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Bruce M Simonson - One of the best experts on this subject based on the ideXlab platform.
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mesozoic spherule impact Ejecta layers
2013Co-Authors: B P Glass, Bruce M SimonsonAbstract:The Cretaceous-Tertiary (K-T), or Cretaceous-Paleogene (K-Pg), boundary impact Ejecta layer; the Late Cretaceous Manson crater Ejecta layer; the Late Triassic spherule/Ejecta layer; and a possible impact Ejecta layer at the Triassic-Jurassic boundary are discussed in this chapter (Table 5.1). As previously mentioned, the K-T boundary Ejecta layer is the most studied and best known distal impact Ejecta layer. The Manson structure is a buried impact crater located in Iowa, USA, which at one time was thought to be the, or a, source crater for the K-T boundary layer. Distal impact Ejecta from this structure have been found in South Dakota and Nebraska. An impact spherule layer containing shocked quartz has been found in Late Triassic deposits in southwestern England. Some researchers have reported finding evidence for an impact Ejecta layer at the Triassic-Jurassic boundary, but others do not find the evidence convincing.
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Mesozoic Spherule/Impact Ejecta Layers
Impact Studies, 2012Co-Authors: B P Glass, Bruce M SimonsonAbstract:The Cretaceous-Tertiary (K-T), or Cretaceous-Paleogene (K-Pg), boundary impact Ejecta layer; the Late Cretaceous Manson crater Ejecta layer; the Late Triassic spherule/Ejecta layer; and a possible impact Ejecta layer at the Triassic-Jurassic boundary are discussed in this chapter (Table 5.1). As previously mentioned, the K-T boundary Ejecta layer is the most studied and best known distal impact Ejecta layer. The Manson structure is a buried impact crater located in Iowa, USA, which at one time was thought to be the, or a, source crater for the K-T boundary layer. Distal impact Ejecta from this structure have been found in South Dakota and Nebraska. An impact spherule layer containing shocked quartz has been found in Late Triassic deposits in southwestern England. Some researchers have reported finding evidence for an impact Ejecta layer at the Triassic-Jurassic boundary, but others do not find the evidence convincing.
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Impact Crater Formation, Shock Metamorphism, and Distribution of Impact Ejecta
Impact Studies, 2012Co-Authors: B P Glass, Bruce M SimonsonAbstract:As previously mentioned, an integral part of the cratering process is the formation and widespread distribution of Ejecta. In order to comprehend how the distribution, thickness, and nature of an impact Ejecta layer varies with distance from its source crater, one needs to understand the cratering process. Thus, we begin this chapter with a brief review of cratering mechanics. This leads into a discussion of shock metamorphism, which occurs during the cratering process and which is important in the identification of impact craters and distal Ejecta layers. At the end of the chapter we briefly discuss some theoretical and experimental data on how Ejecta, including the degree of shock metamorphism of the Ejecta, vary with distance from the source crater. This last subject is addressed again in Chap. 10, but in Chap. 10 we compare observations on how distal Ejecta vary with distance from source craters with theoretical and experimental data of how the thickness and nature of distal Ejecta should vary with distance from the source crater.
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Distal Impact Ejecta Layers: Spherules and More
Elements, 2012Co-Authors: B P Glass, Bruce M SimonsonAbstract:During the formation of large impact structures, layers of melted and crushed rock (Ejecta) are deposited over large areas of the Earth9s surface. Ejecta thrown farther than 2.5 crater diameters are called distal Ejecta. At distances greater than ~10 crater diameters, the distal Ejecta layers consist primarily of millimeter-scale glassy bodies (impact spherules) that form from melt and vapor-condensate droplets. At least 28 distal Ejecta layers have been identified. Distal Ejecta layers can be used to place constraints on cratering models, help fill gaps in the cratering record, and provide direct correlation between impacts and other terrestrial events.
B P Glass - One of the best experts on this subject based on the ideXlab platform.
