Timing and Nature of the Deepening of the Tasmanian Gateway

• Main Authors: Stickley, Catherine E., Brinkhuis, Henk, Schellenberg, Stephen A., Sluijs, Appy, Röhl, Ursula, Fuller, Michael, Grauert, Marianne, Huber, Matthew, Warnaar, Jeroen, Williams, Graham L.
• Format: Text
• Language: unknown
• Published: Purdue University 2004
• Subjects: Micropaleontology; Meteorology and Atmospheric Dynamics: Paleoclimatology; Water masses; Paleoceanography; Cenozoic; Earth Sciences; Antarctic; Pacific; Antarc*; Antarctica
• Online Access: https://docs.lib.purdue.edu/easpubs/160; https://docs.lib.purdue.edu/context/easpubs/article/1199/viewcontent/Stickley_et_al_2004_TimingAndNature.pdf

Tectonic changes that produced a deep Tasmanian Gateway between Australia and Antarctica are widely invoked as the major mechanism for Antarctic cryosphere growth and Antarctic Circumpolar Current (ACC) development during the Eocene/Oligocene (E/O) transition (∼34–33 Ma). Ocean Drilling Program (ODP) Leg 189 recovered near-continuous marine sedimentary records across the E/O transition interval at four sites around Tasmania. These records are largely barren of calcareous microfossils but contain a rich record of siliceous- and organic-walled marine microfossils. In this study we integrate micropaleontological, sedimentological, geochemical, and paleomagnetic data from Site 1172 (East Tasman Plateau) to identify four distinct phases (A–D) in the E/O Tasmanian Gateway deepening that are correlative among ODP Leg 189 sites. Phase A, prior to ∼35.5 Ma: minor initial deepening characterized by a shallow marine prodeltaic setting with initial condensation episodes. Phase B, ∼35.5–33.5 Ma: increased deepening marked by the onset of major glauconitic deposition and inception of energetic bottom-water currents. Phase C, ∼33.5–30.2 Ma: further deepening to bathyal depths, with episodic erosion by increasingly energetic bottom-water currents. Phase D, <30.2 Ma: establishment of stable, open-ocean, warm-temperate, oligotrophic settings characterized by siliceous-carbonate ooze deposition. Our combined evidence indicates that this early Oligocene Tasmanian Gateway deepening initially produced an eastward flow of relatively warm surface waters from the Australo-Antarctic Gulf into the southwestern Pacific Ocean. This “proto-Leeuwin” current fundamentally differs from previous regional reconstructions of eastward flowing cool water (e.g., a “proto-ACC”) during the early Oligocene and thereby represents an important new constraint for reconstructing regional- to global-scale dynamics for this major global change event.