Cape Johnson Guyot

17°08′N 177°15′W / 17.133°N 177.250°W / 17.133; -177.250[1]

Cape Johnson Guyot is a guyot in the Pacific Ocean, more precisely in the Mid-Pacific Mountains, and the type locality of guyots. It is of middle Cretaceous age and a number of fossils have been dredged from it.

Name[edit]

Cape Johnson Guyot is also known as Cape Johnson Seamount or Cape Johnson Tablemount.[2] The guyot was named by Harry Hammond Hess, after his ship the USS Cape Johnson; Hess had also named the kind of flat-topped seamount "guyot" and another seamount was named after Hess himself.[3] The seamount was first described in a 1946 publication.[4] Both Hess and Cape Johnson were discovered during the same cruise[5] and Cape Johnson Guyot is the type locality of guyots.[6]

Geography and geology[edit]

The seamount lies in the Mid-Pacific Mountains[7] on their southern side and is a submarine mountain with a flat top that rises[8] over 3,000 metres (10,000 ft)[9] to a depth of 1,692 metres (5,551 ft)[10][11]-1,778 metres (5,833 ft).[12] The flat top has an oval shape and a surface area of 6 by 12 nautical miles (11 km × 22 km; 6.9 mi × 13.8 mi);[13] it is characterized by a limestone dome on the summit, buried beneath sediments; in turn a volcanic hill is buried within the limestone dome.[14] The top of the seamount has a hummocky appearance which has been interpreted as a sediment cover[15] and its southeastern sector has a bank-like shape that resembles that of an atoll.[16] Cape Johnson Guyot is considered to be of Middle Cretaceous age[17] with an age of 120 million years reported[18] and shallow-water fossils were emplaced on it at that time.[19]

Apatite,[20] basaltic sandstone containing hypersthene,[21] clay,[22] limestone, manganese crusts,[23] manganese oxide, phosphorite[24] and lithified carbonates have been found on Cape Johnson Guyot;[25] some carbonates of biogenic origin have been altered by apatite.[26] Globigerina ooze is also found on the seamount[27] and can reach substantial thickness; such accumulations might be formed by ocean currents.[28] Similar rocks have been found at other guyots of the Mid-Pacific Mountains.[29]

Biology[edit]

During the Cretaceous, corals and rudists lived on Cape Johnson Guyot[30] and fossils have been dated to 91-112 million years ago;[31] some corals[32] and rudists are of Albian to Cenomanian age.[33] Fossils of anthozoa,[34] gastropods, reef-building hexacorals,[35] pelecypods, stromatoporoids[36] and Tridacna were also found.[37] The Cretaceous fossils[38] Actinostroma pacifica,[39] Astrocoenia dietzi,[40] Brachyseris montemarina,[41] the caprinid rudists Caprina mediopacifica, Caprina mulleri[42] - including a detailedly described holotype of the latter[43] - and Cardita sp.,[44] Lophosmilia fundimaritima,[45] Montastrea menardii,[46] Nerinea sp.[47] and Tiarasmilia casteri occur on Cape Johnson Guyot.[48] Caprina mulleri was also found on other Mid-Pacific Mountains.[49] About 300 species of extant foraminifera have been found on the seamount as well,[50] with additional fossil foraminifera[51] including Paleocene-Eocene specimens that were redeposited by ocean currents.[52] Finally, a cetacean bone of undetermined age has also been found on Cape Johnson Guyot.[53]

References[edit]

  1. ^ Hamilton 1956, p.19
  2. ^ Marineregions 2019
  3. ^ BUDDINGTON, p.21
  4. ^ Hamilton 1956, p.18
  5. ^ Hamilton 1953, p.213
  6. ^ Marineregions 2019
  7. ^ Hamilton and Rex 1959, p.787
  8. ^ Hamilton 1953, p.213
  9. ^ Hamilton 1956, p.19
  10. ^ Hamilton 1953, p.213
  11. ^ Hamilton 1956, p.20
  12. ^ Hey and Grigg 1992, p.175
  13. ^ Hamilton 1956, p.20
  14. ^ Winterer, Sager and Firth 1995, p.436
  15. ^ Hamilton 1956, p.18
  16. ^ Hamilton 1956, p.20
  17. ^ Shields 1976, p.47
  18. ^ Morgan 1972, p.12
  19. ^ Winterer, Sager and Firth 1995, p.436
  20. ^ El Wardani 1958, p.240
  21. ^ Heezen and MacGregor 1973, p.667
  22. ^ Hamilton 1956, p.20
  23. ^ Hamilton 1953, p.213
  24. ^ Hill 2005, p.682
  25. ^ Fischer and Garrison 1967, p.489
  26. ^ Hamilton and Rex 1959, p.787
  27. ^ Hamilton 1953, p.213
  28. ^ Hamilton 1953, p.219
  29. ^ Heezen and MacGregor 1973, p.655
  30. ^ Hamilton 1959, p.1409
  31. ^ Hey and Grigg 1992, p.175
  32. ^ Löser 2010, p.158
  33. ^ Hamilton 1956, p.26
  34. ^ Hamilton 1956, p.22
  35. ^ Hamilton 1956, p.20
  36. ^ Hamilton 1956, p.22
  37. ^ UNIVERSITY OF CALIFORNIA SCRIPPS INSTITUTION OF OCEANOGRAPHY. p.5
  38. ^ Cairns 1991, p.31
  39. ^ Hamilton 1956, p.61
  40. ^ Cairns 1991, p.31
  41. ^ Cairns 1991, p.42
  42. ^ Sano et al. 2012, p.849
  43. ^ Masse, Sano and Skelton 2013, p.517
  44. ^ Cairns 1991, p.66
  45. ^ Cairns 1991, p.34
  46. ^ Hamilton 1956, p.59
  47. ^ Cairns 1991, p.64
  48. ^ Löser 2010, p.161
  49. ^ Masse, Sano and Skelton 2013, p.515
  50. ^ Hamilton 1953, p.207
  51. ^ Hamilton 1953, p.213
  52. ^ Hamilton 1953, p.219
  53. ^ Hamilton 1956, p.29

Sources[edit]

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