIA) reports of 10 incinerator plants were quantified and discussed. The relationship between the quantified impact levels and the plant scale factors of BeiTou, LiZe, BaLi, LuTsao, RenWu, PingTung, SiJhou and HsinChu were constructed, and the impact levels of the GangShan (GS) and YongKong (YK) plants were predicted using grey model GM (1, N). Finally, the effects of plant scale factors on impact levels were evaluated using grey model GM (1, N) too. According to the predicted results of GM, the relative errors of topography/geology/soil, air quality, hydrology/water quality, solid waste, noise, terrestrial fauna/flora, aquatic fauna/flora and traffic in the GS plant were 17%, 14%, 15%, 17%, 75%, 16%, 13%, and 37%, respectively. The relative errors of the same environmental items in the YK plant were 1%, 18%, 10%, 40%, 37%, 3%, 25% and 33%, respectively. According to GM (1, N), design capacity (DC) and heat value (HV) were the plant scale factors that affected the impact levels significantly in each environmental item, and thus were the most significant plant scale factors. GM (1, N) was effective in predicting the environmental impact and analyzing the reasonableness of the impact. If there is an EIA for a new incinerator plant to be reviewed in the future, the official committee of the Taiwan EPA could review the reasonableness of impact levels in EIA reports quickly.

Metastable Oxygen Production by Electron-Impact of Oxygen

NASA Astrophysics Data System (ADS)

Hein, Jeffrey; Johnson, Paul; Kanik, Isik; Malone, Charles

2014-05-01

Electron-impact excitation processes involving atomic and molecular oxygen are important in atmospheric interactions. The production of long-lived metastable O(1S) and O(1D) through electron impact of atomic O and molecular O2 play a significant role in the dynamics of oxygen-containing atmospheres (Earth, Europa, Io). Emissions from metastable O (1S --> 1D) produce the well-recognized green light from terrestrial aurora. Electron-impact excitation to 1S and 1D are sensitive channels for determining energy partitioning and dynamics from space weather. Electron-impact excitation cross sections determined through fundamental experimental studies are necessary for modeling of natural phenomena and observation data. The detection of metastable states in laboratory experiments requires a novel approach, since typical detection techniques (e.g., fluorescence by radiative de-excitation) cannot be performed due to the long-lived nature of the excited species. In this work, metastable O is produced through electron impact, and is incident on a cryogenically cooled rare gas matrix. The excimer production and subsequent rapid radiative de-excitation provides measurable signal that is directly related to the originating electron-impact excitation process.

22 CFR 216.7 - Environmental impact statements.

Code of Federal Regulations, 2011 CFR

2011-04-01

... 22 Foreign Relations 1 2011-04-01 2011-04-01 false Environmental impact statements. 216.7 Section... Environmental impact statements. (a) Applicability. An Environmental Impact Statement shall be prepared when agency actions significantly affect: (1) The global environment or areas outside the jurisdiction of any...

23 CFR 771.130 - Supplemental environmental impact statements.

Code of Federal Regulations, 2011 CFR

2011-04-01

... 23 Highways 1 2011-04-01 2011-04-01 false Supplemental environmental impact statements. 771.130... ENVIRONMENT ENVIRONMENTAL IMPACT AND RELATED PROCEDURES § 771.130 Supplemental environmental impact statements... supplemented whenever the Administration determines that: (1) Changes to the proposed action would result in...

Effects of Friction and Plastic Deformation in Shock-Comminuted Damaged Rocks on Impact Heating

NASA Astrophysics Data System (ADS)

Kurosawa, Kosuke; Genda, Hidenori

2018-01-01

Hypervelocity impacts cause significant heating of planetary bodies. Such events are recorded by a reset of 40Ar-36Ar ages and/or impact melts. Here we investigate the influence of friction and plastic deformation in shock-generated comminuted rocks on the degree of impact heating using the iSALE shock-physics code. We demonstrate that conversion from kinetic to internal energy in the targets with strength occurs during pressure release, and additional heating becomes significant for low-velocity impacts (<10 km s-1). This additional heat reduces the impact-velocity thresholds required to heat the targets with the 0.1 projectile mass to temperatures for the onset of Ar loss and melting from 8 and 10 km s-1, respectively, for strengthless rocks to 2 and 6 km s-1 for typical rocks. Our results suggest that the impact conditions required to produce the unique features caused by impact heating span a much wider range than previously thought.

16 CFR Figure 1 to Subpart A of... - Glass Impact Test Structure

Code of Federal Regulations, 2011 CFR

2011-01-01

... 16 Commercial Practices 2 2011-01-01 2011-01-01 false Glass Impact Test Structure 1 Figure 1 to Subpart A of Part 1201 Commercial Practices CONSUMER PRODUCT SAFETY COMMISSION CONSUMER PRODUCT SAFETY ACT... 1 to Subpart A of Part 1201—Glass Impact Test Structure EC03OC91.004 ...

16 CFR Figure 1 to Subpart A of... - Glass Impact Test Structure

Code of Federal Regulations, 2010 CFR

2010-01-01

... 16 Commercial Practices 2 2010-01-01 2010-01-01 false Glass Impact Test Structure 1 Figure 1 to Subpart A of Part 1201 Commercial Practices CONSUMER PRODUCT SAFETY COMMISSION CONSUMER PRODUCT SAFETY ACT... 1 to Subpart A of Part 1201—Glass Impact Test Structure EC03OC91.004 ...

Hypervelocity Impact (HVI). Volume 2; WLE Small-Scale Fiberglass Panel Flat Multi-Layer Targets A-1, A-2, and B-1

NASA Technical Reports Server (NTRS)

Gorman, Michael R.; Ziola, Steven M.

2007-01-01

During 2003 and 2004, the Johnson Space Center's White Sands Testing Facility in Las Cruces, New Mexico conducted hypervelocity impact tests on the space shuttle wing leading edge. Hypervelocity impact tests were conducted to determine if Micro-Meteoroid/Orbital Debris impacts could be reliably detected and located using simple passive ultrasonic methods. The objective of Targets A-1, A-2, and B-2 was to study hypervelocity impacts through multi-layered panels simulating Whipple shields on spacecraft. Impact damage was detected using lightweight, low power instrumentation capable of being used in flight.

Final Environmental Assessment: Replace Hanscom AFB Middle School

DTIC Science & Technology

2012-04-01

term impacts on wastewater facilities are anticipated during the demolition/construction of the Middle School. Portable toilets may be available for...7.14. CUMULATIVE IMPACTS 7-18 SECTION 8. MEASURES TO REDUCE POTENTIAL FOR IMPACT 8-1 SECTION 9. CONSULTATION LETTERS, EMAILS, AND PUBLIC NOTICE 9-1...U.S. Air Force April 2012 1 FINDING OF NO SIGNIFICANT IMPACT Name of Action: Replace Hanscom AFB Middle School Hanscom Air Force Base

Energy attenuation performance of impact protection worn by motorcyclists in real-world crashes.

PubMed

Albanese, Bianca; Gibson, Tom; Whyte, Tom; Meredith, Lauren; Savino, Giovanni; de Rome, Liz; Baldock, Matthew; Fitzharris, Michael; Brown, Julie

2017-05-29

Laboratory studies have demonstrated that impact protectors (IP) used in motorcycle clothing can reduce fracture severities. While crash studies have reported IP are associated with reduced likelihood of soft tissue injury, there is little evidence of their effectiveness in reducing fracture likelihood. This discrepancy might be related to IP quality. There are mandatory requirements for IP supplied with protective clothing in Europe, but not elsewhere. This study examines the energy attenuation performance of IP used by Australian riders. IP were harvested from clothing worn by crashed riders admitted to hospital. The IP were examined and energy attenuation properties were determined using EN 1621-1 test procedures. Impact injury was identified from medical records and defined as fractures, dislocations, and avulsions that occurred following impact to the rider's shoulders, elbows, hips, and/or knees. Fisher's exact test was used to examine the relationship between meeting the EN 1621-1 energy attenuation requirements and impact injury. The association between the average and maximum transmitted force, and impact injury was examined using generalized estimating equations. Motorcycle riders were recruited as part of an in-depth crash study through three hospitals in New South Wales, Australia, between 2012 and 2014. Riders were interviewed, and engineers conducted site, vehicle, and clothing inspections. Clothing was collected, or identical garments were purchased. Clothing was inspected for 62 riders. Of these, 19 wore clothing incorporating 76 IP. Twenty-six of these were impacted in the crash event. Almost all impacted IP (96%) were CE marked, and most (83%) met Level 1 energy attenuation requirements of EN 1621-1 when tested. Of the 26 impacted IP, four were associated with impact injuries, including midshaft and distal clavicle fractures and a scapula and olecranon fracture. No associations between meeting EN 1621-1 requirements and impact injury were found (p = 0.5). There was no association between average force transmitted and impact injury (95% CI: 0.91-1.24); however, as maximum force transmitted increased, the odds of impact injury increased (95% CI: 1.01-1.2). These results indicate a high probability of impact injury at 50 kN, the limit of maximum transmitted force specified in EN 1621-1. The allowable transmitted force of EN 1621-1 may be too high to effectively reduce the probability of impact injury. This is not surprising, given human tolerance levels that are reported in literature. Reducing the force limit below the reported fracture tolerance limits might be difficult with current technology. However, there is scope to reduce the EN 1621-1 maximum limit of 50 kN transmitted force. A reduction in the maximum force limit would improve rider protection and appears feasible, as 77% of tested IP recorded a maximum force <35 kN. This level of transmitted force is estimated to be associated with <20% probability of impact injury. While the performance of IP available to Australian riders is not regulated, most IP was CE marked. The results indicate a significant association between maximum transmitted force, tested according to EN 1621-1 procedures, and impact injury. Further investigation of the EN 1621-1 requirements may be warranted. This work will interest those targeting protective equipment for motorcyclists as a mechanism for reducing injury to these vulnerable road users.

Tool for the Reduction and Assessment of Chemical and Other Environmental Impacts (TRACI) TRACI version 2.1 User’s Guide

EPA Science Inventory

TRACI 2.1 (the Tool for the Reduction and Assessment of Chemical and other environmental Impacts) has been developed for sustainability metrics, life cycle impact assessment, industrial ecology, and process design impact assessment for developing increasingly sustainable products...

Ejecta emplacement: from distal to proximal

NASA Astrophysics Data System (ADS)

Artemieva, N.

2008-09-01

Introduction Most part of impact ejecta is deposited ballistically at some distance from a crater, defined by ejection velocity V and ejection angle α: d=v2sinα/g. In case of giant impacts, planetary curvature should be taken into account [1]. Combined with ejecta scaling [2], these relations allow to define ejecta thickness as a function of distance. Ejecta from large craters are deposited at velocity high enough to mobilize substrate material and to thicken ejecta deposits [3]. Ballistic approximation is valid for airless bodies (if impact vaporization is not vast) or for proximal ejecta of large impact craters, where ejecta mass per unit area is substantially greater than the mass of involved vapor/atmosphere (M-ratio). Deposition of distal ejecta, in which ejecta mass is negligible compared to the atmosphere, may be also treated in a simplified manner, i.e. as 1) passive motion of ejected particles within an impact plume and 2) later, as sedimentation of particles in undisturbed atmosphere (equilibrium between gravity and drag). In all intermediate M-ratio values, impact ejecta move like a surge, i.e. dilute suspension current in which particles are carried in turbulent flows under the influence of gravity. Surges are well-known for near-surface explosive tests, described in detail for volcanic explosions (Plinian column collapse, phreato-magmatic eruption, lateral blast), and found in ejecta from the Chicxulub [4] and the Ries [5]. Important aspects of surge transport include its ability to deposit ejecta over a larger area than that typical of continuous ballistic ejecta and to create multiple ejecta layers. Numerical model Two-phase hydrodynamics. Surges should be modeled in the frame of two-phase hydrodynamics, i.e. interaction between solid/molten particles and atmospheric gas/impact vapor should be taken into account. There are two techniques of solving equations for dust particle motion in a gas flow. The first one describes solid/molten particles as a liquid with specific properties, i.e. finite-difference equations are the same as in standard hydrodynamics [6-8]. Another approach is based on solving equations of motion for representative particles [9]. Each of these markers describes the motion of a large number of real particles with similar sizes, velocities, and trajectories. Equation of motion (gravity, viscosity, and drag) is solved for every marker and then exchange of momentum, heat and energy with surrounding vaporair mixture is taken into account. This approach is used in the SOVA code [10] and allows to vary particle sizes within a broad range (from a few m to a few microns). Implicit procedure of velocity update allows a larger time step. The substantial advantage of the model is its three-dimensional geometry, allowing modeling of asymmetric deposits of oblique impact ejecta. Turbulent diffusion is taken into account in a simplified manner [6]. Fragments size-frequency distribution (SFD) may be of crucial importance: while large fragments move ballistically, the smallest ones are passively involved in gas motion. Ejected material is usually transformed into particles under tension. The initial particle velocity is given by the hydrodynamic velocity, but the object's initial position within the cell is randomly defined. The SFD of solid fragments in high velocity impacts has been studied experimentally [2,11], numerically [12,13], and has been derived from the lunar and terrestrial crater observations [14,15]. Various approaches may be used to implement fragment size in a dynamic model: in Grady-Kipp model the average fragment size is defined by strain rate [12]; alternatively, average ejection velocity [16] or maximum shock compression [17] may be used. All methods may be verified through comparison with known data. Volcanic direct blast. Numerical modeling of pyroclastic flows, checked against recent observations and young deposits, may be then a useful instrument for reconstruction of terrestrial craters' ejecta, which are mostly eroded or buried; and for impact ejecta study on other planets (first of all - on Mars), where remote sensing data are still the only source of our knowledge. In volcanology typical velocities are usually below 300 m/s, temperatures may be as low as 300 K (wet surge) and not higher than 1000 K (dry surge), solid/gas mass ratio ranges between 5-50, particle size rarely exceeds several cm, while the mass fraction of fine micronsized particles is usually poorly defined. Modeling results (thickness and spatial distribution of pyroclastics) are in reasonable agreement with observations of direct blast at Bezymianny volcano (Kamchatka, Russia) in 1956. Crater ejecta - the Ries crater in Germany. Impact ejecta parameters vary in a substantially wider range: distal ejecta velocities reach several km/s, km-sized fragments are typical for large craters, gas content may be high enough for cratering in volatile rich (or water-covered) target or in the presence of a dense atmosphere. Moldavites.. The Ries impact site is characterized by a thick sedimentary layer, from which a large amount of vapor (e.g., CO2) is shock-released. This vapor contributes to the ejected particles acceleration, or at least, to the sustainment of their motion. The initial ejection velocities of material are rather high, up to 10 km/s, which are close to the velocity of the expanding gas. As a result, the particles are not subject to high dynamic pressures that otherwise would disrupt them into fine mist immediately after ejection. The temperature of the entraining gas is rather high, so the particles do not cool quickly during the flight, allowing enough time to have them aerodynamically shaped (typical for tektites), and to lose volatiles [18,19]. Tektites are distributed up to 400-500 km away from the impact, in a fan of ˜75° symmetrically distributed with respect to the downrange direction. Bunte Breccia and fallout Suevite in Otting (Ries crater). The total amount of ejected material is about 160 km3 (with an average sediment/basement proportion of 3:1). The maximum ejection velocity for crystalline rocks does not exceed 1 km/s. There are no basement ejecta in the uprange direction. Ejecta deposited within a ring of 16-18 km radius (similar to the position of the Otting site) have a deposition velocity of ~350 m/s. This velocity allows substantial reworking of ejecta and mixing with target rocks. Otting ejecta consist of a sediment /basement rock mixture. The average shock compression of basement rocks is at least 4 times higher than in sediments for any azimuthal angle (16 GPa versus 4 GPa). Ejecta thickness (tens of m) is in a reasonable agreement with observations. However, our modeling results relevant to ballistic deposition do not allow to reproduce the observed ejecta in the suevite layer of Otting: 1) there is just very little melt in the modeled ejecta and 2) separation of sedimentary rocks from basement rocks (i.e. Bunte Breccia and fallout suevite) does not occur. Separation and gradation of ejected particles by atmosphere (fallout) seems improbable as the total ejecta mass per unit area at these distances is substantially higher than the mass of the involved atmosphere. Deposition of a suevitic layer as a viscous flow [20] seems also improbable, as viscosity of the flow with solid fragments (i.e. with temperature below the solidus) increases dramatically and prevents spreading to a few km from the transient cavity. We need another mechanism of the ejecta flow "fluidization". One possibility is a gas release (mainly water vapor from sediments) which allows dispersal of the smallest particles and suevite deposition above the ballistically deposited Bunte Breccia (similar to pyroclastic surges). Applications for planets Mars. Several attempts have been made to quantitatively describe the process of ejecta emplacement in formation of ramparts [21-25]. They dealt mainly with propagation of fluidized ejecta initially deposited ballistically and included rheologic models for Newtonian or Bingham materials based on observations (runout distance, height of the distal ridge). Our model establishes better initial conditions for ejecta flow formation and provide estimates for the properties of fluidized ejecta directly on the basis of the particles/gas ratio, particle size, and temperaturedensity conditions in the ejecta. Venus. Ejecta deposition on Venus is substantially non-ballistic due to thick Venusian atmosphere. Some of impact craters are surrounded by "dark halos" [26- 28], others have unique dark parabolas, representing surficial deposits of loose material lifted during crater formation [29-30]. Methods of two-phase hydrodynamics may be useful to describe mechanism of their formation. References [1] Dobrovolskis A. (1981) Icarus 47, 203-219. [2] Cintala M.J., et al. (1999) M&PS. 34, 605-623. [3] Oberbeck V.R. (1975) Rev. Geophys. Space Phys. 13, 337-362. [4] Dressler et al. (2004) M&PS 39, 857- 878. [5] Hörz F. et al. (1983) Rev Geophys.Space Phys. 21, 1667-1725. [6] Valentine G.A. and Wohletz K.H. (1989) JGR 94, 1867-1887. [7] Dobran F. and Neri A. (1993) JGR 98, 4231-4259. [8] Neri A. et al. (2003) JGR 108, doi:10.1029/ 2001JB000508. [9] Boothroyd R.G. (1971) Flowing gas-solids suspension, Chapman and Hall Ltd, London. [10] Shuvalov V.V. (1999) Shock waves 9, 381-390. [11] Nakamura A. and Fujiwara A. (1991) Icarus 92, 132- 146. [12] Grady D.E. and Kipp M.E. (1980) Int. J. Rock Mech. Min. Sci. Geomech. Abstr. 17, 147-157. [13] Melosh H.J. et al. (1992) JGR 97, 14735-14759. [14] Gault, D.E. et al. (1963) NASA TND-1767. [15] Vickery A.M. (1986) Icarus 67, 224-236. [16] Melosh H.J. (1984) Icarus 59, 234-260. [17] Shuvalov V.V. (2002) LPSC-33, abstr.#1259. [18] Stöffler et al. (2002) M&PS 37, 1893-1908. [19] Melosh H.J. and Artemieva N.A. (2004) LPSC-35, abstr. #1723. [20] Osinski et al. (2004) Meteoritics Planet. Sci. 39, 1655-1683. [21] Ivanov B.A. et al. (1997) LPSC 28, 637-638. [22] Garvin J.B., Baloga S.M. (1999) LPSC 30, Abst. #1735. [23] Fagents S.A. et al. (2005) LPSC 36, Abst. #2127. [24] Baratoux D. et al. (2002) GRL 29(8), 1210, 10.1029/ 2001GL012779. [25] Barnouin-Jha O.S. and Schultz P.H. (1998) JGR 103(E11), 25,739-25,756. [26] Phillips R,J, et al. (1991) Science 252, 288-297. [27] Ivanov B. et al. (1992) JGR 97, 16,167-181. [28] Takata T. et al. (1995) JGR 100, 23,329-348. [29] Campbell D. et al. (1992) JGR 97, 16,249-277. [30] Bondarenko N.V. and Head J.W. (2004) JGR 109, doi 10.1029/2004JE002256.

National Software Capacity: Near-Term Study

DTIC Science & Technology

1990-05-01

Productivity Gains 17 2. Labor Markets and Human Resource Impacts on Capacity 21 2.1. Career Ladders 21 2.1.1. Industry 21 2.1.2. Civil Service 22 2.1.3...Inflows to and Outflows from Computer-Related Jobs 29 2.3.2. Inflows to and Outflows from the DoD Industrial Contractors 31 3. Major Impacts of Other...Factors on Capacity: 35 A Systems View 3.1. Organizational Impacts on Capacity 35 3.1.1. Requirements Specification and Changes 35 3.1.2. The Contracting

Impaction of permanent mandibular second molar: A retrospective study

PubMed Central

Altieri, Federica; Di Mambro, Alfonso; Galluccio, Gabriella; Barbato, Ersilia

2013-01-01

Objective: To determine the prevalence of impacted mandibular second molar (MM2) and the association between MM2 impaction and crowding. The clinical significance of the angle between first and second mandibular molar and of the space between the first mandibular molar (MM1) and the anterior margin of mandibular ramus in MM2 impaction were also evaluated. Material and Methods: In this retrospective study , from the dental records of 2,945 caucasian young orthodontics patients, 40 subjects with MM2 impaction were included in a study group (SG) and compared with a control group (CG) of 200 subjects without MM2 impactions. The crowding, the angle of inclination of MM2, the distance between MM1 and mandibular ramus, the canine and molar relationships, and the lower centre line discrepancy were measured. For the statistical analysis , descriptive statistics and t-Student for independent sample groups were used. Results: The prevalence of impacted MM2 was 1.36%. The independent-Samples t-Test between SG and CG showed: the presence of crowding (P≤0.001), an higher angle values of MM2 inclination (P≤0.001) and a smaller distance between MM1 and the anterior margin of mandibular ramus (P≤0.001) in the SG. Conclusion: The impaction of MM2 is a relatively rare occurrence in orthodontic caucasian populations. The crowding, a higher angle values of MM2 inclination and a reduced distance between MM1 and the anterior margin of mandibular ramus, at the time of one third of MM2 root formation (T1), characterize MM2 impaction. Key words:Impacted mandibular second molar, impaction, orthodontics. PMID:23524438

Dynamical Origin and Terrestrial Impact Flux of Large Near-Earth Asteroids

NASA Astrophysics Data System (ADS)

Nesvorný, David; Roig, Fernando

2018-01-01

Dynamical models of the asteroid delivery from the main belt suggest that the current impact flux of diameter D> 10 km asteroids on the Earth is ≃0.5–1 Gyr‑1. Studies of the Near-Earth Asteroid (NEA) population find a much higher flux, with ≃ 7 D> 10 km asteroid impacts per Gyr. Here we show that this problem is rooted in the application of impact probability of small NEAs (≃1.5 Gyr‑1 per object), whose population is well characterized, to large NEAs. In reality, large NEAs evolve from the main belt by different escape routes, have a different orbital distribution, and lower impact probabilities (0.8 ± 0.3 Gyr‑1 per object) than small NEAs. In addition, we find that the current population of two D> 10 km NEAs (Ganymed and Eros) is a slight fluctuation over the long-term average of 1.1+/- 0.5 D> 10 km NEAs in a steady state. These results have important implications for our understanding of the occurrence of the K/T-scale impacts on the terrestrial worlds.

Impact of the Internet on Customer Service and Product Development Among the CENDI Agencies

DTIC Science & Technology

1997-08-01

CENDI / 97-2 IMPACT OF THE INTERNET ON CUSTOMER SERVICE AND PRODUCT DEVELOPMENT AMONG THE CENDI AGENCIES Workshops Held February 4, 1997 and...Public Release Distribution Unlimited 20000411 146 CENDI / 97-2 CENDI WORKSHOP ~ FEBRUARY 4,1997 AT DOE THE IMPACT OF THE INTERNET ON CUSTOMER ...priorities. TABLE OF CONTENTS EXECUTIVE SUMMARY 1 Introduction 1 CENDI / 97-2 Background 2 1.0 THE IMPACT OF THE INTERNET ON CUSTOMER

Hypervelocity impact survivability experiments for carbonaceous impactors, part 2

NASA Technical Reports Server (NTRS)

Bunch, T. E.; Paque, Julie M.; Becker, Luann; Vedder, James F.; Erlichman, Jozef

1995-01-01

Hypervelocity impact experiments were performed to further test the survivability of carbonaceous impactors and to determine potential products that may have been synthesized during impact. Diamonds were launched by the Ames two-stage light gas gun into Al plate at velocities of 2.75 and 3.1 km sec(exp -1). FESEM imagery confirms that diamond fragments survived in both experiments. Earlier experiments found that diamonds were destroyed on impact above 4.3 km sec(exp -1). Thus, the upper stability limit for diamond on impact into Al, as determined from our experimental conditions, is between 3.1 and 4.3 km sec(exp -1). Particles of the carbonaceous chondrite Nogoya were also launched into Al at a velocity of 6.2 km sec (exp -1). Laser desorption (L (exp 2) MS) analyses of the impactor residues indicate that the lowest and highest mass polycyclic aromatic hydrocarbons (PAH's) were largely destroyed on impact; those of intermediate mass (202-220 amu) remained at the same level or increased in abundance. In addition, alkyl-substituted homologs of the most abundant pre-impacted PAH's were synthesized during impact. These results suggest that an unknown fraction of some organic compounds can survive low to moderate impact velocities and that synthesized products can be expected to form up to velocities of, at least, 6.5 km sec(exp -1). We also present examples of craters formed by a unique microparticle accelerator that could launch micron-sized particles of almost any coherent material at velocities up to approximately 15 km sec(exp -1). Many of the experiments have a direct bearing on the interpretation of LDEF craters.

76 FR 76935 - Impact of Implementing the Chemical Weapons Convention (CWC) on Commercial Activities Involving...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-12-09

... DEPARTMENT OF COMMERCE Bureau of Industry and Security [Docket No. 111130706-1686-01] Impact of Implementing the Chemical Weapons Convention (CWC) on Commercial Activities Involving ``Schedule 1'' Chemicals Through Calendar Year 2011; Impact of Adding Salts of CWC ``Schedule 1'' Chemicals to ``Schedule 1...

47 CFR 1.1319 - Consideration of the environmental impact statements.

Code of Federal Regulations, 2012 CFR

2012-10-01

... 47 Telecommunication 1 2012-10-01 2012-10-01 false Consideration of the environmental impact... § 1.1319 Consideration of the environmental impact statements. (a) If the action is subject to a... environmental and non-environmental public interest factors. (2) Upon review of an initial decision, the...

47 CFR 1.1317 - The Final Environmental Impact Statement (FEIS).

Code of Federal Regulations, 2010 CFR

2010-10-01

... 47 Telecommunication 1 2010-10-01 2010-10-01 false The Final Environmental Impact Statement (FEIS... PROCEDURE Procedures Implementing the National Environmental Policy Act of 1969 § 1.1317 The Final Environmental Impact Statement (FEIS). (a) After receipt of comments and reply comments, the Bureau will prepare...

Micrometeorite Impact Test of Flex Solar Array Coupon

NASA Technical Reports Server (NTRS)

Wright, K. H.; Schneider, T. A.; Vaughn, J. A.; Hoang, B.; Wong, F.; Gardiner, G.

2016-01-01

Spacecraft with solar arrays operate throughout the near earth environment and are increasingly planned for outer planet missions. An often overlooked test condition for solar arrays that is applicable to these missions is micrometeorite impacts and possibly electrostatic discharge (ESD) events resulting from these impacts. The Marshall Space Flight Center (MSFC) is partnering with Space Systems/Loral, LLC (SSL) to examine the results of simulated micrometeorite impacts on the electrical performance of an advanced, lightweight flexible solar array design. The test is performed at NASA MSFC's Microlight Gas Gun Facility. The SSL-provided coupons consist of three strings, each string with two solar cells in series. Five impacts will be induced at various locations on a powered test coupon under different string voltage (0 volts - 150 volts) and string current (1.1 amperes - 1.65 amperes) conditions. The maximum specified test voltage and current represent margins of 1.5 times for both voltage and current. The test parameters are chosen to demonstrate new array design robustness to any ESD event caused by plasma plumes resulting from a simulated micrometeorite impact. A second unpowered coupon will undergo two impacts: one impact on the front side and one impact on the back side. Following the impact testing, the second coupon will be exposed to a thermal cycle test to determine possible damage propagation and further electrical degradation due to thermally-induced stress. The setup, checkout, and results from the impact testing are discussed. The challenges for impact testing include precise coupon alignment to control impact location; pressure management during the impact process; and measurement of the true transient electrical response during impact on the powered coupon. Results from pre- and post-test visual and electrical functional testing are also discussed.

23 CFR 772.11 - Analysis of traffic noise impacts.

Code of Federal Regulations, 2012 CFR

2012-04-01

... 23 Highways 1 2012-04-01 2012-04-01 false Analysis of traffic noise impacts. 772.11 Section 772.11... PROCEDURES FOR ABATEMENT OF HIGHWAY TRAFFIC NOISE AND CONSTRUCTION NOISE § 772.11 Analysis of traffic noise impacts. (a) The highway agency shall determine and analyze expected traffic noise impacts. (1) For...

23 CFR 772.11 - Analysis of traffic noise impacts.

Code of Federal Regulations, 2013 CFR

2013-04-01

... 23 Highways 1 2013-04-01 2013-04-01 false Analysis of traffic noise impacts. 772.11 Section 772.11... PROCEDURES FOR ABATEMENT OF HIGHWAY TRAFFIC NOISE AND CONSTRUCTION NOISE § 772.11 Analysis of traffic noise impacts. (a) The highway agency shall determine and analyze expected traffic noise impacts. (1) For...

23 CFR 772.11 - Analysis of traffic noise impacts.

Code of Federal Regulations, 2014 CFR

2014-04-01

... 23 Highways 1 2014-04-01 2014-04-01 false Analysis of traffic noise impacts. 772.11 Section 772.11... PROCEDURES FOR ABATEMENT OF HIGHWAY TRAFFIC NOISE AND CONSTRUCTION NOISE § 772.11 Analysis of traffic noise impacts. (a) The highway agency shall determine and analyze expected traffic noise impacts. (1) For...

Dust impact effects recorded by the APV-N experiment during Comet Halley encounters

NASA Astrophysics Data System (ADS)

Oberc, P.; Orlowski, D.; Klimov, S.

1986-12-01

During the Vega 1 and 2 comet Halley encounters plasma wave instrument APV-N entered a region of impulsive noise 220,000 km from nucleus. The noise is attributed to dust grain impacts onto spacecraft body. Regression analysis of impact induced effects recorded during flyby shows that from 100,000 km from closest approach most plasma wave spectra measured by APV-N onboard Vega 1 and 2 are significantly influenced by dust impact effects. Signals associated with large dust impacts are directly recorded on the E2 0.1 to 25 Hz electric field waveform channel.

Low-Energy Impacts onto Lunar Regolith Simulant

NASA Astrophysics Data System (ADS)

Seward, Laura M.; Colwell, J.; Mellon, M.; Stemm, B.

