Reevaluating Links Between Meteorite Impacts and Early Cenozoic Global Warming

Abstract

These hyperthermal events shared common features including rapid warming onsets spanning 1-100 thousand years (kyr), total durations between 0.1 and 2 million years (Myr), near-doubling of atmospheric CO 2 , and negative carbon isotope excursions (CIE) (Foster et al., 2018). The underlying causes for these hyperthermals are debated. The approximately 56 Ma Paleocene-Eocene Thermal Maximum (PETM) was accompanied by a 5-8 K temperature increase (McInerney & Wing, 2011). Hypotheses for its onset include methane clathrate dissociation (Dickens et al., 1995), volcanic eruptions (Storey et al., 2007, magmatic intrusions into hydrocarbon reservoirs (Svensen et al., 2004), and a meteorite impact (Kent et al., 2003). An impact trigger for the PETM was long challenged by the dearth of conclusive evidence for an impact coincident at that time (Dickens & Francis, 2004). However, new evidence has reinvigorated the impact hypothesis, including the discoveries of approximately 55 Myr melt glass spherules, shocked quartz, Ni-rich spinel inclusions (Schaller et al., 2016(Schaller et al., , 2019, and magnetic nanoparticles that could have resulted from impact-related pyrogenesis at the base of the PETM (Kent et al., 2017). Schaller and Fung (2018) attributed the onset of the PETM (not the entire 5-8 K increase) to the formation of the 13-km diameter, 58 ± 3 Ma Marquez Dome impact crater, Texas, where target rocks may have contained hydrocarbons. Another recent study proposed that the smaller 65.3 Ma Lower Chron 29n hyperthermal could also have resulted from the formation of the 24-km diameter Boltysh impact crater, Ukraine, which had granitoid target rocks (Pickersgill et al., 2021).During hypervelocity impacts, the kinetic energy transferred to the target is sufficient to vaporize and melt material, part of which forms the impact vapor plume, expanding into the atmosphere. Depending on the initial target composition, released species such as carbon or sulfur may induce climate changes. Modeling of the 66 Ma Chicxulub impact showed that the main climatic change effect was a drastic cooling (decrease of at least 26 K), because of sunlight shielding from sulfur-bearing gases (Gulick et al., 2019) and soot (Lyons et al., 2020).