bu
Bedrock of unknown type or age
Areas that air photo interpretation suggest as being underlain by bedrock.  Typically are of higher elevation than surrounding glacial deposits and show hints of structure.  Also includes rubble of metasiltstone and chert in the Kantishna River quadrangl
Wilson, F.H., Dover, J.H., Bradley, D.C., Weber, F.R., Bundtzen, T.K., and Haeussler, P.J., 1998, Geologic map of Central (Interior) Alaska:  U.S. Geological Survey Open-File Report 98-133, 3 sheets, scale 1:500,000, 63 p. pamphlet, 13 p. appendix.
Qua
Surficial deposits, undifferentiated
Quaternary
Chiefly silt and very fine sand including thick deposits of micaeous silt in the Koyukuk Flats and Nowitna and Innoko Lowlands.  Local deposits of alluvial fan and glacial outwash gravels
Patton, W.W., Jr., Wilson, F.H., Labay, K.A., and Shew, Nora, in prep., Reconnaissance geologic map and digital data for the Yukon-Koyukuk basin, Alaska - (Integrated digital geologic map databases of the United States):  U.S. Geological Survey Scientifi
Qf
Floodplain and tidal flats deposits
Holocene
Gravel, sand, silt, and peat. Floodplain deposits in Koyukuk Flats and along Yukon River composed mainly of light gray micaceous silt
Qsa
Actively drifting and recently stabilized dune fields
Fine- to coarse-grained sand.  Great Kobuk and Little Kobuk Sand Dunes in the southwestern Ambler River and southeastern Baird Mountains quadrangles, and Nogahabara Sand Dunes in the Kateel River quadrangle.   The Great Kobuk and Little Kobuk dune fields
Qs
Eolian and water-laid sand and silt sheets and stabilized dune fields
Holocene and Pleistocene
Sand and coarse silt.  1)  Baird Mountains, Ambler River, Selawik,  and  Shungnak quadrangles:  Modified and partly dissected sheets of mixed wind-blown and water-laid deposits bordering the south edge of the Brooks Range; 2)  Kateel River and Melozitna
QTgl
Glacial and glaciolacustrine deposits
Pleistocene and Pliocene?
Includes unsorted to poorly sorted till, outwash sand and gravel, alluvium, and eolian deposits.  Along the southern edge of the Brooks Range, unit is characterized by little-modified middle and late Pleistocene drift including prominent morainal ridges
QTgr
Quartz gravel deposits
Quaternary or Tertiary
High-level deposits of quartz pebble gravel; overlies basalt flows of unit Tb
Qab
Alkalic basalt cones and flows
Pleistocene
Unit comprises numerous alkali basalt, basanite, and hawaiite cones, short flows, and maar craters.  Cones and flows have little or no vegetative cover and still preserve some primary flow structures. Locally contains peridotite and pyroxenite xenoliths.
Qtb
Tholeiitic basalt cones and flows
Holocene? and Pleistocene
Black glassy olivine tholeiitic basalt flows erupted from two small craters. Flows exhibit well-developed pahoehoe crusts and lack vegetative cover.   One K/Ar isotopic determination from this unit gave a cooling age of 0.19 Ma
QTb
Basalt flows
Pleistocene and Pliocene
Includes the Wrangell Lava consisting chiefly of basalt and andesite in the southeastern part of the map area and olivine basalt and vesicular andesite in the northern part of the map area
Ts
Small deposits of nonmarine conglomerate, sandstone, shale, and coal
Tertiary
Poorly consolidated nonmarine deposits occur in five areas listed below; the first three are located close to the Kaltag Fault. Pollen  samples from these five areas  range in age from Oligocene to Pliocene.:  1)  Unalakleet quadrangle.  Clay shale, lign
Trs
Rhyolitic volcanic and sedimentary rocks
Tertiary?
Rhyolitic volcanic and minor(?) associated sedimentary rocks are mapped in a small area in the Tanana quadrangle (Chapman and others, 1982; Dover, unpublished data, 1997).  Rhyolitic rocks consist of light- to very light-yellow and yellowish-gray to crea
Td
Dacite and rhyolite lava flows, domes, and volcaniclastic rocks
Eocene and Paleocene
Finely banded dacitic and rhyolitic  lava flows, basal breccia, tuffs, obsidian, and hypabyssal domal intrusive bodies. Spatially associated with andesite and basalt unit (Ta) and forms a compositionally continuous suite with unit Ta.  K/Ar  isotopic coo
Tb
Oligocene
Vesicular and columnar-jointed basalt flows and lahar deposits. Unit yielded a K/Ar cooling age of 32 Ma
Thr
Rhyolite hypabyssal bodies
Miocene to Paleocene, mostly Early Tertiary or Eocene?)