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mesozoic spherule impact Ejecta layers
2013Co-Authors: B P Glass, Bruce M SimonsonAbstract:The Cretaceous-Tertiary (K-T), or Cretaceous-Paleogene (K-Pg), boundary impact Ejecta layer; the Late Cretaceous Manson crater Ejecta layer; the Late Triassic spherule/Ejecta layer; and a possible impact Ejecta layer at the Triassic-Jurassic boundary are discussed in this chapter (Table 5.1). As previously mentioned, the K-T boundary Ejecta layer is the most studied and best known distal impact Ejecta layer. The Manson structure is a buried impact crater located in Iowa, USA, which at one time was thought to be the, or a, source crater for the K-T boundary layer. Distal impact Ejecta from this structure have been found in South Dakota and Nebraska. An impact spherule layer containing shocked quartz has been found in Late Triassic deposits in southwestern England. Some researchers have reported finding evidence for an impact Ejecta layer at the Triassic-Jurassic boundary, but others do not find the evidence convincing.
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Mesozoic Spherule/Impact Ejecta Layers
Impact Studies, 2012Co-Authors: B P Glass, Bruce M SimonsonAbstract:The Cretaceous-Tertiary (K-T), or Cretaceous-Paleogene (K-Pg), boundary impact Ejecta layer; the Late Cretaceous Manson crater Ejecta layer; the Late Triassic spherule/Ejecta layer; and a possible impact Ejecta layer at the Triassic-Jurassic boundary are discussed in this chapter (Table 5.1). As previously mentioned, the K-T boundary Ejecta layer is the most studied and best known distal impact Ejecta layer. The Manson structure is a buried impact crater located in Iowa, USA, which at one time was thought to be the, or a, source crater for the K-T boundary layer. Distal impact Ejecta from this structure have been found in South Dakota and Nebraska. An impact spherule layer containing shocked quartz has been found in Late Triassic deposits in southwestern England. Some researchers have reported finding evidence for an impact Ejecta layer at the Triassic-Jurassic boundary, but others do not find the evidence convincing.
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Impact Crater Formation, Shock Metamorphism, and Distribution of Impact Ejecta
Impact Studies, 2012Co-Authors: B P Glass, Bruce M SimonsonAbstract:As previously mentioned, an integral part of the cratering process is the formation and widespread distribution of Ejecta. In order to comprehend how the distribution, thickness, and nature of an impact Ejecta layer varies with distance from its source crater, one needs to understand the cratering process. Thus, we begin this chapter with a brief review of cratering mechanics. This leads into a discussion of shock metamorphism, which occurs during the cratering process and which is important in the identification of impact craters and distal Ejecta layers. At the end of the chapter we briefly discuss some theoretical and experimental data on how Ejecta, including the degree of shock metamorphism of the Ejecta, vary with distance from the source crater. This last subject is addressed again in Chap. 10, but in Chap. 10 we compare observations on how distal Ejecta vary with distance from source craters with theoretical and experimental data of how the thickness and nature of distal Ejecta should vary with distance from the source crater.
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Distal Impact Ejecta Layers: Spherules and More
Elements, 2012Co-Authors: B P Glass, Bruce M SimonsonAbstract:During the formation of large impact structures, layers of melted and crushed rock (Ejecta) are deposited over large areas of the Earth9s surface. Ejecta thrown farther than 2.5 crater diameters are called distal Ejecta. At distances greater than ~10 crater diameters, the distal Ejecta layers consist primarily of millimeter-scale glassy bodies (impact spherules) that form from melt and vapor-condensate droplets. At least 28 distal Ejecta layers have been identified. Distal Ejecta layers can be used to place constraints on cratering models, help fill gaps in the cratering record, and provide direct correlation between impacts and other terrestrial events.
Satoru Yamamoto - One of the best experts on this subject based on the ideXlab platform.
