HR: 0830h
AB: The offshore Canterbury Basin, on the eastern margin of the South Island, is an excellent location in which to study the influence of strike-slip tectonics, sea level, and contour currents on stratigraphic architecture. The basin is a focus area of the MARGINS Source-to-Sink initiative and the target of an existing Ocean Drilling Program drilling proposal. High-resolution, two-dimensional multichannel seismic (MCS) data were collected in the offshore basin in support of this proposal in January 2000 (R/V{\it Maurice Ewing} cruise EW00-01). The seismic source comprised two GI air guns (45/45 cu.in.) and the streamer was deployed with 12.5 m groups in 96- and 120-channel configurations. A total of 57 profiles (~3500 line-km) was collected, covering ~4840 km$^{2}$; line spacings are 0.8-2 km in the dip (shelf-normal) direction and 2-5.5 km in the strike (shelf-parallel) direction. Penetration, 1.7-2.0 s below seafloor, is sufficient to image the entire Oligocene-Recent section. The basin fill records a transgressive-regressive cycle, the product of tectonic evolution from a rifted (~80 Ma) continental margin to a thermally subsiding passive margin adjacent to the transpressive uplift of the Southern Alps. Maximum regional transgression occurred during the mid-Oligocene, when limestones were deposited throughout the basin, regionally accompanied by reduced terrigenous input. A continuous, high-amplitude reflection marks the base of the limestones. The Marshall Paraconformity (~30 Ma) occurs within the limestone interval and correlates with a weak, discontinuous reflection. Downlap onto this reflection indicates that the paraconformity represents the maximum flooding surface for the post-rift megasequence. Subsequent regression accompanied a sediment influx associated with uplift along the Alpine Fault. The upper Miocene to Recent section contains at least nine unconformity-bounded, probably fourth-order, prograding sequences. The number of sequences and their thicknesses vary along strike, implying that local processes have contributed to their formation. Dominant among such processes are erosion and deposition by contour-following currents. Large, Neogene, upper-slope sediment drifts have been identified previously using commercial MCS data. The new data allow us to delineate their three-dimensional architecture. Mounded reflections are supplemented by channel-like geometries where drifts onlap the underlying slope; channels are oriented along strike. Accretion of successive drifts appears to have been a mechanism of shelf progradation. The largest, youngest drifts occur in the northern basin where they can be 20 km across (dip direction) and up to 1000 m thick. There, they are a product of preferential deposition where a northward-flowing current is deflected eastward by Banks Peninsula and Chatham Rise. Conventional clinoform sequence boundaries can be traced laterally and/or downslope, to drift deposits, indicating that the drifts are an intergral part of sequence development on this margin.
AN: OS21C-22
TI: Global and Local Controls on Depositional Cyclicity: the Canterbury Basin, New Zealand
AU: * Lu, H
EM: hongbo@utig.ig.utexas.edu
AF: University of Texas at Austin, Department of Geological Sciences, C1140, Austin, TX 78712-1101 United States
AU: * Lu, H
EM: hongbo@utig.ig.utexas.edu
AF: University of Texas Institute for Geophysics, 4412 Spicewood Springs Road, Bldg. 600, Austin, TX 78759-8500 United States
AU: Fulthorpe, C S
EM: craig@utig.ig.utexas.edu
AF: University of Texas Institute for Geophysics, 4412 Spicewood Springs Road, Bldg. 600, Austin, TX 78759-8500 United States
AU: Mann, P
EM: paulm@utig.ig.utexas.edu
AF: University of Texas Institute for Geophysics, 4412 Spicewood Springs Road, Bldg. 600, Austin, TX 78759-8500 United States
DE: 3022 Marine sediments--processes and transport
DE: 3025 Marine seismics (0935)
SC: OS
MN: Fall Meeting 2000