[H-CG21] Earth surface processes related to deposition, erosion and sediment transport

[HCG21-06] Grain Size Characteristics of Micro-Microtektites Associated with Australasian tektite event (~800,000 Years Ago)

James Shania¹, *Masayuki Ikeda¹, Yoshimi Kubota², Ochi Yoshihiro¹, Ryuji Tada³, Aki Sakuma¹, Takuya Itaki⁵, Steve Clemens⁴ (1.University of Tokyo, 2.National Museum of Nature and Science , 3.Chiba Institute of technology, 4.Brown University, 5.AIST)

Keywords:bolide impact, Australasian tektite event, Grain size distribution

Tektites are siliceousa glass ejecta material formed by the rapid heating and quenching of terrestrial rocks by the impact of an extraterrestrial object into Earth’s crust. The size of tektites can vary significantly, with the largest reaching tens of cm in diameter and the smallest being sub-millimeter, called microtektite (a diameter of less than 1 mm). While the study of tektites and microtektites has advanced significantly over the last few decades, most studies focus on microtektites with >125 μm diameter. However, smaller microtektites with <125 μm diameter may also have unknown factors surrounding their formation and transportation processes. Here we report the occurrence of <100 μm “micro”-microtektites in the northern South China Sea (ODP Site 1146) immediately below the Matsuyama-Brunhes boundary. This site is close to the inferred location of the impact for Australasian tektite event (AATE) which is the youngest (ca. 0.8 Ma) and the largest (>10% of the Earth’s surface) among the main tektite strewn field. Microtektites are mostly spherical with some teardrop and dumbbell forms of transparent and mostly pale olive green in color. In addition to ~125 μm peak of grain size, some peaks are significantas the main peaks of microtektite grain size. Major element composition of these microtektites agree well with that of the Australasian microtektites reported in previous literatures. These results imply a similar origin of these microtektites with different grain size. These multi-peaks of microtektite grain size may relate to their different transportation processes which may extend AATE strawn field.