2012-10-01

Low-Energy Impacts onto Lunar Regolith Simulant Laura M. Seward1, Joshua E. Colwell1, Michael T. Mellon2, and Bradley A. Stemm1, 1Department of Physics, University of Central Florida, Orlando, Florida, 2Southwest Research Institute, Boulder, Colorado. Impacts and cratering in space play important roles in the formation and evolution of planetary bodies. Low-velocity impacts and disturbances to planetary regolith are also a consequence of manned and robotic exploration of planetary bodies such as the Moon, Mars, and asteroids. We are conducting a program of laboratory experiments to study low-velocity impacts of 1 to 5 m/s into JSC-1 lunar regolith simulant, JSC-Mars-1 Martian regolith simulant, and silica targets under 1 g. We use direct measurement of ejecta mass and high-resolution video tracking of ejecta particle trajectories to derive ejecta mass velocity distributions. Additionally, we conduct similar experiments under microgravity conditions in a laboratory drop tower and on parabolic aircraft with velocities as low as 10 cm/s. We wish to characterize and understand the collision parameters that control the outcome of low-velocity impacts into regolith, including impact velocity, impactor mass, target shape and size distribution, regolith depth, target relative density, and crater depth, and to experimentally determine the functional dependencies of the outcomes of low-velocity collisions (ejecta mass and ejecta velocities) on the controlling parameters of the collision. We present results from our ongoing study showing the positive correlation between impact energy and ejecta mass. The total ejecta mass is also dependent on the packing density (porosity) of the regolith. We find that ejecta mass velocity fits a power-law or broken power-law distribution. Our goal is to understand the physics of ejecta production and regolith compaction in low-energy impacts and experimentally validate predictive models for dust flow and deposition. We will present our results from one-g and microgravity impact experiments.

Survival of fossilised diatoms and forams in hypervelocity impacts with peak shock pressures in the 1-19 GPa range

NASA Astrophysics Data System (ADS)

Burchell, M. J.; Harriss, K. H.; Price, M. C.; Yolland, L.

2017-07-01

Previously it has been shown that diatom fossils embedded in ice could survive impacts at speeds of up to 5 km s-1 and peak shock pressures up to 12 GPa. Here we confirm these results using a different technique, with diatoms carried in liquid water suspensions at impact speeds of 2-6 km s-1. These correspond to peak shock pressures of 3.8-19.8 GPa. We also report on the results of similar experiments using forams, at impact speeds of 4.67 km s-1 (when carried in water) and 4.73 km s-1 (when carried in ice), corresponding to peak shock pressures of 11.6 and 13.1 GPa respectively. In all cases we again find survival of recognisable fragments, with mean fragment size of order 20-25 μm. We compare our results to the peak shock pressures that ejecta from giant impacts on the Earth would experience if it subsequently impacted the Moon. We find that 98% of impacts of terrestrial ejecta on the Moon would have experienced peak pressures less than 20 GPa if the ejecta were a soft rock (sandstone). This falls to 82% of meteorites if the ejecta were a hard rock (granite). This assumes impacts on a solid lunar surface. If we approximate the surface as a loose regolith, over 99% of the impacts involve peak shock pressures below 20 GPa. Either way, the results show that a significant fraction of terrestrial meteorites impacting the Moon will do so with peak shock pressures which in our experiments permit the survival of recognisable fossil fragments.

14 CFR Appendix D to Part 420 - Impact Dispersion Areas and Casualty Expectancy Estimate for an Unguided Suborbital Launch Vehicle

Code of Federal Regulations, 2012 CFR

2012-01-01

...”. ER19Oc00.119 where: k { {1, 2, 3, . . . , n} Ac = casualty area (from table D-1) Ak = populated area Nk = population in Ak Table D-1—Effective Casualty Area (Ac) vs. Impact Range Impact range (nm) Effective casualty...

14 CFR Appendix D to Part 420 - Impact Dispersion Areas and Casualty Expectancy Estimate for an Unguided Suborbital Launch Vehicle

Code of Federal Regulations, 2013 CFR

2013-01-01

...”. ER19Oc00.119 where: k { {1, 2, 3, . . . , n} Ac = casualty area (from table D-1) Ak = populated area Nk = population in Ak Table D-1—Effective Casualty Area (Ac) vs. Impact Range Impact range (nm) Effective casualty...

14 CFR Appendix D to Part 420 - Impact Dispersion Areas and Casualty Expectancy Estimate for an Unguided Suborbital Launch Vehicle

Code of Federal Regulations, 2014 CFR

2014-01-01

...”. ER19Oc00.119 where: k { {1, 2, 3, . . . , n} Ac = casualty area (from table D-1) Ak = populated area Nk = population in Ak Table D-1—Effective Casualty Area (Ac) vs. Impact Range Impact range (nm) Effective casualty...

Metastable Oxygen Production by Electron-Impact of Oxygen

NASA Astrophysics Data System (ADS)

Hein, J. D.; Malone, C. P.; Kanik, I.; Johnson, P. V.

2013-12-01

Electron-impact excitation processes involving atomic and molecular oxygen are important in atmospheric interactions. The production of long-lived metastable O(1S) and O(1D) through electron impact of atomic O and molecular O2 play a significant role in the dynamics of oxygen-containing atmospheres (Earth, Europa, Io). Emissions from metastable O (1S → 1D) produce the well-recognized green light from terrestrial aurora. Electron-impact excitation to 1S and 1D are sensitive channels for determining energy partitioning and dynamics from space weather. Electron-impact excitation cross sections determined through fundamental experimental studies are necessary for modeling of natural phenomena and observation data. The detection of metastable states in laboratory experiments requires a novel approach, since typical detection techniques (e.g., fluorescence by radiative de-excitation) cannot be performed due to the long-lived nature of the excited species. In this work, metastable O is incident on a cryogenically cooled rare gas matrix, where excimer production and subsequent rapid radiative de-excitation provides measurable signal that is directly related to the originating electron-impact excitation process.

A Computational Study of Laminate Transparent Armor Impacted by FSP

DTIC Science & Technology

2009-06-01

of Hsieh et al [1], on targets consisting of 3mm PC-12mm PMMA-3mm PC impacted by 17-gr, 0.22 caliber fragment simulating projectile (FSP) at impact...results from the experiments of Hsieh et al [1], on targets consisting of 3mm PC-12mm PMMA-3mm PC impacted by 17-gr, 0.22 caliber fragment simulating...investigate several different analysis techniques to qualitatively determine their accuracy when compared with experiments of Hsieh et al [1]. The

Common Sense Guide to Mitigating Insider Threats, Fifth Edition

DTIC Science & Technology

2016-12-01

background investigation on its employees. 6.4 Quick Wins and High -Impact Solutions 6.4.1 All Organizations  Have all employees, contractors , and trusted...Studies 15 1.6 Quick Wins and High -Impact Solutions 16 1.6.1 All Organizations 16 1.7 Mapping to Standards 16 Practice 2: Develop a formalized insider...Threat Program 29 2.5 Case Studies 30 2.6 Quick Wins and High -Impact Solutions 31 2.6.1 All Organizations 31 2.6.2 Large Organizations 32 2.7

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peche, Roberto, E-mail: roberto.peche@ehu.es; Rodriguez, Esther, E-mail: esther.rodriguez@ehu.e

This study shows the practical application of the EIA method based on fuzzy logic proposed by the authors (Peche and Rodriguez, 2009) to a simplified case of study-the activity of a petrol station throughout its exploitation. The intensity (p{sub 1}), the extent (p{sub 2}) and the persistence (p{sub 3}) were the properties selected to describe the impacts and their respective assessment functions v-bar{sub i}=f(p-bar{sub i}) were determined. The main actions (A) and potentially affected environmental factors (F) were selected. Every impact was identified by a pair A-F and the values of the three impact properties were estimated for each ofmore » them by means of triangular fuzzy numbers. Subsequently, the fuzzy estimation of every impact was carried out, the estimation of the impact A{sub 1}-F{sub 2} (V-bar{sub 1}) being explained in detail. Every impact was simultaneously represented by its corresponding generalised confidence interval and membership function. Since the membership functions of all impacts were similar to triangular fuzzy numbers, a triangular approach (TA) was used to describe every impact. A triangular approach coefficient (TAC) was introduced to quantify the similarity of each fuzzy number and its corresponding triangular approach, where TAC (V-bar) element of (0, 1] and TAC being 1 when the fuzzy number is triangular. The TACs-ranging from 0.96 to 0.99-proved that TAs were valid in all cases. Next, the total positive and negative impacts-TV-bar{sup +} and TV-bar{sup -} were calculated and later, the fuzzy value of the total environmental impact TV-bar was determined from them. Finally, the defuzzification of TV-bar led to the punctual impact estimator TV{sup (1)} = -88.50 and its corresponding uncertainty interval [{delta}{sub l}(TV-bar),{delta}{sub r}(TV-bar)]=[6.52,6.96], which represent the total value of the EI. In conclusion, the EIA method enabled the integration of heterogeneous impacts, which exerted influence on environmental factors of a very diverse nature in very different ways, into a global impact indicator.« less

Contribution of raindrop impact to the change of soil physical properties and water erosion under semi-arid rainfalls.

PubMed

Vaezi, Ali Reza; Ahmadi, Morvarid; Cerdà, Artemi

2017-04-01

Soil erosion by water is a three-phase process that consists of detachment of soil particles from the soil mass, transportation of detached particles either by raindrop impact or surface water flow, and sedimentation. Detachment by raindrops is a key component of the soil erosion process. However, little information is available on the role of raindrop impact on soil losses in the semi-arid regions where vegetation cover is often poor and does not protect the soil from rainfall. The objective of this study is to determine the contribution of raindrop impact to changes in soil physical properties and soil losses in a semiarid weakly-aggregated agricultural soil. Soil losses were measured under simulated rainfalls of 10, 20, 30, 40, 50, 60 and 70mmh -1 , and under two conditions: i) with raindrop impact; and, ii) without raindrop impact. Three replications at each rainfall intensity and condition resulted in a total of 42 microplots of 1m×1.4m installed on a 10% slope according to a randomized complete block design. The contribution of raindrop impact to soil loss was computed using the difference between soil loss with raindrop impact and without raindrop impact at each rainfall intensity. Soil physical properties (aggregate size, bulk density and infiltration rate) were strongly damaged by raindrop impact as rainfall intensity increased. Soil loss was significantly affected by rainfall intensity under both soil surface conditions. The contribution of raindrop impact to soil loss decreased steadily with increasing rainfall intensity. At the lower rainfall intensities (20-30mmh -1 ), raindrop impact was the dominant factor controlling soil loss from the plots (68%) while at the higher rainfall intensities (40-70mmh -1 ) soil loss was mostly affected by increasing runoff discharge. At higher rainfall intensities the sheet flow protected the soil from raindrop impact. Copyright © 2017 Elsevier B.V. All rights reserved.

Panspermia Survival Scenarios for Organisms that Survive Typical Hypervelocity Solar System Impact Events.

NASA Astrophysics Data System (ADS)

Pasini, D.

2014-04-01

Previous experimental studies have demonstrated the survivability of living cells during hypervelocity impact events, testing the panspermia and litho-panspermia hypotheses [1]. It has been demonstrated by the authors that Nannochloropsis Oculata Phytoplankton, a eukaryotic photosynthesizing autotroph found in the 'euphotic zone' (sunlit surface layers of oceans [2]), survive impacts up to 6.93 km s-1 (approx. shock pressure 40 GPa) [3, 4]. Also shown to survive impacts up to 5.49 km s-1 is the tardigrade species Hypsibius dujardini (a complex micro-animal consisting of 40,000 cells) [5, 6]. It has also been shown that they can survive sustained pressures up to 600 MPa using a water filled pressure capsule [7]. Additionally bacteria can survive impacts up to 5.4 km s-1 (~30 GPa) - albeit with a low probability of survival [1], and the survivability of yeast spores in impacts up to 7.4 km s-1 (~30 GPa) has also recently been demonstrated [8]. Other groups have also reported that the lichen Xanthoria elegans is able to survive shocks in similar pressure ranges (~40 GPa) [9]. Here we present various simulated impact regimes to show which scenarios are condusive to the panspermia hypothesis of the natural transfer of life (via an icy body) through space to an extraterrestrial environment.

Does Visual Performance Influence Head Impact Severity Among High School Football Athletes?

PubMed

Schmidt, Julianne D; Guskiewicz, Kevin M; Mihalik, Jason P; Blackburn, J Troy; Siegmund, Gunter P; Marshall, Stephen W

2015-11-01

To compare the odds of sustaining moderate and severe head impacts, rather than mild, between high school football players with high and low visual performance. Prospective quasi-experimental. Clinical Research Center/On-field. Thirty-seven high school varsity football players. Athletes completed the Nike SPARQ Sensory Station visual assessment before the season. Head impact biomechanics were captured at all practices and games using the Head Impact Telemetry System. Each player was classified as either a high or low performer using a median split for each of the following visual performance measures: visual clarity, contrast sensitivity, depth perception, near-far quickness, target capture, perception span, eye-hand coordination, go/no go, and reaction time. We computed the odds of sustaining moderate and severe head impacts against the reference odds of sustaining mild head impacts across groups of high and low performers for each of the visual performance measures. Players with better near-far quickness had increased odds of sustaining moderate [odds ratios (ORs), 1.27; 95% confidence intervals (CIs), 1.04-1.56] and severe head impacts (OR, 1.45; 95% CI, 1.05-2.01) as measured by Head Impact Technology severity profile. High and low performers were at equal odds on all other measures. Better visual performance did not reduce the odds of sustaining higher magnitude head impacts. Visual performance may play less of a role than expected for protecting against higher magnitude head impacts among high school football players. Further research is needed to determine whether visual performance influences concussion risk. Based on our results, we do not recommend using visual training programs at the high school level for the purpose of reducing the odds of sustaining higher magnitude head impacts.

Rebound mechanics of micrometre-scale, spherical particles in high-velocity impacts.

PubMed

Yildirim, Baran; Yang, Hankang; Gouldstone, Andrew; Müftü, Sinan

2017-08-01

The impact mechanics of micrometre-scale metal particles with flat metal surfaces is investigated for high-velocity impacts ranging from 50 m s -1 to more than 1 km s -1 , where impact causes predominantly plastic deformation. A material model that includes high strain rate and temperature effects on the yield stress, heat generation due to plasticity, material damage due to excessive plastic strain and heat transfer is used in the numerical analysis. The coefficient of restitution e is predicted by the classical work using elastic-plastic deformation analysis with quasi-static impact mechanics to be proportional to [Formula: see text] and [Formula: see text] for the low and moderate impact velocities that span the ranges of 0-10 and 10-100 m s -1 , respectively. In the elastic-plastic and fully plastic deformation regimes the particle rebound is attributed to the elastic spring-back that initiates at the particle-substrate interface. At higher impact velocities (0.1-1 km s -1 ) e is shown to be proportional to approximately [Formula: see text]. In this deeply plastic deformation regime various deformation modes that depend on plastic flow of the material including the time lag between the rebound instances of the top and bottom points of particle and the lateral spreading of the particle are identified. In this deformation regime, the elastic spring-back initiates subsurface, in the substrate.

75 FR 77010 - Nextera Energy Point Beach, LLC; Point Beach Nuclear Plant, Units 1 and 2, Draft Environmental...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-12-10

.... Approximately 1,050 acres (425 hectares) are used for agriculture, and the remaining land is a mixture of woods... radiological impacts in the environment that may result from the proposed EPU. Non-Radiological Impacts Land Use and Aesthetic Impacts Potential land use and aesthetic impacts from the proposed EPU include...

76 FR 51956 - Notice of Availability for the Draft Environmental Impact Statement/Environmental Impact Report...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-08-19

... Desert-- September 15, 2011 at 1 P.M. at the University of California, 75-080 Frank Sinatra Drive, Room... of the Clean Water Act, including permanent impacts up to 24 acres and temporary impacts up to 1,760 acres for the construction of up to 3,770 acres of shallow ponds and associated infrastructure at the...

Field Surveys, IOC Valleys. Biological Resources Survey, Dry Lake Valley, Nevada. Volume II, Part I.

DTIC Science & Technology

1981-08-01

procedures. Project impacts on each species should be * evaluated on a case-by-case basis. The role of the species in the ecosystem , the range and size...2U7 iii Efrtee E-TR-48-fI-I TABLE OF CONTENTS (Cont.) Page 4.0 IMPACTS AND MITIGATIONS ............................. 211 4.1... Impacts .. ........................................ 211 4.1.1 Hydrology ................................. 212 4.1.2 Grazing

Evolutionarily conserved IMPACT impairs various stress responses that require GCN1 for activating the eIF2 kinase GCN2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cambiaghi, Tavane D.; Pereira, Catia M.; Shanmugam, Renuka

2014-01-10

Highlights: •GCN1 is required for mammalian and yeast GCN2 function in a variety of conditions. •Mammalian IMPACT competes with GCN2 for GCN1 binding. •IMPACT and its yeast counterpart YIH1 downregulate GCN1-dependent GCN2 activation. -- Abstract: In response to a range of environmental stresses, phosphorylation of the alpha subunit of the translation initiation factor 2 (eIF2α) represses general protein synthesis coincident with increased translation of specific mRNAs, such as those encoding the transcription activators GCN4 and ATF4. The eIF2α kinase GCN2 is activated by amino acid starvation by a mechanism involving GCN2 binding to an activator protein GCN1, along with associationmore » with uncharged tRNA that accumulates during nutrient deprivation. We previously showed that mammalian IMPACT and its yeast ortholog YIH1 bind to GCN1, thereby preventing GCN1 association with GCN2 and stimulation of this eIF2α kinase during amino acid depletion. GCN2 activity is also enhanced by other stresses, including proteasome inhibition, UV irradiation and lack of glucose. Here, we provide evidence that IMPACT affects directly and specifically the activation of GCN2 under these stress conditions in mammalian cells. We show that activation of mammalian GCN2 requires its interaction with GCN1 and that IMPACT promotes the dissolution of the GCN2–GCN1 complex. To a similar extent as the overexpression of YIH1, overexpression of IMPACT in yeast cells inhibited growth under all stress conditions that require GCN2 and GCN1 for cell survival, including exposure to acetic acid, high levels of NaCl, H{sub 2}O{sub 2} or benomyl. This study extends our understanding of the roles played by GCN1 in GCN2 activation induced by a variety of stress arrangements and suggests that IMPACT and YIH1 use similar mechanisms for regulating this eIF2α kinase.« less

Differentiation regional climate impact indicators at 1.5°C and 2°C warming above pre-industrial levels

NASA Astrophysics Data System (ADS)

Schleussner, C. F.

2016-12-01

Robust appraisals of climate impacts at different levels of global-mean temperature increase are vital to guide assessments of dangerous anthropogenic interference with the climate system. By establishing 1.5°C as the long term temperature limit for global average temperature increase and inviting a special report of the IPCC on the impacts of 1.5°C, the Paris Agreement has put such assessments high on the post-Paris science agenda. Here I will present recent findings of climate impacts at 1.5°C, including extreme weather events, water availability, agricultural yields, sea-level rise and risk of coral reef loss. In particular, I will present findings from a recent study that attempts to differentiate between such impacts at warming levels of 1.5°¸C and 2°C above pre-industrial (Schleussner et al., 2016). By analyzing changes in indicators for 26 world regions as applicable, the study found regional dependent differences between a 1.5°C and 2°C warming. Regional hot-spots of change emerge with tropical regions bearing the brunt of the impacts of an additional 0.5°C warming. These findings highlight the importance of regional differentiation to assess both future climate risks and different vulnerabilities to incremental increases in global-mean temperature. Building on that analysis, I will discuss limitations of existing approaches to differentiate between warming levels and outline opportunities for future work on refining our understanding of the difference between impacts at 1.5°C and 2°C warming. ReferencesSchleussner, C.-F. et al. Differential climate impacts for policy relevant limits to global warming: the case of 1.5°C and 2°C. Earth Syst. Dyn. 7, 327-351 (2016).

Micrometeorite Impact Test of Flex Solar Array Coupon

NASA Technical Reports Server (NTRS)

Wright, K. H.; Schneider, T. A.; Vaughn, J. A.; Hoang, B.; Wong, F.; Gardiner, G.

2016-01-01

Spacecraft with solar arrays operate throughout the near earth environment and are planned for outer planet missions. An often overlooked test condition for solar arrays that is applicable to these missions is micrometeoroid impacts and possibly electrostatic discharge (ESD) events resulting from these impacts. NASA Marshall Space Flight Center (MSFC) is partnering with Space Systems/Loral, LLC (SSL) to examine the results of simulated micrometeoroid impacts on the electrical performance of an advanced, lightweight flexible solar array design. The test is performed at MSFC's Micro Light Gas Gun Facility with SSL-provided coupons. Multiple impacts were induced at various locations on a powered test coupon under different string voltage (0V-150V) and string current (1.1A - 1.65A) conditions. The setup, checkout, and results from the impact testing are discussed.

Elemental Water Impact Test: Phase 1 20-Inch Hemisphere

NASA Technical Reports Server (NTRS)

Vassilakos, Gregory J.

2015-01-01

Spacecraft are being designed based on LS-DYNA simulations of water landing impacts. The Elemental Water Impact Test (EWIT) series was undertaken to assess the accuracy of LS-DYNA water impact simulations. Phase 1 of the EWIT series featured water impact tests of a 20-inch hemisphere dropped from heights of 5 feet and 10 feet. The hemisphere was outfitted with an accelerometer and three pressure gages. The focus of this report is the correlation of analytical models against test data.

Reconstruction of head impacts in FIS World Cup alpine skiing.

PubMed

Steenstrup, Sophie Elspeth; Mok, Kam-Ming; McIntosh, Andrew S; Bahr, Roald; Krosshaug, Tron

2018-06-01

Prior to the 2013/2014 season, the International Ski Federation (FIS) increased the helmet testing speed from 5.4 to 6.8 m/s for alpine downhill, super-G and giant slalom. Whether this increased testing speed reflects head impact velocities in real head injury situations on snow is unclear. We therefore investigated the injury mechanisms and gross head impact biomechanics in seven real head injury situations among World Cup (WC) alpine skiers. We analysed nine head impacts from seven head injury videos from the FIS Injury Surveillance System, throughout nine WC seasons (2006-2015) in detail. We used commercial video-based motion analysis software to estimate head impact kinematics in two dimensions, including directly preimpact and postimpact, from broadcast video. The sagittal plane angular movement of the head was also measured using angle measurement software. In seven of nine head impacts, the estimated normal to slope preimpact velocity was higher than the current FIS helmet rule of 6.8 m/s (mean 8.1 (±SD 0.6) m/s, range 1.9±0.8 to 12.1±0.4 m/s). The nine head impacts had a mean normal to slope velocity change of 9.3±1.0 m/s, range 5.2±1.1 to 13.5±1.3 m/s. There was a large change in sagittal plane angular velocity (mean 43.3±2.9 rad/s (range 21.2±1.5 to 64.2±3.0 rad/s)) during impact. The estimated normal to slope preimpact velocity was higher than the current FIS helmet rule of 6.8 m/s in seven of nine head impacts. © Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2018. All rights reserved. No commercial use is permitted unless otherwise expressly granted.

Molecular-dynamics simulations of energetic C{sub 60} impacts on (2x1)-(100) silicon

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hu, Xiaoyuan; Albe, Karsten; Averback, Robert S.

2000-07-01

Single impacts of energetic C{sub 60} clusters on (2x1)-(100) silicon substrates are studied by molecular-dynamics simulations. The role of impact energies and internal cluster energy are investigated in detail. Six different energy regimes can be identified at the end of the ballistic phase: At thermal energies below 20 eV the fullerene cages undergo elastic deformation, while impinging on the surface, and are mostly chemisorpted on top of the (2x1)-dimer rows. Between 20 and 100 eV the cage structure is preserved after the collision, but the cluster comes to rest within a few monolayers of the silicon surface. At energies ofmore » 100-500 eV the cluster partially decomposes and small coherent carbon caps are embedded in the surface. At higher energies up to 1.5 keV complete decomposition of the fullerene cluster occurs and an amorphous zone is formed in the subsurface area. At energies greater than approximately 1.5 keV craters form and above 6 keV sputtering becomes significant. In all cases the substrate temperature is of minor influence on the final result, but the projectile temperature is important for impacts at lower energies (<1.5 keV). For high energy impacts the ballistics resemble that of single atom impacts. Nearly 1:1 stoichiometry is obtained for impact energies around 1 keV. These results reveal an interesting possibility for controlled implantation of C in Si at high local concentrations, which might allow the formation of silicon carbide. (c) 2000 American Institute of Physics.« less

Confirmation of a meteoritic component in impact-melt rocks of the Chesapeake Bay impact structure, Virginia, USA - Evidence from osmium isotopic and PGE systematics

USGS Publications Warehouse

Lee, S.R.; Horton, J. Wright; Walker, R.J.

2006-01-01

The osmium isotope ratios and platinum-group element (PGE) concentrations of impact-melt rocks in the Chesapeake Bay impact structure were determined. The impact-melt rocks come from the cored part of a lower-crater section of suevitic crystalline-clast breccia in an 823 m scientific test hole over the central uplift at Cape Charles, Virginia. The 187Os/188Os ratios of impact-melt rocks range from 0.151 to 0.518. The rhenium and platinum-group element (PGE) concentrations of these rocks are 30-270?? higher than concentrations in basement gneiss, and together with the osmium isotopes indicate a substantial meteoritic component in some impact-melt rocks. Because the PGE abundances in the impact-melt rocks are dominated by the target materials, interelemental ratios of the impact-melt rocks are highly variable and nonchondritic. The chemical nature of the projectile for the Chesapeake Bay impact structure cannot be constrained at this time. Model mixing calculations between chondritic and crustal components suggest that most impact-melt rocks include a bulk meteoritic component of 0.01-0.1% by mass. Several impact-melt rocks with lowest initial 187Os/188Os ratios and the highest osmium concentrations could have been produced by additions of 0.1%-0.2% of a meteoritic component. In these samples, as much as 70% of the total Os may be of meteoritic origin. At the calculated proportions of a meteoritic component (0.01-0.1% by mass), no mixtures of the investigated target rocks and sediments can reproduce the observed PGE abundances of the impact-melt rocks, suggesting that other PGE enrichment processes operated along with the meteoritic contamination. Possible explanations are 1) participation of unsampled target materials with high PGE abundances in the impact-melt rocks, and 2) variable fractionations of PGE during syn- to post-impact events. ?? The Meteoritical Society, 2006.

A comparison of impact force reduction by polymer materials used for mouthguard fabrication.

PubMed

Gawlak, Dominika; Mańka-Malara, Katarzyna; Mierzwińska-Nastalska, Elżbieta; Gieleta, Roman; Kamiński, Tomasz; Łuniewska, Magdalena

2017-01-01

The essential function of mouthguards is protection against the effects of injuries sustained during sports activities. This purpose will be successfully achieved if appropriate materials ensuring sufficient reduction of the injury force are used for mouthguard fabrication. The objective of the study was to investigate the force reduction capability of selected materials as well as to identify which material reduces the impact force to the highest degree. The material for the study were samples of polymers (6 samples in total), obtained during the process of deep pressing (2 samples), flasking (3 samples) and thermal injection (1 sample), which were tested for impact force damping using an impact device - Charpy impact hammer. The control group comprised of the ceramic material samples subjected to the hammer impact. The statistical analysis applied in this study were one-way Welch ANOVA with post-hoc Games-Howell pairwise comparisons. The test materials reduced the impact force of the impact hammer to varying degrees. The greatest damping capability was demonstrated for the following materials: Impak with 1:1 powder-to-liquid weight ratio polymerized with the conventional flasking technique, and Corflex Orthodontic used in the thermal injection technique of mouthguard fabrication. Impak with 1:1 weight ratio and Corflex Orthodontic should be recommended for the fabrication of mouthguards since they demonstrated the most advantageous damping properties.

Influence of Tennis Racquet Kinematics on Ball Topspin Angular Velocity and Accuracy during the Forehand Groundstroke.

PubMed

Kwon, Sunku; Pfister, Robin; Hager, Ronald L; Hunter, Iain; Seeley, Matthew K

2017-12-01

Forehand groundstroke effectiveness is important for tennis success. Ball topspin angular velocity (TAV) and accuracy are important for forehand groundstroke effectiveness, and have been extensively studied, previously; despite previous, quality studies, it was unclear whether certain racquet kinematics relate to ball TAV and shot accuracy during the forehand groundstroke. This study evaluated potential relationships between (1) ball TAV and (2) forehand accuracy, and five measures of racquet kinematics: racquet head impact angle (i.e., closed or open face), horizontal and vertical racquet head velocity before impact, racquet head trajectory (resultant velocity direction, relative to horizontal) before impact, and hitting zone length (quasi-linear displacement, immediately before and after impact). Thirteen collegiate-level tennis players hit forehand groundstrokes in a biomechanics laboratory, where racquet kinematics and ball TAV were measured, and on a tennis court, to assess accuracy. Correlational statistics were used to evaluate potential relationships between racquet kinematics, and ball TAV (mixed model) and forehand accuracy (between-subjects model; α = 0.05). We observed an average (1) racquet head impact angle, (2) racquet head trajectory before impact, relative to horizontal, (3) racquet head horizontal velocity before impact, (4) racquet head vertical velocity before impact, and (5) hitting zone length of 80.4 ± 3.6˚, 18.6 ± 4.3˚, 15.4 ± 1.4 m·s -1 , 6.6 ± 2.2 m·s -1 , and 79.8 ± 8.6 mm, respectively; and an average ball TAV of 969 ± 375 revolutions per minute. Only racquet head impact angle and racquet head vertical velocity, before impact, significantly correlated with ball TAV (p < 0.01). None of the observed racquet kinematics significantly correlated to the measures of forehand accuracy. These results confirmed mechanical logic and indicate that increased ball TAV is associated with a more closed racquet head impact angle (ranging from 70 to 85˚, relative to the ground) and increased racquet head vertical velocity before impact.

Acoustic Emission Signals in Thin Plates Produced by Impact Damage

NASA Technical Reports Server (NTRS)

Prosser, William H.; Gorman, Michael R.; Humes, Donald H.

1999-01-01

Acoustic emission (AE) signals created by impact sources in thin aluminum and graphite/epoxy composite plates were analyzed. Two different impact velocity regimes were studied. Low-velocity (less than 0.21 km/s) impacts were created with an airgun firing spherical steel projectiles (4.5 mm diameter). High-velocity (1.8 to 7 km/s) impacts were generated with a two-stage light-gas gun firing small cylindrical nylon projectiles (1.5 mm diameter). Both the impact velocity and impact angle were varied. The impacts did not penetrate the aluminum plates at either low or high velocities. For high-velocity impacts in composites, there were both impacts that fully penetrated the plate as well as impacts that did not. All impacts generated very large amplitude AE signals (1-5 V at the sensor), which propagated as plate (extensional and/or flexural) modes. In the low-velocity impact studies, the signal was dominated by a large flexural mode with only a small extensional mode component detected. As the impact velocity was increased within the low velocity regime, the overall amplitudes of both the extensional and flexural modes increased. In addition, a relative increase in the amplitude of high-frequency components of the flexural mode was also observed. Signals caused by high-velocity impacts that did not penetrate the plate contained both a large extensional and flexural mode component of comparable amplitudes. The signals also contained components of much higher frequency and were easily differentiated from those caused by low-velocity impacts. An interesting phenomenon was observed in that the large flexural mode component, seen in every other case, was absent from the signal when the impact particle fully penetrated through the composite plates.

Wild Duck Cluster

NASA Technical Reports Server (NTRS)

2005-01-01

On April 7, 2005, the Deep Impact spacecraft's Impactor Target Sensor camera recorded this image of M11, the Wild Duck cluster, a galactic open cluster located 6 thousand light years away. The camera is located on the impactor spacecraft, which will image comet Tempel 1 beginning 22 hours before impact until about 2 seconds before impact. Impact with comet Tempel 1 is planned for July 4, 2005.

Impacts and Opportunities for Engineering in the Era of Cloud Computing Systems

DTIC Science & Technology

2012-01-31

2012 UNCLASSIFIED 1 of 58 Impacts and Opportunities for Engineering in the Era of Cloud Computing Systems A Report to the U.S. Department...2.1.7 Engineering of Computational Behavior .............................................................18 2.2 How the Cloud Will Impact Systems...58 Executive Summary This report discusses the impact of cloud computing and the broader revolution in computing on systems, on the disciplines of

7 CFR 1755.702 - Copper coated steel reinforced (CCSR) aerial service wire.

Code of Federal Regulations, 2012 CFR

2012-01-01

... requirements—(1) Impact test. (i) All CCSR aerial service wires manufactured in accordance with this section shall comply with the unaged impact test specified in ANSI/ICEA S-89-648-1993, paragraph 8.1.2. (ii) All... impact test specified in ANSI/ICEA S-89-648-1993, paragraph 8.1.3. (2) Abrasion resistance test. All CCSR...

7 CFR 1755.702 - Copper coated steel reinforced (CCSR) aerial service wire.

Code of Federal Regulations, 2013 CFR

2013-01-01

... requirements—(1) Impact test. (i) All CCSR aerial service wires manufactured in accordance with this section shall comply with the unaged impact test specified in ANSI/ICEA S-89-648-1993, paragraph 8.1.2. (ii) All... impact test specified in ANSI/ICEA S-89-648-1993, paragraph 8.1.3. (2) Abrasion resistance test. All CCSR...

7 CFR 1755.702 - Copper coated steel reinforced (CCSR) aerial service wire.

Code of Federal Regulations, 2014 CFR

2014-01-01

... requirements—(1) Impact test. (i) All CCSR aerial service wires manufactured in accordance with this section shall comply with the unaged impact test specified in ANSI/ICEA S-89-648-1993, paragraph 8.1.2. (ii) All... impact test specified in ANSI/ICEA S-89-648-1993, paragraph 8.1.3. (2) Abrasion resistance test. All CCSR...

Deep Impact Autonomous Navigation : the trials of targeting the unknown

NASA Technical Reports Server (NTRS)

Kubitschek, Daniel G.; Mastrodemos, Nickolaos; Werner, Robert A.; Kennedy, Brian M.; Synnott, Stephen P.; Null, George W.; Bhaskaran, Shyam; Riedel, Joseph E.; Vaughan, Andrew T.

2006-01-01

On July 4, 2005 at 05:44:34.2 UTC the Impactor Spacecraft (s/c) impacted comet Tempel 1 with a relative speed of 10.3 km/s capturing high-resolution images of the surface of a cometary nucleus just seconds before impact. Meanwhile, the Flyby s/c captured the impact event using both the Medium Resolution Imager (MRI) and the High Resolution Imager (HRI) and tracked the nucleus for the entire 800 sec period between impact and shield attitude transition. The objective of the Impactor s/c was to impact in an illuminated area viewable from the Flyby s/c and capture high-resolution context images of the impact site. This was accomplished by using autonomous navigation (AutoNav) algorithms and precise attitude information from the attitude determination and control subsystem (ADCS). The Flyby s/c had two primary objectives: 1) capture the impact event with the highest temporal resolution possible in order to observe the ejecta plume expansion dynamics; and 2) track the impact site for at least 800 sec to observe the crater formation and capture the highest resolution images possible of the fully developed crater. These two objectives were met by estimating the Flyby s/c trajectory relative to Tempel 1 using the same AutoNav algorithms along with precise attitude information from ADCS and independently selecting the best impact site. This paper describes the AutoNav system, what happened during the encounter with Tempel 1 and what could have happened.

Prevalence of Impacted Molar Teeth among Saudi Population in Asir Region, Saudi Arabia - A Retrospective Study of 3 Years.

PubMed

Syed, Kamran Bokhari; Zaheer, Kamran Bokhari; Ibrahim, Mohammed; Bagi, Mustafa Abdel; Assiri, Mohammed Abdullah

2013-02-01

To report the prevalence of impacted third molars according to the age, gender and type among Saudi population. This retrospective study involved 3800 panoramic radiographs of subjects aged 18 to 45 years who presented to the College of Dentistry, King Khalid University, Abha, Kingdom of Saudi Arabia for oral care during the period from February 2009 to February 2011. Data collected was entered into a spreadsheet (Excel 2000; Microsoft, US) and analyzed using Statistical Package for Social Sciences (SPSS) version 16.0. A total of 713 impacted teeth were identified (18.76%) (p=0.003). The male to female ratio with impacted third molars was 604:109 (5.54:1) and the ratio of patients with impacted teeth was (5:1). Age group 1 (i.e., 20 to 25 years)had the highest prevalence of third molar tooth impaction (64.5%) and this decreased with increasing age. Incidence of tooth impaction is higher in the mandible than in maxilla. Males had a higher incidence of third molar impaction as compared to the females. Highest incidence is found in the age group of 20-25 years. Mesio-angular impaction was the most predominant type. How to cite this article: Syed KB, Kota Z, Ibrahim M, Bagi MA, Assiri MA. "Prevalence of Impacted Molar Teeth among Saudi Population in Asir Region, Saudi Arabia - A Retrospective Study of 3 Years". J Int Oral Health 2013; 5(1):43-47.

Hypervelocity impact survivability experiments for carbonaceous impactors

NASA Technical Reports Server (NTRS)

Bunch, T. E.; Becker, Luann; Bada, Jeffrey; Macklin, John; Radicatidibrozolo, Filippo; Fleming, R. H.; Erlichman, Jozef

1993-01-01

We performed a series of hypervelocity impact experiments using carbon-bearing impactors (diamond, graphite, fullerenes, phthalic acid crystals, and Murchison meteorite) into Al plate at velocities between 4.2 and 6.1 km/s. These tests were made to do the following: (1) determine the survivability of carbon forms and organize molecules in low hypervelocity impact; (2) characterize carbonaceous impactor residues; and (3) determine whether or not fullerenes could form from carbonaceous impactors, under our experimental conditions, or survive as impactors. An analytical protocol of field emission SEM imagery, SEM-EDX, laser Raman spectroscopy, single and 2-stage laser mass spectrometry, and laser induced fluorescence (LIF) found the following: (1) diamonds did not survive impact at 4.8 km/s, but were transformed into various forms of disordered graphite; (2) intact, well-ordered graphite impactors did survive impact at 5.9 km/sec, but were only found in the crater bottom centers; the degree of impact-induced disorder in the graphite increases outward (walls, rims, ejecta); (3) phthalic acid crystals were destroyed on impact (at 4.2 km/s, although a large proportion of phthalic acid molecules did survive impact); (4) fullerenes did not form as products of carbonaceous impactors (5.9 - 6.1 km/s, fullerene impactor molecules mostly survived impact at 5.9 km/s; and (5) two Murchison meteorite samples (launched at 4.8 and 5.9 km/s) show preservation of some higher mass polycyclic aromatic hydrocarbons (PAHs) compared with the non-impacted sample. Each impactor type shows unique impactor residue morphologies produced at a given impact velocity. An expanded methodology is presented to announce relatively new analytical techniques together with innovative modifications to other methods that can be used to characterize small impact residues in LDEF craters, in addition to other acquired extraterrestrial samples.

Concussion in professional football: reconstruction of game impacts and injuries.

PubMed

Pellman, Elliot J; Viano, David C; Tucker, Andrew M; Casson, Ira R; Waeckerle, Joe F

2003-10-01

Concussion in professional football was studied with respect to impact types and injury biomechanics. A combination of video surveillance and laboratory reconstruction of game impacts was used to evaluate concussion biomechanics. Between 1996 and 2001, videotapes of concussions and significant head impacts were collected from National Football League games. There were clear views of the direction and location of the helmet impact for 182 cases. In 31 cases, the speed of impact could be determined with analysis of multiple videos. Those cases were reconstructed in laboratory tests using helmeted Hybrid III dummies and the same impact velocity, direction, and head kinematics as in the game. Translational and rotational accelerations were measured, to define concussion biomechanics. Several studies were performed to ensure the accuracy and reproducibility of the video analysis and laboratory methods used. Concussed players experienced head impacts of 9.3 +/- 1.9 m/s (20.8 +/- 4.2 miles/h). There was a rapid change in head velocity of 7.2 +/- 1.8 m/s (16.1 +/- 4.0 miles/h), which was significantly greater than that for uninjured struck players (5.0 +/- 1.1 m/s, 11.2 +/- 2.5 miles/h; t = 2.9, P < 0.005) or striking players (4.0 +/- 1.2 m/s, 8.9 +/- 2.7 miles/h; t = 7.6, P < 0.001). The peak head acceleration in concussion was 98 +/- 28 g with a 15-millisecond half-sine duration, which was statistically greater than the 60 +/- 24 g for uninjured struck players (t = 3.1, P < 0.005). Concussion was primarily related to translational acceleration resulting from impacts on the facemask or side, or falls on the back of the helmet. Concussion could be assessed with the severity index or head injury criterion (the conventional measures of head injury risk). Nominal tolerance levels for concussion were a severity index of 300 and a head injury criterion of 250. Concussion occurs with considerable head impact velocity and velocity changes in professional football. Current National Operating Committee on Standards for Athletic Equipment standards primarily address impacts to the periphery and crown of the helmet, whereas players are experiencing injuries in impacts to the facemask, side, and back of the helmet. New tests are needed to assess the performance of helmets in reducing concussion risks involving high-velocity and long-duration injury biomechanics.

Thoracic aortic injury in motor vehicle crashes: the effect of impact direction, side of body struck, and seat belt use.

PubMed

Fitzharris, Michael; Franklyn, Melanie; Frampton, Richard; Yang, King; Morris, Andrew; Fildes, Brian

2004-09-01

Using in-depth, real-world motor vehicle crash data from the United States and the United Kingdom, we aimed to assess the incidence and risk factors associated with thoracic aorta injuries. De-identified National Automotive Sampling System Crashworthiness Data System (U.S.) and Co-operative Crash Injury Study (U.K.) data formed the basis of this retrospective analysis. Logistic regression was used to assess the level of risk of thoracic aorta injury associated with impact direction, seat belt use and, given the asymmetry of the thoracic cavity, whether being struck toward the left side of the body was associated with increased risk in side-impact crashes. A total of 13,436 U.S. and 3,756 U.K. drivers and front seat passengers were analyzed. The incidence of thoracic aorta injury in the U.S. and U.K. samples was 1.5% (n = 197) and 1.9% (n = 70), respectively. The risk was higher for occupants seated on the side closest to the impact than for occupants involved in frontal impact crashes. This was the case irrespective of whether the force was applied toward the left (belted: relative risk [RR], 4.6; 95% confidence interval [CI], 2.9-7.1; p < 0.001) or the right side (belted: RR, 2.6; 95% CI, 1.4-5.1; p < 0.004) of the occupant's body. For occupants involved in side-impact crashes, there was no difference in the risk of thoracic aorta injury whether the impacting force was applied toward the left or toward the right side of the occupant's body. Seat belt use provided a protective benefit such that the risk of thoracic aorta injury among unbelted occupants was three times higher than among belted occupants (RR, 3.0; 95% CI, 2.2-4.3; p < 0.001); however, the benefit varied across impact direction. Thoracic aorta injuries were found to be associated with high impact severity, and being struck by a sports utility vehicle relative to a passenger vehicle (RR, 1.7; 95% CI, 1.2-2.3; p = 0.001). Aortic injuries have been conventionally associated with frontal impacts. However, emergency clinicians should be aware that occupants of side-impact crashes are at greater risk, particularly if the occupant was unbelted and involved in a crash of high impact severity.

Detecting dust hits at Enceladus, Saturn and beyond using CAPS / ELS data from Cassini

NASA Astrophysics Data System (ADS)

Vandegriff, J. D.; Stoneberger, P. J.; Jones, G.; Waite, J. H., Jr.

2016-12-01

It has recently been shown (1) that the impact of hypervelocity dust grains on the Cassini spacecraft can be detected by the Cassini Plasma Spectrometer (CAPS) Electron Spectrometer (ELS) instrument. For multiple Enceladus flybys, fine scale features in the lower energy regime of ELS energy spectra can be explained as short-duration, isotropic plasma clouds due to dust impacts. We have developed an algorithm for detecting these hypervelocity dust impacts, and the list of such impacts during Enceladus flybys will be presented. We also present preliminary results obtained when using the algorithm to search for dust impacts in other regions of Saturn's magnetosphere as well as in the solar wind. (1) Jones, Geraint, Hypervelocity dust impact signatures detected by Cassini CAPS-ELS in the Enceladus plume, MOP Meeting, June 1-5, 2015, Atlanta, GA

Simulation of Comet Impact and Survivability of Organic Compounds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, B T; Lomov, I N; Blank, J G

Comets have long been proposed as a potential means for the transport of complex organic compounds to early Earth. For this to be a viable mechanism, a significant fraction of organic compounds must survive the high temperatures due to impact. We have undertaken three-dimensional numerical simulations to track the thermodynamic state of a comet during oblique impacts. The comet was modeled as a 1-km water-ice sphere impacting a basalt plane at 11.2 km/s; impact angles of 15{sup o} (from horizontal), 30{sup o}, 45{sup o}, 65{sup o}, and 90{sup o} (normal impact) were examined. The survival of organic cometary material, modeledmore » as water ice for simplicity, was calculated using three criteria: (1) peak temperatures, (2) the thermodynamic phase of H{sub 2}O, and (3) final temperature upon isentropic unloading. For impact angles greater than or equal to 30{sup o}, no organic material is expected to survive the impact. For the 15{sup o} impact, most of the material survives the initial impact and significant fractions (55%, 25%, and 44%, respectively) satisfy each survival criterion at 1 second. Heating due to deceleration, in addition to shock heating, plays a role in the heating of the cometary material for nonnormal impacts. This effect is more noticeable for more oblique impacts, resulting in significant deviations from estimates using scaling of normal impacts. The deceleration heating of the material at late times requires further modeling of breakup and mixing.« less

Association of Football Subconcussive Head Impacts With Ocular Near Point of Convergence.

PubMed

Kawata, Keisuke; Rubin, Leah H; Lee, Jong Hyun; Sim, Thomas; Takahagi, Masahiro; Szwanki, Victor; Bellamy, Al; Darvish, Kurosh; Assari, Soroush; Henderer, Jeffrey D; Tierney, Ryan; Langford, Dianne

2016-07-01

An increased understanding of the relationship between subconcussive head impacts and near point of convergence (NPC) ocular-motor function may be useful in delineating traumatic brain injury. To investigate whether repetitive subconcussive head impacts during preseason football practice cause changes in NPC. This prospective, observational study of 29 National Collegiate Athletic Association Division I football players included baseline and preseason practices (1 noncontact and 4 contact), and postseason follow-up and outcome measures were obtained for each time. An accelerometer-embedded mouthguard measured head impact kinematics. Based on the sum of head impacts from all 5 practices, players were categorized into lower (n = 7) or higher (n = 22) impact groups. Players participated in regular practices, and all head impacts greater than 10g from the 5 practices were recorded using the i1Biometerics Vector mouthguard (i1 Biometrics Inc). Near point of convergence measures and symptom scores. A total of 1193 head impacts were recorded from 5 training camp practices in the 29 collegiate football players; 22 were categorized into the higher-impact group and 7 into the lower-impact group. There were significant differences in head impact kinematics between lower- and higher-impact groups (number of impacts, 6 vs 41 [lower impact minus higher impact = 35; 95% CI, 21-51; P < .001]; linear acceleration, 99g vs 1112g [lower impact minus higher impact= 1013; 95% CI, 621 - 1578; P < .001]; angular acceleration, 7589 radian/s2 vs 65 016 radian/s2 [lower impact minus higher impact= 57 427; 95% CI , 31 123-80 498; P < .001], respectively). The trajectory and cumulative burden of subconcussive impacts on NPC differed by group (F for group × linear trend1, 238 = 12.14, P < .001 and F for group × quadratic trend1, 238 = 12.97, P < .001). In the higher-impact group, there was a linear increase in NPC over time (B for linear trend, unstandardized coefficient [SE]:  0.76 [0.12], P < .001) that plateaued and resolved by postseason follow-up (B for quadratic trend [SE]: -0.06 [0.008], P < .001). In the lower-impact group, there was no change in NPC over time. Group differences were first observed after the first contact practice and remained until the final full-gear practice. No group differences were observed postseason follow-up. There were no differences in symptom scores between groups over time. Although asymptomatic, these data suggest that repetitive subconcussive head impacts were associated with changes in NPC. The increase in NPC highlights the vulnerability and slow recovery of the ocular-motor system following subconcussive head impacts. Changes in NPC may become a useful clinical tool in deciphering brain injury severity.

Sarcopenia Is Negatively Related to High Gravitational Impacts Achieved From Day-to-day Physical Activity.

PubMed

Hartley, April; Gregson, Celia L; Hannam, Kimberly; Deere, Kevin C; Clark, Emma M; Tobias, Jon H

2018-04-17

Sarcopenia has been associated with reduced physical activity (PA). We aimed to determine if sarcopenia, and specific components of muscle size, function, and physical performance, are associated with high impacts achieved during habitual PA, as these are related to bone strength in community-dwelling older women. Participants were older women from the Cohort of Skeletal Health in Bristol and Avon. We defined sarcopenia using the EWGSOP criteria. Lower limb peak muscle power and force were assessed using Jumping Mechanography (JM). High vertical impacts were assessed by tri-axial accelerometry (at least 1.5g above gravity). Cross-sectional associations were analyzed by linear regression, adjusting for age, height and weight (or fat mass for models including appendicular lean mass index), comorbidities, smoking, alcohol, and Index of Multiple Deprivation. Our analyses included 380 participants, with mean age 76.7 (SD 3.0) years; 242 (64%) also completed JM. In age-adjusted analysis, a negative relationship was observed between severity of sarcopenia and high, but not medium or low, impacts (p = .03 for trend). Regarding components of sarcopenia underlying this relationship, multivariable analyses revealed that gait speed (β 1.47 [95% CI 1.14, 1.89], [β-1] reflects the proportionate increase in high impacts per SD increase in exposure) and peak force (1.40 [1.07, 1.84]) were independently associated with high impacts. Older women with sarcopenia experienced fewer bone-strengthening high impacts than those with presarcopenia or without sarcopenia. To increase bone strengthening activity in older women, interventions need to improve both lower limb muscle force and walking speed.

Trauma of lung due to impact load.

PubMed

Yen, R T; Fung, Y C; Liu, S Q

1988-01-01

A quantitative evaluation of lung injury due to impact loading is of general interest. Hemorrhage and edema are the usual sequelae to traumatic pulmonary impact. To gain some quantitative understanding of the phenomena, we perfused excised rabbit lung with Macrodex at isogravimetric condition and monitored lung weight continuously after impact. It is shown that a factor of importance is the rigidity of the surface on which the lung rests. The rate of lung weight increase is smaller if the lung was 'freely' supported on a soft cloth, more if it was supported on a rigid plate. This suggests the influence of stress wave reflection. The critical condition correlates with the initial velocity of impact at the surface of the lung, or with the maximum deflection. For a freely supported lung, the rate of lung weight increase was 22% of the initial total lung weight per h after impact when the impact velocity was 11.5 ms-1, 30% when the velocity was 13.2 ms-1, several 100% at 13.5 ms-1, signaling massive lung injury. Since the velocity of sound in rabbit lung is 33.3 ms-1 when the inflation (transpulmonary) pressure is 10 cm H2O, the critical velocity of 13.5 ms-1 corresponds to a Mach number of 0.4. The maximum surface displacement of the lung is almost linearly proportional to the initial velocity of impact. The exact cause of edema and hemorrhage is unknown; we hypothesize that it is due to tensile stress in the alveolar wall caused by the impact.

Human Systems Roadmap Review

DTIC Science & Technology

2016-02-09

Impact of Human Systems Community of Interest D O T M L P F $450M COI Budget Has Broad Impact in Several DOTMLPF Areas Decision Making Selection...and fit to a military career. • 26 personality dimensions such as optimism, excitement seeking, and non- delinquency • Applicant chooses from...Adaptive Collaborative Control Technologies ( IMPACT ) architecture designed • IMPACT “DoD Virtual Lab” established (Year 1) • 1 operator x 6 vehicles

Environmental Assessment for A-29 Light Air Support (LAS) Training Beddown

DTIC Science & Technology

2014-08-21

Nation. Appendix A Updated to include responses/letters from federal and local agencies. Page 1 of 1 FINDING OF NO SIGNIFICANT IMPACT A-29...32 CFR §989, Environmental Impact Analysis Process, the U.S. Air Force (Air Force) assessed the potential environmental consequences associated with...protection measures to avoid or reduce adverse environmental impacts . The EA considers all potential impacts of basing this training unit at three

Development of Encapsulated Dye for Surface Impact Damage Indicator System.

DTIC Science & Technology

1987-09-01

GROUP SUB-GROUP Composites Ultrasonics Dye Impact Microcapsules 11 04 NDE polyurethane 11 1 0Encapsulation Paint 19. ABSTRACT (Continue on reverse if...encapsulation, microencapsule incorporation into the USAF polyurethane paint, dnd initial correlation study of impact damage to impact coating indication. It is...project were to: 1. Refine the microcapsule formulation to be compatible with MIL-C-83286 paint. 2. Fabricate composite panels from isotropic graphite

Droplet-Wall/Film Impact in IC Engine Applications

DTIC Science & Technology

2017-08-14

Report: Droplet-Wall/Film Impact in IC Engine Applications (ARO Topic 1.4.1 under ARO’s Dr. Ralph A. Anthenien) The views, opinions and/or findings...in IC Engine Applications (ARO Topic 1.4.1 under ARO’s Dr. Ralph A. Anthenien) Report Term: 0-Other Email: cklaw@princeton.edu Distribution Statement...associated with spraying in internal combustion engines (ICEs). Fuels sprayed inside engines can impact with the internal surfaces and thus not only

78 FR 65418 - Order 1050.1F Environmental Impacts: Policies and Procedures

Federal Register 2010, 2011, 2012, 2013, 2014

2013-10-31

...: Policies and Procedures AGENCY: Federal Aviation Administration (FAA), DOT. ACTION: Notice requesting comment on proposed Order 1050.1F Environmental Impacts: Policies and Procedures; Re-Opening of Comment..., Environmental Impacts: Policies and Procedures that was published on August 14, 2013. Airports Council...

77 FR 7281 - Energy Conservation Program: Energy Conservation Standards for Distribution Transformers

Federal Register 2010, 2011, 2012, 2013, 2014

2012-02-10

... Manufacturing Transformers H. Customer Subgroup Analysis I. Manufacturer Impact Analysis 1. Overview 2... Justification and Energy Savings 1. Economic Impacts on Customers a. Life-Cycle Cost and Payback Period b. Customer Subgroup Analysis c. Rebuttable-Presumption Payback 2. Economic Impact on Manufacturers a...

Hypervelocity Impact (HVI). Volume 5; WLE High Fidelity Specimen Fg(RCC)-1

NASA Technical Reports Server (NTRS)

Gorman, Michael R.; Ziola, Steven M.

2007-01-01

During 2003 and 2004, the Johnson Space Center's White Sands Testing Facility in Las Cruces, New Mexico conducted hypervelocity impact tests on the space shuttle wing leading edge. Hypervelocity impact tests were conducted to determine if Micro-Meteoroid/Orbital Debris impacts could be reliably detected and located using simple passive ultrasonic methods. The objective of Target Fg(RCC)-1 was to study hypervelocity impacts through the reinforced carbon-carbon (RCC) panels of the Wing Leading Edge. Fiberglass was used in place of RCC in the initial tests. Impact damage was detected using lightweight, low power instrumentation capable of being used in flight.

Hypervelocity Impact (HVI). Volume 3; WLE Small-Scale Fiberglass Panel Flat Target C-1

NASA Technical Reports Server (NTRS)

Gorman, Michael R.; Ziola, Steven M.

2007-01-01

During 2003 and 2004, the Johnson Space Center's White Sands Testing Facility in Las Cruces, New Mexico conducted hypervelocity impact tests on the space shuttle wing leading edge. Hypervelocity impact tests were conducted to determine if Micro-Meteoroid/Orbital Debris impacts could be reliably detected and located using simple passive ultrasonic methods. The objective of Target C-1 was to study hypervelocity impacts on the reinforced carbon-carbon (RCC) panels of the Wing Leading Edge. Fiberglass was used in place of RCC in the initial tests. Impact damage was detected using lightweight, low power instrumentation capable of being used in flight.

Survival of organic materials in hypervelocity impacts of ice on sand, ice, and water in the laboratory.

PubMed

Burchell, Mark J; Bowden, Stephen A; Cole, Michael; Price, Mark C; Parnell, John

2014-06-01

The survival of organic molecules in shock impact events has been investigated in the laboratory. A frozen mixture of anthracene and stearic acid, solvated in dimethylsulfoxide (DMSO), was fired in a two-stage light gas gun at speeds of ~2 and ~4 km s(-1) at targets that included water ice, water, and sand. This involved shock pressures in the range of 2-12 GPa. It was found that the projectile materials were present in elevated quantities in the targets after impact and in some cases in the crater ejecta as well. For DMSO impacting water at 1.9 km s(-1) and 45° incidence, we quantify the surviving fraction after impact as 0.44±0.05. This demonstrates successful transfer of organic compounds from projectile to target in high-speed impacts. The range of impact speeds used covers that involved in impacts of terrestrial meteorites on the Moon, as well as impacts in the outer Solar System on icy bodies such as Pluto. The results provide laboratory evidence that suggests that exogenous delivery of complex organic molecules from icy impactors is a viable source of such material on target bodies.

Shock-absorbing effect of shoe insert materials commonly used in management of lower extremity disorders.

PubMed

Shiba, N; Kitaoka, H B; Cahalan, T D; Chao, E Y

1995-01-01

The efficacy of 3 shock-absorbing materials was compared by determining impact characteristics with a drop test method and also by testing the effect of each material when used as a shoe insert in 16 asymptomatic subjects. Peak vertical ground reaction force (F1, F2, F3) and temporal force factors (T1, T2, T3) were obtained with a force plate at a high-frequency sampling rate. Impact force, impact time, impact slope, and impact energy were determined. A standard weight was dropped from 3 heights on each material covering the force plate while reduction of peak force was compared. Impact force was attenuated most effectively by Insert 3 (polymeric foam rubber) and averaged 11% less than that in shoes without inserts. Impact time was increased for all 3 inserts. Impact slope and impact energy were reduced significantly in Insert 3. There was a significant difference in peak vertical force F1 for all 3 inserts, in vertical force F2 for Insert 2 (viscoelastic polymeric material), and in vertical force F3 for Insert 2. Drop-test studies showed that at all ball heights, the highest mean peak force was observed consistently in Insert 2.

Shocked monazite chronometry: integrating microstructural and in situ isotopic age data for determining precise impact ages

NASA Astrophysics Data System (ADS)

Erickson, Timmons M.; Timms, Nicholas E.; Kirkland, Christopher L.; Tohver, Eric; Cavosie, Aaron J.; Pearce, Mark A.; Reddy, Steven M.

2017-03-01

Monazite is a robust geochronometer and occurs in a wide range of rock types. Monazite also records shock deformation from meteorite impact but the effects of impact-related microstructures on the U-Th-Pb systematics remain poorly constrained. We have, therefore, analyzed shock-deformed monazite grains from the central uplift of the Vredefort impact structure, South Africa, and impact melt from the Araguainha impact structure, Brazil, using electron backscatter diffraction, electron microprobe elemental mapping, and secondary ion mass spectrometry (SIMS). Crystallographic orientation mapping of monazite grains from both impact structures reveals a similar combination of crystal-plastic deformation features, including shock twins, planar deformation bands and neoblasts. Shock twins were documented in up to four different orientations within individual monazite grains, occurring as compound and/or type one twins in (001), (100), ( 10bar{1} ), {110}, { 212 }, and type two (irrational) twin planes with rational shear directions in [0bar{1}bar{1}] and [bar{1}bar{1}0]. SIMS U-Th-Pb analyses of the plastically deformed parent domains reveal discordant age arrays, where discordance scales with increasing plastic strain. The correlation between discordance and strain is likely a result of the formation of fast diffusion pathways during the shock event. Neoblasts in granular monazite domains are strain-free, having grown during the impact events via consumption of strained parent grains. Neoblastic monazite from the Inlandsee leucogranofels at Vredefort records a 207Pb/206Pb age of 2010 ± 15 Ma (2 σ, n = 9), consistent with previous impact age estimates of 2020 Ma. Neoblastic monazite from Araguainha impact melt yield a Concordia age of 259 ± 5 Ma (2 σ, n = 7), which is consistent with previous impact age estimates of 255 ± 3 Ma. Our results demonstrate that targeting discrete microstructural domains in shocked monazite, as identified through orientation mapping, for in situ U-Th-Pb analysis can date impact-related deformation. Monazite is, therefore, one of the few high-temperature geochronometers that can be used for accurate and precise dating of meteorite impacts.

HTGR technology economic/ business analysis and trade studies impacts. Impacts of HTGR commericialization on the U.S. economy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Silady, Fred

The approach to this task was to initially review the 2012 Business Plan and supporting analyses for the above impacts. With that understanding as a base, the Business Plan impacts are updated in terms of the GDP and job creation as a result of additional studies and inputs such as the revised market assessment from Task 1.1. For the impacts on U.S. competitiveness, the NGNP Industry Alliance team members have been utilized to provide inputs on supplier infrastructure development and on vendor capability.

Final Range Environmental Assessment for Test Areas C-87 and D-51 at Eglin Air Force Base, Florida

DTIC Science & Technology

2015-05-01

beneficial. The following terms are used to describe the magnitude of impacts in this REA: • No Effect: The action would not cause a detectable change...Negligible: The impact would be at the lowest level of detection ; the impact would not be significant. C87 AND D51 FINAL EA_MAY 2015_V2...EN0522151022TPA 1-6 SECTION 1 — PURPOSE OF AND NEED FOR THE PROPOSED ACTION • Minor: The impact would be slight but detectable ; the impact would not be

Evaluating Impact. Education Research Paper.

ERIC Educational Resources Information Center

McKay, Veronica, Ed.; Treffgarne, Carew, Ed.

Papers in this collection address issues related to participatory approaches to assessing impact. The first section, "What Is an Impact Study and How Should We Do It?" contains: (1) "Participatory Impact Assessment" (John Shotton); (2) "Participatory Action Research as an Approach to Impact Assessment" (Victoria…

Lateral automobile impacts and the risk of traumatic brain injury.

