Print this pageMapping Turbidite System Pathways on the Louisiana Continental Slope with GLORIA and Multibeam Bathymetry
TWICHELL, DAVID C.
GLORIA sidescan sonar images in concert with multibeam bathymetry provide detailed understanding of turbidite system pathways on the Louisiana Continental Slope, the filling of salt withdrawal basins by coarse- grained sediment, and the subsequent deformation of these pathways by movement of the underlying salt. Two turbidite systems were mapped; system A was traced from the seaward edge of a Pleistocene-aged delta to the rise, while system B was traced across part of the upper slope before it disappeared. Each system crossed areas where salt was shallow and places where it was deeply buried. Where the pathways cross shallow salt, they are narrow (less than 2 km wide) and, in places, have the appearance of a braided stream. Where the salt was deeply buried under salt-withdrawal basins, the pathways broadened to fill the basins creating high-backscatter areas (coarse-grained deposits) that reached 18 km in diameter. The course of turbidite system A varied through time. A salt-withdrawal basin was filled, and sedimentation initially was redirected to the west, but then this site was abandoned when the pathway was redirected through the southeast corner of the original basin and extended to the continental rise because of changes in basin morphology. Since abandonment of system A during the last rise in sealevel, the mobility of the underlying salt continued to reshape its deposits. The pathway no longer has continuous downslope gradients, and in the salt-withdrawal basins the high-backscatter sand deposits fill up to the present basin rims, suggesting that there has been as much as 600 m subsidence of the basin floors since the pathways were active.