Expedition 317 summary

Integrated Ocean Drilling Program (IODP) Expedition 317 was devoted to understanding the relative importance of global sea level (eustasy) versus local tectonic and sedimentary processes in controlling continental margin sedimentary cycles. The expedition recovered sediments from the Eocene to recent period, with a particular focus on the sequence stratigraphy of the late Miocene to recent, when global sea level change was dominated by glacioeustasy. Drilling in the Canterbury Basin, on the eastern margin of the South Island of New Zealand, takes advantage of high rates of Neogene sediment supply, which preserves a high-frequency (0.1-0.5 m.y.) record of depositional cyclicity. Because of its proximity to an uplifting mountain chain (the Southern Alps) and strong ocean currents, the Canterbury Basin provides an opportunity to study the complex interactions between processes responsible for the preserved sequence stratigraphic record. Currents have locally built large, elongate sediment drifts within the prograding Neogene section. These elongate drifts were not drilled during Expedition 317, but currents are inferred to have strongly influenced deposition across the basin, including locations lacking prominent mounded drifts. Upper Miocene to recent sedimentary sequences were cored in a transect of three sites on the continental shelf (landward to basinward, Sites U1353, U1354, and U1351) and one on the continental slope (Site U1352). The transect provides a stratigraphic record of depositional cycles across the shallow-water environment most directly affected by relative sea level change. Lithologic boundaries provisionally correlative with seismic sequence boundaries were identified in cores from each site, providing insight into the origins of seismically resolvable sequences. This record will be used to estimate the timing and amplitude of global sea level change and to document the sedimentary processes that operate during sequence formation. Sites U1353 and U1354 provide significant double-cored, high-recovery sections through the Holocene, allowing for high-resolution study of recent glacial cycles in a continental shelf setting. Continental slope Site U1352 represents a complete section from modern slope terrigenous sediment to hard Eocene limestone, with all the associated lithologic, biostratigraphic, physical, geochemical, and microbiological transitions. This site also provides a record of ocean circulation and fronts during the last approximately 35 m. The early Oligocene ( approximately 30 Ma) Marshall Paraconformity was the deepest drilling target of Expedition 317 and was hypothesized to represent intensified current erosion or nondeposition associated with the initiation of thermohaline circulation following the separation of Australia and Antarctica. Expedition 317 set a number of scientific ocean drilling records: (1) deepest hole drilled in a single expedition and second deepest hole in the history of scientific ocean drilling (Hole U1352C, 1927 m); (2) deepest hole and second deepest hole drilled by the R/V JOIDES Resolution on a continental shelf (Hole U1351B, 1030 m; Hole U1353B, 614 m); (3) shallowest water depth for a site drilled by the JOIDES Resolution for scientific purposes (Site U1353, 84.7 m water depth); and (4) deepest sample taken during scientific ocean drilling for microbiological studies (Site U1352, 1925 m). Expedition 317 supplements previous drilling of sedimentary successions for sequence stratigraphic and sea level objectives, particularly drilling on the New Jersey margin (Ocean Drilling Program [ODP] Legs 150, 150X, 174A, and 174AX and IODP Expedition 313) and in the Bahamas (ODP Leg 166), but includes an expanded Pliocene section. Completion of at least one transect across a geographically and tectonically distinct siliciclastic margin was the necessary next step in deciphering continental margin stratigraphy. Expedition 317 also complements ODP Leg 181, the focus of which was drift development in more distal parts of the Eastern New Zealand Oceanic Sedimentary System ( ENZOSS).86 page(s