Quaternary deformation around the Palo Negro area, Pampa Norte, Argentina

BRUNETTO, ERNESTO; IRIONDO, MARTÍN; ZAMBONI, LUIS; GOTTARDI MARÍA GRISELDA

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Oxford; Año: 2010 vol. 29 p. 627 - 641

0895-9811

The Pampa Norte region is a great plain characterized by low slopes and accumulation of hundreds of meters of thick loose sediments. A high morphostructure denominated San Guillermo block stands out in the central plain, the Tostado–Selva scarp forming its western boundary. It is located in an intra plate setting characterized by low tectonic activity. However recent uplift can be inferred by means of terrain analysis and the sedimentology of the Palo Negr o Fm. Pond deposits (Palo Negro Fm.) observ ed in the scarp suggest topographic inversion during the Late Quaternary in the Palo Negro area. The morphology indicates that the deformation was widely distributed, forming a gentle (ca. 5 m amplitude and 13 km wavelength) asymmetric fold. Low sinuosity lineaments located in the base of the scarp, coinciden t 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 reverse kinematics on blind faults.A deformation style with reactivation of pre-existing faults is consistent with structural observations. Seismic reflect ors suggest the presence of Cretaceous high-angle normal faults, and the orientation of lineaments is similar to the orientation of the graben systems and transverse accommodation zones originated during the opening of the South Atlantic Ocean.One OSL dating of 67.4 ± 5.1 kyr B.P (from Palo Negro Fm. supposed as deposited on a flat plain floor) and a height differenc e of 9.5 m measured in the Tostado–Selva scarp account for an averaged uplift rate of 0.14 mm/year.