Title

Larger Benthic Foraminifers of the Marion Plateau, Northeastern Australia (Odp Leg 194): Comparison of Faunas from Bryozoan (Sites 1193 and 1194) and Red Algal (Sites 1196-1198) Dominated Carbonate Platforms

Document Type

Conference Proceeding

Publication Date

2006

Digital Object Identifier (DOI)

https://doi.org/10.2973/odp.proc.sr.194.009.2006

Abstract

Two Neogene carbonate platforms on the Marion Plateau, off northeastern Australia, were drilled during Ocean Drilling Program Leg 194. Approximately 510 m of mixed shelf and slope sediments were penetrated at Site 1193, and ~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, though stony corals were common to abundant in some intervals. Larger benthic foraminifers (LBF) were abundant at both sites, with common genera including Amphistegina, Cycloclypeus, Lepidocyclina, Miogypsina, and Operculina.

Five LBF assemblages were distinguished using thin sections cut from recovered cores. Assemblage A was found in mixed carbonate-terrigenous clastic neritic facies (less than 100 m) associated with basement flooding. Operculina complanata was common in terrigenous mud-rich facies, whereas Lepidocyclina spp. with relatively primitive, nonstellate morphologies dominated in more carbonate-rich facies. These taxa are characteristic of larger foraminiferal (LF) Associations 1–5, indicative of latest Oligocene to early Miocene ages. Nannofossil dates are similar (~18–24 Ma) for the units immediately above basement. Depositional environments ranged from deltaic muds with oyster and Operculina shells to a striking interval of in situ, large, flat Lepidocyclina badjirraensis at Site 1198, indicating a deep oligophotic (~100–150 m) paleoenvironment. Assemblage B was found in platform facies at Sites 1193 and 1196 and in corresponding slope sediments at Sites 1197 and 1198. This assemblage is characterized by predominantly nonstellate lepidocyclinids and ovate miogypsinids. Units containing this assemblage are interpreted to be late early Miocene (~16–18 Ma) and indicate deposition in a range of euphotic paleodepths, as interpreted from LBF morphologies. Assemblage C, found at Site 1196 (183–326 meters below seafloor), is characterized by Flosculinella, Austrotrillina, soritids, and smaller miliolid foraminifers. This LF 8 association is considered middle Miocene (~13.3–15.2 Ma), an assumption consistent with nannofossil dates from the interval. The assemblage and associated sediments indicate shallow (less than 12 m), somewhat restricted platform conditions, including seagrass meadows. 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 lepidocyclinid morphologies to predominantly stellate forms, as well as by vermiform miogypsinids. Units containing this assemblage are interpreted to be middle Miocene (~11.9–16.4 Ma). At Sites 1193 and 1194, the middle Miocene regression is recorded by changes in foraminiferal taxa and LBF morphologies. Assemblage E was found in upper platform facies at Site 1196, in corresponding periplatform sediments at Sites 1197 and 1198, and also in transported sediments at Sites 1193 and 1194. Amphistegina dominated this assemblage, with stellate Lepidocyclina as a common component. Nannofossil and planktonic foraminiferal biostratigraphy in periplatform sediments indicate a late Miocene to earliest Pliocene age for this assemblage.

The cool–subtropical climate was critical to the depositional history of the Marion Plateau throughout the Miocene. Fluvial input, ocean currents, and paleochemistry played critical roles in inhibiting reef development on the northern platform while promoting it on the southern platform. On the southern platform, strong, warm, southward-flowing currents favored coralline algal dominance. Behind the coralline algal rim, coralline algae, stony corals, and LBF thrived. The carbonate factory on the southern platform kept pace with sea level pulses throughout the Miocene, most dramatically during the early middle Miocene when miliolid LBF indicate 180 m of shallow (less than 12 m) restricted platform sedimentation. Shallow-water carbonate sedimentation on the southern platform terminated in the late Miocene or early Pliocene, and strong currents over the platform have precluded subsequent pelagic sedimentation.

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Yes

Citation / Publisher Attribution

Larger Benthic Foraminifers of the Marion Plateau, Northeastern Australia (Odp Leg 194): Comparison of Faunas from Bryozoan (Sites 1193 and 1194) and Red Algal (Sites 1196-1198) Dominated Carbonate Platforms, in F.S. Anselmetti, A.R. Isern, P. Blum & C. Betzler (Eds.), Proceedings of the Ocean Drilling Program: Scientific Results, 194, 31 p.

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