The stratigraphic and spatial distributions of phosphatic and organic-matter rich Middle Cambrian sediments of the Georgina Basin are outlined in terms of sequence stratigraphic concepts. This approach has permitted an integrated analysis of Middle Cambrian depositional patterns and their time constraints. It has also provided insights into aspects of the basins structure, the timing of subsidence of its primary Components, and frequency of relative sea level fluctuations. Middle to early Late Cambrian sediments of the Georgina Basin are interpreted to occur in two stratigraphic sequences. In each sequence phosphorites, phosphatic limestones and organic-matter rich shales comprise a suite of repeating lithofacies restricted to retrogradational parasequence sets of the transgressive systems tract. The position of facies within each transgressive systems tract depends on relative sea level, palaeogeography and palaeotectonics. In sequence 1 (early Middle Cambrian), phosphogenesis is related to gradual transgression of a continent with irregular palaeotopography. Sequence 1a is interpreted to be of local significance, related to early subsidence of the Mt Isa Block during the late Ordian to early Templetonian. A rapid fall in relative sea level terminated sediment accumulation in sequence 1 and led to the development of a subaerial exposure surface. Sediments of the transgressive systems tract in stratigraphic sequence 2 are of lateTempletonian to early Undillan age. Deposition in sequence2 ceased in the Mindyallan. Rocks of the transgressive systemstract occur in three retrogradational parasequence sets. Recognition of sequence boundaries has helped clarify lateralbiofacies, leading to improved reconstructions of thepalaeogeographic distribution of the phosphorites and organic-matter rich shales.
