Meteorites that produce K-feldspar-rich ejecta blankets correspond to mass extinctions

Meteorite impacts load the atmosphere with dust and cover the Earth's surface with debris. They have long been debated as a trigger of mass extinctions through Earth's history. Impact winters generally last <100 years, whereas ejecta blankets persist for 103-105 years. Here we show that only meteorite impacts that emplaced ejecta blankets rich in K-feldspar (Kfs) correlate to Earth system crises (n=11, p<0.000005). Kfs is a powerful ice-nucleating aerosol yet is normally rare in atmospheric dust mineralogy. Ice nucleation plays an important role in cloud microphysics, which modulates global albedo. A conceptual model is proposed whereby the anomalous prevalence of Kfs is posited to have two key effects on cloud dynamics: 1) reducing the average albedo of mixed-phase cloud, which effected a hotter climate; 2) weakening of the cloud albedo feedback, which increased climate sensitivity. These mechanisms offer an explanation as to why this otherwise benign mineral is correlated so strongly with mass extinction events: every K-feldspar-rich ejecta blanket corresponds to a severe extinction episode over the past 600 Myr. This model may also explain why many kill mechanisms only variably correlate with extinction events through geological time: they coincide with these rare periods of climate destabilization by atmospheric Kfs.Supplementary material:https://doi.org/10.6084/m9.figshare.c.5690646

Introduction

ABSTRACT This paper does not have an abstract. CONFERENCE The Large Meteorite Impacts and Planetary Evolution Conference VI (LMI VI) took place between 30 September and 3 October 2019 on the campus of the University of Brasília (UnB) in Brasília, Brazil. This series of essentially quintennial conferences has been a mainstay for three decades. It was initiated with the aim to review major research outcomes, share ideas, and fertilize new collaborations in the impact cratering and planetary science fields. The timing for LMI VI, related to the state of impact cratering research, was a good one. For example, the studies resulting from the important IODP-ICDP (International Ocean Discovery Program–International Continental Scientific Drilling Program) project, in which a deep drill core was retrieved from the peak ring of the Chicxulub impact structure—the smoking gun for the Cretaceous-Paleogene (K-Pg) boundary impact event coincident with the mass extinction at that time—were nearing completion and could be presented, in part, at LMI VI. Numerous other advances in impact research had been made in the preceding years (for example, state-of-the-art microstructural studies on accessary minerals with electron backscatter diffraction [EBSD]) and were extensively discussed at the conference. And, finally, interest in impact cratering has significantly increased in recent years, not only...

Dedication of Large Meteorite Impacts and Planetary Evolution VI to Álvaro Penteado Crósta

ABSTRACT This paper does not have an abstract. Originally, Álvaro Penteado Crósta (born on 7 August 1954) intended to be one of the volume editors of this GSA Special Paper. He was also looking forward to participating in the Large Meteorite Impacts and Planetary Evolution VI conference in October 2019, for which he had long served on the organizing committee. Unfortunately, a long and serious illness derailed both these plans. Therefore, we are instead honoring our dear friend and valued colleague, Álvaro Crósta, for his longstanding and successful impact cratering work, as the mainstay of impact cratering studies in Brazil and indeed in South America, by dedicating this Special Paper to him. Álvaro Crósta has been a Full Professor (Professor Titular) of Geoscience in the fields of remote sensing, mineral exploration, and planetary geology at the Instituto de Geociências of the Universidade Estadual de Campinas (UNICAMP) in Brazil. He has had a highly distinguished academic career, culminating in his tenure (2012–2017) as vice-rector of his university. In 2017, Álvaro was inducted as a Full Member (Membro Titular) into the Academia Brasileira de Ciências...

