Foraminiferal Litho-Biofacies of Linked Delta—Fan Deposystems in the Northern Gulf of Mexico: Paleontologic and Lithologic Characteristics
Richard H. Fillon, 2013. "Foraminiferal Litho-Biofacies of Linked Delta—Fan Deposystems in the Northern Gulf of Mexico: Paleontologic and Lithologic Characteristics", Shelf Margin Deltas and Linked Down Slope Petroleum Systems–Global Significance and Future Exploration Potential, Harry H. Roberts, Norman C. Rosen, Richard H. Fillon, John B. Anderson
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Foraminiferal assemblages in deep-water sediments contain: (1) indigenous benthic taxa that represent combined bottom-water and bottom-sediment controlled benthic environments (biotopes); (2) planktonic taxa that settle, after death, from near-surface habitats into benthic biotopes; and, (3) allochthonous benthic shelf taxa that are transported downslope into deep-water biotopes either as empty tests or as displaced living populations. Each of these categories of foraminiferal taxa contained in deep-water foraminiferal assemblages carries information on the sedimentary processes, lithology, and reservoir properties of deep-water biotopes, and on derivative foraminiferal biofacies called litho-biofacies.
Turbidites and particularly associated poorly-sorted submarine fan deposits known as debrites are distinguished from other deep-water sediment types by the relatively large volumes of displaced shelf sediments they contain. Turbiditic sand bodies deposited preferentially in subtle topographic depressions or in less subtle bathymetrically isolated subbasins, e.g., salt-bounded slope minibasins, are local in extent because they are limited to filling seabed relief as stacked fan lobes or prograding fan clinoforms. Between the pulses of high-energy bottom currents that deposit the sand, benthic environments in these topographic depressions frequently reflect low current energy, poor oxygenation of bottom water and sediments, and increased deposition of lighter detrital components such as clays and marine or terrestrial organic matter. These unique and contrasting environments support diverse diagnostic assemblages of indigenous benthic foraminifera that provide biostratigraphers with opportunities to make very detailed interpretations of depositional variables in complex deep-water settings.
This paper reviews the extensive literature covering the foraminiferal ecology of the most common deep-water lithofacies and describes representative litho-biofacies, including: barren sand; flysch-type turbidite; deltaic biomechanical debrite; basin margin calcareous bank; drowned-shelf distal prodeltaic hemipelagite; dysoxic basin hemipelagite; sapropelite; confined subbasin ponded hemipelagite; unconfined slope and rise hemipelagite; pelagite; and condensed and transitional deposits. Definitions based on this work can be used in the detailed assessment of deep-water depositional systems.