Abstract:
Continental margins are composed of thick sedimentary deposits containing a record of past global sea-level (eustatic) fluctuations that must be understood in order to assess predictions of future eustatic changes. The Ocean Drilling Program and Integrated Ocean Drilling Program (IODP) have drilled on several siliciclastic and carbonate passive continental margins with a range of sediment supply rates to extract information about eustatic timing and amplitudes. IODP Expedition 317 drilled in the offshore Canterbury Basin, eastern South Island of New Zealand, in water depths of 85 m to 320 m. One of the main objectives of Expedition 317 was to test the concepts of sequence stratigraphy by documenting lithologies, ages and depositional environments within sequences. Carbonate and siliciclastic sediments of Eocene to recent age were recovered. The offshore basin sediments were deposited at high accumulations rates due to its proximity to the Southern Alps. Currents related to Antarctic circumpolar circulation have also influenced deposition. The sediments contain shallow to deep-water facies that permit tracking of depositional environments in response to eustasy. Multichannel seismic data of the EW00-01 survey provide the seismic stratigraphic framework (Lu and Fulthorpe, 2004). Nineteen regional seismic sequence boundaries (U1-U19) were identified within the Miocene to recent section. Through shipboard and post-cruise analyses, these seismic surfaces have been correlated to the lithology using a multiproxy approach combining X-ray fluorescence elemental analyses at 5 cm scale, grain size, biostratigraphic ages, and an oxygen isotope record (Hoyanagi et al., 2010). Late Pleistocene lithologic surfaces correlate with sequence boundaries U18 and U19 across the shelf: sharp contacts separate coarse lithologies containing shells above, from fine mud beneath. The contacts are generally extensively bioturbated. The shelly, coarse-grained beds are interpreted as transgressive deposits. Above, 4 to 5 m thick, greenish mud rich in Ca and Sr is interpreted as a highstand deposit. Overlying lowstand sediments are enriched in Fe, Si, K, Ti and Al, in order of decreasing abundance. Iron-rich minerals amphibole, epidote, chlorite and biotite may have originated from metamorphic sources to the south.