NSAclass,lable,name,age,description,symbol,overprint,sources
100,Qu,"Unconsolidated and poorly consolidated sediments, undivided",Quaternary,"Surficial material deposited by water, wind, freeze-thaw cycles, and glaciers",40,,"Till, A.B., Dumoulin, J.A., Phillips, J.D., Stanley, R.G., Crews, Jesse, in prep., Generalized bedrock geologic map, Yukon Flats region, east-central Alaska:  U.S. Geological Survey Scientific Investigations Series Map SIM-XXX, scale 1:500,000."
640,Ts,Clasitc sedimentary rocks,Tertiary,"Mudstone, coal, sandstone, and conglomerate deposited in lacustrine and fluvial environments exposed in the southern, western, and northeastern part of the map area. In the southern and western part of the map area, sandstone and conglomerate are common, siltstone and shale are less common, and many localities have minor plant fossils and debris or thin (<2m thick) layers of lignite.  Conglomerates have clasts as large as boulder-sized (Chapman and others, 1982; Weber and others, 1992).  Paleocene, Eocene, Oligocene and Miocene pollen have been recovered from several sites (Weber and others, 1994, Chapman and others, 1982, unpublished oil industry data, written commun., 2002).  In the northeastern map area, the sequence contains basalt as well as mudstone, sandstone, gravels, and silt and is Miocene and Pliocene in age (Fouch and others, 1994)",70,,"Till, A.B., Dumoulin, J.A., Phillips, J.D., Stanley, R.G., Crews, Jesse, in prep., Generalized bedrock geologic map, Yukon Flats region, east-central Alaska:  U.S. Geological Survey Scientific Investigations Series Map SIM-XXX, scale 1:500,000."
1056,Tb,Basalt flows and rare cinder cones,Tertiary,"Vesicular, massive olivine basalt flows that range from 20 to 300 m thick exposed in the northeastern and northwestern parts of the map area, in the Brooks Range and Porcupine provinces. The best exposed and studied localilties are in the northeast (Coleen quadrangle; Fouch and others, 1994), where flows are interlayered with sedimentary rocks and have yielded 40Ar/39Ar ages that range from 15.7+/-0.1 to 14.4+/-0.1 Ma (Kunk and others, 1994)",142,,"Till, A.B., Dumoulin, J.A., Phillips, J.D., Stanley, R.G., Crews, Jesse, in prep., Generalized bedrock geologic map, Yukon Flats region, east-central Alaska:  U.S. Geological Survey Scientific Investigations Series Map SIM-XXX, scale 1:500,000."
1103,Tv,Volcanic rocks,Tertiary,"Locally thick packages that include basalt, andesite, dacite, and rhyolite flows and domes exposed in the southwestern part of the map area, all in the Brooks Range province.  The largest accumulation of these rocks is on the west side of the Ruby geanticline, where a sequence as thick as 2 km, predominantly dacite in composition, depositionally overlies sedimentary rocks of the Yukon-Koyukuk basin in the west and rocks of the Angayucham-Tozitna terrane in the east (Moll-Stalcup and Arth, 1989).  Andesite and rhyodacite are also present in the area.  Hornblende and biotite K/Ar ages from exposures near the bottom of the sequence yielded ages of 59.5 +/- 1.7 and 59.6 +/- 1.8 Ma respectively (Patton and Miller, 1973); a flow in an uncertain position in the sequence yielded a U-Pb zircon age of 62.4 +/- 0.3 Ma (A.B. Till, unpub. data).  In the Rampart area, rock compositions are limited to interbedded basalt and rhyolite flows, tuff-breccias, and ignimbrite (Reifenstuhl and others, 1997a).  40Ar/39Ar whole-rock ages on basalt dikes and flows range from 57.8 +/- 0.3 to 60.0 +/- 0.2 Ma (Reifenstuhl and others, 1997b).  A rhyolite flow near the Yukon River yielded a U-Pb zircon age of 59.5 +/- 0.5 Ma (A.B.Till, unpub. data)",14,,"Till, A.B., Dumoulin, J.A., Phillips, J.D., Stanley, R.G., Crews, Jesse, in prep., Generalized bedrock geologic map, Yukon Flats region, east-central Alaska:  U.S. Geological Survey Scientific Investigations Series Map SIM-XXX, scale 1:500,000."
1320,Tg,Granitic rocks,Tertiary,"Quartz monzonite, biotite granite, and alaskite exposed in the Rampart area of the Brooks Range province and in the Yukon-Tanana province. The two bodies in the Rampart area exposed between the Yukon River and Victoria Creek fault locally have igneous lineations (aligned long axes of crystals) and strongly deformed contact aureoles, indicating deformation occurred during intrusion.  The pluton on the Yukon River yielded a U-Pb zircon age of 60.5 +/- 0.2 Ma; the Manley pluton, on the southern boundary of the map area in the Tanana quadrangle, yielded a U-Pb zircon age of 60.9 +/- 1.0 Ma (A.B.Till, unpub. data).   40Ar/39Ar ages have been obtained from these and other plutons in this unit and range from 54 to 64 Ma (Reifenstuhl and others, 1997b, Wilson and others, 1994).  Two 66-Ma plutons in the Yukon-Tanana province at the boundary of units PzpCw and PzpCy are included in Kg, but have geologic similarities to adjacent plutons mapped as Tg",27,,"Till, A.B., Dumoulin, J.A., Phillips, J.D., Stanley, R.G., Crews, Jesse, in prep., Generalized bedrock geologic map, Yukon Flats region, east-central Alaska:  U.S. Geological Survey Scientific Investigations Series Map SIM-XXX, scale 1:500,000."
1510,TKs,Sedimentary rocks,Tertiary and Cretaceous,"Sandstone, mudstone, thin coal seems, and conglomerate exposed in the Takonduk and Rampart areas. In the Tatonduk area, the unit occurs just east of the Kandik basin and along the Tintina fault zone. Late Cretaceous, Paleocene, and Eocene pollen have been recovered from exposures within and immediately south of the map area (Miyaoka, 1990), and from shallow core holes (unpublished oil industry data, written commun., 2002).  In the western Rampart area, along the Victoria Creek fault zone, quartz and chert rich fluvial conglomerate, sandstone, and mudstone are typical, and palynoflora of probable Maastrichtian age (Farmer and others, 2003) as well as those of early Tertiary age (Chapman and others, 1982) have been collected. Younger part of the unit likely correlative to unit Ts",260,,"Till, A.B., Dumoulin, J.A., Phillips, J.D., Stanley, R.G., Crews, Jesse, in prep., Generalized bedrock geologic map, Yukon Flats region, east-central Alaska:  U.S. Geological Survey Scientific Investigations Series Map SIM-XXX, scale 1:500,000."
2030,Kkyu,"Sedimentary rocks of the Yukon-Koyukuk basin, undivided",Cretaceous,"Marine volcanic-clast conglomerate, graywacke, sandstone, mudstone, shale, calcareous sandstone, siltstone and shale, and minor non-marine sandstone and shale. Exposed in along the western boundary of the map.  Mollusks from the marine part of the unit are Albian; rare plant fossils from the non-marine part of the section range from late Early Cretaceous to Late Cretaceous in age (Patton and others, in press).  Marine rocks are thought to represent an oceanic basin that participated in the arc-continent collision that involved rocks of the Brooks Range province; non-marine rocks contain clasts of the Angayucham-Tozitna terrane (JDat) and quartz-rich rocks of units DpCs and PzpCb, and therefore record the unroofing of the southern Brooks Range and Ruby geanticline (Patton and others, 1994)",592,,"Till, A.B., Dumoulin, J.A., Phillips, J.D., Stanley, R.G., Crews, Jesse, in prep., Generalized bedrock geologic map, Yukon Flats region, east-central Alaska:  U.S. Geological Survey Scientific Investigations Series Map SIM-XXX, scale 1:500,000."
2122,Kku,"Sedimentary rocks of the Kandik basin, undivided",Cretaceous,"Carbonaceous shale, siltstone, quartz arenite, argillite, graywacke, sandstone, and conglomerate; parts of the section are rich in volcanic clasts.  Early Cretaceous (Valanginian and Berriasian) megafossils have been identified. Although correlations have been made between units in the Kandik basin and units in the Manley basin that contain Albian fossils (e.g., Dover, 1994), no unequivocally Albian strata have been identified in the Kandik basin (Johnsson, 2000).  Equivalent to the Kandik Group (Brabb, 1969)",494,,"Till, A.B., Dumoulin, J.A., Phillips, J.D., Stanley, R.G., Crews, Jesse, in prep., Generalized bedrock geologic map, Yukon Flats region, east-central Alaska:  U.S. Geological Survey Scientific Investigations Series Map SIM-XXX, scale 1:500,000."
2492,Kg,Granitic rocks,Cretaceous,"Small plugs to large, batholithic plutons, largely of mid-Cretaceous age, exposed in the Ruby geanticline, Manley basin, and Yukon-Tanana Upland.  Ruby geanticline plutons are generally evolved and yield U-Pb zircon and K/Ar ages of 112-90 Ma (Patton and others, 1994). In the Manley basin and western Yukon-Tanana Upland, plutons are slightly younger; they have yielded K/Ar and 40Ar/39Ar ages that range from 110 to 88 Ma (Newberry, 2000; Mortensen and others, 2000).  A belt of  90-88 Ma quartz-alkalic plutons in the western part of the province have been correlated with the Tombstone alkalic suite in the Yukon Territory (Dover, 1994; Mortensen and others, 2000)",99,,"Till, A.B., Dumoulin, J.A., Phillips, J.D., Stanley, R.G., Crews, Jesse, in prep., Generalized bedrock geologic map, Yukon Flats region, east-central Alaska:  U.S. Geological Survey Scientific Investigations Series Map SIM-XXX, scale 1:500,000."
2810,KJu,"Sedimentary rocks, undifferentiated",Cretaceous? and Jurassic?,"Scattered occurrences of shale, argillite and quartzite up to 300m thick exposed in central and northern part of Porcupine province (Brosg and Reiser, 1969; Brabb, 1970). Bivalves of Jurassic or Cretaceous age reported from one exposure in the Coleen quadrangle (Brosg and Reiser, 1969)",450,,"Till, A.B., Dumoulin, J.A., Phillips, J.D., Stanley, R.G., Crews, Jesse, in prep., Generalized bedrock geologic map, Yukon Flats region, east-central Alaska:  U.S. Geological Survey Scientific Investigations Series Map SIM-XXX, scale 1:500,000."
2860,Mzmv,Fine-graned sedimentary rocks and tuff,Cretaceous? and Jurassic?,"Slate, shale, siltstone, argillite, tuff, and minor quartzite and conglomerate exposed just south of the Tintina fault system and immediately northeast of the Manley basin. No direct age control.  Equivalent to the Vrain unit (""KJv"") of Weber and others (1992) and ""MzPzat"" unit of Foster and others (1983).  Parts of the unit thought to be correlative with the upper Glenn Shale (KJg) (Weber and others, 1992)",964,,"Till, A.B., Dumoulin, J.A., Phillips, J.D., Stanley, R.G., Crews, Jesse, in prep., Generalized bedrock geologic map, Yukon Flats region, east-central Alaska:  U.S. Geological Survey Scientific Investigations Series Map SIM-XXX, scale 1:500,000."
2861,KJg,"Glenn Shale, upper part",Late Cretaceous and Jurassic?,"Carbonaceous shale that contains minor thin (up to 5m) beds of fine-grained sandstone, exposed in the southern part of the Porcupine province. Depositionally overlain by sedimentary rocks of the Kandik basin (Kku).  Early Cretaceous megafossils have been collected from several localities within the unit (Miyaoka, 1990).  The Glenn Shale is included in two units on this map, a division that is consistent with recent mapping.  Brabb (1969), in his original description of the type section, noted that the section was faulted.  The age assigned to the unit was based on collections in the type section (Triassic and Early Cretaceous) and from exposures elsewhere (probable Jurassic; Brabb, 1969).  Dover and Miyaoka (1988) and Dover (1992) mapped the upper and lower parts of the unit separately, and show a fault between the two in the type section.  Dover (1992) noted that the upper part of the Glenn Shale is structurally detached from underlying rocks in most places, and that the upper part overlies units other than the lower Glenn Shale in at least one area.  No unequivocal Jurassic fossils have been identified in the upper Glenn Shale, nor has it been found in an unequivocally depositional relationship to the lower part of the Glenn Shale (Dover and Miyaoka, 1988; Johnsson, 2000)",952,,"Till, A.B., Dumoulin, J.A., Phillips, J.D., Stanley, R.G., Crews, Jesse, in prep., Generalized bedrock geologic map, Yukon Flats region, east-central Alaska:  U.S. Geological Survey Scientific Investigations Series Map SIM-XXX, scale 1:500,000."
