Abstract or ref. 2129:
Two distinct types of archaeocyathan buildups occur within the Lower Cambrian Todd River Dolomite: a high energy, intemittently emergent, bioherm and grainstone reef-shoal (30-50m thick), and low energy open-shelf bioherms and patch reefs up to 8m thick and 20m across. The primary fabric of these buildups has been largely destroyed by dolomitisation. Facies relationships indicate that high and low energy buildups are temporal equivalents, and that the high energy reef-shoal now present in the N'Dhala Thrust Sheet was flanked to the east and south by a low energy shelf studded with bioherms and patch reefs. The reef-shoal was capped locally by microbial mudflats. The best potential for hydrocarbon accumulations appears to be local open-shelf buildups draped by thick halite deposits in autochthonous and para-autochthonous areas. 