ORGANIC COMPOSITION OF YOUNGER DRYAS BLACK MAT

The presence of a dark stratal layer, known as Younger Dryas black mat, has been reported globally at many different sites. Samples of this black mat have been carbon dated to approximately 12,800 years BP, which coincides with the Younger Dryas Stadial, a period of extensive cooling. One hypothesis for the presence of the black mat layer is that a bolide event triggered widespread fires across at least four continents, and the ensuing soot caused a blanketing effect, resulting in a cooling period. In support of this hypothesis, previous studies have reported the presence of nanodiamonds, microspherules, and other cosmic material within the black mat, as evidence.

 In this study, thirty-four terrestrial samples were analyzed for their relative soot abundance and stable carbon isotopic ratios (δ¹³C_soot), levoglucosan (a marker for biomass combustion), and lignin oxidation products (proxy for terrigenous organic matter). The δ¹³C_soot in most of the black mat samples were remarkably similar, ranging from approximately -19‰ to -24‰. Levoglucosan from within the black mat layer at a site in Sheriden, OH was 3921.1 ng/gdw, while the layer below the black mat at the same site contained only 30.9 ng/gdw of levoglucosan. The δ¹³C_soot in the black mat at Sheriden was -19.71 ± 1.18‰. In contrast, δ¹³C_soot at the same site was -6.78 ± 0.03‰ and -2.66 ± 0.33‰, above and below the black mat, respectively. These results suggest that the black mat at all of the sites studied was combustion-derived, and uniform in source of combustion. The composition of the black mat at Sheriden and many of the other sites also suggests that the fuel was transported from remote areas supporting the hypothesis of intense, widespread, coeval wildfires.