HR: 0800h
AN: T51A-0439    [Abstracts]
TI: Filtering Stratigraphic Patterns Associated With Internally Generated- Versus Externally Driven-Processes: An Example from the Late Pliocene Fisk Basin, Gulf of Mexico
AU: Lyons, W J
AF: EAPS, MIT, 77 Mass Ave, 54-814, Cambridge, MA 02139
AU: * Mohrig, D
EM: mohrig@mit.edu
AF: EAPS, MIT, 77 Mass Ave, 54-814, Cambridge, MA 02139
AB: The stratigraphy of a basin fill can be viewed as a time sequence of surfaces providing a long view of earth-surface dynamics. These surfaces and the strata between them record external forcings such as tectonism, climate and sea level that interacted with and were overprinted by internally generated fluctuations in the depositional systems themselves. Accurate reconstructions of these external forcings therefore require decoding the stratigraphic record into its externally and internally generated signals. Here we present such a deconvolution for the Late Pliocene stratigraphy of the Fisk Basin, located on the upper continental slope about 350 km southwest of New Orleans, LA. We separate signals by systematically comparing spatial patterns of sedimentation against the pattern of basin subsidence. At short time intervals these patterns are different and capture the internally generated (autogenic) variability in the transport/deposition system. At long time intervals these fluctuations average out and the two patterns become one in the same, defining the averaging window required to approximate steady state topography. Though our analysis is for a submarine basin, the technique can be applied to any basin fill having the necessary data set. Fisk Basin is 20 km wide and 30 km long and entirely imaged by a high-quality 3D seismic grid. Multiple well penetrations provide excellent lithologic and biostratigraphic age control for the approximately 1.5 km thick Late Pliocene section. Nine surfaces mapped basin wide subdivide this section into 8 intervals recording the interplay between basin subsidence and sedimentation over 1.2 Ma. Similarity between patterns of sedimentation and subsidence, measured as the standard deviation of their ratio, decays exponentially with increasing time interval. The e-folding length for this decay is 0.47 Ma. This value indicates that autogenic fluctuations average out at a time scale that is long relative to characteristic times for known variability in external forcings. This overlap in scale complicates the separation of apparent trends in stratigraphic properties such as bed thickness and stacking patterns into their stochastic (autogenic) and deterministic (externally derived) components.
DE: 8105 Continental margins and sedimentary basins
DE: 3022 Marine sediments--processes and transport
DE: 3025 Marine seismics (0935)
DE: 1824 Geomorphology (1625)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting