Geologic and Isostatic Gravity Map of the Nenana Basin Area, Central Alaska

By Gina M. Frost, David F. Barnes, and Richard G. Stanley

Pamphlet to accompany Geologic Investigations Series I–2543

2002

U.S. Department of the Interior U.S. Geological Survey GEOLOGIC AND ISOSTATIC GRAVITY MAP OF THE NENANA BASIN AREA, CENTRAL ALASKA By Gina M. Frost, David F. Barnes, and Richard G. Stanley

INTRODUCTION sistency is responsible for many of the small con- tour irregularities. Ninety percent of the measure- The Nenana basin area is a prospective petroleum ments are estimated to have an accuracy of about province in central Alaska, and this geologic and isostatic 1.5 mgal or about a quarter of the 5 mgal contour gravity map is part of a petroleum resource assess- interval. Data collection and analysis were assisted ment of the area. by R.V. Allen, R.C. Jachens, M.A. Fisher, T.R. Bruns, The geology was compiled from published sources J.G. Blank, J.W. Bader, Z.C. Valin, J.W. Cady, R.L. (Chapman and others, 1971, 1975a, 1975b, 1982; Morin, and P.V. Woodward. Chapman and Yeend, 1981; Csejtey and others, 1986; The most promising area for petroleum explo- Jones and others, 1983; Péwé and others, 1966; ration is a prominent 25 mgal isostatic gravity low Reed, 1961; and Weber and others, 1992), as shown north of Nenana (T. 2 S., R. 8 W.). This gravity on the index map (map sheet). Map units are low probably corresponds to the deepest part of a organized and presented according to the scheme sedimentary basin filled by Cenozoic strata that includes of lithotectonic terranes proposed by Jones and others nonmarine fluvial and lacustrine deposits of the Eocene (1987) and Silberling and Jones (1984); we recog- to Miocene Usibelli Group. Smaller gravity lows are nize, however, that this terrane scheme is contro- associated with outcrops of these sedimentary rocks versial and likely to be revised in the future. In some north of Suntrana (T. 12 S., R. 6-9 W.) and Sable cases, we combined certain terranes because we were Pass (T. 16 S., R. 11 W.). A broad low on the north unable to match the terrane boundaries given by Jones flank of the Alaska Range east of the Wood River and others (1987) and Silberling and Jones (1984) (T. 10 S., R. 1 E.) indicates another basin under the with specific faults shown on existing geologic maps. Tanana lowland that extends eastward off the map Postaccretion cover deposits represent overlap as- area towards Delta Junction, where its presence was semblages that depositionally overlie accreted ter- confirmed by both gravity and seismic data (Barnes ranes. Plutonic igneous rocks shown on this map and others, 1991). include several plutons that are clearly postaccretionary, based on isotopic ages and (or) field relations. It Gravity modelling suggests that the base of the is possible that some of the plutons predate accre- Usibelli Group in the area north of Nenana (T. 2 tion, but this has not been demonstrated. Accord- S., R. 8 W.) is about 3,000 to 3,350 m beneath the ing to Jones and others (1982), the terranes in the ground surface (Barnes, 1961; Hite and Nakayama, area of our map were assembled during late Meso- 1980; Kirschner, 1988). Organic geochemical studies zoic or earliest Cenozoic time. indicate that mudstones and coals in the Usibelli Group The gravity contours are derived from data used are potential sources of petroleum; calculations based in earlier compilations (Barnes, 1961, 1977; Hackett, on borehole temperatures suggest that, in the area 1981; Valin and others, 1991; Frost and Stanley, of the gravity low, these rocks may have been buried 1991) that are supplemented by some National Oceanic deeply enough to generate oil and gas (Stanley and and Atmospheric Administration data along the Alaska others, 1990). Two exploratory wells, the Union 1 Pipeline level line (W.E. Strange, written commun., Nenana No. 1 and the ARCO Totek Hills No. 1 , 1980). The earlier compilations were used for simple were drilled some distance away from the gravity low Bouguer maps, prepared primarily by non-digital in areas where the Usibelli Group is thin (Grether methods, and are superseded by this map. The present and Morgan, 1988; Kirschner, 1988). Mudlogs show map is the result of digital processing that includes that both wells were dry holes that bottomed in schist the 1967 Geodetic Reference System, the IGSN-71 and had gas shows associated with coal beds in the datum, digital terrain corrections, and conversion to Usibelli Group, but no reported signs of oil. isostatic gravity so that geologic structures on the We thank Florence R. Weber and Richard W. margin of the Alaska Range are more clearly por- Saltus for their reviews of this effort, and Béla Csejtey, trayed (Simpson and others, 1986). Computation Jr., and Robert M. Chapman for their reviews of an procedures are described in part by Barnes (1972, earlier effort. 1984), Jachens and Roberts (1981), and Barnes and others (1994). The calculations used a crustal density of 2.67 g/cm3, a density contrast at the base of the 1 Additional gravity and some seismic data in the vicinity of the Union isostatic root of 0.4 g/cm3, and a root thickness at Nenana No. 2 well may be found in: Sinclair Oil and Gas Co., Union sea level of 25 km. The distribution of data within Oil Co. of Calif., the Pure Oil Co., and the Ohio Oil Co., 1962, the map area is uneven and locally controls the shape Geologic report to accompany application for the Nenana develop- of the computer-generated contours. Altimetry was ment contract: unpublished report on file at U.S. Geological Survey, used for most of the elevation control and its incon- Anchorage, Alaska, 3 pages, 2 plates.

1 DESCRIPTION OF MAP UNITS Tertiary Usibelli Group (unit Tu), is over- lain by Quaternary surficial deposits (unit [References listed in brackets at the end of each map unit description are the principal ones used in preparing the Qs), and appears to be deformed around description and showing the unit’s distribution on the map. an intrusion of Pliocene hornblende dac- Map units and (or) unit ages are queried as they are in the ite (unit Thd). Because of the lack of mapping sources.] diagnostic fossils, the age of the Nenana Gravel is uncertain, but it is younger than POSTACCRETION COVER DEPOSITS the underlying upper Miocene Grubstake Qs Surficial deposits (Quaternary)—Unconsoli- Formation of the Usibelli Group and older dated gravel, sand, silt, and clay. Includes than the Pliocene hornblende dacite in- lake deposits, colluvium, swamp deposits, trusive rocks of Jumbo Dome. The Nenana landslide debris (including blocks of bed- Gravel represents a series of coalescing rock), flood-plain alluvium, stream gravel, alluvial fans that developed on the north alluvial fan deposits, dune sand, morainal side of the Alaska Range as it rose during deposits, glacial outwash, loess, tailings, late Miocene and Pliocene time. [Csejtey and perennially frozen silt. [Chapman and and others, 1992, 1986; Wahrhaftig, others, 1971, 1975a, 1975b, 1982; 1987] Chapman and Yeend, 1981; Csejtey and TKs Sedimentary rocks (Miocene to Late Cre- others, 1992, 1986; Jones and others, taceous)—Well-consolidated to friable 1983; Péwé and others, 1966; Reed, nonmarine conglomerate, sandstone, mud- 1961; and Weber and others, 1992] stone, and coal. In places these rocks are Qv Volcanic rocks (Quaternary)—Basaltic pyro- arranged in repeated fining-upward se- clastic debris associated with cinder cones quences, suggesting deposition by streams. or maars located southwest of Buzzard Fossil plant leaves and pollen indicate a Creek (T. 10 S., R. 4-5 W.). Radiocar- range in age from Late Cretaceous to