3270,JMsu,"Strangle Woman Creek sequence of Brosge' and Reiser (1969), undivided",Jurassic to Mississippian,"Rock types include very fine grained to conglomeratic sandstone; gray limestone and dolostone; dark gray, very fine grained, thin-bedded limestone and black chert; and coarse-grained, conglomeratic, quartz sandstone that contain minor potassium feldspar, exposed in the northern part of the Porcupine province. The carbonate rocks of this unit were assigned to the Lisburne Group by Brosg and Reiser, 1969).  Dark, fine-grained quartzite contains Early Jurassic (Hettangian) ammonites (Brosg and Reiser (1969).  Unit also contains Permian or Carboniferous brachiopods and corals and Late Mississippian corals (Brosg and Reiser, 1969), as well as tightly dated Carboniferous conodonts.  Conodont faunas range from late Kinderhookian-middle Osagean to latest Chesterian-early Atokan in age; they indicate chiefly shallow-water, locally high-energy depositional settings, but the oldest sample suggests a slope environment (A.G. Harris, USGS Emeritus, written commun., 2000).  Juxtaposition of Lower Jurassic and Carboniferous-Permian strata seen in this unit is also seen in unit JMpu. The contact of this unit with the large granitic body, Cg, is not well exposed or understood ",532,,"Till, A.B., Dumoulin, J.A., Phillips, J.D., Stanley, R.G., Crews, Jesse, in prep., Generalized bedrock geologic map, Yukon Flats region, east-central Alaska:  U.S. Geological Survey Scientific Investigations Series Map SIM-XXX, scale 1:500,000."
3280,JMpu,"Younger strata of the Porcupine River sequence of Brosge' and Reiser (1969), undivided",Jurassic to Mississippian,"Main rock types are ferruginous, very fine grained sandstone; gray to black pyritic siltstone and silty shale; laminated, red and green chert; silty, shaly, and cherty limestone; coarse-grained to conglomeratic, locally feldspathic sandstone, mafic flows, and minor mafic conglomerate. Mafic rocks are geographically widespread within the unit (Brosg and Reiser, 1969; Brosg and others, 1966).  Carboniferous, Permian, and Jurassic megafauna are reported (Brosg and Reiser, 1969). Lithologic and faunal similarities to the Siksikpuk and Kuna Formations (Dumoulin and others, 2004) suggest ties between JMpu and correlative rocks of northern Alaska, but faunal links to strata to the south (e.g., Tahkandit Limestone, units TRPgt and PCta) also exist",452,,"Till, A.B., Dumoulin, J.A., Phillips, J.D., Stanley, R.G., Crews, Jesse, in prep., Generalized bedrock geologic map, Yukon Flats region, east-central Alaska:  U.S. Geological Survey Scientific Investigations Series Map SIM-XXX, scale 1:500,000."
4730,KJmu,"Sedimentary rocks of the Manley basin, undivided",Cretaceous and Jurassic,"Quartzite, shale, siltstone, graywacke, polymictic conglomerate exposed in the western part of the province.  Equivalent to the Minto, Wilber Creek, and Wolverine quartzite units of Weber and others (1992) and the Manley terrane of Jones and others (1987). Most of these rocks have been folded, faulted, and weakly metamorphosed, but most primary sedimentary textures are preserved.  The Minto unit, a thin, less deformed package of limited extent is thought to lie unconformably on the older rocks.  Older parts of the unit contain marine megafauna of Jurassic and Early Cretaceous (including Albian) age and the Minto unit has yielded plant fossils of Late Cretaceous(?) age (Weber and others, 1994)",560,,"Till, A.B., Dumoulin, J.A., Phillips, J.D., Stanley, R.G., Crews, Jesse, in prep., Generalized bedrock geologic map, Yukon Flats region, east-central Alaska:  U.S. Geological Survey Scientific Investigations Series Map SIM-XXX, scale 1:500,000."
5012,TrPs,Sedimentary rocks,Triassic? to early Permian,"Argillite, siltstone, sandstone, shale, chert, limestone, conglomerate, and limestone debris flows exposed along the southwestern margin of the Manley basin. The unit is structurally imbricated with the sedimentary rocks of the Manley basin (KJmu). Conodonts, foraminifera, and megafossils yielded Permian and less definite late Paleozoic ages (Weber and others, 1994); Triassic Radiolaria were also recovered (Weber and others,1992)",340,,"Till, A.B., Dumoulin, J.A., Phillips, J.D., Stanley, R.G., Crews, Jesse, in prep., Generalized bedrock geologic map, Yukon Flats region, east-central Alaska:  U.S. Geological Survey Scientific Investigations Series Map SIM-XXX, scale 1:500,000."
5035,TrPgt,"Glenn Shale, lower part, and Tahkandit Limestone, undivided",Triassic and Permian,"Thin-bedded fossiliferous limestone, calcareous shale and rare thin oil shale of the lower part of the Glenn Shale, and massive bioclastic limestone, glauconitic sandstone, and minor chert pebble conglomerate of the Tahkandit Limestone. Most of the exposures of this unit are in the southern part of the Porcupine province, but two small lenses (equivalent to lower Glenn Shale only) occur in the central Yukon-Tanana province, along a fault that separates KJmu from PzpCw (""Beaver Creek thrust"" of Weber and others, 1992). Combination of the two units into one follows the detailed mapping of Dover (1992) and Dover and Miyaoka (1988).  Reasons for separating the lower from the upper part of the Glenn Shale on this map are given in the description of the upper part of the Glenn Shale (KJg).   In the central Yukon-Tanana province, exposures of this unit are lithologically similar to the lower part of the Glenn Shale and have yielded Permian to Triassic conodonts (Weber and others, 1994).  In the southern part of the Porcupine province, the lower part of the Glenn Shale yielded Middle to Late Triassic megafossils, and the limestone of the Tahkandit yielded Permian megafossils and conodonts (Brabb and Grant, 1971; Miyaoka, 1990; A.G. Harris, USGS Emeritus, written commun., 2000)",720,,"Till, A.B., Dumoulin, J.A., Phillips, J.D., Stanley, R.G., Crews, Jesse, in prep., Generalized bedrock geologic map, Yukon Flats region, east-central Alaska:  U.S. Geological Survey Scientific Investigations Series Map SIM-XXX, scale 1:500,000."
5036,PCta,Sedimentary rocks of the Tatonduk area,Permian to Cambrian,"Limestone, argillite, shale, chert, quartz arenite and conglomerate exposed in the southern part of the Porcupine province.   The sequence includes several formal stratigraphic units, which are not enumerated here (see Dover, 1994).  Lower Paleozoic rocks include both basinal and shelf facies; youngest rocks include the Permian Step Conglomerate (Brabb, 1969) and parts of the Permian Tahkandit Limestone (Brabb and Churkin, 1969); other parts of the Tahkandit Limestone are mapped together with the lower Glenn Shale (TrPgt) due to the difficulty of showing the relatively thin unit on this regional-scale map.  The Cambrian through Permian fauna contained in this unit have strong North American affinities (Blodgett and others, 2002)",514,,"Till, A.B., Dumoulin, J.A., Phillips, J.D., Stanley, R.G., Crews, Jesse, in prep., Generalized bedrock geologic map, Yukon Flats region, east-central Alaska:  U.S. Geological Survey Scientific Investigations Series Map SIM-XXX, scale 1:500,000."
