Paleoambientes y estratigrafía secuencial de depósitos marinos marginales del Ordovícico de la sierra de Zapla (sierras Subandinas, noroeste argentino) y su relación con la Cuenca Andina Central

Biostratigraphy and paleoenvironmental characterization of the Middle Ordovician from the Sierras Subandinas (NW Argentina) based on organic-walled microfossils and sequence stratigraphy

“…This unit contains the only truly marine shelly fauna concentrated in few storm beds above the fine-grained interval that characterizes a maximum flooding stage. This interval is the only one that can be positively correlated with sections in the Cordillera Oriental to the west (base of Santa Gertrudis Formation and Sepulturas Formation) and Bolivia (Anzaldo and Coroico Formations) (Astini, 2003;Astini et al, 2003;Astini and Marengo, 2006). Albanesi et al (2007) have recently confirmed an age not younger than late Darriwilian for the upper section of the Capillas Formation, based on its conodont fauna.…”

“…Thus, the boundary between them is interpreted as a major sequence boundary recording bypassing and later retrogressive stacking representing a typical transgressive systems tract. Development of surfaces with dense vertical millimeter to centimeter-scale in diameter Skolithos-like forms filled with very mature coarse sandstones are interpreted as representing Glossifungites ichnofacies (Astini and Marengo, 2006), typically indicating firm-ground development and by-pass erosion and filling contemporaneous with interfluves exposure and previous to subaqueous reworking during advancing ravinement surfaces (e.g., McEachern and Pemberton, 1992;McEachern et al, 1999).…”

“…Present-day knowledge allows refinement of the formerly suggested foreland systems model that considered sedimentary dispersal to the foredeep largely derived from the western Puna arc (Bahlburg and Furlong, 1996). There is now enough evidence to support a doubly feed system with an extremely important input from the east, related to major deltaic complexes sourced from the craton (Astini and Marengo, 2006) that accounted for additional loading and active flexure within the back-bulge depozone (Fig. 2).…”

“…4). This gray to greenish color unit shows stacking patterns of meter-scale amalgamated sandy beds with superbly recorded tidal bundling, frequent reactivation surfaces with mud drapes and mud couplets suggesting strong tidal influence (Astini and Marengo, 2006), alternating with thoroughly bioturbated muddy packages. Sandy fluvial to tide-dominated estuarine fills and subtidal heterolithic intervals are interpreted for the Lagunilla Member that distinctly overlie the subaerially exposed Laja Morada Member.…”

“…After the amalgamation of Gondwana, continuous subduction took place along the Proto-Andean margin, partly responsible for development of wide retroforeland basins (Astini, 2003;Astini and Marengo, 2006), part of which have been considered "pericratonal areas" within South America (cf. Harrington, 1962).…”