bon ages indicate that the debris erupted Miocene. Thickness may be as much about 3,000± 230 years ago. [Albanese, as 1,500 m. Unit TKs is present along 1982; Péwé and others, 1966; Wahrhaftig, T. 4-5 N., R. 14-22 W. [Chapman and 1970a] others, 1982; Paige, 1959] Thd Hornblende dacite (Pliocene)—Shallow in- Tu Usibelli Group (Miocene to Eocene)—Poorly trusive rocks of Jumbo Dome (T. 11 S., consolidated nonmarine conglomerate, sand- R. 6 W.). K-Ar age determination on stone, mudstone, subbituminous and lig- basaltic hornblende yielded 2.79± 0.25 Ma. nite coal, and minor tuff. This unit crops Apparently intrudes Nenana Gravel (unit out widely in the northern foothills of the Tn). [Csejtey and others, 1992, 1986; Alaska Range (T. 8-16 S., R. 1 E.-R. 14 Wahrhaftig, 1970d] W.) and also is present in the subsurface Tvs Volcanic and sedimentary rocks (Tertiary)— of the middle Tanana basin, where it has Rhyolitic lava, breccia, tuff, and welded been penetrated by two exploratory wells tuff; flow banding, lamination, and spheru- (both dry holes), the Union Nenana No. litic texture common. Gray cherty rocks 1 and the ARCO Totek Hills No. 1. The are rare and form thin beds or nodules; Usibelli Group is generally less than 900 tuffaceous siltstone, shale, and argillite are m thick. Locally, the Usibelli Group is thin bedded to laminated. Tertiary age divided into five formations; in ascending inferred from structural setting and lack order, these are the Healy Creek, Sanc- of rock alteration; relation to Upper tuary, Suntrana, Lignite Creek, and Grub- Cretaceous to Miocene sedimentary rocks stake Formations. Much of the Usibelli (unit TKs) is uncertain. Thickness un- Group consists of repeated fining-upward known, probably at least 90 to 120 m. sequences of conglomerate, sandstone, Unit Tvs occurs at T. 5-6 N., R. 13-15 mudstone, and coal that were deposited W. [Chapman and others, 1982] by streams flowing southward across the Tn Nenana Gravel (Pliocene and Miocene)— present site of the Alaska Range, which Mainly buff to reddish-brown, poorly then did not exist. Interstratified with these consolidated, pebble to boulder conglom- fluvial deposits are locally thick sequences erate and coarse sandstone that contains of mudstone that probably accumulated in minor interbeds of mudstone and lignite. large, shallow lakes. Fossil plant leaves These rocks are exposed at T. 8-16 S., and pollen and a single radiometric age R. 1 E.-R. 18 W. Unit Tn is more than from an interbed of volcanic tuff indicate that 1,300 m thick. Thickness and pebble the Usibelli Group ranges in age from Eocene size decrease northward; imbrication and to Miocene. Coal has long been produced crossbedding indicate deposition by north- in commercial quantities from mines in the Healy ward-flowing streams. The Nenana Gravel Creek and Lignite Creek areas (T. 11-12 S., rests unconformably on the underlying R. 6-7 W.). Geochemical studies show that

2 coals and mudstones in the Usibelli Group are intruded by dikes and sills that range in com- potential source rocks of petroleum. [Buffler position from basalt to rhyolite and by and Triplehorn, 1976; Csejtey and others, 1992, granitoids of Cretaceous to Tertiary age (units 1986; Stanley, 1987a, 1988; Stanley and oth- TKgr and Tgr). The maximum reported thick- ers, 1990; Wahrhaftig and others, 1969; ness is about 3,000 m. The sedimentary rocks Wahrhaftig, 1987] rest with pronounced angular unconform- Tmg Mount Galen Volcanics of Decker and Gil- ity on deformed and metamorphosed rocks bert (1978) (early Oligocene and late of Precambrian(?) to Cretaceous age. Much Eocene)—Andesitic and basaltic lava flows, of the conglomerate, sandstone, mudstone, breccia, and tuff north of Mount Galen, which and coal in the Cantwell Formation is re- is just south of the map area (T. 17 S., R. peated in