Abstract
The Younger Dryas (YD) impact hypothesis posits that fragments of a large, disintegrating asteroid/comet struck North America, South America, Europe, and western Asia ~12,800 years ago. Multiple airbursts/impacts produced the YD boundary layer (YDB), depositing peak concentrations of platinum, high-temperature spherules, meltglass, and nanodiamonds, forming an isochronous datum at >50 sites across ~50 million km² of Earth’s surface. This proposed event triggered extensive biomass burning, brief impact winter, YD climate change, and contributed to extinctions of late Pleistocene megafauna. In the most extensive investigation south of the equator, we report on a ~12,800-year-old sequence at Pilauco, Chile (~40°S), that exhibits peak YD boundary concentrations of platinum, gold, high-temperature iron- and chromium-rich spherules, and native iron particles rarely found in nature. A major peak in charcoal abundance marks an intense biomass-burning episode, synchronous with dramatic changes in vegetation, including a high-disturbance regime, seasonality in precipitation, and warmer conditions. This is anti-phased with northern-hemispheric cooling at the YD onset, whose rapidity suggests atmospheric linkage. The sudden disappearance of megafaunal remains and dung fungi in the YDB layer at Pilauco correlates with megafaunal extinctions across the Americas. The Pilauco record appears consistent with YDB impact evidence found at sites on four continents.
Highlights
At the YDB layer (PB-8/PB-9 boundary), the percentage of non-arboreal vegetation increased sharply from ~45% to ~85% of pollen, representing the largest change exhibited in the pollen record from Pilauco
This paper describes in detail multiple types of spherulitic objects including authigenic, volcanic, detrital, framboidal, and YDB spherules, and Supplementary Table S8 summarizes a number of the unique and distinguishing characteristics of each type
Numerous other investigations[1,10,20,44,46] have shown that these various particles cannot be differentiated using reflected-light microscopy, but require the use of SEM-EDS as originally specified by Firestone et al[1]
Summary
Southern Chile supports cosmic-impact triggering of Received: 27 March 2018 Accepted: 19 December 2018 Published: xx xx xxxx biomass burning, climate change, and megafaunal extinctions at. Multiple airbursts/impacts produced the YD boundary layer (YDB), depositing peak concentrations of platinum, high-temperature spherules, meltglass, and nanodiamonds, forming an isochronous datum at >50 sites across ~50 million km[2] of Earth’s surface. This proposed event triggered extensive biomass burning, brief impact winter, YD climate change, and contributed to extinctions of late Pleistocene megafauna. Studies of the Younger Dryas boundary (YDB) layer report peak abundances of a diverse suite of proposed cosmic impact-related proxies at more than 50 sites, located mostly within the Northern Hemisphere, but with two previous sites in the Southern Hemisphere (Venezuela[5,6] and Antarctica[7]). PB-9: this unit ranges in age from ~12,770 ± 160 (550 cm) to 10,250 ± 150 (640 cm) with an average deposition rate of ~28 yr cm−1
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