Impact fingerprints of the 4 kyr BP dust event based on archaeological, soil, lake and marine archives

• Main Authors: Courty, M. A., Cortese, Giuseppe, Crisci, A., Crosta, X., De Wever, P., Fedoroff, M., Guichard, F., Mermoux, M., Smith, D., Thiemens, M. H.
• Format: Conference Object
• Language: unknown
• Published: 2007
• Subjects: Antarctic; Kerguelen; Heard Island; The Corridor; Antarc*
• Online Access: https://epic.awi.de/id/eprint/16964/; https://epic.awi.de/id/eprint/16964/1/Cou2007a.pdf; https://hdl.handle.net/10013/epic.26811; https://hdl.handle.net/10013/epic.26811.d001

The 4 kyr BP impact event has been identified from deep-sea, soil and archaeological records as the worldwide pulverisation of a volatile-rich debris jet(1). High resolution sequences show two stages of ejecta fallout linked to the impact-triggered doublet gaseous regime(2): scattered solid debris at the ground surface and spray of the vaporized hot fireball with thermal blast and local ignition. Ejecta debris consist of flow-textured impact glass, impact breccia and incompletely melted marine clasts: volcano-clastic sandy mudstone, calcareous mud, granite-gneiss, schists, volcanic breccia, kerogen and algal mud. Marine microfossils, organo-mineral markers, and the debris-fallout spatial pattern indicate two potential impact craters: an Antarctic source with an admixture of volcanic glass and ice rafted debris, from the vicinity of Heard Island and the Kerguelen plateau; a low latitude, shallow water one with hydrocarbons possibly from the Gulf of Mexico. Fine mixing of target materials from far distant source craters emphasizes a unique impact-ejecta. This matches the theoretical view of a debris jet channelled along the corridor cut through the atmosphere by the incoming projectile, raised upward, and dispersed widely(3). The isotopic anomaly of the sulphur phase in the kerogen volatile-component, indicating mass independent fractionation due to photolytic transformation, suggests launching at great heights, beyond the O2-O3 UV shield, responsible for climate disturbances. The incomplete melting of target rocks and global dispersion of impact breccia out of the craters would result from splash of small-sized projectile at rather great water depth and a low angle impact (10-15 degrees) into porous, highly compressible marine sediments. The spatially variable distribution of the organo-mineral and melt components, and the wide range of phase transformation reflect non-equilibrium shock-melting and micro-scale thermal processes in the heterogeneous vapor plume ejected from the impact sites. The 4 kyr BP event provides the first opportunity to compare on a variety of scales the environmental effects of globally dispersed ejecta from a multiple-site oceanic impact and the complex responses of human societies to frightening manifestations.