TY - JOUR
T1 - Hydrothermal formation of iron-oxyhydroxide chimney mounds in a shallow semi-enclosed bay at Satsuma Iwo-Jima Island, Kagoshima, Japan
AU - Kiyokawa, Shoichi
AU - Kuratomi, Takashi
AU - Hoshino, Tatsuhiko
AU - Goto, Shusaku
AU - Ikehara, Minoru
N1 - Funding Information:
This study was supported by Grants-in-Aid (KAKEN) from the Japanese Ministry of Education, Culture, Sports, Science, and Technology (grant nos. JP18654086, JP22340151, JP22253008, JP25287132, JP26257211, and JP20H01996). We acknowledge the assistance of the 2016 short-term research dispatch–invite program of Kyushu University and the Kochi Core Center. This study was undertaken with the cooperation of the Center for Advanced Marine Core Research (CMCR) of Kochi University (05A019, 05B002,13A002, 13B002, 14A009, 14B007, 15A050, 15A045, 16A038, 16B034, 17A003, 17B003, 18A003, 18B003, 19A050, and 19B045).
Funding Information:
We also thank Hidekazu Tokuyama and Takuya Matsuzaki from the Center for Advanced Marine Core Research, Kochi University (KCC), for their help with core observations and analysis, and for allowing us to keep samples in their fridge storage facility. Takashi Ito (Ibaraki University) and Kosei Yamaguchi are especially thanked for discussions regarding deposition of the iron formations. We extend additional thanks to Tastuo Ohoyama, Satoshi Hidaka, Hideyoshi Imabeppu, Hisashi Ooiwane, and numerous individuals from Mishima village for their help. We are indebted to Kenichi Sugimoto of the Windy Network Corporation for generating the topographic map, and Seichiro Uehara of the Department of Earth and Planetary Material Science, Kyushu University, for the use of their X-ray diffractometer. Toyokazu Maeda of Maetec Co. helped us with the land and ocean camera systems (the Moguriview and Rikuview systems). Mes Rie Tajiri of Tajiri Thin Section Laboratory was a great help in making the thin sections. We acknowledge Tomomi Ninomiya, Tomoaki Nagata, Takuya Ueshiba, Fumihiko Ikegami, Yuto Minowa, Takuto Harada, Naoya Sakamoto, and Koki Hori for their help with this research and data collection. We would like to thank G. Jiang, M. Lechte, and unnamed reviewers for their detailed and devoted reviews. This study was supported by Grants-in-Aid (KAKEN) from the Japanese Ministry of Education, Culture, Sports, Science, and Technology (grant nos. JP18654086, JP22340151, JP22253008, JP25287132, JP26257211, and JP20H01996). We acknowledge the assistance of the 2016 short-term research dispatch-invite program of Kyushu University and the Kochi Core Center. This study was undertaken with the cooperation of the Center for Advanced Marine Core Research (CMCR) of Kochi University (05A019, 05B002,13A002, 13B002, 14A009, 14B007, 15A050, 15A045, 16A038, 16B034, 17A003, 17B003, 18A003, 18B003, 19A050, and 19B045).
Publisher Copyright:
© 2021. Geological Society of America.
PY - 2021
Y1 - 2021
N2 - Hydrothermal iron-oxyhydroxide chimney mounds (iron mounds) have been discovered in a fishing port in Nagahama Bay, located on the southwest coast of Satsuma Iwo-Jima Island, south of Kyushu Island, Japan. In the fishing port, uncovered ∼1.0-m-high iron mounds in shallow waters formed under relatively calm conditions. Typically, the fishing port has orange-colored turbid waters that mix with outer ocean waters during high tide. Colloidal iron-oxyhydroxides form due to the oxidation of ferrous iron in hydrothermal waters (pH = 5.5; temperature = 55 °C) as they mix with seawater. The mounds are made of two types of material: hard, dark brown-orange, high-density material; and soft, brownish orange-yellow, low-density material. Computed tomography scans of the harder iron mound material revealed a cabbage-like structure consisting of micropipe structures with diameters of 2–5 mm. These micropipes have relatively hard walls made of iron oxyhydroxides (FeOH) and are identified as discharge pipes. Nucleic acid staining genetic sequencing and scanning electron microscope observations suggest that the mounds formed mainly from bacterial stalks with high concentrations of FeOH colloidal matter. In the harder parts of the mounds, these “fat stalks,” which contain oxyhydroxide colloidal aggregates, are en-twined and concentrated. The softer material contains twisted stalk-like structures, which are coated with FeOH colloidal particles. Deoxyribonucleic acid (DNA) examination of the iron mounds revealed the presence of iron-oxidizing bacteria, especially at the mound surface. We estimate that the iron mounds accumulated at a rate of ∼1700 tons/1000 m2/yr. This is an order of magnitude higher than the rate of FeOH sedimentation via chemical precipitation of FeOH colloids within the fishing port. This suggests that biogenic activity, resulting in the production of entwined FeOH stalks, leads