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The AAPG/Datapages Combined Publications Database

GCAGS Transactions

Abstract


Gulf Coast Association of Geological Societies Transactions
Vol. 53 (2003), Pages 227-242

Multiple Overlapping Foraminiferal Litho-Biofacies: Applications to Deep-Water Sedimentology and Reservoir Properties of Turbidites

Richard H. Fillon

ABSTRACT

Foraminiferal assemblages in deep-water sediments contain: (1) indigenous benthic taxa that represent combined bottom-water/bottom-sediment subenvironments; (2) planktonic taxa that settle from near-surface habitats into benthic environments after death; and, (3) allochthonous benthic shelf taxa that are transported downslope into deep-water biotopes as empty tests or as displaced living populations. Developing a better understanding of the succession and dominance of subenvironments within a complex deposystem is the ultimate goal of litho-biofacies analysis. While a robust turbidite litho-biofacies model can easily be constructed for deep-water turbidite sections, in practice, because of the nature of well cuttings its application in detailed reservoir analysis is more complicated. Sample by sample comparison of taxonomic data with a litho-biofacies model requires an understanding of how the mixing of cuttings in the returning stream of drilling mud can cause litho-biofacies that were mutually exclusive in situ to appear to overlap in the biostratigraphic record. Because even the most detailed paleontologic analyses of cuttings record taxa representing several distinct turbidite subenvironments in each sample, in assessing deep-water subenvironments it is necessary to use a qualitative or quantitative strategy to help unscramble the litho-biofacies signal. A graphical partial signal deconvolution approach has been used successfully to distinguish multiple overlapping litho-biofacies in a variety of deep-water environments. It is more important to un-mix turbiditic litho-biofacies than bathy-metric biofacies. Turbidite systems are typically deposited within a single paleobathymetric zone, but contain many depositional subenvironments, which are key to understanding their reservoir potential.

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