The pre-Mississippian "Neruokpuk Formation," northeastern Alaska and northwestern Yukon: review and new regional correlation

Abstract

Since the early 1900's, regional reconnaissance in Alaska and the Yukon has failed to resolve the stratigraphy and structure of the pre-Mississippian Neruokpuk Formation. Its age and distribution have been defined and redefined as new data have slowly accumulated. In most recently published reconnaissance maps of the Yukon, the "Neruokpuk" includes nearly all of the pre-Mississippian strata in the British Mountains and is assigned a Precambrian age. In contrast, approximately half of contiguous strata in adjacent Alaska are interpreted as early Paleozoic in age and are excluded from the Neruokpuk. Recent detailed studies in the Firth River area of the Yukon have documented intense small-scale imbrication of fossiliferous Lower Cambrian to Devonian(?) units that were previously mapped as Precambrian Neruokpuk.A remarkable similarity between the lithologies of lower Paleozoic rocks in the British Mountains and the Selwyn Basin 1000 km to the southeast is strengthened by biostratigraphic ties in Lower Cambrian, Lower Ordovician, and Lower Silurian strata. This correlation between basin facies suggests that shelf and slope facies of upper Proterozoic through lower Paleozoic strata may also be correlatable between the two areas. The paleogeographic implications of these correlations indicate that pre-Mississippian strata in Arctic Alaska and the Yukon are part of a single Arctic–Pacific continental margin.The Neruokpuk Formation name should be restricted in Canada to the quartzite-dominant unit, contiguous with similar strata to which the restricted Neruokpuk definition applies in Alaska. The current broad definition, based on an assumed Proterozoic age but including many rock types, should be discontinued.

Character, relative age and implications of fractures and other mesoscopic structures associated with detachment folds: an example from the Lisburne Group of the northeastern Brooks Range, Alaska

“…The oldest rocks are slightly metamorphosed, deformed Proterozoic to Devonian sedimentary and volcanic rocks. These are unconformably overlain by northerly-derived, Mississippian to Lower Cretaceous passive margin sedimentary rocks of the Ellesmerian sequence (Reiser, 1970;Reiser et al, 1980;Lane, 1991;Moore et al, 1994). Jurassic and Lower Cretaceous clastic rocks of the Beaufortian sequence record initial rifting that ultimately led to the formation of the present-day northern Alaska continental margin (Hubbard et al, 1987).…”

Detrital geochronology of pre-Mississippian strata in the northeastern Brooks Range, Alaska: Insights into the tectonic evolution of northern Laurentia

“…The presence of Ordovician, Silurian, and Devonian zircon and muscovite from map units that were originally assigned to the Cambrian and Ordovician (e.g., Reiser et al, 1980) requires a reassessment of NE Brooks Range stratigraphy. Challenges associated with stratigraphic correlation across the Alaska-Yukon border in the NE Brooks Range have persisted because fossil localities are sparse and structural complexities disrupt the lateral continuity of major map units (e.g., Lane, 1991). In the following we incorporate our new radiometric ages to make inferences about the structural and stratigraphic architecture of the NE Brooks Range and then place our findings within the context of the early Paleozoic tectonic evolution of northern Laurentia.…”

“…Table DR7. Lerand, 1973;Lane, 1991;Lane et al, 2016); however, the structural complexity and unfossiliferous nature of these units impedes our current understanding of basin architecture, regional stratigraphic relationships, and correlations with age-equivalent units across the northern margin of Laurentia.…”

“…A commonly accepted model is that pre-Mississippian strata of the northeastern (NE) Brooks Range were deposited along a Neoproterozoic-Early Devonian passive margin that developed north (in present coordinates) of the Yukon block of northwest Laurentia (Fig. 1), before being deformed in the Early-Middle Devonian Romanzof orogeny (e.g., Lane, 1991Lane, , 2007Moore et al, 1994;Cecile et al, 1999;Colpron and Nelson, 2011;Beranek et al, 2010;Lane et al, 2016). In contrast, others have argued that the North Slope has pre-Mississippian origins in northeast Laurentia, and that it did not attain its pre-Canada Basin position until sometime before the Late Devonian or Early Mississippian (Sweeney, 1982;Dumoulin et al, 2000;Macdonald et al, 2009;Strauss et al, 2013;Cox et al, 2015).…”

Geologic map of Alaska

“…Unit thickness is 90 to 180 m. In Eagle quadrangle, correlative units (included in this map unit) include greenish-gray laminated quartzite that has interbeds of greenish-gray and dark-gray argillite and minor grayish-red argillite, siliceous shale, chert, and dark-gray sandy limestone (Foster, 1976). Unit includes type area of the Adams Argillite in the Charley River quadrangle of east-central Alaska (Brabb and Churkin, 1969) as well as rocks that are apparently correlative in the Demarcation Point quadrangle of northeast Alaska (Reiser and others, 1980) Gordey and Makepeace, 2003), the Neruokpuk Schist of Leffingwell (1919) (see, for example, Reiser and others 1980;Lane, 1991) or, in some sources, Neruokpuk Formation or Neruokpuk Quartzite in Alaska and Yukon, the Nilkoka Group (Péwé and others, 1966) in central Alaska, and the informal Wickersham unit in Alaska (Weber and others, 1992). The unit is distinctly characterized by the presence of maroon and green slate and grit; however, it is quite variable in lithology and metamorphic grade.…”