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Three distinct oxygen isotope events, which appear to record successive stages in the growth of the east Antarctic ice sheet, have been identified and dated paleomagnetically in middle and upper Miocene sediments from the Pacific Ocean. These stages are as follows: (1) late Magnetic Epoch 15 to early Magnetic Epoch 12 (c. 15 to 12 m.y.B.P.); (2) early Magnetic Epoch 11 (c. 11 m.y.B.P.); and (3) early Magnetic Epoch 6 (c. 6.7 m.y.B.P.). An additional slight cooling is recorded in Magnetic Epoch 10 at c. 10 m.y.B.P. These events can be tied to changes in paleo-oceanography, paleobiogeography, and opal accumulation in the Pacific Ocean, and, in turn, can be identified in the Monterey. The initiation of the east Antarctic ice sheet at c. 14 to 12 m.y.B.P., and its attendant c anges in surface circulation and paleoproductivity, is correlated to the beginning of the Monterey Shale. In addition to the beginning of massive opal accumulation along the California coast, increased silica accumulation in the equatorial Pacific is noted. This is accompanied by changes in diatom communities marking the beginning of present-day circulation patterns. The role of the Southern Ocean as an arbiter in the Miocene and Pliocene silica budget is noted and discussed.
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