ORGANIC DEPOSITS ASSOCIATED WITH AN AVULSION BELT, FORMING IN THE CUMBERLAND MARSHES OF SASKATCHEWAN, CANADA

The Cumberland Marshes are located in east-central Saskatchewan, Canada and have an area of 5000 km2. The region consists of different types of fluvial features: old and new channel systems, meandering channels, levees, marshes, lakes, bogs, floodplains, crevasse splays. Before its most recent avulsion, which began in the 1870s, the Saskatchewan River had a single channel. The avulsion caused the Saskatchewan River to change its course northward and an avulsion belt was formed. The avulsion belt is unstable, with frequent channel switching and sediment deposition. Organic-rich materials are known to be deposited on river floodplains; they need a stable setting to form without sediment-input. The objective of this research is to locate and study the accumulation and preservation of organic material on floodplains in a modern avulsive river systems in the Cumberland Marshes, Saskatchewan, Canada. We predicted that organic deposits are formed only in stable areas, which are located outside the avulsion belt. Also, we predicted that the accumulation of organic materials is greatest on parts of floodplains that are distal to active river channels. Samples were taken using a gouge auger from six different floodplains inside and outside the avulsion belt. Using the loss-on-ignition method, total organic content (TOC) was determined for all samples. The results show that organic deposits are formed within and outside the avulsion belt, which is not consistent with our first prediction. However, our second prediction is confirmed; results indicate that organic deposits with greater TOC are farther away from the active river channels.