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Velocity distributions of high-velocity Ejecta from regolith targets
Icarus, 2005Co-Authors: Satoru Yamamoto, Toshihiko Kadono, Seiji Sugita, Takafumi MatsuiAbstract:Abstract We measured the velocity distributions of impact Ejecta with velocities higher than ∼100 m s−1 (high-velocity Ejecta) for impacts at variable impact angle α into unconsolidated targets of small soda-lime glass spheres. Polycarbonate projectiles with mass of 0.49 g were accelerated to ∼250 m s−1 by a single-stage light-gas gun. The impact Ejecta are detected by thin aluminum foils placed around the targets. We analyzed the holes on the aluminum foils to derive the total number and volume of Ejecta that penetrated the aluminum foils. Using the minimum velocity of the Ejecta for penetration, determined experimentally, the velocity distributions of the high-velocity Ejecta were obtained at α = 15 ° , 30°, 45°, 60°, and 90°. The velocity distribution of the high-velocity Ejecta is shown to depend on impact angle. The quantity of the high-velocity Ejecta for vertical impact ( α = 90 ° ) is considerably lower than derived from a power-law relation for the velocity distribution on the low-velocity Ejecta (less than 10 m s−1). On the other hand, in oblique impacts, the quantity of the high-velocity Ejecta increases with decreasing impact angle, and becomes comparable to those derived from the power-law relation. We attempt to scale the high-velocity Ejecta for oblique impacts to a new scaling law, in which the velocity distribution is scaled by the cube of projectile radius (scaled volume) and a horizontal component of impactor velocity (scaled ejection velocity), respectively. The high-velocity Ejecta data shows a good correlation between the scaled volume and the scaled ejection velocity.
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Velocity distribution of powdery Ejecta
Advances in Space Research, 1997Co-Authors: Satoru Yamamoto, Akiko M. NakamuraAbstract:We have performed new impact experiments onto particulate targets to determine the velocity distribution of Ejecta with velocities higher than several hundred m sec−1. The Ejecta were detected by thin Al foil of different thicknesses and the resulting holes on them were studied. Our results of the volume of Ejecta with high velocity lie below a scaling formula based on data from low velocity Ejecta (Housen et al. 1983). However, the differences were within about one order of magnitude.
Henning Dypvik - One of the best experts on this subject based on the ideXlab platform.
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Distribution of Ejecta from small impact craters
Meteoritics & Planetary Science, 2013Co-Authors: Valery Shuvalov, Henning DypvikAbstract:The present study focuses both on the influence of impact scale on Ejecta expansion and on specific features of Ejecta deposits around relatively small craters (i.e., those a few kilometers in width). The numerical model is based on the SOVA multimaterial multidimensional hydrocode, considering subaerial vertical impacts only, applying a 2-D version of the code to projectiles of 100, 300, and 1000 m diameter. Ejecta can roughly be divided into two categories: “ballistic” Ejecta and “convective” Ejecta; the ballistic Ejecta are the Ejecta with which the air interacts only slightly, while the convective Ejecta motion is entirely defined by the air flow. The degree of particle/air interaction can be defined by the time/length of particle travel before deceleration. Ejecta size-distributions for the impacts modeled can be described by the same power law, but the size of maximum fragment increases with scale. There is no qualitative difference between the 100 m diameter projectile case and the 300 m diameter projectile impact. In both cases, fine Ejecta decelerate in the air at a small distance from launching point and then rise to the stratosphere by air flows induced by the impacts. In the 1000 m-scale impact, the mass of Ejecta is so large that it moves the atmosphere itself to high altitudes. Thus, the atmosphere cannot decelerate even the fine Ejecta and they consequently expand to the rarefied upper atmosphere. In the upper atmosphere, even fine Ejecta move more or less ballistically and therefore may travel to high altitudes.
