Convolute Lamination in Non-Graded Sequences

Convolute lamination and other sedimentary structures have been observed repeatedly in sequences characterized also by graded bedding. As a result, practically all have come to be regarded individually as proofs of turbidity-current deposition. But gravity-deformed stratification and load structures as well as flutes, grooves, current bedding, and ripple mark are already recorded in non-graded sequences representing quite varied environments. This paper records examples of convolute lamination also in diverse, non-graded deposits, leaving only repetitious graded bedding and anomalous resedimented organisms or detritus as chief evidences of ancient turbidity currents. Existing terminology and classification of the physical sedimentary structures in question mix genetic and descriptive factors, thus conceal more fundamental relations of the two chief formative processes involved-gravity-induced versus current-induced flow. Most structures involve both processes to varying degrees; however, classifications have imposed an unrealistic dichotomy between these processes. Morphologically similar contorted statification can be produced by two and probably three or more different processes. In many cases two of these have acted together simultaneously.