Subsidence

Introduction

What 

Current Projects

Flexural Subsidence of Laramide Structures

Recent Projects

Testing Boundary Conditions (Clair Atlas BS'19)

This study tested the impact of many parameters that influence basin geometry and highlights those with the greatest impact. A simplified basin model was first utilized to test the sensitivity of a hypothetical basin to parameters such as load extent and geometry. These results establish characteristic patterns seen when varying the model load. Then a modern peripheral foreland basin, the Ganga Basin in Indian, was modeled as a test. Elastic thickness, load shape, load extent, plate boundary conditions, plate boundary location, sediment infill density, and distance to the free edge are explored and analyzed. Unique to this study is the use of variable elastic thickness and variable sediment infill density. Modeling basins with variable elastic thickness from load through the clamped edge is a more realistic approach as elastic thickness is lowest in the orogen and increases with distance from it. Additionally, varying sediment infill density allows the model to account for compaction of sediment under the mountain belt and within the basin. The findings reveal that many parameters do not have a large influence on the basin shape as long as they remain within a certain range (load extent, load geometry, distance to the free edge, distance to the clamped edge), while other parameters change the resultant basin geometry drastically with relatively small variations (infill density, elastic thickness). The results specify which parameters have high sensitivity and thus an accurate value must be determined and which parameters have a low sensitivity in which case an estimate or range of values is appropriate.

Coupled Flexural-Dynamic Subsidence (Brandon Tufano, MS'16)

The development of accommodation in sedimentary basins falls into two broad categories; regional basin-scale subsidence and localized processes.  This study presents a modeling approach which yields estimates of regional flexural and dynamic subsidence within a retro-foreland basin.  The Western Canada Sedimentary Basin was chosen for this study because of the abundance of well data and numerous previous studies that can be used to constrain the model.  Six cross sections were modeled and matched to the observed basin isopach defined by present-day structural surfaces and estimates of eroded overburden.  In contrast to previous studies, these models use a laterally varying lithospheric flexural rigidity constrained by present-day estimates. 

The dynamic subsidence component for each of these cross sections matches favorably to direct estimates based on mantle convection modeling of the subducting Farallon Plate beneath North America during the Cretaceous.  It is this dynamic component that lead to regional accommodation more than 250 km east of the present-day thrust front in the Western Canada Sedimentary Basin because the short wavelength flexural component does not contribute to subsidence this far across the basin.  It follows then that initial subsidence in retro-foreland basins is attributed to the dynamic component.  The flexural component is only important for regions within the flexural foreland. The width of this region is determined by the flexural rigidity of the lithosphere.

The modeling approach presented in this study can be used in other retro-foreland basins to estimate the overall basin geometry where less data is available to provide an empirical solution.  This has direct implications for predicting the distribution of facies in poorly constrained basins.  Furthermore, regional subsidence models can be subtracted from observed basin isopachs to yield estimates of local accommodation.

Publications

Tufano, B.C., and Pietras, J.T., 2017, Coupled flexural-dynamic subsidence modeling approach for retro-foreland basins: Example from the Western Canada Sedimentary Basin: GSA Bulletin, v. 129, p. 1622-1635.