Fine-grained porphyritic rhyolite composed of phenocrysts of plagioclase rimmed by orthoclase in a groundmass of plagioclase, orthoclase, quartz, and altered mafic minerals.  Unit probably correlates and forms a compositional continuum with a nearby gran
Tad
Andesite and basalt lava flows and volcaniclastic rocks (Ta) and dacite and rhyolite lava flows, domes, and volcaniclastic rocks (Td), undivided
Confined to west-central part of Melozitna quadrangle where field data are insufficient to map units Ta and Td separately
Ta
Andesite and basalt lava flows and volcaniclastic rocks
Subaerial, columnar-jointed, andesite and basalt lava flows that locally contain interbedded tuffs, breccias, and agglomerates.  Lava flows composed chiefly of pyroxene andesite and less commonly of hornblende-bearing high-silica andesite, olivine-bearin
Tt
Tuff and tuff breccia
Eocene or Paleocene
Tuff and breccia are composed of abundant lithic fragments of flow-banded rhyolite  and partially welded pumice in a matrix of devitrified glass shards, altered plagioclase, quartz, and mafic minerals.  Unit contains subordinate altered andesite and daci
Tg
Granite
Fine-grained equigranular to sparsely porphyritic granite characterized by plagioclase laths mantled by orthoclase.  One K/Ar isotopic determination from this unit  yielded a cooling age of 56 Ma
TKd
Dacite and rhyolite lava flows, domes, and volcaniclastic and hypabyssal rocks
early Tertiary and Late Cretaceous
Dacite, rhyolite, and trachyandesite lava flows, domes, sills, dikes, and interlayered breccias and tuffs.  Composed of phenocrysts of  plagioclase, quartz, sanidine, and biotite in a groundmass of quartz and feldspar.  Locally in Unalakleet and Medfra q
TKad
Andesite and basalt lava flows and volcaniclastic rocks (TKa) and dacite and rhyolite lava flows, domes, and volcaniclastic and hypabyssal rocks (TKd), undivided
TKi
Shallow intrusive rocks of silicic and intermediate composition
Tertiary and Late Cretaceous
Includes a wide variety of shallow intrusive rocks including rhyolite, dacite, trachyite, and andesite plugs, domes, sills, and dikes and larger more coarsely crystalline bodies of granite, granodiorite, tonalite, and monzonite porphyry
TKvr
Rhyolite and related rocks
Tertiary and/or Cretaceous
Consists of light gray to pink rhyolitic volcanic rocks and minor dacite, including flows, tuff, welded(?) tuff and breccia.  Exposures of this unit include the volcanic rocks of the Big Creek -- Tokatjikh Creek area of the Melozitna quadrangle (mapped a
TKa
Columnar-jointed andesite, basaltic andesite, and basalt lava flows.  Composed of phenocrysts of plagioclase and pyroxene in a fine-grained  groundmass of plagioclase microlites, granular pyroxene, and dark glass.  K/Ar isotopic cooling ages range from 6
TKvc
Volcano-plutonic complexes
early Tertiary and Cretaceous
Complexes are composed of small, closely-spaced rhyolite, dacite, andesite, granite, granodiorite, tonalite, and monzonite porphyry bodies, which intrude Cretaceous sedimentary deposits of the Yukon-Koyukuk basin.  Intrusive bodies are too small and too
TKg
Granite and granodiorite
Fine to coarse-grained, equigranular to porphyritic, biotite granite and rarely muscovite-biotite granite.  K/Ar isotopic cooling  ages for this unit range from 71 to 63 Ma
TKm
Monzonite
Medium- to coarse-grained, equigranular, biotite and hornblende monzonite, quartz monzonite, monzodiorite, and quartz diorite.  Subordinate monzogabbro and gabbro.  K/Ar isotopic cooling  ages from this unit range from 70 to 66 Ma
TDg
Gabbro and diabase
Tertiary? to Devonian?