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Ejecta formation and crater development of the Mjølnir impact
Meteoritics & Planetary Science, 2004Co-Authors: Valery Shuvalov, Henning DypvikAbstract:Crater-Ejecta correlation is an important element in the analysis of crater formation and its influence on the geological evolution. In this study, both the Ejecta distribution and the internal crater development of the Jurassic/Cretaceous Mjolnir crater (40 km in diameter; located in the Barents Sea) are investigated through numerical simulations. The simulations show a highly asymmetrical Ejecta distribution, and underscore the importance of a layer of surface water in Ejecta distribution. As expected, the Ejecta asymmetry increases as the angle of impact decreases. The simulation also displays an uneven aerial distribution of Ejecta. The generation of the central high is a crucial part of crater formation. In this study, peak generation is shown to have a skewed development, from approximately 50-90 sec after impact, when the peak reaches its maximum height of 1-1.5 km. During this stage, the peak crest is moved about 5 km from an uprange to a downrange position, ending with a final central position which has a symmetrical appearance that contrasts with its asymmetrical development.
Peter H. Schultz - One of the best experts on this subject based on the ideXlab platform.
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Early-Stage Coupling for Oblique Impacts in Granular Material
2010Co-Authors: B. Hermalyn, Peter H. Schultz, James T. HeineckAbstract:Introduction and Background: Impact events control the distribution of materials on planetary surfaces. Early-time processes, during which the projectile is still coupling its energy and momentum to the target, affect the emplacement of distal Ejecta and play a greater role at larger planetary scales. These effects are especially apparent in oblique impacts, which often display earlystage asymmetries in the Ejecta deposits. The early-time Ejecta velocity distribution for oblique impacts has not been studied in detail for granular materials. Here we examine the time-resolved Ejecta dynamics for oblique hypervelocity impacts through a novel imaging technique.
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Interactions between an impact generated Ejecta curtain and an atmosphere
International Journal of Impact Engineering, 1999Co-Authors: Olivier S. Barnouin-jha, Peter H. SchultzAbstract:A theoretical model investigates the interaction between an Ejecta curtain and a variety of differing atmospheric conditions in order to determine the Ejecta entrainment capacity of winds generated by an advancing curtain. The model assesses the curtain shape, the position along the curtain where flow separation occurs, the velocity of winds winnowing Ejecta out of the effectively impermeable portions of the curtain and the velocity of winds flow separating at its top. Wind velocities allow estimating the size range of Ejecta entrained. Tested against laboratory impacts into coarse sand, the model results duplicate observation of curtain shape and size of Ejecta entrained. The position where flow separation occurs is duplicated when the curtain porosity is assumed to increase with time.
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Erosion of Ejecta at Meteor Crater, Arizona
Journal of Geophysical Research, 1993Co-Authors: John A. Grant, Peter H. SchultzAbstract:New methods for estimating erosion at Meteor Crater, Arizona, indicate that continuous Ejecta deposits beyond 1/4-1/2 crater radii from the rim (0.25R-0.5R) have been lowered less than 1 m on the average. This conclusion is based on the results of two approaches: coarsening ofunweathered Ejectainto surface lag deposits and calculation of the sediment budget within a drainage basin on the Ejecta. Preserved Ejecta morphologies beneath thin alluvium revealed by ground-penetrating radar provide qualitative support for the derived estimates. Although slightly greater erosion (2-3 m) of less resistant Ejecta locally has occurred, such deposits were limited in extent, particularly beyond 0.25R-0.5R from the present rim. Subtle but preserved primary Ejecta features (e.g., distal Ejecta lobes and blocks) further support our estimate of minimal erosion of Ejecta since the crater formed --50,000 years ago. Unconsolidated deposits formed during other sudden extreme events (e.g., landslides) exhibit similarly low erosion over the same time frame; the common factor is the presence of large fragments or large fragments in a matrix of finer debris. At Meteor Crater, fluvial and eolian processes remove surrounding fines leaving behind a surface lag of coarse-grained Ejecta fragments that armor surfaces and slow vertical lowering.
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Atmospheric effects on Ejecta emplacement
Journal of Geophysical Research, 1992Co-Authors: Peter H. SchultzAbstract:Laboratory experiments allow the investigation of complex interactions between impacts and an atmosphere. Although small in scale, they can provide essential first-order constraints on the processes affecting late-stage ballistic Ejecta and styles of Ejecta emplacement around much larger craters on planetary surfaces. The laboratory experiments involved impacting different fine-grained particulate targets under varying atmospheric pressure and density (different gas compositions). During crater formation, ballistic Ejecta form the classic cone-shaped profile observed under vacuum conditions. As atmospheric density increases (for a given pressure), however, the Ejecta curtain bulges at the base and pinches above. This systematic change in the Ejecta curtain reflects the combined effects of deceleration of Ejecta smaller than a critical size and entrainment of these Ejecta within atmospheric vortices created as the outward moving wall of Ejecta displaces the atmosphere. Additionally, a systematic change in emplacement style occurs as a function of atmospheric pressure (largely independent of density): contiguous Ejecta rampart superposing ballistically emplaced deposits (0.06 to 0.3 bar); Ejecta flow lobes (0.3 to 0.7 bar); and radial patterns (>0.8 bar). Underlying processes controlling such systematic changes in emplacement style were revealed by observing the evolution of the Ejecta curtain, by changing target materials (including layered targets and low-density particulates), by varying atmospheric density, by changing impact angle, and by comparing the Ejecta run-out distances with first-order models of turbidity flows. Three distinct Ejecta emplacement processes can be characterized. Ejecta ramparts result from coarser clasts sorted and driven outward by vortical winds behind the outward moving Ejecta curtain. This style of “wind-modified” emplacement represents minimal Ejecta entrainment and is enhanced by a bimodal size distribution in the Ejecta. Such “eddy-supported flows” are observed to increase in run-out distance (scaled to crater size) with increasing atmospheric pressure. By analogy with turbidity flows, this scaled distance should increase as R1/2 for a given atmospheric pressure and degree of entrainment. Ejecta flows with much greater run-out distances develop as the turbulent power in atmospheric response winds increase. Such flows overrun and scour the inner Ejecta facies, thereby producing distinct inner and outer facies. The degree of Ejecta entrainment depends on the dimensionless ratio of drag to gravity forces acting on individual Ejecta and the intensity of the winds created by the outward moving curtain. Entrainment increases with increasing atmospheric density and ejection velocity (crater size) but decreases with Ejecta density and size. The intensity of curtain-generated winds increases with ejection velocity (crater size). The dimensionless drag ratio characterizing the laboratory experiments can be applied to Mars since the reduced atmospheric density is offset by the increased ejection velocities for kilometer-scale events. For a given crater size (ejection velocity) and atmospheric conditions, a wide range of nonballistic Ejecta emplacement styles could occur simply by varying Ejecta sizes even without the presence of water. Alternatively, the onset crater diameter for nonballistic emplacement styles can reflect the range of Ejecta sizes possible from the diverse martian geologic history (massive basalts to fine-grained aeolian deposits). Scaling considerations further predict that Ejecta run-out distances scaled to crater size on Mars should increase as R1/2; hence long run-out flows dependent on crater diameter need not reflect depth to a buried reservoir of water. On Venus, however, the dense atmosphere maximizes entrainment and results in Ejecta flow densities approaching a constant fraction of the atmospheric density. Under such conditions, Ejecta run-out distances should decrease as R−1/2.
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Styles of Ejecta emplacement under atmospheric conditions
1991Co-Authors: Peter H. SchultzAbstract:Laboratory experiments provide essential first-order constraints on processes affecting ballistic Ejecta and styles of Ejecta emplacement under different atmospheric environments at planetary scales. The NASA-Ames Vertical Gun allows impacting different fine-grained particulate targets under varying atmospheric pressure and density, thereby helping to isolate controlling variables. Further analysis now permits characterizing distinct modes of emplacement that reflect the degree of Ejecta entrainment within a turbidity flow created by Ejecta curtain movement through the atmosphere.
