AVULSIONS AND ALLUVIAL RIDGE EVOLUTION DISPLAYED ON THE TAQUARI RIVER DFS, PANTANAL BASIN, BRAZIL

Based on a time series of satellite images from the Taquari distributive fluvial system (DFS) in the Pantanal Basin, Brazil, we hypothesize that progradational avulsions form a significant portion of an alluvial ridge deposit and that depositional zones can be delineated as the avulsion forms into a new alluvial ridge that progrades down-DFS. The Coronal avulsion of the Taquari River has been ongoing since the 1970s, with most of the activity occurring since 1996. As of July 2010, the imagery shows that the avulsion is not yet complete, with discharge being routed to both the parent channel and the avulsion channels in the floodbasin. The avulsion was initiated as flow was diverted from the parent channel to the northern floodbasin through two small crevasses, allowing the development and evolution of splays, with a single splay stabilizing only since 1999. The avulsion area is marked by the growth of new splays, the formation of an avulsion belt, and progradation of avulsion deposits into the floodbasin. As reported for the Saskatchewan River avulsion in the Cumberland Marshes, the avulsion channels on the Taquari system are beginning to coalesce to form a single meandering channel with levees. The avulsion belt can be divided into zones that migrate down-DFS with time. The most proximal zone consists of a new meanderbelt with developing levees. Downstream from this zone, multiple avulsion channels cross a raised ridge formed by rapid sedimentation on the avulsion lobe. Distally on the avulsion lobe, these avulsion channels bifurcate into many smaller channels that are surrounded by low levees and floodbasin deposits. Beyond the avulsion lobe, the DFS remains flooded and floodbasin deposits dominate with few channels crossing this zone. The parent channel of the Taquari displays similar zones, however since this river position has been at its present location for some time, these zones are located distally on the DFS.