Quaternary Deformation around the Palo Negro area, Pampa Norte, Argentina.

BRUNETTO, E; IRIONDO, M; ZAMBONI, L.; GOTTARDI, M.G.

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

ELSEVIER

Lugar: Amsterdam; Año: 2009

0895-9811

The Pampa Norte region is a great plain characterized by low slopes and accumulation of hundreds of meters thick loose sediments. A main high morphostructure denominated San Guillermo block stands out in the central plain, being its western boundary the Tostado-Selva scarp. It is located in an intraplate setting characterized by low tectonic activity. However recent uplift can be inferred by means of terrain analysis and the sedimentology of the Palo Negro Formation. Pond deposits (Palo Negro Formation) observed in the scarp suggest topographic inversion during the Late Quaternary, in the Palo Negro area. The morphology indicates that the deformation was widely distributed in surface forming a gentle (circa 5 m amplitude and 13 km wavelength) asymmetric fold. Low sinuosity lineaments located in the base of the scarp, coincident with knick points in the topographic profile, can be interpreted as the projection of tip lines by high-angle fault-propagation. This geometry is compatible with a reverse kinematics on blind faults. A deformation style by reactivation of pre-existing faults is consistent with structural observations due to both seismic reflectors suggest presence of Cretaceous high-angle normal faults and the orientation of lineaments is similar to the orientation of the graben systems and transversal accommodation zones originated during the opening of South Atlantic Ocean. One OSL dating of 67,4 ± 5,1 kyrs. B.P. (from Palo Negro Formation supposed as deposited on a flat plain floor) and a height difference of 9.5 m measured in the Tostado-Selva scarp account for an averaged uplift rate of 0.14 mm/years.