Spheroids at the Cretaceous-Tertiary boundary are altered impact droplets of basaltic composition

Montanari, A.; Hay, Richard L.; Álvarez, Walter; Asaro, Frank; Michel, Helen V.; Alvarez, Luis W.; Smit, Jan

doi:10.1130/0091-7613(1983)11<668:satcba>2.0.co;2

Cited by 166 publications

(88 citation statements)

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“…silicate (Montanari et al, 1983) and spinel (Smit and Kyte, 1984) have been found. These spherules are regarded as cosmogenic and impact ejecta (microtektites), completely altered through diagenesis after deposition.…”

Section: Discussionmentioning

confidence: 99%

Green Spherules as Indicators of the Cretaceous/Tertiary Boundary in Deep Sea Drilling Project Hole 603B

Klaver¹,

Kempen²,

Bianchi³

et al. 1987

Initial Reports of the Deep Sea Drilling Project

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Dark green spherules occur in the lower part of a turbidite in Section 603B-22-3, at the 70 cm level. In all probability these spherules originally consisted of massive glass, but now appear to have become completely altered into smectite. The presence of numerous microscopic fissures in the spherules probably mediated in the alteration process.Judging by the presence of similar spherules at the Cretaceous/Tertiary (K/T) boundary in DSDP Hole 390B, the green spherules are thought to represent diagenetically altered impact ejecta from one large or several smaller extraterrestrial objects at the end of the Cretaceous. The presence of anomalously high concentrations of Ni, Co, and As higher up in the turbidite are in agreement with an expected enrichment of these elements in the K/T boundary clay. However, precise Ir analyses are necessary in order to confirm this.

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Section: Discussionmentioning

confidence: 99%

Green Spherules as Indicators of the Cretaceous/Tertiary Boundary in Deep Sea Drilling Project Hole 603B

Klaver¹,

Kempen²,

Bianchi³

et al. 1987

Initial Reports of the Deep Sea Drilling Project

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“…They have also been found in Precambrian-and Late Eocene spherules (Glass and Simonson 2013). The Ni-rich spinels have been recognized as magnetites by Montanari et al (1983), as spinels by Kyte and Smit (1986) and as magnesioferrites by Bohor et al (1986). They range in size from <5 µm up to 50 µm (Bohor et al 1986;.…”

Section: Discussionmentioning

confidence: 99%

“…This thin layer is distributed globally from the impact site and contains, as significant components, altered spherules of impact melt (Montanari et al 1983;Sharpton et al 1992;Pollastro and Bohor 1993;Bohor and Glass 1995;references in Sharpton andWard 1990, Ryder et al 1996).…”

Section: Introductionmentioning

confidence: 99%

Spherules associated with the cretaceous–paleogene boundary in Poland

Brachaniec¹,

Karwowski²,

Szopa³

2014

Acta Geologica Polonica

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ABSTRACT:Brachaniec, T., Karwowski, Ł. and Szopa, K. 2014. Spherules associated with the Cretaceous-Paleogene boundary in Poland. Acta Geologica Polonica, 64 (1), 99-108. Warszawa.The succession of the Lechówka section near Chełm in south-eastern Poland presents the first complete record of the Cretaceous-Paleogene (K-Pg) boundary in Poland. Samples of the boundary clay were examined for microtektites and shocked minerals to confirm the impact origin of the sediment. The spheroidal fraction reveals morphological and mineralogical features, e.g., spherules, similar to material from the K-Pg boundary as described from elsewhere. The impact genesis of the spherules is confirmed by the presence of nickel-rich spinel grains on their surfaces. The spinels are considered to be primary microlites and, thus, the spherules at Lechówka can be classified as microkrystites. No shocked minerals were noted. The deposits with spherules comprise Aland Mg-rich smectite (Cheto smectite). This almost pure Mg-rich smectite, forming up to 100% of the clay fraction, derived from the weathering of the impact glass. It is proposed that the spherules isolated from the Cretaceous-Paleogene boundary clay at Lechówka come from the Chicxulub crater in Mexico.

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“…This layer is also mostly composed of spherules, and Smit (1999) estimated the spherule concentration to be -20000/cm2. At least three types of spherules have been described from the global K-T layer (Montanari et al, 1983;Smit et al, 1992). Spherules composed largely of glauconite or potassium feldspar have similar dendritic textures, which Smit et al (1992) suggested may be derived from clinopyroxenes.…”

Section: Physical Tracersmentioning

confidence: 99%

Tracers of the extraterrestrial component in sediments and inferences for Earth's accretion history

Kyte¹

2002

Catastrophic Events and Mass Extinctions: Impacts and Beyond

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The study of extraterrestrial matter in sediments began with the discovery of cosmic spherules during the HMS Challenger Expedition (1873-1876), but has evolved into a multidisciplinary study of the chemical, physical, and isotopic study of sediments. Extraterrestrial matter in sediments comes mainly from dust and large impactors from the asteroid belt and comets. What we know of the nature of these source materials comes from the study of stratospheric dust particles, cosmic spherules, micrometeorites, meteorites, and astronomical observations.The most common chemical tracers of extraterrestrial matter in sediments are the siderophile elements, most commonly iridium and other platinum group elements. Physical tracers include cosmic and impact spherules, Ni-rich spinels, meteorites, fossil meteorites, and ocean-impact melt debris. Three types of isotopic systems have been used to trace extraterrestrial matter. Osmium isotopes cannot distinguish chondritic from mantle sources, but provide a useful tool in modeling long-term accretion rates. Helium isotopes can be used to trace the long-term flux of the fine fraction of the interplanetary dust complex. Chromium isotopes can provide unequivocal evidence of an extraterrestrial source for sediments with high concentrations of meteoritic Cr.The terrestrial history of impacts, as recorded in sediments, is still poorly understood. Helium isotopes, multiple Ir anomalies, spherule beds, and craters all indicate a comet shower in the late Eocene. The Cretaceous-Tertiary boundary impact event appears to have been caused by a single carbonaceous chondrite projectile, most likely of asteroid origin. Little is known of the impact record in sediments from the rest of the Phanerozoic. Several impact deposits are known in the Precambrian, including several possible megaimpacts in the Early Archean.

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Spheroids at the Cretaceous-Tertiary boundary are altered impact droplets of basaltic composition

Cited by 166 publications

References 0 publications

Green Spherules as Indicators of the Cretaceous/Tertiary Boundary in Deep Sea Drilling Project Hole 603B

Green Spherules as Indicators of the Cretaceous/Tertiary Boundary in Deep Sea Drilling Project Hole 603B

Spherules associated with the cretaceous–paleogene boundary in Poland

Tracers of the extraterrestrial component in sediments and inferences for Earth's accretion history

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