Wickersham and Neruokpuk units

Unit symbol: CPxwn
Age range Cambrian and Proterozoic (1600 to 485.4 Ma)
Lithology: Sedimentary
Group name: Wickersham and Neruokpuk units
Three widely distributed and similar units in east-central and northeast Alaska and Yukon are included here. Known locally as the Hyland Group in Yukon (see 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. It is a dominantly clastic sequence of poorly sorted quartzite, feldspathic quartzite, grit, calcareous siltstone and fine-grained sandstone, and subordinate dark limestone and chert locally that contains maroon and green (Cambrian) Oldhamia-bearing slate in its upper part. The lower part of the Wickersham has been described as a dominantly poorly sorted to bimodal quartzite, gritty quartzite, and granule conglomerate that characteristically contains sparse, single-crystal milky white to blue quartz granules (“eyes”) in a slightly cherty quartzofeldspathic-wacke matrix (Weber and others, 1992). In central Alaska, unit consists typically of gray, maroon, and green slaty argillite interlayered with gray and greenish-gray grit and quartzite, phyllite, slate, minor limestone, and chert. Potassium or sodium feldspar grains are locally abundant, and rare argillite rip-up clasts have been reported (Foster and others, 1983; Weber and others, 1992). In northeast Alaska, the Neruokpuk Schist of Leffingwell (1919) (Reiser and others, 1980) can be described as undergoing a lithologic transition from south to north. Southern exposures consist of interbedded thin- to thick-bedded, resistant massive quartz wacke and semischist, subordinate phyllite and argillite, and rare calcareous sandstone. In northern exposures, unit is generally less metamorphosed and consists of mostly greenish to brownish gray and grayish black, fine- to coarse-grained quartz wacke that locally grades to sublitharenite and lithic graywacke and local granule grit conglomerate. Unit also includes siltstone of similar composition, as well as red, green, and black phyllitic slate and rare limy beds (Reiser and others, 1980). In both central and northeastern Alaska, Cambrian limestone and dolostone of similar description is present. In the Livengood quadrangle, the limestone is dense to very finely crystalline, nonfossiliferous, micaceous, sandy, or sparsely sandy. It contains monocrystalline, rounded to subrounded, matrix supported quartz grains and is discontinuously thinly and horizontally bedded or platy to shaly (Weber and others, 1992). In the Demarcation Point quadrangle, the limestone is dark-gray to grayish-black, thick- to medium-bedded, and medium- to light-gray-weathering. It is, in part, pelletoidal, pisolitc, and recrystallized, and it commonly contains abundant floated rounded quartz grains. Locally it grades to coarse-grained calcareous sandstone and calcareous grit conglomerate that has a distinctive intricate net of white calcite veins (Reiser and others, 1980). Unit also includes red, green, and orange partly calcareous slate and argillite, quartzite, and greenstone of the Strangle Woman Creek sequence of Brosgé and Reiser (1969) in the Coleen quadrangle. The Strangle Woman Creek sequence also includes minor greenstone, which is included here. Rocks adjacent to the Coleen quadrangle outcrops, in the Yukon, are the country rock to the Old Crow batholith (unit MDgi) and are described as “red, green and grey slaty argillite; fine grained, light grey quartzite; dolomite;” they have been tentatively assigned to the Pinguicula or Fifteen Mile units of Mesoproterozoic age (Gordey and Makepeace, 2003), which here is considered equivalent to the Wickersham or Neruokpuk units. In east-central Alaska, the Wickersham is exposed south of or within strands of the Tintina Fault System; north of the fault system in Yukon the Wickersham equivalent unit is the Hyland Group (Gordey and Makepeace, 2003). Unit also includes a very small area of mafic intrusive rocks in the Black River quadrangle that are possibly equivalent to Hart River Volcanics of the Yukon

Source map information

Source map Reiser, H.N., Brosge, W.P., Dutro, J.T., Jr., and Detterman, R.L., 1971, Preliminary geologic map, Mt. Michelson quadrangle, Alaska: U.S. Geological Survey Open-File Report 71-237, 2 sheets, scale 1:200,000.
Symbol Cu
Unit name Volcanic and carbonate rocks: Undifferentiated phyllite; graywacke, volcanic and carbonate rocks.
Description Undifferentiated red, green, gray phyllite; gray-wacke, volcanic and carbonate rocks.
Lithology Metamorphic

Correlated geologic units

Label CZng
Description Neruokpuk, fine to coarse sandstone, grit and pebble conglomerate, poorly sorted, turbiditic, locally feldspathic; siltstone and slaty argillite interbeds; local maroon, green and Oldhamia bearing slate in upper part
Geologic age Neoproterozoic to Cambrian
Geologic setting Sedimentary, slope-and-deep-water
Lithology Form Importance
Phyllite < Metaclastic < Metasedimentary < Metamorphic Major
Chert < Chemical < Sedimentary Bed Major
Mafic-hypabyssal < Hypabyssal < Igneous Incidental
Limestone < Carbonate < Sedimentary Calcareous Incidental