Northern Alaska sedimentary rocks

Unit symbol: JPzs
Age range Middle Jurassic to Carboniferous (358.9 to 168.3 Ma)
Lithology: Sedimentary
Group name: Northern Alaska sedimentary rocks
Unit includes two similar rock assemblages in the Wiseman and Chandalar quadrangles and a large part of the central Chandler Lake quadrangle. These assemblages include stratigraphic units common to the Brooks Range that are not separately mapped. The first assemblage, spatially associated with the Doonerak Window (see below, units SCs and OCdv), is composed of quartzite, phyllite, siltstone, conglomerate, shale, sandstone, limestone, argillaceous limestone, dolomitic limestone, and cherty dolostone of Triassic to Carboniferous age that unconformably overlies lower Paleozoic rocks (unit S_s) (Dillon and others, 1986). Formal rock units included, but not separately mapped in this assemblage, are the Kekiktuk Conglomerate (Mek) and Kayak Shale (Mk) of the Endicott Group, the undivided Lisburne Group (Clg), the Echooka Formation (Pe) of the Sadlerochit Group, Shublik Formation (Trgs, KPu) and Karen Creek Sandstone (Trkc). This assemblage was mapped as unit TrCs by Till and others (2008a). Exposed to the northwest of this assemblage is a second assemblage, mapped by Till and others (2008a) as JCs, which is composed of “sandstone, shale, argillaceous limestone, limestone, dolostone, mudstone, chert, and siltstone in north-central Wiseman quadrangle. The unit conformably overlies the Kanayut Conglomerate * * *” (Till and others, 2008a). (The Kanayut Conglomerate of the Endicott Group is mapped as part of unit MDegk herein). This second assemblage consists of the Kayak Shale (Mk) of the Endicott Group, the Lisburne Group (Clg), and the Siksikpuk (TrIPeg) and Otuk Formations (JTro) of the Etivluk Group. Both of these assemblages of Till were included in unit TrCs of Dillon and others (1986). “Various workers (e.g., Dutro and others, 1976; Mull, 1982; Mull and others, 1987a; Adams and others, 1997) have suggested that the general stratigraphy of TrCs is more like that of coeval parautochthonous rocks in the northeastern Brooks Range * * * than that of equivalent strata in the central part of the range that have been assigned to the Endicott Mountains allochthon (EMA; Moore and others, 1994). TrCs does differ from JCs, the nearest coeval strata in the EMA [Endicott Mountains allochthon]; the most notable contrast is the presence of somewhat deeper water facies in parts of both the Carboniferous and Permian successions in JCs. However, Lisburne Group facies in TrCs are generally similar to coeval rocks exposed to the northeast in the central Chandler Lake quadrangle (Dumoulin and others, 1997)” (Till and others, 2008a)

Source map information

Source map Dillon, J.T., Brosge, W.P., and Dutro, J.T., Jr., 1986, Generalized geologic map of the Wiseman quadrangle, Alaska: U.S. Geological Survey Open-File Report 86-219, 1 sheet, scale 1:250,000.
Symbol TrCs
Unit name Sedimentary rocks
Description Includes: Shublik and Otuk Formations - Black shale, siltstone, limestone, and black chert; Sadlerochit Group - black shale, and bluff calcareous siltstone; Siksikpuk Formation - black, red, and green shale and siltstone; buff calcareous siltstone; Lisburne Group - gray cherty limestone, black chert, and shale; Kayak Shale - black shale and limestone; Kekiktuk Conglomerate - quartzite, conglomerate, and felsic volcaniclastic interlayers.
Lithology Sedimentary

Correlated geologic units

Label TrCs
Description Sedimentary rocks, which include: Shublik and Otuk Formations; Sadlerochit Group; Siksikpuk Formation; Lisburne Group; Kayak Shale; Kekiktuk Conglomerate, and felsic volcaniclastic interlayers
Geologic age Devonian to Triassic
Geologic setting Undivided
Lithology Form Importance
Shale < Mudstone < Clastic < Sedimentary Bed Major
Phyllite < Metaclastic < Metasedimentary < Metamorphic Zeolitic (prehnite-pumpellyite) Indeterminate, major
Siltstone < Clastic < Sedimentary Bed Indeterminate, major
Limestone < Carbonate < Sedimentary Bed Minor
Conglomerate < Clastic < Sedimentary Bed Minor
Siltstone < Clastic < Sedimentary Calcareous Minor
Felsic-volcanic < Volcanic < Igneous Volcaniclastic Incidental