The Miocene Albarracín Formation is a 1400-m-thick fluvial and alluvial succession interfingered with significant volcaniclastic deposits. Six fission track ages on zircons from intercalated ignimbrites constrain the age of the succession and allow rates of sediment accumulation and vertical movements in the basin to be estimated. The age of the Albarracín infill ranges from 18.0 ± 2.6 Ma to an extrapolated 7.1 Ma at the top of the preserved sequence. The rates of sediment accumulation increase upwards in the succession varying from less than 0.04 mm/a (18-13.2 Ma) to 0.09 mm/a (13.2-9.1 Ma) and finally to 0.44 mm/a (9.1-8.3 Ma). The onset of the Central Cordillera thrust system is assumed to be at about 8.4 Ma as evidenced by the sudden increase of Precordillera clasts in the conglomerates. A minimum incision rate of 0.14 mm/a is determined for the San Juan River at the front of the Precordillera since 7 Ma to present. © 2001 Elsevier Science Ltd. All rights reserved.

This work was partially funded by projects Grups de Recerca Consolidats (II Pla de Recerca de Catalunya) 1997 SGR 00020 and DGICYT PB98-1189.