Weathering and Uplift of South Island New Zealand Recorded in the Geochemistry of Sediments in the Bounty Trough Deep Sea Fan
Abstract
The Bounty Fan (BF) represents the abyssal marine terminus of the eastern South Island sedimentary system (ESISS) of New Zealand, which begins in the actively uplifting Southern Alps. ODP Site 1122, located on the northern levee of the Bounty Channel as it incises the abyssal Bounty Fan, contains a 617.8 m succession of early Miocene to Holocene turbidites, pelagic/hemipelagic sediments and current-modified deposits. Contourite and turbidite horizons from the ~16 Ma history of site 1122 were analyzed and compared to ESISS river sediments in order to investigate the weathering and uplift history of the source rocks delivering sediment to the BF. The major and trace element geochemistry of BF sediments is similar to that of parent rocks. Although sand- size fluvial bedload sediments from ESISS rivers display different compositions to parent rocks, the incorporation of the silt and finer fraction of ESISS bedload in BF sediments serves to preserve parent rock geochemical signatures. ESISS parent lithologies are dominated by Mesozoic sedimentary rocks and their metamorphosed equivalents. Therefore, it is possible that at least two episodes of sedimentary recycling have occurred without the destruction of `grandparent' rock geochemical signature. A major hiatus in deposition in the BF occurs from 11 Ma to &~3.5 Ma. The geochemical and petrologic similarity of the sediments on either side of the unconformity indicates that they are derived from a similar provenance. The cause of the hiatus is unlikely to be due to a cut-off of the "source", because the deformation that began with Alpine Fault inception at 23 Ma has produced an estimated 20 km of exhumation since 10 Ma. Different scenarios involving the change to the location of the sedimentary "sink" during the hiatus, that allow the subsequent sediments to maintain a similar source composition and degree of weathering, will be considered.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFMOS12A..04M
- Keywords:
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- 1020 Composition of the continental crust;
- 1030 Geochemical cycles (0330);
- 1039 Alteration and weathering processes (3617);
- 1050 Marine geochemistry (4835;
- 4845;
- 4850);
- 1065 Major and trace element geochemistry