CUY MINERALOGYIN FLUVIAL SEDIMENTSOF THE COLORADO RIVER, ARGENTINA. THEIR :l.UNERAÃ?OGlCALOOMPOSITIONAND EVOLUTIONIN THE DIRECTION OF TRANSPORT.

Abstract

The clay mineralogy of Colorado River sediments is: smectiteexpansive interlayer 10-14 M, illite, clorite and kaolinite. Marked changes in the relative content of clay minerals have been detected alon,g the Colorado River. Thus, illite is more abundant in the proximal areas while smectite prevails in the medium and distal areas. These changes in the relative amount of clay minerals are thought to be produced by: a) incorporation of smectite altered glass-shards towards the distal sector of the river; b) emichment in smectite downstream due to grain-size sorting of the clay fraction. The provenance of the clay mineral suite is mainly volcanic. The volcaniclastic cainozoic sequences located in the Cordillera de los Andes are the main source rocks, though primar y (juvenile) pyroclastic fall materials are also important toward the medium and distal Colorado River areas. Some policyclic clay minerals from older Colorado River deposits (mesozoic and cainozoic sequences) could be supplied from the valley floor erosion.