PubMed

Bazarian, Jeffrey J; Fisher, Susan Gross; Flesher, William; Lillis, Robert; Knox, Kerry L; Pearson, Thomas A

2004-08-01

We determine the relative risk and severity of traumatic brain injury among occupants of lateral impacts compared with occupants of nonlateral impacts. This was a secondary analysis of the National Highway Traffic Safety Administration's National Automotive Sampling System, Crashworthiness Data Systems for 2000. Analysis was restricted to occupants of vehicles in which at least 1 person experienced an injury with Abbreviated Injury Scale score greater than 2. Traumatic brain injury was defined as an injury to the head or skull with an Abbreviated Injury Scale score greater than 2. Outcomes were analyzed using the chi2 test and multivariate logistic regression, with adjustment of variance to account for weighted probability sampling. Of the 1,115 occupants available for analysis, impact direction was lateral for 230 (18.42%) occupants and nonlateral for 885 (81.58%) occupants. One hundred eighty-seven (16.07%) occupants experienced a traumatic brain injury, 14.63% after lateral and 16.39% after nonlateral impact. The unadjusted relative risk of traumatic brain injury after lateral impact was 0.89 (95% confidence interval [CI] 0.51 to 1.56). After adjusting for several important crash-related variables, the relative risk of traumatic brain injury was 2.60 (95% CI 1.1 to 6.0). Traumatic brain injuries were more severe after lateral impact according to Abbreviated Injury Scale and Glasgow Coma Scale scores. The proportion of fatal or critical crash-related traumatic brain injuries attributable to lateral impact was 23.5%. Lateral impact is an important independent risk factor for the development of traumatic brain injury after a serious motor vehicle crash. Traumatic brain injuries incurred after lateral impact are more severe than those resulting from nonlateral impact. Vehicle modifications that increase head protection could reduce crash-related severe traumatic brain injuries by up to 61% and prevent up to 2,230 fatal or critical traumatic brain injuries each year in the United States.

The Impact of Teachers' Unions. Final Report.

ERIC Educational Resources Information Center

Gustman, Alan L.; Segal, Martin

This study examines the impact of teachers' organizations on the compensation of public school teachers. Part 1 focuses on the impact of collective bargaining on teachers' salaries; part 2 deals with interstate variations in teachers' pensions and the influence of teachers' organizations on these variations. In part 1, the authors estimate the…

Impact Testing of Explosives and Propellants

DTIC Science & Technology

1992-06-01

in order to better understand the test results. The physical behavior of tile drop weight impact test can be modeled on a computer with all of the...SPRING ELEMENTS OF SIMPLIFIED IMPACT MACHINE A-4 NSV’CDDITR-92/280 4 j DISTRIBUTION Copies C~e ATTN ONR 1132P (R MILLER ) 1 ATTN 6-A-145 1 ONT2OT(L V...LIBRARY OF CONGRESS (J W FORBES) 1 WASHINGTON DC 20540 (R11 GUIRGUIS ) 1 (P K GUSTAVSON) I INTERNAL DISTRIBUTION (R N HAY) ! E231 2 (It D JONES) 1 E232 3 (K

High Resolution PET Imaging Probe for the Detection, Molecular Characterization, and Treatment Monitoring of Prostate cancer

DTIC Science & Technology

2011-07-01

impact on overall probe performance, including spatial resolution, energy resolution and timing resolution. We will show that 1 mm3 voxels will...ring, description of a strategy to remove scattered events, followed by characterization of impact of timing properties of the probe. In summary, the...described by the total distance d¼d1+d2 and a¼ d1=ðd1þd2Þ. We also want to account for impact angles, y1 and y2, defined versus line perpendicular to

CBR1 rs9024 genotype status impacts the bioactivation of loxoprofen in human liver.

PubMed

Lombraña, Adolfo Quiñones; Li, Nasi; Del Solar, Virginia; Ekin Atilla-Gokcumen, G; Blanco, Javier G

2018-05-31

Loxoprofen is an anti-inflammatory drug that requires bioactivation into the trans-OH metabolite to exert pharmacological activity. Evidence suggests that carbonyl reductase 1 (CBR1) is important during the bioactivation of loxoprofen. Here, we examined the impact of the functional single nucleotide polymorphism CBR1 rs9024 on the bioactivation of loxoprofen in a collection of human liver samples. The synthesis ratios of trans-OH loxoprofen/cis-OH loxoprofen were 33% higher in liver cytosols from donors homozygous for the CBR1 rs9024 G allele in comparison to the ratios in samples from donors with heterozygous GA genotypes. Complementary studies examined the impact of CBR1 rs9024 on the bioactivation of loxoprofen in lymphoblastoid cell lines. CBR1 rs9024 genotype status impacts the synthesis of the bioactive trans-OH metabolite of loxoprofen in human liver. This article is protected by copyright. All rights reserved.

Photon emission from massive projectile impacts on solids.

PubMed

Fernandez-Lima, F A; Pinnick, V T; Della-Negra, S; Schweikert, E A

2011-01-01

First evidence of photon emission from individual impacts of massive gold projectiles on solids for a number of projectile-target combinations is reported. Photon emission from individual impacts of massive Au(n) (+q) (1 ≤ n ≤ 400; q = 1-4) projectiles with impact energies in the range of 28-136 keV occurs in less than 10 ns after the projectile impact. Experimental observations show an increase in the photon yield from individual impacts with the projectile size and velocity. Concurrently with the photon emission, electron emission from the impact area has been observed below the kinetic emission threshold and under unlikely conditions for potential electron emission. We interpret the puzzling electron emission and correlated luminescence observation as evidence of the electronic excitation resulting from the high-energy density deposited by massive cluster projectiles during the impact.

Photon emission from massive projectile impacts on solids

PubMed Central

Fernandez-Lima, F. A.; Pinnick, V. T.; Della-Negra, S.; Schweikert, E. A.

2011-01-01

First evidence of photon emission from individual impacts of massive gold projectiles on solids for a number of projectile-target combinations is reported. Photon emission from individual impacts of massive Aun+q (1 ≤ n ≤ 400; q = 1–4) projectiles with impact energies in the range of 28–136 keV occurs in less than 10 ns after the projectile impact. Experimental observations show an increase in the photon yield from individual impacts with the projectile size and velocity. Concurrently with the photon emission, electron emission from the impact area has been observed below the kinetic emission threshold and under unlikely conditions for potential electron emission. We interpret the puzzling electron emission and correlated luminescence observation as evidence of the electronic excitation resulting from the high-energy density deposited by massive cluster projectiles during the impact. PMID:21603128

Physical Activity Producing Low, but Not Medium or Higher, Vertical Impacts Is Inversely Related to BMI in Older Adults: Findings From a Multicohort Study

PubMed Central

Elhakeem, Ahmed; Hannam, Kimberly; Deere, Kevin C; Hartley, April; Clark, Emma M; Moss, Charlotte; Edwards, Mark H; Dennison, Elaine; Gaysin, Tim; Kuh, Diana; Wong, Andrew; Cooper, Cyrus; Cooper, Rachel; Tobias, Jon H

2018-01-01

Abstract Background High impact physical activity (PA) is thought to improve skeletal health, but its relation to other health outcomes are unclear. We investigated associations between PA impact magnitude and body mass index (BMI) in older adults. Methods Data were taken from the Cohort for Skeletal Health in Bristol and Avon (COSHIBA), Hertfordshire Cohort Study, and MRC National Survey of Health and Development. Vertical acceleration peaks from 7-day hip-worn accelerometer recordings were used to classify PA as low (0.5 < g < 1.0g), medium (1 < g < 1.5g), or higher (≥1.5g) impact. Cohort-specific associations of low, medium, and higher impact PA with BMI were examined using linear regressions and estimates combined using random-effects meta-analysis. Results A total of 1182 participants (mean age = 72.7 years, 68% female) were included. Low, medium, and higher impact PA were inversely related to BMI in initial models. After adjustment for confounders and other impacts, low, but not medium or higher, impacts were inversely related to BMI (−0.31, p < .001: overall combined standard deviation change in BMI per doubling in the number of low impacts). In adjusted analyses of body composition measured by dual-energy X-ray absorptiometry in COSHIBA, low, but not medium or higher, impacts were inversely related to total body fat mass (−0.19, p < .001) and android:gynoid fat mass ratio (−0.16, p = .01), whereas high impact PA was weakly and positively associated with lean mass (0.05, p = .06). Conclusions Greater exposure to PA producing low magnitude vertical impacts was associated with lower BMI and fat mass at older age. Low impact PA may help reduce obesity risk in older adults. PMID:29028919

Assessment of Third Molar Impaction Pattern and Associated Clinical Symptoms in a Central Anatolian Turkish Population

PubMed Central

Yilmaz, Selmi; Adisen, Mehmet Zahit; Misirlioglu, Melda; Yorubulut, Serap

2016-01-01

Objectives The purpose of this study was to assess the pattern of third molar impaction and associated symptoms in a Central Anatolian Turkish population. Material and Methods A total of 2,133 impacted third molar teeth of 705 panoramic radiographs were reviewed. The positions of impacted third molar teeth on the panoramic radiographs were documented according to the classifications of Pell and Gregory and of Winter. The presence of related symptoms including pain, pericoronitis, lymphadenopathy and trismus was noted for every patient. Distributions of obtained values were compared using the Pearson χ2 test. Nonparametric values were analyzed using the Mann-Whitney U test and Kruskal-Wallis test. Results The mean age of the subjects was 30.58 ± 11.98 years (range: 19-73); in a review of the 2,133 impacted third molar teeth, the most common angulation of impaction in both maxillaries was vertical (1,177; 55%). Level B impaction was the most common in the maxilla (425/1,037; 39%), while level C impaction was the most common in the mandible (635/1,096; 61%). Pain (272/705; 39%) and pericoronitis (188/705; 27%) were found to be the most common complications of impaction. Among 705 patients (335 males, 370 females), pericoronitis was more prevalent in males (101; 30%) and usually related to lower third molars (236; 22%). The retromolar space was significantly smaller in females (p < 0.05). Moreover, there was a significant difference in retromolar space for the area of jaw (maxillary: 11.3 mm; mandibular: 14.2 mm) and impaction level (A: 14.7 mm; B: 11.1 mm; C: 10.3 mm; p < 0.05). Conclusion The pattern of third molar impaction in a Central Anatolian Turkish population was characterized by a high prevalence rate of level C impaction with vertical position. Pain and pericoronitis were the most common symptoms usually associated with level A impaction and vertical position. PMID:26566129

Assessment of Third Molar Impaction Pattern and Associated Clinical Symptoms in a Central Anatolian Turkish Population.

PubMed

Yilmaz, Selmi; Adisen, Mehmet Zahit; Misirlioglu, Melda; Yorubulut, Serap

2016-01-01

The purpose of this study was to assess the pattern of third molar impaction and associated symptoms in a Central Anatolian Turkish population. A total of 2,133 impacted third molar teeth of 705 panoramic radiographs were reviewed. The positions of impacted third molar teeth on the panoramic radiographs were documented according to the classifications of Pell and Gregory and of Winter. The presence of related symptoms including pain, pericoronitis, lymphadenopathy and trismus was noted for every patient. Distributions of obtained values were compared using the Pearson χ2 test. Nonparametric values were analyzed using the Mann-Whitney U test and Kruskal-Wallis test. The mean age of the subjects was 30.58 ± 11.98 years (range: 19-73); in a review of the 2,133 impacted third molar teeth, the most common angulation of impaction in both maxillaries was vertical (1,177; 55%). Level B impaction was the most common in the maxilla (425/1,037; 39%), while level C impaction was the most common in the mandible (635/1,096; 61%). Pain (272/705; 39%) and pericoronitis (188/705; 27%) were found to be the most common complications of impaction. Among 705 patients (335 males, 370 females), pericoronitis was more prevalent in males (101; 30%) and usually related to lower third molars (236; 22%). The retromolar space was significantly smaller in females (p < 0.05). Moreover, there was a significant difference in retromolar space for the area of jaw (maxillary: 11.3 mm; mandibular: 14.2 mm) and impaction level (A: 14.7 mm; B: 11.1 mm; C: 10.3 mm; p < 0.05). The pattern of third molar impaction in a Central Anatolian Turkish population was characterized by a high prevalence rate of level C impaction with vertical position. Pain and pericoronitis were the most common symptoms usually associated with level A impaction and vertical position. © 2015 S. Karger AG, Basel.

47 CFR 1.1315 - The Draft Environmental Impact Statement (DEIS); Comments.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 47 Telecommunication 1 2011-10-01 2011-10-01 false The Draft Environmental Impact Statement (DEIS); Comments. 1.1315 Section 1.1315 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL PRACTICE AND PROCEDURE Procedures Implementing the National Environmental Policy Act of 1969 § 1.1315 The Draft...

23 CFR 771.130 - Supplemental environmental impact statements.

Code of Federal Regulations, 2010 CFR

2010-04-01

... 23 Highways 1 2010-04-01 2010-04-01 false Supplemental environmental impact statements. 771.130... ENVIRONMENT ENVIRONMENTAL IMPACT AND RELATED PROCEDURES § 771.130 Supplemental environmental impact statements... significant environmental impacts that were not evaluated in the EIS; or (2) New information or circumstances...

Evidence for a chondritic impactor, evaporation-condensation effects and melting of the Precambrian basement beneath the 'target' Deccan basalts at Lonar crater, India

NASA Astrophysics Data System (ADS)

Das Gupta, Rahul; Banerjee, Anupam; Goderis, Steven; Claeys, Philippe; Vanhaecke, Frank; Chakrabarti, Ramananda

2017-10-01

The ∼1.88 km diameter Lonar impact crater formed ∼570 ka ago and is an almost circular depression hosted entirely in the Poladpur suite of the ∼65 Ma old basalts of the Deccan Traps. To understand the effects of impact cratering on basaltic targets, commonly found on the surfaces of inner Solar System planetary bodies, major and trace element concentrations as well as Nd and Sr isotopic compositions were determined on a suite of selected samples composed of: basalts, a red bole sample, which is a product of basalt alteration, impact breccia, and impact glasses, either in the form of spherules (<1 mm in diameter) or non-spherical impact glasses (>1 mm and <1 cm). These data include the first highly siderophile element (HSE) concentrations for the Lonar spherules. The chemical index of alteration (CIA) values for the basalts and impact breccia (36.4-42.7) are low while the red bole sample shows a high CIA value (55.6 in the acid-leached sample), consistent with its origin by aqueous alteration of the basalts. The Lonar spherules are classified into two main groups based on their CIA values. Most spherules show low CIA values (Group 1: 34.7-40.5) overlapping with the basalts and impact breccia, while seven spherules show significantly higher CIA values (Group 2: >43.0). The Group 1 spherules are further subdivided into Groups 1a and 1b, with Group 1a spherules showing higher Ni and mostly higher Cr compared to the Group 1b spherules. Iridium and Cr concentrations of the spherules are consistent with the admixture of 1-8 wt% of a chondritic impactor to the basaltic target rocks. The impactor contribution is most prominent in the Group 1a and Group 2 spherules, which show higher Ni/Co, Ni/Cr and Cr/Co ratios compared to the target basalts. In contrast, the Group 1b spherules show major and trace element compositions that overlap with those of the impact breccia and are characterized by high EFTh (Enrichment Factor for Th defined as the Nb-normalized concentration of Th relative to that of the average basalt) as well as fractionated La/Sm(N), and higher large ion lithophile element (LILE) concentrations compared to the basalts. The relatively more radiogenic Sr and less radiogenic Nd isotopic composition of the impact breccia and non-spherical impact glasses compared to the target basalts are consistent with melting and mixing of the Precambrian basement beneath the Deccan basalt with up to 15 wt% contribution of the basement to these samples. Variations in the moderately siderophile element (MSE) concentration ratios of the impact breccia as well as all the spherules are best explained by contributions from three components - a chondritic impactor, the basaltic target rocks at Lonar and the basement underlying the Deccan basalts. The large variations in concentrations of volatile elements like Zn and Cu and correlated variations of EFCu-EFZn, EFPb-EFZn, EFK-EFZn and EFNa-EFZn, particularly in the Group 1a spherules, are best explained by evaporation-condensation effects during impact. While most spherules, irrespective of their general major and trace element composition, show a loss in volatile elements (e.g., Zn and Cu) relative to the target basalts, some spherules, mainly of Group 1, display enrichments in these elements that are interpreted to reflect the unique preservation of volatile-rich vapour condensates resulting from geochemical fractionation in a vertical direction within the vapour cloud.

Block Distribution Analysis of Impact Craters in the Tharsis and Elysium Planitia Regions on Mars

NASA Astrophysics Data System (ADS)

Button, N.; Karunatillake, S.; Diaz, C.; Zadei, S.; Rajora, V.; Barbato, A.; Piorkowski, M.

2017-12-01

The block distribution pattern of ejecta surrounding impact craters reveals clues about their formation. Using images from High Resolution Imaging Science Experiment (HiRISE) image onboard the Mars Reconnaissance Orbiter (MRO), we indentified two rayed impact craters on Mars with measurable ejecta fields to quantitatively investigate in this study. Impact Crater 1 (HiRISE image PSP_008011_1975) is located in the Tharsis region at 17.41°N, 248.75°E and is 175 m in diameter. Impact Crater 2 (HiRISE image ESP_018352_1805) is located in Elysium Planitia at 0.51°N, 163.14°E and is 320 m in diameter. Our block measurements, used to determine the area, were conducted using HiView. Employing methods similar to Krishna and Kumar (2016), we compared block size and axis ratio to block distance from the center of the crater, impact angle, and direction. Preliminary analysis of sixteen radial sectors around Impact Crater 1 revealed that in sectors containing mostly small blocks (less than 10 m2), the small blocks were ejected up to three times the diameter of the crater from the center of the crater. These small block-dominated sectors lacked blocks larger than 10 m2. Contrastingly, in large block-dominated sectors (larger than 30 m2) blocks rarely traveled farther than 200 m from the center of the crater. We also seek to determine the impact angle and direction. Krishna and Kumar (2016) calculate the b-value (N(a) = Ca-b; "N(a) equals the number of fragments or craters with a size greater than a, C is a constant, and -b is a power index") as a method to determine the impact direction. Our preliminary results for Impact Crater 1 did not clearly indicate the impact angle. With improved measurements and the assessment of Impact Crater 2, we will compare Impact Crater 1 to Impact Crater 2 as well as assess the impact angle and direction in order to determine if the craters are secondary craters. Hood, D. and Karunatillake, S. (2017), LPSC, Abstract #2640 Krishna, N., and P. S. Kumar (2016), Icarus, 264, 274-299

Sarcopenia Is Negatively Related to High Gravitational Impacts Achieved From Day-to-day Physical Activity

PubMed Central

Hartley, April; Gregson, Celia L; Hannam, Kimberly; Deere, Kevin C; Clark, Emma M; Tobias, Jon H

2018-01-01

Abstract Background Sarcopenia has been associated with reduced physical activity (PA). We aimed to determine if sarcopenia, and specific components of muscle size, function, and physical performance, are associated with high impacts achieved during habitual PA, as these are related to bone strength in community-dwelling older women. Methods Participants were older women from the Cohort of Skeletal Health in Bristol and Avon. We defined sarcopenia using the EWGSOP criteria. Lower limb peak muscle power and force were assessed using Jumping Mechanography (JM). High vertical impacts were assessed by tri-axial accelerometry (at least 1.5g above gravity). Cross-sectional associations were analyzed by linear regression, adjusting for age, height and weight (or fat mass for models including appendicular lean mass index), comorbidities, smoking, alcohol, and Index of Multiple Deprivation. Results Our analyses included 380 participants, with mean age 76.7 (SD 3.0) years; 242 (64%) also completed JM. In age-adjusted analysis, a negative relationship was observed between severity of sarcopenia and high, but not medium or low, impacts (p = .03 for trend). Regarding components of sarcopenia underlying this relationship, multivariable analyses revealed that gait speed (β 1.47 [95% CI 1.14, 1.89], [β-1] reflects the proportionate increase in high impacts per SD increase in exposure) and peak force (1.40 [1.07, 1.84]) were independently associated with high impacts. Conclusions Older women with sarcopenia experienced fewer bone-strengthening high impacts than those with presarcopenia or without sarcopenia. To increase bone strengthening activity in older women, interventions need to improve both lower limb muscle force and walking speed. PMID:29182712

43 CFR 46.400 - Timing of environmental impact statement development.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 43 Public Lands: Interior 1 2010-10-01 2010-10-01 false Timing of environmental impact statement... IMPLEMENTATION OF THE NATIONAL ENVIRONMENTAL POLICY ACT OF 1969 Environmental Impact Statements § 46.400 Timing of environmental impact statement development. The bureau must prepare an environmental impact...

10 CFR 51.91 - Final environmental impact statement-contents.

Code of Federal Regulations, 2010 CFR

2010-01-01

... 10 Energy 2 2010-01-01 2010-01-01 false Final environmental impact statement-contents. 51.91... Implementing Section 102(2) Final Environmental Impact Statements-General Requirements § 51.91 Final environmental impact statement—contents. (a)(1) The final environmental impact statement will include responses...

Impact of the community-based newborn care package in Nepal: a quasi-experimental evaluation

PubMed Central

Paudel, Deepak; Shrestha, Ishwar B; Siebeck, Matthias; Rehfuess, Eva

2017-01-01

Objective To evaluate the impact of the community-based newborn care package (CBNCP) on six essential practices to improve neonatal health. Methods CBNCP pilot districts were matched to comparison districts using propensity scores. Impact on birth preparedness, antenatal care seeking, antenatal care quality, delivery by skilled birth attendant, immediate newborn care and postnatal care within 48 hours were assessed using Demographic and Health Survey (DHS) and Health Management Information System (HMIS) data through difference-in-differences and multivariate logistic regression analyses. Findings Changes over time in intervention and comparison areas were similar in difference-in-differences analysis of DHS and HMIS data. Logistic regression of DHS data also did not reveal any significant improvement in combined outcomes: birth preparedness, adjusted OR (aOR)=0.8 (95% CI 0.4 to 1.7); antenatal care seeking, aOR=1.0 (0.6 to 1.5); antenatal care quality, aOR=1.4 (0.9 to 2.1); delivery by skilled birth attendant, aOR=1.5 (1.0 to 2.3); immediate newborn care, aOR=1.1 (0.7 to 1.9); postnatal care, aOR=1.3 (0.9 to 1.9). Health providers’ knowledge and skills in intervention districts were fair but showed much variation between different providers and districts. Conclusions This study, while representing an early assessment of impact, did not identify significant improvements in newborn care practices and raises concerns regarding CBNCP implementation. It has contributed to revisions of the package and it being merged with the Integrated Management of Neonatal and Childhood Illness programme. This is now being implemented in 35 districts and carefully monitored for quality and impact. The study also highlights general challenges in evaluating the impacts of a complex health intervention under ‘real life’ conditions. PMID:28982810

78 FR 37324 - Preparation of Environmental Reports for Nuclear Power Plant License Renewal Applications

Federal Register 2010, 2011, 2012, 2013, 2014

2013-06-20

... Commission's 1996 findings on the environmental impacts of renewing the operating license of a nuclear power.... Specifically, the final rule amends Table B-1 by redefining the number and scope of the environmental impact... is publishing Revision 1 to NUREG-1437, ``Generic Environmental Impact Statement for License Renewal...

Problem Gambling Family Impacts: Development of the Problem Gambling Family Impact Scale.

PubMed

Dowling, N A; Suomi, A; Jackson, A C; Lavis, T

2016-09-01

Although family members of problem gamblers frequently present to treatment services, problem gambling family impacts are under-researched. The most commonly endorsed items on a new measure of gambling-related family impacts [Problem Gambling Family Impact Measure (PG-FIM: Problem Gambler version)] by 212 treatment-seeking problem gamblers included trust (62.5 %), anger (61.8 %), depression or sadness (58.7 %), anxiety (57.7 %), distress due to gambling-related absences (56.1 %), reduced quality time (52.4 %), and communication breakdowns (52.4 %). The PG-FIM (Problem Gambler version) was comprised of three factors: (1) financial impacts, (2) increased responsibility impacts, and (3) psychosocial impacts with good psychometric properties. Younger, more impulsive, non-electronic gaming machine (EGM) gamblers who had more severe gambling problems reported more financial impacts; non-EGM gamblers with poorer general health reported more increased responsibility impacts; and more impulsive non-EGM gamblers with more psychological distress and higher gambling severity reported more psychosocial impacts. The findings have implications for the development of interventions for the family members of problem gamblers.

M-X Environmental Technical Report. Socioeconomic Impact Estimates for White Pine County, Nevada. Detailed Tables.

DTIC Science & Technology

1980-12-22

8217AP0A095 772 HENNINGSON DURHAM AND RICHARDSON SANTA BARBARA CA F/G 16/1 B-B ENVIRONMENTAL TECHNICAL REPORT. SOCIOECONOMIC IMPACT ESTIMA--ETC(U) DEC... Environmental Technical Reports,. 53ocioeconctnic’ Final r1eport Impact . Estimates for White Pine County, Nevada. ____________ Detailed Tables 6. PERFORMING...background information for the analysis contained in the M-X Deploment Area Selection and Land Withirawal/Acquisition Draft Environmental Impact Statement

Patterns of injury to restrained children in side impact motor vehicle crashes: the side impact syndrome.

PubMed

Orzechowski, Kelly M; Edgerton, Elizabeth A; Bulas, Dorothy I; McLaughlin, Patrick M; Eichelberger, Martin R

2003-06-01

Injury patterns among children in frontal collisions have been well documented, but little information exists regarding injuries to children in side impact collisions. Restrained children 14-years-old or younger admitted to the hospital for crash injuries were analyzed. Data concerning injuries, medical treatment, and outcome were correlated with crash data. Case reviews achieved consensus regarding injury contact points. Side impacts were compared with frontal impacts. These results were then compared with data from the National Automotive Sampling System. There were no differences between the groups with respect to age, sex, restraint type, or seat position. Compared with frontal crashes, children in side impacts were more likely to have an Injury Severity Score > 15 (odds ratio [OR], 3.1; 95% confidence interval [CI], 1.7-5.8) and were more likely to have Abbreviated Injury Scale score 2+ injuries to the head (OR, 2.5; 95% CI, 1.4-4.4), chest (OR, 4.0; 95% CI, 2.0-8.0), and cervical spine (OR, 3.7; 95% CI, 1.2-11.3). When compared with National Automotive Sampling System data, similar trends were seen regarding Abbreviated Injury Scale score 2+ injuries to the head, chest, and extremities. In this study population, side impacts resulted in more injuries to the head, cervical spine, and chest. Knowledge of this pattern-the side impact syndrome-can help guide diagnosis, treatment, and prevention strategy.

Multichannel fiber laser Doppler vibrometer studies of low momentum and hypervelocity impacts

NASA Astrophysics Data System (ADS)

Posada-Roman, Julio E.; Jackson, David A.; Cole, Mike J.; Garcia-Souto, Jose A.

2017-12-01

A multichannel optical fiber laser Doppler vibrometer was demonstrated with the capability of making simultaneous non-contact measurements of impacts at 3 different locations. Two sets of measurements were performed, firstly using small ball bearings (1 mm-5.5 mm) falling under gravity and secondly using small projectiles (1 mm) fired from an extremely high velocity light gas gun (LGG) with speeds in the range 1 km/s-8 km/s. Determination of impact damage is important for industries such as aerospace, military and rail, where the effect of an impact on the structure can result in a major structural damage. To our knowledge the research reported here demonstrates the first trials of a multichannel fiber laser Doppler vibrometer being used to detect hypervelocity impacts.

43 CFR 46.415 - Environmental impact statement content, alternatives, circulation and filing requirements.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 43 Public Lands: Interior 1 2010-10-01 2010-10-01 false Environmental impact statement content... Impact Statements § 46.415 Environmental impact statement content, alternatives, circulation and filing requirements. The Responsible Official may use any environmental impact statement format and design as long as...

43 CFR 46.415 - Environmental impact statement content, alternatives, circulation and filing requirements.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 43 Public Lands: Interior 1 2011-10-01 2011-10-01 false Environmental impact statement content... Impact Statements § 46.415 Environmental impact statement content, alternatives, circulation and filing requirements. The Responsible Official may use any environmental impact statement format and design as long as...

41 CFR 60-3.4 - Information on impact.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 41 Public Contracts and Property Management 1 2010-07-01 2010-07-01 true Information on impact. 60... on impact. A. Records concerning impact. Each user should maintain and have available for inspection records or other information which will disclose the impact which its tests and other selection procedures...

41 CFR 60-3.4 - Information on impact.

Code of Federal Regulations, 2013 CFR

2013-07-01

... 41 Public Contracts and Property Management 1 2013-07-01 2013-07-01 false Information on impact... on impact. A. Records concerning impact. Each user should maintain and have available for inspection records or other information which will disclose the impact which its tests and other selection procedures...

Survival of Organic Materials in Hypervelocity Impacts of Ice on Sand, Ice, and Water in the Laboratory

PubMed Central

Bowden, Stephen A.; Cole, Michael; Parnell, John

2014-01-01

Abstract The survival of organic molecules in shock impact events has been investigated in the laboratory. A frozen mixture of anthracene and stearic acid, solvated in dimethylsulfoxide (DMSO), was fired in a two-stage light gas gun at speeds of ∼2 and ∼4 km s−1 at targets that included water ice, water, and sand. This involved shock pressures in the range of 2–12 GPa. It was found that the projectile materials were present in elevated quantities in the targets after impact and in some cases in the crater ejecta as well. For DMSO impacting water at 1.9 km s−1 and 45° incidence, we quantify the surviving fraction after impact as 0.44±0.05. This demonstrates successful transfer of organic compounds from projectile to target in high-speed impacts. The range of impact speeds used covers that involved in impacts of terrestrial meteorites on the Moon, as well as impacts in the outer Solar System on icy bodies such as Pluto. The results provide laboratory evidence that suggests that exogenous delivery of complex organic molecules from icy impactors is a viable source of such material on target bodies. Key Words: Organic—Hypervelocity—Shock—Biomarkers. Astrobiology 14, 473–485. PMID:24901745

Post-impact alteration of the Manson impact structure

NASA Technical Reports Server (NTRS)

Crossey, L. J.; Mccarville, P.

1993-01-01

Core materials from the Manson impact site (Manson, Iowa) are examined in order to evaluate post-impact alteration processes. Diagenetic interpretation of post-impact events is based on petrologic, mineralogic, and geochemical investigation of core materials including the following: target strata, disturbed and disrupted strata, ejecta, breccias, microbreccias, and impact melt. The diagenetic study utilizes research cores obtained by the continental scientific drilling project (CSDP) at the Manson structure, as well as core and cuttings of related materials. Samples include impactites (breccias, microbreccias, and melt material), crater fill material (sedimentary clast breccias), disturbed and disrupted target rocks, and reference target material (Amoco Eisheid No. 1 materials). The study of multiple cores will permit development of a regional picture of post-impact thermal history. The specific objectives are as follows: (1) provide a detailed description of authigenic and alteration mineralogy from diverse lithologies encountered in research drill cores at the Manson impact structure, and (2) identify and relate significant post-impact mineral alteration to post-impact thermal regime (extent and duration). Results will provide mineralogical and geochemical constraints on models for post-impact processes including the following: infilling of the crater depression; cooling and hydrothermal alteration of melt rocks; and subsequent long-term, low-temperature alteration of target rocks, breccias, and melt rocks. Preliminary petrologic and x-ray diffraction examination of fracture linings and void fillings from research core M1 indicate the presence of quartz, chlorite, mixed-layer clays, gypsum/anhydrite, calcite, and minor pyrite.

Footprint of Deepwater Horizon blowout impact to deep-water coral communities

PubMed Central

Fisher, Charles R.; Hsing, Pen-Yuan; Kaiser, Carl L.; Yoerger, Dana R.; Roberts, Harry H.; Shedd, William W.; Cordes, Erik E.; Shank, Timothy M.; Berlet, Samantha P.; Saunders, Miles G.; Larcom, Elizabeth A.; Brooks, James M.

2014-01-01

On April 20, 2010, the Deepwater Horizon (DWH) blowout occurred, releasing more oil than any accidental spill in history. Oil release continued for 87 d and much of the oil and gas remained in, or returned to, the deep sea. A coral community significantly impacted by the spill was discovered in late 2010 at 1,370 m depth. Here we describe the discovery of five previously unknown coral communities near the Macondo wellhead and show that at least two additional coral communities were impacted by the spill. Although the oil-containing flocullent material that was present on corals when the first impacted community was discovered was largely gone, a characteristic patchy covering of hydrozoans on dead portions of the skeleton allowed recognition of impacted colonies at the more recently discovered sites. One of these communities was 6 km south of the Macondo wellhead and over 90% of the corals present showed the characteristic signs of recent impact. The other community, 22 km southeast of the wellhead between 1,850 and 1,950 m depth, was more lightly impacted. However, the discovery of this site considerably extends the distance from Macondo and depth range of significant impact to benthic macrofaunal communities. We also show that most known deep-water coral communities in the Gulf of Mexico do not appear to have been acutely impacted by the spill, although two of the newly discovered communities near the wellhead apparently not impacted by the spill have been impacted by deep-sea fishing operations. PMID:25071200

Persistent, Long-term Cerebral White Matter Changes after Sports-Related Repetitive Head Impacts

PubMed Central

Bazarian, Jeffrey J.; Zhu, Tong; Zhong, Jianhui; Janigro, Damir; Rozen, Eric; Roberts, Andrew; Javien, Hannah; Merchant-Borna, Kian; Abar, Beau; Blackman, Eric G.

2014-01-01

Introduction Repetitive head impacts (RHI) sustained in contact sports are thought to be necessary for the long-term development of chronic traumatic encephalopathy (CTE). Our objectives were to: 1) characterize the magnitude and persistence of RHI-induced white matter (WM) changes; 2) determine their relationship to kinematic measures of RHI; and 3) explore their clinical relevance. Methods Prospective, observational study of 10 Division III college football players and 5 non-athlete controls during the 2011-12 season. All subjects underwent diffusion tensor imaging (DTI), physiologic, cognitive, and balance testing at pre-season (Time 1), post-season (Time 2), and after 6-months of no-contact rest (Time 3). Head impact measures were recorded using helmet-mounted accelerometers. The percentage of whole-brain WM voxels with significant changes in fractional anisotropy (FA) and mean diffusivity (MD) from Time 1 to 2, and Time 1 to 3 was determined for each subject and correlated to head impacts and clinical measures. Results Total head impacts for the season ranged from 431–1,850. No athlete suffered a clinically evident concussion. Compared to controls, athletes experienced greater changes in FA and MD from Time 1 to 2 as well as Time 1 to 3; most differences at Time 2 persisted to Time 3. Among athletes, the percentage of voxels with decreased FA from Time 1 to 2 was positively correlated with several helmet impact measures. The persistence of WM changes from Time 1 to 3 was also associated with changes in serum ApoA1 and S100B autoantibodies. WM changes were not consistently associated with cognition or balance. Conclusions A single football season of RHIs without clinically-evident concussion resulted in WM changes that correlated with multiple helmet impact measures and persisted following 6 months of no-contact rest. This lack of WM recovery could potentially contribute to cumulative WM changes with subsequent RHI exposures. PMID:24740265

Assessing the impacts of 1.5 °C global warming - simulation protocol of the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP2b)

NASA Astrophysics Data System (ADS)

Frieler, Katja; Lange, Stefan; Piontek, Franziska; Reyer, Christopher P. O.; Schewe, Jacob; Warszawski, Lila; Zhao, Fang; Chini, Louise; Denvil, Sebastien; Emanuel, Kerry; Geiger, Tobias; Halladay, Kate; Hurtt, George; Mengel, Matthias; Murakami, Daisuke; Ostberg, Sebastian; Popp, Alexander; Riva, Riccardo; Stevanovic, Miodrag; Suzuki, Tatsuo; Volkholz, Jan; Burke, Eleanor; Ciais, Philippe; Ebi, Kristie; Eddy, Tyler D.; Elliott, Joshua; Galbraith, Eric; Gosling, Simon N.; Hattermann, Fred; Hickler, Thomas; Hinkel, Jochen; Hof, Christian; Huber, Veronika; Jägermeyr, Jonas; Krysanova, Valentina; Marcé, Rafael; Müller Schmied, Hannes; Mouratiadou, Ioanna; Pierson, Don; Tittensor, Derek P.; Vautard, Robert; van Vliet, Michelle; Biber, Matthias F.; Betts, Richard A.; Bodirsky, Benjamin Leon; Deryng, Delphine; Frolking, Steve; Jones, Chris D.; Lotze, Heike K.; Lotze-Campen, Hermann; Sahajpal, Ritvik; Thonicke, Kirsten; Tian, Hanqin; Yamagata, Yoshiki

2017-11-01

In Paris, France, December 2015, the Conference of the Parties (COP) to the United Nations Framework Convention on Climate Change (UNFCCC) invited the Intergovernmental Panel on Climate Change (IPCC) to provide a special report in 2018 on the impacts of global warming of 1.5 °C above pre-industrial levels and related global greenhouse gas emission pathways. In Nairobi, Kenya, April 2016, the IPCC panel accepted the invitation. Here we describe the response devised within the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP) to provide tailored, cross-sectorally consistent impact projections to broaden the scientific basis for the report. The simulation protocol is designed to allow for (1) separation of the impacts of historical warming starting from pre-industrial conditions from impacts of other drivers such as historical land-use changes (based on pre-industrial and historical impact model simulations); (2) quantification of the impacts of additional warming up to 1.5 °C, including a potential overshoot and long-term impacts up to 2299, and comparison to higher levels of global mean temperature change (based on the low-emissions Representative Concentration Pathway RCP2.6 and a no-mitigation pathway RCP6.0) with socio-economic conditions fixed at 2005 levels; and (3) assessment of the climate effects based on the same climate scenarios while accounting for simultaneous changes in socio-economic conditions following the middle-of-the-road Shared Socioeconomic Pathway (SSP2, Fricko et al., 2016) and in particular differential bioenergy requirements associated with the transformation of the energy system to comply with RCP2.6 compared to RCP6.0. With the aim of providing the scientific basis for an aggregation of impacts across sectors and analysis of cross-sectoral interactions that may dampen or amplify sectoral impacts, the protocol is designed to facilitate consistent impact projections from a range of impact models across different sectors (global and regional hydrology, lakes, global crops, global vegetation, regional forests, global and regional marine ecosystems and fisheries, global and regional coastal infrastructure, energy supply and demand, temperature-related mortality, and global terrestrial biodiversity).

Impact of molar-incisor hypomineralization on oral health-related quality of life in schoolchildren.

PubMed

Dantas-Neta, Neusa Barros; Moura, Lúcia de Fátima Almeida de Deus; Cruz, Priscila Figueiredo; Moura, Marcoeli Silva; Paiva, Saul Martins; Martins, Carolina Castro; Lima, Marina de Deus Moura de

2016-10-24

This study evaluated the impact of molar-incisor hypomineralization (MIH) on oral health-related quality of life (OHRQoL) according to the perceptions of schoolchildren and their parents/caregivers. This cross-sectional study consisted of a sample of 594 schoolchildren between 11 and 14 years of age and their parents/caregivers who answered the questionnaires CPQ11-14ISF:16 and P-CPQ, respectively. The main independent variable of this study was MIH of the schoolchildren. Experience of dental caries, malocclusion, and socioeconomic status were treated as confounding variables. Statistical analysis used descriptive analysis and Poisson regression with robust variance. The prevalence of MIH was 18.9%. The overall P-CPQ score ranged from 0 to 35 (average = 7.26 ± 6.84), and the overall CPQ11-14ISF:16 score ranged from 0 to 47 (average = 11.92 ± 7.98). Severe MIH was associated with a greater negative impact of the "functional limitation" domain (RR = 1.41; 95%CI = 1.01-1.97), according to parents'/caregivers' perceptions. Severe MIH was associated with a greater negative impact of the "oral symptom" domain (RR = 1.30; 95%CI = 1.06-1.60) and functional limitation domain (RR = 1.42; 95%CI = 1.08-1.86), according to the schoolchildren's perceptions. Schoolchildren with severe MIH had a greater negative impact on the oral symptom and functional limitation domains than those without MIH. According to parents'/caregivers' perceptions, schoolchildren with severe MIH had a greater negative impact on the functional limitation domain than those without MIH.

Video Analysis Verification of Head Impact Events Measured by Wearable Sensors.

PubMed

Cortes, Nelson; Lincoln, Andrew E; Myer, Gregory D; Hepburn, Lisa; Higgins, Michael; Putukian, Margot; Caswell, Shane V

2017-08-01

Wearable sensors are increasingly used to quantify the frequency and magnitude of head impact events in multiple sports. There is a paucity of evidence that verifies head impact events recorded by wearable sensors. To utilize video analysis to verify head impact events recorded by wearable sensors and describe the respective frequency and magnitude. Cohort study (diagnosis); Level of evidence, 2. Thirty male (mean age, 16.6 ± 1.2 years; mean height, 1.77 ± 0.06 m; mean weight, 73.4 ± 12.2 kg) and 35 female (mean age, 16.2 ± 1.3 years; mean height, 1.66 ± 0.05 m; mean weight, 61.2 ± 6.4 kg) players volunteered to participate in this study during the 2014 and 2015 lacrosse seasons. Participants were instrumented with GForceTracker (GFT; boys) and X-Patch sensors (girls). Simultaneous game video was recorded by a trained videographer using a single camera located at the highest midfield location. One-third of the field was framed and panned to follow the ball during games. Videographic and accelerometer data were time synchronized. Head impact counts were compared with video recordings and were deemed valid if (1) the linear acceleration was ≥20 g, (2) the player was identified on the field, (3) the player was in camera view, and (4) the head impact mechanism could be clearly identified. Descriptive statistics of peak linear acceleration (PLA) and peak rotational velocity (PRV) for all verified head impacts ≥20 g were calculated. For the boys, a total recorded 1063 impacts (2014: n = 545; 2015: n = 518) were logged by the GFT between game start and end times (mean PLA, 46 ± 31 g; mean PRV, 1093 ± 661 deg/s) during 368 player-games. Of these impacts, 690 were verified via video analysis (65%; mean PLA, 48 ± 34 g; mean PRV, 1242 ± 617 deg/s). The X-Patch sensors, worn by the girls, recorded a total 180 impacts during the course of the games, and 58 (2014: n = 33; 2015: n = 25) were verified via video analysis (32%; mean PLA, 39 ± 21 g; mean PRV, 1664 ± 619 rad/s). The current data indicate that existing wearable sensor technologies may substantially overestimate head impact events. Further, while the wearable sensors always estimated a head impact location, only 48% of the impacts were a result of direct contact to the head as characterized on video. Using wearable sensors and video to verify head impacts may decrease the inclusion of false-positive impacts during game activity in the analysis.

Age and effects of the Odessa meteorite impact, western Texas, USA

NASA Astrophysics Data System (ADS)

Holliday, Vance T.; Kring, David A.; Mayer, James H.; Goble, Ronald J.

2005-12-01

The Odessa meteorite craters (Texas, United States) include a main crater (˜160 m diameter, ˜30 m deep) plus four smaller meteorite craters. The main crater was sampled by coring (to 22 m depth) to better understand its origin and history. Dating by optically stimulated luminescence indicates that it was produced immediately prior to ca. 63.5 ± 4.5 ka. Sediment filling the crater includes impact breccias produced at the time of impact; wind-dominated silts with minor amounts of pond sediments deposited ca. 63.5 ka, probably just after the impact, and ca. 53 ± 2 ka; wind-dominated silt ca. 38 ± 1.7 ka; and playa muds with a wind-blown silt component younger than 36 ka. The environment was arid or semiarid at the time of impact based on characteristics of soils on the surrounding landscape. The impact caused severe damage within 2 km and produced >1000 km/hr winds and thermal pulse. Animals within a 1 1.5-km-diameter area were probably killed. This is only the second well-dated Pleistocene hypervelocity impact crater in North America.

Investigation and Comparison between New Satellite Impact Test Results and NASA Standard Breakup Model

NASA Technical Reports Server (NTRS)

Sakuraba, K.; Tsuruda, Y.; Hanada, T.; Liou, J.-C.; Akahoshi, Y.

2007-01-01

This paper summarizes two new satellite impact tests conducted in order to investigate on the outcome of low- and hyper-velocity impacts on two identical target satellites. The first experiment was performed at a low velocity of 1.5 km/s using a 40-gram aluminum alloy sphere, whereas the second experiment was performed at a hyper-velocity of 4.4 km/s using a 4-gram aluminum alloy sphere by two-stage light gas gun in Kyushu Institute of Technology. To date, approximately 1,500 fragments from each impact test have been collected for detailed analysis. Each piece was analyzed based on the method used in the NASA Standard Breakup Model 2000 revision. The detailed analysis will conclude: 1) the similarity in mass distribution of fragments between low and hyper-velocity impacts encourages the development of a general-purpose distribution model applicable for a wide impact velocity range, and 2) the difference in area-to-mass ratio distribution between the impact experiments and the NASA standard breakup model suggests to describe the area-to-mass ratio by a bi-normal distribution.

Relationships between impact on employment, working conditions, socio-occupational categories and symptoms of post-traumatic stress disorder after the industrial disaster in Toulouse, France.

PubMed

Diene, Eloi; Agrinier, Nelly; Albessard, Artus; Cassadou, Sylvie; Schwoebel, Valerie; Lang, Thierry

2012-08-01

The aims of this paper were (1) to analyze the prevalence of symptoms of post-traumatic stress disorder (S-PTSD) in a population of workers 1 year after an industrial disaster; and (2) to assess the role of factors of vulnerability such as the occupational impact of a disaster and economic conditions. A cross-sectional survey assessing the relationships between socio-occupational category, impact on employment and S-PTSD was conducted by the self-administered impact of event scale-revised. The prevalence of S-PTSD in workers in the peripheral zone (<3 km around the explosion site) was 12% in men and 18% in women. Factors significantly associated with S-PTSD in men were non-managerial socio-occupational category: employees (ORa = 4.3; [2.3; 7.8]), factory workers/laborers (ORa = 3.7; [1.8; 7.6]), intermediate professions (ORa = 3.3; [1.9; 5.9]), and artisans (ORa = 3; [1.3; 7.7]); and layoff (ORa = 2.6; [1.5; 4.5]) or unusable workplace after the explosion (ORa = 1.8; [1.1; 2.8]). In women, factors significantly associated with S-PTSD were the socio-occupational categories of employees and factory workers (ORa = 2.2; [1.4; 3.5]), artisans (ORa = 2.7; [1.3; 5.7]) and intermediate professions, (ORa = 1.5; [1; 2.3]) and reporting of an occupational accident (ORa = 1.5; [1.1; 2.2]). Impact on the workplace and socioeconomic conditions were associated with S-PTSD. The epidemiological approach in disaster situations needs to be improved, particularly in the social and occupational dimension when economically active populations are involved. Vulnerable subgroups, defined by occupational impact and low socioeconomic category, should be taken into account.

Impact experiments of porous gypsum-glass bead mixtures simulating parent bodies of ordinary chondrites: Implications for re-accumulation processes related to rubble-pile formation

NASA Astrophysics Data System (ADS)

Yasui, Minami; Arakawa, Masahiko

2011-08-01

Laboratory impact experiments were conducted for gypsum-glass bead targets simulating the parent bodies of ordinary chondrites. The effects of the chondrules included in the parent bodies on impact disruption were experimentally investigated in order to determine the impact conditions for the formation of rubble-pile bodies after catastrophic disruption. The targets included glass beads with a diameter ranging from 100 μm to 3 mm and the volume fraction was 0.6, similar to that of ordinary chondrites, which is about 0.65-0.75. Nylon projectiles with diameters of 10 mm and 2 mm were impacted at 60-180 m s -1 by a single-stage gas gun and at 4 km s -1 by a two-stage light gas gun, respectively. The impact strength of the gypsum-glass bead target was found to range from 56 to 116 J kg -1 depending on the glass bead size, and was several times smaller than that of the porous gypsum target, 446 J kg -1 in low-velocity collisions. The impact strengths of the 100 μm bead target and the porous gypsum target strongly depended on the impact velocity: those obtained in high-velocity collisions were several times greater than those obtained in low-velocity collisions. The velocities of fragments ejected from two corners on the impact surface of the target, measured in the center of the mass system, were slightly dependent on the target materials, irrespective of impact velocity. These results suggest that chondrule-including planetesimals (CiPs) can reconstruct rubble-pile bodies in catastrophic disruptions at the size of the planetesimal smaller than that of planetesimals without chondrules.

[Impact factor of Latin American medical journals].

PubMed

Téllez-Zenteno, José F; Morales-Buenrostro, Luis E; Estañol, Bruno

2007-04-01

Latin American medical journals have a low impact factor. Higher quality articles originated in Latin American countries are published in North American or European journals. To analyze the impact factor of Latin-American journals according to the language of publication. The data base of periodic journals of the Thomson ISI (Journal of Citation Report) in the year 2004 was used for the analysis. Four countries with more than one journal in the data base of the Thomson ISI were included (Argentina, Brazil, Chile and Mexico). Few Latin-American journals are included in the Thomson ISI data base. The mean impact factor was 0.76 (0.23-3.2) for eight Mexican journals, 0.66 (0.10-2.1) for eight Chilean journals, 0.39 (0.06-0.7) for five Argentinian journals and 0.41 (0.09-1.1) for 16 Brazilian journals. The mean impact factor for 11 journals written in English was 0.74 (0.12-2.1), 0.53 (0.09-3.2) for 18 bilingual journals and 0.28 (0.06-0.56) for eight journals written in native language. The differences between countries and languages were not statistically significant. The journal impact factor was similar in the four countries studied. A non-significant higher impact factor was observed in Latin-American journals published in English.

Rearfoot and midfoot or forefoot impacts in habitually shod runners.

PubMed

Boyer, Elizabeth R; Rooney, Brandon D; Derrick, Timothy R

2014-07-01

Shear loading rates (LR) have not been investigated in runners with a mid- or forefoot strike (FFS) versus rearfoot strike (RFS). The purpose of this study was to compare three-dimensional ground reaction forces (GRF) and LR during impact in habitual rearfoot strikers (hRF) and habitual forefoot strikers (hFF) strikers. Thirty competitive runners performed 10 overground running trials with both foot strike styles. Peak three-dimensional and resultant GRF and instantaneous LR during impact were compared. Vertical LR significantly decreased for hRF using an FFS (RFS = 148 ± 36 body weight [BW]·s(-1), FFS = 98 ± 31 BW·s(-1)) but was similar for hFF running with either foot strike (FFS = 136 ± 35 BW·s(-1), RFS = 135 ± 28 BW·s(-1)). Posterior impact forces were present during FFS but not during RFS, and posterior LR was significantly greater for both groups during FFS (-58 ± 17 vs -19 ± 6 BW·s(-1)). Medial impact forces were also present during FFS but not during RFS, and medial LR was significantly larger for both groups during FFS (-21 ± 7 vs -6 ± 6 BW·s(-1)). Interestingly, hFF had greater impact peaks and LR in all directions compared with hRF during FFS. This may be explained by hFF using a smaller strike index (hFF = 62% ± 9%, hRF = 67% ± 9%; P = 0.02), which was significantly inversely related to vertical LR and impact peak. Peak resultant and vertical LR are not ubiquitously lower when using a shod FFS versus RFS despite an absence of resultant and vertical impact peaks. Furthermore, there were impact peaks in the posterior and medial directions, leading also to greater LR in these directions during FFS. Therefore, transitioning from RFS to FFS in traditional running shoes may not offer long-term protection against impact-related running injuries because hFF running with an FFS demonstrated many GRF and LR similar to or greater than RFS.

Relevance of impacter shape to nonvisible damage and residual tensile strength of a thick graphite/epoxy laminate

NASA Technical Reports Server (NTRS)

Poe, C. C., Jr.

1990-01-01

A study was made to determine the relevance of impacter shape to nonvisible damage and tensile residual strength of a 36 mm (1.4 in.) thick graphite/epoxy motor case. The shapes of the impacters were as follows: 12.7 mm (0.5 in.) and 25.4 mm (1.0 in.) diameter hemispheres, a sharp corner, and a 6.3 mm (0.25 in.) diameter bolt-like rod. The investigation revealed that damage initiated when the contact pressure exceeded a critical level. However, the damage was not visible on the surface until an even higher pressure was exceeded. The damage on the surface consisted of a crater shaped like the impacter, and the damage below the surface consisted of broken fibers. The impact energy to initiate damage or cause visible damage on the surface increased approximately with impacter diameter to the third power. The reduction in strength for nonvisible damage increased with increasing diameter, 9 and 30 percent for the 12.7 mm (0.5 in.) and 25.4 mm (1.0 in.) diameter hemispheres, respectively. The corner impacter made visible damage on the surface for even the smallest impact energy. The rod impacter acted like a punch and sliced through the composite. Even so, the critical level of pressure to initiate damage was the same for the rod and hemispherical impacters. Factors of safety for nonvisible damage increased with increasing kinetic energy of impact. The effects of impacter shape on impact force, damage size, damage visibility, and residual tensile strength were predicted quite well assuming Hertzian contact and using maximum stress criteria and a surface crack analysis.

Participation in High-Impact Sports Predicts Bone Mineral Density in Senior Olympic Athletes

PubMed Central

Leigey, Daniel; Irrgang, James; Francis, Kimberly; Cohen, Peter; Wright, Vonda

2009-01-01

Background: Loss of bone mineral density (BMD) and resultant fractures increase with age in both sexes. Participation in resistance or high-impact sports is a known contributor to bone health in young athletes; however, little is known about the effect of participation in impact sports on bone density as people age. Hypothesis: To test the hypothesis that high-impact sport participation will predict BMD in senior athletes, this study evaluated 560 athletes during the 2005 National Senior Games (the Senior Olympics). Study Design: Cross-sectional methods. The athletes completed a detailed health history questionnaire and underwent calcaneal quantitative ultrasound to measure BMD. Athletes were classified as participating in high impact sports (basketball, road race [running], track and field, triathalon, and volleyball) or non-high-impact sports. Stepwise linear regression was used to determine the influence of high-impact sports on BMD. Results: On average, participants were 65.9 years old (range, 50 to 93). There were 298 women (53.2%) and 289 men (51.6%) who participated in high-impact sports. Average body mass index was 25.6 ± 3.9. The quantitative ultrasound-generated T scores, a quantitative measure of BMD, averaged 0.4 ± 1.3 and −0.1 ± 1.4 for the high-impact and non-high-impact groups, respectively. After age, sex, obesity, and use of osteoporosis medication were controlled, participation in high-impact sports was a significant predictor of BMD (R2 change 3.2%, P < .001). Conclusions: This study represents the largest sample of BMD data in senior athletes to date. Senior participation in high-impact sports positively influenced bone health, even in the oldest athletes. Clinical Relevance: These data imply that high-impact exercise is a vital tool to maintain healthy BMD with active aging. PMID:23015914

49 CFR 581.5 - Requirements.

Code of Federal Regulations, 2014 CFR

2014-10-01

... the damage criteria of §§ 581.5(c)(1) through 581.5(c)(9) when impacted by a pendulum-type test device... of 1.5 m.p.h., and when impacted by a pendulum-type test device in accordance with the procedures of... original contours 30 minutes after completion of each pendulum and barrier impact, except where such damage...

49 CFR 581.5 - Requirements.

Code of Federal Regulations, 2011 CFR

2011-10-01

... the damage criteria of §§ 581.5(c)(1) through 581.5(c)(9) when impacted by a pendulum-type test device... of 1.5 m.p.h., and when impacted by a pendulum-type test device in accordance with the procedures of... original contours 30 minutes after completion of each pendulum and barrier impact, except where such damage...

49 CFR 581.5 - Requirements.

Code of Federal Regulations, 2012 CFR

2012-10-01

... the damage criteria of §§ 581.5(c)(1) through 581.5(c)(9) when impacted by a pendulum-type test device... of 1.5 m.p.h., and when impacted by a pendulum-type test device in accordance with the procedures of... original contours 30 minutes after completion of each pendulum and barrier impact, except where such damage...

49 CFR 581.5 - Requirements.

Code of Federal Regulations, 2010 CFR

2010-10-01

... the damage criteria of §§ 581.5(c)(1) through 581.5(c)(9) when impacted by a pendulum-type test device... of 1.5 m.p.h., and when impacted by a pendulum-type test device in accordance with the procedures of... original contours 30 minutes after completion of each pendulum and barrier impact, except where such damage...

49 CFR 581.5 - Requirements.

Code of Federal Regulations, 2013 CFR

2013-10-01

... the damage criteria of §§ 581.5(c)(1) through 581.5(c)(9) when impacted by a pendulum-type test device... of 1.5 m.p.h., and when impacted by a pendulum-type test device in accordance with the procedures of... original contours 30 minutes after completion of each pendulum and barrier impact, except where such damage...

75 FR 74131 - Notice of Finding of No Significant Impact for the Washington State Portion of the Pacific...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-11-30

... Environmental Assessment AGENCY: Federal Railroad Administration (FRA), United States Department of... Transportation (WSDOT) prepared a Tier-1 Environmental Assessment (Tier-1 EA) that evaluates the impacts of a... have a significant impact on the quality of the human or natural environment and has issued a Finding...

75 FR 18242 - Florida Power and Light, St. Lucie Units 1 and 2; Independent Spent Fuel Storage Installation...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-04-09

... Environmental Assessment and Finding of No Significant Impact. FOR FURTHER INFORMATION CONTACT: B. Jennifer... for FPL to use Amendment 1 to CoC 1030 for their ISFSI loading campaign. Environmental Impacts of the... be no significant environmental impact if the exemption is granted. The staff has determined that the...

River food webs: an integrative approach to bottom-up flow webs, top-down impact webs, and trophic position.

PubMed

Benke, Arthur C

2018-03-31

The majority of food web studies are based on connectivity, top-down impacts, bottom-up flows, or trophic position (TP), and ecologists have argued for decades which is best. Rarely have any two been considered simultaneously. The present study uses a procedure that integrates the last three approaches based on taxon-specific secondary production and gut analyses. Ingestion flows are quantified to create a flow web and the same data are used to quantify TP for all taxa. An individual predator's impacts also are estimated using the ratio of its ingestion (I) of each prey to prey production (P) to create an I/P web. This procedure was applied to 41 invertebrate taxa inhabiting submerged woody habitat in a southeastern U.S. river. A complex flow web starting with five basal food resources had 462 flows >1 mg·m -2 ·yr -1 , providing far more information than a connectivity web. Total flows from basal resources to primary consumers/omnivores were dominated by allochthonous amorphous detritus and ranged from 1 to >50,000 mg·m -2 ·yr -1 . Most predator-prey flows were much lower (<50 mg·m -2 ·yr -1 ), but some were >1,000  mg·m -2 ·yr -1 . The I/P web showed that 83% of individual predator impacts were weak (<10%), whereas total predator impacts were often strong (e.g., 35% of prey sustained an impact >90%). Quantitative estimates of TP ranged from 2 to 3.7, contrasting sharply with seven integer-based trophic levels based on longest feeding chain. Traditional omnivores (TP = 2.4-2.9) played an important role by consuming more prey and exerting higher impacts on primary consumers than strict predators (TP ≥ 3). This study illustrates how simultaneous quantification of flow pathways, predator impacts, and TP together provide an integrated characterization of natural food webs. © 2018 by the Ecological Society of America.

Vesta: A Geological Overview

NASA Astrophysics Data System (ADS)

Ralf, Jaumann; Russell, C. T.; Raymond, C. A.; Pieters, C. M.; Yingst, R. A.; Williams, D. A.; Buczkowski, D. L.; Schenk, P.; Denevi, B.; Krohn, K.; Stephan, K.; Roatsch, T.; Preusker, F.; Otto, K.; Mest, S. C.; Ammannito, E.; Blewett, D.; Carsenty, U.; DeSanctis, C. M.; Garry, W.; Hiesinger, H.; Keller, H. U.; Kersten, E.; Marchi, S.; Matz, K. D.; McCord, T. B.; McSween, H. Y.; Mottola, S.; Nathues, A.; Neukum, G.; O'Brien, D. P.; Schmedemann, N.; Scully, J. E. C.; Sykes, M. V.; Zuber, M. T.

2012-10-01

The Dawn spacecraft has collected over 28,000 images and a wealth of spectral data providing nearly complete coverage of Vesta’s surface with multiple views. These data enable analysis of Vesta’s diverse geology including impact craters of all sizes and unusual shapes, a variety of ejecta blankets, large troughs extending around the equatorial region, impact basins, enigmatic dark material, and considerable evidence for mass wasting and surface alteration features (1). Two large impact basins, Veneneia (400km) underlying the larger Rheasilvia basin (500km) dominate the south pole (1,2). Rheasilvia exhibits a huge central peak, with total relief of -22km to 19km, and steep scarps with mass wasting features. Vesta’s global tectonic patterns (two distinct sets of large troughs almost parallel to the equator) strongly correlate with the locations of the two south polar impact basins, and were likely created by their formation (1,3). Numerous unusual asymmetric impact craters and ejecta indicate the strong role of topographic slope in cratering processes on Vesta (1). Such very steep topographic slopes are near to the angle of repose; slope failures make resurfacing due to impacts and their associated gravitational slumping and seismic effects an important geologic process on Vesta (1). Outcrops in crater walls indicate reworked crustal material and impact melt in combination with clusters of pits that show thermal surface processes (4). Relatively dark material of still unknown origin is intermixed in the regolith layers and partially excavated by younger impacts yielding dark outcrops, rays and ejecta (1,5). Finally, Vesta’s surface is younger than expected (6). (1) Jaumann, et al., 2012, Science 336, 687-690; (2) Schenk et al., 2012, Science 336, 964-967; (3) Buczkowski, et al., 2012, GRL, submitted; (4) Denevi, et al., 2012, Science, submitted; (5) McCord, et al., 2012, Nature, submitted; (6) Marchi, et al., 2012, Science 336, 690-694.

Material Evidence for Ocean Impact from Shock-Metamorphic Experiments

NASA Astrophysics Data System (ADS)

Miura, Y.; Takayama, K.; Iancu, O. G.

1993-07-01

Continental impact reveals an excavated crater that has few fresh fine ejecta showing major high shock metamorphism due to weathering [1]. A giant ocean impact rarely remains as an excavated crater mainly due to crushing by dynamic plate-tectonic movements on the crust [2]. However, all impact materials, including fine-grained ejecta, can be obtained with artificial impact experiments [3]. The purpose of this study is to discuss material evidence for ocean impact based on shock-metamorphic experiments. Artificial impact experiments indicate that fine shocked quartz (SQ) aggregates can be formed on several target rocks (Table 1) [1]. It is found in Table 1 that (1) the largest-density deviation of SQ grain is found not at the wall-rock or the impact crater but at fine-grained ejecta, and (2) silica-poor rocks of basalt, gabbro, and anorthosite can also make fine SQ aggregates by impact. Table 1, which appears here in the hard copy, shows formations of fine shocked quartz aggregates from ocean-floor rocks of basalt, gabbroic anorthosite, and granite [3]. An asteroid (about 10 km across) hits the Earth ~65 m.y. ago [4] to result in global catastrophe by titanic explosion and climate change. But shocked quartz grains found in the K/T boundary layer were considered to come from crystalline continental rocks [5]. The present result as listed in Table 1 indicates that fine SQ aggregates can also be formed at sea-floor basaltic and gabbroic rocks [3]. The present result of formation of the SQ grains from sea- floor target rocks is nearly consistent with the finding of a sea-impact crater at the K/T boundary near the Caribbean [6]. Impact-induced volcanism at the K/T boundary can explained by the penetration from thin ocean crust to upper mantle reservoirs, if giant impact of a 10-km- diameter asteroid hit the ocean [2,7]. The present result can explain "phreatomagmatic (magmatic vapor) explosion," which is created by abrupt boiling between high-temperature magma and cold sea water to produce a titanic explosion of the asteroid disintegrated in a mass of exploding steam and vaporizing soil, including the SQ aggregates, and to create the Atlantic Ocean floor by the continental drift [8]. References: [1] Miura Y. (1991) Shock Waves, 1, 35-41. [2] Miura Y. and Takayama K. (1993) Symp. Shock Waves (Japan), 2, 193-196. [3] Miura Y. et al. (1992) Proc. Shock Waves, 18, 403-408, Springer-Verlag. [4] Alvarez L. W. et al. (1980) Science, 208, 1095-1107. [5] Bohor B. F. et al. (1984) Science, 224, 867-869. [6] Hildebrand A. R. et al. (1991) Geology, 19, 867-871. [7] Barlow N. G. (1990) Geol. Soc. Am. Spec. Pap. 247, 181-187. [8] Hartmann W. K. and Miller R. (1991) The History of Earth, 165, Workman.

The Predictability of Extratropical Transition and of its Impact on the Downstream Flow

DTIC Science & Technology

2008-03-28

is predicted to reach a continent as an extratropical storm . Arguably the larger impact on predictability, however, occurs due to the above mentioned...Office of Naval Research Project The Predictability of Extratropical Transition and of its Impact on the Downstream Flow Award Number: N00014-06-1...12 0 76128 Karlsruhe 0 March 28, 2008 1 * 4 -d 60-( CONTENTS 3 Contents 1 Objectives 5 2 Scientific Importance 6 3 Extratropical Transition in

Dust Impacts In the Outer Solar System Detected by Voyagers 1 and 2

NASA Astrophysics Data System (ADS)

Gurnett, D. A.; Persoon, A. M.; Granroth, L. J.; Kurth, W. S.

2011-12-01

The plasma wave instruments (PWS) on the Voyager 1 and 2 spacecraft, which are currently at about 119 and 97 AU, have been consistently detecting a low rate of dust impacts as the spacecraft proceed outward from the Sun into interstellar space. Because of the high radial velocity of the spacecraft, ~ 17 and 15 km/sec, when a dust particle strikes the spacecraft it is almost instantly vaporized and ionized, thereby producing a rapidly expanding cloud of plasma that causes a voltage pulse in the PWS electric antenna. The voltage pulse has a very rapid rise time of about 10 μs and is an easily identifiable waveform in the wideband electric field data. Due to a failure in the Voyager 2 waveform receiver no impact data are available from Voyager 2 beyond about 60 AU. However, the Voyager 1 waveform receiver is still working. Because of the very high data rates involved, 115.2 kb/s, antenna voltage waveforms can only be recorded for less than a minute per week, so the effective observing time is very small. Nonetheless, once the regions around the outer planets are excluded, a consistent background impact rate of a few impacts per hour is observed by both spacecraft. The impact rate appears to be increasing slightly with increasing radial distance, from about 3 ± 1 impacts per hour at 30 AU, to 6 ± 4 impacts per hour at 110 AU. If the impact cross-section of the spacecraft is assumed to be determined by the spacecraft high gain antenna, which has an area of 10.75 square meters, the corresponding particle flux varies from about 0.75 x 10-14 m-2 s-1 at 30 AU, to about 1.5 x 10-14 m-2 s-1 at 110 AU. Although we have no reliable method of estimating the size or origin of the particles, we note that this flux is consistent with the flux of submicron particles (10-15 to 10-9 g) arriving from interstellar space as detected by the Ulysses spacecraft at radial distances inside of 5 AU. Therefore, we believe that the particles are probably of interstellar origin.

TRACI THE TOOL FOR THE REDUCTION AND ASSESSMENT OF CHEMICAL AND OTHER ENVIRONMENTAL IMPACTS - VERSION 2 CHANGES

EPA Science Inventory

The Tool for the Reduction and Assessment of Chemical and other environmental Impacts (TRACI) was developed to allow the quantification of environmental impacts for a variety of impact categories which are necessary for a comprehensive impact assessment. See Figure 1. TRACI is c...

Some principles to guide wilderness campsite management

Treesearch

David N. Cole

1990-01-01

Seven principles, derived from research on wilderness campsites, are proposed: (1) campsite impacts are complex; (2) impact is inevitable with repetitive use of campsites; (3) impact occurs rapidly, recovery occurs slowly; (4) the relationship between use and impact is asymptotic; (5) certain sites are more durable than others; (6) certain users cause less impact than...

Macroeconomic impact of pandemic influenza and associated policies in Thailand, South Africa and Uganda.

PubMed

Smith, Richard D; Keogh-Brown, Marcus R

2013-09-01

Research has shown the value of conducting a macroeconomic analysis of the impact of influenza pandemics. However, previous modelling applications focus on high-income countries, and there is a lack of evidence concerning the potential impact of an influenza pandemic on lower- and middle-income countries. To estimate the macroeconomic impact of pandemic influenza in Thailand, South Africa and Uganda with particular reference to pandemic (H1N1) 2009. A single-country whole-economy Computable General Equilibrium (CGE) model was set up for each of the three countries in question and used to estimate the economic impact of declines in labour attributable to morbidity, mortality and school closure. Overall GDP impacts were less than 1% of GDP for all countries and scenarios. Uganda's losses were proportionally larger than those of Thailand and South Africa. Labour-intensive sectors suffer the largest losses. The economic cost of unavoidable absence in the event of an influenza pandemic could be proportionally larger for low-income countries. The cost of mild pandemics, such as pandemic (H1N1) 2009, appears to be small, but could increase for more severe pandemics and/or pandemics with greater behavioural change and avoidable absence. © 2013 Blackwell Publishing Ltd.

Macroeconomic impact of a mild influenza pandemic and associated policies in Thailand, South Africa and Uganda: a computable general equilibrium analysis.

PubMed

Smith, Richard D; Keogh-Brown, Marcus R

2013-11-01

Previous research has demonstrated the value of macroeconomic analysis of the impact of influenza pandemics. However, previous modelling applications focus on high-income countries and there is a lack of evidence concerning the potential impact of an influenza pandemic on lower- and middle-income countries. To estimate the macroeconomic impact of pandemic influenza in Thailand, South Africa and Uganda with particular reference to pandemic (H1N1) 2009. A single-country whole-economy computable general equilibrium (CGE) model was set up for each of the three countries in question and used to estimate the economic impact of declines in labour attributable to morbidity, mortality and school closure. Overall GDP impacts were less than 1% of GDP for all countries and scenarios. Uganda's losses were proportionally larger than those of Thailand and South Africa. Labour-intensive sectors suffer the largest losses. The economic cost of unavoidable absence in the event of an influenza pandemic could be proportionally larger for low-income countries. The cost of mild pandemics, such as pandemic (H1N1) 2009, appears to be small, but could increase for more severe pandemics and/or pandemics with greater behavioural change and avoidable absence. © 2013 John Wiley & Sons Ltd.

Military Interoperable Digital Hospital Testbed (MIDHT)

DTIC Science & Technology

2015-12-01

and Analyze the resulting technological impact on medication errors, pharmacists ’ productivity, nurse satisfactions/workflow and patient...medication errors, pharmacists productivity, nurse satisfactions/workflow and patient satisfaction. 1.1.1 Pharmacy Robotics Implementation...1.2 Research and analyze the resulting technological impact on medication errors, pharmacist productivity, nurse satisfaction/workflow and patient

PREDICTIVE SIMULATION MODELING FOR ANTIANDROGEN IMPACTS ON RODENT PROSTATE

EPA Science Inventory

Predictive simulation modeling for antiandrogen impacts on rodent prostate
HA Barton1, RW Setzer1, LK Potter1,2
1US EPA, ORD, NHEERL, ETD, PKB, Research Triangle Park, NC and 2Curriculum in Toxicology, UNC, Chapel Hill, NC

Changes in rodent prostate weight and functi...

Modeling Photosynthesis of Spartina alterniflora (smooth cordgrass) Impacted by the Deepwater Horizon Oil Spill Using Bayesian Inference

NASA Astrophysics Data System (ADS)

Wu, W.; Biber, P. D.; Peterson, M. S.; Gong, C.

2012-12-01

We studied the impact of the Deepwater Horizon oil spill on photosynthesis of coastal saltmarsh plants in Mississippi from July 2010 to November 2011 using field measurements and a hierarchical Bayesian (HB) model. We sampled three locations in Davis Bayou, Mississippi (30.375°N, 88.790°W) representative of a range of oil spill impacts. Measured photosynthesis was negative (respiration only) at the heavily oiled location in July 2010 only, and rates started to increase by August 2010. Photosynthesis at the medium oiled location was lower than at the control location in July 2010 and it continued to decrease in September 2010. During the winter months in 2010-2011, the contrast between the control and the two impacted locations was not as obvious as in the growing season of 2010. Photosynthesis increased through spring 2011 at the three locations and decreased starting with October at the control location and a month earlier (September) at the impacted locations. Using the field data, we developed an HB model. The model simulations agreed well with the measured photosynthesis, and they captured most of the variability of the measured data. Based on the posteriors of the parameters, air temperature and photosynthetic active radiation (PAR) positively influenced photosynthesis whereas the leaf stress level negatively affected photosynthesis. The photosynthesis rates at the heavily impacted location had recovered to the status of the control location about 140 days after the initial impact, while the impact at the medium location was never severe enough to make photosynthesis significantly lower than that at the control location over the study period. The uncertainty in modeling photosynthesis rates mainly came from the individual and micro-site scales, less from the leaf scale. Medians with 95% confidence intervals for the measured photosynthesis rate (μmol C m-2 s-1 - y axis) at the locations of A) Control, B) Medium impact, and C) Heavy impact in each month from July 2010 to November 2011. At the x-axis representing the photosynthetic active radiation intensity, 1 = around 400 μmol C m-2 s-1, 2 = around 800 μmol C m-2 s-1, 3 = around 1200 μmol C m-2 s-1, 4 = around 1600 μmol C m-2 s-1, and 5 = around 2000 μmol C m-2 s-1.

Survival of the Tardigrade Hypsibius Dujardini during Hypervelocity Impact Events up to 5.49 km s-1

NASA Astrophysics Data System (ADS)

Pasini, D.

2014-04-01

Studies have previously been conducted to verify the survivability of living cells during hypervelocity impact events to test the panspermia and lithopanspermia hypotheses [1, 2]. It has been demonstrated that bacteria survive impacts up to 5.4 km s-1 (approx. shock pressure 30 GPa) - albeit with a low probability of survival [1], whilst larger, more complex, objects (such as seeds) break up at ~1 km s-1 [2]. The survivability of yeast spores in impacts up to 7.4 km s-1 has also recently been shown [3]. Previous work by the authors demonstrated the survivability of Nannochloropsis Oculata Phytoplankton, a eukaryotic photosynthesizing autotroph found in the 'euphotic zone' (sunlit surface layers of oceans [4]), at impact velocities up to 6.07 km s-1 [5]. Other groups have also reported that lichens are able to survive shocks in similar pressure ranges [6]. However, whilst many simple single celled organisms have now been shown to survive such impacts (and the associated pressures) as those encountered during the migration of material from one planet to another [1, 3, 5], complex multicellular organisms have either largely not been tested or, those that have been, have not survived the process [2]. Hypsibius dujardini, like most species of tardigrade, are complex organisms composed of approximately 40,000 cells [7]. When humidity decreases they enter a highly dehydrated state known as a 'tun' and can survive extreme temperatures (as low as - 253°C or as high as 151°C), as well as exposure to Xrays and the vacuum of space [7]. Here we test the shock survivability of Hypsibius dujardini by firing a nylon projectile onto a frozen sample of water containing frozen tardigrades using a light gas gun (LGG) [8]. The recovered ice and water were then analysed under an optical microscope to check the viability of any remnant organisms that may have survived impact, and the pressures generated.

The Customer Isn't Always Right-Conservation and Animal Welfare Implications of the Increasing Demand for Wildlife Tourism.

PubMed

Moorhouse, Tom P; Dahlsjö, Cecilia A L; Baker, Sandra E; D'Cruze, Neil C; Macdonald, David W

2015-01-01

Tourism accounts for 9% of global GDP and comprises 1.1 billion tourist arrivals per annum. Visits to wildlife tourist attractions (WTAs) may account for 20-40% of global tourism, but no studies have audited the diversity of WTAs and their impacts on the conservation status and welfare of subject animals. We scored these impacts for 24 types of WTA, visited by 3.6-6 million tourists per year, and compared our scores to tourists' feedback on TripAdvisor. Six WTA types (impacting 1,500-13,000 individual animals) had net positive conservation/welfare impacts, but 14 (120,000-340,000 individuals) had negative conservation impacts and 18 (230,000-550,000 individuals) had negative welfare impacts. Despite these figures only 7.8% of all tourist feedback on these WTAs was negative due to conservation/welfare concerns. We demonstrate that WTAs have substantial negative effects that are unrecognised by the majority of tourists, suggesting an urgent need for tourist education and regulation of WTAs worldwide.

Impact fragmentation of polyurethane and polypropylene cylinder

NASA Astrophysics Data System (ADS)

Kishimura, Hiroaki; Noguchi, Daisuke; Preechasupanya, Worrayut; Matsumoto, Hitoshi

2013-11-01

The impact fragmentation of a bulk polyurethane elastomer (PU) and polypropylene (PP) cylinder have been investigated using a Cu plate projectile launched by a propellant gun at a velocity of 0.53-1.4 km/s. A projectile drills into a PU sample and forms a cavity in the sample. A small number of tiny fragments are formed. When the projectile smashes in at 1.4 km/s, the PU cylinder bursts and PU fragments form. On the other hand, a brittle fracture occurs on the PP cylinder. The mass of fragments from the PU sample generated at a lower impact velocity is distributed in the lognormal form, whereas the mass of fragments from the PU sample generated by a 1.4 km/s impact follows a power-law distribution. The fragment mass distribution of the PP sample generated at a lower impact velocity obeys the power-law form, whereas that generated at a higher impact velocity follows the lognormal form.

Global economic impacts of severe Space Weather.

NASA Astrophysics Data System (ADS)

Schulte In Den Baeumen, Hagen; Cairns, Iver

Coronal mass ejections (CMEs) strong enough to create electromagnetic effects at latitudes below the auroral oval are frequent events, and could have substantial impacts on electric power transmission and telecommunication grids. Modern society’s heavy reliance on these domestic and international networks increases our susceptibility to such a severe Space Weather event. Using a new high-resolution model of the global economy we simulate the economic impact of large CMEs for 3 different planetary orientations. We account for the economic impacts within the countries directly affected as well as the post-disaster economic shock in partner economies through international trade. For the CMEs modeled the total global economic impacts would range from US 380 billion to US 1 trillion. Of this total economic shock 50 % would be felt in countries outside the zone of direct impact, leading to a loss in global GDP of 0.1 - 1 %. A severe Space Weather event could lead to global economic damages of the same order as other weather disasters, climate change, and extreme financial crisis.

External Auditory Canal Dimensions, Age, and Cerumen Retention or Impaction in Persons With Down Syndrome.

PubMed

Dy, Alexander Edward S; Lapeña, José Florencio F

2018-04-01

To investigate associations between age, external auditory canal (EAC) dimensions, and cerumen retention/impaction among persons with Down syndrome (DS). This cross-sectional study evaluated EAC dimensions, cerumen retention/impaction, and middle ear status with pneumatoscopy after extraction in 130 persons with DS. Descriptive and inferential statistics correlated age, presence of impacted/retained cerumen, and EAC diameter. Of 260 ears in 67 males and 63 females with average age of 9.48 years, 72.3% (188) had EAC of ≤4 mm. Those ≤1 year were 4.97 times more likely to have cerumen problems than those >1 year (95% CI, 1.45-17.02, P = .011). The odds of having cerumen problems with an EAC diameter of ≤4 mm were 3.31 times higher than with a diameter of 5 mm (95% CI, 1.46-7.50, P = .004), and odds of having cerumen impaction were as much as 6.19 times higher (95% CI, 2.38-16.08, P < .001). Male gender and low-lying external ear were also associated with increased odds of cerumen problems. There is a high prevalence of cerumen retention/impaction in persons with DS compared to the general Philippine population and a higher prevalence rate for EAC stenosis than elsewhere. A canal diameter of 4 mm and below and age 1 year or less are associated with a significantly higher likelihood of cerumen retention/impaction.

Influence of Tennis Racquet Kinematics on Ball Topspin Angular Velocity and Accuracy during the Forehand Groundstroke

PubMed Central

Kwon, Sunku; Pfister, Robin; Hager, Ronald L.; Hunter, Iain; Seeley, Matthew K.

2017-01-01

Forehand groundstroke effectiveness is important for tennis success. Ball topspin angular velocity (TAV) and accuracy are important for forehand groundstroke effectiveness, and have been extensively studied, previously; despite previous, quality studies, it was unclear whether certain racquet kinematics relate to ball TAV and shot accuracy during the forehand groundstroke. This study evaluated potential relationships between (1) ball TAV and (2) forehand accuracy, and five measures of racquet kinematics: racquet head impact angle (i.e., closed or open face), horizontal and vertical racquet head velocity before impact, racquet head trajectory (resultant velocity direction, relative to horizontal) before impact, and hitting zone length (quasi-linear displacement, immediately before and after impact). Thirteen collegiate-level tennis players hit forehand groundstrokes in a biomechanics laboratory, where racquet kinematics and ball TAV were measured, and on a tennis court, to assess accuracy. Correlational statistics were used to evaluate potential relationships between racquet kinematics, and ball TAV (mixed model) and forehand accuracy (between-subjects model; α = 0.05). We observed an average (1) racquet head impact angle, (2) racquet head trajectory before impact, relative to horizontal, (3) racquet head horizontal velocity before impact, (4) racquet head vertical velocity before impact, and (5) hitting zone length of 80.4 ± 3.6˚, 18.6 ± 4.3˚, 15.4 ± 1.4 m·s-1, 6.6 ± 2.2 m·s-1, and 79.8 ± 8.6 mm, respectively; and an average ball TAV of 969 ± 375 revolutions per minute. Only racquet head impact angle and racquet head vertical velocity, before impact, significantly correlated with ball TAV (p < 0.01). None of the observed racquet kinematics significantly correlated to the measures of forehand accuracy. These results confirmed mechanical logic and indicate that increased ball TAV is associated with a more closed racquet head impact angle (ranging from 70 to 85˚, relative to the ground) and increased racquet head vertical velocity before impact. Key points The study confirmed previous research that two key racquet kinematic variables, near impact, are significantly correlated to ball topspin angular velocity, during the forehand groundstroke: racquet head impact angle (i.e., open or closed racquet face) and racquet vertical velocity, before impact. The trajectory (direction of resultant velocity) and horizontal velocity of the racquet head before impact, and length of hitting zone were not significantly correlated to ball topspin angular velocity, or shot placement accuracy, during the tennis forehand groundstroke, for skilled male players. Hitting zone length was smaller than expected for skilled tennis players performing the forehand groundstroke. PMID:29238250

Comprehensive Coach Education Reduces Head Impact Exposure in American Youth Football.

PubMed

Kerr, Zachary Y; Yeargin, Susan W; Valovich McLeod, Tamara C; Mensch, James; Hayden, Ross; Dompier, Thomas P

2015-10-01

Despite little evidence that defines a threshold of head impact exposure or that participation in youth sports leads to long-term cognitive impairments, it is prudent to identify methods of reducing the frequency of head impacts. To compare the mean number of head impacts between youth football players in practice and games between leagues that implemented the Heads Up Football (HUF) educational program and those that did not (NHUF). Cohort study; Level of evidence, 2. During the 2014 season, head impact exposure was measured using xPatch accelerometers from 70 youth football players aged 8 to 15 years from 5 leagues. Data were collected during both games and practices. The NHUF group comprised 32 players from 8 teams within 3 leagues. The HUF group comprised 38 players from 7 teams within 2 leagues. Independent-sample t tests evaluated differences in head impact exposure across groups (ie, HUF and NHUF). Players (mean ± SD: age, 11.7 ± 1.4 years; height, 152.2 ± 10.5 cm; weight, 51.6 ± 9.6 kg) experienced a total of 7478 impacts over 10g, of which 4250 (56.8%) and 3228 (43.2%) occurred in practices and games, respectively. The majority of impacts occurred within the NHUF group (62.0%), followed by the HUF group (38.0%). With a 10g impact threshold, the mean number of impacts during practice per individual event was lower in the HUF group (mean ± SD, 5.6 ± 2.9) than in the NHUF group (mean ± SD, 8.9 ± 3.1; difference, 3.4; 95% CI, 2.9-3.9). This difference was attenuated when the threshold was changed to 20g but remained significant (difference, 1.0; 95% CI, 0.7-1.3). At both the 10g and 20g impact thresholds, no differences were found in games. Players who participated in HUF leagues accumulated fewer head impacts per practice at both the 10g and 20g thresholds. Youth football leagues should consider the HUF educational program, while exploring additional interventions, to help reduce the number of head impacts in players.

Comprehensive Coach Education Reduces Head Impact Exposure in American Youth Football

PubMed Central

Kerr, Zachary Y.; Yeargin, Susan W.; Valovich McLeod, Tamara C.; Mensch, James; Hayden, Ross; Dompier, Thomas P.

2015-01-01

Background: Despite little evidence that defines a threshold of head impact exposure or that participation in youth sports leads to long-term cognitive impairments, it is prudent to identify methods of reducing the frequency of head impacts. Purpose: To compare the mean number of head impacts between youth football players in practice and games between leagues that implemented the Heads Up Football (HUF) educational program and those that did not (NHUF). Study Design: Cohort study; Level of evidence, 2. Methods: During the 2014 season, head impact exposure was measured using xPatch accelerometers from 70 youth football players aged 8 to 15 years from 5 leagues. Data were collected during both games and practices. The NHUF group comprised 32 players from 8 teams within 3 leagues. The HUF group comprised 38 players from 7 teams within 2 leagues. Independent-sample t tests evaluated differences in head impact exposure across groups (ie, HUF and NHUF). Results: Players (mean ± SD: age, 11.7 ± 1.4 years; height, 152.2 ± 10.5 cm; weight, 51.6 ± 9.6 kg) experienced a total of 7478 impacts over 10g, of which 4250 (56.8%) and 3228 (43.2%) occurred in practices and games, respectively. The majority of impacts occurred within the NHUF group (62.0%), followed by the HUF group (38.0%). With a 10g impact threshold, the mean number of impacts during practice per individual event was lower in the HUF group (mean ± SD, 5.6 ± 2.9) than in the NHUF group (mean ± SD, 8.9 ± 3.1; difference, 3.4; 95% CI, 2.9-3.9). This difference was attenuated when the threshold was changed to 20g but remained significant (difference, 1.0; 95% CI, 0.7-1.3). At both the 10g and 20g impact thresholds, no differences were found in games. Conclusion: Players who participated in HUF leagues accumulated fewer head impacts per practice at both the 10g and 20g thresholds. Youth football leagues should consider the HUF educational program, while exploring additional interventions, to help reduce the number of head impacts in players. PMID:26779546

Electromagnetic Controlled Cortical Impact Device for Precise, Graded Experimental Traumatic Brain Injury

PubMed Central

BRODY, DAVID L.; DONALD, CHRISTINE Mac; KESSENS, CHAD C.; YUEDE, CARLA; PARSADANIAN, MAIA; SPINNER, MIKE; KIM, EDDIE; SCHWETYE, KATHERINE E.; HOLTZMAN, DAVID M.; BAYLY, PHILIP V.

2008-01-01

Genetically modified mice represent useful tools for traumatic brain injury (TBI) research and attractive preclinical models for the development of novel therapeutics. Experimental methods that minimize the number of mice needed may increase the pace of discovery. With this in mind, we developed and characterized a prototype electromagnetic (EM) controlled cortical impact device along with refined surgical and behavioral testing techniques. By varying the depth of impact between 1.0 and 3.0 mm, we found that the EM device was capable of producing a broad range of injury severities. Histologically, 2.0-mm impact depth injuries produced by the EM device were similar to 1.0-mm impact depth injuries produced by a commercially available pneumatic device. Behaviorally, 2.0-, 2.5-, and 3.0-mm impacts impaired hidden platform and probe trial water maze performance, whereas 1.5-mm impacts did not. Rotorod and visible platform water maze deficits were also found following 2.5- and 3.0-mm impacts. No impairment of conditioned fear performance was detected. No differences were found between sexes of mice. Inter-operator reliability was very good. Behaviorally, we found that we could statistically distinguish between injury depths differing by 0.5 mm using 12 mice per group and between injury depths differing by 1.0 mm with 7-8 mice per group. Thus, the EM impactor and refined surgical and behavioral testing techniques may offer a reliable and convenient framework for preclinical TBI research involving mice. PMID:17439349

Influence of Composition on the Environmental Impact of a Cast Aluminum Alloy

PubMed Central

Gómez, Patricia; Elduque, Daniel; Sarasa, Judith; Pina, Carmelo; Javierre, Carlos

2016-01-01

The influence of alloy composition on the environmental impact of the production of six aluminum casting alloys (Al Si12Cu1(Fe), Al Si5Mg, Al Si9Cu3Zn3Fe, Al Si10Mg(Fe), Al Si9Cu3(Fe)(Zn) and Al Si9) has been analyzed. In order to perform a more precise environmental impact calculation, Life Cycle Assessment (LCA) with ReCiPe Endpoint methodology has been used, with the EcoInvent v3 AlMg3 aluminum alloy dataset as a reference. This dataset has been updated with the material composition ranges of the mentioned alloys. The balanced, maximum and minimum environmental impact values have been obtained. In general, the overall impact of the studied aluminum alloys varies from 5.98 × 10−1 pts to 1.09 pts per kg, depending on the alloy composition. In the analysis of maximum and minimum environmental impact, the alloy that has the highest uncertainty is AlSi9Cu3(Fe)(Zn), with a range of ±9%. The elements that contribute the most to increase its impact are Copper and Tin. The environmental impact of a specific case, an LED luminaire housing made out of an Al Si12Cu1(Fe) cast alloy, has been studied, showing the importance of considering the composition. Significant differences with the standard datasets that are currently available in EcoInvent v3 have been found. PMID:28773536

Influence of Composition on the Environmental Impact of a Cast Aluminum Alloy.

PubMed

Gómez, Patricia; Elduque, Daniel; Sarasa, Judith; Pina, Carmelo; Javierre, Carlos

2016-05-25

The influence of alloy composition on the environmental impact of the production of six aluminum casting alloys (Al Si12Cu1(Fe), Al Si5Mg, Al Si9Cu3Zn3Fe, Al Si10Mg(Fe), Al Si9Cu3(Fe)(Zn) and Al Si9) has been analyzed. In order to perform a more precise environmental impact calculation, Life Cycle Assessment (LCA) with ReCiPe Endpoint methodology has been used, with the EcoInvent v3 AlMg3 aluminum alloy dataset as a reference. This dataset has been updated with the material composition ranges of the mentioned alloys. The balanced, maximum and minimum environmental impact values have been obtained. In general, the overall impact of the studied aluminum alloys varies from 5.98 × 10 -1 pts to 1.09 pts per kg, depending on the alloy composition. In the analysis of maximum and minimum environmental impact, the alloy that has the highest uncertainty is AlSi9Cu3(Fe)(Zn), with a range of ±9%. The elements that contribute the most to increase its impact are Copper and Tin. The environmental impact of a specific case, an LED luminaire housing made out of an Al Si12Cu1(Fe) cast alloy, has been studied, showing the importance of considering the composition. Significant differences with the standard datasets that are currently available in EcoInvent v3 have been found.

Long-term microparticle flux variability indicated by comparison of Interplanetary Dust Experiment (IDE) timed impacts for LDEF's first year in orbit with impact data for the entire 5.77-year orbital lifetime

NASA Technical Reports Server (NTRS)

Simon, Charles G.; Mulholland, J. Derral; Oliver, John P.; Cooke, William J.; Kassel, Philip C., Jr.

1993-01-01

The electronic sensors of the Interplanetary Dust Experiment (IDE) recorded precise impact times and approximate directions for submicron to approximately 100 micron size particles on all six primary sides of the spacecraft for the first 346 days of the LDEF orbital mission. Previously-reported analyses of the timed impact data have established their spatio-temporal features, including the demonstration that a preponderance of the particles in this regime are orbital debris and that a large fraction of the debris particles are encountered in megameter-size clouds. Short-term fluxes within such clouds can rise several orders of magnitude above the long-term average. These unexpectedly large short-term variations in debris flux raise the question of how representative an indication of the multi-year average flux is given by the nearly one year of timed data. One of the goals of the IDE was to conduct an optical survey of impact sites on detectors that remained active during the entire LDEF mission, to obtain full-mission fluxes. We present here the comparisons and contrasts among the new IDE optical survey impact data, the IDE first-year timed impact data, and impact data from other LDEF micrometeoroid and debris experiments. The following observations are reported: (1) the 5.77 year long-term integrated microparticle impact fluxes recorded by IDE detectors matched the integrated impact fluxes measured by other LDEF investigators for the same period; (2) IDE integrated microparticle impact fluxes varied by factors from 0.5 to 8.3 for LDEF days 1-346, 347-2106 and 1-2106 (5.77 years) on rows 3 (trailing edge, or West), 6 (South side), 12 (North side), and the Earth and Space ends; and (3) IDE integrated microparticle impact fluxes varied less than 3 percent for LDEF days 1-346, 347-2106 and 1-2106 (5.77 years) on row 9 (leading edge, or East). These results give further evidence of the accuracy and internal consistency of the recorded IDE impact data. This leads to the further conclusion that the utility of long-term ratios for impacts on various sides of a stabilized satellite in low Earth orbit (LEO) is extremely limited. These observations and their consequences highlight the need for continuous, real time monitoring of the dynamic microparticle environment in LEO.

A novel accelerometer-based method to describe day-to-day exposure to potentially osteogenic vertical impacts in older adults: findings from a multi-cohort study.

