Cyclostratigraphy and Stable Isotopes in the Oligocene- Miocene Succession of the Campos Basin, Brazil

N. C. Azambuja Filho and R. L. M. Azevedo

The Oligocene-Miocene succession of Campos Basin consists of ritmical interbedding of marlstones and mudstones, with few chalk and turbidite layers, deposited in a bathyal environment.

The hemipelagic sedimentation have recorded the orbital beat of precession, obliquity and eccentricity, based on spectral analyses of calcium carbonate content data, taken from core samples.

A study of oxygen stable isotopes, has allowed the recognition of significant fluctuations in ^dgr¹⁸O values for the Oligocene/ Lowe Miocene succession. These sediments have recorded important oceanographic events such as the Oi1, Oi2, and Oi2a recognized by Miller et al (1991) in DSDP boreholes, and the influence of the Antarctic glaciations. The results of this study confinii that global geochemical changes, in the marine environment, provide means for reliable chronostratigraphic correlations between oceanic and marginal basins, which is tought to contribute to a more accurate evaluation of biologic, sedimentologic and tectonic events.

The existence of intervals with in-and out-of-phase ^dgr¹⁸O related to %CaCO₃, reflects the importance of regional events of carbonate

productivity versus siliciclastic dilution in the deep-water and its relationship with the global oscillations of the ^dgr¹⁸O record. The combination of cyclostratigraphy and chemiostratigraphy has shown that there still is a vast area to be explored in order to understand ancient sedimentary records.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California