The Roper Group (minimum age approximately 1300 x 10^6yr) is a shallow water sequence of sandstone, siltstone, and shale, with minor, sub-economic oolitic ironstone. The depositional environments of the Group as a whole, range from fluvial, through deltaic or estuarine, to marine, and a number of different environments of deposition for the ironstones can be recognised. Shales from the McMinn Formation at the top of the Group have yielded an assemblage of microfossils. The microbiota includes algal cells and filaments, large acritarchs and giant filaments of uncertain affinity. A probable life cycle and an example of endospory may indicate that some of the organisms are eukaryotic. The flora is very advanced for its geological age, but this is probably because most other Precambrian microbiotas come from carbonate, stromatolitic environments, where simpler and more conservative forms would have pre-dominated. The microfossils are in a particularly good state of preservation because of the low degree of thermal metamorphism which the sediments have undergone. Geochemical and petrographic studies of the organic matter indicate that its composition and level of organic maturation are appropriate for the generation of oil. The rank of the organic matter is locally increased by proximity to dolerite sills which intrude the Group as a whole.
