Climatic and tectonic implications of the late Miocene Jakokkota flora, Bolivian Altiplano

When compared to a database of modern foliar physiognomy and climate, the p hysiognomy of a new collection of dicotyledonous leaves from the 10.66 +/- 0.06 Ma Jakokkota flora, Bolivian Altiplano, implies a mean annual temperat ure (MAT) of 18.6-21.0 +/- 2.5 degrees C. Similarly, a literature-derived s ample of the early-middle Miocene Potosi flora, Cordillera Oriental, implie s a MAT of 21.5-21.7 +/- 2.1 degrees C. We estimate that both floras experi enced a growing season precipitation of 50 +/- 40 cm. The paleoclimate thus appears considerably warmer than the current highland climate, with MATs o f 8-9 degrees C; the paleoprecipitation is indistinguishable from modern le vels. A comparison of the Miocene MATs with the modern MATs, with the effec ts of latitudinal continental drift and global climate change subtracted, s uggests that the Jakokkota flora grew at an elevation of 590-1610 +/- 1000 m, and the Potosi flora grew at an elevation of 0-1320 +/- 1000 m. Both pal eoelevation estimates are significantly lower than the present elevations o f 3940 and 4300 m, respectively, requiring a substantial component of Andea n uplift since 10.7 Ma. This uplift history is consistent with two-stage te ctonic models of Andean orogeny. (C) 1998 Elsevier Science Ltd. All rights reserved.