Fresh to altered gabbroic and diabasic intrusive bodies.  Unit intrudes rocks as old as middle Paleozoic and as young as Cretaceous.  May represent a wide range of ages
Kcc
Carbonate-clast conglomerate, sandstone, and shale
Cretaceous
Poorly sorted nonmarine and shallow-water shelf deposits consisting  of carbonate-rich conglomerate (calcirudite), sandstone (calcarenite), and shale (calcilutite).  Unit contains abundant plant debris and thin seams of bituminous coal.  Clast-supported
Kcvg
Carbonate- and volcanic-clast graywacke and mudstone
Cyclically interbedded fine- to coarse-grained highly calcareous graywacke; hard, fine- to medium-grained, carbonaceous, volcanic graywacke; and dark carbonaceous mudstone.  Graywacke is typically graded and sole-marked. Carbonized plant debris is abunda
Kcg
Carbonate-clast graywacke and mudstone
Fine-grained to gritty graywacke and laminated micaceous mudstone turbidite deposits composed largely of carbonate detritus and lesser amounts of quartz, chert, volcanic rock, and mica clasts.  Contains abundant carbonized plant debris. The mudstone inte
Ksu
Shale, siltstone, and sandstone, undivided
Chiefly dark carbonaceous, generally nonfossilferous shale, siltstone and fine-grained sandstone.  Poorly exposed except where altered to a dark slaty hornfels in the vicinity of plutonic and hypabyssal intrusive rocks. Locally includes a limestone-clast
Kss
Shallow marine sandstone, siltstone, and shale
Late Cretaceous
Fine-to medium-grained, thinly cross-bedded, fossiliferous sandstone and poorly exposed dark siltstone and shale.  Clasts composed of 40 to 45 percent quartz, 45 to 50 percent volcanic and sedimentary  lithic fragments, and  5 to 15 percent feldspar, chi
Ks
Fluvial and shallow marine sandstone and shale, undivided
Nonmarine, fluvial, delta-plain deposits that grade downward into marine delta-front deposits. Fluvial deposits are characterized by fine-grained, locally cross-bedded quartzose sandstone interbedded with micaeous shale and siltstone. Near the base, the
Ksc
Fluvial and shallow marine sandstone and conglomerate
Fine- to coarse-grained, thinly cross-bedded  sandstone and quartz-chert pebble conglomerate interbedded with dark shale and siltstone.  Sandstone clasts composed of as much as 45 percent quartz and chert,  25 to 45 percent metamorphic rock, as much as 1
Kqc
Quartz- and metagraywacke-clast conglomerate, sandstone, and shale
Composed chiefly of well-sorted and well-rounded clasts of white quartz and/or metagraywacke in a quartzose and micaceous matrix; schist, chert, greenstone, and limestone clasts  occur in subordinate amounts. Conglomerate is interbedded with quartzose, c
TKic
Complexes of shallow intrusive rocks and altered Cretaceous sedimentary rocks of the Yukon-Koyukuk basin, undivided
Kmc
Mafic igneous-clast conglomerate, sandstone, and mudstone
Consists of massive poorly stratified and poorly sorted conglomerate composed of pebble- to cobble-size clasts in a graywacke and mudstone matrix.  Clasts predominately mafic intrusive and extrusive rocks, varied colored chert, and locally metagraywacke.
Kms
Marine sandstone and siltstone
The shallow marine deposits in the lower part of the unit Ks are mapped separately along the Yukon River and in a belt to the west extending from the southern edge of the Norton Bay quadrangle to the western Kateel River quadrangle.  These deposits compo
Kvgm
Volcanic graywacke and mudstone
Cretaceous, Albian
Chiefly dark-greenish-gray, fine-grained to gritty, poorly sorted turbiditic graywacke composed largely of first- and second-cycle volcanic debris, but locally containing abundant granitic and metamorphic rock debris.  Dark-gray mudstone interbeds.  Grad
Kvc
Volcanic-clast conglomerate, sandstone, and shale
Massive, poorly stratified pebble to boulder conglomerate, interbedded with dark graywacke and dark finely laminated mudstone.  Unit composed of debris flows and alluvial fan deposits.  Consists chiefly of andesitic volcanic rock detritus, but locally in
Kwcf
Wilber Creek flysch
Interlayered siltstone, shale, sandstone, and conglomerate originally subdivided into coarse- and fine-grained units (Weber and others, 1992).  Siltstone and sandstone are medium- to medium-dark-gray and greenish-gray, moderately sorted and very fine- to
Kqs
Quartz-carbonate sandstone
Early Cretaceous
Fine- to coarse-grained  quartz-carbonate sandstone and conglomerate, quartzose limestone, and pebbly mudstone and siltstone.  Sandstone clasts composed chiefly of quartz, carbonate rock, and quartz-mica schist debris.  Unit contains abundant marine moll
Kcs
Offshore calcareous sandstone, siltstone, and shale
Fine- to coarse-grained, moderately to highly calcareous, turbiditic sandstone interbedded with dark-gray shale and siltstone.  The sandstone occurs in beds 20 to 40 inches (50 to 100 centimeters)  thick grading upward into finely cross-laminated, muscov
Ungalik Conglomerate
Obsolete map unit
Kvg
Volcanic-clast  graywacke and mudstone
Hard, fine-grained to conglomeratic, locally tuffaceous, graywacke and dark-gray finely laminated mudstone. The graywacke is composed of matrix-supported clasts of intermediate and mafic volcanic and intrusive rocks and chert.  Clasts of quartz and of me
Kvm
Volcanic graywacke and conglomerate
early Late or late Early Cretaceous?)
Poorly sorted, fine- to coarse-grained graywacke, sandstone, grit, and pebble- to cobble conglomerate composed chiefly of volcanic rock and chert detritus in the Medfra and Ophir quadrangles (Patton and others, 1980; Chapman and others, 1985)).  Contains
Kgc
Early Cretaceous?
Poorly sorted fine- to coarse-grained graywacke sandstone, grit, and pebble to cobble conglomerate composed chiefly of volcanic rock and chert detritus. Interbedded dark mudstone.   Unit is tentatively assigned an Early Cretaceous age. It locally contain
Krd
Rhyolite, dacite, and trachyte lava flows and volcaniclastic rocks
Rhyolite, dacite, and trachyte flows and crystal and lithic tuffs, felsic ash-fall tuffs, tuffaceous graywacke, and volcanic conglomerate.   One K/Ar isotopic determination from this unit gave a cooling age of 87 Ma
Kvl
Volcanic rocks
Largely dacite, andesite, and basalt and subordinate andesitic to basaltic subvolcanic rocks.  Ranges from flows, including agglomerate, to tuff and also dikes and sills; all are variably hydrothermally(?) altered.  Subvolcanic rocks are chiefly found in
Ktg
Tuff, volcanic graywacke, and mudstone
Chiefly crystal and lithic tuffs and volcanic graywacke interbedded with laminated mudstone.   Tuffs and graywacke characterized by abundant potassium feldspar crystals and potassium-rich volcanic rocks fragments.  Unit contains rare mafic and intermedia
Kv
Flows of andesite and basalt, interbedded with tuff, tuff breccia, agglomerate, volcanic conglomerate, and volcanic graywacke.   Flows typically  have phenocrysts of  plagioclase and pyroxene set in a matrix of devitrified glass, altered plagioclase micr
Kbd
Spilitic basalt and diabase
Fine-grained, amygdaloidal, spilitic pillow basalt flows and medium- to coarse-grained spilitic diabase intrusive rocks.  Contains subordinate andesitic and basaltic tuffs.   Appears to overlie unit  Kv and to underlie unit Krd
Kft
Shoshonitic tuffs and lava flows
Lithic tuffs, pillowed andesite flows, diabase, and volcanic conglomerate of shoshonitic composition, characterized chemically  by very high K20, Rb, and Ba contents and low TiO2 content.  Tuffs consists of coarse-grained volcanic rock fragments, crystal
Kgu
Granitic rocks of uncertain affinities
Cretaceous?
Medium to coarse-grained granitic intrusive and hypabyssal rocks
Kgd
Granodiorite and granite
Generally fine- to medium-grained equigranular, but locally porphyritic, hornblende-biotite granodiorite, and alaskitic biotite granite.   Locally includes tonalite and quartz monzodiorite.  K/Ar isotopic cooling ages range from 89 to 78 Ma
Kmum
Mafic and ultramafic rocks
Gabbro, diorite, serpentinite, and mafic volcaniclastic rocks.  Ranges from small, structurally bounded, pervasively sheared, discordant bodies of serpentinized ultramafic rocks wholly enclosed in pelitic schist in the Anchorage quadrangle (Winkler (1992
Ksm
Syenite and monzonite
Consists chiefly of hornblende syenite, biotite-hornblende monzonite, and monzodiorite, and lesser amounts of biotite diorite and biotite quartz monzonite.  One K/Ar isotopic determination yielded a cooling age of 76 Ma
Kg
Granitic rocks
Largely granitic, but range from tourmaline-bearing granite to diorite.  Intrusions range from dikes and sills, to small and large plutons.  Widely distributed includes granite plutons in the Mount Hayes quadrangle, and quartz monzonite and granodiorite
Kgr
Unit consists chiefly of biotite and muscovite-biotite granite and granodiorite.  K/Ar isotopic cooling  ages range from 112 to 96 Ma and two U/Pb zircon analyses give crystallization ages of 112 and 109 Ma
Knsy
Syenite, monzonite, and nepheline syenite; nepheline syenite unit
large bodies of nepheline syenite  and related rocks shown separately on the map
Ksy
Syenite, monzonite, and nepheline syenite
Unit composed of syenite, monzonite, and subordinate quartz monzonite, monzodiorite, quartz syenite, and nepheline syenite and related mafic alkaline rocks including malignite, ijolite, shonkinite, and pyroxenite.  K/Ar isotopic cooling ages from units
KJwc
Wilber Creek flysch and Wolverine quartzite, undivided
Early Cretaceous or Late Jurassic
Locally mapped unit consisting of units KJwc and Kwcf in the Tanana quadrangle
KJw
Wolverine quartzite
Light- to dark-gray, very fine- to medium-grained, well-sorted, quartzite containing interbedded black to dark-gray shale and medium-light- to medium-gray siltstone.  Rare coquina-like beds contain poorly preserved fragments of Buchia and other fossils t
Jgt
Trondhjemite and tonalite
Late and Middle Jurassic
Trondhjemite, tonalite, and subordinate quartz diorite, diorite, and gabbro.  Trondhjemite consists of 50 to 60 percent plagioclase, 25 to  45 percent quartz, 4 to 8 percent mafic minerals (chiefly biotite and subordinate amphibole).  Tonalite has 50 to
MzPzum
Mafic-ultramfic complexes
Mesozoic and Paleozoic?
