Structural evolution of the Early Tertiary Cantwell Basin, south central Alaska

Abstract

The Cantwell Basin is a Paleogene intermontane basin located in south central Alaska. The Cantwell Formation which fills the basin is as much as 4000 m thick and consists of a lower sedimentary sequence of fluvial and alluvial fan origin and an upper sequence of calc‐alkaline volcanic rocks. The east trending Cantwell Basin developed as a southward thickening asymmetrical graben between the Hines Creek and Denali faults. Substantial dip‐slip displacement and local, dextral strike‐slip displacement on the Hines Creek fault during basin subsidence was followed by dip‐slip displacement in late Cenozoic time. Strike‐slip movement along the Denali fault, to the south, exerted primary control on basin subsidence and subsequent structural inversion. During the Paleocene, Kula plate motion was nearly perpendicular to the axis of the Cantwell Basin; however, Kula plate motion was oblique to southeastern Alaska and produced regional dextral slip on the Denali fault system. The Cantwell Basin appears to have developed as a pull‐apart basin in which northwest striking syndepositional normal faults linked the Denali fault with the western part of the Hines Creek fault. In early Eocene time an increased rate of plate convergence resulted in substantial displacement on the Denali fault. Concurrent counterclockwise rotation of southern Alaska produced a regional constraining bend in the Denali fault and resulted in strong compressional deformation of the Cantwell Basin.

Cretaceous to Miocene magmatism, sedimentation, and exhumation within the Alaska Range suture zone: A polyphase reactivated terrane boundary

“…The Cantwell Formation consists of two distinct lithologic units, a lower sedimentary unit, and an upper volcanic unit (Wolfe and Wahrhaftig, 1970). The sedimentary unit, sometimes referred to as the lower Cantwell Formation (Ridgway et al, 1997), consists of conglomerate, sandstone, siltstone, mud rock, shale, minor coal, and sparse volcanic rocks that locally exhibit a maximum preserved thickness of ~4000 m (Hickman et al, 1990). Cantwell strata yield diverse fossils, including dinosaur footprints, invertebrate traces, and plant megafossils important for high-latitude ecosystem reconstructions (Fiorillo et al, 2009(Fiorillo et al, , 2011(Fiorillo et al, , 2014(Fiorillo et al, , 2016Tomsich et al, 2010Tomsich et al, , 2014.…”

Crustal structure across the central Alaska Range: Anatomy of a Mesozoic collisional zone

“…The central section to the south, which contains both the Alaska Range and Northern Talkeetna Mountains, consists of a complex assemblage of Paleozoic to Cretaceous metamorphic, sedimentary, and igneous rocks. These rocks are overlain by sedimentary and volcanic strata of the Late Jurassic to Late Cretaceous Kahiltna basin and Late Cretaceous to Eocene Cantwell basin (Figures 2 and 3a) [ Hickman et al , 1990; Csejtey et al , 1992; Ridgway et al , 1997; Cole et al , 1999; Ridgway et al , 2002].…”

Reconnaissance geology and U-Pb geochronology of the west flank of the Coast Mountains between Juneau and Skagway, southeastern Alaska

“…This fault is thought to be the southern continuation of the Denali fault, which has dextral offset estimated to be 350-400 km (Lanphere, 1978;Nokleberg et al, 1985) and more recently determined to bẽ 370 km (Lowey, 1998). The age of motion along the Denali fault is most likely early Tertiary (Nokleberg et al, 1985), and was thought by Hickman et al (1990) to be Paleocene. Splays of the Chatham Strait fault, such as the Chilkoot Inlet and Taiya Inlet faults, may have accommodated some of the structural complexities associated with the abrupt bend in the Denali-Chatham Strait fault system in the Haines area (Fig.…”