Orogeny, orography, and the origin of the first rainforests: Paleobotany of the temporally-calibrated synorogenic Denver Basin, Colorado

Denver Museum Of Nature And Science, Denver CO

Investigators

Abstract

OROGENY, OROGRAPHY, AND THE ORIGIN OF THE FIRST RAINFORESTS: PALEOBOTANY OF THE TEMPORALLY-CALLIBRATED SYNOROGENIC DENVER BASIN, COLORADO Kirk Johnson and Robert Raynolds EAR-0345910 ABSTRACT The strata and fossil plants of the time-calibrated Denver Basin provide a unique, natural laboratory in which to evaluate and quantify the influence of regression, orogeny, orography, and extinction on the evolution of ancient ecosystems. Evidence from the basin suggests that the tropical rainforest ecosystem first evolved in areas of extremely high rainfall on the eastern flanks of the uplifting Laramide Front Range in the extraordinarily low biodiversity World that followed the Cretaceous-Tertiary (K-T) cataclysm. This project will test three major hypotheses: 1. Floras and Landscapes: Fossil floras and their proxy climate data can be mapped onto paleogeography and linked to significant environmental events such as the regression of the Western Interior Seaway, the Laramide Orogeny, and the K-T extinction event to provide insight about the evolution of floras, climates, ecosystems and landscapes. 2. Origin of Rainforests: Orographic conditions caused by the Laramide Orogeny and an adjacent seaway resulted in localized high rainfall. These conditions, in the warm but biologically depauperate post-K-T world of the early Paleocene, set the stage for the evolution of tropical rainforest ecosystems. 3. Ghost Canyons and Ancient Fans: Alluvial fans form on the margins of synorogenic basins during times of high relief due to the localization of mountain-sourced river systems into incised valleys. These fans are paleogeomorphic features that controlled ancient vegetation patterns and strongly influence modern day hydrology. This project will integrate research across broad areas of paleontology, geology and hydrology to answer specific questions about biotic evolution and extinction on an evolving synorogenic landscape. This work will also provide data that is directly relevant to the understanding of the distribution and quantity of groundwater resources of the Colorado Front Range.