New Zealand Journal of Marine and Freshwater Research abstracts
Sediment texture of the continental shelf and upper slope off the west coast of South Island, New Zealand
P. K. PROBERT K. M. SWANSON
New Zealand Oceanographic Institute Division of Marine and Freshwater Science Department of Scientific and Industrial Research P. O. Box 12-346, Wellington North New Zealand
Department of Geology University of Canterbury Private Bag, Christchurch 1 New Zealand
Abstract
Surface sediments on the continental shelf and upper slope off the west coast of the South Island, New Zealand, from north of Karamea Bight (40°45'S) to the Whataroa River mouth (43°07'S) consist almost entirely of sands and muds. Inshore (< 50 m depth) sediment is predominantly fine sand to coarse silt. Silt-clay content increases towards mid-shelf depths, and areas of mud occur at depths of about 90-140 m. Sediments tend to become coarser again on the outer shelf, and sandy mud or muddy sand covers the outer shelf and upper slope. The west coast shelf experiences a high input of fluvial sediment, probably c. 12-26 X 10
6 tonnes y~' for the study area. Sedimentation rate on the shelf is estimated to average at least 1-2 mm
y-1. Sedimentation is probably appreciably lower than this in the north of the area and higher in the south, and this is reflected in shelf grain-size parameters and sediment carbonate content. There are north-to-south decreases in mean grain size and in the ranges of sorting and skewness: shelf sediments tend to become finer and more uniform in texture towards the south. Carbonate content ranges from 0-70%, generally increasing with depth, but with a marked north-south contrast. In the north, carbonate values increase to c. 15% by 200 m depth and to 60-70% by 650-700 m, whereas off the southernmost transect, carbonate values are < 5% by 500 m and reach only c. 40% by 1100 m. Shelf and upper-slope sediments (<935 m) contain lig-nin (mostly at levels of < 5 mggdry sediment')* also indicating an input of land-derived material.
Keywords Tasman Sea; New Zealand; South Island; west coast; continental shelf; continental slope; sediments; grain-size parameters; carbonate; lignin; river discharge; sedimentation
New Zealand Journal of Marine and Freshwater Research, 1985, Vol. 19: 563-573 Received 2 August 1984; accepted 24 April 1985
PDF file of entire paper: medium quality (883K); (scanned from paper original: notes about this process)
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