Basin‐Floor Topography and the Scaling of Turbidites

Turbidite bed thickness distributions from deep‐water settings result from the interaction of an initial magnitude/frequency of source‐derived flow volumes, modified within the receiving basin by (1) variable flow rheologies, (2) environmental controls such as channels and lobes, and (3) basin‐floor topography. This study attempts to isolate the effects of basin‐floor topography on turbidite bed thickness distributions using outcrop examples where the ancient sea‐floor topography has been reconstructed and is thought to dominate the signal. The Eocene and Oligocene Taveyannaz and Annot Sandstones of eastern Switzerland and France were deposited in confined intraslope basin and base‐of‐slope settings. The deposits of the confined basin record flow ponding and flow stripping; the base‐of‐slope deposits record the amalgamation of turbidites. Bed thickness data for both the confined basin and proximal base‐of‐slope settings are best approximated by an exponential distribution; the data from the more distal base‐of‐slope setting are better described by a power law. Statistical experiments presented here demonstrate that these distributions can be generated by the modification of an input signal with a power‐law distribution. In the case of the confined basin, flow ponding causes dramatic thickening of beds. However, flow stripping counteracts this, particularly for the thicker beds, and may account for a very large proportion of the input volume of sediment bypassing the basin even before the basin is filled. For the base‐of‐slope setting, erosion and nondeposition of beds will result in the preferential preservation of thicker beds; the thick‐bed population is also enhanced in the data by the unidentifiable amalgamation of beds. Differentiation between distributions that characterize these settings requires careful analysis of the thinnest and thickest portions of the populations and is aided by plotting the data as the log of cumulative number against bed thickness.