Thin (<10 m), extensive dolostones conformably capping late Precambrian glaciogenic rocks in the Kimberley region and the Adelaide Geosyncline commonly comprise micritic dolomite apparently of ‘primary’ or early diagenetic origin. Their aphanitic texture, the presence of algal and cryptalgal lamination, tepee structures and intraclastic rocks, and the lack of saline evaporites or their pseudomorphs, suggest deposition mainly in supratidal to lagoonal environments under a seasonally evaporitic/humid climate. Less common oolitic or pelletal rocks and a finely laminated shaly dolostone facies also suggest peritidal to marine influences.