Main Types of Aptian–Cenomanian Sedimentary Rocks on Guyots of the Magellan Mountains, Pacific Ocean

Resumo

The typical rocks composing the base of the sedimentary cover of the guyots on the Magellan Seamounts are described. The upper part of the volcanic basement of the guyots is overlain by Aptian deposits of shallow reef ecosystems represented by terrigenous (beach) and organic-chemical (coral, shell-and-detritus, and oolitic) carbonate rocks. These deposits encircle the western part of the Fedorov and Ilyichev guyots, and the satellite buildings of the Alba and Pallada guyots in the form of an almost complete ring, extending from the edge of the plateau summit to 2500–3000 m depth. Down the slope they are replaced by planktonic (nanoforaminiferal) sediments and edaphogenic breccias. The appearance of pelagic limestone is associated with a sea-level rise during the Late Albian–Cenomanian eustatic transgression. Exposures of reef and planktonic limestones of up to 300 km² in area are also recorded on some guyots.