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J.A. Bergen1, T.J. Bralower1, P.J. Sikora2, J.A. Stein3
(1) University of North Carolina, Chapel Hill, NC
(2) Energy & Geoscience Intitute, Salt Lake City, UT
(3) BP-Amoco, Houston, TX

Abstract: Towards refining the Cretaceous timescale and sequence stratigraphic calibrations

Considerable advances have been made during the previous decade in refining Cretaceous timescales and correlations to sequence chronostratigraphy. High-resolution megafossil biostratigraphies have figured prominently in the construction of Cretaceous timescales. Conversely, calcareous microfossils are the primary biostratigraphic tool in the Cenozoic.

Microfossils can impact future development of Cretaceous timescales and sequence calibration. Most microfossil data have not been incorporated and there remains considerable work ahead. Microfossils are primary in calibration of the geomagnetic polarity record because they are more abundant in pelagic sediments in which magnetostratigraphic studies are concentrated. Microfossils also have advantages in their occurrence and geographic dispersal. Calcareous microfossils have figured most prominently in the Cretaceous, but their resolution can be greatly enhanced. Palynology has been largely ignored outside of the oil industry, but is a necessary tool in the calibration of radiometric ages and passive margin profiles.

We will show examples throughout the Cretaceous of the utility of microfossils in the construction of Cretaceous timescales and calibration to sequence chronostratigraphy. We will present integrated plans and methodologies. The first steps are the calibration of radiometric ages and stage-substage boundaries. Once completed, the geomagnetic polarity record can be then calibrated and scaled between radiometric tie-points. Within the long mid-Cretaceous normal, other methods enter into correlation and scaling. Orbital records provide the ultimate calibration and a number of such records are available. We will also demonstrate the biostratigraphic resolution necessary to correlate these cycles. Finally, microfossil data need to be assembled from outcrop reference sections for European basins, but also from other passive margins.

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