FORMATION OF FLUIDIZATION PIPES DURING LIQUEFACTION - EXAMPLES FROM THE URATANNA FORMATION (LOWER CAMBRIAN), SOUTH-AUSTRALIA

Usually well preserved fluidization pillars and sand filled fluidizati on pipes occur within submarine channel sands of the basal Uratanna Fo rmation (Lower Cambrian) in the Adelaide Geosyncline of South Australi a. The morphology of these structures reflects complex lateral and ver tical movement of fluids during liquefaction and dewatering. Fluidizat ion pipes acted as conduits for highly concentrated, upward directed f luid flow. The formation and maintenance of these pipes was dependent upon the development of a pipe wall composed of clay plugged fine sand . Formed during initial fluidization, this lining acted as a permeabil ity barrier, confining and concentrating fluidized flow within the pip e. Each of the pipes is surrounded by a cylindrical fluidization halo in which leakage through the pipe lining produced partial fluidization of the surrounding sediment. Fine scale structures within these haloe s indicate that fluids flowed radially and upward out of the fluidizat ion pipes at an acute angle. These fluids merged with and influenced t he orientation and size of adjacent fluidization pillars. The fluidiza tion pipes of the Uratanna Formation may represent unusual preservatio n of the unstable fluid flow conditions that occur during incipient fl uidization of sand beds.