TY - JOUR
T1 - Rapid sedimentation of iron oxyhydroxides in an active hydrothermal shallow semi-enclosed bay at Satsuma Iwo-Jima Island, Kagoshima, Japan
AU - Kiyokawa, Shoichi
AU - Ueshiba, Takuya
N1 - Funding Information:
We thank Tatsuo Oyama, Satoshi Hidaka, Hideyoshi Imabeppu, Kazuyoshi Tokuda, Hiroshi Sato, Hisataka Sato, and numerous individuals in Mishima village for their help. We are indebted to Kenichi Sugimoto, Toshihiro Ogawa, Yoshinori Matsumoto, and Yusuke Sugimoto of the Windy Network Corporation for generating the topographic map. We thank Dr. Minoru Ikehara of the Center for Advanced Marine Core Research, Kochi University, for use of the energy dispersive X-ray spectrometer and other equipment; Dr. Seichiro Uehara of Earth and Planetary Material Science, Kyushu University, for use of the X-ray diffractometer; and Dr. Koichiro Watanabe of the Research Institute of the Environment for Sustainability, Faculty of Engineering, Kyushu University, for use of the X-ray fluorescence spectrometer. We thank Dr. Shusaku Goto, Prof. Takashi Ito, and Dr. Kosei Yamaguchi for helpful discussions. We acknowledge Tomomi Ninomiya, Tomoaki Nagata, Takashi Kuratomi, and Takuto Harada for help with data collection. This research was supported by a Grant-in-Aid for Scientific Research (KAKENHI) from the Ministry of Education, Culture, Sports, Science, and Technology (MEXT) of Japan (Grant Nos 18654086 and 22340151 ), a 2006 Seed Funding Grant-in-Aid from the Japan Science and Technology Agency (JST) , and the Professor Tatsuro Matsumoto Scholarship Fund . This study was performed under the Cooperative Research Program of the Center for Advanced Marine Core Research (CMCR), Kochi University, Japan (programs 05A019, 05B002, and 06B019).
Publisher Copyright:
© 2015 Elsevier B.V.
PY - 2015/4/5
Y1 - 2015/4/5
N2 - Hydrothermal activity is common in the fishing port of Nagahama Bay, a small semi-enclosed bay located on the southwest coast of Satsuma Iwo-Jima Island (38. km south of Kyushu Island, Japan). The bay contains red-brown iron oxyhydroxides and thick deposits of sediment. In this work, the high concentration and sedimentation rates of oxyhydroxide in this bay were studied and the sedimentary history was reconstructed. Since dredging work in 1998, a thickness of ~. 1.0-1.5. m of iron oxyhydroxide-rich sediments has accumulated on the floor of the bay. To estimate the volume of iron oxyhydroxide sediments and the amount discharged from hydrothermal vents, sediment traps were operated for several years and 13 sedimentary core samples were collected to reconstruct the 10-year sedimentary history of Nagahama Bay. To confirm the timing of sedimentary events, the core data were compared with meteorological records obtained on the island, and the ages of characteristic key beds were thus identified. The sedimentation rate of iron oxyhydroxide mud was calculated, after correcting for sediment input from other sources.The sediments in the 13 cores from Nagahama Bay consist mainly of iron oxyhydroxide mud, three thick tephra beds, and a topmost thick sandy mud bed. Heavy rainfall events in 2000, 2001, 2002, and 2004-2005 coincide with tephra beds, which were reworked from Iwo-Dake ash deposits to form tephra-rich sediment. Strong typhoon events with gigantic waves transported outer-ocean-floor sediments and supplied quartz, cristobalite, tridymite, and albite sands to Nagahama Bay. These materials were redeposited together with bay sediments as the sandy mud bed.Based on the results from the sediment traps and cores, it is estimated that the iron oxyhydroxide mud accumulated in the bay at the relatively rapid rate of 33.3cm/year (from traps) and 2.8-4.9cm/year (from cores). The pore water contents within the sediment trap and core sediments are 73%-82% and 47%-67%, respectively. The estimated production of iron oxyhydroxide for the whole fishing port from trap cores is 142.7-253.3t/year/5000m2. From sediment cores, however, the accumulation of iron oxyhydroxide sediments on the sea floor is 39-95t/year/5000m2. This finding indicates that the remaining 63%-73% of iron was transported out to sea from Nagahama Bay. Even with a high rate of iron oxyhydroxide production, the sedimentation rate of iron oxyhydroxides in the bay is considerably higher than that observed in modern deep-ocean sediments. This example of rapid and abundant oxyhydroxide sedimentation might provide a modern analog for the formation of iron deposits in the geological record, such as ironstones and banded iron formations.
AB - Hydrothermal activity is common in the fishing port of Nagahama Bay, a small semi-enclosed bay located on the southwest coast of Satsuma Iwo-Jima Island (38. km south of Kyushu Island, Japan). The bay contains red-brown iron oxyhydroxides and thick deposits of sediment. In this work, the high concentration and sedimentation rates of oxyhydroxide in this bay were studied and the sedimentary history was reconstructed. Since dredging work in 1998, a thickness of ~. 1.0-1.5. m of iron oxyhydroxide-rich sediments has accumulated on the floor of the bay. To estimate the volume of iron oxyhydroxide sediments and the amount discharged from hydrothermal vents, sediment traps were operated for several years and 13 sedimentary core samples were collected to reconstruct the 10-year sedimentary history of Nagahama Bay. To confirm the timing of sedimentary events, the core data were compared with meteorological records obtained on the island, and the ages of characteristic key beds were thus identified. The sedimentation rate of iron oxyhydroxide mud was calculated, after correcting for sediment input from other sources.The sediments in the 13 cores from Nagahama Bay consist mainly of iron oxyhydroxide mud, three thick tephra beds, and a topmost thick sandy mud bed. Heavy rainfall events in 2000, 2001, 2002, and 2004-2005 coincide with tephra beds, which were reworked from Iwo-Dake ash deposits to form tephra-rich sediment. Strong typhoon events with gigantic waves transported outer-ocean-floor sediments and supplied quartz, cristobalite, tridymite, and albite sands to Nagahama Bay. These materials were redeposited together with bay sediments as the sandy mud bed.Based on the results from the sediment traps and cores, it is estimated that the iron oxyhydroxide mud accumulated in the bay at the relatively rapid rate of 33.3cm/year (from traps) and 2.8-4.9cm/year (from cores). The pore water contents within the sediment trap and core sediments are 73%-82% and 47%-67%, respectively. The estimated production of iron oxyhydroxide for the whole fishing port from trap cores is 142.7-253.3t/year/5000m2. From sediment cores, however, the accumulation of iron oxyhydroxide sediments on the sea floor is 39-95t/year/5000m2. This finding indicates that the remaining 63%-73% of iron was transported out to sea from Nagahama Bay. Even with a high rate of iron oxyhydroxide production, the sedimentation rate of iron oxyhydroxides in the bay is considerably higher than that observed in modern deep-ocean sediments. This example of rapid and abundant oxyhydroxide sedimentation might provide a modern analog for the formation of iron deposits in the geological record, such as ironstones and banded iron formations.
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U2 - 10.1016/j.sedgeo.2015.01.010
DO - 10.1016/j.sedgeo.2015.01.010
M3 - Article
AN - SCOPUS:84923108172
VL - 319
SP - 98
EP - 113
JO - Sedimentary Geology
JF - Sedimentary Geology
SN - 0037-0738
ER -