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Abstract

Limnic deposits in Plio-Pleistocene graben basins in the Apennine Mountains provide detailed records of magnetostratigraphy leading into the Pleistocene. Their lacustrine clays retain both pollen that record the vegetation and, in magnetic signals, the history of magnetic reversals and a record of the orbital variations. The magnetically defined precessional units, with mean thicknesses of 3–8 m depending on accumulation rate, are modulated in amplitude by the eccentricity cycles, and are commonly associated with (and at times overshadowed by) obliquity cycles. The magnetic stratigraphy of the Upper Valdarno and Valtiberina basins serves to trace these cyclicities through the late Gauss and early Matuyama chrons, and the Olduvai. These cyclic rec rds set a chronologic framework for the history of both basins. Varied accumulation rates, beginning of oscillations between moister and drier plant assemblages, and a rise in the strengt of the obliquity signal coincide with the 400 ky eccentricity low at 2.84 Ma.

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