Las cuencas Paleógenas en la Cordillera Oriental

DEL PAPA, C.; HONGN, F.; PAYROLA, P.; DO CAMPO, MARGARITA; WHITE, T.; ARAMAYO, A

Aportes Sedimentológicos a la Geología del Noroeste Argentino

Asociación Argentina de sedimentología

Lugar: Salta; Año: 2012; p. 57 - 66

The Paleogene evolution of northwestern Argentina included geodynamical changes from post-rift basins (SantaBárbara 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 ofdebate and ongoing research. The age of these strata are known from mammalian biostratigraphy, and U/Pb radiometricdates from zircons from a volcanic tuff and detrital zircons from sandstones.The Santa Bárbara Subgroup, comprised of the Mealla, Maíz Gordo and Lumbrera Formations, representssedimentation in extended basins with proximal fluvial (conglomeratic to sandy systems) sedimentation grading to finesandyrivers, deltas and lakes in the distal zones. The presence of gleyed paleosols and the primary lacustrine transgressionin 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 post-rift basindeposition (Lumbrera inferior) to the initial stages of contractional foreland basin sedimentation (Lumbrera superior).This change is represented by an omission surface and abrupt changes in the sedimentary facies and related mammalianassociations below and above the surface. The paleontological record allows correlation of the Lumbrera superiorwith 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 becomesan angular unconformity proximal to paleostructures. The foreland basin is comprised of thick wedge-shaped basinsin which a number of discontinuities and syndepositional structures (fan-like strata) display an irregular pattern ofoverlapping sedimentary units. Based on these characteristics we recognize the following sedimentary sequences:LCI, LCII, LCIII, AI and AII, each 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 foreland basin deposits and the syntectonic features in thelower parts of the QLC and Casa Grande Formations indicate that many faults (east and west verging) were activein the Cordillera Oriental during the Eocene. Moreover some paleostructures involve basement suggesting thatdouble vergence and thick-skin tectonics were active during the early stages of foreland evolution.