Anastomoses (Joppa Member, Ste. Genevieve Limestone, Middle Mississippian; Crystal Onyx Cave, near Cave City, Kentucky, USA) 4 : 無料・フリー素材/写真
Anastomoses (Joppa Member, Ste. Genevieve Limestone, Middle Mississippian; Crystal Onyx Cave, near Cave City, Kentucky, USA) 4 / 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 in Mississippian limestone in a Tertiary-Quarternary cave in Kentucky, USA.Crystal Onyx Cave is a relatively small, speleothem-rich cave on the eastern flank of Prewitts Knob, southwest of the town of Cave City, Kentucky, USA. The walls of the cave are limestones and dolostones of the Ste. Genevieve Limestone (upper Middle Mississippian).Crystal Onyx Cave was discovered in 1960 as a sinkhole. The name of the cave refers to the whitish-colored travertine (composed of calcite). Fifty-three Indian bones dating to about 680 B.C. were found wrapped up at the bottom of the main shaft of this cave.The above photo depicts anastomoses in the ceiling of a cave passage in Crystal Onyx Cave. Anastomoses are networks of channels formed by dissolution of calcium carbonate at partings and bedding planes in limestones. Dissolution occurs as slightly acidic groundwater seeps or moves 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 or complete dissolution. The result is a cave ceiling with a network of channels.The photos in this album were taken in boreal summer 2008. The cave closed in 2008 or 2009 when a cell phone company (Bluegrass) bought the entire hill of Prewitts Knob to prevent competition from other cell phone companies. The hill now has cell phone towers.Locality: Prewitts Knob, ~2 air miles southwest of Cave City, northwestern Barren County, southwest-central Kentucky, USA (37° 06' 36.27" North latitude, 85° 58' 26.12" West longitude) |
| 撮影日 | 2008-07-17 16:21:15 |
| 撮影者 | James St. John |
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