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The Role of Biostratigraphy and Biochronology in Constraining Sequence Stratigraphic Interpretation

Abstract

Biostratigraphy has been a critical tool in the early development (1970s) of seismic stratigraphy. It has provided the age control on seismic and depositional sequences and the chronostratigraphic significance of sequence boundaries inferred from it. Today, biostratigraphy must remain central to the correlations of stratigraphic successions in exploration, although re-invented in the light of fine-tuned biochronology derived from high resolution biostratigraphic frameworks correlated to magnetochronology and orbital cyclicity recorded in outcrops and continuously cored deep-sea sections. Biostratigraphic schemes that integrate data from different microfossil groups thus have the potential to considerably improve the dating of stratigraphic sections, even when recovered in the form of cuttings, and constitute a uniquely independent test of the patterns described from seismic and sequence stratigraphy. We illustrate this with an integrated biostratigraphic study of six Neogene siliciclastic successions (wells) in the northeastern Gulf of Mexico (Main Pass-Green Canyon). Our study differs considerably from previous ones in documenting widespread occurrences of unconformities, most of which are associated with multi-million-year hiatuses, the thickness and temporal completeness of successions varying along depth, with the deeper successions thicker but temporally less complete than the shallower sections. This pattern, which is unrelated to sea level history, has been consistently documented in other basins (Florida Slope, Jamaica, New Jersey Margin, NW Europe) despite their different tectonic regimes. Unconformities and their related hiatuses are part of the sedimentary record and their consistent occurrences along depth profiles is revealing of depositional processes that have been neglected until now.