The use of slump structures as palaeoslope orientation estimators

The two main methods of estimating palaeoslope direction from slump structure orientation data are reviewed. The mean axis method takes the downslope direction as the perpendicular to the mean slump fold axis. The separation are method estimates the downslope direction by the bisector of a planar separation angle between groups of slump folds with opposite downplunge asymmetry. The advantages and disadvantages of each method are considered in detail, by reference first to idealized slump fold distributions and then to a compilation of sixty natural slump fold axis distributions, mostly from published data. Among the advantages of the mean axis method are the ease of deriving confidence limits for estimates and its applicability where fold asymmetry data are unavailable. The main advantage of the separation are method is its validity for strongly skewed fold axis samples. The statistical robustness of the mean axis method, however, due to its reliance on average properties of data, makes it more generally reliable than the separation arc method which depends on extreme properties of data. A procedure for determining palaeoslope directions is suggested which reflects the respective strengths of the two methods.