Globally distributed iridium layer preserved within the Chicxulub impact structure

The Cretaceous-Paleogene (K-Pg) mass extinction is marked globally by elevated concentrations of iridium, emplaced by a hypervelocity impact event 66 million years ago. Here, we report new data from four independent laboratories that reveal a positive iridium anomaly within the peak-ring sequence of the Chicxulub impact structure, in drill core recovered by IODP-ICDP Expedition 364. The highest concentration of ultrafine meteoritic matter occurs in the post-impact sediments that cover the crater peak ring, just below the lowermost Danian pelagic limestone. Within years to decades after the impact event, this part of the Chicxulub impact basin returned to a relatively low-energy depositional environment, recording in unprecedented detail the recovery of life during the succeeding millennia. The iridium layer provides a key temporal horizon precisely linking Chicxulub to K-Pg boundary sections worldwide.

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Seasonal calibration of the end-cretaceous Chicxulub impact event

Scientific Reports ◽

10.1038/s41598-021-03232-9 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Robert A. DePalma ◽

Anton A. Oleinik ◽

Loren P. Gurche ◽

David A. Burnham ◽

Jeremy J. Klingler ◽

...

Keyword(s):

Mass Extinction ◽

Insect Behavior ◽

Global Scale ◽

Impact Event ◽

Growth Band ◽

Isotopic Analyses ◽

Timing Data ◽

Post Impact ◽

Chicxulub Impact ◽

The Impact

AbstractThe end-Cretaceous Chicxulub impact triggered Earth’s last mass-extinction, extinguishing ~ 75% of species diversity and facilitating a global ecological shift to mammal-dominated biomes. Temporal details of the impact event on a fine scale (hour-to-day), important to understanding the early trajectory of mass-extinction, have largely eluded previous studies. This study employs histological and histo-isotopic analyses of fossil fish that were coeval with a unique impact-triggered mass-death assemblage from the Cretaceous-Paleogene (KPg) boundary in North Dakota (USA). Patterns of growth history, including periodicity of ẟ18O and ẟ13C and growth band morphology, plus corroborating data from fish ontogeny and seasonal insect behavior, reveal that the impact occurred during boreal Spring/Summer, shortly after the spawning season for fish and most continental taxa. The severity and taxonomic symmetry of response to global natural hazards are influenced by the season during which they occur, suggesting that post-impact perturbations could have exerted a selective force that was exacerbated by seasonal timing. Data from this study can also provide vital hindsight into patterns of extant biotic response to global-scale hazards that are relevant to both current and future biomes.

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The Boltysh impact structure: An early Danian impact event during recovery from the K-Pg mass extinction

Science Advances ◽

10.1126/sciadv.abe6530 ◽

2021 ◽

Vol 7 (25) ◽

pp. eabe6530

Author(s):

Annemarie E. Pickersgill ◽

Darren F. Mark ◽

Martin R. Lee ◽

Simon P. Kelley ◽

David W. Jolley

Keyword(s):

Mass Extinction ◽

Crater Lake ◽

Temporal Association ◽

Earth System ◽

Impact Event ◽

The Earth ◽

Relationship Of ◽

Chicxulub Impact ◽

The Impact ◽

Impact Events

Both the Chicxulub and Boltysh impact events are associated with the K-Pg boundary. While Chicxulub is firmly linked to the end-Cretaceous mass extinction, the temporal relationship of the ~24-km-diameter Boltysh impact to these events is uncertain, although it is thought to have occurred 2 to 5 ka before the mass extinction. Here, we conduct the first direct geochronological comparison of Boltysh to the K-Pg boundary. Our 40Ar/39Ar age of 65.39 ± 0.14/0.16 Ma shows that the impact occurred ~0.65 Ma after the mass extinction. At that time, the climate was recovering from the effects of the Chicxulub impact and Deccan trap flood volcanism. This age shows that Boltysh has a close temporal association with the Lower C29n hyperthermal recorded by global sediment archives and in the Boltysh crater lake sediments. The temporal coincidence raises the possibility that even a small impact event could disrupt recovery of the Earth system from catastrophic events.