PubMed

Hannam, K; Deere, K C; Hartley, A; Clark, E M; Coulson, J; Ireland, A; Moss, C; Edwards, M H; Dennison, E; Gaysin, T; Cooper, R; Wong, A; McPhee, J S; Cooper, C; Kuh, D; Tobias, J H

2017-03-01

This observational study assessed vertical impacts experienced in older adults as part of their day-to-day physical activity using accelerometry and questionnaire data. Population-based older adults experienced very limited high-impact activity. The accelerometry method utilised appeared to be valid based on comparisons between different cohorts and with self-reported activity. We aimed to validate a novel method for evaluating day-to-day higher impact weight-bearing physical activity (PA) in older adults, thought to be important in protecting against osteoporosis, by comparing results between four cohorts varying in age and activity levels, and with self-reported PA levels. Participants were from three population-based cohorts, MRC National Survey of Health and Development (NSHD), Hertfordshire Cohort Study (HCS) and Cohort for Skeletal Health in Bristol and Avon (COSHIBA), and the Master Athlete Cohort (MAC). Y-axis peaks (reflecting the vertical when an individual is upright) from a triaxial accelerometer (sampling frequency 50 Hz, range 0-16 g) worn at the waist for 7 days were classified as low (0.5-1.0 g), medium (1.0-1.5 g) or higher (≥1.5 g) impacts. There were a median of 90, 41 and 39 higher impacts/week in NSHD (age 69.5), COSHIBA (age 76.8) and HCS (age 78.5) participants, respectively (total n = 1512). In contrast, MAC participants (age 68.5) had a median of 14,322 higher impacts/week. In the three population cohorts combined, based on comparison of beta coefficients, moderate-high-impact activities as assessed by PA questionnaire were suggestive of stronger association with higher impacts from accelerometers (0.25 [0.17, 0.34]), compared with medium (0.18 [0.09, 0.27]) and low impacts (0.13 [0.07,0.19]) (beta coefficient, with 95 % CI). Likewise in MAC, reported moderate-high-impact activities showed a stronger association with higher impacts (0.26 [0.14, 0.37]), compared with medium (0.14 [0.05, 0.22]) and low impacts (0.03 [-0.02, 0.08]). Our new accelerometer method appears to provide valid measures of higher vertical impacts in older adults. Results obtained from the three population-based cohorts indicate that older adults generally experience very limited higher impact weight-bearing PA.

40Ar/39Ar age of the Manson impact structure, Iowa, and correlative impact ejecta in the Crow Creek member of the Pierre Shale (Upper Cretaceous), South Dakota and Nebraska

USGS Publications Warehouse

Izett, G.A.; Cobban, W.A.; Dalrymple, G.B.; Obradovich, J.D.

1998-01-01

A set of 34 laser total-fusion 40Ar/39Ar analyses of sanidine from a melt layer in crater-fill deposits of the Manson impact structure in Iowa has a weighted-mean age of 74.1 ?? 0.1 Ma. This age is about 9.0 m.y. older than 40Ar/39Ar ages of shocked microcline from the Manson impact structure reported previously by others. The 74.1 Ma age of the sanidine, which is a melt product of Precambrian microcline clasts, indicates that the Manson impact structure played no part in the Cretaceous-Tertiary (K-T) mass extinction at 64.5 Ma. Moreover, incremental-heating 40Ar/39Ar ages of the sanidine show that it is essentially free of excess 40Ar and has not been influenced by postcrystallization heating or alteration. An age spectrum of the matrix of the melt layer shows effects of 39Ar recoil, including older ages in the low-temperature increments and younger ages in the high-temperature increments. At 17 places in eastern South Dakota and Nebraska, shocked quartz and feldspar grains are concentrated in the lower part of the Crow Creek Member of the Pierre Shale (Upper Cretaceous). The grains are largest (3.2 mm) in southeastern South Dakota and decrease in size (0.45 mm) to the northwest, consistent with the idea that the Manson impact structure was their source. The ubiquitous presence of shocked grains concentrated in a thin calcarenite at the base of the Crow Creek Member suggests it is an event bed recording an instant of geologic time. Ammonites below and above the Crow Creek Member limit its age to the zone of Didymoceras nebrascense of earliest late Campanian age. Plagioclase from a bentonite bed in this zone in Colorado has a 40Ar/39Ar age of 74.1 ?? 0.1 Ma commensurate with our sanidine age of 74.1 Ma for the Manson impact structure. 40Ar/39Ar ages of bentonite beds below and above the Crow Creek are consistent with our 74.1 ?? 0.1 Ma age for the Manson impact structure and limit its age to the interval ?? 74.5 0.1 to 73.8 ?? 0.1 Ma. Recently, two origins for the Crow Creek have been proposed - eastward transgression of the Late Cretaceous sea and a Manson impact-triggered tsunami. We conclude that most data are in accord with an impact origin for the Crow Creek Member and are at odds with the marine transgression hypothesis.

Effect of neck flexor muscle activation on impact velocity of the head during backward falls in young adults.

PubMed

Choi, W J; Robinovitch, S N; Ross, S A; Phan, J; Cipriani, D

2017-11-01

Falls are a common cause of traumatic brain injuries (TBI) across the lifespan. A proposed but untested hypothesis is that neck muscle activation influences impact severity and risk for TBI during a fall. We conducted backward falling experiments to test whether activation of the neck flexor muscles facilitates the avoidance of head impact, and reduces impact velocity if the head contacts the ground. Young adults (n=8) fell from standing onto a 30cm thick gymnastics mat while wearing a helmet. Participants were instructed to fall backward and (a) prevent their head from impacting the mat ("no head impact" trials); (b) allow their head to impact the mat, but with minimal impact severity ("soft impact" trials); and (c) allow their head to impact the mat, while inhibiting efforts to reduce impact severity ("hard impact" trials). Trial type associated with peak magnitude of electromyographic activity of the sternocleidomastoid (SCM) muscles (p<0.017), and with the vertical and horizontal velocity of the head at impact (p<0.001). Peak SCM activations, expressed as percent maximal voluntary isometric contraction (%MVIC), averaged 75.3, 67.5, and 44.5%MVIC in "no head impact", "soft impact", and "hard impact" trials, respectively. When compared to "soft impact" trials, vertical impact velocities in "hard impact" trials averaged 87% greater (3.23 versus 1.73m/s) and horizontal velocities averaged 83% greater (2.74 versus 1.50m/s). For every 10% increase in SCM %MVIC, vertical impact velocity decreased 0.24m/s and horizontal velocity decreased 0.22m/s. We conclude that SCM activation contributes to the prevention and modulation of head impact severity during backward falls. Copyright © 2017 Elsevier Ltd. All rights reserved.

32 CFR 989.1 - Purpose.

Code of Federal Regulations, 2011 CFR

2011-07-01

... Acquisition Programs and Major Automated Information System Acquisition Programs. 1 To comply with NEPA and... ANALYSIS PROCESS (EIAP) § 989.1 Purpose. (a) This part implements the Air Force Environmental Impact Analysis Process (EIAP) and provides procedures for environmental impact analysis both within the United...

Impact resistance of hybrid composite fan blade materials

NASA Technical Reports Server (NTRS)

Friedrich, L. A.

1974-01-01

Improved resistance to foreign object damage was demonstrated for hybrid composite simulated blade specimens. Transply metallic reinforcement offered additional improvement in resistance to gelatin projectile impacts. Metallic leading edge protection permitted equivalent-to-titanium performance of the hybrid composite simulated blade specimen for impacts with 1.27 cm and 2.54 cm (0.50 and 1.00 inch) diameter gelatin spheres.

Reprint of: Ionization probabilities of Ne, Ar, Kr, and Xe by proton impact for different initial states and impact energies

NASA Astrophysics Data System (ADS)

Montanari, C. C.; Miraglia, J. E.

2018-01-01

In this contribution we present ab initio results for ionization total cross sections, probabilities at zero impact parameter, and impact parameter moments of order +1 and -1 of Ne, Ar, Kr, and Xe by proton impact in an extended energy range from 100 keV up to 10 MeV. The calculations were performed by using the continuum distorted wave eikonal initial state approximation (CDW-EIS) for energies up to 1 MeV, and using the first Born approximation for larger energies. The convergence of the CDW-EIS to the first Born above 1 MeV is clear in the present results. Our inner-shell ionization cross sections are compared with the available experimental data and with the ECPSSR results. We also include in this contribution the values of the ionization probabilities at the origin, and the impact parameter dependence. These values have been employed in multiple ionization calculations showing very good description of the experimental data. Tables of the ionization probabilities are presented, disaggregated for the different initial bound states, considering all the shells for Ne and Ar, the M-N shells of Kr and the N-O shells of Xe.

Impact data from a transport aircraft during a controlled impact demonstration

NASA Technical Reports Server (NTRS)

Fasanella, E. L.; Alfaro-Bou, E.; Hayduk, R. J.

1986-01-01

On December 1, 1984, the FAA and NASA conducted a remotely piloted air-to-ground crash test of a Boeing 720 transport aircraft instrumented to measure crash loads of the structure and the anthropomorphic dummy passengers. Over 330 time histories of accelerations and loads collected during the Full-Scale Transport Controlled Impact Demonstration (CID) for the 1-sec period after initial impact are presented. Although a symmetric 1 deg. nose-up attitude with a 17 ft/sec sink rate was planned, the plane was yawed and rolled 13 deg. at initial (left-wing) impact. The first fuselage impact occurred near the nose wheel well with the nose pitched down 2.5 deg. Peak normal (vertical) floor accelerations were highest in the cockpit and forward cabin near the nose wheel well and were approximately 14G. The remaining cabin floor received normal acceleration peaks of 7G or less. The peak longitudinal floor accelerations showed a similar distribution, with the highest (7G) in the cockpit and forward cabin, decreasing to 4G or less toward the rear. Peak transverse floor accelerations ranged from about 5G in the cockpit to 1G in the aft fuselage.

High Resolution Emission Spectroscopy of the Alpha Pi-1 - Chi Sigma-1(+) Fourth Positive Band System of CO from Electron Impact

NASA Technical Reports Server (NTRS)

Beegle, Luther W.; Ajello, Joseph M.; James, Geoffrey K.; Alvarez, Marcos; Dziczek, Dariusz

2000-01-01

We report electron-impact induced fluorescence spectra [300 mA full width at half maximum (FWHM)] of CO for 20 and 100 eV impact energies of the spectral region of 1300 to 2050 A and high resolution spectra (FWHM) of the v'=5 to v"=l and the v'=3 to v"=O bands showing that the rotational structure of the band system are modeled accurately. The excitation function of the (0,1) band (1597 A) was measured from electron impact in the energy range from threshold to 750 eV and placed on an absolute scale from modem calibration standards.

Development of head injury assessment reference values based on NASA injury modeling.

PubMed

Somers, Jeffrey T; Granderson, Bradley; Melvin, John W; Tabiei, Ala; Lawrence, Charles; Feiveson, Alan; Gernhardt, Michael; Ploutz-Snyder, Robert; Patalak, John

2011-11-01

NASA is developing a new crewed vehicle and desires a lower risk of injury compared to automotive or commercial aviation. Through an agreement with the National Association of Stock Car Auto Racing, Inc. (NASCAR®), an analysis of NASCAR impacts was performed to develop new injury assessment reference values (IARV) that may be more relevant to NASA's context of vehicle landing operations. Head IARVs associated with race car impacts were investigated by analyzing all NASCAR recorded impact data for the 2002-2008 race seasons. From the 4015 impact files, 274 impacts were selected for numerical simulation using a custom NASCAR restraint system and Hybrid III 50th percentile male Finite Element Model (FEM) in LS-DYNA. Head injury occurred in 27 of the 274 selected impacts, and all of the head injuries were mild concussions with or without brief loss of consciousness. The 247 noninjury impacts selected were representative of the range of crash dynamics present in the total set of impacts. The probability of head injury was estimated for each metric using an ordered probit regression analysis. Four metrics had good correlation with the head injury data: head resultant acceleration, head change in velocity, HIC 15, and HIC 36. For a 5% risk of AIS≥1/AIS≥2 head injuries, the following IARVs were found: 121.3/133.2 G (head resultant acceleration), 20.3/22.0 m/s (head change in velocity), 1,156/1,347 (HIC 15), and 1,152/1,342 (HIC 36) respectively. Based on the results of this study, further analysis of additional datasets is recommended before applying these results to future NASA vehicles.

Impacts of recurrent aphthous stomatitis on quality of life of 12- and 15-year-old Thai children.

PubMed

Krisdapong, Sudaduang; Sheiham, Aubrey; Tsakos, Georgios

2012-02-01

To assess the prevalence and characteristics of oral impacts attributed to recurrent aphthous stomatitis (RAS) in 12- and 15-year-olds Thais. A national oral health survey was conducted. Child-OIDP and OIDP indices were used to collect oral impacts in 1,100 12- and 871 15 year olds. RAS-related impacts were reported in 24.7% of 12 and 36.2% of 15 year olds. Girls were more likely than boys to report RAS-related impacts. Among all perceived causes of oral impacts, RAS ranked second for 12 and first for 15 year olds. Among 12 and 15 years olds, 79.8 and 86.8% respectively had impacts on eating, 81.0 and 84.4% on cleaning teeth and 51.7 and 60.3% on emotional stability. For individual children, impacts affected between 1-6 daily performances. Impacts were of 'little' and 'moderate' intensity for 12 and 15 year olds, respectively. RAS-related impacts occurred mostly in combination with impacts from other oral conditions. Combined with other oral conditions, the impacts were worse, in terms of score, intensity and extent, than when RAS occurred alone. RAS-related impacts were common in 12- and 15-year-old Thai children and mostly affected eating, cleaning teeth and emotional stability. RAS tended to occur with other conditions leading to more severe, more extensive impacts on quality of life.

Normal impact of a low-velocity projectile against a taut string-like membrane

NASA Astrophysics Data System (ADS)

Zhao, Yifei; Sun, Zhili

2018-07-01

For the impact system in which a moving projectile transversely impacts against a taut fabric band, 1-D linearized model applies because of low-velocity, sufficient pretension, and the sizes of the objects. This projectile-to-band impact model can serve as the physical prototype of applications in engineering such as cable-membrane architectures and seat belts. In this fundamental work, the response properties under central and non-central impacts are investigated analytically from the viewpoint of wave propagations, while comparisons and verifications are made with finite element (FE) analysis. For a central impact after the first separation, band can catch up with the projectile such that a contact-impact state is re-established when m is in the small interval neighbouring m = 1. For a non-central impact, the projectile would be subjected to a combination of translation and rotation due to asymmetric wave propagations. From every certain instant, the projectile is subjected to an additional rotational acceleration (principal moment) with an abrupt or zero initial value in the anti-clockwise or clockwise direction. The swing amplitude of a small-j or a flat projectile is susceptible to significant fluctuations, and vice versa. The band with a rather large off-centre ratio for the impacted zone and a rather short length of the shorter segment would facilitate a larger accumulation of swing amplitude in a single direction soon after the impact. The linearized impact models proposed can be used to well describe the small-deflection responses for the system, based on 1-D wave propagations or the dependence of quasi-static band deflection on time if the impact duration is much longer than the double wave transit time for the band.

Chemical fractionation resulting from the hypervelocity impact process on metallic targets

NASA Astrophysics Data System (ADS)

Libourel, Guy; Ganino, Clément; Michel, Patrick; Nakamura, Akiko

2016-10-01

In a regime of hypervelocity impact cratering, the internal energy deposited in target + projectile region is large enough to melt and/or vaporize part of the material involved, which expands rapidly away from the impact site. Fast and energetic impact processes have therefore important chemical consequences on the projectile and target rock transformations during major impact events. Several physical and chemical processes occurred indeed in the short duration of the impact, e.g., melting, coating, mixing, condensation, crystallization, redox reactions, quenching, etc., all concurring to alter both projectile and target composition on the irreversible way.In order to document such hypervelocity impact chemical fractionation, we have started a program of impact experiments by shooting doped (27 trace elements) millimeter-sized basalt projectiles on metallic target using a two stages light gas gun. With impact velocity in the range from 0.25 to 7 km.s-1, these experiments are aimed i) to characterize chemically and texturally all the post-mortem materials (e.g., target, crater, impact melt, condensates, and ejectas), in order ii) to make a chemical mass balance budget of the process, and iii) to relate it to the kinetic energy involved in the hypervelocity impacts for scaling law purpose. Irrespective of the incident velocities, our preliminary results show the importance of redox processes, the significant changes in the ejecta composition (e.g., iron enrichment) and the systematic coating of the crater by the impact melt [1]. On the target side, characterizations of the microstructure of the shocked iron alloys to better constrain the shielding processes. We also show how these results have great implications in our understanding on the current surface properties of small bodies, and chiefly in the case of M-type asteroids. [1] Ganino C, Libourel G, Nakamura AM & Michel P (2015) Goldschmidt Abstracts, 2015 990.

10 CFR 51.32 - Finding of no significant impact.

Code of Federal Regulations, 2010 CFR

2010-01-01

... 10 Energy 2 2010-01-01 2010-01-01 false Finding of no significant impact. 51.32 Section 51.32... Section 102(2) Finding of No Significant Impact § 51.32 Finding of no significant impact. (a) A finding of no significant impact will: (1) Identify the proposed action; (2) State that the Commission has...

Randomized trials published in higher vs. lower impact journals differ in design, conduct, and analysis.

PubMed

Bala, Malgorzata M; Akl, Elie A; Sun, Xin; Bassler, Dirk; Mertz, Dominik; Mejza, Filip; Vandvik, Per Olav; Malaga, German; Johnston, Bradley C; Dahm, Philipp; Alonso-Coello, Pablo; Diaz-Granados, Natalia; Srinathan, Sadeesh K; Hassouneh, Basil; Briel, Matthias; Busse, Jason W; You, John J; Walter, Stephen D; Altman, Douglas G; Guyatt, Gordon H

2013-03-01

To compare methodological characteristics of randomized controlled trials (RCTs) published in higher vs. lower impact Core Clinical Journals. We searched MEDLINE for RCTs published in 2007 in Core Clinical Journals. We randomly sampled 1,140 study reports in a 1:1 ratio in higher (five general medicine journals with the highest total citations in 2007) and lower impact journals. Four hundred sixty-nine RCTs proved eligible: 219 in higher and 250 in lower impact journals. RCTs in higher vs. lower impact journals had larger sample sizes (median, 285 vs. 39), were more likely to receive industry funding (53% vs. 28%), declare concealment of allocation (66% vs. 36%), declare blinding of health care providers (53% vs. 41%) and outcome adjudicators (72% vs. 54%), report a patient-important primary outcome (69% vs. 50%), report subgroup analyses (64% vs. 26%), prespecify subgroup hypotheses (42% vs. 20%), and report a test for interaction (54% vs. 27%); P < 0.05 for all differences. RCTs published in higher impact journals were more likely to report methodological safeguards against bias and patient-important outcomes than those published in lower impact journals. However, sufficient limitations remain such that publication in a higher impact journal does not ensure low risk of bias. Copyright © 2013 Elsevier Inc. All rights reserved.

Positive Impacts of Modeling Instruction on Self-Efficacy

NASA Astrophysics Data System (ADS)

Sawtelle, Vashti; Brewe, Eric; Kramer, Laird H.

2010-10-01

Analysis of the impact of Modeling Instruction (MI) on the sources of self-efficacy for students in Introductory Physics 1 will be presented. We measured self-efficacy through a quantitative diagnostic (SOSESC) developed by Fencl and Scheel [1] to investigate the impact of instruction on the sources of self-efficacy in all introductory physics classes. We collected both pre- semester data and post-semester data, and evaluated the effect of the classroom by analyzing the shift (Post-Pre). At Florida International University, a Hispanic-serving institution, we find that traditional lecture classrooms negatively impact the self-efficacy of all students, while the MI courses had no impact for all students. Further, when disaggregating the data by gender and sources of self-efficacy, we find that Modeling Instruction positively impacted the Verbal Persuasion source of self-efficacy for women. This positive impact helps to explain high rates of retention for women in the MI classes.

Central Radar System, Over-the-Horizon Backscatter

DTIC Science & Technology

1990-03-09

1,2-Dibromo-3- chloropropane (DBCP) 0.3 TABLE 41-6 (Continued). MINNESOTA RECOMMENDED ALLOWABLE LIMITS (RAL) FOR DRINKING WATER WELLS Compound RAL (ug/ 1 ...TABLE OF CONTENTS ENVIRONMENTAL IMPACT ANALYSIS PROCESS OVERVIEW ............ TECHNICAL STUDY 1 FACILITIES...TECHNICAL STUDY 10 0 TECHNICAL STUDY 1 CENTRAL RADAR SYSTEM OVER-THE-HORIZON BACKSCATTER RADAR PROGRAM 0 ENVIRONMENTAL IMPACT

DEVELOPING A PREDICTIVE SIMULATION MODEL FOR ANTIANDROGEN IMPACTS ON RODENT PROSTATE

EPA Science Inventory

Developing a predictive simulation model for antiandrogen impacts on rodent prostate
HA Barton1, RW Setzer1, LK Potter1,2
1US EPA, ORD, NHEERL, ETD, PKB, Research Triangle Park, NC and 2Curriculum in Toxicology, UNC, Chapel Hill, NC

Alterations in rodent prostate wei...

Iridium Concentrations and Abundances of Meteoritic Ejecta from the Eltanin Impact in Sediment Cores from Polarstern Expedition ANT XII/4

NASA Technical Reports Server (NTRS)

Kyte, Frank T.

2002-01-01

The abundances of meteoritic ejecta from the Eltanin asteroid impact have been examined in several sediment cores recovered by the FS Polarstern during expedition ANT XII/4 using elemental concentrations of iridium and weights of coarse ejecta debris. Three cores with well-preserved impact deposits, PS204-1, PS2708-1, and PS2709-1, each contain Ir and ejecta fluences similar to those found in USNS Eltanin core E13-4. Small Ir anomalies and traces of ejecta were found in cores PS2706-1 and PS2710-1, but since these cores lack well-defined deposits, these are considered to be reworked and not representative of the fallout. No evidence of ejecta was found in cores PS2802-1 and PS2705-1. These results confirm earlier speculation that the Eltanin impact resulted in deposits of ejecta with up to 1 gram/sq centimeter of depris over a wide area of the ocean floor. However, there are sill large uncertainties over the actual regional or global extent of this unique sediment deposit.

Study of ice cluster impacts on amorphous silica using the ReaxFF reactive force field molecular dynamics simulation method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rahnamoun, A.; Duin, A. C. T. van

We study the dynamics of the collisions between amorphous silica structures and amorphous and crystal ice clusters with impact velocities of 1 km/s, 4 km/s, and 7 km/s using the ReaxFF reactive molecular dynamics simulation method. The initial ice clusters consist of 150 water molecules for the amorphous ice cluster and 128 water molecules for the crystal ice cluster. The ice clusters are collided on the surface of amorphous fully oxidized and suboxide silica. These simulations show that at 1 km/s impact velocities, all the ice clusters accumulate on the surface and at 4 km/s and 7 km/s impact velocities, some of the ice cluster moleculesmore » bounce back from the surface. At 4 km/s and 7 km/s impact velocities, few of the water molecules dissociations are observed. The effect of the second ice cluster impacts on the surfaces which are fully covered with ice, on the mass loss/accumulation is studied. These studies show that at 1 km/s impacts, the entire ice cluster accumulates on the surface at both first and second ice impacts. At higher impact velocities, some ice molecules which after the first ice impacts have been attached to the surface will separate from the surface after the second ice impacts at 7 km/s impact velocity. For the 4 km/s ice cluster impact, ice accumulation is observed for the crystal ice cluster impacts and ice separation is observed for the amorphous ice impacts. Observing the temperatures of the ice clusters during the collisions indicates that the possibility of electron excitement at impact velocities less than 10 km/s is minimal and ReaxFF reactive molecular dynamics simulation can predict the chemistry of these hypervelocity impacts. However, at impact velocities close to 10 km/s the average temperature of the impacting ice clusters increase to about 2000 K, with individual molecules occasionally reaching temperatures of over 8000 K and thus it will be prudent to consider the concept of electron excitation at these higher impact velocities, which goes beyond the current ReaxFF ability.« less

Health impact assessment of traffic noise in Madrid (Spain).

PubMed

Tobías, Aurelio; Recio, Alberto; Díaz, Julio; Linares, Cristina

2015-02-01

The relationship between environmental noise and health has been examined in depth. In view of the sheer number of persons exposed, attention should be focused on road traffic noise. The city of Madrid (Spain) is a densely populated metropolitan area in which 80% of all environmental noise exposure is attributed to traffic. The aim of this study was to quantify avoidable deaths resulting from reducing the impact of equivalent diurnal noise levels (LeqD) on daily cardiovascular and respiratory mortality among people aged ≥65 years in Madrid. A health impact assessment of (average 24h) LeqD and PM2.5 levels was conducted by using previously reported risk estimates of mortality rates for the period 2003-2005: For cardiovascular causes: LeqD 1.048 (1.005, 1.092) and PM2.5 1.041(1.020, 1.062) and for respiratory causes: LeqD 1.060 (1.000, 1.123) and PM2.5 1.030 (1.000, 1.062). The association found between LeqD exposure and mortality for both causes suggests an important health effect. A reduction of 1dB(A) in LeqD implies an avoidable annual mortality of 284 (31, 523) cardiovascular- and 184 (0, 190) respiratory-related deaths in the study population. The magnitude of the health impact is similar to reducing average PM2.5 levels by 10µg/m(3). Regardless of air pollution, exposure to traffic noise should be considered an important environmental factor having a significant impact on health. Copyright © 2014 Elsevier Inc. All rights reserved.

23 CFR 777.9 - Mitigation of impacts.

Code of Federal Regulations, 2012 CFR

2012-04-01

... IMPACTS TO WETLANDS AND NATURAL HABITAT § 777.9 Mitigation of impacts. (a) Actions eligible for Federal... wetlands or natural habitats. The following actions qualify for Federal-aid highway funding: (1) Avoidance and minimization of impacts to wetlands or natural habitats through realignment and special design...

23 CFR 777.9 - Mitigation of impacts.

Code of Federal Regulations, 2013 CFR

2013-04-01

... IMPACTS TO WETLANDS AND NATURAL HABITAT § 777.9 Mitigation of impacts. (a) Actions eligible for Federal... wetlands or natural habitats. The following actions qualify for Federal-aid highway funding: (1) Avoidance and minimization of impacts to wetlands or natural habitats through realignment and special design...

23 CFR 777.9 - Mitigation of impacts.

Code of Federal Regulations, 2014 CFR

2014-04-01

... IMPACTS TO WETLANDS AND NATURAL HABITAT § 777.9 Mitigation of impacts. (a) Actions eligible for Federal... wetlands or natural habitats. The following actions qualify for Federal-aid highway funding: (1) Avoidance and minimization of impacts to wetlands or natural habitats through realignment and special design...

Hypervelocity impact cratering calculations

NASA Technical Reports Server (NTRS)

Maxwell, D. E.; Moises, H.

1971-01-01

A summary is presented of prediction calculations on the mechanisms involved in hypervelocity impact cratering and response of earth media. Considered are: (1) a one-gram lithium-magnesium alloys impacting basalt normally at 6.4 km/sec, and (2) a large terrestrial impact corresponding to that of Sierra Madera.

Heat treatment effects on impact toughness of 9Cr 1MoVNb and 12Cr 1MoVW steels irradiated to 100 dpa

NASA Astrophysics Data System (ADS)

Klueh, R. L.; Alexander, D. J.

1998-10-01

Plates of 9Cr-1MoVNb and 12Cr-1MoVW steels were given four different heat treatments: two normalizing treatments were used and for each normalizing treatment two tempers were used. Miniature Charpy specimens from each heat treatment were irradiated to ≈20 dpa at 365°C and to ≈100 dpa at 420°C in the Fast Flux Test Facility (FFTF). In previous work, the same steels were irradiated in FFTF to 4-5 dpa at 365°C and 35-36 dpa at 420°C. The tests indicated that prior austenite grain size, which was varied by the different normalizing treatments, affected the impact behavior of the 9Cr-1MoVNb but not the 12Cr-1MoVW. Tempering had relatively little effect on the impact behavior of both steels. Conclusions are presented on how heat treatment can be used to optimize impact properties.

CPO Prediction: Accuracy Assessment and Impact on UT1 Intensive Results

NASA Technical Reports Server (NTRS)

Malkin, Zinovy

2010-01-01

The UT1 Intensive results heavily depend on the celestial pole offset (CPO) model used during data processing. Since accurate CPO values are available with a delay of two to four weeks, CPO predictions are necessarily applied to the UT1 Intensive data analysis, and errors in the predictions can influence the operational UT1 accuracy. In this paper we assess the real accuracy of CPO prediction using the actual IERS and PUL predictions made in 2007-2009. Also, results of operational processing were analyzed to investigate the actual impact of EOP prediction errors on the rapid UT1 results. It was found that the impact of CPO prediction errors is at a level of several microseconds, whereas the impact of the inaccuracy in the polar motion prediction may be about one order of magnitude larger for ultra-rapid UT1 results. The situation can be amended if the IERS Rapid solution will be updated more frequently.

Assessing Man’s Impact on Wetlands,

DTIC Science & Technology

1980-12-01

AD-A94 652 ARMY MILITARY PERSONNEL CENTER ALEXANDRIA VA F/S 8/6 ASSESSZNG MAN’S IMPACT ON WE LANDS,(U) UNCLASSIFIED 0 GALLOWAY 1 A uhuhfuhfhumEIliE...EElliE mrhhmhhhhEEohE mmmmmmmmm Assessing Mns Impact on Wetlands By G.E. Galloway rpp fo f A.l - 5 UN RI pulcto N-RI7-3 D 1 i ILI ’!UNt’ Sea Grant...TITLE (and Subtitle) - - 5. TYPE OF REPORT & PERIOD COVERED /Assessing Man’s Impact on Wetlands December 1980 6. PERFORMING ORG. REPORT NUMBER 7- AU HOR

Oral mucosal lesions' impact on oral health-related quality of life in preschool children.

PubMed

de Oliveira, Luísa Jardim Corrêa; Torriani, Dione Dias; Correa, Marcos Britto; Peres, Marco Aurélio; Peres, Karen Glazer; Matijasevich, Alicia; Dos Santos, Iná da Silva; Barros, Aluisio J D; Demarco, Flávio Fernando; Tarquinio, Sandra Beatriz Chaves

2015-12-01

The aim of this study was to assess the prevalence of oral mucosal lesions and their impact on oral health-related quality of life (OHRQoL) in children aged 5 years. A sample of 1118 children from Pelotas' birth cohort, born in 2004 (response rate of 85.8%), were selected to participate in the study. Data were collected using a questionnaire applied to mothers and from the oral examinations of the children. OML were identified by type, site, and size. Early Childhood Oral Health Impact Scale (ECOHIS) was used to assess caregivers' perception on children's OHRQoL. Descriptive, bivariate, and multivariate Poisson regression analyses were carried out, considering the impact on OHRQoL (total ECOHIS score) as the outcome. The prevalence of the OML was 30.1% (95% CI 27.5-32.9). Ulcers were the more prevalent type of lesion (29.4%), and the most affected site was the gums (31.0%). In bivariate analysis, there was a positive association between the presence of OML and OHRQoL impact measured by the following: mean overall score of ECOHIS (P < 0.001); extent (P < 0.001); prevalence (P = 0.030); and intensity (P = 0.010). After adjustments for sociodemographic and oral health variables, children with OML presented higher impact on OHRQoL [rate ratio (RR) 1.38 95% CI 1.11; 1.72] comparing with their counterparts. Analyzing specific domains, children with OML also presented higher impact on children symptoms (RR 1.46 95% CI 1.20; 1.66) and family functional (RR 3.14 95% CI 1.59; 6.22) domains. Almost one-third of children presented with oral mucosal lesions, and these lesions impaired children's oral health-related quality of life. © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Impact ionisation mass spectrometry of platinum-coated olivine and magnesite-dominated cosmic dust analogues

NASA Astrophysics Data System (ADS)

Hillier, Jon K.; Sternovsky, Z.; Kempf, S.; Trieloff, M.; Guglielmino, M.; Postberg, F.; Price, M. C.

