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Vitor S. Abreu1, Jan Hardenbol2, Geoffrey Haddad3, Gerald Baum4, Peter Vail4
(1) Unocal Corporation, Sugar Land, TX
(2) Global Sequence Chronostartigraphy Inc, Houston, TX
(3) Elf-Aquitaine, Pau, France
(4) Rice University, Houston, TX

Abstract: Oxygen isotope synthesis: A Cretaceous ice-house?

A Cretaceous (Aptian) to Cenozoic composite oxygen isotope curve is presented and correlated to eustatic records, global tectonic events and to the Antarctica glacial history. The curve was built using deep water benthonic foraminifera from DSDP/ODP sites. In addition, well-dated outcrop and subsurface whole rock samples were used. This composite record provides insight about the evolution of deep-water temperatures and/or ice volume changes from the Aptian to the present.

There is a positive correlation between the stable isotope record and Vail's eustatic curve based on the coastal onlap record at least for almost the entire Cenozoic, providing stronger basis for global sequence stratigraphic interpretations.

Two important observations can be made from the isotope record. First, three low-frequency isotope cycles are recognized, encompassing most of the Upper Cretaceous (named Uki), most of the Paleogene (named Pi) and most of the Neogene (named Ni) period. These low-frequency cycles correspond well with the sequence stratigraphic supercycle sets Upper Zuni A, Tejas B and Tejas A, respectively, although a pronounced lower Eocene negative shift in cycle Pi does not correspond to a significant sea-level rise in the sequence stratigraphic record. Second, oxygen isotope values for deep-water benthonic foraminifera during the Aptian to lower Albian stages and Campanian to Maastrichtian stages are similar to those observed during middle Eocene time. Due to the evidence for middle Eocene Antarctic glaciation, similarity between Cretaceous and Eocene isotope values could indicate the presence of polar ice as early as the Aptian stage.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana