COMPARISON AND TENTATIVE CORRELATION OF DEVONIAN–TRIASSIC STRATA ACROSS TECTONIC TERRANE BOUNDARIES ALONG THE DENALI FAULT, ALASKA RANGE, SOUTHERN ALASKA

While much of southern Alaska has been proposed to consist largely of geologically distinct “tectonic terranes”, lithologic similarities are beginning to emerge between Devonian–Triassic strata throughout much of this region. On the basis on new stratigraphic and provenance data from the Farewell (Mystic, Dillinger, and Nixon Fork subterranes) and Chulitna terranes, we present a comparison of age-equivalent Devonian–Triassic strata from throughout the south-central and southwestern part of the Alaska Range (Farewell, Chulitna, Pingston, McKinley terranes) in strata exposed north and south of the Denali fault.

New geologic mapping, measured stratigraphic sections, and provenance data from the Chulitna and Farewell terranes reveal three separate stratigraphic intervals that are sporadically exposed throughout the Alaska Range. Each of the following three units are exposed both north and south of the Denali fault and consist of (1) Devonian(?) to younger serpentinite lineaments that are extensive in and around the Chulitna terrane and occur as isolated strands in the McKinley and Pingston terranes, (2) Devonian–Permian siliciclastic marine (Sheep Creek Formation and equivalent units) and nonmarine strata (Mt. Dall conglomerate and equivalent units) of the Farewell terrane, and (3) Upper Paleozoic(?)–Upper Triassic pillow basalts, limestone units, and volcaniclastic and siliciclastic strata that are exposed throughout the Chulitna terrane as well as the Farewell terrane.

Recent correlation of Phanerozoic strata (specifically Mesozoic siliciclastic units) from across previously defined “tectonic terranes” in south-central Alaska has provided a basis for understanding exhumation and sedimentation during Jurassic–Cretaceous island-arc collisional events. A similar comparative approach with Devonian–Triassic strata in south-central and southwestern Alaska may provide the first step toward a more comprehensive understanding of Paleozoic orogenic events that occurred during the early stages of tectonic development in the northern parts of the North American Cordillera.