Foraminifera and their habitats within a cool-water carbonate succession following glaciation, early Permian (Sakmarian), Western Australia

One of the best-developed carbonate successions of the Lower Permian in eastern Gondwana is the Callytharra Formation, deposited above glacially influenced sediments in a narrow elongate rift basin far from the open ocean. This formation and the underlying Carrandibby Formation provide evidence for faunal changes that accompanied the melting of the Sakmarian Gondwanan ice sheets. Diverse smaller benthic foraminifera including organic-cemented agglutinated, hyaline, and porcelaneous calcitic forms, accompany a heterozoan macrofauna (mainly bryozoans, crinoids and brachiopods). Fusulinid foraminifera and calcareous algae are absent. Seven foraminiferal assemblage zones subdivide the succession and parallel changes in associated macrofauna and lithofacies. Environmental changes determined from the succession include (1) a transition from nearshore, low-energy, low-salinity, cool waters to higher-energy, normal-marine waters supporting bryozoan, crinoidal and non-skeletal-macroalgal meadows; and (2) a transition from well-oxygenated, shallow-water, sandy substrates to deeper-water, less-oxygenated, muddy substrates. Faunal comparisons suggest that at paleolatitudes higher than 45degreesS, in widely separated interior basins in eastern Gondwana, a change from low-diversity, siliceous-agglutinated to high-diversity, Calcitornella-rich, foraminiferal assemblages took place during the Sakmarian. This change may have been associated with a reduction in melt-water influx into the interior basins from retreating Gondwanan ice sheets. The warming was insufficient to allow colonization of the shallow seas by fusulinids and calcareous algae, which only ranged as far south as 45degreesS paleolatitude.