Glacioeustatic Fluctuation: The Mechanism Linking Stable Isotope Events and Sequence Stratigraphy From the Early Oligocene to Middle Miocene

Vitor Abreu and Geoffrey Haddad

One of the most difficult challenges of sequence stratigraphy is the establishment of synchronism between events observed in widely-separated basins. Problems arise because the resolution of the best stratigraphic methods is not good enough to establish the synchronism of similar-aged events on a global scale. Unless a common mechanism affecting global eustasy is assumed, such as variations in the ice volume, there is no a priori reason to expect that sequences of similar age in widely-separated basins are indeed synchronous.

The stable oxygen isotope composition of marine carbonates is a proxy for sea level which has been underutilized in sequence stratigraphy. Identification of isotope events is based on d¹⁸O data from DSDP and ODP sites 522, 529, 563, 608, and 747 drilled in the Atlantic and Indian oceans. These records were used by Miller et al (1991) to define Oligocene and Miocene oxygen isotope zones. In addition, we present isotope data from PETROBAS Well A drilled in the Campos Basin (Brazil).

Ages of isotope events correspond well with the ages of sequence boundaries and maximum flooding surfaces identified by Haq et al (1988), Vakarcs et al (1995), and Hardenbol et al (1995). Because of the good correlation between the isotope and sequence stratigraphic records, we reconfirm that ice-volume change is the common mechanism driving sea- level fluctuations from the Oligocene to present.

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