Evolución de la Cuenca de Antepaís desde la zona de la Cumbre Calchaquí hasta la Sierra de Santa Bárbara, Eoceno inferior-Mioceno medio, provincia de Salta, Argentina

C.I. GALLI, R.M. HERNÁNDEZ

Abstract


Tertiary foreland basin evolution in northwestern Argentina is addressed in the light of new chronostratigraphic information. We interpret strata from the Lumbrera (II) Fo rmation deposits (the top of the Santa Bárbara Subgroup, Salta Group) to the Angastaco Formation deposits (Payogastilla Group) and its temporal equivalent, the Metán Subgroup (base of Orán Group). Middle Eocene foreland basin development began in response to intense tectonic activity in the west. The triangular-shaped region received ephemeral stream and dry mudflat deposits of the Lumbrera (II) Formation. During the Oligocene stage of tectonic quiescence a lens-shaped basin developed where ephemeral streams, dry mudflats and eolian strata were deposited in the Los Colorados Formation at the base of the Payogastilla Group. The second stage of tectonic activity started in the early to middle Miocene (to 12.5 Ma approximately). This established a foreland basin system in which characteristic wedge top, foredeep, forebulge and backbulge depozones are recognized. In the wedge top depozone (Valle Calchaquí) thick braided stream facies accumulated in the lower and middle section of the A n gastaco Fo rmation in the Payogastilla Group. In the foredeep depozone, proximal, medial and distal ephemeral stream and play a lake strata of the Río Seco and the Anta formations (Metán Subgroup) were deposited. The middle Miocene was tectonically quiescent. Eastward progradation of proximal facies continued in the wedge top, foredeep, forebulge and backbulge depozones. These deposits constitute the upper portion of the Angastaco Formation and ephemeral systems of the Jesús María Formation (the top of Metán Subgroup).

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