Impact ejecta at the Paleocene-Eocene boundary

Abstract

Extraterrestrial impacts have left a substantial imprint on the climate and evolutionary history of Earth. A rapid carbon cycle perturbation and global warming event about 56 million years ago at the Paleocene-Eocene (P-E) boundary (the Paleocene-Eocene Thermal Maximum) was accompanied by rapid expansions of mammals and terrestrial plants and extinctions of deep-sea benthic organisms. Here, we report the discovery of silicate glass spherules in a discrete stratigraphic layer from three marine P-E boundary sections on the Atlantic margin. Distinct characteristics identify the spherules as microtektites and microkrystites, indicating that an extraterrestrial impact occurred during the carbon isotope excursion at the P-E boundary.

A first report of microtektites from the shell beds of southwestern Florida

“…) found in the Florida material (Schaller et al. ). Additionally, in both instances the associated impacts occurred much earlier than the Pliocene age for the shell beds, in either the Eocene or Paleocene (McCall ; Schaller et al.…”

“…Additionally, recent analysis from drill cores has revealed a small tektite field also exists along the east coast of North America (stretching offshore from Florida to Canada), that records a previously unknown impact event from the Paleocene–Eocene boundary (Schaller et al. ).…”

“…Additionally, in both instances the associated impacts occurred much earlier than the Pliocene age for the shell beds, in either the Eocene or Paleocene (McCall ; Schaller et al. ). North of the Quality Aggregates Quarry collection site, on the west side of Peninsular Florida (around the Suwannee River) and in the Panhandle, there are extensive surface exposures of the upper Eocene Ocala Limestone and, in Citrus and Levy counties, surface exposures of the middle Eocene Avon Park Formation (Scott , ), which could contain a large amount of NASF material (Si‐spherules have been found in a layer of these units [Means, personal communication]).…”

Initial 40Ar‐39Ar Ages of the Paleocene‐Eocene Boundary Impact Spherules

“…Because the precision on the microtektite ages reported in this paper is well outside the bounds necessary to revisit the age of the CIE onset, we do not address the age of the P-E boundary in this contribution. This is in part because the K content of the P- (Schaller et al, 2016) compared with the carbon isotope excursion (pink). The bulk carbonate δ 13 C from WL and MV is from Wright and Schaller (2013), and Site 1051B is from Katz et al (1999).…”

“…E spherules is very low (generally <0.5 wt.%; see Table 1; Schaller & Fung, 2018) and their sizes are relatively small (average 302-μm diameter at the Atlantic Coastal Plain sites and 274 μm at Site 1051B; Schaller et al, 2016), making dating individual grains by 40 Ar-39 Ar an analytical challenge. Rather, the 40 Ar-39 Ar analyses provide the means to establish whether the cooling age of the spherules is consistent with their depositional age, thereby testing the hypothesis presented above.…”