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Revista de la Asociación Argentina de Sedimentología

versión impresa ISSN 1853-6360


MURUAGA, Claudia M. Petrography and provenance of tertiary sandstones in the Subbasin of Hualfín, Catamarca province, northwestern Argentina. Rev. Asoc. Argent. Sedimentol. [online]. 2001, vol.8, n.2, pp.15-35. ISSN 1853-6360.

This paper documents the sandstone composition and provenance of the tertiary succession in a study area located at Northwestern Pampean Ranges. The stratigraphic succession, in the southwestern part of the Santa Maria- Hualfin Basin (Bossi et al. 1997), is about 3000 m thick (Fig. 1). It is mainly formed of volcaniclastic fluvial sediments, belonging to the Hualfin Formation (Lower Cretaceous) and Santa Maria Group (Galván y Ruiz Huidobro, 1965; Bossi y Palma, 1982; Bossi et al., 1987, Middle Miocene to Upper Pliocene). This group is composed by four formations (from the base to the top): Las Arcas, Chiquimil (divided in three members: Los Baños, El Áspero y El Jarillal), Andalhuala and Corral Quemado. The crystalline basement is composed of low-grade metamorphic rocks (Loma Corral Formation) intruded by the ortogneis of Chango Real Formation. Hualfin Formation is composed of fine sandstones with few massive conglomerates lens and shales, with a high diagenetic grade. The Tertiary sediments consist of sandstones with interbedded shales of Las Arcas Formation and sandstones with interbedded conglomerate levels in Los Baños Member of Chiquimil Formation. The regional volcanic event is mainly represented by 200m thick of volcaniclastic conglomerates belonging to El Áspero Member (Bossi et al., 1987), which has andesitic lavas in its middle section. The proportion of the conglomerates increases steadily until they become dominant (Corral Quemado Formation), in the upper part of the succession. The samples from two detail stratigraphic sections were studied: one close to the Villavil village (3,500 m thick) and the other, toward the north side of El Durazno Range (2,300m thick). Lacustrine and fluvial axial deposits in the Villavil section represent distal facies assemblages. On the other hand, the stratigraphic section at the El Durazno Range shows proximal facies assemblages represented by alluvial fan deposits. The composition and petrography of 71 selected samples of fine and medium sandstones were studied using conventional petrographic, X-ray diffraction and SEM techniques. The variation range of the modal composition is moderate and supports the representative value of the selected samples. The modal composition and detritic modes (Table 1 y 2) were determined with 400-500 point counts in blue resine impregnated thin sections. Rock fragments are the main components of the sandstones as framework grains, although quartz proportion is dominant in the lowest part of the Villavil section and almost all succession in El Durazno section. Andesine (An34 - An50) is the principal feldspar and the K-feldspar is always a minor component. Andesitic volcanic, high and low grade metamorphic and, minor sedimentary rock fragments have been identified. The volcanic fragments are divided in four types: Lv1, holocrystalline porfiric texture with euhedral to subhedral plagioclase laths in some felted microlite groundmass; Lv2, microgranular felsitic texture, with quartz and feldspar crystals; Lv3, hyalocrystalline porfiric texture, lathwork plagioclase, crowded of opaque minerals (the groundmass are kaolinized and oxidized) and Lv4, represented by kaolinized pyroclastic fragments. Accessory minerals are biotite, muscovite, pyroxenes, amphiboles, zircon, tourmaline epidote and opaque minerals. Rare components are apatite, granate and staurolite. The detrital silty matrix (less than 12 %) is composed of monocrystalline quartz, feldspar and opaque minerals. Clay and calcite cements can be observed in many thin sections. Some samples show low proportion of iron oxide and zeolitic cement. The analysis of argillaceous cements, through X-ray diffraction and SEM, indicate that they are composed of smectite and illite, with minor amounts of chlorite and pore pockets filled with kaolinite "booklets". Interbedded shales have been analyzed by X-diffraction and show similar mineralogical composition to the argillaceous cements. The Hualfin depocenter is part of the Santa Maria-Hualfin Basin, defined as a intracratonic basin, with an hemigraben configuration at both sides of the basin, where two tectonic stages were defined (Muruaga, 1998; Bossi et al. 1999, 2000; Muruaga y Bossi, 1999). Stratigraphic and areal variations of the detrital modes allow to infer compositional changes and tendencies in provenance areas and characterize the source area during Tertiary. These variations show the different tectosedimentary stages in the evolution of the basin. However, the plotted data in Dickinson diagrams (1979, 1983, 1985; QFL and QmFLt, Figs. 3 y 4) showed an evolution from recycled orogen to magmatic arc, as a general trend. The Villavil section showed a compositional evolution from continental block provenance for the samples of the lower units to the magmatic arc in the Los Baños Member. El Áspero Member marks the maximun volcanic supply to the basin. Then, there was a new displacement to the basement block provenance, coincident with the first raising of the source area (QmPK diagram, Fig. 5a). Again, the El Durazno section shows the same evolution, but with a more quartzitic composition and the enrichment of K-feldspar with the stratigraphic trend (Fig.6a). This is coincident with the closer provenance area, proximal sedimentary facies and granitic gneiss source rock. Combined studies of sedimentary facies, dispersal patterns (Fig. 2, Table 3) and petrologic parameters of the Miocene sandstones suggest a provenance from the northern and western margins of the Hualfin basin. The present Altohuasi- Culampajá Ranges and Papachacra Range were the source area to the sedimentary rocks in the basin.

Palabras clave : Petrografía sedimentaria; Procedencia; Areniscas; Neógeno.

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