The complexes consist of: 1) a cumulate magmatic suite composed of interlayered dunite, wehrlite, olivine clinopyroxenite, and gabbro, 2) a mantle suite composed of harzburgite, dunite, and minor clinopyoxenite, and 3) a metamorphic sole consisting of a
JMc
Chert, cherty tuff, argillite, crystal-lithic tuff, volcanic breccia, and conglomerate
Jurassic? to Mississippian
Chiefly banded radiolarian chert  interbedded with argillite, cherty  tuff, fine- to coarse-grained crystal and lithic tuff, and volcanic breccia and conglomerate.  Breccia and conglomerate are composed of poorly sorted clasts of mafic volcanic rocks and
Spiculite and sandy limestone
Late Triassic
Composed of quartz-carbonate sandstone and conglomerate in the lower part of unit and spiculitic chert in the upper part.  Sandstone and conglomerate consist of detrital carbonate, quartz, and chert clasts, and calcareous fossil debris.  Spiculite is com
Trc
Carbonatite
Triassic
Intensely magnetic dolomite-calcite-magnetite-apatite-rich rock in two sill-like bodies in the southeastern Tanana quadrangle.  40Ar/39Ar age of about 200 Ma reported on contact metamorphic mica reported by Reifenstuhl and others (1998) and interpreted a
Mzi
Intrusive rocks
Mesozoic?
Undated parts of the Alaska-Aleutian Range batholith in the Tyonek quadrangle.  Chiefly quartz diorite, diorite, and gabbro (Reed and Elliott, 1970)
TrPs
Sedimentary rocks, undivided
Triassic to Permian
Dominantly dark gray, typically phyllitic, siliceous to carbonaceous argillite and shale, with subordinate but characteristic clast-supported chert-rich conglomerate, greenish-gray chert, tuffaceous volcaniclastic rocks, yellowish- to reddish-brown highl
TrMts
Tozitna assemblage (north):  Sedimentary rocks
Triassic to Mississippian
Chert, metachert, metatuff, quartzite, phyllite, and other associated incipiently metamorphosed sedimentary rocks; includes basalt and amygdaloidal pillow basalt in places.  Corresponds to the Rampart Group of Brosge and others (1969) in the Tanana quadr
TrMg
Graywacke, grit, and argillite
Triassic? to Mississippian?
Fine- to medium-grained, commonly calcareous graywacke and granule conglomerate, which contain clasts of chert, shale, argillite, and volcanic rocks.   Graywacke and conglomerate are interbedded with argillite.  Unit contains microfossils and bryozoan an
TrMica
Innoko assemblage:  Chert, argillite, and volcaniclastic rocks
Dominantly medium-dark- to dark-gray, thin-banded, bedded radiolarian-bearing chert having thin interbeds of slaty argillaceous rocks, including argillite, slate, and phyllite.  Also includes subordinate intermediate to basaltic volcanic and volcaniclast
JPztm
Tozitna assemblage (south):  Mafic and ultramafic rocks, undivided
Jurassic? and/or Paleozoic?
Gabbro sills and subordinate quartz diorite, quartz monzonite, and pyroxenite.  Undated; age and assignment to the Tozitna assemblage based on lithologic associations and regional comparisons.  Corresponds to informal Pzmi unit of Puchner (1984) in weste
MzPzi
Intrusive and volcanic rocks, undivided
Mesozoic or Paleozoic
Granodiorite of Rainbow Mountain in the Mount Hayes quadrangle (unit grrm, Nokleberg and others, 1992a), diorite in the Circle and Bid Delta quadrangles (unit MzPzd, Foster and others, 1983; unit Pzd, Weber and others, 1978), and gabbro and quartz diorit
JTrtmu
Tozitna assemblage (north):  Mafic and ultramafic rocks
Jurassic? to Triassic
Diabase, gabbro, leucogabbro, and greenstone; ultramafic rocks include serpentinized peridotite, harzburgite, and werhlite.  Locally, may include minor associated sedimentary rocks.  Tentative age range based on K-Ar age of 210+/-6 Ma reported by Brosge
TrMbc
Pillow  basalt, chert, and minor agglomerate
Altered aphanitic and porphyritic pillow basalt.  Phenocrysts in the porphyritic basalt are composed chiefly of olivine and pyroxene.  Basalt is interlayered with chert and subordinate beds of agglomerate containing clasts of basalt and chert.  Chert con
JMtru
Tozitna assemblage (north):  Greenstone, chert, and ultramafic rocks, undivided
Jurassic? to Mississippian?
