Input of river-derived sediment to the New Zealand continental shelf: II mineralogy and composition
- Author
- G.J. Churchman, J.L. Hunt, G.P. Glasby, R.M. Renner, G.A. Griffiths
- Year
- 1988
- Journal / Source
- Estuarine, Coastal and Shelf Science
- Volume
- 27
- Number
- 4
- Pages
- 397-411
- Summary
- Clay mineralogies and elemental compositions of river-borne sediments from New Zealand were examined as indicators of likely sources of the lithogenous component of sediments on the continental shelf. Relative occurrences of kaolin and smectite enabled the rivers to be fitted into three main groups. These correspond closely with geography as follows: (1) most of the rivers from North Island; (2) all the rivers from the north-east coast of South Island; (3) most of the rivers from the remainder of South Island. Elemental analyses of their sediments also led to a geographical grouping of rivers. Six main groups resulted from a Q-mode cluster analysis of elemental compositions. These were: the northernmost river (Wairoa River); the east coast of North Island; the west coast of North Island; the east coast of South Island; the south-east and west coasts of South Island; the west coast of South Island. There is substantial overlap between the groupings by clay mineralogy and by composition. The results can be interpreted mainly in terms of the geologies of source areas. Exceptions to regional trends reflect either an unusual geology in the source areas or low sediment loads, where soils contribute significantly to the sediments. The terrigenous component of offshore sediments and New Zealand riverine sediments have similar compositions, suggesting that the former are derived in a relatively unmodified form from riverine sediments.