5133,JDat,"Angayucham-Tozitna terrane, undivided",Late Jurassic to Devonian,"Lithologically diverse, structurally imbricated igneous and sedimentary rocks of oceanic affinity exposed on all flanks of the Yukon Flats basin. Igneous rocks include ultramafic, mafic extrusive and intrusive, andesitic, and rare dacitic to rhyolitic igneous rocks. Mafic igneous rocks are most characteristic of the unit and locally contain minor amounts of interbedded chert and limestone. Sedimentary rocks are typically volumetrically subordinate to the igneous rocks.    Chert is the most common sedimentary lithology, but the presence of argillite, shale, and graywacke is characteristic; rare limestone and oil shale are known.  Sedimentary rocks are volumetrically significant in the large exposure of the unit in the northeastern part of the map area (Coleen quadrangle; Brosg and Reiser, 1969). Both igneous and sedimentary rocks are partially to fully recrystallized to low-grade metamorphic assemblages (Dusel-Bacon and others, 1989; A.B. Till, unpub. data); one exposure in the Beaver quadrangle records amphibolite to granulite facies metamorphism (Ghent and others, 2001). In the southern Brooks Range and Ruby geanticline, the terrane structurally overlies metamorphosed sedimentary rocks of unit DpCs.   Hornblendes from four exposures of gabbro in the Rampart area and Christian quadrangle have yielded K-Ar ages that range from 207 to 174 Ma (Brosg and others, 1969; Brosg and Reiser, 2000), but low potassium contents of the amphiboles (and low radiogenic yields in the geochronologic analysis) place the accuracy of these ages in question. A gabbro near Rampart yielded a U-Pb zircon age of 231-230 Ma (Triassic; R. Friedman, written commun. 2004).  Radiolarians, conodonts, and pollen from sedimentary rocks interlayered with the mafic rocks and from the predominantly sedimentary sections yielded ages of Devonian, Mississippian, Pennsylvanian, Permian, Triassic, and Early Jurassic.  Unit includes rocks previously assigned to the Angayucham and Tozitna terranes (Jones and others, 1987), Rampart Group (Brosg and others, 1969), Circle Volcanics (Mertie, 1930; Foster and others, 1983), and Christian complex (Reiser and others, 1965)",306,,"Till, A.B., Dumoulin, J.A., Phillips, J.D., Stanley, R.G., Crews, Jesse, in prep., Generalized bedrock geologic map, Yukon Flats region, east-central Alaska:  U.S. Geological Survey Scientific Investigations Series Map SIM-XXX, scale 1:500,000."
5209,MzPza,Low-grade metamorphic rocks,Mesozoic? and Paleozoic,"Phyllite, argillaceous metachert, limestone, and associated mafic rocks. Exposed only in southeast part of the map area adjacent to Tintina fault. Includes some areas dominated by argillite, equivalent to ""Mza"" of Foster (1992), and other lithologically complex packages (their ""PzPun"") thought to include rocks with affinities both north and south of the Tintina fault zone. Equivalent to ""MzPzm"" of Dover (1992), which is described as ""typically blastomylonitic"". The age of the protoliths and metamorphic event(s) are unknown; age assignment based on age of lithologically similar rocks along the fault zone",322,,"Till, A.B., Dumoulin, J.A., Phillips, J.D., Stanley, R.G., Crews, Jesse, in prep., Generalized bedrock geologic map, Yukon Flats region, east-central Alaska:  U.S. Geological Survey Scientific Investigations Series Map SIM-XXX, scale 1:500,000."
5213,TrPzd,"Metasedimentary and metavolcanic rocks, sedimentary rocks of the Doonerak area",Triassic to late Paleozoic,"Fine-grained metasedimentary rocks that contain lenticular bodies of carbonate rocks; metavolcanic and metavolcaniclastic rocks of island arc affinity, and a thin sequence of  shale, siltstone and limestone (Dillon and others, 1986; Moore and others, 1994).  Exposed in the northwestern part of the map area.  Cambrian, Ordovician, and Silurian megafossils have been recovered from the metasedimentary rocks (Moore and others, 1994). Just below the fault on the northern contact of the unit, these lower Paleozoic rocks are depositionally overlain by a sequence of sedimentary rocks of Mississippian to Triassic age (Dillon and others, 1986).   This unit represents rocks buried by faulting during the early phases of Brooks Range deformation and uplifted into an arch during the Tertiary (O'Sullivan and others, 1997). The older rocks in the core of the arch are thought to represent basement to the foreland of the Brooks Range (Moore and others, 1994)",956,,"Till, A.B., Dumoulin, J.A., Phillips, J.D., Stanley, R.G., Crews, Jesse, in prep., Generalized bedrock geologic map, Yukon Flats region, east-central Alaska:  U.S. Geological Survey Scientific Investigations Series Map SIM-XXX, scale 1:500,000."
5335,Pzvu,"Sedimentary rocks of the Venetie terrane of Silberling and others (1994), undivided",Paleozoic,"Lithic and quartz wacke, metamorphosed wacke, metasandstone, phyllite, slate, shale, quartzite, chert, and minor greenstone (Brosg and Reiser, 2000).  Devonian (?) plants and spores, Mississippian (?) Radiolaria, and Permian conodonts have been recovered from this unit. May be at least in part correlative with unit DpCs. The unit was included in the Slate Creek subterrane by Moore and others (1994)",445,,"Till, A.B., Dumoulin, J.A., Phillips, J.D., Stanley, R.G., Crews, Jesse, in prep., Generalized bedrock geologic map, Yukon Flats region, east-central Alaska:  U.S. Geological Survey Scientific Investigations Series Map SIM-XXX, scale 1:500,000."
5335,Pzcm,Metamorphic rocks,Paleozoic?,"Semischist, phyllite, and thin layers of mafic rock exposed in the extreme northeast corner of the Porcupine province.  Rocks are generally fine grained, and the metamorphic assemblage locally includes biotite and garnet. Contact with adjacent granite is intrusive, but contact with sedimentary rocks is poorly exposed and not understood",477,,"Till, A.B., Dumoulin, J.A., Phillips, J.D., Stanley, R.G., Crews, Jesse, in prep., Generalized bedrock geologic map, Yukon Flats region, east-central Alaska:  U.S. Geological Survey Scientific Investigations Series Map SIM-XXX, scale 1:500,000."
5470,Pzum,Ultramafic rocks,Paleozoic?,"Serpentinite and lesser gabbro and rodingite rubble limited to one small area in the southwest part of the province. Based on trace element data, Reifenstuhl and others (1998) considered these rocks to have formed originally in an oceanic arc or ridge setting; the unit likely marks the trace of a major structure within the deformed sedimentary rocks of the Manley basin (KJmu).  Hornblende from gabbro has yielded a disturbed 40Ar/39Ar age spectrum suggestive of early Paleozoic age (Reifenstuhl and others, 1998)",429,,"Till, A.B., Dumoulin, J.A., Phillips, J.D., Stanley, R.G., Crews, Jesse, in prep., Generalized bedrock geologic map, Yukon Flats region, east-central Alaska:  U.S. Geological Survey Scientific Investigations Series Map SIM-XXX, scale 1:500,000."
5560,DZs,Metamorphosed sedimentary rocks,Devonian to Proterozoic,"Variably metamorphosed and deformed shale, siltstone, fine- to medium-grained sandstone, graywacke, quartz and chert wacke, and minor conglomerate, carbonate, and mafic rocks.  Quartz-rich rocks that contain chert clasts are common. Sedimentary structures are preserved locally, but the unit is penetratively deformed elsewhere, especially near the contacts with subjacent metamorphic rocks, where contacts appear gradational. In general, the unit has not been studied in any detail and may contain several sequences of sedimentary rocks, not necessarily of a common origin.  Metamorphic grade is greenschist-facies in most parts of the unit but prehnite-pumpellyite facies on the west side of the Ruby geanticline (Dusel-Bacon and others, 1989). The unit sits structurally above large belts of metamorphosed continental margin sediments (unit PzpCb) and structurally below the oceanic assemblage of the Angayucham-Tozitna terrane (JDat), and therefore may be composed of structurally juxtaposed sedimentary packages.  Some age data are available.  Five localities in the large exposure of the unit in the central Tanana quadrangle yielded Late Devonian (Famennian) conodonts (A.G. Harris, USGS Emeritus, written commun., 2000).  Two detrital zircon samples from the same area have been analyzed; one contains populations of zircons similar to those contained in the Wickersham and Yukon-Tanana terranes, while the other contains a limited population that lacks those populations (Bradley and others, in press). Therefore, it is possible that part of the unit in the Tanana quadrangle contains infolded rocks from the Wickersham or Yukon-Tanana terranes, which would extend the age of the unit into the Late Proterozoic.    Early Devonian palynoflora were collected from exposures in the southern Brooks Range (Gottschalk and others, 1998); Early-Middle Devonian conodonts and Devonian brachiopods were recovered from exposures in the Beaver quadrangle (A.G. Harris, USGS Emeritus, written commun., 2000; Brosg and others, 1973).  Includes part of the Slate Creek subterrane of the Arctic Alaska terrane of Moore and others (1994), and the Slate Creek thrust panel  of the Angayucham-Tozitna terrane of Patton and others (1994).   Also informally called the phyllite-graywacke belt.  May be in part correlative with Venetie terrane of the Brooks Range (unit Pzvu), and metasedimentary rocks exposed along the Tintina fault system on the southern flank of the Yukon Flats basin (DSc)",435,,"Till, A.B., Dumoulin, J.A., Phillips, J.D., Stanley, R.G., Crews, Jesse, in prep., Generalized bedrock geologic map, Yukon Flats region, east-central Alaska:  U.S. Geological Survey Scientific Investigations Series Map SIM-XXX, scale 1:500,000."
5561,DZs,Metamorphosed sedimentary rocks,Devonian to Proterozoic,"Variably metamorphosed and deformed shale, siltstone, fine- to medium-grained sandstone, graywacke, quartz and chert wacke, and minor conglomerate, carbonate, and mafic rocks.  Quartz-rich rocks that contain chert clasts are common. Sedimentary structures are preserved locally, but the unit is penetratively deformed elsewhere, especially near the contacts with subjacent metamorphic rocks, where contacts appear gradational. In general, the unit has not been studied in any detail and may contain several sequences of sedimentary rocks, not necessarily of a common origin.  Metamorphic grade is greenschist-facies in most parts of the unit but prehnite-pumpellyite facies on the west side of the Ruby geanticline (Dusel-Bacon and others, 1989). The unit sits structurally above large belts of metamorphosed continental margin sediments (unit PzpCb) and structurally below the oceanic assemblage of the Angayucham-Tozitna terrane (JDat), and therefore may be composed of structurally juxtaposed sedimentary packages.  Some age data are available.  Five localities in the large exposure of the unit in the central Tanana quadrangle yielded Late Devonian (Famennian) conodonts (A.G. Harris, USGS Emeritus, written commun., 2000).  Two detrital zircon samples from the same area have been analyzed; one contains populations of zircons similar to those contained in the Wickersham and Yukon-Tanana terranes, while the other contains a limited population that lacks those populations (Bradley and others, in press). Therefore, it is possible that part of the unit in the Tanana quadrangle contains infolded rocks from the Wickersham or Yukon-Tanana terranes, which would extend the age of the unit into the Late Proterozoic.    Early Devonian palynoflora were collected from exposures in the southern Brooks Range (Gottschalk and others, 1998); Early-Middle Devonian conodonts and Devonian brachiopods were recovered from exposures in the Beaver quadrangle (A.G. Harris, USGS Emeritus, written commun., 2000; Brosg and others, 1973).  Includes part of the Slate Creek subterrane of the Arctic Alaska terrane of Moore and others (1994), and the Slate Creek thrust panel  of the Angayucham-Tozitna terrane of Patton and others (1994).   Also informally called the phyllite-graywacke belt.  May be in part correlative with Venetie terrane of the Brooks Range (unit Pzvu), and metasedimentary rocks exposed along the Tintina fault system on the southern flank of the Yukon Flats basin (DSc)",435,,"Till, A.B., Dumoulin, J.A., Phillips, J.D., Stanley, R.G., Crews, Jesse, in prep., Generalized bedrock geologic map, Yukon Flats region, east-central Alaska:  U.S. Geological Survey Scientific Investigations Series Map SIM-XXX, scale 1:500,000."