2018-07-01

Impact ionisation mass spectrometry enables the composition of cosmic dust grains to be determined in situ by spacecraft-based instrumentation. The proportion of molecular ions in the impact plasma is a function of the impact velocity, making laboratory calibration vital for the interpretation of the mass spectra, particularly at the low velocities typical of lunar or asteroid encounters. Here we present an analysis of laboratory impact ionisation mass spectra from primarily low (<15 km s-1) velocity impacts of both olivine and magnesite-dominated particles onto the SUrface Dust Mass Analyzer (SUDA) laboratory mass spectrometer. The cation mass spectra show characteristic peaks due to their constituent elements, with Mg, Al, Si, C, Ca, O and Fe frequently present. Contaminant species from the conductive coating process (B, Na, K, C, Pt) also occur, at varying frequencies. Possible saponite or talc inclusions in the magnesite particles are revealed by the presence of Si, Fe, Ca and Al in the magnesite mass spectra. Magnesium is clearly present at the lowest impact velocities (3 km s-1), at which alkali metals were presumed to dominate. Peaks attributed to very minor amounts of water or hydroxyl present in the grains are also seen at low velocities in both cation and anion mass spectra, demonstrating the feasibility of impact ionisation mass spectrometry in identifying hydrated or hydrous minerals, during very low velocity encounters or with very low abundances of water or hydroxy groups, in the impinging grains. Velocity thresholds for the reliable identification of the major elements within the magnesite and olivine cation spectra are presented. Additionally, relative sensitivity factors for Mg (5.1), Fe (1.5) and O (0.6) with respect to Si, in the olivine particles, at impact speeds >19 km s-1, were found to be very similar to those previously determined for orthopyroxene-dominated particles, despite different target and projectile materials. This confirms that quantitative analyses of mineral dust grain composition in space is viable despite initially poorly-constrained mineralogy.

Selection of spatial scale for assessing impacts of groundwater-based water supply on freshwater resources.

PubMed

Hybel, A-M; Godskesen, B; Rygaard, M

2015-09-01

Indicators of the impact on freshwater resources are becoming increasingly important in the evaluation of urban water systems. To reveal the importance of spatial resolution, we investigated how the choice of catchment scale influenced the freshwater impact assessment. Two different indicators were used in this study: the Withdrawal-To-Availability ratio (WTA) and the Water Stress Index (WSI). Results were calculated for three groundwater based Danish urban water supplies (Esbjerg, Aarhus, and Copenhagen). The assessment was carried out at three spatial levels: (1) the groundwater body level, (2) the river basin level, and (3) the regional level. The assessments showed that Copenhagen's water supply had the highest impact on the freshwater resource per cubic meter of water abstracted, with a WSI of 1.75 at Level 1. The WSI values were 1.64 for Aarhus's and 0.81 for Esbjerg's water supply. Spatial resolution was identified as a major factor determining the outcome of the impact assessment. For the three case studies, WTA and WSI were 27%-583% higher at Level 1 than impacts calculated for the regional scale. The results highlight that freshwater impact assessments based on regional data, rather than sub-river basin data, may dramatically underestimate the actual impact on the water resource. Furthermore, this study discusses the strengths and shortcomings of the applied indicator approaches. A sensitivity analysis demonstrates that although WSI has the highest environmental relevance, it also has the highest uncertainty, as it requires estimations of non-measurable environmental water requirements. Hence, the development of a methodology to obtain more site-specific and relevant estimations of environmental water requirements should be prioritized. Finally, the demarcation of the groundwater resource in aquifers remains a challenge for establishing a consistent method for benchmarking freshwater impacts caused by groundwater abstraction. Copyright © 2015 Elsevier Ltd. All rights reserved.

Testing the Role of Impacts in Warming Early Mars: Comparisons Between 1-D and GCM Results

NASA Astrophysics Data System (ADS)

Steakley, K.; Kahre, M. A.; Murphy, J. R.; Haberle, R. M.; Kling, A.

2017-12-01

Comet and asteroid impacts have been explored as a potential mechanism for producing warmer and wetter conditions for early Mars and possibly contributing to valley network formation. However, criticisms have been made regarding the timing of large impacts compared to valley network activity and the ability of such impacts to induce long lasting climate changes and the appropriate amount of precipitation. We test the impact heating hypothesis for the late Noachian Mars atmosphere by revisiting the scenarios described in Segura et al. (2008, JGR Planets 113, E11007) with a 3D global climate model (GCM). Segura et al. (2008) showed with a 1-D model that impacts ranging 30-100 km in diameter could in certain cases induce months to years of above-freezing temperatures and tens of cm to meters of rainfall in atmospheres with 150-mbar, 1-bar, or 2-bar surface pressures. We impose the same initial conditions into the Ames Research Center Mars GCM with updated water cycle physics that includes bulk cloud formation, sedimentation, precipitation (liquid or snow), a Manabe moist convection scheme, and the radiative effects of both liquid and ice clouds. Initial conditions in the GCM match those described in Segura et al. (2008) as closely as possible and include a hot post-impact debris layer, a warm atmosphere, and water vapor profiles consistent with the water abundances mobilized by the impact. Scenarios with 30-, 50- and 100- km impactors in 150-mbar, 1-bar, and 2-bar surface pressure cases are explored both with and without radiatively active water clouds. Our goals are to determine how global rainfall totals and global surface temperatures from the GCM compare with the simpler 1-D Segura et al. (2008) model, to examine what rainfall patterns emerge in the GCM and how they compare to the observed valley network distribution, and to more carefully assess the role of cloud microphysics and radiative effects on the duration and intensity of post-impact climates.

Besieged by Trojans: Material Exchange between Tethys and its Coorbital Moons

NASA Astrophysics Data System (ADS)

Nayak, Michael; Rhoden, Alyssa R.; Asphaug, Erik

2016-10-01

Two small Trojan moons are coorbital with the Saturnian moon Tethys: Calypso (20-km diameter) resides in the trailing L5 Lagrangian point of Tethys' orbit around Saturn, while Telesto (25-km diameter) occupies the leading L4 Lagrangian point. Due to their fixed location with respect to Tethys, consistent material transfer to Tethys occurs whenever there is a primary impact on either of the Trojan moons. Here we investigate this material exchange, and its implications for the cratering history of Tethys. Multiple craters in excess of 1-km in diameter are seen on both Trojan moons [1]. We model the evolution of ejecta escaping from the largest five and seven craters on Calypso and Telesto respectively. The Maxwell Z-model [2] is used, with an implicit gravity-regime cratering assumption, to approximate outbound ejecta velocity distributions. The smallest craters considered on Calypso and Telesto are 1.35 and 1.9 km in diameter respectively; these impacts would have generated a significant amount of sesquinary ejecta [3] in orbits coorbital to that of Tethys. We model the evolution of these sesquinary ejecta in the Saturnian gravity system across 100 years and track their impact locations [e.g. 4]. Our results show that a large fraction of sesquinary ejecta created by primary impacts to either Trojan is likely to impact Tethys; the coorbital nature of the source bodies results in a significant fraction of this ejecta being incident at low impact velocities and low (oblique) impact angles. We present results of ongoing work to convolve these results with observed crater populations and morphologies on Tethys. The persistence of sesquinary impactors inbound to Tethys suggests that such impacts are a relatively frequent process. Additional sources of impactor material, such as from material excavated by primary impacts to Tethys and later reaccreted, will also be discussed. [1] Thomas et al., 2013, Icarus [2] Melosh, 1989, Oxford Univ. Press [3] Zahnle et al., 2008, Icarus [4] Nayak and Asphaug, 2016, Nature Communications.

1:1 iPad Implementation: A Study on Efficacy and Achievement in Reading

ERIC Educational Resources Information Center

Orman, John Paul

2017-01-01

The purpose of this study was to determine 1:1 iPad implementation's impact on students' reading achievement from 2013-2017 and student efficacy in using the technology to learn at one independent middle school in Grades 5-8. To determine the impact of the 1:1 iPad initiative on reading achievement, this mixed methods study examined five years of…

Can Functional Movement Assessment Predict Football Head Impact Biomechanics?

PubMed

Ford, Julia M; Campbell, Kody R; Ford, Cassie B; Boyd, Kenneth E; Padua, Darin A; Mihalik, Jason P

2018-06-01

The purposes of this study was to determine functional movement assessments' ability to predict head impact biomechanics in college football players and to determine whether head impact biomechanics could explain preseason to postseason changes in functional movement performance. Participants (N = 44; mass, 109.0 ± 20.8 kg; age, 20.0 ± 1.3 yr) underwent two preseason and postseason functional movement assessment screenings: 1) Fusionetics Movement Efficiency Test and 2) Landing Error Scoring System (LESS). Fusionetics is scored 0 to 100, and participants were categorized into the following movement quality groups as previously published: good (≥75), moderate (50-75), and poor (<50). The LESS is scored 0 to 17, and participants were categorized into the following previously published movement quality groups: good (≤5 errors), moderate (6-7 errors), and poor (>7 errors). The Head Impact Telemetry (HIT) System measured head impact frequency and magnitude (linear acceleration and rotational acceleration). An encoder with six single-axis accelerometers was inserted between the padding of a commercially available Riddell football helmet. We used random intercepts general linear-mixed models to analyze our data. There were no effects of preseason movement assessment group on the two Head Impact Telemetry System impact outcomes: linear acceleration and rotational acceleration. Head impact frequency did not significantly predict preseason to postseason score changes obtained from the Fusionetics (F1,36 = 0.22, P = 0.643, R = 0.006) or the LESS (F1,36 < 0.01, P = 0.988, R < 0.001) assessments. Previous research has demonstrated an association between concussion and musculoskeletal injury, as well as functional movement assessment performance and musculoskeletal injury. The functional movement assessments chosen may not be sensitive enough to detect neurological and neuromuscular differences within the sample and subtle changes after sustaining head impacts.

Effect of hoof angle on joint contact area in the equine metacarpophalangeal joint following simulated impact loading ex vivo.

PubMed

McCarty, C A; Thomason, J J; Gordon, K; Hurtig, M; Bignell, W

2015-11-01

To add to the existing data on impact loading of the metacarpophalangeal (MCP) joint as a precursor to assessing the potential role of impact in joint disease. To examine the effect of impact loading on contact areas of the first phalanx (P1) and proximal sesamoids (PS) with the third metacarpal (McIII) under 3 hoof-strike conditions (toe-first, flat, heel-first). Randomised, repeated controlled experiment using cadaver material. Eight cadaver limbs were subjected to randomised, repeated controlled trials where the hoof was struck by a pendulum impact machine (impact velocity 3.55 m/s) under 3 strike conditions. Data from pressure sensitive film placed over medial and lateral McIII condyles and lateromedially across the dorsal aspect of McIII were quantified: total areas of P1 and PS contact (cm(2) ) at maximum recorded pressure; centroid locations of contact areas relative to the sagittal ridge (cm) and transverse ridge (cm) and dispersion of pixels (cm(4) ) for each McIII condyle (medial/lateral). The effect of the strike conditions on each variable were statistically tested using repeated-measures ANOVA (α = 0.05). Contact area between P1 and McIII condyles fell in well-defined areas bounded by the sagittal and transverse ridge, contact areas from PS were smaller and widely dispersed across McIII palmar border. Ratio of contact area of P1 to PS was 2.83 (P<0001). Hoof strike had no significant effect on contact area (P>0.54) CONCLUSIONS: Contact at impact (primarily from P1 and distally situated on McIII), contrasts with contact areas at midstance from both P1 and PS, symmetrically placed. Under impact, the greatest contact area was on the dorsal aspect of the medial condyle and coincides with the area subjected to the greatest increase in subchondral bone stiffening in joint disease. © 2014 EVJ Ltd.

Results from the BRACE 1.5 study: Climate change impacts of 1.5 C and 2 C warming

NASA Astrophysics Data System (ADS)

O'Neill, B. C.; Anderson, B.; Monaghan, A. J.; Ren, X.; Sanderson, B.; Tebaldi, C.

2017-12-01

In 2015, 195 countries negotiated the Paris Agreement on climate change, which set long-term goals of limiting global mean warming to well below 2 C and possibly 1.5 C. This event stimulated substantial scientific interest in climate outcomes and impacts on society associated with those levels of warming. Recently, the first set of global climate model simulations explicitly designed to meet those targets were undertaken with the Community Earth System Model (CESM) for use by the research community (Sanderson et al, accepted). The BRACE 1.5 project models societal impacts from these climate outcomes, combined with assumptions about future socioeconomic conditions according to the Shared Socioeconomic Pathways. These analyses build on a recently completed study of the Benefits of Reduced Anthropogenic Climate changE (BRACE), published as a set of 20 papers in Climatic Change, which examined the difference in impacts between two higher scenarios resulting in about 2.5 C and 3.7 C warming by late this century. BRACE 1.5 consists of a set of six papers to be submitted to a special collection in Environmental Research Letters that takes a similar approach but focuses on impacts at 1.5 and 2 C warming. We ask whether impacts differ substantially between the two climate scenarios, accounting for uncertainty in climate outcomes through the use of initial condition ensembles of CESM simulations, and in societal conditions by using alternative SSP-based development pathways. Impact assessment focuses on the health and agricultural sectors; modeling approaches include the use of a global mutli-region CGE model for economic analysis, both a process-based and an empirical crop model, a model of spatial population change, a model of climatic suitability for the aedes aegypti mosquito, and an epidemiological model of heat-related mortality. A methodological analysis also evaluates the use of climate model emulation techniques for providing climate information sufficient to support impact assessment in low warming scenarios.

Analysis of the impact of spatial resolution on land/water classifications using high-resolution aerial imagery

USGS Publications Warehouse

Enwright, Nicholas M.; Jones, William R.; Garber, Adrienne L.; Keller, Matthew J.

2014-01-01

Long-term monitoring efforts often use remote sensing to track trends in habitat or landscape conditions over time. To most appropriately compare observations over time, long-term monitoring efforts strive for consistency in methods. Thus, advances and changes in technology over time can present a challenge. For instance, modern camera technology has led to an increasing availability of very high-resolution imagery (i.e. submetre and metre) and a shift from analogue to digital photography. While numerous studies have shown that image resolution can impact the accuracy of classifications, most of these studies have focused on the impacts of comparing spatial resolution changes greater than 2 m. Thus, a knowledge gap exists on the impacts of minor changes in spatial resolution (i.e. submetre to about 1.5 m) in very high-resolution aerial imagery (i.e. 2 m resolution or less). This study compared the impact of spatial resolution on land/water classifications of an area dominated by coastal marsh vegetation in Louisiana, USA, using 1:12,000 scale colour-infrared analogue aerial photography (AAP) scanned at four different dot-per-inch resolutions simulating ground sample distances (GSDs) of 0.33, 0.54, 1, and 2 m. Analysis of the impact of spatial resolution on land/water classifications was conducted by exploring various spatial aspects of the classifications including density of waterbodies and frequency distributions in waterbody sizes. This study found that a small-magnitude change (1–1.5 m) in spatial resolution had little to no impact on the amount of water classified (i.e. percentage mapped was less than 1.5%), but had a significant impact on the mapping of very small waterbodies (i.e. waterbodies ≤ 250 m2). These findings should interest those using temporal image classifications derived from very high-resolution aerial photography as a component of long-term monitoring programs.

Comparison of the efficacy and safety of 2% lidocaine HCl with different epinephrine concentration for local anesthesia in participants undergoing surgical extraction of impacted mandibular third molars: A multicenter, randomized, double-blind, crossover, phase IV trial.

PubMed

Karm, Myong-Hwan; Park, Fiona Daye; Kang, Moonkyu; Kim, Hyun Jeong; Kang, Jeong Wan; Kim, Seungoh; Kim, Yong-Deok; Kim, Cheul-Hong; Seo, Kwang-Suk; Kwon, Kyung-Hwan; Kim, Chul-Hwan; Lee, Jung-Woo; Hong, Sung-Woon; Lim, Mi Hyoung; Nam, Seung Kwan; Cho, Jae Min

2017-05-01

The most commonly impacted tooth is the third molar. An impacted third molar can ultimately cause acute pain, infection, tumors, cysts, caries, periodontal disease, and loss of adjacent teeth. Local anesthesia is employed for removing the third molar. This study aimed to evaluate the efficacy and safety of 2% lidocaine with 1:80,000 or 1:200,000 epinephrine for surgical extraction of bilateral impacted mandibular third molars. Sixty-five healthy participants underwent surgical extraction of bilateral impacted mandibular third molars in 2 separate visits while under local anesthesia with 2% lidocaine with different epinephrine concentration (1:80,000 or 1:200,000) in a double-blind, randomized, crossover trial. Visual analog scale pain scores obtained immediately after surgical extraction were primarily evaluated for the 2 groups receiving different epinephrine concentrations. Visual analog scale pain scores were obtained 2, 4, and 6 hours after administering an anesthetic. Onset and duration of analgesia, onset of pain, intraoperative bleeding, operator's and participant's overall satisfaction, drug dosage, and hemodynamic parameters were evaluated for the 2 groups. There were no statistically significant differences between the 2 groups in any measurements except hemodynamic factors (P >.05). Changes in systolic blood pressure and heart rate following anesthetic administration were significantly greater in the group receiving 1:80,000 epinephrine than in that receiving 1:200,000 epinephrine (P ≤.01). The difference in epinephrine concentration between 1:80,000 and 1:200,000 in 2% lidocaine liquid does not affect the medical efficacy of the anesthetic. Furthermore, 2% lidocaine with 1:200,000 epinephrine has better safety with regard to hemodynamic parameters than 2% lidocaine with 1:80,000 epinephrine. Therefore, we suggest using 2% lidocaine with 1:200,000 epinephrine rather than 2% lidocaine with 1:80,000 epinephrine for surgical extraction of impacted mandibular third molars in hemodynamically unstable patients.

Comparison of the efficacy and safety of 2% lidocaine HCl with different epinephrine concentration for local anesthesia in participants undergoing surgical extraction of impacted mandibular third molars

PubMed Central

Karm, Myong-Hwan; Park, Fiona Daye; Kang, Moonkyu; Kim, Hyun Jeong; Kang, Jeong Wan; Kim, Seungoh; Kim, Yong-Deok; Kim, Cheul-Hong; Seo, Kwang-Suk; Kwon, Kyung-Hwan; Kim, Chul-Hwan; Lee, Jung-Woo; Hong, Sung-Woon; Lim, Mi Hyoung; Nam, Seung Kwan; Cho, Jae Min

2017-01-01

Abstract Background: The most commonly impacted tooth is the third molar. An impacted third molar can ultimately cause acute pain, infection, tumors, cysts, caries, periodontal disease, and loss of adjacent teeth. Local anesthesia is employed for removing the third molar. This study aimed to evaluate the efficacy and safety of 2% lidocaine with 1:80,000 or 1:200,000 epinephrine for surgical extraction of bilateral impacted mandibular third molars. Methods: Sixty-five healthy participants underwent surgical extraction of bilateral impacted mandibular third molars in 2 separate visits while under local anesthesia with 2% lidocaine with different epinephrine concentration (1:80,000 or 1:200,000) in a double-blind, randomized, crossover trial. Visual analog scale pain scores obtained immediately after surgical extraction were primarily evaluated for the 2 groups receiving different epinephrine concentrations. Visual analog scale pain scores were obtained 2, 4, and 6 hours after administering an anesthetic. Onset and duration of analgesia, onset of pain, intraoperative bleeding, operator's and participant's overall satisfaction, drug dosage, and hemodynamic parameters were evaluated for the 2 groups. Results: There were no statistically significant differences between the 2 groups in any measurements except hemodynamic factors (P >.05). Changes in systolic blood pressure and heart rate following anesthetic administration were significantly greater in the group receiving 1:80,000 epinephrine than in that receiving 1:200,000 epinephrine (P ≤.01). Conclusion: The difference in epinephrine concentration between 1:80,000 and 1:200,000 in 2% lidocaine liquid does not affect the medical efficacy of the anesthetic. Furthermore, 2% lidocaine with 1:200,000 epinephrine has better safety with regard to hemodynamic parameters than 2% lidocaine with 1:80,000 epinephrine. Therefore, we suggest using 2% lidocaine with 1:200,000 epinephrine rather than 2% lidocaine with 1:80,000 epinephrine for surgical extraction of impacted mandibular third molars in hemodynamically unstable patients. PMID:28538371

Impact of the community-based newborn care package in Nepal: a quasi-experimental evaluation.

PubMed

Paudel, Deepak; Shrestha, Ishwar B; Siebeck, Matthias; Rehfuess, Eva

2017-10-05

To evaluate the impact of the community-based newborn care package (CBNCP) on six essential practices to improve neonatal health. CBNCP pilot districts were matched to comparison districts using propensity scores. Impact on birth preparedness, antenatal care seeking, antenatal care quality, delivery by skilled birth attendant, immediate newborn care and postnatal care within 48 hours were assessed using Demographic and Health Survey (DHS) and Health Management Information System (HMIS) data through difference-in-differences and multivariate logistic regression analyses. Changes over time in intervention and comparison areas were similar in difference-in-differences analysis of DHS and HMIS data. Logistic regression of DHS data also did not reveal any significant improvement in combined outcomes: birth preparedness, adjusted OR (aOR)=0.8 (95% CI 0.4 to 1.7); antenatal care seeking, aOR=1.0 (0.6 to 1.5); antenatal care quality, aOR=1.4 (0.9 to 2.1); delivery by skilled birth attendant, aOR=1.5 (1.0 to 2.3); immediate newborn care, aOR=1.1 (0.7 to 1.9); postnatal care, aOR=1.3 (0.9 to 1.9). Health providers' knowledge and skills in intervention districts were fair but showed much variation between different providers and districts. This study, while representing an early assessment of impact, did not identify significant improvements in newborn care practices and raises concerns regarding CBNCP implementation. It has contributed to revisions of the package and it being merged with the Integrated Management of Neonatal and Childhood Illness programme. This is now being implemented in 35 districts and carefully monitored for quality and impact. The study also highlights general challenges in evaluating the impacts of a complex health intervention under 'real life' conditions. © Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2017. All rights reserved. No commercial use is permitted unless otherwise expressly granted.

Traces of Catastrophe: A Handbook of Shock-Metamorphic Effects in Terrestrial Meteorite Impact Structures

NASA Technical Reports Server (NTRS)

French, Bevan M.

1998-01-01

This handbook of Shock-Metamorphic Effects in Terrestrial Meteorite Impact Structures emphasizes terrestrial impact structures, field geology, and particularly the recognition and petrographic study of shock-metamorphic effects in terrestrial rocks. Individual chapters include: 1) Landscapes with Craters: Meteorite Impacts, Earth, and the Solar System; 2) Target Earth: Present, Past and Future; 3) Formation of Impact Craters; 4) Shock-Metamorphic Effects in Rocks and Minerals; 5) Shock-Metamorphosed Rocks (Impactities) in Impact Structures; 6) Impact Melts; 7) How to Find Impact Structures; and 8) What Next? Current Problems and Future Investigations.

High-speed laser-launched flyer impacts studied with ultrafast photography and velocimetry

DOE PAGES

Banishev, Alexandr A.; Shaw, William L.; Bassett, Will P.; ...

2016-02-16

Pulsed lasers can launch thin metal foils at km s -1, but for precision measurements in shock compression science and shock wave spectroscopy, where one-dimensional shock compression is vital, flyer plate impacts with targets must have a high degree of flatness and minimal tilt, and the flyer speeds and impact times at the target must be highly reproducible. We have developed an apparatus that combines ultrafast stroboscopic optical microscopy with photon Doppler velocimetry to study impacts of laser-launched Al and Cu flyer plates with flat, transparent glass targets. The flyer plates were 0.5 mm in diameter, and ranged from 12-100more » μm thick, with flyer speeds up to 6.25 km s -1. The velocity variations over 30-60 launches from the same flyer plate optic can be as low as 0.6%, and the impact time variations can be as low as 0.8 ns. Stroboscopic image streams (reconstructed movies) show uniform, flat impacts with a glass target. As a result, these stroboscopic images can be used to estimate the tilt in the flyer-target impact to be <1mrad.« less

16 CFR 1.83 - Whether to commence the process for an environmental impact statement.

Code of Federal Regulations, 2010 CFR

2010-01-01

... 16 Commercial Practices 1 2010-01-01 2010-01-01 false Whether to commence the process for an environmental impact statement. 1.83 Section 1.83 Commercial Practices FEDERAL TRADE COMMISSION ORGANIZATION, PROCEDURES AND RULES OF PRACTICE GENERAL PROCEDURES Procedures for Implementation of the National Environmental Policy Act of 1969 § 1.83 Whethe...

The role of polymorphonuclear neutrophils during HIV-1 infection.

PubMed

Yaseen, Mahmoud Mohammad; Abuharfeil, Nizar Mohammad; Yaseen, Mohammad Mahmoud; Shabsoug, Barakat Mohammad

2018-01-01

It is well-recognized that human immunodeficiency virus type-1 (HIV-1) mainly targets CD4 + T cells and macrophages. Nonetheless, during the past three decades, a huge number of studies have reported that HIV-1 can directly or indirectly target other cellular components of the immune system including CD8 + T cells, B cells, dendritic cells, natural killer cells, and polymorphonuclear neutrophils (PMNs), among others. PMNs are the most abundant leukocytes in the human circulation, and are known to play principal roles in the elimination of invading pathogens, regulating different immune responses, healing of injured tissues, and maintaining mucosal homeostasis. Until recently, little was known about the impact of HIV-1 infection on PMNs as well as the impact of PMNs on HIV-1 disease progression. This is because early studies focused on neutropenia and recurrent microbial infections, particularly, during advanced disease. However, recent studies have extended the investigation area to cover new aspects of the interactions between HIV-1 and PMNs. This review aims to summarize these advances and address the impact of HIV-1 infection on PMNs as well as the impact of PMNs on HIV-1 disease progression to better understand the pathophysiology of HIV-1 infection.

Effect of dental pain and caries on the quality of life of Brazilian preschool children.

PubMed

Freire, Maria do Carmo Matias; Corrêa-Faria, Patrícia; Costa, Luciane Rezende

2018-04-09

To investigate the impact of dental pain on daily performances among five-year-old Brazilian children. The study used data of 7,280 five-year-old children participating in the 2010 Brazilian Oral Health Survey (SBBrasil 2010 Project). Children were clinically examined and their parents or carers were interviewed at their homes. The outcome was the prevalence of the oral impacts on daily performance, and the explanatory variable was dental pain in the last six months. Other independent variables were children's gender and skin color/race, family income, household overcrowding, and caries experience (dmft). Rao-Scott test and Poisson regression for complex samples were carried out. The prevalence of impacts on daily performances was 26.1% (95%CI 22.3-30.2). Significant associations were found between the outcome and pain, caries experience, and sociodemographic variables. After adjusting for the independent variables, only pain and caries remained significant. Impacts on daily performances were more frequent among children with pain (PR = 1.14, 95%CI 1.06-1.23) compared to those without pain. Children with low dmft (PR = 1.90, 95%CI 1.39-2.60) and those with high dmft (PR = 3.53, 95%CI 2.78-4.49) had a higher prevalence of impact than those with no caries experience. Dental pain and caries had strong negative impacts on the five-year-old children's daily performances regardless of their demographic and socioeconomic characteristics.

Comparison of the Marginal Cost-Effectiveness of Various Recruiting Resources for High School Graduate Enlistments: Analysis of National, Local and ’Walk-in’ Leads and Yield Rates.

DTIC Science & Technology

1982-11-01

FOR FY80 3 2.1 National Advertising and NOIC Leads 3 2.2 Local Advertising CLAMS) and Local Leads 4 2.3 Recruiters and HSG Contracts 4 2.4 Mix of...Recruiting Efforts and Advertising 5 3.0 ANALYSIS OF LOCAL LEADS s 3.1 Data Limitations s 3.2 Results and Interpretation 6 4.0 ANALYSIS OF NOIC LEADS 8 5.0...Impact of Local Leads is S.2.3 Impact of Recruiters 15 S.2.4 Direct Impact of Advertising on HSG Contracts Over and Above Impact on Leads: Impact of

21 CFR 25.42 - Environmental impact statements.

Code of Federal Regulations, 2010 CFR

2010-04-01

...) Alternatives to the action; (4) The relationship between local short-term uses of the environment and the... 21 Food and Drugs 1 2010-04-01 2010-04-01 false Environmental impact statements. 25.42 Section 25... ENVIRONMENTAL IMPACT CONSIDERATIONS Preparation of Environmental Documents § 25.42 Environmental impact...

21 CFR 25.42 - Environmental impact statements.

Code of Federal Regulations, 2011 CFR

2011-04-01

...) Alternatives to the action; (4) The relationship between local short-term uses of the environment and the... 21 Food and Drugs 1 2011-04-01 2011-04-01 false Environmental impact statements. 25.42 Section 25... ENVIRONMENTAL IMPACT CONSIDERATIONS Preparation of Environmental Documents § 25.42 Environmental impact...

Vehicle impact simulation for curb and barrier design : volume 1, impact simulation procedures.

DOT National Transportation Integrated Search

1998-10-01

The objectives of this study were to perform computer simulations of vehicle-curb and vehicle-berm impacts, to characterize : the behavior of a wide range of vehicle types after such impacts, and to produce design and evaluation trajectory data for u...

21 CFR 25.52 - Environmental impact statements.

Code of Federal Regulations, 2010 CFR

2010-04-01

... 21 Food and Drugs 1 2010-04-01 2010-04-01 false Environmental impact statements. 25.52 Section 25... ENVIRONMENTAL IMPACT CONSIDERATIONS Public Participation and Notification of Environmental Documents § 25.52 Environmental impact statements. (a) If FDA determines that an EIS is necessary for an action involving...

Assessing Environmental Impact: A Secondary School Learning Activity

ERIC Educational Resources Information Center

Nous, Albert P.

This packet contains information on teaching about environmental impact. Background information is included on the role of environmental impact on our society and environmental risk is also discussed. Environmental impacts are studied using Stages of Assessment. Learning activities and seven lesson plans include: (1) "The Community…

22 CFR 216.7 - Environmental impact statements.

Code of Federal Regulations, 2013 CFR

2013-04-01

... 22 Foreign Relations 1 2013-04-01 2013-04-01 false Environmental impact statements. 216.7 Section... Environmental impact statements. (a) Applicability. An Environmental Impact Statement shall be prepared when... nation (e.g., the oceans); (2) The environment of the United States; or (3) Other aspects of the...

22 CFR 216.7 - Environmental impact statements.

Code of Federal Regulations, 2014 CFR

2014-04-01

... 22 Foreign Relations 1 2014-04-01 2014-04-01 false Environmental impact statements. 216.7 Section... Environmental impact statements. (a) Applicability. An Environmental Impact Statement shall be prepared when... nation (e.g., the oceans); (2) The environment of the United States; or (3) Other aspects of the...