Cretaceous and Paleogene Manganese-Encrusted Hardgrounds from Central Pacific Guyots

Abstract

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 intermediatewater 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 A c 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.

Composition and origin of ferromanganese crusts from equatorial western Pacific seamounts

“…The age of some crusts has been estimated at 70 Ma, and oth-* Corresponding author. E-mail: wangguozhi66@163.com ers are estimated to have formed in the mid-Cretaceous period (Watkins et al, 1995a;Klemm et al, 2005;Wu et al, 2011). Young crusts that were formed in recent times have also been found (Rehkämper et al, 2004).…”

Characterization and interpretation of discontinuity surfaces in a Jurassic ramp setting (High Atlas, Morocco)

“…Secondary mineralization of the lithified carbonate sea floor is often related to condensation and a break in sedimentation associated with the formation of long-lived sub-aquatic marine hardgrounds (Föllmi et al, 1991;Pomoni-Papaioannou, 1994;Clari et al, 1995;Watkins et al, 1995). Care must be taken, however, not to confuse synsedimentary mineralization with late diagenetic remobilization and deposition of iron and manganese oxides and other soluble phases onto flow barriers in the subsurface (Immenhauser et al, 2000).…”

238U/235U in calcite is more susceptible to carbonate diagenesis

“…Our geochemical data are derived from ODP Site 871 on Limalok Guyot in the Pacific Ocean, drilled during ODP Leg 144 (Premoli-Silva et al, 1993). At Hole 871C, ~ 300 m of a Paleogene carbonate platform (from 133.7 to 422.9 meters below seafloor (mbsf)) overlying a volcanic edifice was cored (Premoli Silva et al, 1993;Watkins et al, 1995;Wilson et al, 1998).…”