Along-Strike Variation in the Signature of Contourite Deposition: Canterbury Basin, New Zealand
Abstract
Initiation of Alpine Fault movement in the late Oligocene or early Miocene precipitated siliciclastic input to the offshore Canterbury Basin. Rates of sediment input have accelerated in response to increasing convergence rates at the fault since ~10 Ma. These sediments prograded into the path of a current flowing northeastward, parallel to the margin. In the present day, this system involves: 1) the Southland Current, inboard of the Southland Front (part of the Subtropical Front) over the ~300 m isobath and 2) a parallel local gyre of the Antarctic Circumpolar Current circulating clockwise within the head of Bounty Trough and extending current influence to ~900 m. Sediment/current interaction resulted in development of large (up to 1000 m thick) elongate sediment drifts on prograding Negoene paleoslopes. However, the influence of currents on deposition varies markedly along strike. Because the locus of drift development migrated northeastward through time, large drifts developed in the northeast, near ODP Site 1119, while coeval sequences to the southwest at the IODP Expedition 317 drilling transect are more clinoformal. These geomorphological contrasts occur in spite of the fact that both regions were swept by the same currents. This variability is matched at core scale: evidence for along-strike processes at Expedition 317 sites in the southwest, where sequences are clinoformal, is mixed with that for downslope deposition. In contrast, cores from Site 1119 to the northeast are interpreted as representing almost entirely contourite deposition. The mounded, elongate drifts constitute dramatic seismic evidence of contourite deposition. However, subdued seismic evidence of contourite deposition is also present in the southwestern zone lacking mounded drifts. Furthermore, some clinoform fronts in this part of the basin display a convex upward geometry that contrasts with the predominantly concave-upward clinoform fronts off New Jersey and may represent a form of plastered drift. The role of along-strike processes in sequence stratigrahy remains unclear and sediment transport in the sequence stratigraphic model is viewed as essentially 2D. Nevertheless, along-strike transport is sometimes called upon to explain real-world variations from the model. Therefore, understanding the interaction of along-strike and downslope processes within a sequence stratigraphic framework in a location where a current is known to have been present, but whose seismic stratigraphic signature varies greatly, has global implications for both sequence stratigraphy and models of clinoform development.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFMPP13F..04F
- Keywords:
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- 3002 MARINE GEOLOGY AND GEOPHYSICS / Continental shelf and slope processes;
- 3022 MARINE GEOLOGY AND GEOPHYSICS / Marine sediments: processes and transport;
- 3025 MARINE GEOLOGY AND GEOPHYSICS / Marine seismics;
- 3036 MARINE GEOLOGY AND GEOPHYSICS / Ocean drilling