Distinct Responses of Intra-plate Sedimentation to Different Subsidence Mechanisms: Insights from Forward Landscape Evolution Simulations

Here we present data from synthetic landscape evolution simulations designed to investigate the surface process manifestations of different tectonic subsidence mechanisms. Our interests lie in large (>200km wide) intra-plate sedimentary basins, such as the Cretaceous Western Interior Seaway (WIS) in North America. The three end-member surface subsidence mechanisms we test are: 1) stationary isostatic subsidence for lithospheric cooling and thinning, 2) stationary dynamic subsidence for slab shallowing, and 3) migratory dynamic subsidence for mantle downwelling underneath a moving plate. Results suggest that 1) traditional sediment backstripping based on local isostasy makes problematic predictions of subsidence due to flexure even for large basins, 2) isostatic subsidence tends to result in continuing sedimentation and fixed pattern of sedimentation and river drainage network, while dynamic subsidence can result in regional unconformity due to the erosion following the rebound phase and river drainage networks are dynamic, and 3) only migratory subsidence can form tilted strata, whose slope depend on the geometry of the subsidence signal, and migrating depocenter. Since both migrating depocenter and tilted strata are observed in the WIS stratigraphy, the WIS is likely formed by a migratory dynamic subsidence due to Farallon slab subduction under westward-moving North American plate during Cretaceous.

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