Lighthouse Cave - travertine dripstone (stalactite cross-section) (San Salvador Island, Bahamas) 2 : 無料・フリー素材/写真
Lighthouse Cave - travertine dripstone (stalactite cross-section) (San Salvador Island, Bahamas) 2 / 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 | Travertine dripstone (broken stalactite showing cross-section) in Lighthouse Cave, near Dixon Hill Lighthouse, northeastern San Salvador Island, eastern Bahamas.Lighthouse Cave is hosted in eolian, cross-bedded, aragonitic calcarenite limestones of the Owl’s Hole Formation (Middle Pleistocene). This cave is a classic example of a flank margin cave. They form at the flanks of carbonate islands and at the margins of fresh-groundwater lenses. As such, flank margin caves are phreatic features. In the vinicity of the seawater-freshwater mixing zone (halocline) of a groundwater lens (see diagram - www.carbonatecreek.com/caves/images/carbisland.gif), relatively rapid dissolution of limestone occurs due to the high aggressivity of the water. Limestone dissolution at Lighthouse Cave occurred during the MIS 5e highstand (early Late Pleistocene ~119-131 ka).Flank margin caves have no surface entrances. Access to flank margin caves occurs only after surficial erosion intercepts chambers or passages. Lighthouse Cave was drained of water during the long-duration lowstand accompanying the Wisconsinan Glaciation (middle & late Late Pleistocene). Today, the lowest levels of Lighthouse Cave are partially flooded. Tidal fluctuations indicate connectivity with the ocean.Dripstone speleothem (stalactites, stalagmites, columns) composed of travertine is common at Lighthouse Cave. Published information indicates that speleothem formation has occurred since about 71 ka. Bell holes, bell pits, and sawtooth draperies are also present. |
| 撮影日 | 2011-03-23 10:40:36 |
| 撮影者 | James St. John |
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