9317078 Gregory The history of Andean uplift is of great interest to both climatic and tectonic studies. The Andes form the only major barrier to zonal atmospheric circulation in the southern hemisphere and they extend throughout the tropics, a sensitive zone where small changes in climate impact on a global scale. In terms of tectonics, the Andes are one of the few modern examples of an ocean-continent subduction zone with associated crustal deformation. As of now, the development of Andean elevation is poorly constrained. The objective of this study is to estimate the paleoclimate and paleoelevation of late Tertiary floras from the Bolivian Altiplano using a new leaf physiognomy-based method. An existing multiple regression model explains 93.3% of the variance in mean annual temperature (MAT) using leaf physiognomy of modern vegetation. This model will be updated by adding sites from modern tropical forests. A new MAT-leaf physiognomy relationship will be derived and will be used to estimate the paleoMAT of the samples from the Bolivian sites. When combined with coeval sea level temperature and terrestrial lapse rate, the paleoMAT data from the Altiplano can be used to estimate paleoelevation. These estimates of paleoclimate and paleoelevation will address the following climatically and tectonically important questions: 1) As the only barrier to circulation in the southern hemisphere, how did uplift of the Andes impact global circulation, especially in terms of the production of water vapor? Could Andean uplift have been partly responsible for late Tertiary global cooling? 2) Did the uplift of the Andes predate or postdate the desiccation of the Altiplano? Was this desiccation a function of the elevation of the Andes, or of global climate changes? 3) How do botanically derived estimates of Oligocene-Miocene tropical paleoclimate compare with those from general circulation model (GCM) climate reconstructions? 4) Was uplift of the Bolivian Altipla no coincident with crustal shortening or did elevation develop in the late Miocene-Pliocene?
