Published:January 01, 2004
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.
Figures & Tables
Cyclostratigraphy: Approaches and Case Histories
This volume is derived from an SEPM international workshop entitled Multidisciplinary Approach to Cyclostratigraphy, organized by the editors in May 2001 and held in Sorrento (Naples, Italy). In the Introduction we offer a brief history of how concepts of orbital cyclicity and its effects on the Earth evolved, an appraisal of the present state of research, and an overview of the papers in this volume. The main body of the volume consists of the contributed studies. These include a paper on conceptual and pragmatic approaches to stratification cycles by one of the pioneers of cyclostratigraphy, Walther Schwarzacher, who, in the 1940s, discovered the hierarchical expression of orbital cycles in rocks. The other contributions are specific studies of cyclic sequences, extending from the Quaternary back to the Triassic, covering the range from continental deposits to the deep sea, and employing a wide variety of techniques for extracting and processing the information.