Poorly dated spilitic basalt and diabase largely altered to greenstone.  Locally, includes minor sedimentary rocks, generally low metamorphic grade cataclastic assemblage of generally dark gray chert and siliceous argillite.  Also includes subordinate vo
JMtu
Tozitna assemblage (south):  Mafic, ultramafic, and sedimentary rocks, undivided
Jurassic to Mississippian
Basalt, gabbro, diabase, basaltic tuff, and chert.  May include minor ultramafic rocks and other associated low metamorphic grade metasedimentary rocks in the Nulato, Ophir, and Ruby quadrangles that resemble the Tozitna assemblage north of the Kaltag fa
JDv
Altered basalt, gabbro, chert, argillaceous rocks, tuff, graywacke, and carbonate rocks
Jurassic to Devonian
Variably altered and metamorphosed flows and shallow intrusives of basalt, diabase, and gabbro interbedded with varying proportions of chert, argillite, slate, phyllite, volcaniclastic rocks,  graywacke, and carbonate rocks. The basalt, diabase, and gabb
KJm
Melange
Early Cretaceous? and Jurassic
Melange consists of blocks of carbonate rocks, chert, metagraywacke, and altered mafic volcanic and intrusive rocks in a matrix of phyllite.  Within the melange unit the large blocks of carbonate rocks from units  |ca and |cr  and altered basalt, diabase
TPza
Amphibolite facies metamorphic rocks
Earliest Tertiary to Paleozoic
Dominantly medium- to medium-dark-gray garnetiferous quartz-mica schist and amphibolite, but includes slate and shale in the Livengood quadrangle.  Locally has gneissic texture.  Minor marble and very minor quartzite occur in unit in the Tanana quadrangl
MzZma
Metabasite
Mesozoic? to Proterozoic?
Varies from thinly layered greenschist to more massively layered greenstone bodies representing altered mafic and intermediate volcanic and  shallow intrusive rocks. The characteristic mineral are chlorite, albite, actinolite, and epidote.  Unit may incl
MzZmr
Massive greenstone to thinly layered greenschist bodies that probably represent metamorphosed mafic to ultramafic intrusive rocks and mafic to intermediate flows and tuffs.  Unit  is intercalated with with units PzZsr Pzcr, and Dgnr.
MzZms
Greenstone and greenschist bodies representing altered mafic and intermediate volcanic and intrusive rocks
Pzrmi
Ruby metamorphic complex -- Metamorphosed mafic igneous rocks
Paleozoic?
Metamorphosed mafic igneous rocks, ranging from metagabbro and metadiabase to greenstone, amphibolite, and garnet amphibolite.  Variable intensity of sheared within unit.  Unit Pzm of Dover (unpublished mapping, 1997), not mapped separately by Chapman an
MzZfm
Metabasite (MzZma) and felsic schist (Df), undivided
DCd
East Fork Hills Formation
Devonian to Cambrian
Deep-water deposits of finely laminated limestone and dolomitic limestone.  Subordinate chert and siliceous siltstone.  Formation was originally assigned an Ordovician to Devonian age on the basis of a sparse conodont fauna (Dutro and Patton, 1982. More
Pzcs
Carbonate rocks
Paleozoic
Chiefly massively bedded light gray to tan dolomitic and calcareous marble.  Locally interbedded black to dark gray calcareous marble and subordinate impure marble and calcareous schist.  Unit locally contains an abundant conodont fauna of Ordovician to
PzZus
Pelitic schist, calc schist, and quartzite (PzZss) and carbonate rocks (Pzcs), undivided
Paleozoic and Proterozoic?
Scattered exposures along the western edge of the map area extending from the Norton Bay quadrangle to the southwestern part of the Selawik quadrangle
PzZss
Pelitic schist, calc schist, and quartzite
Quartz-muscovite-graphite schist, calc schist, quartzofeldspathic schist, phyllite, and quartzite.  Unit is locally interlayered with unit |cs and is therefore, at least in part, Paleozoic in age.  Some of the unit may be as old as Proterozoic.  Samples
Pzcr
Gray to white, partly to wholly recrystallized limestone, marble, dark-gray dolomitic marble, and impure schistose limestone.  Unit occurs in layers as much as 25m thick intercalated with quartz-mica schist, mica schist, graphitic schist, metabasite, and
Pzvs
Volcanic and sedimentary rocks
late or middle Paleozoic
Dark-greenish-gray mafic volcanic rocks and interbeds of black phyllite, chert-pebble conglomerate, light-green tuff, and graywacke (Reed and Nelson, 1980).  Volcanic rocks include pillow basalt, breccia agglomerate, tuff, and massive basalt flows.  Dist
MzZrc
Complex of the Reindeer Hills
Mesozoic to Proterozoic?
Undivided assemblage of interlayered impure marble, quartz-mica schist, and quartzite intruded by aplite  and amphibolite dikes.  Includes some ductily deformed metasomatized contact marble with biotite- and epidote-rich bands.  Field data are insufficie
Pzca
Ranges from light gray to white partly recrystallized limestone  to coarsely crystalline marble. Dark finely crystalline dolomitic marble.  Interbedded calc schist, chloritic schist, and quartzite in subordinate amounts.  Unit ranges in age from Ordovici
MzPzq
Quartzite, grit, argillite, and quartz-mica schist
early Paleozoic and Proterozoic?
