PRONIVAL (PROTALUS) RAMPARTS - A REVIEW OF FORMS, PROCESSES, DIAGNOSTIC-CRITERIA AND PALEOENVIRONMENTAL IMPLICATIONS

Most of the literature on pronival (protalus) ramparts deals with supp osed fossil examples with very few studies devoted to active features and/or observed processes. Not surprisingly, this has led to circular reasoning and assumptions about typical rampart form, constituent mate rial and genesis that have been shown to be inadequate or spurious fro m the few detailed investigations of actively forming ramparts so far carried out. Nevertheless, reliance continues to be placed on the char acteristics of fossil features in the search for previously unidentifi ed fossil examples. This article provides a critical review of rampart terminology, morphology and sedimentology, mechanisms, 'diagnostic' c riteria, position in a continuum of talus-derived landforms and palaeo climatic significance. It is suggested that the descriptor pronival is preferable to the widely used protalus, as the latter is misleadingly restrictive in terms of the known range of possible locations. Greate r variability in terms of form and mechanisms of formation than most w orkers assume is indicated by recent studies of active features, with multiple as well as single ridges, fines and edge-worn as well as coar se angular clasts being found, and a variety of supranival and also su bnival processes regarded as possibly contributing to rampart formatio n. It is concluded that only when further investigations of actively f orming ramparts have been carried out, will it be possible to compile a reliable List of criteria for distinguishing ramparts from moraines, protalus rock glaciers and other bedrock cliff-foot depositional form s. Correct identification of fossil ramparts may then lead to a better understanding of 1) their place in a continuum of talus-derived landf orms; and 2) their potential as palaeoclimatic indicators.