A search for shocked quartz grains and impact ejecta in early Silurian sediments on Gotland, Sweden

AbstractAll bentonite and bentonite-resembling layers thicker than a few millimetres from a 120m-thick Early Silurian sequence on Gotland, Sweden, were searched for shocked quartz grains of comet or asteroid impact origin. Although more than 200000 quartz grains from 86 bentonite samples were studied, not one single grain with multiple planar shock features was found. The studied sequence represents sedimentation during a period of about 2 million years. Impact frequencies, estimated from the cratering record and astronomical observations, indicate that during a 2-myr- period on average 20 comet or asteroid bodies larger than 0.5 km in diameter strike the Earth. The number of smaller impacting bodies is many times higher. In the light of this high frequency of impacts, the absence of any shocked-quartz-bearing fallout layer in our sequence indicates that lateral spreading of such ejecta is relatively restricted during small- and medium-scale impact events.The results also show that shocked quartz in general is absent or extremely rare in volcanic ash. This strengthens the case for an impact-related origin of shocked quartz grains in the Cretaceous–Tertiary boundary days.

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Shocked quartz in distal ejecta from the Ries impact event (Germany) found at ~ 180 km distance, near Bernhardzell, eastern Switzerland

Scientific Reports ◽

10.1038/s41598-021-86685-2 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Sanna Holm-Alwmark ◽

Carl Alwmark ◽

Ludovic Ferrière ◽

Matthias M. M. Meier ◽

Sofie Lindström ◽

...

Keyword(s):

Impact Structure ◽

Impact Cratering ◽

Impact Ejecta ◽

Deformation Features ◽

Different Depths ◽

Shocked Quartz ◽

Depositional Age ◽

Impact Events ◽

Planar Deformation Features ◽

Quartz Grains

AbstractImpact ejecta formation and emplacement is of great importance when it comes to understanding the process of impact cratering and consequences of impact events in general. Here we present a multidisciplinary investigation of a distal impact ejecta layer, the Blockhorizont, that occurs near Bernhardzell in eastern Switzerland. We provide unambiguous evidence that this layer is impact-related by confirming the presence of shocked quartz grains exhibiting multiple sets of planar deformation features. Average shock pressures recorded by the quartz grains are ~ 19 GPa for the investigated sample. U–Pb dating of zircon grains from bentonites in close stratigraphic context allows us to constrain the depositional age of the Blockhorizont to ~ 14.8 Ma. This age, in combination with geochemical and paleontological analysis of ejecta particles, is consistent with deposition of this material as distal impact ejecta from the Ries impact structure, located ~ 180 km away, in Germany. Our observations are important for constraining models of impact ejecta emplacement as ballistically and non-ballistically transported fragments, derived from vastly different depths in the pre-impact target, occur together within the ejecta layer. These observations make the Ries ejecta one of the most completely preserved ejecta deposit on Earth for an impact structure of that size.

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Asteroid impact ejecta units overlain by iron-rich sediments in 3.5–2.4 Ga terrains, Pilbara and Kaapvaal cratons: Accidental or cause–effect relationships?

Earth and Planetary Science Letters ◽

10.1016/j.epsl.2006.03.045 ◽

2006 ◽

Vol 246 (3-4) ◽

pp. 149-160 ◽

Cited By ~ 21

Author(s):

A GLIKSON

Keyword(s):

Asteroid Impact ◽

Impact Ejecta

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Chelyabinsk Meteorite

Oxford Research Encyclopedia of Planetary Science ◽

10.1093/acrefore/9780190647926.013.22 ◽

2021 ◽

Author(s):

Olga Popova

Keyword(s):

