ABSTRACT The continental slope off central Louisiana has' extremely complex surface topography as well as subsurface structures that are primarily inherited from salt tectonics, with other features generated by differential sedimentation, erosion, and mass movement. Dominant geologic features of the area include shallow diapirs, intraslope basins, sediment deformation features, and various types of faults. Oil seeps, gas seeps, and gas hydrates are also common to the area, and numerous faults in this province provide migration pathways for fluids and gases. Although the sediments are dominantly terrigenous clays, carbonates are significant. Carbonates occur as highly calcareous hemipe1agics, carbonate-cemented clays, shell hashes, hardgrounds, mounds, and bioherms. Seismic reflection profiling has led to the conclusion that most surface topography is related to salt diapirs. However, both field and laboratory data suggest that numerous smaller scale topographic features are calcareous and are commonly linked to the precipitation of carbonate (dominantly aragonite). These zones of lithification appear to range from small localized nodules and cemented burrows to mounds with relief of up to tens of feet. Geochemical analyses of host sediments indicate the presence of crude oil and associated light hydrocarbons generated outside the realm of surface sediments. Microbial oxidation of methane provides an abundant source of CO2 in interstitial waters and triggers chemical precipitation of carbonates characterized by extreme depletion of the C-13 isotope (? C-l3 values from -30 to -48 per mil). In addition, the seeps and associated calcareous hardgrounds provide a setting for carbonate-secreting organisms that require a hard substrate and perhaps a hydrocarbon-related nutrient source, thus encouraging the buildup of carbonates into significant topographic features. Carbonates in slope sediments cause practical problems for platform placement and pipeline routing. The problems range from the occurrence of sensitive soils, through sediments with strengths that vary greatly over short distances, to massive hard- and rough- bottomed regions. INTRODUCTION Louisiana's continental slope (Fig. 1) is a bathymetrically and sedimentologically complicated area that provides a variety of engineering challenges s both hydrocarbon exploration and production move into deeper water. The slope is underlain by a massive salt unit (Louanne Salt, Jurassic), which largely controls its major topographic and structural variations. The salt has been deformed into a variety of diapiric spines, domes, and ridges, some of which reach the surface or are close enough to influence sea-floor topography and near- sea- floor stratigraphy. Resu1ting seafloor complexity of the slope is expressed in highly irregular depth contours (Fig. 1). Processes of salt tectonics have produced numerous interslope basins and topographic highs. Bouma (1) notes that major depressions on the slope or intras10pe basins are diverse but can be divided into three basic categories: blocked canyon basins, interdomal basins, and collapse basins. As Bouma and Coleman (2) point out, bathymetric and structural maps of the slope lack the necessary detail to acc1, lrately portray the gradients and complexities of relief that actually exist. Early workers (3, 4) thought this irregular topography could be attributed to faulting, slumping, and other mass-movement processes. With the advent of marine seismic reflection profiling, diapirs of both salt and shale became obviously linked to sea-floor topography of the slope (e.g., 5, 6, 7).