Paleotemperature Estimates of Paleoelevation: Factors That Affect Resolution
The elevation of mountain belts and high plateaus is the consequence of a complex interplay between tectonics, climate, and topography and is a first-order expression of the thickness, temperature, and strength of the lithosphere. Topography directly affects atmospheric circulation and climate through determination of weather tracks, position of stationary planetary waves, distribution of precipitation, and surface temperature. Isotopic proxies, fossils, and climate-model results, indicate that paleotopography has had profound influence on climate dynamics and paleoecological gradients in numerous settings and at different times in geological history. Presently, the only direct proxy for paleoelevation prior to about 15 Ma is paleotemperature derived from paleothermometers including fossil leaves, isotopes, and lipid-based proxies. These methods estimate atmospheric and soil mean annual temperature (MAT); paleoelevation is then determined by applying a temperature-elevation lapse rate to the difference in MAT between synlatitudinal sites where the calibration site is at or near sea level. Resolution in these paleoelevation estimates relies on four factors: error in the paleothermometers, behavior of the modern and in turn the paleo-continental surface temperature field, geochronological resolution, and availability and choice of testable settings. Of these, work has primarily focused on accurately quantifying and reducing the error in paleotemperature estimates; however, the remaining three factors significantly degrade the accuracy of paleoelevation estimates by introducing unrecognized micro- and long-term climate variation and assuming meridional and/or zonal temperature and isotope gradients. The result is poor characterization of the variance in temperature and thus paleoelevation estimates. As such, the resolution of paleoelevation can be greatly improved by 1) sampling multiple sites in proximal, contemporaneous or temporally constrained, synlatitudinal basins; 2) characterizing zonal and meridional modern and paleo-temperature and/or isotope gradients; and 3) applying multiple proxies to the same setting. Application of these guidelines is leading to new estimates of local Laramide relief in Western Interior of North America during the Paleogene and a better understanding of terrestrial temperature curves through the Cenozoic.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009