Stratigraphy and Sediment Accumulation Patterns of the Upper Cenozoic Pelagic Carbonate Caps of Guyots in the Northwestern Pacific Ocean

摘要

Many of the guyots of the Northwestern Pacific Ocean are capped by sequences of uncemented pelagic carbonate. Examination of three of these pelagic caps from Limalok, Lo-En, and Wodejebato guyots in the Marshall Islands indicates that sediment accumulation throughout the late Paleogene and late Cenozoic was characterized by episodes of deposition during the earliest Miocene, late early to early middle Miocene, late middle Miocene, mid-Pliocene, and Quaternary, separated by periods of little or no accumulation. The Miocene record consists of extensively winnowed foraminifer oozes, which suggest relatively energetic currents in the intermediate waters. The Pliocene and Quaternary sequences contain finer grained nannofossil oozes, suggesting lower intermediate-water current velocities. Comparison with guyots from more northern locations indicates a highly predictable relationship between modern latitude and pelagic cap thickness, with thickness decreasing toward the north. Stratigraphic and seismic reflection evidence suggests that erosion is the major factor contributing to the diminution and eventual destruction of the pelagic caps as they are rafted northward by the motion of the Pacific Plate.