Stratigraphic and Structural Framework for Denali National Park and Preserve, central Alaska Range: Implications of Upper Paleozoic-Cretaceous Stratigraphy for Mesozoic Tectonics and Paleogeography
thesisposted on 16.12.2020, 02:37 by Brandon M KeoughBrandon M Keough
Paleozoic-Mesozoic stratigraphy exposed in the central Alaska Range includes a diverse assemblage of tectonostratigraphic basement terranes overprinted by late Mesozoic basin
formation and Cenozoic strike-slip displacement. In this thesis, I present a stratigraphic and structural framework for upper Paleozoic-Cretaceous strata exposed in Denali National Park and Preserve. The stratigraphic architecture of the study area is characterized by two distinct Upper Paleozoic-Mesozoic stratigraphic packages that are unconformably overlain by the Upper Cretaceous Cantwell Formation. Sedimentological, provenance, and geologic mapping data suggest that one basement assemblage, the Northern package, consists of Upper Triassic-Lower Cretaceous submarine strata deposited along the northwestern Laurentian margin. The other assemblage, termed the Southern package, is exotic to the ancestral continental margin and is associated with Permian-Upper Triassic submarine strata of the Farewell terrane. Provenance data from this package place new constraints on the Late Paleozoic paleogeographic position of the Farewell terrane prior to its accretion to the continental margin, likely by the Late Jurassic. The results of geologic mapping along the Toklat River corridor show that the Northern and Southern packages are deformed and structurally juxtaposed within a triangle zone bounded by the Hines Creek and Denali fault systems. This is the best exposure of stratigraphy associated with the Farewell terrane juxtaposed with strata representative of the ancestral continental margin known to date. New 1:24,000-scale geologic mapping coupled with a stratigraphic and provenance analysis of the Cantwell Formation provides new insights into sedimentation and deformation during the post-collisional phase of development of the Alaska Range suture zone (ARSZ). Results of this study define three stages of basin development. These stages are represented by alluvialfluvial, tidally influenced fluvial, and marginal marine deposits, respectively. Results of geologic mapping record progressive Late Cretaceous-Eocene deformation of the Cantwell Formation in a triangle zone and the transition from compressional to strike-slip tectonics in the Eocene. This deformation coincides with regional exhumation of the ARSZ and reconfiguration of the paleosouthern Alaskan margin with the establishment of the modern convergent margin configuration.