A distinctive carbonate shallowing-upward sequence occurs within the upper Riphean (750-800 Ma) Hunnberg Formation of Nordaustlandet, Svalbard. Clastic limestones deposited in an open coastal marine environment pass upward into columnar stromatolitic bioherms, and these, in turn, are overlain by finely laminated lagoonal dolomites. Early diagenetic silicification has preserved microbiotas in each of the three major facies. The plankton assemblage found in open coastal cherts contains more than two dozen taxa. Fossil assemblages of the Hunnberg Formation are useful biostratigraphically; the open coastal plankton biota is clearly latest Riphean in aspect. They also contribute to our understanding of the paleoecological distribution of late Precambrian plankton. This distribution is of potential value in paleoenvironmental reconstruction and is equally important in helping to define the ecological context in which evolutionary interpretations of early microbes must be made. The Hunnberg microbiota contains 33 taxa, of which two are formally described as new; Cymatiosphaeroides kullingii n. gen. et n. sp. and Trachyhystrichosphaera vidalii n. sp.--Modified journal abstract.

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