Sedimentary record of the tectonic growth of a collisional continental margin: Upper Jurassic–Lower Cretaceous Nutzotin Mountains sequence, eastern Alaska Range, Alaska

Abstract

Upper Jurassic-Lower Cretaceous sedimentary strata of the Nutzotin basin, the Nutzotin Mountains sequence, crop out in the Nutzotin and Mentasta Mountains of the eastern Alaska Range. These strata represent one of the best-exposed and leastmetamorphosed examples of a basin that is interpreted to have formed during collision of an allochthonous volcanic arc (i.e., the Wrangellia terrane) with a continental margin. New stratigraphic, geologic mapping, and provenance data indicate that the Nutzotin basin formed as a retroarc foreland basin along the northern margin (present coordinates) of the Wrangellia terrane. Coeval with basin development along the northern margin, sedimentary basins and plutons located along the southern margin of the Wrangellia terrane were being incorporated into a regional fold-and-thrust belt. This fold-and-thrust belt, located south of the Nutzotin basin, exposed multiple structural levels of the Wrangellia terrane that were eroded and provided sediment that was transported northward and deposited in the Nutzotin basin. New sedimentologic and stratigraphic data from the ϳ3 km thick (minimum thickness) Nutzotin Mountains sequence define a three-part stratigraphy. The lower part consists of Upper Jurassic (Oxfordian to Tithonian) conglomerate with outsized limestone clasts (>10 m in diameter) and interbedded sandstone and shale that grade basinward into mainly black shale with minor micritic limestone and isolated lenses of conglomerate. The middle part of the stratigraphy consists of Upper Jurassic (Tithonian) to Lower Cretaceous (Valanginian) normal-graded sandstone and shale interbedded with massive tabular sandstone and lenticular conglomerate. The upper part of the stratigraphy consists of Upper Jurassic (Tithonian) to Lower Cretaceous

Comment on “U‐Pb and Hf Isotope Analysis of Detrital Zircons From Mesozoic Strata of the Gravina Belt, Southeast Alaska” by Yokelson Et Al. (2015)

“…The Gravina belt, Dezadeash Formation, and Nutzotin Mountains sequence are characterized by a distinct assemblage of Late Jurassic to Early Cretaceous volcanolithic turbidites up to 3000 m thick, with locally important interbedded conglomerate and volcanic rocks. The turbidites are unmetamorphosed to regionally metamorphosed up to subgreenschist facies (Dodds & Campbell, ), and preserved sedimentary structures document that they were derived from the west (Cohen & Lundberg, ; Eisbacher, ; Lowey, ; Manuszak & Ridgway, ; Manuszak et al, ). The Gravina‐Nutzotin belt is interpreted as submarine fan deposits and submarine volcanic flows sourced from a contemporaneous volcanoplutonic arc situated along the inboard margin of the Alexander‐Wrangellia terranes and shed eastward into an adjacent basin (Berg et al, ; Cohen & Lundberg, ; Eisbacher, ; Kozinski, ; Lowey, ; Manuszak et al, ).…”

Provenance signature of changing plate boundary conditions along a convergent margin: Detrital record of spreading-ridge and flat-slab subduction processes, Cenozoic forearc basins, Alaska

“…2;Foster and Keith, 1994;Mihalynuk et al, 1994;Monger and Nokleberg, 1996;Gehrels, 2001). During Middle Jurassic to Late Cretaceous time, the Wrangellia composite terrane collided with the outboard margin of the Yukon composite terrane (Pavlis, 1982;McClelland et al, 1992;Trop et al, 2002;Trop et al, 2005;Manuszak et al, 2007). Today, the Yukon and Wrangellia composite terranes are separated by the Alaska Range suture zone, where thousands of meters of Upper Jurassic to Upper Cretaceous marine strata were deposited in the Kahiltna basin and subsequently exhumed ( Fig.…”

Flysch deposition and preservation of coherent bedding in an accretionary complex: Detrital zircon ages from the Upper Cretaceous Valdez Group, Chugach terrane, Alaska

“…The Chugach terrane developed along the southern edge of the Wrangellia composite terrane and contains three faultbounded units (Fig. 3;Plafker et al, 1989): a Triassic-Jurassic blueschist unit, a Jurassic-Cretaceous mélange unit, and a Cretaceous-Eocene fl ysch unit (Berg et al, 1972;Manuszak et al, 2007). The boundaries of the Chugach terrane are the Border Ranges fault system to the north and the Contact fault system to the south (Plafker et al, 1989).…”

“…Detrital zircons with ages of 210-170 Ma, 170-150 Ma, and 150-125 Ma may have been derived from several potential source regions, such as the Talkeetna arc (202-153 Ma;Amato et al, 2007;Rioux et al, 2007), Chitina arc (171-140 Ma;Plafker et al, 1989;Roeske et al, 2003), Chisana arc (130-120 Ma; Berg et al, 1972;Manuszak et al, 2007), and the Coast Mountains Batholith (230-45 Ma;Gehrels et al, 2009), as well as in the Upper Jurassic-Lower Cretaceous part of the McHugh Complex (Amato and Pavlis, 2010).…”