Deep-water canyons and sequence-stratigraphic framework of the Upper Jurassic Naknek Formation, south-central Alaska

Abstract

Front cover. Oblique aerial view southeastward of Chisik Island summit area. This mountain-scale exposure of Naknek Formation exhibits evidence of a Late Jurassic deep-water canyon incised into slope strata of Snug Harbor Siltstone Member (gray-brown, wedge-shaped succession at left of exposure) and ultimately backfilled with basin-floor sandstones of the Pomeroy Arkose Member (at and below the summit ridge). Stratigraphic studies of the Naknek Formation along the ~80-km-long Iniskin-Tuxedni bays outcrop belt led to the recognition of three deep-water paleocanyons. These discoveries and related work permit the first sequence-stratigraphic interpretation for the Naknek Formation in the hydrocarbon-bearing Cook Inlet forearc basin. See figures 4 and 17A for photogeologic rendition and sequence-stratigraphic interpretation, respectively, of this Chisik Island locality. This part of the exposure is ~275 m tall, for sense of scale. Photograph by T.M. Herriott.

Exploring the law of detrital zircon: LA-ICP-MS and CA-TIMS geochronology of Jurassic forearc strata, Cook Inlet, Alaska, USA

“…However, faunal assemblages noted by Detterman and Westermann (1992) also suggest that lowermost Tonnie may be latest Bathonian, and Pomeroy is potentially as old as Oxfordian. The Chisik is not fossiliferous, but stratigraphic and biostratigraphic relations indicate that this unit is probably Oxfordian, and may be associated with Callovian-Oxfordian transition climate change (Herriott et al, 2017). Recent DZ LA-ICP-MS studies in southern Alaska yielded Chinitna and Naknek constraints that are notably younger than biostratigraphic correlations suggest (Finzel and Ridgway, 2017;Reid et al, 2018;Stevens Goddard et al, 2018;Herriott et al, 2019).…”

“…1). In this area, the Chinitna Formation comprises an ∼700-m-thick succession of principally shallow-marine strata of the Tonnie Siltstone and Paveloff Siltstone Members (Herriott et al, 2016;Herriott and Wartes, 2017; Fig. 1).…”

“…1). The overlying Naknek Formation in the area is an ∼1500-m-thick interval of shallow-and deep-marine strata of the Chisik Conglomerate, lower sandstone (informal), Snug Harbor Siltstone, and Pomeroy Arkose members (Herriott et al, 2017;Fig. 1).…”

Vein formation during progressive Paleogene faulting and folding within the lower Cook Inlet basin, Alaska

“…Unconformably overlying the Chinitna Formation is the upper Jurassic Naknek Formation. The basal Chisik Conglomerate Member fills deep-water canyons in the underlying Chinitna Formation (Detterman and Hartsock, 1966;Herriott et al, 2017). The overlying Snug Harbor Siltstone Member is primarily thin bedded and fossiliferous , and the top unit, the Pomeroy Arkose Member, is an arkosic sandstone (Detterman and Hartsock, 1966;Herriott et al, 2017).…”

“…The basal Chisik Conglomerate Member fills deep-water canyons in the underlying Chinitna Formation (Detterman and Hartsock, 1966;Herriott et al, 2017). The overlying Snug Harbor Siltstone Member is primarily thin bedded and fossiliferous , and the top unit, the Pomeroy Arkose Member, is an arkosic sandstone (Detterman and Hartsock, 1966;Herriott et al, 2017). The Naknek Formation represents submarine fans that record exhumation of the plutonic roots of the Jurassic Talkeetna arc (Detterman and Hartsock, 1966;Trop et al, 2005;Wartes et al, 2013;Herriot et al, 2017).…”