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Mapping Turbidite System Pathways on the Lousiana Continental Slope with GLORIA and Multibeam Bathymetry

David C. Twichell, Jr., USGS, Woods Hole, MA
Hans Nelson, USGS, Menlo Park, CA

Presented at American Association of Petroleum Geologists (AAPG) April, 1997

ABSTRACT

Study Location Map.

Shaded-relief image of the Continental Slope south of Texas and Louisiana based on NOS multibeam bathymetric data. Sun illumination is from the NE. The modern Mississippi delta is shown in dark green, a Pleistocene aged, shelf-edge delta in light green, Bryant Canyon, as mapped by Lee et al. (1996) in yellow, and the location of the detailed GLORIA and bathymetry images is shown in pink.

Previous Work

Summary of previous work relating to turbidite systems pathways on the Louisiana slope. Bright green outlines Pleistocene-aged shelf-edge deltas mapped by Suter and Berryhill (1985), black outlines the distribution of shallow salt bodies (after Diegel et al, 1995), yellow shows the path of Bryant Canyon system as mapped using seismic profiles by Lee et al (1996), and the contour lines are derived from the NOS multibeam bathymetry (Grim, 1992).

Shaded-relief image of the study area.

Shaded-relief image derived from the NOS multibeam bathymetry. Sun illumination is from the NE. Yellow lines marks the location of the thalweg of Bryant Canyon that is shown in the adjacent plot.



Thalweg gradients of turbidite system pathways. Green line on the adjacent shaded-relief image shows location of the thalweg of the Eastern system, yellow line shows location of the Bryant Canyon system, and orange line shows location of the westward extension of the Bryant Canyon system. Note the abrupt changes in gradient where the thalweg crosses the salt-withdrawal basins.

GLORIA image of the study area.

  GLORIA image shows high-backscatter returns as white and low-backscatter returns as dark tones. Yellow boxes show the location of three perspective views and the arrows show the look direction. The adjacent 3.5-kHz profiles across the three basins shown in the perspective views showing the differences in echo-character.
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Perspective Views click on the images for a closer view Vertical arrows in perspectives show profile locations.
	A. La Salle Basin Note the subdued morphology of the basin in the upper panel and the low-backscatter signature of the basin-floor sediments on the GLORIA image which has been draped over the bathymetry in the lower panel.
	B. Bienville Basin Upper panel shows steeper gradients of basin walls, and GLORIA image in lower panel shows high-backscatter slump deposits (shown by diagonal arrows) partially covering the basin floor.
	C. Beaumont Basin The bathymetry in the upper panel shows the steep-walled nature of the basin, and the GLORIA imagery in the lower panel shows a uniform high-backscatter return from the entire basin floor. Note that the high-backscatter extends up the basin walls to the rim of the basin.

Interpretation summarizing the extent of Bryant Canyon as revealed by GLORIA.

  GLORIA image with summary interpretation. Brown areas show slump deposits that were identified by integrating the GLORIA imagery with the multibeam bathymetry. The orange line marks the path of Bryant Canyon as mapped by Lee et al (1996) using seismic data. The yellow shows the extent of the Bryant Canyon system as revealed by the GLORIA imagery. Note that the GLORIA data show several additional basins being influenced by this system than could be mapped with the siesmic data. Red lines show locations of adjacent 3.5-kHz profiles.

3.5-kHz and 10-kHz profiles across the Bryant Canyon turbidite system at the locations shown by the red lines on the GLORIA image with interpretation. Note the prolonged return from the seafloor with no subbottom reflections on Profiles B and C and the hyperbolae on profile D where these profiles cross the pathway of the turbidite system.

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Schematic summary of evolution of a basin influenced by turbidite sedimentation.

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