Turbidite deposition in the Cambrian Kanmantoo Group, South Australia

The Kanmanloo Group of South Australia is a thick (similar to km) successio n of predominantly elastic marine sedimentary and metasedimentary rocks tha t were deposited very rapidly in a localised basin (Kanmantoo Trough) durin g the Early Cambrian. Despite structural complexity and varying grades of m etamorphism, a surprising amount of primary sedimentological information is still available. Although a variety of depositional facies are represented , the group is dominated by parallel, sharp-based, mineralogically immature sandstone interbedded with mudstone. The sandstone beds are most commonly fine to medium grained, massive and lacking in obvious grading except at th e top. Single beds often reach several metres in thickness and amalgamation of beds is not uncommon, We argue that these sandstone beds could be the p roducts of sustained high-density turbidity currents. Triggering mechanisms for such turbidity currents remain uncertain, but they may have been initi ated as hyperpycnal flows during catastrophic flood events at the mouths of highload-capacity rivers, or from the failure of unstable buildups of sedi ment on delta slopes. Palaeocurrent studies from sole marks suggest a south erly source, which was probably an active orogenic terrain in formerly cont iguous Antarctica. it is likely that a major delta complex lay at the south ern end of the basin.