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Abstract: Deep-Sea Stratigraphic Sections: Narrow Windows on Geologic Time

BERGGREN, WILLIAM A., Woods Hole Oceanographic lnstitution; MARIE-PIERRE AUBRY, Universite de Montpellier

The accuracy of geological interpretations is intimately dependent upon the correctness of the temporal interpretation of stratigraphic sections. For parts of the stratigraphic record that are fiddled with unconformities, such as the upper Paleocene-lower Eocene interval, composite (virtual) reference sections provide the relative chronology of events and constitute the means of temporal correlations through stratigraphic analysis, of marine and terrestrial sections. Ultimately, the composite reference section assists in determining the best criterion(a)/event(s) to characterize epoch/series boundaries, and to select the most suitable Global Stratotype Section and Point (GSSP) to place the “golden spike”.

The benefit of the composite reference section is that it is predictive, and functions in two ways, as we show for the upper Paleocene-lower Eocene stratigraphic record. First, it predicts events that have not yet been recorded in the stratigraphic record. For example, an additional carbon isotope excursion is believed/expected to have occurred close to the NP9/NP10 biochronal boundary whereas the well known carbon isotopic negative excursion occurred in mid Biochron NP9 (Aubry, 1996; Sinha et al., 1996). Also, composite reference sections constitute the support for predicting and modelling temporal changes. For instance, late Paleocene-early Eocene changes in the isotopic composition of carbon in organic terrestrial matter have been derived through the record of changes of isotopic composition of dissolved inorganic carbon in the ocean (Stott et al., 1996; Sinha et al., 1996). Second, it helps in determining which temporal windows need to be documented and in which areas. As we demonstrate, we now have a satisfactory documentation of the latest Paleocene-earliest Eocene (Biochron NP10) history of changes in isotopic composition of dissolved inorganic carbon in the eastern North Atlantic and Pacific Oceans, but almost no documentation of such history in the Southern Ocean. Conversely, we have a good documentation of late Paleocene (late Biochron NP9) history of such changes in the Southern Ocean, but not in the Pacific and eastern North Atlantic Oceans. Planning for future deep sea drilling and for sampling of outcrop sections should take into account the temporal coverage of sections currently available.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah