Deciphering Possible Paleoceanographic vs. Tectonic vs. Eustatic Signals in the Passive-Margin Bounty Fan, South Island, New Zealand

Kathleen Marsaglia¹, Candace E. Martin², Christopher Q. Kautz², Shawn Shapiro¹, and Lionel Carter^3
1Dept. Geological Sciences, California State University Northridge, Northridge, CA
²Dept. of Geology, University of Otago, Dunedin, New Zealand
³Antarctic Research Centre, Victoria University, Wellington, New Zealand

Variations in sediment supply/accumulation in passive-margin fan systems are often ascribed to eustacy. In the case of the Bounty Fan System off South Island, New Zealand, sediment accumulation may have also been negatively influenced by tectonism and deep-ocean currents. This connection was made by linking the non-marine depositional history of the onshore source area and the marine sedimentary history detailed at Ocean Drilling Program Site 1122 on the Bounty levee. A significant hiatus (11-3.5 Ma) at Site 1122 could be explained by the combined effects of enhanced erosion by the Antarctic Circumpolar Current, as well as of onshore disruption of the fluvial drainage linked to Alpine Fault plate- boundary tectonics. The latter is evidenced by lacustrine facies and intraplate mafic volcanism associated with range and basin faulting. There is no distinct change in sediment provenance across this hiatus to suggest major changes in sediment source, but a significant post-hiatus spike in the Chemical Index of Alteration (CIA) as defined by bulk geochemistry of Site 1122 sediment is consistent with the offshore flushing of more weathered sediment upon re-establishment of through-going fluvial drainage.

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas