| Allison Guyot | |
|---|---|
  Allison | |
| Height | 1.5 kilometres (4,900 ft) |
| Summit area | 35 by 70 kilometres (22 mi × 43 mi) |
| Location | |
| Group | Mid-Pacific Mountains |
| Coordinates | 18°16′N 179°20′E / 18.26°N 179.33°E[1] |
| Geology | |
| Type | Guyot |
Allison Guyot (formerly known as Navoceano Guyot) is a tablemount (guyot) in the underwater Mid-Pacific Mountains of the Pacific Ocean. It is a trapezoidal flat mountain rising 1,500 metres (4,900 ft) above the seafloor to a depth of less than 1,500 metres (4,900 ft), with a summit platform 35 by 70 kilometres (22 by 43 mi) wide. The Mid-Pacific Mountains lie west of Hawaii and northeast of the Marshall Islands, but at the time of their formation were located in the Southern Hemisphere.
The tablemount was probably formed by a hotspot in the present-day Southern Pacific before plate tectonics moved it to its current location. Several hotspots, including the Easter, Marquesas and Society hotspots, may have been involved in the formation of the Mid-Pacific Mountains. Volcanic activity is dated to have occurred circa 111–85 million years ago and formed a volcanic island. Subsequently, carbonate deposition commenced as Allison Guyot subsided and eventually buried the island, forming an atoll-like structure and a carbonate platform. Among other animals, crocodilians lived on Allison Guyot.
The platform emerged above sea level during the Albian and Turonian ages. It drowned about 99 ± 2 million years ago for unknown reasons; possibly a phase of renewed emergence damaged the reefs, or it was located in unfavourable waters. Later, pelagic sedimentation commenced on the seamount and led to the deposition of sediments including limestone, ooze and sand, which bear traces of climatic events and ocean currents.