Tectonic, Oceanographic, and Climatic Controls on the Cretaceous‐Cenozoic Sedimentary Record of the Australian‐Antarctic Basin

Abstract

Understanding the patterns and characteristics of sedimentary deposits on the conjugate Australian‐Antarctic margins is critical to reveal the Cretaceous‐Cenozoic tectonic, oceanographic, and climatic conditions in the basin. However, unraveling its evolution has remained difficult due to the different seismic stratigraphic interpretations on each margin and sparse drill sites. Here, for the first time, we collate all available seismic reflection profiles on both margins and use newly available offshore drilling data to develop a consistent seismic stratigraphic framework across the Australian‐Antarctic basins. We find sedimentation patterns similar in structure and thickness, prior to the onset of Antarctic glaciation, enabling the basinwide correlation of four major sedimentary units and their depositional history. We interpret that during the warm and humid Late Cretaceous (~83–65 Ma), large onshore river systems on both Australia and Antarctica resulted in deltaic sediment deposition offshore. We interpret that the onset of clockwise bottom currents during the early Paleogene (~58–48 Ma) formed prominent sediment drift deposits along both continental rises. We suggest that these currents strengthened and progressed farther east through the Eocene. Coevally, global cooling (<48 Ma) and progressive aridification led to a large‐scale decrease in sediment input from both continents. Two major Eocene hiatuses recovered by the Integrated Ocean Discovery Program site U1356A at the Antarctic continental slope likely formed during this preglacial phase of low sedimentation and strong bottom currents. Our results can be used to constrain future paleo‐oceanographic modeling of this region and aid the understanding of the oceanographic changes accompanying the transition from a greenhouse to icehouse world.

The Evolving Paleobathymetry of the Circum‐Antarctic Southern Ocean Since 34 Ma: A Key to Understanding Past Cryosphere‐Ocean Developments

“…Sedimentation in the Southern Ocean prior to the Oligocene (Figure 7) was dominated by vast fluvial deltas on the continental shelves and current‐controlled sediment transport and deposition in the isolated basins that evolved after Gondwana breakup (Gohl, Uenzelmann‐Neben, et al, 2013; Gulick et al, 2017; Sauermilch, Whittaker, et al, 2019). Most of the sedimentation took place in the basins of the continental shelves (Prydz Bay, Weddell Sea, Ross Sea, Amundsen Sea, Bellingshausen Sea, and Sabrina Coast) and in the deep sea leeward of basement highs (Gunnerus Ridge, Astrid Ridge) and LIPs (Figure 7).…”

“…The chronostratigraphic core data and associated seismic core‐log integration data allow us to correlate and trace dated seismic horizons of layers, formation boundaries, and unconformities over large distances. On most conjugate margins, the seismic stratigraphy is significantly better constrained due to the availability of exploration wells (e.g., Sauermilch, Whittaker, et al, 2019; Totterdell et al, 2000). To properly correlate drill core data to seismic reflection data, we calculated synthetic seismograms at key sites (e.g., Wilkes Land margin Exp.…”

“…In these cases, we used available velocity‐depth models as sample sections to compare and interpolate the velocities associated with strata of different depth (Huang et al, 2014; Lindeque, Gohl, Wobbe, et al, 2016; Uenzelmann‐Neben & Gohl, 2012). In the Australian‐Antarctic sector, sonobuoy data were used for a potentially more accurate P wave velocity‐depth conversion of the sedimentary column (see Sauermilch, Whittaker, et al, 2019, for details). From the collected velocity data, we produced regional velocity grids, and used them to convert horizon data from time to depth domain.…”

“…During glacial periods, deeply cut glacial troughs can allow for the intrusion of bottom‐water onto the shelf, triggering melting of the ice sheet from below. The conjugate margins are not directly influenced by ice masses, but the reorganization and variations in vigor of the ocean currents shape sedimentation patterns along the margins (e.g., Horn & Uenzelmann‐Neben, 2015; Sauermilch, Whittaker, et al, 2019; Uenzelmann‐Neben & Huhn, 2009).…”

“…We also present an interpretation and discussion of the patterns of sedimentation through time focusing on the mechanisms within the entire Southern Ocean. Further in‐depth analyses of specific aspects of the sedimentary patterns in the Southern Ocean are provided in accompanying publications (Hochmuth & Gohl, 2019; Paxman et al, 2019; Sauermilch, Whittaker, et al, 2019).…”