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[BCG04-P03] Cycles and causes of laminated textures developed in silica hot spring sediments
Keywords:Silica deposit, Laminated texture, Cyanobacteria
Hot springs containing a lot of mineral components precipitate minerals after they gush out. Some of the hot spring deposits are similar in components and sedimentary textures to laminated sediments deposited in the ocean during the Precambrian period. Iron-rich hot spring deposits have been studied as banded iron formations and carbonate-rich hot spring deposits as modern analogues of stromatolites (e.g., Takashima et al., 2011, Okumura et al., 2011). In this study, we clarify the cycles and formation processes of laminated silica hot spring sediments.
Tamatebako hot spring is located in Ibusuki City, Kagoshima Prefecture. It has two sources, one flowing from a salt field located upstream, the other is a blowout from a pipe installed downstream.
First, it is known that the sediments of the salt field flow path show laminated texture in the mm order by the colored layer with a lot of metal and the white layer with filament microorganisms coated with minerals in the mm order. The colored layer is dense and white layer is pore. To estimate deposition rate, the tile was installed in the flow path from the salt field, and the thickness of silica sediments was about 1mm in 137 days. In addition, the colored layer deposited in the summer period and the white layer from autumn to winter. The cross section of the pink sediment in the downstream shows colored layers with metals and white layers with filament microorganisms repeated at intervals of about 1 mm. It is presumed to correspond to the upstream sediments of the white layer and the colored layer, respectively. Further 50-120 micron and about 10 micron laminated textures and crystal growth were confirmed in the dense layer. Toluidine Blue staining of sediments shows the existence of organic matter in parallel to the sedimentary surface. Photosynthetic bacteria were observed on the sediment surface by Fluorescence microscopy. Elemental mapping also shows that the colored layer contains iron and manganese. The surface of the green deposit is very uneven. The cross section is similar to that of pink sediments. The surface of sediment is covered with filamentous photosynthetic bacteria and concentrate metals.
From the deposition rate experiment, the annual deposition rate was calculated about 2.7mm. This value roughly agrees with the laminated textures of the colored layer and the white layer in mm order. The mm order laminated textures seem to represent seasonal changes. The colored layer containing a lot of metal deposited in summer and a white layer in seasons other than summer. According to the presence of photosynthetic bacteria and the fact that microorganisms in the white layer, mm order laminated textures seem to reflect the metabolism of photosynthesis. Photosynthetic bacteria exist in the sediment because of negative phototaxis in summer with strong sunlight and comes out to the sediment surface in periods with weak sunlight. In the white layer, the bacteria itself attaches minerals as a nucleus. On the other hand, in the colored layer, crystals are growing, and there are few filamentous microorganisms, but organic matter has been confirmed. From these facts, it is considered that EPS which is a metabolic product in microorganisms causes metal concentration and crystal growth. In addition, 10 micron order laminated textures observed in the colored layer, may have a daily cycle.
<References>
Takashima et al. (2011) Bacterial symbiosis forming laminated iron-rich deposits in Okuoku-hachiurou hot spring, Akita Prefecture, Japan. Island Arc, 20, 294-304.
Okumura et al. (2011) Microbial processes forming daily lamination in an aragonite travertine, Nagano-yu hot spring, Southwest Japan. Geomicrobiology Journal, 28, 135-148.
Tamatebako hot spring is located in Ibusuki City, Kagoshima Prefecture. It has two sources, one flowing from a salt field located upstream, the other is a blowout from a pipe installed downstream.
First, it is known that the sediments of the salt field flow path show laminated texture in the mm order by the colored layer with a lot of metal and the white layer with filament microorganisms coated with minerals in the mm order. The colored layer is dense and white layer is pore. To estimate deposition rate, the tile was installed in the flow path from the salt field, and the thickness of silica sediments was about 1mm in 137 days. In addition, the colored layer deposited in the summer period and the white layer from autumn to winter. The cross section of the pink sediment in the downstream shows colored layers with metals and white layers with filament microorganisms repeated at intervals of about 1 mm. It is presumed to correspond to the upstream sediments of the white layer and the colored layer, respectively. Further 50-120 micron and about 10 micron laminated textures and crystal growth were confirmed in the dense layer. Toluidine Blue staining of sediments shows the existence of organic matter in parallel to the sedimentary surface. Photosynthetic bacteria were observed on the sediment surface by Fluorescence microscopy. Elemental mapping also shows that the colored layer contains iron and manganese. The surface of the green deposit is very uneven. The cross section is similar to that of pink sediments. The surface of sediment is covered with filamentous photosynthetic bacteria and concentrate metals.
From the deposition rate experiment, the annual deposition rate was calculated about 2.7mm. This value roughly agrees with the laminated textures of the colored layer and the white layer in mm order. The mm order laminated textures seem to represent seasonal changes. The colored layer containing a lot of metal deposited in summer and a white layer in seasons other than summer. According to the presence of photosynthetic bacteria and the fact that microorganisms in the white layer, mm order laminated textures seem to reflect the metabolism of photosynthesis. Photosynthetic bacteria exist in the sediment because of negative phototaxis in summer with strong sunlight and comes out to the sediment surface in periods with weak sunlight. In the white layer, the bacteria itself attaches minerals as a nucleus. On the other hand, in the colored layer, crystals are growing, and there are few filamentous microorganisms, but organic matter has been confirmed. From these facts, it is considered that EPS which is a metabolic product in microorganisms causes metal concentration and crystal growth. In addition, 10 micron order laminated textures observed in the colored layer, may have a daily cycle.
<References>
Takashima et al. (2011) Bacterial symbiosis forming laminated iron-rich deposits in Okuoku-hachiurou hot spring, Akita Prefecture, Japan. Island Arc, 20, 294-304.
Okumura et al. (2011) Microbial processes forming daily lamination in an aragonite travertine, Nagano-yu hot spring, Southwest Japan. Geomicrobiology Journal, 28, 135-148.