Flexural Analysis of Two Broken Foreland Basins: Late Cenozoic Bermejo Basin and Early Cenozoic Green River Basin

Peter B. Flemings, Teresa E. Jordan, Shawn Reynolds

Lithospheric flexure that generates basins in a broken foreland setting (e.g., the Laramide foreland of Wyoming) is a three-dimensional system related to shortening along basin-bounding faults. We modeled the elastic flexure in three dimensions for two broken foreland basins: the early Cenozoic Green River basin and the analogous late Cenozoic Bermejo basin of Argentina. Each basin is located between a thrust belt and a reverse-fault-bounded basement uplift. Both basins are asymmetric toward the basement uplifts and have a central basement high: the Rock Springs uplift and the Pie de Palo uplift, respectively.

The model applies loads generated by crustal thickening to an elastic lithosphere overlying a fluid mantle. Using the loading conditions of the Bermejo basin based on topography, limited drilling, and reflection and earthquake seismology, the model predicts the current Bermejo basin geometry. Similarly, flexure under the loading conditions in the Green River basin, which are constrained by stratigraphy, well logs, and seismic profiling and summed for Late Cretaceous (Lance Formation) through Eocene (Wasatch Formation), successfully models the observed geometry of the pre-Lance surface. Basin depocenters (> 4 km for the Green River basin; > 7 km for the Bermejo basin) and central uplifts are predicted to result from constructive interference of the nonparallel applied loads.

Our Bermejo model implies that instantaneous basin geometry is successfully modeled by crustal loading, whereas the Green River basin analysis suggests that basin evolution can be modeled over large time steps (e.g., 20 Ma). This result links instantaneous basin geometry to overall basin evolution and is a first step in predicting stratigraphic development.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.