Biostratigraphic significance of stromatolites in upward shallowing sequences of the early Proterozoic duck creek dolomite, Western Australia

The branching columnar stromatolite Pilbaria perplexa Walter 1972 and the microdigitate Asperia ashburtonia Grey 1985 occur together in upward shallowing sedimentary sequences in the 2 Ga Duck Creek Dolomite. The distribution of stromatolite taxa is controlled principally by sedimentary environment. P. perplexa grew in shallow lagoons with the larger P. cf. perplexa extending into the low intertidal zone. A. ashburtonia occupied a high intertidal or supratidal setting, probably in laterally restricted pools. Throughout the world pilbariform and asperiform stromatolites occur in stratigraphic units of different ages. Within each group, the taxa are not identical, although morphologies are broadly similar. The taxonomic variations may be due to evolutionary development, rather than environmental factors.