5965,Pzqs,Sedimentary and igneous rocks,"Permian, Carboniferous, and Devonian","Quartz-rich sedimentary rocks, associated carbonate rocks and minor mafic volcanic rocks.  The quartz-rich rocks are by far the most common lithologies and consist of chert arenite, quartz-chert wacke, quartzite, chert-pebble conglomerate, minor mudstone and siltstone; these rocks occur throughout the Porcupine province.  The unit includes associated small bodies of Devonian, Carboniferous, and Permian carbonate rocks, mostly exposed in the southern part of the province.  In the Charley River quadrangle the unit also includes shale, argillite, and limestone that contains Permian and Carboniferous brachiopods, and Devonian basalt, tuff, limestone, chert, argillite, and quartzite of the Woodchopper Volcanics (Brabb and Churkin, 1969).  No direct age control is available from the widely distributed siliciclastic rocks in the unit.  As noted by Dover (1992, 1994), in the Charley River quadrangle the paucity of age data and lithologic similarities among siliciclastic rocks makes unit assignations difficult. There, siliciclastic rocks mapped as Permian Step Conglomerate by Brabb and Churkin (1969) were later mapped as Devonian Nation River Formation by Dover (1994). Since age control is lacking for the dominant lithology, and the minor lithologies for which age control is available are restricted to the southern part of the province, it is possible that the unit may include rocks older than Devonian",412,,"Till, A.B., Dumoulin, J.A., Phillips, J.D., Stanley, R.G., Crews, Jesse, in prep., Generalized bedrock geologic map, Yukon Flats region, east-central Alaska:  U.S. Geological Survey Scientific Investigations Series Map SIM-XXX, scale 1:500,000."
6300,KDe,Sedimentary rocks of the Endicott Mountains allochthon of Moore and others (1994),Cretaceous to Devonian,"Thick marine and non-marine sedimentary sequence dominated by Devonian and Mississippian clastic and carbonate rocks of the Endicott and Lisburne Groups (Moore and others, 1994)",958,,"Till, A.B., Dumoulin, J.A., Phillips, J.D., Stanley, R.G., Crews, Jesse, in prep., Generalized bedrock geologic map, Yukon Flats region, east-central Alaska:  U.S. Geological Survey Scientific Investigations Series Map SIM-XXX, scale 1:500,000."
6328,Mbu,"Rocks of Bruooks Range sequence of Brosge' and Reiser (2000), undivided",Mississippian,"Consists of gray to brown, fine- to medium-grained, partly crinoidal limestone (Lisburne Group); black shale, laminated siltstone, chert, and orange-weathering limestone (Kayak Shale); and unnamed black siltstone and shaly phosphatic limestone (Brosg and Reiser, 1969). Exposed in the northeastern part of the map area. The black siltstone and shaley phosphatic limestone may be correlative with the phosphatic ""drowned platform"" facies of the Lisburne Group (Dumoulin and others, 2002) in the central and western Brooks Range. Contains mega- and microfossils of Mississippian age",956,,"Till, A.B., Dumoulin, J.A., Phillips, J.D., Stanley, R.G., Crews, Jesse, in prep., Generalized bedrock geologic map, Yukon Flats region, east-central Alaska:  U.S. Geological Survey Scientific Investigations Series Map SIM-XXX, scale 1:500,000."
6970,DCpu,"Older strata of the Porcupine River sequence of Brosge' and Reiser (1969), undivided",Devonian to Cambrian,"Succession includes dark gray limestone and lesser dolostone that contains Middle Devonian corals; the Salmontrout Limestone of Early Devonian age (Churkin and Brabb, 1965); and light to dark gray, locally mottled dolostone and limestone of Silurian and older age (Brosg and Reiser, 1969).  Subordinate lithologies are gray and black chert, black shale, red and green shale and sandstone, and limestone cobble conglomerate (Brosg and others, 1966; Brosg and Reiser, 1969).  The unit is exposed in northern part of the Porcupine province.  Most precise ages for older part of succession based on Late Silurian and Late(?) Ordovician corals and Cambrian(?) trilobites (Brosg and Reiser, 1969).  Conodonts of Early Silurian and middle Middle Ordovician ages also occur in these strata (A.G. Harris, USGS Emeritus, written commun., 2000). Brosg and others (1966) describe this succession in the Porcupine River canyon, in the northern part of the Porcupine province on the boundary between the Black River and Coleen quadrangles.  Less lithologic detail is available for unit in southern part of map area, but a similar suite of ages is indicated by corals, stromatoporoids, brachiopods, and gastropods (Brabb, 1970) as well as by conodonts (A.G. Harris, USGS Emeritus, written commun., 2000). Lithofacies and faunal data suggest that most of DCpu formed in a relatively shallow-water shelf or platform setting, but Upper Silurian and Lower Devonian graptolitic shale, limestone, and chert in the Porcupine River area (Churkin and Brabb, 1967; Coleman, 1985) accumulated in a slope or basin environment and may correlate with the Road River Formation (Churkin and Brabb, 1965; Brabb and Churkin, 1969), which is included in unit PCta in the southern part of the province.  Conodonts and megafossils in DCpu have chiefly Laurentian (North American) affinities (Oliver and others, 1975; Rohr and Blodgett, 1994; Dumoulin and others, 2002; Blodgett and others, 2002)",513,,"Till, A.B., Dumoulin, J.A., Phillips, J.D., Stanley, R.G., Crews, Jesse, in prep., Generalized bedrock geologic map, Yukon Flats region, east-central Alaska:  U.S. Geological Survey Scientific Investigations Series Map SIM-XXX, scale 1:500,000."
6990,DSc,Metamorphosed sedimentary rocks,Devonian and Silurian,"Chert and chert-pebble conglomerate, calcarenite, conglomeratic limestone, limestone, metasiltstone and argillite, mafic intrusive rocks, and rare dolostone exposed between the Tintina fault zone and the Yukon Flats basin, in the northern part of the Yukon-Tanana province.   Conodonts recovered from the unit have broad age ranges, are Late Devonian (Famennian) or are Silurian in age (A.G. Harris, USGS Emeritus, written commun., 2000).  This unit may be in part correlative with DpCs, which contains Famennian conodonts and similar lithologies in the central Tanana quadrangle.   Silurian conodonts were collected along the northern contact of DSc and may be from a fault slice of older rocks",434,,"Till, A.B., Dumoulin, J.A., Phillips, J.D., Stanley, R.G., Crews, Jesse, in prep., Generalized bedrock geologic map, Yukon Flats region, east-central Alaska:  U.S. Geological Survey Scientific Investigations Series Map SIM-XXX, scale 1:500,000."
7050,Cg,Granite,Carboniferous,"Granite and quartz monzonite, exposed in large body on the northeast boundary of the map.  Northern contact with adjacent metamorphic rocks is intrusive; southern boundary is shown as a fault but is not well exposed nor well understood. K/Ar mica ages range from 354 to 302 Ma (Brosg and Reiser, 1969)",44,,"Till, A.B., Dumoulin, J.A., Phillips, J.D., Stanley, R.G., Crews, Jesse, in prep., Generalized bedrock geologic map, Yukon Flats region, east-central Alaska:  U.S. Geological Survey Scientific Investigations Series Map SIM-XXX, scale 1:500,000."
