Tracking sediment input of the Tully River

Sedimentology and geochemistry of the northern Rockingham Bay area

Marissa Land, BSc Honours student, James Cook University

Recent catchment management strategies aimed at reducing the amount of nutrient and sediment export into inner-shelf marine waters are based on research predominantly gathered from aerial observations and water quality analysis. Little research has focused on the sediment being distributed from rivers and deposited on the seafloor.

This project investigates sediment dispersal and composition in the northern Rockingham Bay area in NE Queensland. There, several rivers, including the Tully River, are contributing siliciclastic material onto the shelf. The aim of the project is to use geochemical, mineralogical and lithological analysis of surficial sediment to outline areas under the influence of high detrital influx from river plumes.

To gain an understanding of the distribution of sediment from the Tully River mouth, samples have been collected along transects extending from the coastline offshore. Changes in the carbonate content and mineralogy of samples will indicate the extent of siliciclastic material transported onto the shelf. Sample grain size and lithological characteristics will establish an understanding of the physical processes that influence the transportation and deposition of terrestrial sediment. Geochemical analyses will be used to identify trace minerals that will fingerprint deposits distributed directly from the Tully River.