Stratigraphic distribution of selected acritarchs in the Ordovician subsurface, Canning Basin, Western Australia

Abstract

Palynological investigation of 80 core samples from four boreholes, drilled through the Lower to Middle Ordovician marine sections of the central-northeastern Canning Basin, northwestern Australia, reveals diverse acritarch associations including a number of stratigraphically significant species. The stratigraphic succession studied, embracing the Willara Formation and conformably overlying Goldwyer Formation, has been independently dated as early Arenig to Llanvirn by conodont faunas ( Oepikodus communis through Phragmodus- Plectodina zonal interval). Nine morphologically distinctive acritarch species have relatively narrow vertical ranges within the study interval and likely constitute serviceable palynostratigraphic indices for the Ordovician in and possibly beyond the Western Australian study area. Three new species, Comasphaeridium setaricum, Polyancistrodorus kunzeanensis, and Stelomorpha calix, are established; and one new combination, Baltisphaeridium variocavatum (Playford and Martin, 1984), is proposed. Other stratigraphically significant species include Petaloferidium comptum Playford and Martin, 1984 and Peteinosphaeridium sp. cf. P. exornatum Tongiorgi et al., 1995; together with Dorsennidium symmetricum (Lu, 1987) Sarjeant and Stancliffe, 1994, Peteinosphaeridium coronula Yin et al., 1998, and Striatotheca rarirrugulata (Cramer et al., 1974) Eisenack et al., 1976, which are found for the first time in Australia. The vertical distribution, and hence the stratigraphic utility, of each of the above species is documented through the studied sections.