Palaeoceanographic significance of recent foraminiferal biofacies on the southern shelf of Western Australia; a preliminary study

Abstract

The southern shelf of Western Australia lies close to the Subtropical Convergence, in a region strongly influenced by the warm Leeuwin Current from the north and the cold, more massive Western Australian Current from the south. Fresh Holocene and relict Pleistocene foraminiferal specimens are mixed in dredged sediment samples, similar in composition to those from other parts of the southern Australian margin. The Holocene planktonic assemblages are dominated in the west by subtropical forms (Globigerinoides trilobus s.I., Globorotalia menardii and Neogloboquadrina dutertrei) and in the east by the temperate species Globorotalia inflata. Three Holocene benthic assemblages are distributed from the inner shelf to the upper slope, also showing a strong longitudinal gradation from west to the east. The change from warm-water assemblages to temperate assemblages is progressive and continuous, but the southwest comer is marked by the southerly limit of some larger benthic taxa including Heterostegina, and the area off Esperance is the furthermost extent of an abundant, though patchy, living Amphisorus-Marginopora association. This W → E gradation indicates that the Leeuwin Current has played a key role in influencing the distribution of foraminifera as from at least the last interglacial, because this pattern exists not only in the Holocene but also in the relict foraminiferal biofacies.