In search of historical roots of the extraterrestrial impact theory, II: two unknown German pioneers from the 1850s, Ludwig Pfeil and Karl Reichenbach

The mid-nineteenth century is not regarded as the time when the theory of extraterrestrial catastrophism developed. However, two German scholars independently introduced original concepts of terrestrial impacts of large celestial bodies at that time. Ludwig Pfeil (1803–1896), a self-educated wealthy landowner, and Karl Reichenbach (1788–1869), an eminent scientist and industrialist, independently proposed in the 1850s that the Earth is an aggregate of meteoritic masses and has experienced many impact-induced cataclysms throughout its geological history. Until 1891, Pfeil analyzed the effects of the collision of a comet's gaseous body with Earth. He tried to simulate the effects of tsunami waves generated by impacts into the ocean and inferred the route of “cometary currents” from the morphology and orientation of coastlines and associated mountain ranges. Reichenbach speculated about fertilization of the terrestrial surface by extraterrestrial dust in the context of an accretionary origin for Earth that also manifested in meteoritic sources of volcanic extrusions. He linked the Mesozoic succession of “buried living worlds” to geological catastrophes, caused by successive meteorite impacts. These cosmic bombardment concepts were comprehensively criticized by contemporary researchers, but soon found many conceptual successors in the German-speaking science community. Therefore, Pfeil and Reichenbach should be regarded as pioneers of the impact theory.

Volcanic spherules condensed from supercritical fluids in the Payenia volcanic province, Argentina

Spherules can be formed by high-temperature processes during volcanic eruptions, lightning strikes and meteorite impacts. Here we report four different types of spherules and spheroidal particles associated with tephra deposits from two separate volcanic fields in the southern Payenia province of Argentina. These silicate and carbonate spherules represent <0.01% of the sampled material, with individual spherules <200 µm in size. Thirty particles were imaged. Only the transparent spherules are smooth, perfect spheres; other morphologies include ellipsoids and aggregated dumbbells. The spheroids are either hollow or solid. Major element analyses show that the spherules and spheroids have silica-rich, Fe-rich, carbonate and basaltic compositions. Chemical analysis of the carbonate spheroids shows some variability in the trace element content between the cores and rims, suggesting element mobility and loss towards the margins. All the analysed carbonate spheroids have elevated Sr/Y, La/Y and La/Ce ratios outside the range for sedimentary carbonates. All four spherule types are considered to be volcanic in origin, with the excess CO2 required for the formation of the carbonate spherules potentially sourced from the basement lithologies. Based on the major and trace element analyses, we conclude that the silica-rich and carbonate spherules formed by instantaneous condensation from supercritical CO2-rich hydrous fluids saturated with dissolved silicates.Supplementary material: Appendix A, containing the full analytical dataset collected by electron probe microanalysis and secondary ion mass spectrometry, is available at https://doi.org/10.6084/m9.figshare.c.5108689

Zircon Microstructures Record Deformation History of Shock- and Tectonically-generated Pseudotachylites: a Case Study from the Vredefort Impact Structure, South Africa

High-strain rate deformation can cause in situ melting of rocks, resulting in the formation of dark, micro- to nanocrystalline pseudotachylite veins. On Earth, pseudotachylite veins form during meteorite impacts, large landslides, and earthquakes. Within the Vredefort impact structure, both impact-generated and (pre-impact) tectonically-generated pseudotachylite veins have been described, but are challenging to distinguish. Here, we demonstrate a genetic distinction between two pseudotachylite veins from Vredefort by studying their petrography, degree of recrystallization and deformation, cross-cutting relationships and the deformation microstructures in associated zircon. We conclude that Vein 1 is pre-impact and tectonically-generated, and Vein 2 is impact-generated. In agreement, zircon microstructures in Vein 1 contain planar deformation bands (PDBs), attributed to tectonic deformation, whereas zircon microstructures in Vein 2 reveal microtwin lamellae, indisputable evidence of shock metamorphism. Thus, deformation microstructures in zircon may provide a new criterion for distinguishing the genetic origin of pseudotachylite veins. Zircons that have been removed from their context (i.e., alluvial or detrital zircon, zircon from Lunar breccia) should be interpreted with caution in terms of their deformation history. For example, zircon with PDBs cannot reliably be used as a marker for shock deformation, because this feature has been shown to form in purely tectonic settings.