Date of this Version
Manganese-encrusted hardgrounds and associated sediments from four guyots in the western Pacific Ocean were investigated using lithostratigraphic and biostratigraphic examination of thin sections. Biostratigraphic data from manganese-encrusted hardgrounds constrain the age of platform drowning to early middle Eocene for Limalok Guyot, latest Maastrichtian to early Paleocene for Wodejebato Guyot, and middle late Albian for MIT Guyot. Microstratigraphic examination of the hardgrounds reveals a complex Cretaceous and Paleogene history of bioerosion, pelagic sediment accumulation, manganese encrustation, and phosphatization. Fourteen distinct episodes of pelagic sediment accumulation occurred, with five in the Cretaceous, three in the Paleocene, and seven in the Eocene. These episodes are thought to correspond with periods of decreased current velocities in the intermediate water masses that bathed the guyot summit plateaus. At least five episodes of manganese growth are documented: one in the Late Cretaceous to early Paleocene, and four in the Eocene. It is suggested that these correspond to periods of intensified intermediate-water current velocities. Five episodes of phosphatization are recognized. Two of these, Late Cretaceous to early Paleocene and latest Eocene to early Oligocene, probably correspond to events that have been recognized elsewhere in the Pacific. A third event (early middle Eocene) appears to correspond to the deposition of Horizon Ac elsewhere in the world's oceans. It is suggested that increased upwelling during this event stimulated phosphatization on the guyot summits. The other two Eocene events are quite minor and may be localized to the Marshall Islands.