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Ocean resurge-induced impact melt dynamics on the peak-ring of the Chicxulub impact structure, Mexico

International Journal of Earth Sciences ◽

10.1007/s00531-021-02008-w ◽

2021 ◽

Author(s):

Felix M. Schulte ◽

◽

Axel Wittmann ◽

Stefan Jung ◽

Joanna V. Morgan ◽

...

Keyword(s):

Impact Structure ◽

Physical Processes ◽

Hydrothermal Conditions ◽

Chemical Examination ◽

Impact Melt ◽

Target Rock ◽

Single Process ◽

Chicxulub Impact ◽

The Impact

AbstractCore from Hole M0077 from IODP/ICDP Expedition 364 provides unprecedented evidence for the physical processes in effect during the interaction of impact melt with rock-debris-laden seawater, following a large meteorite impact into waters of the Yucatán shelf. Evidence for this interaction is based on petrographic, microstructural and chemical examination of the 46.37-m-thick impact melt rock sequence, which overlies shocked granitoid target rock of the peak ring of the Chicxulub impact structure. The melt rock sequence consists of two visually distinct phases, one is black and the other is green in colour. The black phase is aphanitic and trachyandesitic in composition and similar to melt rock from other sites within the impact structure. The green phase consists chiefly of clay minerals and sparitic calcite, which likely formed from a solidified water–rock debris mixture under hydrothermal conditions. We suggest that the layering and internal structure of the melt rock sequence resulted from a single process, i.e., violent contact of initially superheated silicate impact melt with the ocean resurge-induced water–rock mixture overriding the impact melt. Differences in density, temperature, viscosity, and velocity of this mixture and impact melt triggered Kelvin–Helmholtz and Rayleigh–Taylor instabilities at their phase boundary. As a consequence, shearing at the boundary perturbed and, thus, mingled both immiscible phases, and was accompanied by phreatomagmatic processes. These processes led to the brecciation at the top of the impact melt rock sequence. Quenching of this breccia by the seawater prevented reworking of the solidified breccia layers upon subsequent deposition of suevite. Solid-state deformation, notably in the uppermost brecciated impact melt rock layers, attests to long-term gravitational settling of the peak ring.

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The Kara astrobleme size, age and potential paleo-ecological effects of the impact event (European Arctic Zone, Russia)

10.5194/egusphere-egu21-8523 ◽

2021 ◽

Author(s):

Tatyana Shumilova

Keyword(s):

Mass Extinction ◽

Black Shales ◽

Ecological Effects ◽

Impact Event ◽

Arctic Zone ◽

Russian Science ◽

Future Possibility ◽

Impact Melt ◽

European Arctic ◽

The Impact

The Kara astrobleme is one of the biggest meteoritic craters which is set at the Baydarata Bay of the Kara sea (European Arctic Zone, Russia). It is a result of the catastrophic impact event occurred close to the K/&#1058; extinction. The Kara astrobleme is the largest European crater at the modern erosion level.&#160; At present it is estimated with the diameter from rim to rim about 65 km. While, some scientists have proposed its larger initial size &#8211; up to 120 km diameter, but no any well presented proof has been provided for the hypothesis. In 2015-2019 we have provided wide geological observations at the Kara crater and the near-set Ust`-Kara area (UKA) impactites. We have found for the first time that the UKA impactites, described in earlier Russian scientists publications as a synchronic independent crater of the same bolide, can be presented with bottom-flow impactites from the Kara crater (Shumilova et al., 2020). The found bottom-flow impactites abundant with belt-like impact melt bodies enriched in coesite and liquation structures similar to the Kara UHPHT vein and vein-like melt bodies with UHPHT impact glasses. Thus, they belong to UHPHT impactites. According to our air-bird view observations and impactites outcrops description at the UKA we support the hypothesis of the larger Kara crater getting 100-120 km in diameter of the initially originated size. Such giant meteorite event should be followed by catastrophic effects at the planet level, such as mass extinction. The present accepted Kara impact event age followed by the most recent measurements by 40Ar-39Ar method is equal to 70.3 &#177; 2.2 Ma (Trieloff et al., 1998), that is a bit earlier than the Cretaceous/Tertiary boundary (K/&#1058;) mass extinction at 66 Ma. But, previously, Kara age has been proposed by 65.7 Ma as a probable K/T impact (Kolesnikov et al., 1988; Nazarov et al., 1992). According to different data, the Kara event age lies within the range from 60 to 81 Ma (Masaitis & Mashchak, 1982; Nazarov et al., 1989; Kolesniov et al., 1990; Koeberl et al., 1990). It is clear that the accuracy of the age measurements depend on the quality of the studied samples, including their crystallinity, velocity of impact melt cooling and alteration, and from the used type of a method. By the moment, we have found out &#8220;in situ&#8221; crystallized zircons within the just discovered real UHPHT impact melt glasses (Shumilova et al., 2018, 2020). The UHPHT glasses do not have any alteration, thus, they can be used for accurate age measurements. Taking a future possibility for more accurate age analysis in the nearest future we can propose a correct vision of the possibility of the giant Kara influence to K-T mass extinction or other ecological effects. In any case following to the giant size of the Kara event touched the sedimentary rocks abundant with black shales and carbonates, which should be a result of essential atmospheric changes. The study has been supported by the Russian Science Foundation project #17-17-01080.

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In-situ observation of damage evolution in polycarbonate subjected to hypervelocity impact

2019 15th Hypervelocity Impact Symposium ◽

10.1115/hvis2019-011 ◽

2019 ◽

Author(s):

Nobuaki Kawai ◽

Mikio Nagano ◽

Sunao Hasegawa ◽

Eiichi Sato

Keyword(s):

Real Time ◽

Stress Wave ◽

Damage Evolution ◽

Impact Damage ◽

Hypervelocity Impact ◽

The Other ◽

Impact Event ◽

Real Time Imaging ◽

The Impact ◽

Impact Events

Abstract In the fields of space engineering and planetary science, hypervelocity impact phenomena have been studied as they relate to the space debris problem and planetary impact. With regard to hypervelocity-impact-induced damage, many studies focus on the evaluation of impact-damage geometry and morphology, for example, to construct the ballistic limit equations and/or penetrating equations for space structures, and to predict the size and shape of crater and fragments generated by planetary impact [1-4]. While the final state or late stage of an impact event are of primal interest, damage accumulation at early stages affect the overall outcome of the impact event. The understanding of hypervelocity-impact-damage processes lead to improvement of material-response models for hypervelocity impact and higher fidelity simulations of hypervelocity impact events. Under such a background, we have performed real-time imaging of hypervelocity-impact events on transparent materials to investigate the impact-damage formation and evolution processes [5-7]. In our previous work, the stress-wave-propagation behavior and damage evolution were observed by means of a transmitted light shadowgraph. In these measurements, the shape of the longitudinal-stress-wave front, crater and spall fracture were successfully visualized. On the other hand, these shadowgraph images provide little information about damage microstructure. The shadowgraph has difficulty in visualizing ramped waves, such as the release wave, and also for the shear wave which is not accompanied by the change of volumetric strain. Those play important role in initiating damage. This occurs because the intensity of the shadowgraph image depends on the second spatial derivative of the refractive index. In this study, we try two types of real-time imaging of impact events. One is imaging by using scattered light on the impacted target to visualize the microstructure of the impact-induced damage, the other is a shadowgraph using polarized light to visualize propagation of the impact-induced stress field.

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Deposition and age of Chicxulub impact spherules on Gorgonilla Island, Colombia

Geological Society of America Bulletin ◽

10.1130/b35287.1 ◽

2019 ◽

Vol 132 (1-2) ◽

pp. 215-232

Author(s):

Paula Mateo ◽

Gerta Keller ◽

Thierry Adatte ◽

André M. Bitchong ◽

Jorge E. Spangenberg ◽

...

Keyword(s):

Mass Extinction ◽

Tectonic Activity ◽

Sea Level Fluctuations ◽

Variable Extent ◽

Stratigraphic Position ◽

Radiolarian Biostratigraphy ◽

Absolute Age ◽

Chicxulub Impact ◽

The Impact ◽

Primary Impact

AbstractThe end-Cretaceous mass extinction (66 Ma) has long been associated with the Chicxulub impact on the Yucatan Peninsula. However, consensus on the age of this impact has remained controversial because of differing interpretations on the stratigraphic position of Chicxulub impact spherules relative to the mass extinction horizon. One side argues that the impact occurred precisely at the Cretaceous-Paleogene boundary, thus coinciding with the mass extinction; the other side argues that the impact predated the Cretaceous-Paleogene boundary, based on the discovery of primary impact spherules deposits in NE Mexico and Texas near the base of planktic foraminiferal zone CF1, dated at 170 k.y. before the Cretaceous-Paleogene boundary. A recent study of the most pristine Chicxulub impact spherules discovered on Gorgonilla Island, Colombia, suggested that they represent a primary impact deposit with an absolute age indistinguishable from the Cretaceous-Paleogene boundary. Here, we report on the Gorgonilla section with the main objective of evaluating the nature of deposition and age of the spherule-rich layer relative to the Cretaceous-Paleogene boundary.The Gorgonilla section consists of light gray-yellow calcareous siliceous mudstones (pelagic deposits) alternating with dark olive-brown litharenites (turbidites). A 3-cm-thick dark olive-green spherule-rich layer overlies an erosional surface separating Maastrichtian and Danian sediments. This layer consists of a clast-supported, normally graded litharenite, with abundant Chicxulub impact glass spherules, lithics (mostly volcanic), and Maastrichtian as well as Danian microfossils, which transitions to a calcareous mudstone as particle size decreases. Mineralogical analysis shows that this layer is dominated by phyllosilicates, similar to the litharenites (turbidites) that characterize the section. Based on these results, the spherule-rich layer is interpreted as a reworked early Danian deposit associated with turbiditic currents. A major hiatus (>250 k.y.) spanning the Cretaceous-Paleogene boundary and the earliest Danian is recorded at the base of the spherule-rich layer, based on planktic foraminiferal and radiolarian biostratigraphy and carbon stable isotopes. Erosion across the Cretaceous-Paleogene boundary has been recorded worldwide and is generally attributed to rapid climate changes, enhanced bottom-water circulation during global cooling, sea-level fluctuations, and/or intensified tectonic activity. Chicxulub impact spherules are commonly reworked and redeposited into younger sediments overlying a Cretaceous-Paleogene boundary hiatus of variable extent in the Caribbean, Central America, and North Atlantic, while primary deposits are rare and only known from NE Mexico and Texas. Because of their reworked nature, Gorgonilla spherules provide no stratigraphic evidence from which the timing of the impact can be inferred.

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Distinguishing shock-related microstructures in gneisses from the Vredefort impact structure, South Africa

10.5194/egusphere-egu21-2494 ◽

2021 ◽

Author(s):

Fabian Dellefant ◽

Claudia Trepmann ◽

Stuart Gilder ◽

Iuliia Sleptsova ◽

Melanie Kaliwoda ◽

...

Keyword(s):

South Africa ◽

Magnetic Properties ◽

Frictional Heating ◽

Rapid Quenching ◽

Impact Structure ◽

Impact Event ◽

Lightning Strikes ◽

Fine Grained ◽

The Impact ◽

Drill Cores

Shocked gneiss (~8 GPa) from the Vredefort impact structure (South Africa) contain planar fractures in quartz decorated by magnetite and ilmenite, which are commonly attributed to the impact event. However, the surface at Vredefort is riddled by lightning strikes, which also produce rapid pressure-temperature pulses that can modify the microstructure and the magnetic properties of the rocks. To understand the differences between lightning and impact-related shock effects, we investigated samples from two, 10 m-deep drill cores by Raman spectroscopy, polarized light microscopy/U-stage and electron microscopy/electron backscatter diffraction techniques. Magnetite and ilmenite within planar fractures in quartz occur at all depths, and are therefore intrinsic to the impact event, independent of lightning. Primary iron-bearing minerals were locally heated by the generation of shear fractures in neighboring quartz, leading to small volumes (micrometer scales) of melt intruding into nearby fractures. Frictional heating and rapid quenching of feldspar and quartz is indicated by localized, fine-grained aggregates along intragranular planar fractures as well as transgranular pseudotachylytic veins. On the other hand, altered ilmenite grains with exsolved magnetite occur only in gneisses from the uppermost 80 cm of both drill cores. When in contact with biotite, the ilmenite-magnetite boundaries are altered to chlorite, and the ilmenite is partly transformed to anatase. These alteration products contain fine-grained magnetite. It appears that lightning strikes altered the existing ilmenite-magnetite in the Vredefort samples to produce smaller, more single-domain like magnetite grains, consistent with the observed magnetic properties of the samples

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Impact-induced hydrothermal dissolution in pyroxene: Petrographic and geochemical characterization of basalt-dominated polymict impact breccias from the Vargeão Dome, Brazil

Large Meteorite Impacts and Planetary Evolution VI ◽

10.1130/2021.2550(24) ◽

2021 ◽

Author(s):

Jennifer Epstein ◽

Lidia Pittarello ◽

Álvaro P. Crósta ◽

Christian Koeberl

Keyword(s):

Hydrothermal Alteration ◽

Hydrothermal Fluids ◽

Terrestrial Planets ◽

Impact Structure ◽

Impact Event ◽

Southern Brazil ◽

Geochemical Characterization ◽

Heterogeneous Nature ◽

The Impact

ABSTRACT Constraints on impact-related hydrothermal alteration are important to enable the reconstruction of the possible processes affecting the surface of other terrestrial planets, such as Mars. Terrestrial impact structures excavated in basaltic targets provide the opportunity for analog studies. In Brazil, seven impact structures have been confirmed so far. Three of them, Vargeão Dome, Vista Alegre, and Cerro do Jarau, were formed in the same basaltic province belonging to the Paraná Basin, and they have several common characteristics. Oxidized basaltic breccias locally containing sandstone clasts occur in all these structures. In this work, selected samples of such breccias from the Vargeão Dome impact structure in southern Brazil were petrographically and geochemically investigated to further constrain the effects of the postimpact hydrothermal alteration. The breccia matrix shows typical oxidation effects induced by postimpact hydrothermal fluids, which highlight its heterogeneous nature, related to the impact event, and mixing components from different pre-impact stratigraphic formations. The detection of partially dissolved exsolution lamellae in pyroxene and of related alteration products constrains the effects of hydrothermal alteration in the basalts of the Vargeão Dome, which could serve as a terrestrial analog for planetary studies.

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The Cleanskin impact structure, Northern Territory and Queensland, Australia: A reconnaissance study

Large Meteorite Impacts and Planetary Evolution VI ◽

10.1130/2021.2550(03) ◽

2021 ◽

Author(s):

T. Kenkmann ◽

P.W. Haines ◽

I.P. Sweet ◽

K. Mitchell

Keyword(s):

Remote Sensing ◽

Northern Territory ◽

Impact Structure ◽

Impact Event ◽

Deformation Features ◽

Apparent Diameter ◽

The Impact ◽

Planar Deformation Features ◽

Impact Origin ◽

Quartz Grains

ABSTRACT We report on the Cleanskin structure (18°10′00″S, 137°56′30″E), situated at the border between the Northern Territory and Queensland, Australia, and present results of preliminary geological fieldwork, microscopic analyses, and remote sensing. The Cleanskin structure is an eroded complex impact structure of ~15 km apparent diameter with a polygonal outline caused by two preexisting regional fault sets. The structure has a central uplift of ~6 km diameter surrounded by a rather shallow ring syncline. Based on stratigraphy, the uplift in the center may not exceed ~1000 m. The documentation of planar deformation features (PDFs), planar fractures (PFs), and feather features (FFs) in quartz grains from sandstone members of the Mesoproterozoic Constance Sandstone confirms the impact origin of the Cleanskin structure, as proposed earlier. The crater was most likely eroded before the Cambrian and later became buried beneath Cretaceous strata. We infer a late Mesoproterozoic to Neoproterozoic age of the impact event. In this chapter, the Cleanskin structure is compared with other midsized crater structures on Earth. Those with sandstone-dominated targets show structural similarities to the Cleanskin structure.

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Deccan Volcanism or the Chicxulub Impact: The Chicken or Egg Question

10.5194/egusphere-egu2020-22414 ◽

2020 ◽

Author(s):

Gerta Keller

Keyword(s):

Mass Extinction ◽

Impact Crater ◽

Global Climate ◽

Mass Extinctions ◽

Deccan Volcanism ◽

Asteroid Impact ◽

Global Climate Warming ◽

Chicxulub Impact Crater ◽

Chicxulub Impact ◽

The Impact

The Cretaceous&#8211;Paleogene boundary (KTB or KPB) mass extinction is primarily known for the demise of the dinosaurs, the Chicxulub impact, and the rancorous forty-year-old controversy over the cause of this mass extinction. For the first 30 years, the controversy primarily revolved around the age of the impact claimed as precisely KTB based on the assumption that it caused the mass extinction. The iridium (Ir) anomaly at the KTB was claimed proof of the asteroid impact, but no Ir was ever associated with impact evidence and recent findings reveal no extraterrestrial component in PGEs or the KTB Ir anomaly. Impact melt rock glass spherules are also claimed as indisputable evidence of the KTB age impact, but such spherule layers are commonly reworked from the primary (oldest) layer in late Maastrichtian, KTB and Danian sediments; thus only the oldest impact spherule layer documented near the base of zone CF1 ~200 ky below the KTB can approximate the impact&#8217;s age. Similarly, the impact breccia in the Chicxulub impact crater predates the KTB. The best age derived from Ar/Ar dating of impact glass spherules is within 200 ky of the KTB and thus no evidence for the KTB age. All evidence strongly suggests the Chicxulub impact most likely predates the mass extinction ~ 200 ky and played no role in it. Deccan volcanism (LIP) was dismissed as potential cause or even contributor to the KTB mass extinction despite the fact that all other mass extinctions are associated with Large Igneous Province (LIP) volcanism but none with an asteroid impact. During the last decade, Deccan volcanism gained credence based on a succession of discoveries: 1) the mass extinction in between the longest Deccan lava flows across India; 2) high-precision dating of the entire sequence of Deccan volcanism based on UPb zircon dating; 3) recognition of four distinct eruption pulses all related to global climate warming with the largest pulse beginning 20 ky prior to and ending at the KTB; 4) Identifying the climate link to Deccan volcanism based on age dating and mercury from Deccan eruptions in marine sediments; and 5) Identifying the KTB mass extinction directly related to the major Deccan eruption pulse, hyperthermal warming and ocean acidification all linked to global mercury fallout from Deccan eruptions in marine sediments. Despite this remarkable culmination of evidence, the controversy continues with impact proponents arguing that Deccan volcanism didn&#8217;t exist at the KTB &#8211; the impact was the sole cause.

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