Multiple flow and support mechanisms and the development of inverse grading in a subaquatic glacigenic debris flow

Subaquatic glacigenic debris flows of Late Wisconsinan age occur as lobes within an ice-marginal glaciomarine lithofacies at Victoria, British Columbia. Flow was initiated by release of supraglacial debris during an interval of glacial ablation prior to advance and deposition of lodgement till. Many of the lobes developed a common morphology during deposition, consisting of an outer layer surrounding an inner core of rafted material. In the largest lobe reworking of the sediment during flow produced improved sorting, a coarsening of mean grain size, and a shift in skewness toward the negative. This occurred simultaneously within the core and outer layer as a result of different transformations in mechanisms of flow and support. Normal grading, produced in the outer layer, was conveyed around the nose and buried in an inverse position along the base of the flow. These data enable us to present a model that may be applicable to similar flows elsewhere. The flow studied demonstrates that transformations between flow types and sediment support mechanisms can occur simultaneously and serially in subaquatic debris flows.