Sequential restoration of Paradox Basin salt anticlines: Reconstruction of younger, eroded datums

Abstract

Structural restoration is often accomplished by taking a folded, faulted stratigraphic horizon and transforming it back to its original, horizontal geometry. 2D sequential restoration uses a range of older to younger stratigraphic datums to reconstruct the geometric evolution of structural features through a history of multiple deformation events. For surface geology exposures, erosion may have eliminated some portions of younger horizons; these eroded gaps in stratigraphy can be mended using thickness trends to bridge the gaps. If a horizon has been fully exhumed, reconstruction of the missing stratigraphy can be inferred from burial history indicators in older, preserved units and from regional bridging from surrounding, less uplifted areas. In the Paradox Basin, late Cenozoic uplift of the Colorado Plateau has removed 1–2 km of Upper Cretaceous and Lower Tertiary stratigraphic units. Previous structural restorations have followed the structural evolution of the salt anticlines contained in the Paradox Basin from the late Paleozoic deposition of the salt-bearing Paradox Formation to end Jurassic deposition of the Morrison Formation. Yet, significant faulting and folding events continued through the Cretaceous and Tertiary. In order to capture the development of these structural features, this study reconstructs an inferred picture of the missing Upper Cretaceous and Lower Tertiary stratigraphy for Paleocene and mid-Eocene datums. Three Paradox Basin sections give an interpreted structural deformation of the salt anticlines for the Laramide event that affected much of the nearby Colorado Plateau and central Rocky Mountains. Restoration of unfaulted fold shapes show an early and very modest contractional shortening; interpreted Laramide fold amplification of the salt anticlines (∼100–150 m shortening per anticline) is followed by a later and more significant normal faulted extension (∼500 m extension per anticline). Both contraction and extension are detached from subjacent basement (= sub-Paradox) involvement. Location of basement shortening/stretching is beyond the extent of the interpreted sections and may lie within the structural features at the margins of the Paradox Basin.