Anastomoses & dissolution-pitted dolostone (Joppa Member, Ste. Genevieve Limestone, Middle Mississippian; Diamond Caverns, Kentucky, USA) 1 : 無料・フリー素材/写真
Anastomoses & dissolution-pitted dolostone (Joppa Member, Ste. Genevieve Limestone, Middle Mississippian; Diamond Caverns, Kentucky, USA) 1 / James St. John
| ライセンス | クリエイティブ・コモンズ 表示 2.1 |
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| 説明 | Anastomoses are networks of channels formed by dissolution of carbonate bedrock at partings and bedding planes. Dissolution occurred as slightly acidic groundwater seeped or moved horizontally through the bedrock in the phreatic zone (at or below the water table). All groundwater is at least slightly acidic - the acid is usually carbonic acid (H2CO3) and some organic acids are also usually present. Carbonic acid forms by a simple chemical reaction: water + carbon dioxide = carbonic acid (H2O + CO2 --> H2CO3). This happens as raindrops fall through the atmosphere and also occurs as water percolates downward through soil and bedrock. The partial pressure of carbon dioxide gas is higher in soil gas, so even more carbonic acid forms in that environment. In landscapes with limestone bedrock, the slightly acidic groundwater dissolves the calcium carbonate (calcite) in the rock. This dissolutional action can result in caves and cave systems.Once anastomoses are formed, beds below the parting plane or bedding plane are removed by gravitational collapse into a large underlying passage, or by complete dissolution. The result is a cave ceiling with a network of channels.Shown above are anastomoses developed in light-colored dolostones, which are composed of dolomite (CaMg(CO3)2 - calcium magnesium carbonate). This cave ceiling is part of Diamond Caverns in Kentucky, which is developed in the Ste. Genevieve Limestone (upper Meramecian Series, upper Middle Mississippian). The light-colored dolostones are in the Joppa Member. The distinctive pitting is characteristic of Joppa Member dolostones in this & nearby caves. The pits form by differential dissolution by slightly acidic groundwater.Locality: Diamond Caverns, ~1.7 air-miles north-northwest of the town of Park City, northwestern Barren County, west-central Kentucky, USA |
| 撮影日 | 2010-08-01 17:06:30 |
| 撮影者 | James St. John |
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