ABSTRACT: Biostratigraphic Reality in Sequence Stratigraphy and Chronostratigraphy

Laurent de Verteuil, Geoffrey Norris

Advocates of sequence stratigraphy embrace two major hypotheses. First, that changes in relative sea level (^DgrRSL) affect depositional systems in ways that are predictable in space and time; second, that the vast majority of Cenozoic and Mesozoic cases of ^DgrRSL resulted from synchronous eustatic events. The development and testing of both these hypotheses is contingent upon the availability of a methodology for temporal correlation that is completely independent of lithostratigraphy. In this paper the methodological problems associated with the temporal correlation of sequence boundaries are discussed, and it will be shown that biostratigraphic methods are inappropriate for addressing the problem of obtaining absolute ages for surfaces or erosion and nondeposition. Th example given compares offshore sequences of the Baltimore Canyon Trough with unconformity horizons in a 250 m continuously cored Miocene section from the outer Atlantic Coastal Plain of Maryland that has been zoned by dinoflagellate cyst biostratigraphy.

Consideration of the stated and implied biostratigraphic methodology of sequence stratigraphy has led to the following conclusions: (1) In relation to the concepts embodied in the International Stratigraphic Guide, the "chronostratigraphic stages" proposed by Haq et al. (1988) are unorthodox entities. (2) With the continued development in the deep ocean basins of a high-resolution framework for temporal correlation, using biostratigraphy, magnetostratigraphy, and geochronology, the stratotype concept is becoming increasingly impractical. (3) The absolute "dating" by sequence stratigraphers of condensed sections in the transgressive systems tract, using "age diagnostic microfossils," is based upon a best fit approximation only. (4) The limits to the temporal resolution, inherent to dif erent biostratigraphic methods used to date rock sequences, merit more careful consideration in the testing of sequence stratigraphic hypotheses.

AAPG Search and Discovery Article #90998 AAPG Eastern Section Meeting, London, Ontario, Canada, September 10-12, 1990