Formation conditions of oxidized Ni-rich spinel and their relevance to the K/T boundary event

Abstract

Highly oxidized Ni-rich spinel crystals have been found throughout the world at the Cretaceous-Tertiary (K/T) boundary. Although these crystals are believed to derive from the K/T impactor, their formation conditions remain obscure. In this chapter, we present experimental results concerning the crystallization of oxidized Ni-rich spinel from melts of chondritic composition. The effects of varying oxygen fugacity, temperature, duration of the heat exposure, and cooling rate on the morphology, abundance, and composition of spinel have been studied for two types of chondrite, a CI-type carbonaceous chondrite (Orgueil) and an LL6-type ordinary chondrite (Saint Severin). This study supports the view that the spinel crystals reported worldwide at the K/T boundary are derived from meteoritic material that equilibrated at ƒ O 2 ≥ 10 -2 bar and T ≤ 1520°C. Such formation conditions rule out derivation of K/T spinel from known volcanic or impact processes. In particular, K/T spinel cannot be formed in terrestrial magmas that evolved under extremely low oxygen fugacities, near the fayalite-magnetite-quartz (FMQ) buffer. For the same reason, direct crystallization from impact melt rocks or direct condensation from the cloud of vaporized target and projectile material can be excluded. We propose that spinel crystals from the K/T boundary have crystallized in liquid ablation droplets produced during the interaction with the atmosphere of large meteoroids decelerated at low altitudes, under high oxygen fugacities. Our scenario implies multiple meteoroid impacts all over the Earth, resulting either from the fragmentation of the K/T impactor upon an oblique impact or from the encounter with a fragmented comet.

Chronostratigraphy, composition, and origin of Ni-rich spinel from the Late Eocene Fuente Caldera section in Spain: One impact or more?

“…Several experimental (Hill and Roeder 1974;Murck and Campbell 1986;Gayraud et al 1996;Toppani and Libourel 2003) and theoretical (Siret and Robin 2003;Siret 2004;Ebel and Grossman 2005) studies conducted on spinel crystallization have shown that the spinel composition is primarily controlled by the oxygen fugacity, temperature, and initial composition of the crystallizing material. Variable compositions in primary spinel crystals thus imply variations in the physical and chemical environment from which they were crystallized.…”

“…This scenario is consistent with laboratory experiments Gault 1982, 1990) and hydrocode modeling (Pierazzo and Melosh 2000) of oblique impacts showing that a large fraction (>70%) of the projectile survives the impact in the solid and liquid state and is rapidly expelled from the crater by the expanding vapor from the shocked target. High-velocity interaction with the atmosphere for meteoritic material is known as a source for Ni-rich spinel (Robin et al 1992;Gayraud et al 1996). It is therefore likely that atmospheric reentry of mixed projectile/target impact debris is a source for this mineral.…”

“…Indeed, spinel crystals can be extracted without damage from diagenetically altered sediments and then easily sorted and counted according to specific chemical criteria using an automated particle counting and classification system (Robin et al 1991). Nickel-rich spinel differs from terrestrial spinel in its high nickel content, reflecting the high abundance of this element in the parent material, and a high ferric/ferrous ratio resulting from crystallization in an O 2 -rich environment (Robin et al 1992;Gayraud et al 1996;Toppani and Libourel 2003). Spinel is found in meteorite fusion crusts, cosmic spherules from deep-sea sediments, and polar ice (Robin et al 1992), and in a variety of impact debris in the sedimentary record: at the Cretaceous/Paleogene boundary (65 Myr ago) (Smit and Kyte 1984), in a Lower-Middle Jurassic hardground (~180 Myr ago) from the southern Alps in Italy (Jéhanno et al 1988), in Late Pliocene sediments (~2 Myr ago) from the Antarctic basin (Margolis et al 1991), in Oligocene sediments (~30 Myr ago) from the central North Pacific (Kyte and Bostwick 1995), and in the Global Stratotype Section and Point for the Eocene/Oligocene boundary of Massignano in Italy (Pierrard et al 1998).…”

First petrographic results on impactites from the Yaxcopoil‐1 borehole, Chicxulub structure, Mexico

“…Recent publications that question this association (Keller et al 2003a(Keller et al , 2004 are based on very limited data that are quite questionable. Crucial evidence in support of a collision with an extraterrestrial projectile at that time includes the widespread deposition of glass spherules around the Caribbean and beyond (e.g., Sigurdsson et al 1991;Smit et al 1992;Premo and Izett 1992;Koeberl and Sigurdsson 1992;Koeberl 1993;Oskarsson et al 1996;Chaussidon et al 1996;Hough et al 1998;Smit 1999), the global distribution of shock metamorphic quartz (Bohor 1990;Owen et al 1990;Alvarez et al 1995;Bostwick and Kyte 1996;Goto et al 2002), anomalous PGE concentrations with chondritic character (Alvarez et al 1980;Kyte et al 1980;Smit and Hertogen 1980;Orth et al 1981;Schmitz 1988;Evans et al 1995), Nirich spinels (Cisowski 1990;Kyte and Bostwick 1995;Gayraud et al 1996), the presence of fullerenes (Heymann et al 1994(Heymann et al , 1996Buseck 2002), evidence for a global occurrence of wildfires (Argyle et al 1986;Wolbach et al 1985Wolbach et al , 1990Kring and Durda 2001), and nano-to microdiamonds found worldwide in the K/T boundary clay layer (Gilmour et al 1992;Hough et al 1997). The major mass extinction event at the K/T boundary has been widely linked to this cosmic catastrophe (e.g., Alvarez et al 1980;…”

Accretion of extraterrestrial matter recorded in the Triassic and Jurassic bedded chert sequence, southwest Japan

“…Radiometric age data are after Gradstein et al (2012). cosmic spinel Kyte and Smit, 1986;Margolis et al, 1991;Byerly and Lowe, 1994;Kyte and Bohor, 1995;Krull-Davatzes et al, 2010 Kyte andBohor, 1995;Gayraud et al, 1996Ebel and Grossman, 2005Robin et al, 1992, 1993Gayraud et al, 1996Gayraud et al, 2010 5 cm and K/Pg Montanari et al, 1983Smit, 1999;Glass et al, 2004;Liu et al, 2009 microtektite microcrystallite Glass and Burns, 1988;Glass et al, 2004;French andKoeberl, 2010 Jones andKodis, 1982;Melosh, 1989;Alvarez, 1996 Ni , Fig. 7 Sato et al, 2013) in bedded cherts and claystones from the Sakahogi section.…”