Evaluating the Roles of Sediment Supply and Tectonics Using Growth-Strata Analysis, Sequence Stratigraphy, Forward Stratigraphic Modeling and Sediment Volume Calculations: An Example from the Cordilleran Foreland Basin, USA

Although the importance of sediment supply is widely accepted, most studies of the ancient must assume constant supply because it is difficult to quantify or model. Because changes in sediment supply or tectonics can result in similar architectures it is not possible to know the exact stratigraphic response to specific tectonic processes without assessing drivers independently. We present a comprehensive analysis of two contrasting stratigraphic architectures within a Campanian low-aspect-ratio (LAR) clastic wedge in the Cordilleran Foreland basin (CFB) that 1) quantifies sediment supply for onlapping and offlapping sequence sets within the LAR wedge, 2) tests limits of diffusion-based, forward stratigraphic modeling (Dionisos) to calculate supply and 3) uses growth-strata correlation to disentangle structural drivers. Previous correlations of Aschoff and Steel (2011) were extended using a database of 78 well-logs and 30 stratigraphic profiles. The new correlation and isopachs provide the 3D perspective needed to quantify supply and highlight affects of Laramide uplifts using growth-strata and thinning. Stratal volumes were calculated for offlapping and onlapping parts of the LAR wedge using the regional sequence-stratigraphic framework and isopach maps covering ~600,000 km2 of the CFB; stratal volumes were decompacted and converted to sediment flux using biostratigraphic age-control. Volume calculations yielded sediment fluxes of 63,049 km3My-1 for the offlapping and 65,859 km3My-1 for the onlapping sequence set. Forward stratigraphic modeling, using numerous known input variables, yielded sediment fluxes of 27,217 km3My-1 for offlapping and 27,308 km3My-1 for onlapping sequence set. Both methods yielded similar sediment fluxes, indicating little variation in supply despite contrasting stratal architecture. Uplift of the Uinta Mtns. was constrained to upper Campanian based on new isopach maps showing an East-West trending depozone along the southern Uinta Mountains, and correlation of growth-strata to basin-fill. Backstripping by Liu et al.
(2011) suggest that dynamic subsidence migrated far eastward, away from the main depozone of the LAR wedge during the Sevier-Laramide transition. Migration of dynamic subsidence may have catalyzed the 3rd-order LAR wedge but higher frequency architectural changes within the wedge were likely due to local Laramide structures such as the San Rafael Swell (SRS) and the Uinta Uplift, not sediment supply.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California