Energy Deposition ◽

Seismic Waves ◽

The Body ◽

Structure And Properties ◽

Ural Mountains ◽

Asteroid Impact ◽

Unusual Event ◽

The Earth ◽

First Time

The asteroid impact near the Russian city of Chelyabinsk on February 15, 2013, was the largest airburst on Earth since the 1908 Tunguska event, causing a natural disaster in an area with a population exceeding 1 million. On clear morning at 9:20 a.m. local time, an asteroid about 19 m in size entered the Earth atmosphere near southern Ural Mountains (Russia) and, with its bright illumination, attracted the attention of hundreds of thousands of people. Dust trail in the atmosphere after the bolide was tens of kilometers long and was visible for several hours. Thousands of different size meteorites were found in the areas south-southwest of Chelyabinsk. A powerful airburst, which was formed due to meteoroid energy deposition, shattered thousands of windows and doors in Chelyabinsk and wide surroundings, with flying glass injuring many residents. The entrance and destruction of the 500-kt Chelyabinsk asteroid produced a number of observable effects, including light and thermal radiation; acoustic, infrasound, blast, and seismic waves; and release of interplanetary substance. This unexpected and unusual event is the most well-documented bolide airburst, and it attracted worldwide attention. The airburst was observed globally by multiple instruments. Analyses of the observational data allowed determination of the size of the body that caused the superbolide, its velocity, its trajectory, its behavior in the atmosphere, the strength of the blast wave, and other characteristics. The entry of the 19-m-diameter Chelyabinsk asteroid provides a unique opportunity to calibrate the different approaches used to model meteoroid entry and to calculate the damaging effects. The recovered meteorite material was characterized as brecciated LL5 ordinary chondrite, in which three different lithologies can be distinguished (light-colored, dark-colored, and impact-melt). The structure and properties of meteorites demonstrate that before encountering Earth, the Chelyabinsk asteroid had experienced a very complex history involving at least a few impacts with other bodies and thermal metamorphism. The Chelyabinsk airburst of February 15, 2013, was exceptional because of the large kinetic energy of the impacting body and the damaging airburst that was generated. Before the event, decameter-sized objects were considered to be safe. With the Chelyabinsk event, it is possible, for the first time, to link the damage from an impact event to a well-determined impact energy in order to assess the future hazards of asteroids to lives and property.

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The Biography of the Earth

10.1093/oso/9780197502464.003.0011 ◽

2021 ◽

pp. 200-213

Author(s):

Elisabeth Ervin-Blankenheim

Keyword(s):

Small Mammals ◽

Ecological Niche ◽

Late Jurassic ◽

Big Bang ◽

Ecological Niches ◽

Asteroid Impact ◽

The Earth ◽

The One ◽

Extinction Events ◽

The Universe

The story of the Phanerozoic Eon continues in this chapter with the Mesozoic Era. The first period in the Mesozoic, the Triassic, was bookended by two extinction events, the one at the beginning, discussed in the prior chapter at the end of the Permian Period, the Great Dying, and then another at the end of the period, related to the further breakup of Pangea. Dinosaurs evolved and diversified during the Mesozoic to occupy nearly each and every ecological niche on the planet, with large dinosaurs and small dinosaurs, ones that flew, those that ate vegetation, and those that preyed upon the herbivores—making this time a dino-dominated age. In the late Jurassic Period, small mammals, many of them insectivores, were starting to become prevalent. The era ended with a “big bang” of a different type than is theorized as the start of the universe—with the Chicxulub asteroid impact 66 million years ago that ended the lives of most of the dinosaurs, the non-avian lines, and opened up new ecological niches for the next “masters of the universe,” the mammals.

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The Frequency and Predicted Consequences of Cosmic Impacts in the Last 65 Million Years

Symposium - International Astronomical Union ◽

10.1017/s0074180900193428 ◽

2004 ◽

Vol 213 ◽

pp. 289-294

Author(s):

Michael Paine ◽

Benny Peiser

Keyword(s):

Financial Support ◽

Global Climate ◽

Catastrophic Event ◽

The Past ◽

The Earth ◽

Global Events ◽

Impact Events

Sixty five million years ago a huge asteroid collided with the Earth and ended the long reign of the dinosaurs. In the aftermath of this catastrophic event, the mammals arose and eventually mankind came to dominate the surface of the planet. The Earth, however, has not been free from severe impacts since the time of the dinosaur killer. We examine the likely frequency of major impact events over the past 65 million years, the evidence for these impacts and the predicted consequences of various types of impacts. It is evident that the mammals had to survive frequent severe disruptions to the global climate, and it is likely that over the past 5 million years hominids were faced with several catastrophic global events. Smaller but strategically located impact events could bring down our civilisation if they occurred today. Mankind has recently developed the expertise to predict and mitigate future impacts, but political and financial support are lacking.

