CETMIC   05378
CENTRO DE TECNOLOGIA DE RECURSOS MINERALES Y CERAMICA
Unidad Ejecutora - UE
artículos
Título:
COMPOSITION AND DIAGENETIC PROCESSES OF SANDSTONE AND TUFF DEPOSITS OF THE CENOMANIAN CARDIEL FORMATION, CARDIEL LAKE AREA, PROVINCE OF SANTA CRUZ.
Autor/es:
RENATO R. ANDREIS, PATRICIA E. ZALBA AND MARTÍN E. MOROSI
Revista:
Revista de la Asociacion Geologica Argentina
Editorial:
Asociacion Geologica Argentina
Referencias:
Lugar: Buenos Aires; Año: 2006
ISSN:
0004-4822
Resumen:
The Cardiel Formation (Cenomanian), around 200 m in thickness in the
studied area, includes different types of volcaniclastic deposits, mainly
represented by fine tuffs and massive bentonites, and subordinated epiclastics
such as lithic sandstones of yellowish-brown, dusky yellow, or light olive
hues, siltstones and claystones. Reddened paleosols with some small axial roots
and weak prismatic structures appear on top of siltstones, tuffs and
bentonites. Tufites and tuffs contain the same neovolcanic components, abundant
glass shards and minor pumices. Different types of glass shards can be
differentiated whitin this unit, whereas pumice fragments are represented by
different vesicular varieties. Vitreous tuffaceous clasts are abundant in the
tufites. Almost all samples contain not only diagenetically-derived, but also
pedogenetically-infiltrated montmorillonite, as well as zeolites. Predominant
Ca-Na-K clinoptilolite (Si/Al>4) and minor analcime (Si/Al near 3) were identified.
Smectite and clinoptilolite may either replace glass-shards or pumices, or fill
pore spaces, whereas smectite also appears as thin cutans. The sequence of
diagenetic processes includes the conversion (hydrolysis) of glass to smectite,
and later to zeolites. Furthermore, zeolites preceded calcite growth (sometimes
replacing glass-shards or pumices), which in turn, formed prior to pervading
ferric oxides-hydroxides. The vertical distribution of zeolites can be explained
taking into account the presence of percolating waters in an open hydrologic
system. The zeolite content throughout the whole profile links the
mineralogical association observed within the sediments of the Cardiel
Formation to the clinoptilolite zone. Paleoenvironmental reconstructions for
the Cardiel Formation point out to tidal currents taking place in wide lagoons;
tuffaceous and bentonitic deposits covered those ancient lagoons forming wide,
flat plains on which paleosols developed. Paleocurrents measured on sandstone
beds indicate main sediment transport directions towards the north, northeast,
and less frequently to the southwest. The abundance of glass shards thorough
this unit indicates a magmatic origin related to the volcanoes situated along
the Andean Mountains possibly associated with
alternating plinian and subplinian eruptions with brief phreato-plinian
processes.