Dynamic origin of anomalous subsidence of Jurassic Ordos basin

The Jurassic Ordos basin is generally considered an intracontinental basin characterized by rapid subsidence rate along western margin and slow subsidence rate within basin interior. However, the formation mechanism of Ordos basin was not yet well understood. Flexural backstripping of stratigraphic record spanning from 174-153Ma, along three well sections perpendicular to the western margin of Ordos basin clearly demonstrates that there were long wavelength anomalous subsidence components, termed residual subsidence, in addition to those induced by thrust loads and sediment loads. Flexural components exhibit similar spatial and temporal trends along three sections. Simulations demonstrates that the foredeep is only 80-100 km wide, corresponding to effective thickness of 15-20 km. Contribution by flexural component relative to cumulative subsidence decreases from 50-60% to -15% within foredeep from thrust front towards basin interior, while residual subsidence could account for 40-50% of cumulative subsidence for areas outboard extent of foredeep. From 174-153 Ma, residual subsidence increases from ~150 m to ~330 m, ~200 m to ~390 m, ~180 m to ~480 m in southern, middle and northern section respectively. Our results indicate that thrust loads could act as the dominant driver for subsidence of foredeep while other mechanism needs to be raised to explain the basin-wide anomalous residual subsidence. The general agreement regarding both magnitude and trends along all three sections between dynamic topography predicted by geodynamic models and residual subsidence separated from flexural modeling, indicates that the anomalous subsidence component might be of dynamic origin, related to subduction of paleo-Pacific plate initiated from latest Early Jurassic.