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

The southern shelf of Western Australia lies close to the Subtropical Conve rgence, in a region strongly influenced by the warm Leeuwin Current from th e north and the cold, more massive Western Australian Current from the sout h. Fresh Holocene and relict Pleistocene foraminiferal specimens are mixed in dredged sediment samples, similar in composition to those from other par ts of the southern Australian margin. The Holocene planktonic assemblages a re dominated in the west by subtropical forms (Globigerinoides trilobus s.l ., Globorotalia menardii and Neogloboquadrina dutertrei) and in the east by the temperate species Globorotalia inflata. Three Holocene benthic assembl ages 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 corner is marked by the southerly limit of some larger be nthic taxa including Heterostegina, and the area off Esperance is the furth ermost 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 a t least the last interglacial, because this pattern exists not only in the Holocene but also in the relict foraminiferal biofacies. (C) 1999 Elsevier Science B.V. All rights reserved.