Abstract:
Two Neogene carbonate platforms on the Marion Plateau, off northeastern Australia, were drilled during ODP Leg 194. Approximately 510 m of mixed shelf and slope sediments were penetrated at Site 1193; approximately 672 m of shallow-water platform sediments were penetrated at Site 1196. Shallow-water carbonates at Site 1193 were dominated by bryozoans. At Site 1196 coralline red algae dominated, with stony corals common in some intervals. Larger benthic foraminifers (LBF) were abundant at both sites; five LBF assemblages were distinguished using thin sections cut from recovered cores. Assemblage A was found in mixed carbonate-terrigenous clastic, neritic facies (<100 m) following basement flooding. Operculina complanata was most common in terrigenous mud-rich facies, while Lepidocyclina spp. with relatively primitive, non-stellate morphologies dominated carbonate-rich facies. These taxa are characteristic of latest Oligocene to early Miocene ages; consistent with nannofossil dates of 18-24 Ma for units immediately above basement. Assemblage B, found in platform facies at sites 1193 and 1196 and in corresponding slope sediments at sites 1197 and 1198, is characterized by predominantly non-stellate lepidocyclinids and ovate miogypsinids. Units containing this assemblage are interpreted to be late-early Miocene ( approximately 16-18 Ma). Assemblage C, found at Site 1196 (183-326 mbsf), is characterized by Flosculinella, Austrotrillina, soritids, and smaller miliolid foraminifers. The middle Miocene (13.3-15.2 Ma) interpretation is consistent with nannofossil dates from the interval. Assemblage D was found in platform facies at sites 1193, 1194, and 1196 and in corresponding slope sediments at sites 1197 and 1198. This assemblage is characterized by the transition from mixed concentric and stellate lepidocyclinids to predominantly stellate forms. Units containing this assemblage are interpreted to be middle Miocene ( approximately 11.9-16.4 Ma). Assemblage E, dominated by Amphistegina with common stellate Lepidocyclina, was found at Site 1196 in upper platform facies, in corresponding periplatform sediments at sites 1197 and 1198, and also in transported sediments at sites 1193 and 1194. Nannofossil and planktic foraminiferal biostratigraphy in periplatform sediments indicate a late Miocene age for this assemblage.