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The AAPG/Datapages Combined Publications Database

Journal of Sedimentary Research (SEPM)

Abstract


Journal of Sedimentary Petrology
Vol. 61 (1991)No. 7. (December), Pages 1164-1172

Albian Pelagic Rhythms (Piobbico Core)

Alfred G. Fischer (1), Timothy D. Herbert (2), Giovanni Napoleone (3), Isabella Premoli Silva (4), Maurizio Ripepe (3)

ABSTRACT

The Piobbico core of Aptian-Albian pelagic rhythmites in Italy has been used to explore ways of extracting quantitative time-series of geological, chemical, physical and biological parameters from stratigraphic sequences. Recognition of the precession, obliquity, and eccentricity cycles (the Option frequencies) has permitted time-resolution to the 104-year level. Individually, these time-series curves furnish a potential basis for precise correlations. Collectively, they track the evolution of the depositional system in detail, including its response to orbital forcing. Orbital cycles primarily influenced oceanic fertility and carbonate productivity by foraminifera and coccoliths, as well as the aeration of bottom waters (redox cycle). Three short magnetic reversals occur w thin the Ticinella praeticinensis zone. Frequency spectra of variations in magnetic intensity, inclination and declination yield Milankovitch frequencies which are only partly explained as responses to mineralogy. A computer simulation used Berger's astronomically calculate precession index to drive 1) carbonate flux and 2) depth of bioturbation. This achieved a stratigraphy remarkably similar to that observed. Each step in the computer simulation transfers spectral power from precession to eccentricity. Work on the Piobbico core continues, while Project ALBICORE aims to explore the patterns of rhythmicity in the praeticinensis zone of other areas.

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