fining-upward sequences of flu- 15 W.). Thickness to 1,000 m. K-Ar ages vial origin. Intercalated with the fluvial on plagioclase and hornblende range from deposits are thick sequences of mudstone 40.1± 1.2 Ma to 34.8± 1.4 Ma. [Decker that, most likely, were deposited in lakes. and Gilbert, 1978; Jones and others, 1983] The age of the Cantwell Formation is based Tv Volcanic rocks (Oligocene to Paleocene)— on the occurrence of Late Cretaceous and Compositions range from rhyolite to basalt; Paleocene palynomorphs, Paleocene plant includes extrusive rocks (flows, tuffs, and fossils, and Paleocene radiometric ages from breccias) as well as dikes, sills, and shallow volcanic rocks. Geochemical studies indicate intrusive rocks. K-Ar age determinations that some mudstones and coals are poten- range from 54.7± 2.4 Ma to 32.5± 1.0 Ma. tial source rocks of petroleum. Unit KTcs These rocks crop out in the vicinity of Sugar crops out at T. 14-17 S., R. 1 E.-R. 15 W. Loaf Mountain (T. 13 S., R. 6-7 W.), the [Csejtey and others, 1992, 1986; Gilbert Dora Peak area (T. 12-13 S., R. 6 W.), near and others, 1976; Stanley, 1987b; Wolfe Mount Healy (T. 13 S., R. 8 W.), south of and Wahrhaftig, 1970; R.G. Stanley, Hideyo, Moody Creek at T. 13 S., R. 5 W., near Haga, and R.A. Ballog, unpublished Mount Lathrop (T. 12 S., R. 4 W.), near biostatigraphic data; Ridgway and others, Needle Rock (T. 11 S., R. 4-5 W.), the Wyo- 1994] ming Hills area (T. 14 S., R. 12 W.), south Kv Volcanic rocks (Late Cretaceous)—Gray to of Hines Creek at T. 14 S., R. 8 W., northeast black porphyritic basalt that forms a swarm of Fairbanks (T. 1 S., R. 1 E.), near Carlo of dikes limited to a small area at T. 13 Creek (T. 15-16 S., R. 6 W.), and in iso- S., R. 4 W. K-Ar age is 79.1 Ma. [Csejtey lated outcrops at T. 11 S., R. 11 W. and and others, 1992, 1986] T. 13 S., R. 3 W. [Albanese and Turner, 1980; Csejtey and others, 1992, 1986; Péwé PLUTONIC ROCKS and others, 1966; Robinson and others, Tgr Granitic rocks (Oligocene to Paleocene)—Wide 1990] variety of epizonal granitic rocks that con- Cantwell Formation (Paleocene and Late sist of granite, granodiorite, tonalite, and Cretaceous)—Divided into: quartz monzodiorite, quartz monzonite, and Tcv Volcanic rocks (Paleocene)—Unit Tcv, syenite. K-Ar ages range from about 62 termed the Teklanika Formation by Gilbert to 37 Ma and are interpreted to represent and others (1976), is a moderately de- Paleocene to early Oligocene ages of intru- formed sequence of andesite, basalt, sion. Unit Tgr is exposed at Manley Hot rhyolite and dacite flows, felsic pyroclastic Springs Dome (T. 2-3 N., R. 15-16 W.), rocks, related intrusive rocks, and a few Tolovana Hot Springs Dome (T. 6 N., R. interbeds of sandstone and mudstone. The 6 W. and T. 4 N., R. 8 W.), Nenana Mountain contact with the underlying sedimentary (T. 16 S., R. 1-2 W.), south of the McKinley rocks (unit KTcs) is conformable in places Fault (T. 17 S., R. 2-4 W.), between the but unconformable in others. Unit Tcv is Wyoming Hills (T. 14-15 S., R. 12-13 W.) reportedly more than 3,700 m thick. Ra- and Brooker Mountain (T. 16 S., R. 18 W.), diometric ages and field relations suggest Pyramid Mountain (T. 15 S., R. 5 W.), near that the volcanic rocks were erupted during Panorama Mountain (T. 16 S., R. 5 W.), the Paleocene. These rocks are exposed and in an isolated outcrop at T. 15 S., R. at T. 14-17 S., R. 5-13 W. [Csejtey and 4 W. [Chapman and others, 1982, p. 11; others, 1992, 1986; Gilbert and others, Csejtey and others, 1992, 1986; Weber and 1976; Wolfe and Wahrhaftig, 1970] others, 1992] KTcs Sedimentary rocks (Paleocene and Late TKgr Granitic rocks (Paleocene and Late Creta- Cretaceous)—Mainly well-indurated nonma- ceous)—Plutons, dikes, and stocks of rine conglomerate, sandstone, mudstone, and granite, granodiorite, granite porphyry, bituminous coal; locally includes interstratified monzonite, quartz monzonite, syenite, volcanic rocks resembling those in unit Tcv. diorite, and dacite. K-Ar ages range from In many places the sedimentary rocks are about 71 to 59 Ma and are interpreted

