Middle Eocene deformation and sedimentation in the Puna-Eastern Cordillera transition (23º–26º S): Inheritance of preexisting anisotropies on the pattern of initial Andean shortening

F. HONGN; C. DEL PAPA; J. POWELL; I. PETRINOVIC; R. MON; V. DERACO

GEOLOGY

Geological Society of America

Año: 2007 vol. 35 p. 271 - 274

0091-7613

The Quebrada Los Colorados Formation, at the north end of Calchaquí Valley, preserves evidence of syndepositional deformation since the Middle Eocene (~40 Ma) that includes (1) an angular unconformable relationship with the Salta Group (Paleogene), (2) internal unconformities, changes in vertical facies succession and provenance, and (3) mammalian fossils (Notoungulates) of Middle Eocene age. The fossil record is correlatable to the Casa Grande Formation that also unconformably overlies the Salta Group, so that both units record Middle Eocene deformation along the Puna eastern border outlining previous first-order mechanic anisotropies related to the Cretaceous rift basin border. Along the Puna western margin, Eocene deformation coincides with thermal (magmatic arc) and mechanical (basin inversion) anisotropies. Thus, the distribution of Eocene deformation defines an irregular pattern instead of systematic eastwards propagation as a consequence of the heritage of preexisting heterogenities.