Bayesian chronological analyses consistent with synchronous age of 12,835–12,735 Cal B.P. for Younger Dryas boundary on four continents

Abstract

The Younger Dryas impact hypothesis posits that a cosmic impact across much of the Northern Hemisphere deposited the Younger Dryas boundary (YDB) layer, containing peak abundances in a variable assemblage of proxies, including magnetic and glassy impact-related spherules, high-temperature minerals and melt glass, nanodiamonds, carbon spherules, aciniform carbon, platinum, and osmium. Bayesian chronological modeling was applied to 354 dates from 23 stratigraphic sections in 12 countries on four continents to establish a modeled YDB age range for this event of 12,835-12,735 Cal B.P. at 95% probability. This range overlaps that of a peak in extraterrestrial platinum in the Greenland Ice Sheet and of the earliest age of the Younger Dryas climate episode in six proxy records, suggesting a causal connection between the YDB impact event and the Younger Dryas. Two statistical tests indicate that both modeled and unmodeled ages in the 30 records are consistent with synchronous deposition of the YDB layer within the limits of dating uncertainty (∼100 y). The widespread distribution of the YDB layer suggests that it may serve as a datum layer.Younger Dryas | comet | Bayesian | radiocarbon | synchroneity A ccording to the Younger Dryas Impact Hypothesis (YDIH)(1), a major cosmic episode of multiple airbursts/impacts occurred at 12,800 ± 300 calendar years before 1950 (Cal B.P. represents calendar years before A.D. 1950, unless otherwise noted; 95% probability) or 12,950-12,650 Cal B.P. at 68% probability. This event produced the Younger Dryas boundary (YDB) layer, displaying peaks in a variable assemblage of spherules (glassy and/or magnetic-inferred to be impact ejecta and therefore, for simplicity, referred to below as impact-related spherules), high-temperature minerals and melt glass, nanodiamonds, charcoal, carbon spherules, glass-like carbon, aciniform carbon (soot), nickel, iridium, platinum, and osmium. The event may have triggered the Younger Dryas episode of abrupt climate change, contributed to the end-Pleistocene megafaunal extinctions, and initiated human population reorganization/ decline across the Northern Hemisphere (1-5). Because a temporally singular event is proposed, the YDIH requires dates on the YDB layer to be essentially isochronous across four continents within the limits of dating methods.In a test of synchroneity, it is ideal to have numerous, highly accurate, and precise dates to develop robust chronological models (6). The term "date" represents a measured value, and "age" refers to real or modeled calendar years. However, when developing high-precision chronologies, there are multiple challenges that are amplified in Pleistocene age deposits. Modern accelerator mass spectrometry (AMS) radiocarbon ( 14 C) measurements are typically very precise, with uncertainties of ±20 y to ±30 y at 11,000 14 C years B.P., but high precision does not mean high accuracy. Numerous problems can produce erroneous ages Significance A cosmic impact event at ∼12,800 Cal B.P. formed the Younger Dryas boundary (YDB) l...

Widespread platinum anomaly documented at the Younger Dryas onset in North American sedimentary sequences

“…( b ) Radiocarbon date from Clovis occupation surface “Clovis Floor” at Topper is from an adjacent excavation block. In a paper by Kennett et al 21,. a Bayesian analysis of dates from Topper and Barber Creek demonstrated synchronous deposition of the YDB layer within the limits of dating uncertainty (~100 y)21.…”

“…The chronostratigraphic position of the YDB for each site was determined based on ( a ) linear interpolation of 12 AMS dates; ( b ) interpolation of 7 conventional and AMS radiocarbon dates based on second-order polynomial regression; ( c ) logarithmic interpolation of 5 conventional and AMS radiocarbon dates and the stratigraphic position of temporally diagnostic hafted bifaces; and ( d ) 3 AMS dates selected from the YDB layer7. A Bayesian analysis of dates from all western and Midwestern study sites demonstrates synchronous deposition of the YDB layer within the limits of dating uncertainty (~100 y)21. See Supplementary Figures 4–7 and Supplementary Table 3 for more detail on stratigraphy and dating for sites.…”

Comprehensive analysis of nanodiamond evidence relating to the Younger Dryas Impact Hypothesis

“…However, nanodiamonds (and ‘n‐diamond’) have been reported in sediments and in carbonaceous forms within sediments that do not date to the YDB (Firestone et al , , 2010a; Yang et al , ; van Hoesel et al , , ; Bement et al , ; Kinzie et al , ). Most importantly, and despite widespread claims of synchroneity by YD impact proponents (see Kennett et al , ,b), age control is poor or non‐existent at nearly all sites where ‘nanodiamonds’ are reported ‘at’ the YDB layer (e.g. see Blaauw et al , ; Ives and Froese, ; Wittke et al , ; van Hoesel et al , , ; Holliday et al , ; Meltzer et al , ).…”

“…There are no recognized impact structures in North America that date to the onset of the YD stadial. Several geomorphic features have been suggested as possible YD craters: oriented shallow depressions in Alaskan, Canadian and Siberian permafrost (Allan and Delair, , ), the Carolina Bays (Melton and Schriever, ; Allan and Delair, , ; Firestone and Topping, ; Firestone et al , , ; Firestone, ; Kinzie et al , ; Kennett et al , ), small playa basins of the High Plains (Firestone et al , ) and deep depressions in four of the Great Lakes (Firestone et al, , ; Firestone, ); however, there is no evidence to support their impact origin (see Holliday et al , ). The 4‐km‐diameter, circular Corossol structure in the Gulf of St. Lawrence has also been suggested as a possible YD‐age crater based on the discovery of a single 4‐cm‐long breccia clast suggesting impact metamorphism (Higgins et al , ).…”

“…While there are no known impact structures in North America that date to the YD onset, YD impact proponents nonetheless argue that physical evidence of the impact/bolide event is present in sediments, at multiple sites in North America, South America, Europe and the Middle East that are claimed to be chronologically synchronous with the Bølling‐Ållerod/YD boundary (YDB) layer (see, Kennett et al , ,b). Elevated concentrations of a range of minerals interpreted as products of impact/bolide processes and geochemical indicators of the impactor/bolide are reported in these inferred YDB layers.…”