3 to represent Late Cretaceous to Paleocene Mapped only near Boulder Ridge (T. 4 N., ages of intrusion. Unit TKgr crops out north R. 16-17 W.). These rocks were mapped of the Bitzshtini Mountains (T. 2-3 S., R. as unit |ar by Chapman and others (1982) 22 W.), along the Yukon River between and as unit |cs by Chapman and others Stevens and Morelock Creeks (T. 5-7 N., (1975a). [Chapman and others, 1982, R. 16-18 W.), south of Cascaden Ridge, 1975a] which is just off the map area (T. 7 N., PDs Schistose rocks (Permian? to Devonian?)— R. 7 W.), east of Fang Mountain near Riley Quartz-mica-garnet schist, some quartzite Creek (T. 15 S., R. 8 W.), along the Nenana schist, calcareous schist, marble and slate- River near McKinley Village (T. 15 S., R. phyllite; schistose chert, hornfels, and skarn 6-7 W.), near Chilchukabena Lake (T. 10- occur locally. Pegmatite, quartz, and felsic 11 S., R. 20 W.), northeast of Fairbanks dikes are common; some mafic dikes are (T. 1 S., R. 1 E.), in isolated outcrops present. A small body of gneissic gran- between Murphy Dome (T. 2 N., R. 4 W.) ite and pegmatite at the head of Garnet and Pedro Dome (T. 2 N., R. 1 E.), near Creek (T. 6 N., R. 14 W.) is included. Ages Ester Dome (T. 1 N., R. 3 W.), and in and protoliths of rocks uncertain; age isolated outcrops between the Minto Fault probably Devonian to Permian. Unit may and Slate Creek (T. 6-7 N., R. 4-5 W.). conformably overlie unit DOl, but contacts [Chapman and others, 1982, p. 11, 1975b; are poorly exposed. Thickness unknown Chapman and Yeend, 1981, p. B31; but may be as much as 600 to 900 m. Csejtey and others, 1992, 1986; Péwé and This unit is mapped only in the Russian- others, 1966; Weber and others, 1992] Ruby-Garnet Creeks area (T. 6-7 N., R. Kgr Granitic rocks (Cretaceous)—Tonalite, quartz 13-14 W.). These rocks were mapped as monzonite, monzonite, granite, and some unit Pzsr by Chapman and others (1982, granodiorite, quartz diorite, diorite, quartz 1975a). [Chapman and others, 1982, monzodiorite, and syenite. K-Ar ages on 1975a] rocks from the Healy quadrangle range from DSl Limestone, dolomite, greenstone, schist, and about 106 to 49 Ma; however, the early chert (Devonian and Silurian)—Limestone, Tertiary ages are suspected to represent dolomite, greenstone, and chloritic schist. a Tertiary reheating event as indicated by Minor amounts of phyllite, calcareous schist, discordant ages on biotite-hornblende min- quartz-mica schist, quartzite, and chert are eral pairs on some of the rocks (Csejtey included. Mapped only along and north and others, 1992, 1986, p. 34). Unit of the Yukon River (T. 4-7 N., R. 16-22 Kgr occurs at Roughtop Mountain (T. 4 W.), but rocks are similar to those in unit N., R. 16 W.), Elephant Mountain and Wol- DOl, which crops out south of the Yukon verine Mountain (T. 5-6 N., R. 11-12 W.), River. Poorly preserved colonial rugose Pedro Dome (T. 2 N., R. 1 E.), Sawtooth corals from Raven Ridge (T. 7 N., R. 16- Mountain (T. 6 N., R. 9-10 W.), Eureka 17 W.) are identified as ranging in age from Dome (T. 4-5 N., R. 13-14 W.), Mystic Silurian to Permian; however, field rela- Mountain (T. 11 S., R. 1 W.), Nenana tions suggest that a Silurian to Devonian Mountain (T. 15-16 S., R. 1 E.), the age is most probable (Chapman and oth- Anderson Mountain area (T. 12-13 S., ers, 1982, p. 9). Unit is presumed to cor- R. 1 E.-R. 3 W.), south of Keavy Peak relate in part with unit DSt (White Mountains (T. 12 S., R. 2-3 W.), south of the Hines terrane) (Chapman and others, 1982, p. Creek Fault at T. 13-14 S., R. 1 E., and 9). Upper and lower contacts poorly south of the McKinley Fault at T. 17 S., defined. Thickness unknown, but prob- R. 1 E. [Chapman and others, 1982; ably at least 460 m. These rocks were Csejtey and others, 1992, 1986; Weber mapped as unit |lc by Chapman and others and others, 1992] (1982, 1975a). [Chapman and others, 1982, 1975a] ACCRETED TERRANES DOl Limestone, dolomite, greenstone, and schist (Devonian, Silurian, and Ordovician?)— Baldry and Ruby terranes, undivided Dominantly light-gray crystalline limestone PDa Argillaceous rocks (Permian? to Middle or and dolomite; minor chert. Some basal- Late Devonian?)—Gray siltstone, slate, tic greenstone, chloritic schist, argillite, phyllite, argillite, and minor sandstone. phyllite, quartz-mica schist, quartzite, and Contact relations, thickness, and age uncer- metachert are included. No fossils or tain; apparently younger than unit Oc and continuous sections. Interpreted by Chapman older than unit KJcs (Manley terrane). Most and others (1982) to include rocks of Or- probable ages are Middle or Late Devo- dovician(?), Silurian, and Devonian age. Ap- nian to Permian (Chapman and others, parently overlies unit Oc. Several thin 1982, p. 7). Probably about 300 m thick. chert-pebble conglomerate beds in basal

4 30 to 60 m; upper contact of unit DOl not ver quadrangles (Chapman and others, seen. Mapped only south of the Yukon 1982, p. 11). Thickness unknown, but River (T. 4-6 N., R. 13-21 W.). May be probably at least 600 m. These rocks were correlative in part with unit DSl north of mapped as unit |p_sq by Chapman and the Yukon River, unit DSt (White Moun- others (1982) and as unit |sq by Chapman tains terrane), and part of unit SZa and others (1975a). [Chapman and oth- (Livengood terrane) (F.R. Weber, written ers, 1982, 1975a] commun., 1992). Thickness uncertain, but Oc Chert (Late Ordovician)—Gray chert and minor probably at least 150 m to as much as 460 interbedded slaty shale, chert breccia, and m. These rocks were mapped as unit |l quartzite. Chert is thin to medium bed- by Chapman and others (1982, 1975a). ded, sheared, and fractured. These rocks [Chapman and others, 1982, 1975a] occur in T. 4-7 N., R. 12-19 W. Nature |c Clastic rocks (middle and early Paleozoic?)— of upper and lower contacts uncertain; Upper part contains gray calcareous schis- probably grades upward into unit SOvs. tose siltstone and sandstone. Lower part Interpreted to be correlative with the contains poorly sorted sandstone, granule Livengood Dome Chert (unit Old, Livengood conglomerate, siltstone, and semischist with terrane, T. 7 N., R. 9-11 W.) by Chapman commonly 15 to 46 m of gray metachert and others (1982, p.10; 1980) and is near the top. Subordinate phyllite inter- therefore assigned a Late Ordovician age. bedded throughout upper and lower parts. May be correlative in part with part of unit Age uncertain; probably early Paleozoic SZa (Livengood terrane) (F.R. Weber, writ- (possibly Devonian) (Chapman and others, ten commun., 1992). Thickness unknown, 1982, p. 8). Thickness unknown, but prob- possibly 300 to 600 m. [Chapman and ably at least 900 to more than 1,200 m. others, 1982, 1980, 1975a] Mapped only in Minook Creek area (T. 5- 7 N., R. 12-15 W.). These rocks were Dillinger terrane mapped as units |c and |w by Chapman DOsa Sandstone, argillite, and limestone (Middle and others (1982, 1975a). [Chapman and Devonian to Ordovician)—Gray sandstone, others, 1982, 1975a] black argillite, and thin gray limestone SOvs Volcanic and sedimentary rocks (Silurian interbeds. A 200-m-thick interbed of gray and (or) Ordovician)—Foliated basaltic massive crystalline limestone lies near the lava, tuff, slate, slaty shale, phyllite, and top of the section. Complexly folded and some limestone and chert. Volcanic rocks faulted, regionally metamorphosed, and are partly altered and include some dia- stratigraphically