Sedimentation in the Barinas Basin and Uplift of Merida Andes Venezuela, Constrained by New Temporal Data

Johan P. Erikson, Shari A. Kelley, Matt Heizler, and Peter K. Zeitler

We have obtained two new data sets relevant to temporal evolution of the Barinas and Maracaibo basins and Merida Andes of western Venezuela. Apatite fission-track ages on clasts from the uppermost Parangula and lower Rio Yuca Formations of the Barinas basin date cooling due to uplift and erosion in the Merida Andes (from which the clasts were originally derived) and provide a maximum possible age for these formations. Ages of 11-14 Ma were obtained over ~1100 m of stratigraphic section. Based on these late Middle Miocene ages and the likelihood of a time lag of at least 3 m.y. between apatite cooling and deposition, the uppermost Parangula and lower Rio Yuca Formations are no older than early Late Miocene.

⁴⁰Ar³⁹Ar analyses of potassium feldspar from in situ granite sample yielded regional differences in the ages of rapid cooling associated with early Andean uplift. Rapid cooling and uplift began in several samples in earliest Miocene time. One sample from the southwestern corner of the Merida Andes indicates cooling began in early Late Miocene time.

Combining these results with existing data indicates that early phases of Andean uplift and shortening were older and of larger magnitude than previously recognized. In contrast, Barinas basin orogenic sedimentation began later than generally perceived. Consequently, NW-directed overthrusting on the Maracaibo side of the Merida Andes must have been large in earliest Miocene time. Southeast-directed backthrusting and subsidence of the Barinas basin were delayed until Late Miocene time.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California