Detrital zircon maximum depositional dates for the Jurassic Chinitna and Naknek Formations, lower Cook Inlet, Alaska: A preliminary view

Abstract

Oblique aerial view east-southeastward across the head of Oil Bay. Strata exposed along the shoreline and uplands near Oil Bay comprise Jurassic forearc basin units of lower Cook Inlet. Detrital zircon samples collected from sandstone beds that crop out above the tidal flats at photograph-center are the subject of this report. The east shore of Oil Bay (visible below skyline-center) is ~4 km long, for sense of scale. See figure 1 for further context. Photograph by T.M. Herriott. This publication is PRELIMINARY in nature and meant to allow rapid release of field observations or initial interpretations of geology or analytical data. It has undergone limited peer review but does not necessarily conform to DGGS editorial standards. Interpretations or conclusions contained in this publication are subject to change.

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

“…Comparisons of our LA-ICP-MS dates with published DZ LA-ICP-MS dates from Jurassic strata of southern Alaska are hampered by stratigraphic, biostratigraphic, and analytical complexities. However, we collected samples 09BG010-14.5A (this study) and 09BG010-14.5C (Herriott et al, 2019) from the same bed, and KDEs of these LA-ICP-MS results indicate a modest systematic offset (−2.2% at mode for 09BG010-14.5C; Fig. 2) that may reflect matrix effects.…”

“…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).…”

Supplemental Material: Dissecting 20 million years of deep-water forearc sediment routing using an integrated basin-wide Bayesian chronostratigraphic framework

“…Their sedimentary deposits can record the signal of geodynamic processes in both the terrestrial sediment source area (e.g., underplating, uplift, and magmatism) and the basin (e.g., trench accretion and subduction erosion). However, isolating these signals in ancient forearc strata is difficult, in part, because forearc basin fills are commonly tectonically deformed or fragmented both during and after basin sedimentation (Mitchell et al, 2010;Takano et al, 2013;Hessler and Fildani, 2015;Orme et al, 2015;Noda, 2016;Greene and Surpless, 2017;Herriott et al, 2019). The submarine slopes of forearc regions are often characterized by structural complexity, which can lead to local controls on sediment thickness, timing of sedimentation, and sediment routing system morphology (Bourget et al, 2011;Paquet et al, 2011;Takano et al, 2013;Hessler and Fildani, 2015;Orme and Graham, 2018; Fig.…”

“…Resolving the chronology of sedimentary basin fills, including submarine channel deposits, is paramount for understanding sediment routing system evolution and establishing links to tectonic processes (Kimbrough et al, 2001;Fildani et al, 2009;Takano et al, 2013;Daniels et al, 2018;Englert et al, 2018;Pinter et al, 2018;Herriott et al, 2019). This requires the creation of chronostratigraphic frameworks that accurately constrain the architecture of the deposits (e.g., deposit geometry, spatial distribution, and paleoflow direction) as well as the timing of sedimentation along large outcrop belts (Fildani et al, 2008;Takano et al, 2013).…”