CONSTRAINING THE EFFECTS OF DYNAMIC TOPOGRAPHY IN THE LATE CRETACEOUS CORDILLERAN FORELAND BASIN THROUGH 3D FLEXURAL BACKSTRIPPING

Mantle-induced dynamic topography (i.e., subsidence and uplift) has been increasingly recognized as an important process in retroarc foreland basins. However, characterizing and distinguishing the effects (i.e., location, extent, and magnitude) of dynamic topography in ancient foreland basins remains challenging because the spatio-temporal footprint of dynamic topography and flexural topography (i.e., generated by topographic loading) can overlap. This study employs 3D flexural backstripping of Upper Cretaceous strata in the central part of the North American Cordilleran foreland basin (CFB) to better constrain the effects of dynamic topography. The extensive stratigraphic database and good age control of the CFB permit the regional application of 3D flexural backstripping in this basin for the first time.

Dynamic topography started to influence the development of the CFB during 90-80 Ma and became the dominant subsidence mechanism during 80-75 Ma. The extent of dynamic subsidence is approximately 400 by 500 km, within which significant dynamic subsidence (> 200 m) occurs in an irregular-shaped (i.e., lunate) subregion (~ 450 by 150 km). The maximum magnitude of dynamic subsidence is up to 300±100 m. With the maximum magnitude of dynamic uplift being constrained to be 200-300 m, the gross amount of dynamic topography in the Late Cretaceous CFB is 500-600 m. Although the location of dynamic subsidence revealed by tectonic subsidence maps is generally consistent with isopach map trends, tectonic subsidence maps developed through 3D flexural backstripping provide more accurate constraints of the areal extent, magnitude, and rate of dynamic topography (as well as flexural subsidence) in the CFB through the Late Cretaceous. This improved understanding of dynamic topography in the CFB is critical for refining current geodynamic models of foreland basins and understanding the surface expression of mantle processes.