CONTROL OF SUBDUCTION-RELATED DYNAMIC SUBSIDENCE MIGRATION ON SHORELINE DEVELOPMENT IN THE CORDILLERAN FORELAND BASIN: NEW DATA AND REGIONAL SYNTHESIS

Dickinson (1974) embraced the burgeoning theory of plate tectonics to interpret the formation of sedimentary basins, emphasizing the close linkage between tectonic setting and basin-fill. The role of subduction in retro-arc basin formation was somewhat de-emphasized in the 1980-90’s as thrust-belt uplift and flexural controls were scrutinized. Flexural backstripping by Liu et al. (2011, 2014) in the Cordilleran Foreland Basin (CFB) indicated that subduction-related dynamic subsidence (“hidden load” of Cross, 1991) played an important role, sparking re-evaluation of subduction controls on retroarc foreland basins. The present study shows new stratigraphic data and regional synthesis of Campanian-Maastrichtian correlations in MT, WY, UT and CO that suggests subduction of the conjugate Shatsky Rise controlled shoreline development and draining of the Western Interior Seaway. This study: 1) defines 3, ~600 km wide, E-NE migrating depocenters that each show a systematic high-to-low accommodation stacking pattern, 2) delineates high-resolution Campanian-Maastrichtian shorelines that sequentially deviate from a thrust-belt parallel orientation to bisect the Shatsky Rise, and 3) demonstrates depositional process change as a function of dynamic subsidence migration. Dynamic basins span ~600 km, migrating in an E-NE, stepwise pattern independent of the foredeep. Each basin consists of older, vertically-stacked strata, overlain by a forced-regressive sequence and unconformity. Campanian to Maastrichtian shorelines in the CFB initially parallel the foredeep subsidence but make a sharp eastward turn to intersect the position of the Shatsky Rise and its dynamic topography. Early Campanian marine shorelines throughout the CFB parallel the N-S trend of the foredeep, but Middle to Late Campanian shorelines turn eastward in UT-CO, bisecting the postulated position of the Shatsky Rise at this time. Maastrichtian shorelines of the Fox Hills Ss. follow a similar trend, bisecting the Shatsky Rise but also define a drainage divide in north-central WY/SD. Sedimentary processes within these shorelines show an up-section evolution from early, river-wave dominance followed by tide-wave dominance and valleying. These data and synthesis further support the linkage between foreland basin-fill and subduction.