PALEOENVIRONMENTAL VARIATION BASED ON THE MINERALOGY AND ROCK-MAGNETIC PROPERTIES OF SEDIMENT FROM SITES 885 AND 886 1

Variation in the mineralogy and rock magnetic properties of Sites 885 and 886 sediment can be explained by changing environmental conditions in the sediment source areas and sediment column. Climatic variations produce changes in the mineralogy and magnetics at these sites consistent with aridification of the Asian source area and cooling forced by tectonic activity. Asian aridification is noted by gradual reduction of a kaolinite-rich mineral assemblage from the late Miocene to an abrupt mineralogy change at 3.8 Ma to a chloriteand illite-rich mineral assemblage. At the same time, the eolian mass accumulation rate and ferrimagnetic grain size increases. This event precedes the onset of Asian loess deposition by over 1 m.y., but it is consistent with a coupled environmental mechanism that explains the rapid onset of loess sedimentation at 2.5 Ma. Both the mineralogy and rock magnetics are overprinted with a diagenetic signal that suggests the sediments proximal to Sites 885 and 886 may have been suboxic to anoxic in the early Pliocene.

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