HR: 0800h
AN: T11A-0361    [Abstracts]
TI: Characteristics of a Faunal Succession of Foraminifera in Tsunami-deposits and Recognition of Sauce Area of Particles- A Case Study of the Holocene Tsunami Deposits at Tateyama, Southern Part of the Boso Peninsula, Central Japan-
AU: * Uchida, J
EM: utty@es.sci.kumamoto-u.ac.jp
AF: Jun-ichi Uchida, Faculty of Science, Kumamoto University, 39-1,Kurokami 2-chome, Kumamoto, Japan, Kumamoto, 860-8555 Japan
AU: Abe, K
EM: abekohei@arsia.geo.tsukuba.ac.jp
AF: Kohei Abe, Graduate School of Life and Environmental Science, Tsukuba University, 1-1-1, Tennodai, Tsukuba, Japan, Tsukuba, 305-8572 Japan
AU: Hasegawa, S
EM: shiro@sci.kumamoto-u.ac.jp
AF: Jun-ichi Uchida, Faculty of Science, Kumamoto University, 39-1,Kurokami 2-chome, Kumamoto, Japan, Kumamoto, 860-8555 Japan
AU: Fujiwara, O
EM: o.fujiwara@aist.go.jp
AF: Osamu Fujiwara, Active Fault Research Center, National Institute of Advanced Industrial Science and Technology, Site 7, 1-1-1 Higashi, Tsukuba, Ibaraki, Japan, Tsukuba, 305-8567 Japan
AU: Kamataki, T
EM: t.kamataki@aist.go.jp
AF: Osamu Fujiwara, Active Fault Research Center, National Institute of Advanced Industrial Science and Technology, Site 7, 1-1-1 Higashi, Tsukuba, Ibaraki, Japan, Tsukuba, 305-8567 Japan
AU: Irizuki, T
EM: irizuki@riko.shimane-u.ac.jp
AF: Toshiaki Irizuki, Interdisciplinary Faculty of Science and Engineering, Shimane University, 1060, Nishikawatsu-cho, Matsue, Japan, Matsue, 690-8504 Japan
AU: Hirakawa, K
EM: hkazu@ees.hokudai.ac.jp
AF: Kazuomi Hirakawa, Graduate School of Environmental Science, N10W5, Kita-ku, Sapporo, Japan, Sapporo, 060-0810 Japan
AB: The faunal succession of foraminifera reflects the characters of tsunamis, such as magnitude and direction of each tsunami, and coastal topography. In addition, foraminiferal assemblages contain deep-sea species in some parts indicating the sauce of particles transported by the tsunami. To recognize the characteristics of faunal sequence in tsunami sediments, we analyzed foraminiferal fauna in the Holocene sand layer, and try to estimate the sauce area of sediment particles of the layer transported from off-shore sea-bottom. Several widely-traceable sand layers regarded as tsunami deposits are intercalated among the Holocene drowned valley deposits at Tateyama in the southern Boso Peninsula, central Japan (Fujiwara et al., 2003). The stratigraphic succession of each tsunami deposit is subdivided into four units, as follows; Unit Tna: dark colored medium to coarse sand at basal part, Unit Tnb: fine to coarse sand, Unit Tnc: very fine sand, and Unit Tnd: sandy silt layer with plant fragments in the uppermost part. For the foraminiferal analysis, we took up the 20 cm thick sand layer with the underlying mud layer (~ 8,000-8,100 cal years BP) as a squarer pillar from an outcrop, and cut it into 1cm-slices at the laboratory. The results of the analyses are shown as follows: (1) Percentage of planktonic foraminifera in total foraminifera (%Plankton) and Benthic Foraminiferal Number (N/g) are 40-66% and 120-410/g in the sand layer, respectively. These values are as high as those at about 90-130m deep in open ocean. (2) The benthic foraminiferal assemblage in the underlying mud is characterized by the inner bay species. (3) In Unit Tna to Tnb, it consists of various inner sublittoral species. (4) Relative frequency of bathyal species increases from Unit Tnb to Unit Tnc. (5) The tests of bathyal species in Unit Tnc are small in size and well-sorted, suggesting that they were transported for long distance. (6) In Unit Tnd, the proportion of inner sublittoral and inner bay species are dominant, alternately. These results show that this tsunami suspended surface sediments at about 90-130m deep and transported them to inner bay. To recognize relationship between faunal succession of foraminifera and characters of tsunamis, many of case studies as mentioned above are needed.
DE: 3022 Marine sediments: processes and transport
DE: 4564 Tsunamis and storm surges
DE: 4944 Micropaleontology (0459, 3030)
DE: 4950 Paleoecology
DE: 7221 Paleoseismology (8036)
SC: Tectonophysics [T]
MN: Fall Meeting 2005