7990,CPt,Sedimentary rocks of the Tindir Group,Cambrian? and Proterozoic,"Phyllite, slate, siltstone, argillite, quartzite, red beds, carbonate-clast conglomerate, dolostone, limestone, basalt, chert, and glacial diamictite exposed in the southeast part of the Porcupine province.  See Dover (1994) for a summary of the formal units included in this sequence.  Carbonate rocks, quartzite, and argillite are the most common and widespread lithologies (Dover, 1994). The Cambrian(?) age is based on several occurrences of the trace fossil Oldhamia (Miyaoka, 1990).  The Proterozoic age is based on lithologic correlation with areally extensive successions of sedimentary rocks that were deposited on the ancient North American continental margin during and after rifting of its western margin (Eberlein and Lanphere, 1988; Dover, 1994).  The lower part of the Tindir Group is considered correlative with the Mackenzie Supergroup, while the upper part of the Group is likely correlative with the Windemere Supergroup (Young, 1982, 1992; Rainbird and others, 1996)",601,,"Till, A.B., Dumoulin, J.A., Phillips, J.D., Stanley, R.G., Crews, Jesse, in prep., Generalized bedrock geologic map, Yukon Flats region, east-central Alaska:  U.S. Geological Survey Scientific Investigations Series Map SIM-XXX, scale 1:500,000."
8440,PzZl,Sedimentary and igneous rocks corresponding to the Livengood area swquence of Weber and others (1992),Paleozoic to Proterozoic,"Argillite, phyllite, quartzite, graywacke, siltite, grit and limestone of the Wickersham unit, mafic intrusive and extrusive rocks and fine grained sedimentary rocks interlayered with serpentinite, equivalent to ""PzZm"" and ""CZum"" units; dolomite, chert, argillite, and minor greenstone, tuff, and volcanic graywacke and basalt flows equivalent to the Amy Creek unit;  chert and lesser sedimentary breccia, siliceous slate, rare greenstone, tuff, limestone and mafic flows and sills equivalent to the Livengood Dome Chert;  lime mudstone, wackestone, debris flows equivalent to the Lost Creek unit; shale, siltstone, graywacke, polymict conglomerate, and fossiliferous limestone equivalent to the Cascaden Ridge unit; cherty argillite, chert, siliceous slate, mafic intrusive and extrusive rocks of the Troublesome unit, and limestone associated with phyllite, quartzose sandstone, graywacke, and polymict conglomerate of the Quail unit.  Gabbro associated with the serpentinite of ""CZum"" yielded a 40Ar/39Ar hornblende age of 535.3 +/-  2.7 Ma (Athey and others, 2004).  Weber and others (1994) reported all paleontologic control on the age the rocks in this unit. Late Ordovician graptolites were recovered from sedimentary rocks of the Livengood Dome Chert; megafossils from the lime mudstone of the Lost Creek unit are Silurian; fossiliferous siltstone and limestone of the Cascaden Ridge unit is Middle Devonian, based on a variety of megafossils and conodonts; biogenic lime  mudstone and wackestone of the Quail unit are Late Devonian. Siliciclastic rocks of the Quail unit are thought to be correlative with the Devonian Nation River Formation (Weber and others, 1992).   Parts of this unit have been correlated with Selwyn Basin and the Farewell terrane, (Dover,1994; Grantz and others, 1991; Chapman and others,1982). Fauna contained in parts of the unit are similar to those in the Nixon Fork sequence of the Farewell terrane (Blodgett and others, 2002; Dumoulin and others, 2002), which is thought to have been located between North America and Siberia during the early Paleozoic (Bradley and others, 2003)",475,,"Till, A.B., Dumoulin, J.A., Phillips, J.D., Stanley, R.G., Crews, Jesse, in prep., Generalized bedrock geologic map, Yukon Flats region, east-central Alaska:  U.S. Geological Survey Scientific Investigations Series Map SIM-XXX, scale 1:500,000."
8441,PzZw,Sedimentary and igneous rocks corresponding to the older parts of the Fairbanks-White Mountains area sequence of Weber and others (1992),Paleozoic to Proterozoic,"Argillite, grit, quartzite, graywacke, phyllite, limestone, and dolomite, equivalent to the Wickersham unit;  alkali basalt, agglomerate, volcanic conglomerate, and associated limestone, sandstone and chert, equivalent to the Fossil Creek Volcanics; mudstone, limestone, packstone and grainstone, lime mudstone and wackestone equivalent to the Tolovana Limestone; and conglomerate, graywacke, siltstone, and quartzite that is cut by mafic sills, equivalent to the Beaver bend and Globe units of (Weber and others, 1992). Exposed in a belt east of the  Manley basin.  All fossil ages for the unit are reported in Weber and others (1994).  The part of the sequence that includes the grit contains the Precambrian to Cambrian trace fossil Oldhamia; sedimentary rocks associated with the alkali basalt yielded mega-and micro-fossils of Ordovician age; and Silurian and Middle Devonian megafossils and Silurian conodonts were recovered from thick limestone.  This unit contains Ordovician and Silurian rocks absent from unit PzZs and lacks the Devonian volcanics found in unit PzZs.  Parts of this unit have been correlated with lithologically similar strata in the Selwyn basin and Cassiar platform of western Canada (Dover, 1994, Tempelman-Kluit, 1984)",266,,"Till, A.B., Dumoulin, J.A., Phillips, J.D., Stanley, R.G., Crews, Jesse, in prep., Generalized bedrock geologic map, Yukon Flats region, east-central Alaska:  U.S. Geological Survey Scientific Investigations Series Map SIM-XXX, scale 1:500,000."
