Allison Guyot

Allison Guyot
Allison is located in Pacific Ocean
Allison
Allison
Height1.5 kilometres
Summit area35 x 70 kilometres
Location
GroupMid-Pacific Mountains
Coordinates18°16′N 179°20′E / 18°16′N 179°20′E / 18.26; 179.33[1]
Geology
TypeGuyot

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 above the seafloor to a depth of less than 1,500 m, with a summit platform 35 by 70 kilometres 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.

Name and research history

Allison Guyot is named after E.C. Allison, an oceanographer and paleontologist at the San Diego State College;[2] formerly it was named "Navoceano Guyot".[3] The name "Hamilton Guyot" has also been applied to Allison Guyot but is not correct;[4] Hamilton Guyot is a separate formation in the Mid-Pacific Mountains.[5] The seamount is the source of the Ocean Drilling Program[a] drill core 865A,[8] which was bored into the summit platform of Allison Guyot[9] in 1992[10] but did not reach the volcanic structure of the underwater mountain.[11] Two other cores 865C and 865B were obtained during the same operation; Allison Guyot is Site 865 Ocean Drilling Program.[8] These drill cores were part of a larger project to investigate and clarify the history of the flat-topped submarine mountains in the Pacific Ocean.[12]

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