Abstract:
Integrated Ocean Drilling Program (IODP) Expedition 317 drilled three shelf sites (1351,1353, and 1354) and one slope site (1352) along a transect of the Canterbury Margin located off the east coast of South Island, New Zealand. The primary goal of the Expedition was to understand how eustasy versus local tectonic and sedimentary processes control sedimentary cycles along this continental margin. Recovered lithologies are composed mainly of alternating mud with thin sand/clay rich intervals. Likely sources for these sediments would have been large onshore river systems originating from the Southern Alps, although there is evidence for significant along shelf/slope sediment transport. South Island, New Zealand has a unique distribution of rock types from Torlesse clastic sedimentary rocks to variable metamorphosed equivalents (Otago schist). Sands from several of these rivers were collected and analyzed for comparison of offshore Expedition 317 sandy units. These rivers drain lithologies ranging from Torlesse sandstone/argillite (Rakaia and Rangatita Rivers) to semi-schist (Waitaki River) to schist (Clutha River). River sand detrital modes reflect this changing lithologies ranging from more quartzo-lithic (Torlesse) to more quartzo-feldspathic (schist). The sediment to semi-schist to schist transition is evident in the detailed proportion. Offshore sandy units are fairly uniform in composition: predominantly quartzo- feldspathic, with lesser quartz and lithic components. There are no significant differences in composition among the samples from shelf and slope sites. There are significant differences in the sand composition from the onshore river sands and the offshore core sands, suggesting that some compositional modification of river sands by shelf processes.