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The Mesoproterozoic Stac Fada Member, NW Scotland: an impact origin confirmed but refined

Journal of the Geological Society ◽

10.1144/jgs2020-056 ◽

2020 ◽

Vol 178 (1) ◽

pp. jgs2020-056

Author(s):

G. R. Osinski ◽

L. Ferrière ◽

P. J. A. Hill ◽

A. R. Prave ◽

L. J. Preston ◽

...

Keyword(s):

Volcanic Eruptions ◽

High Energy ◽

Impact Structure ◽

Gravity Flows ◽

Impact Ejecta ◽

Ejecta Blanket ◽

Chicxulub Impact ◽

Melted Material ◽

Impact Origin ◽

Primary Impact

The origin of the Stac Fada Member has been debated for decades with several early hypotheses being proposed, but all invoking some connection to volcanic activity. In 2008, the discovery of shocked quartz led to the hypothesis that the Stac Fada Member represents part the continuous ejecta blanket of a meteorite impact crater, the location of which was, and remains, unknown. In this paper, we confirm the presence of shock-metamorphosed and -melted material in the Stac Fada Member; however, we also show that its properties are unlike any other confirmed and well documented proximal impact ejecta deposits on Earth. Instead, the properties of the Stac Fada Member are most similar to the Onaping Formation of the Sudbury impact structure (Canada) and impact melt-bearing breccias from the Chicxulub impact structure (Mexico). We thus propose that, like the Sudbury and Chicxulub deposits, Melt Fuel Coolant Interactions – akin to what occur during phreatomagmatic volcanic eruptions – played a fundamental role in the origin of the Stac Fada Member. We conclude that these rocks are not primary impact ejecta but instead were deposited beyond the extent of the continuous ejecta blanket as high-energy ground-hugging sediment gravity flows.

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Stochastic accretion of the Earth

10.5194/epsc2020-652 ◽

2020 ◽

Author(s):

Paolo Sossi ◽

Ingo Stotz ◽

Seth Jacobson ◽

Alessandro Morbidelli ◽

Hugh O'Neill

Keyword(s):

Building Blocks ◽

Physical Processes ◽

Volatile Elements ◽

Volatile Element ◽

Elemental Abundances ◽

Stable Isotope Fractionation ◽

The Earth ◽

Gravitational Pull ◽

Atmospheric Loss ◽

Impact Events

The Earth is depleted in volatile elements relative to chondritic meteorites, its possible building blocks. Abundances of volatile elements descend roughly log-linearly with their calculated volatilities during solar nebula condensation [1, 2]. This depletion, however, is not accompanied by any stable isotope fractionation, which would otherwise be expected during vaporisation/condensation and atmospheric loss attending accretion [3, 4]. Thus, the physical processes that led to the formation of the Earth are yet to be reconciled with its chemical composition. Here, we integrate N-body simulations of planetary formation [5] within a framework that combines estimates for the compositions of planetary building blocks with volatile element losses during collisions, to link Earth&#8217;s elemental- and isotopic make-up with accretion mechanisms. The smooth pattern of volatile depletion in the Earth reflects the stochastic accretion of numerous, smaller, partially-vaporised precursor bodies whose elemental abundances are set by the heliocentric distances at which they formed. Impact events engender vaporisation, but atmospheric loss is only efficient during the early stages of accretion when volatile species can readily escape the gravitational pull of the proto-Earth. The chemical and isotopic compositions of the most volatile elements are controlled by that of late-accreting material, during which time the proto-Earth is sufficiently large so as to limit atmospheric loss. Stable isotopes of moderately- and highly volatile elements thus retain near-chondritic compositions. [1] O&#8217;Neill and Palme (2008), Phil. Trans. R. Soc. 4205-38 [2] Braukm&#252;ller et al. (2019), Nat. Geosci., 564-9 [3] Wang and Jacobsen (2016), Nature, 521-4 [4] Sossi et al. 2018, Chem. Geol. 73-84 [5] Jacobson and Morbidelli (2014), Phil. Trans. R. Soc. 20130174

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