Mixed assemblage of laminated fine-to coarse-grained quartzite, grit, and argillite grading upward into very fine-grained quartzite, argillite, phyllite, and chert.  In southeast corner of Medfra quadrangle unit is metamorphosed to greenschist facies com
Pzpa
Phyllite and subordinate metagraywacke
Dark phyllite and minor metagraywacke that have a penetrative fabric ranging from slaty cleavage to weakly schistose.  Unit locally contains slices of little deformed shallow-water Devonian carbonate rocks that are enveloped in basalt flows and debris-fl
Pzpr
Phyllite
Phyllite and subordinate fine-grained metagraywacke cut by abundant vein quartz.  The phyllite and metagraywacke are overprinted by a low-grade penetrative metamorphic fabric, but turbidite features, such as sole marks and graded bedding, are locally dis
Pzg
Metagraywacke and subordinate phyllite
Fine- to medium-grained metagraywacke and metasiltstone  composed chiefly of quartz and chert clasts, but in places containing a significant component of volcanic rock and feldspar clasts.  Overprinted by low-grade penetrative metamorphic fabric, but tur
PDms
Sedimentary rocks
Permian? to Devonian?
Indeterminate or poorly identified units in Livengood quadrangle.  Black and greenish-gray siliceous slate, thinly interbedded gray chert, shaly chert, and minor breccia, siliceous, locally sandy siltstone displaying turbiditic sedimentary structures, re
Ps
Sanstone, sandy limestone, and conglomerate
Permian
Fine- to coarse-grained sandstone, limy sandstone, sandy limestone, siltstone and shale.  Sandstone ranges from clean quartz arenite to a lithic arenite containing as much as 25 percent muscovite and metamorphic rock fragments.   Where unit unconformably
TrDc
Chert, argillite, and limestone
Triassic? to Devonian
Varicolored radiolarian chert, lenticular beds of fossiliferous limestone and interbedded argillite.  Subordinate beds of sandy limestone, grit, and arkosic sandstone.  Unit contains abundant radiolaria, condonts, and foraminifera that range in age from
Dgnr
Granitic gneiss
Devonian
Strongly foliated quartzofeldspathic gneiss.  Consists of a coarse- to medium-grained porphyroclastic biotite-quartz-feldsparñmuscovite mylonite gneiss containing resistant augen of K-feldspar in a ductile matrix of mica, quartz, and feldspar.   A U/Pb z
Dgna
Foliated gneissic granite composed of albite, potassium feldspar, quartz, muscovite, and biotite.  Intruded by aplite dikes.  Pluton yielded a probable Devonian U/Pb zircon crystallization age.  Correlative in age with unit Dgnr in the Ruby terrane
Mgq
Globe quartzite
Mississippian
Light gray, massive or thinly laminated quartzite and medium- to dark-gray slate, phyllite, and laminated claystone.  Unfossiliferous; age inferred on the basis of intrusion by Triassic rocks and by lithologic and stratigraphic similarity with the Keno H
DSp
Paradise Fork Formation
Early Devonian and Silurian
Deep-water turbiditic and hemipelagic deposits of dark, thin-bedded, fissile to laminated limestone, limy shale, and siltstone.  The formation has an abundant graptolite, conodont, and ostracod fauna.  It was originally assigned an Early to Late Silurian
SZa
Amy Creek unit
Silurian to Late Proterozoic
In Livengood quadrangle were described by Weber and others (1992), consists chiefly of medium-grained gray dolostone, and light-gray, yellow-gray, or buff dolomitic mudstone, packstone, and wackestone.  Coarser-grained rocks show abundant peloids and cro
Dtr
Troublesome unit and possibly correlative rocks
Devonian?
Rhythmically interbedded dark-gray to black cherty argillite to chert, and thin beds of black to gray, siliceous slate as mapped in the Livengood quadrangle.  Associated with extensive mafic intrusive and extrusive rocks.  Unidentified radiolaria are onl
Pzlsl
Schist, phyllite, limestone, and greenstone
Early Paleozoic
Light- to medium-green chloritic schist, light- to medium-gray with silvery sheen phyllite, light- to medium-gray and greenish-gray, sandy in part, largely recrystallized limestone, and light- to medium-green greenstone.  Schist and phyllite are partly c
DSw
Whirlwind Creek Formation
Devonian and late Silurian
Shallow-water deposits consisting of several repeated cycles.  In the lower part of the formation the cycles grade from algal laminated dolomite into pelletoidal limestone and then into silty limestone and siltstone.  In the upper part  the cycles grade
DSt
Tolovana Limestone
Middle Devonian to Early Silurian
Lower part of alternating green and maroon lime mudstone, succeeded by yellowish-brown weathering, silty to shaly lime mudstone and wackestone, and a main, upper part of light-weathering peloid- and ooid-rich lime packstone and grainstone and rare dolost
Df
Felsic schist
Schistose felsic volcanic rocks, including flows, tuffs, and porphyritic hypabyssal? rocks, interlayered with metasedimentary rocks belonging to units  |<sa and |ca.  An important component of this unit is the widely recognized "button schist" -a porphyr
Dcs
Calcareous schist
Light-brown weathering calcareous schist interbedded with gray quartz-mica schist and marble.  Brooks Range schist belt.
