Abstract
Arranging the soundings of past Japanese Navy Hydrographic Office for the purpose of GEBCO (General Bathymetric Chart of the Ocean), the authors found many guyots in the environs of the Marshall and East Caroline Islands. The flat tops of these guyots are situated at 1, 500-2, 000 m deep in which two different flat plains or terraces are known so that detailed sounding in future may ascertain the presence of two different levels of flat tops.
The diameters of the bases of atolls are generally larger than those of guyots in both Islands. The submarine volcanoes (coral reef and guyot) in the East Caroline Islands are larger in base diameter and smaller in height than those of the Marshall Islands.
Assuming that the top of guyot is the submerged wave-cut plain, the authors considered following geologic history; submarine volcanoes in the regions of the Mid Pacific Rise (Seamounts, ) North Central Ridge, South Central Ridge, Marshall Ridge, Gilbert Ridge and East Caroline Ridge had been truncated in late Cretaceous Period and submerged with the subsidence of vast West Pacific Basin or “Darwin Rise”. After then, volcanisms superposed in the Marshall Ridge Region pre Eocene Age and in the East Caroline Ridge Region during Miocene to Pliocene Age.
