Biochronology and biostratigraphy of the Uquía Formation (Pliocene-Early Pleistocene, NW of Argentina) and its significance in the Great American Biotic Interchange

REGUERO, M. A., CANDELA, A. M. Y ALONSO, R.E.

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

Elsevier

Año: 2007 vol. 23 p. 1 - 16

0895-9811

The Uquía Formation crops out in the Quebrada de Humahuaca in Jujuy province, Eastern Cordillera, NW Argentina. This unit is composed of a sequence of fluviatile sediments, and water-laid air-fall tuff beds; it is about 250 m thick, and is unconformably overlain by a Pleistocene conglomeradic unit and Quaternary alluvium. The sediments have been folded into a syncline and broken by several faults that generally trends northwest-southeast. Following Castellanos stratigraphy we characterize his three units (Lower, Middle and Upper) of the Uquía Formation. Biochronologically, the Lower Unit is assigned to the late Chapadmalalan, the Middle Unit (“Uquian fauna”) to the late Vorohuean and Sanandresian, and the Upper Unit to the Ensenadan. Biostratigraphic evidence provides calibration of important biochronologic events in the Great American Biotic Interchange (GABI): the first appearances of Erethizon, Hippidion and proboscideans at about 2.5 Ma (late Pliocene) in South America. Geological and paleobiological evidence suggest that during the late Pliocene the area could have been a wide intermountain valley at ~1400-1700 m elevation, with a more humid environment than that of the present-day, and some wet-dry seasonality, that permitted the coexistence of forest and open areas. Uquian mammals also indicate that Northwest Argentina and the Pampean region have represented distinct biogeographical areas since at least the late Pliocene.