Marion Plateau carbonate platforms and adjacent slopes (Fig. F1) were drilled during Ocean Drilling Program Leg 194; objectives included calibrating the magnitude of Miocene sea level changes and elucidating development of subtropical carbonate platforms in current-dominated environments (Shipboard Scientific Party, 2002). The original working hypothesis was that the northern platform (Site 1193) developed in the early to middle Miocene, whereas the southern platform represented late Miocene development (Pigram et al., 1992).
Shipboard analyses of cores, core catcher samples, and thin sections by the Leg 194 Shipboard Scientific Party (2002) revealed contrasting cool–subtropical carbonate platform facies at Sites 1193 and 1196. Platform facies at Site 1193 (Fig. F2) are dominated by bryozoans and coralline algae with abundant larger benthic foraminifers (LBF). Facies at Site 1196 (Fig. F3) are dominated by coralline red algae, with LBF and hermatypic corals abundant in some intervals. Both nannofossils and LBF provided biostratigraphic evidence that most of the southern platform developed before or during the middle Miocene (Shipboard Scientific Party, 2002), indicating that most differences in platform development are related to paleoenvironmental rather than temporal differences.
LBF assemblages provided crucial data for interpretation of the biostratigraphy, depositional environments, and sea level history of Marion Plateau carbonate platforms during shipboard analysis of cores retrieved during Leg 194 (Shipboard Scientific Party, 2002). LBF were common constituents not only in most platform sediments, but also in periplatform deposits in slope facies. Miocene LBF have been widely studied in Australia and southeast Asia; therefore, biofacies and ranges of many taxa are relatively well known (Chapronière, 1980, 1981, 1984; Betzler and Chapronière, 1993; Chapronière and Betzler, 1993; Betzler, 1997). Assemblages, morphologies, mineralogies, and abundances of LBF also provide clues to paleoenvironmental conditions, including paleodepth, temperature, carbonate saturation state, nutrient supply, light, and water motion, all of which are critical to understanding sea level amplitudes, platform depositional environments, and paleoceanographic history of the sites and intervals sampled. The purpose of this paper is to summarize biostratigraphic and paleoenvironmental interpretations based upon LBF assemblages found at Sites 1193–1198, with the goal of contributing to understanding the depositional history of the Marion Plateau.