--> Detrital zircon LA-ICPMS U-Pb geochronology of Arctic Alaska Basin sedimentary rocks

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Detrital zircon LA-ICPMS U-Pb geochronology of Arctic Alaska Basin sedimentary rocks


New detrital zircon U-Pb ages were determined by laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) for several quartz-rich horizons from cores and cuttings from boreholes across Arctic Alaska. Results are presented here for rocks in the Chukchi Sea, National Petroleum Reserve Alaska (NPRA), and North Slope. The samples are from middle Paleozoic basement and the Middle Mississippian to Upper Jurassic-Lower Cretaceous Ellesmerian and Beaufortian (Rift) mega-sequences (Holm-Denoma, 2017). Our results suggest two sources for pre-Mississippian age basement detrital zircon age populations: a northern Laurentia type 1 signature (Hadlari et al., 2012), and a Caledonian signature, implying a linkage between the Caledonian orogeny and the Arctic during the Early Paleozoic (Miller et al., 2017). Laurentian and Caledonian type basement rocks on the western North Slope are similar to detrital zircon age spectra of pre-Mississippian rocks found in the Northeast Brooks Range platformal and basinal successions (Strauss et al., 2019). Reflection seismic and potential field data in the Northeast Chukchi Basin and western NPRA show platformal pre-Mississippian rocks that were possibly peri-cratonal, outboard of the Cambrian shelf edge of North America (Sherwood, 1992). These platformal rocks were progressively drowned due to tectonic loading during Caledonian orogenesis and then covered by Ordovician-Silurian forearc rocks (Bjornerud, 1992). Ellesemerian and Beaufortian detrital zircon U-Pb age populations, including samples from boreholes in the Chukchi Sea, are remarkably similar and span the Mesoarchean to Devonian. Age populations include major peaks between ~500-390 Ma, a broad spread of ages between ~1900-950 Ma, and a minor peak between ~2800-2400 Ma. The observed western Arctic Alaska Precambrian detrital zircon age spectra are largely consistent with lineages from Neoproterozoic to early Paleozoic sedimentary rocks of the northwestern Laurentian passive margin; specifically these age spectra are similar to hybrid or mixed populations of cratonal and marginal sequences (e.g., Adams Argillite, Lane and Gehrels, 2014). Samples from rocks above the pre-Mississippian basement inherited basement age spectra, indicating a local source of sedimentation during Mississippian-Pennsylvanian rifting following the Ellesmerian orogeny. In addition, the overall detrital zircon age spectra of Arctic Alaska samples are remarkably similar to rocks of the Devonian clastic wedge in Arctic Canada and the Yukon (Gottlieb et al., 2014 and references therein; Holm-Denoma, 2017). Our results suggest consistent Devonian clastic wedge sourcing of zircons and widespread, well mixed, sediment dispersal in post-Mississippian Ellesmerian and Beaufortian (rift) sequence marine rocks. Similarities between detrital zircon age spectra from Chukchi wells and other Laurentian-sourced Arctic Alaska samples suggest that areas west of the Hanna Trough axis in the Chukchi Sea contain Devonian clastic wedge-derived sediments (Holm-Denoma, 2017). Restoration of western Arctic Alaska against the margin of the Canadian Arctic Islands using a simple rotation model generally aligns the Hanna Trough axis in the Chukchi Sea to the Sverdrup Basin axis (Embry, 1990; Sherwood, 1992). Triassic clastic strata from the westernmost tip of Arctic Alaska contain <300 Ma zircon, which is postulated to have been derived syndepositionally from eastern Arctic Russia (e.g. Miller et al., 2006; Midwinter et al., 2016). The absence of <380 Ma zircon in Berriasian-Valanginian sandstone samples deposited just west of the Hanna Trough axis implies that sediment derived from eastern Arctic Russia during the Triassic may not have been deposited in this location, in contrast to the Sverdrup Basin. It is possible that deposits with Triassic-derived detritus are present over the Chukchi Platform further to the west of the Hanna Trough.