Las cuencas paleógenas en la Cordillera Oriental

CECILIA DEL PAPA; FERNANDO HONGN; PATRICIO PAYROLA; MARGARITA DO CAMPO; TIMOTHY WHITE; ALEJANDRO ARAMAYO

Relatorio Aportes Sedimentológicos a la Geología del Noroeste Argentino

SCS Publisher

Lugar: Salta; Año: 2012; p. 57 - 66

The Paleogene evolution of northwestern Argentina included geodynamical changes from post-rift basins (Santa Bárbara Subgroup, Salta Group) to the initial stages of a foreland basin (Quebrada de los Colorados Formation – (QLC), Payogastilla Group and Casa Grande Formation). The timing and style of this transformation are a matter of debate and ongoing research. The age of these strata are known from mammalian biostratigraphy, and U/Pb radiometric dates from zircons from a volcanic tuff and detrital zircons from sandstones. The Santa Bárbara Subgroup, comprised of the Mealla, Maíz Gordo and Lumbrera Formations, represents sedimentation in extended basins with proximal fluvial (conglomeratic to sandy systems) sedimentation grading to fine-sandy rivers. The presence of gleyed paleosols and the primary lacustrine transgression in the Maíz Gordo Formation is suggestive of a record of the Initial Eocene Thermal Maximum (IETM).The Lumbrera Formation is notable because it includes the transition from the final stages of the postrift basin deposition (Lumbrera inferior) to the initial stages of the contractional foreland basin (Lumbrera superior). This change is represented by an omission surface and abrupt changes in the sedimentary facies and related mammalian associations below and above this surface. The paleontological record allows correlation of the Lumbrera superior with the Quebrada de los Colorados and Casa Grande Formations of the foreland basin.The contact between the Santa Bárbara Subgroup and the foreland basin units is an unconformity that becomes an angular unconformity proximal to paleostructures. The foreland is compresed of thick wedge-shape basins in which a number of discontinuities and syndepositional structures (fan-like strata) display an irregular pattern of overlapping of the sedimentary units. Based on these characteristics we recognize the following sedimentary sequences: LCI, LCII, LCIII, AI and AII, each of one defined by sedimentary discontinuities. The deposits include floodplain, meandering and coarse braided fluvial, alluvial fans and eolian systems. The angular unconformity between the post-rift and the foreland deposits and the syntectonic features in the lower parts of QLC and Casa Grande Formations indicate that many faults (east and west verging) were active in the Cordillera Oriental during the Eocene. Moreover some paleostructures involve basement suggesting the double vergence and thick-skin tectonics were active during the early stages of foreland evolution.