Geology of the Pantanal

To the North and East of the Pantanal lies the Central Brazilian shield, one of the oldest continental land masses on Earth. To the West lies the Andes mountains, a much more recent formation. Before the Andes, the Pantanal existed for a long time at the edge of the South American continent, as a coastal plain that was formed by the erosion of material from high parts of the Central Brazilian shield to lower parts. Then with the subduction of the Pacific plate underneath South America, the Andes formed and the Paraná Basin (containing the Pantanal) became a low point between two higher mountainous regions of igneous formation. The top several hundred meters of the Pantanal are sedimentary deposits carried down from the surrounding mountains over millions of years.

In recent geologic history, the Pantanal has undergone many changes; before the seasonal wetland it was today, the region used to be a desert, and before that, people have hypothesized that it was an inland brackish lagoon draining into the Pacific Ocean. 

-Palani