Spatial-temporal changes in Andean plateau climate and elevation from stable isotopes of mammal teeth

Paleoelevation constraints from fossil leaf physiognomy and stable isotopes of sedimentary carbonate suggest that significant surface uplift of the northern Andean plateau, on the order of 2.5 +/- 1 km, occurred between similar to 10.3 and 6.4 Ma. Independent spatial and temporal constraints on paleoelevation and paleoclimate of both the northern and southern plateau are important for understanding the distribution of rapid surface uplift and its relation to climate evolution across the plateau. This study focuses on teeth from modern and extinct mammal taxa (including notoungulates, pyrotheres, and litopterns) spanning similar to 29 Ma to present, collected from the Altiplano and Eastern Cordillera of Bolivia (16.2 degrees S to 21.4 degrees S), and lowland Brazil. Tooth enamel of large, water-dependent mammals preserves a record of surface water isotopes and the type of plants that animals ingested while their teeth were mineralizing. Previous studies have shown that the delta O-18 of modern precipitation and surface waters decrease systematically with increasing elevations across the central Andes. Our results from high elevation sites between 3600 and 4100 on show substantially more positive delta O-18 values for late Oligocene tooth samples compared to <10 Ma tooth delta O-18 values. Late Oligocene teeth collected from low elevation sites in southeast Brazil show delta O-18 values similar (within 2 parts per thousand) to contemporaneous teeth collected at high elevation in the Eastern Cordillera. This affirms that the Andean plateau was at a very low elevation during the late Oligocene. Late Oligocene teeth from the northern Eastern Cordillera also yield consistent delta C-13 values of about -9 parts per thousand, indicating that the environment was semi-arid at that time. Latitudinal gradients in delta O-18 values of late Miocene to Pliocene fossil teeth are similar to modern values for large mammals, suggesting that by similar to 8 Ma in the northern Altiplano and by similar to 3.6 Ma in the southern Altiplano, both regions had reached high elevation and established a latitudinal rainfall gradient similar to modern. (C) 2009 Elsevier B.V. All rights reserved.