Patton, W.W., Jr., and Miller, T.P., 1973, Bedrock geologic map of Bettles and southern part of Wiseman quadrangles, Alaska:  U.S. Geological Survey Miscellaneous Field Studies Map MF-492, scale 1:250,000.
PzZua
Pelitic schist, calc schist, and quartzite (|<sa) and carbonate rocks (|ca), undivided
Paleozoic and Proterozoic
PzZsa
Quartz-mica schist and lesser amounts of calc schist, quartzite, graphitic  schist, chlorite schist, and quarto-feldspathic schist. Polydeformed greenschist-blueschist-facies characterized by quartz-muscovite-chlorite-albiteñglaucophane   assemblages. A
Ont
Novi Mountain and Telsitna Formations, undivided
Ordovician
Novi Mountain Formation: Shallow water deposits.  Predominately calcareous siltstone and shale in lower part.  Upper part characterized by cycles beginning with massive limestone commonly containing flat carbonate pebbles at the base and grading upward t
Oc
Chert and argillite
Banded chert, argillite, fine-grained thin-bedded limestone, and silty dolomite.  Beds separated by carbonaceous partings.  Unit interpreted to be a deep-water sequence composed of turbiditic and hemipelagic deposits.   Unit locally contains conodonts an
Ofc
Fossil Creek Volcanics
Two members, one largely volcanic, one largely sedimentary.  Volcanic member consists of alkali basalt, agglomerate, and volcaniclastic conglomerate.  Agglomerate and conglomerate contain well-rounded clasts of basalt, granite, quartzite, limestone, cher
Olc
Chert
Dark gray and black chert, siliceous slate, argillite, and less abundant greenstone, impure limestone, and dolostone.  Age assigned on basis of graptolites.  Includes the Livengood Dome Chert in the Livengood, Circle, and Tanana quadrangles, unit Pzlc in
Ocl
Limestone
Distinctive marker bed of lime mudstone within chert unit, locally characterized by coated ooids.  Thickness varies from 10 to several ten's of meters, probably in part due structural thickening and repetition.  Only mapped locally.  Corresponds to unit
PzZq
CZwa
Wickersham grit, Argillaceous upper unit
Cambrian? and Late Proterozoic
Dominantly argillaceous, containing distinctive tan-weathering gray calcareous siltstone and fine-grained sandstone, subordinate quartzite and chert, and locally, a few black clastic limestone interbeds.  Corresponds to the CZwa unit of Weber and others
PzZi
Paleozoic? and Proterozoic
Granite, granodiorite, diorite, and gabbro that have  a slight to moderate gneissic fabric.  The northwesternmost of the two bodies is Proterozoic  and has yielded a U/Pb zircon crystallization  age of 705 Ma.   The southeasternmost body is of uncertain
PzZsr
Quartz-mica schist, chlorite schist, quartzofeldspathic schist, quartzite, and micaeous and graphitic schist.  Regionally metamorphosed to greenschist-facies, but also locally includes high-pressure greenschist-blueschist-facies (distinguished by the pre
Zc
Calc schist, quartz-mica schist, and greenstone
Proterozoic
Calc schist, thin bedded schistose impure marble, and fine-grained massive sandy marble.  Contains subordinate quartz-mica schist and small bodies of greenstone.  Unit underlies unit Ont and gradationally overlies unit Zs
Zs
Pelitic schist, quartzite, quartzo-feldspathic gneiss, and greenstone
Chiefly pelitic and quartzose metasedimentary rocks of greenschist metamorphic facies.  Micaeous quartzite and quartz-chlorite schist grade into quartz-muscovite-biotite-garnet     schist.  Subordinate calc schist and marble.  Unit locally includes small
Zv
Metavolcanic rocks
Late Proterozoic
Banded, fine-grained, foliated,  felsic volcanic  rocks. Chiefly porphyry composed of large phenocrysts of embayed quartz and plagioclase in a very fine-grained quartzo-feldspathic groundmass that has a distinct micaceous overprint.  Subordinate fine-gra
Ynqd
Metamorphic basement rocks of the Nixon Fork sequence, Meta-quartz diorite
middle Proterozoic?
Sheared metamorphosed porphyritic quartz diorite.  Contains biotite phenocrysts as large as 1 cm and numerous micro-veinlets of quartz (Silberman and others, 1979).  K-Ar age on biotite yielded an age of 921+/-25 Ma and muscovite from mylonite along bord
MzZkc
Complex of the Kokrines Hills
Undivided assemblage of: 1) biotite granite and  granite gneiss including augen gneiss, 2) quartzofeldspathic schist, quartzite, pelitic schist and amphibolite metamorphosed to upper amphibolite to lower granulite facies, and 3) marble and calc-silicate