Asociaciones mineralógicas de las arcilla en la cuenca Ischigualasto-Ischichuca.: Parte I: Perfiles de La Torre

• Gerardo E. Bossi ^[1]
  1. [1] Fundación e Instituto Miguel Lillo
• Localización: Acta geológica lilloana, ISSN-e 0567-7513, Vol. 11, Nº 1 (Texto completo no disponible), 1970, págs. 1-26
• Idioma: español
• Texto completo no disponible (Saber más ...)
• Resumen

  • Clay mineral assemblages from continentalPermian and Triassic formations of La Torre, La Rioja;Argentin, are described. Each formation is characterized on the basis of paticular clay mineral assemblages. Depositional environments and paleoclimates are discus sed after making combined analyses of clay mineral assemblages, sedimentary features, and provenance.

    These clay minerals have been studied with X-ray and spectrochemical anaysis. Cation saturations with Li*, K*, Na*, NH4 and Mg** combined with glycerol solbation and heating at various temperatures,have been used for identification.

    The stratigraphic sequence consists in four sedimentary formations: Talampaya (Permian?), Tarjados (Triassic?), Lomas blancas (Triassic) and Río Chiflón (Triassic), from older to younger. Paleocurrent and minerlaogical analyses of the sandstones indicate that these formation, mostly fluvial, have been derived from crystalline granitic rocks of possible Precambrian age located toward the east, and southeast. Part of the material have been derived from volcanic sources in the west side of the basin.

    Talampay and Tarjados Formations are red non cyclical sandstones facies; the first one is characterized by a kaolinite (60%)-illite assembalage, and the second by a montmorillonite (60-95%)-illite-beidellite assemblage. The monstmorillonite is mainlly of the high charge variety.

    Lomas Blancas and ÇRío Chiflón Formation are fluvial facies with well developed cyclothems. the first one is characterized by a strong segregation of the clay mineralogy betwwen the sandstones and the dark bituminous shales intercalated. Beidellite and mont morillonite occur mainly in the fine sediments while illite, kaolinite and mixed layers illite-smectite in the sandstones lithotopes. Río chiflón Formation has a complex clay mineral assemblages. Kaolinite wich is important in the previous formation is minor or lacking. Montmorillonite (partially chloritized), beidellite, dioctahedral vermiculite, beidellite, illite and dioctahedral chlorite are the main minerals. The chloritized montmorillonite and vermiculite occur in separated assemblages. They seem to be soil or diagenetic transformations of hugh charged montmoriollonite.

    Hot climates alternating dry and humid seasons could esplain most of the mineralogic and sedimentological character of the stratigraphic sequence.