TESTING SIMILARITIES BETWEEN MODERN AND ANCIENT DRAINAGE DIVIDES IN THE CANADIAN ROCKY MOUNTAINS

In orogenic systems, the position and mobility of drainage divides through time impacts sediment transport, exhumation, and basin evolution. In some cases, the uplifted fold-thrust belt serves as the drainage divide, preventing fluvial transport of magmatic arc zircons to the foreland. Jurassic through Paleocene strata of the Canadian Alberta foreland basin provide a record of tectonic and climatic conditions throughout orogenic evolution, but critical questions remain regarding the location of the drainage divide through time. Previous detrital zircon U-Pb provenance analysis of Alberta foreland strata shows a shift from diverse recycled sources in Jurassic through Lower Cretaceous strata, to age spectra with abundant <250 Ma zircons in Upper Cretaceous through Paleocene strata. The significant volume of near-depositional age zircons requires either extensive air fall ash transport, consistent with a drainage divide located in the Omineca magmatic and metamorphic belt, and/or drainage divide migration west into the Intermontane Superterrane, which would allow for cross-Cordilleran fluvial transport. Here we report new detrital zircon U-Pb geochronology ages from 8 modern river sand samples collected along a north-south transect in Alberta from Calgary to Grande Cache. We compare our results with published geochronologic datasets on Jurassic-Paleocene units to test which age populations are explained by the modern drainage divide and to clarify source-to-sink dynamics.