17:15 〜 18:30
[BCG04-P13] タイ東北部イジェクタ層中に埋没した現地性テクタイト破片からの層状テクタイト塊復元と飛来方位の推定
キーワード：オーストラリアーアジアテクタイトイベント、層状テクタイト
Layered tektites are a unique type of tektites found mostly in southern part of Indochina Peninsula. Although they are considered to have been formed in the proximity of the impact site, its formation mechanism and mode of emplacement are not well-understood. Especially, fragments of layered tektites that occasionally occur in the lateritized breccia (so-called laterite layer and we consider this breccia as an ejecta curtain deposit) have been considered as of reworked origin until our recent study that demonstrated their in-situ occurrence (Tada T. et al., 2020). Here, we present further details on the occurrence of tektite fragments within the lateritized breccia based on a CT-scan analysis.
We took an orientated block sample of 25x15x10 cm in size from the upper part of the lateritized breccia in North Eastern Thailand in which 46 pieces of large (> 1 cm) fragments of a layered tektite with the total mass of 300 g were contained. We further excavated the surrounding area. In total, a ca. 40x30 cm area with ca. 10 cm thickness was excavated in search of additional tektite fragments, and we found 7 pieces of additional large tektite fragments. With 53 pieces, which amount to 370 g and comprise 52 % of the total tektite fragments (>5mm) recovered, we reconstructed a mass of tektite that is a folded sheet of layered tektite forming a flattened cone shape of ca. 20 cm long and ~8 cm wide and ~5 cm thick. One side of the surface of the reconstructed layered tektite mass shows a rough surface with pitted texture and healed cracks suggesting that the original surface is well-preserved, whereas the other side of the surface shows lineation parallel to the internal layers suggesting that the original surface was peeled off possibly due to abrasion and internal layered structure is exposed.
We conducted CT-scan analysis of the block sample in order to examine spatial relationship among the large fragments within the block sample before we disaggregated it. The result provides useful information on the way of emplacement of the layered tektite mass such as flight direction of the layered tektite mass. Implication of the result will be discussed.
Reference
Tada et al. Progress in Earth and Planetary Science (2020) 7:66 https://doi.org/10.1186/s40645-020-00378-4
We took an orientated block sample of 25x15x10 cm in size from the upper part of the lateritized breccia in North Eastern Thailand in which 46 pieces of large (> 1 cm) fragments of a layered tektite with the total mass of 300 g were contained. We further excavated the surrounding area. In total, a ca. 40x30 cm area with ca. 10 cm thickness was excavated in search of additional tektite fragments, and we found 7 pieces of additional large tektite fragments. With 53 pieces, which amount to 370 g and comprise 52 % of the total tektite fragments (>5mm) recovered, we reconstructed a mass of tektite that is a folded sheet of layered tektite forming a flattened cone shape of ca. 20 cm long and ~8 cm wide and ~5 cm thick. One side of the surface of the reconstructed layered tektite mass shows a rough surface with pitted texture and healed cracks suggesting that the original surface is well-preserved, whereas the other side of the surface shows lineation parallel to the internal layers suggesting that the original surface was peeled off possibly due to abrasion and internal layered structure is exposed.
We conducted CT-scan analysis of the block sample in order to examine spatial relationship among the large fragments within the block sample before we disaggregated it. The result provides useful information on the way of emplacement of the layered tektite mass such as flight direction of the layered tektite mass. Implication of the result will be discussed.
Reference
Tada et al. Progress in Earth and Planetary Science (2020) 7:66 https://doi.org/10.1186/s40645-020-00378-4