Rocks from the Cascade Seamount: an archive of the unzipping of Gondwana and the initiation of the ACC?

• Main Authors: Mundana, R, Johnson, SC, Whittaker, JM, Carey, R, Sauermilch, I, Fox, JM
• Format: Conference Object
• Language: English
• Published: . 2017
• Subjects: Earth Sciences; Physical Geography and Environmental Geoscience; Palaeoclimatology; Antarctic; The Antarctic; Antarc*
• Online Access: http://ecite.utas.edu.au/115847

The Cascade Seamount, on the East Tasman Plateau, is enigmatic with regard to its formationand subsidence history. Understanding the timing and rate of subsidence of the region is animportant factor for determining the initiation of the Antarctic Circumpolar Current.Currently situated ~2000m below sea level, the Seamount has archived much of this history.However, our understanding of its evolution is limited by poorly constrained samplesrecovered from two separate locations. One, from a fishing excursion, recovered rocks fromvarious unknown locations on the seamount while an ODP drill hole collected samples on theEast Tasman Rise ~23km from the Seamount (~2000m bsl). The two, limited, sample setscomprise of shallow water sediments but have led to opposing subsidence histories for thearea being proposed. Fundamentally, it is the ODP drill hole that has been used as the onlyconstraint for the area in the tectonic modeling that has been conducted (Stickley et al. 2004).The recent RV Investigator voyage to the Cascade Seamount (August, 2016) aimed toelucidate this problem through high-resolution mapping and dredging with the aim to furtherunderstand and characterize the Seamount. We present the initial results of the macro- andmicro-features of the rocks recovered from the top and flanks of the Seamount. The highresolutionbathymetry data identified a series of terraces on the flanks of the Seamount fromwhich a series of shallow water sedimentary rocks and conglomeratic units were recovered.Here, we describe these rocks, and discuss their formation. These descriptions andinterpretations, coupled with the new geophysical data, provide a critical insight into thesubsidence history of the Seamount. The ability to understand the history of the CascadeSeamount and the East Tasman Plateau provides a new and important tie-point inunderstanding the final stages of the regional evolution and initiation of the AntarcticCircumpolar Current.