FORAMINIFERAL BIOFACIES ON THE MIDLATITUDE LINCOLN SHELF, SOUTH AUSTRALIA - OCEANOGRAPHIC AND SEDIMENTOLOGICAL IMPLICATIONS

Foraminiferal assemblages on the southern mid-latitude Lincoln Shelf c omprise mixtures, more strongly in shallow waters, of Holocene and rel ict Pleistocene specimens. Over 200 benthic and 15 planktonic species were recorded, and a higher diversity was found in the central and dee per parts of the shelf and slope. Cluster analysis identified five ass emblages or biofacies. Nearshore assemblage A (<50 m) and inner mid-sh elf assemblage B (50-90 m) are dominated by relict and Recent shallow- water species. The outer mid-shelf assemblage C (90-120 m) contains mo re cibicidids and is transitional between the shallow- and deep-water assemblages. Outer shelf assemblage D (120-170 m) is characterized by cibicidids and anomalinids and by a higher planktonic and benthic dive rsity, and it can be subdivided into three sub-assemblages D1-D3. Unli ke others, assemblage D was not recognized from the most western trans ect samples. The outer shelf to slope assemblage E (170-400 m) is typi cally deep-water, having forms like Hoeglundina elegans, Pullenia bull oides and Melonis affinis. The western, Great Australian Eight sector has the larger epifaunal benthic Sorites-Marginopora group, while the infauna is higher in the eastern, Neptune sector of the shelf. We attr ibute these contrasts to the influence of the warm Leeuwin Current and to the mixing between gulf, shelf and oceanic waters, respectively. A former lagoonal environment is largely responsible for the accumulati on of relict tests during lower sea-level periods of the late Pleistoc ene when climate was more arid. The lack of Recent sediments preserved on the inner shelf is considered to be due to strong wave abrasion ca using sediment starvation. Richer foraminiferal assemblages from the o uter shelf to upper slope parallel an increasingly calcareous sediment . Faunal evidence indicates a warmer, nearly oligotrophic condition on Lincoln Shelf, compared to the mesotrophy on the adjacent Lacepede Sh elf. This difference may be due to the separation of these two shelves by Kangaroo Island acting as a local oceanographic (environmental) an d biogeographic barrier.