to the rapid accumulation of FeOH beds and that biogenic activity within the water mass rich in FeOH colloids is an efficient means of generating thick iron-rich sedimentary sequences. As such, we propose that some ancient iron formations may have also formed through the biogenic production of FeOH stalks rather than solely through chemical sedimentation in a water mass rich in FeOH colloids. It appears that these rapidly forming biogenic FeOH iron mounds, distributed over a wide area of ocean floor, are also relatively protected from erosion and diagenetic alteration (reduction). Previous studies have reported that ancient iron formations were commonly deposited in deeper environments via direct iron oxidation from the water column in a ferruginous ocean. However, there are several hydrothermal vent inflows preserved with FeOH that would have formed appropriate redox boundary conditions in an otherwise anoxic ocean. Under these conditions, iron mound mat-type sedimentary deposits might have formed and been well preserved and affected by early diagenesis where higher heat flow occurred in the Archean ocean. The FeOH mounds in Nagahama Bay provide an example of the iron formation sedimentary environment and important information for estimating the past depositional state of iron formations.
AB - Hydrothermal iron-oxyhydroxide chimney mounds (iron mounds) have been discovered in a fishing port in Nagahama Bay, located on the southwest coast of Satsuma Iwo-Jima Island, south of Kyushu Island, Japan. In the fishing port, uncovered ∼1.0-m-high iron mounds in shallow waters formed under relatively calm conditions. Typically, the fishing port has orange-colored turbid waters that mix with outer ocean waters during high tide. Colloidal iron-oxyhydroxides form due to the oxidation of ferrous iron in hydrothermal waters (pH = 5.5; temperature = 55 °C) as they mix with seawater. The mounds are made of two types of material: hard, dark brown-orange, high-density material; and soft, brownish orange-yellow, low-density material. Computed tomography scans of the harder iron mound material revealed a cabbage-like structure consisting of micropipe structures with diameters of 2–5 mm. These micropipes have relatively hard walls made of iron oxyhydroxides (FeOH) and are identified as discharge pipes. Nucleic acid staining genetic sequencing and scanning electron microscope observations suggest that the mounds formed mainly from bacterial stalks with high concentrations of FeOH colloidal matter. In the harder parts of the mounds, these “fat stalks,” which contain oxyhydroxide colloidal aggregates, are en-twined and concentrated. The softer material contains twisted stalk-like structures, which are coated with FeOH colloidal particles. Deoxyribonucleic acid (DNA) examination of the iron mounds revealed the presence of iron-oxidizing bacteria, especially at the mound surface. We estimate that the iron mounds accumulated at a rate of ∼1700 tons/1000 m2/yr. This is an order of magnitude higher than the rate of FeOH sedimentation via chemical precipitation of FeOH colloids within the fishing port. This suggests that biogenic activity, resulting in the production of entwined FeOH stalks, leads to the rapid accumulation of FeOH beds and that biogenic activity within the water mass rich in FeOH colloids is an efficient means of generating thick iron-rich sedimentary sequences. As such, we propose that some ancient iron formations may have also formed through the biogenic production of FeOH stalks rather than solely through chemical sedimentation in a water mass rich in FeOH colloids. It appears that these rapidly forming biogenic FeOH iron mounds, distributed over a wide area of ocean floor, are also relatively protected from erosion and diagenetic alteration (reduction). Previous studies have reported that ancient iron formations were commonly deposited in deeper environments via direct iron oxidation from the water column in a ferruginous ocean. However, there are several hydrothermal vent inflows preserved with FeOH that would have formed appropriate redox boundary conditions in an otherwise anoxic ocean. Under these conditions, iron mound mat-type sedimentary deposits might have formed and been well preserved and affected by early diagenesis where higher heat flow occurred in the Archean ocean. The FeOH mounds in Nagahama Bay provide an example of the iron formation sedimentary environment and important information for estimating the past depositional state of iron formations.
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U2 - 10.1130/B35782.1
DO - 10.1130/B35782.1
M3 - Article
AN - SCOPUS:85114217813
VL - 133
SP - 1890
EP - 1908
JO - Bulletin of the Geological Society of America
JF - Bulletin of the Geological Society of America
SN - 0016-7606
IS - 9-10
ER -