Middle to late Miocene environments of southern Ecuador: Temperature, elevation, and fossil plants of the Nabon Basin

Paleobotanical methods are used to document changes in temperature and elevation that have occurred in northern South America during the uplift of the Andes. The leaf morphology of the fossil flora of the Nabón Basin, located in southern Ecuador, is used to estimate the Middle to Late Miocene temperature and elevation of the basin. Seventeen published equations of paleotemperature estimation are tested on 30 modern neotropical floras to determine which equation should be used to estimate paleotemperature of the Nabón Basin. None of the published equations accurately estimates the temperature of low-temperature, high-elevation neotropical sites, suggesting that temperature of these sites would be more accurately predicted by an equation that has incorporated data from such sites. Leaf morphology and temperature data from 43 modern neotropical sites, including several with low temperature and high elevation, are used to calculate a multiple linear regression equation suitable for estimating the paleotemperatures of fossil sites deposited at a range of elevations and precipitation regimes in northern South America. Paleotemperature is estimated for four stratigraphic levels in the Nabón Basin using this regression equation. Paleotemperature of the basin decreased from 21.9° ± 5.4°C to 16.0° ± 5.5°C between 12.0 and 11.2 Ma. Elevation is estimated using a lapse rate calculated from temperature and elevation data from 467 modern neotropical sites. Estimated paleoelevation increased from 885 ± 1089 m to 1968 ± 1106 m in the Nabón Basin. This elevation change reflects a surface uplift rate of 1.35 mm/yr ± 2.75 mm/yr to 2.71 mm/yr ± 5.49 mm/yr over 0.4 to 0.8 Ma. Uplift rate calculated since basin deposition, based on a change in elevation of 1578 m, is 0.14 ± 0.10 mm/yr. Four new fossil plant species are described, extending the known Miocene geographic ranges of two common modern South American genera into Ecuador for the first time, and the temporal range of another genus to the Miocene in South America.