Composición de los agregados no dispersables de sedimentos pampeanos

Dispersion by conventional treatrnents for grain-size analysis do not work efficiently when used in Pampean sediments modified either by pedogenesis or groundwater circulation. Although aggregation decreases when free Fe oxides are removed, most of the sedirnent remains aggregated by a Si-Al rich cement which forms sand size nodules made up of smaller size particles. Total dispersion of samples is obtained with a 0,5 M NaOH dispersing agent on a hot plate. This produces the remo val of amorphous and poorly crystallized aluminosilicate cements. However, trus procedure is not generally used due lo lhe high alkali-sample ratio required. The origin of silica cement found in nodules is probably related to Si02 leaching during pedogenesis.