Sedimentological analysis of cored sections within the Merrimelia Formation (basal Gidgealpa Group, Cooper Basin, South Australia) reveals a complex glacigenic environment, including glaciolacustrine, deltaic, shorezone, fluvial, aeolian and other associated terrestrial facies (over 20 different facies have been identified). These facies are observed within terminoglacial and proglacial environments and interfinger laterally and vertically constantly throughout the Merrimelia Formation, exhibiting rapid environment change related to the position of ice sheet. Detailed sedimentological and petrographical (Cubitt 1998) analysis suggests that Tirrawarra sandstone-type sandstones facies belong within the Merrimelia depositional realm. Provenance data (Cubitt 1998) indicates that the lithic component of the Tirrawarra Sandstone (sensu stricto), is sourced from reworked Merrimelia coeval depositional facies. It is proposed that the fluvial sandstones of the Merrimelia Formation are part of the same fluvial deposystem as the Tirrawarra Sandstone (sensu stricto) as the two sandstone sequences are the natural progression of coarsening sediment as more detritus was released from melting glaciers during deglaciation. It is suggested that there no longer remain any sedimentological, stratigraphical or petrographical (Cubitt 1998) reasons why the Tirrawarra Sandstone (sensu stricto) and the Merrimelia Formation glaciofluvial sandstones should not be grouped together as Tirrawarra-type facies within the Merrimelia glacigenic domain. Facies architecture across the basin on both field and basin wide scales has identified two regional lacustrine episodes, both of which are followed by a period of lacustrine basin clastic infill. Such cycles represent ice advance and retreat, allowing two deglaciation phases and one ice advance phase to be identified.