Modeling the formation of the K–Pg boundary layer

Abstract

35In this paper we investigate the formation of the Cretaceous-Paleogene (K-Pg) boundary 36 layer through numerical modeling. The K-Pg layer is widely agreed to be composed of meteoritic 37 material and target rock from the Chicxulub impact site, that has been ejected around the globe 38 and mixed with local material during final deposition. The observed composition and thickness of 39 the K-Pg boundary layer changes with azimuth and distance from the impact site. We have run a 40 suite of numerical simulations to investigate whether we can replicate the observational data, with 41 a focus on the distal K-Pg layer and the impact glasses at proximal sites such as Beloc, Haiti. 42Previous models of the K-Pg ejecta have assumed an initial velocity distribution and tracked the 43 ejecta to its final destination. Here, we attempt to model the entire process, from impact to the 44 arrival of the ejecta around the globe. Our models replicate the observed ejecta thickness at 45 proximal sites, and the modeled ejecta is composed of sediments and silicate basement rocks, in 46 agreement with observational data. Models that use a 45° impact angle are able to replicate the 47 total ejecta and iridium volume at distal sites, and the majority of the ejecta is composed of 48 meteorite and target sediments. Sub-vertical impacts generate too little iridium, and oblique 49 impacts of ≤ 30 degrees generate too much. However, in contrast to observations, models that 50 involve ballistic transport of ejecta lead to ejecta thickness decreasing with increasing distance, 51and are unable to transport shocked minerals (quartz and zircon) from the Chicxulub basement 52 rocks around the globe. We suggest that much of the K-Pg ejecta is transported non-ballistically, 53and that the most plausible mechanism is through re-distribution from a hot, expanding 54 atmosphere. The results are important for future investigations of the environmental effects of the 55 Chicxulub impact. 56

The Chicxulub Asteroid Impact and Mass Extinction at the Cretaceous-Paleogene Boundary

“…Asteroid impact models [e.g., (40)] predict that an impact large enough to generate the Chicxulub crater would induce earthquakes (magnitude > 11), shelf collapse around the Yucatan platform, and widespread tsunamis sweeping the coastal zones of the surrounding oceans (7). Moreover, models suggest the Chicxulub impact had sufficient energy to eject and distribute material around the globe (7), possibly enhanced by decomposition of the volatile-rich carbonate and sulfate sediments (41). Near-surface target material was ejected ballistically at velocities up to a few km/s as part of the ejecta curtain.…”

Volume 364: Chicxulub: Drilling the K-Pg Impact Crater

“…The mineralogical and geochemical characterization of the peak-ring rocks will provide key information on target rock composition (Koeberl et al, 2012). We will also search for an extraterrestrial signature using platinum group element (PGE) analyses and Os and Cr isotopes (Gelinas et al, 2004;Tagle and Hecht, 2006;Trinquier et al, 2006;Goderis et al, 2012;Sato et al, 2013 to determine whether a measurable fraction of the projectile remains at the impact site or whether most projectile material ends up within the global K-Pg layer (Artemieva and Morgan, 2009). High-resolution 40 Ar/ 39 Ar analyses and electron microscopy on shocked and melted impactites, as well as U/Pb dating of zircon and other geo-and thermochronometers, will be used to study their pressure-temperature-time and deformational history and for highprecision dating of the Chicxulub impact.…”

“…Placing constraints on the impact energy with numerical simulations and on the lithology, shock state, and porosity of the target rocks is important because these are all critical input parameters for modeling the environmental effects of this impact (Pope et al, 1997;Pierazzo et al, 2003). Solid, melted, and vaporized material from the asteroid and target rocks are ejected away from the impact site within an expanding plume (Figure F10), and the mass, velocity, and composition of these ejecta are dependent on impact angle (Artemieva and Morgan, 2009;Morgan et al, 2013). The duration and strength of the thermal pulse delivered at the Earth's surface by reentering ejecta varies with direction and distance from Chicxulub , and this variation affects the likelihood of ignition of flora (Belcher et al, 2015).…”

An experimental assessment of the ignition of forest fuels by the thermal pulse generated by the Cretaceous–Palaeogene impact at Chicxulub

“…The 3D hydrocode SOVA (Shuvalov 1999), which uses the ANEOS equations of state for geological materials (Thompson & Lauson 1972), was used to model the impactor colliding with the Earth and the ejection of material away from Chicxulub (Artemieva & Morgan 2009). An impact angle of 45° is used as this is the most likely angle of impact and because it can broadly reproduce the observed mass and meteoritic composition of the red clay (ejecta) layer that is found across the globe (Artemieva & Morgan 2009). Once above the atmosphere the ejecta is assumed to travel on a ballistic path and then SOVA is used to model the heating of ejecta as it travels through the atmosphere.…”