8442,PzZs,Sedimentary and igneous rocks corresponding to older parts of the Schwatka-Rampart area sequence of Webber and others (1992),Paleozoic to Proterozoic,"Grit, argillite, quartzite, siltite, graywacke, phyllite, and minor limestone; interlayered mafic volcanic rocks and limestone, minor associated greenstone, limestone, and limestone debris flows, and a group of fine-grained metamorphic and sedimentary rocks (Weber and others, 1992). The unit is exposed in belt immediately west of the Victoria Creek fault zone.  It is equivalent to the Wickersham, Schwatka, and ""PDms"" (""metamorphic and sedimentary rocks"") units of Weber and others (1992).  The part of the sequence that includes the grit yielded the trace fossil Oldhamia, of Precambrian to Cambrian age; limestone interlayered with mafic volcanic rocks yielded Devonian megafossils and Early and Middle Devonian conodonts (Weber and others, 1994). Late Devonian conodonts were obtained from clasts in limestone debris flows (Weber and others, 1994).  Middle Devonian mafic volcanic rocks of the unit were correlated by Grantz and others (1991) and Dover (1994) with the Devonian Woodchopper Volcanics (Mertie, 1930) of the Charley River quadrangle. The Woodchopper Volcanics have been included in unit Pzqs on this map.  Lacks rocks of Ordovician and Silurian age; contained Devonian rocks do not correlate with those present in units PzZw and PzZl",364,,"Till, A.B., Dumoulin, J.A., Phillips, J.D., Stanley, R.G., Crews, Jesse, in prep., Generalized bedrock geologic map, Yukon Flats region, east-central Alaska:  U.S. Geological Survey Scientific Investigations Series Map SIM-XXX, scale 1:500,000."
8630,PzpCy,"Metamorphic rocks of the Yukon-Tanana Upland, undivided",Paleozoic to Precambrian?,"Fault-bounded assemblages of lithologically and metamorphically distinct metaigneous and metasedimentary rocks that have Paleozoic and Precambrian(?) protoliths exposed in the south-central part of the map (Dusel-Bacon and others, 2002).  Structurally lower assemblages, most with continental affinities, have been deformed in a ductile manner and metamorphosed to greenschist and amphibolite facies. A Late Devonian to Mississippian magmatic episode produced felsic (metavolcanic and metaplutonic) and mafic metaigneous rocks that are present in several of these assemblages (Dusel-Bacon and others, 2004). Recent efforts at U-Pb geochronology reveal that the Yukon-Tanana felsic metaigneous rocks are younger than felsic metavolcanic and metaplutonic rocks in the Brooks Range, although they were previously considered to be correlative (McClelland and others, 2006). Weakly metamorphosed oceanic rocks were tectonically emplaced over the higher-grade assemblages during the Mesozoic (Dusel-Bacon and others, 2002). This unit extends far into Canada where similar assemblages and histories have been observed (see references in Dusel-Bacon and others, 2004).  Complex nomenclature regarding these rocks is reviewed in Foster (1992) and Dusel-Bacon and others (2002).  Small exposures of Cretaceous and Tertiary volcanic rocks and Tertiary sedimentary rocks are included in the unit as they can not be shown at this map scale (Foster, 1992)",65,,"Till, A.B., Dumoulin, J.A., Phillips, J.D., Stanley, R.G., Crews, Jesse, in prep., Generalized bedrock geologic map, Yukon Flats region, east-central Alaska:  U.S. Geological Survey Scientific Investigations Series Map SIM-XXX, scale 1:500,000."
8850,PzpCh,Metasedimentary and metaigneous rocks of the Hammond terrane,Paleozoic and (or) Precambrian,"Thick sequences of lower Paleozoic metacarbonate rocks commonly called the Skajit Limestone (Moore and others, 1994), thick sequences of metasiliciclastics, metamorphosed calcareous sedimentary rocks, and minor mafic metagabbro and metafelsite exposed immediately north of unit PzpCb.  West of the map area, Late Proterozoic metamorphic rocks are known (Till, 1989; McClelland, 2006). Cambrian, Ordovician, Silurian, and Devonian fossils have been collected within the area shown on this map (Dumoulin and Harris, 1994); Mississippian rocks occur in the unit west of the map area (Moore and others, 1994). Lower Paleozoic rocks contain fauna that have Siberian affinities (Dumoulin and others, 2002). A large volume of the rocks included in this terrane are of an unknown age.  Multiple deformational events, both ductile and brittle, and multiple metamorphic events have affected these rocks (Till and others, 1988; O'Sullivan and others, 1997)",322,,"Till, A.B., Dumoulin, J.A., Phillips, J.D., Stanley, R.G., Crews, Jesse, in prep., Generalized bedrock geologic map, Yukon Flats region, east-central Alaska:  U.S. Geological Survey Scientific Investigations Series Map SIM-XXX, scale 1:500,000."
8852,PzpCm,Metamorphic rocks,Paleozoic and (or) Precambrian? ,"Pelitic schist, amphibolite, metaquartzite, marble, and granitic orthogneiss that occur as three lenses in or near the Kobuk and Victoria Creek fault systems.  Not all lithologies are found in all three lenses.  Protolith ages are unknown.   Metamorphic assemblages formed at amphibolite facies.  The southern of two lenses along the Victoria Creek fault yielded three biotite and white mica 40Ar/39Ar ages of 61 Ma (Reifenstuhl and others, 1997a), which are interpreted as metamorphic cooling ages.  One of the lenses along the Kobuk fault system yielded a 40Ar/39Ar age of 54.8 +/- 1.3 Ma (Roeske and others, 2003). Other rocks metamorphosed during the early Tertiary occur between the Tozitna fault and Yukon River but are too small to show on the map. The eastern of the two lenses associated with the Kobuk fault zone is equivalent to the Mosquito terrane of Jones and others, 1988",95,,"Till, A.B., Dumoulin, J.A., Phillips, J.D., Stanley, R.G., Crews, Jesse, in prep., Generalized bedrock geologic map, Yukon Flats region, east-central Alaska:  U.S. Geological Survey Scientific Investigations Series Map SIM-XXX, scale 1:500,000."
9325,PzpCb,Metasedimentary and metaigneous rocks of the southern Brooks Range and Ruby geanticline,Paleozoic and (or) Precambrian,"Quartz-mica schist and lesser calcareous schist, marble, mafic schist, and granitic orthogneiss, exposed along the southern Brooks Range and axis of the Ruby geanticline.  Early Devonian microfossils were collected from marble in the Wiseman quadrangle (Moore and others, 1997).  U-Pb zircon ages from orthogneisses, which occur in both the Brooks Range and the Ruby geanticline, are Middle Devonian (Aleinikoff and others, 1993; Patton and others, 1987), older than the Late Devonian orthogneisses of unit PzpCy in the Yukon-Tanana province.   Proterozoic orthogneisses are known in comparable units in the Brooks Range west of the map area (Karl and Aleinikoff, 1990).  Protoliths are thought to have had a continental affinity and undergone high-pressure metamorphism (blueschist-facies) and penetrative ductile deformation in the middle Jurassic or earlier",53,,"Till, A.B., Dumoulin, J.A., Phillips, J.D., Stanley, R.G., Crews, Jesse, in prep., Generalized bedrock geologic map, Yukon Flats region, east-central Alaska:  U.S. Geological Survey Scientific Investigations Series Map SIM-XXX, scale 1:500,000."