upward-shallowing marine basic rocks. Sedimentary rocks are gen- sequence of slope and basinal turbidites, erally thin bedded. Sequence apparently hemipelagic deposits, and lesser amounts overlies unit Oc and is overlain by unit DOl; of shelf deposits. These rocks are exposed both contacts are gradational. These field north of the McKinley Fault at T. 16-17 relations suggest that unit SOvs is of S., R. 9-10 W. Gastropod fossils in one Ordovician and (or) Silurian age (Chapman of the thin limestone interbeds provided and others, 1982, p. 10). May be cor- Ordovician to Devonian ages; Middle De- relative in part with part of unit SZa vonian fossils were reported from a massive (Livengood terrane) (F.R. Weber, written limestone interbed near the headwater area commun., 1992). Mapped only in the area of the Sanctuary River (T. 16 S., R. 9 W.). between Rock and Minook Creeks (T. 5- Limestone pebbles that occur in the over- 6 N., R. 13-14 W.) and just north of lying Cantwell Formation (unit KTcs) were Roughtop Mountain (T. 4 N., R. 16 W.). probably derived from unit DOsa and contain Thickness unknown, but probably at least conodont fossils ranging in age from Or- 70 to 100 m. These rocks were mapped dovician to Early Devonian. Based on the as unit |vs by Chapman and others (1982). above fossil data, unit DOsa is considered [Chapman and others, 1982, 1975a] to range in age from Ordovician to Middle |p_sq Schist, quartzite, phyllite, and slate (early Devonian. These rocks were mapped as Paleozoic and Precambrian)—Quartz-mica unit DOs by Csejtey and others (1986) and schist, quartzite, phyllite, slate, and mi- as unit |d by Jones and others (1983). nor amounts of chert, shaly limestone, [Csejtey and others, 1992, 1986; Jones siltstone, and graywacke. Unit is mapped and others, 1983, 1982] only north of the Yukon River (T. 4-6 N., R. 17-22 W.). Underlies unit DSl (Baldry Livengood terrane and Ruby terranes, undivided), but the contact is poorly defined. Age uncertain; Dq Quail unit (Late Devonian)—Informal unit of unit is generally correlative with pelitic schist Weber and others (1992). Phyllite, cal- units of the Melozitna, Bettles, and Bea- careous phyllite, siltstone, quartzose sand-

5 stone, graywacke, and conglomerate. These rocks were mapped as unit DOd by Limestone bodies at the base are as much Chapman and others (1971), unit Op_d as 30 m thick and have a lateral extent by Frost and Stanley (1991), and the Pre- of several hundred meters; Weber and cambrian(?) to Ordovician Amy Creek unit others (1992) interpreted them to be local of Weber (1989). [Chapman and others, biogenic buildups on unit Dt. Age based 1971; Frost and Stanley, 1991; Weber, on fossils (corals, stromatoporoids, and 1989; Weber and others, 1992] conodonts). This unit is mapped at the Old Livengood Dome Chert (Late Ordovician)— Sawtooth Mountain area (T. 6-7 N., R. 8- Chert, siliceous slate, and rare greenstone, 11 W.). These rocks were mapped as unit tuff, and limestone. Age based on grap- Dcl by Chapman and others (1971), unit tolites in shaly layers within the chert Dcg by Frost and Stanley (1991), and part (Chapman and others, 1980). At least 1 of the Middle Devonian Cascaden Ridge km thick. This unit is mapped between unit of Weber (1989). [Chapman and Sawtooth Mountain (T. 6-7 N., R. 9-11 others, 1971; Frost and Stanley, 1991; W.) and Livengood Dome, which is just Weber, 1989; Weber and others, 1992] north of the mapped area (T. 9 N., R. 4- Dt Troublesome unit (Devonian?)—Informal unit 5 W.). [Chapman and others, 1980; Weber of Weber and others (1992). Argillite, chert, and others, 1992] siliceous slate, and extensive mafic intru- _Zum Ultramafic and mafic rocks (Early Cambrian sive and extrusive rocks. No identifiable and (or) Late Proterozoic)—Serpentinite fossils, but radiolaria have been reported and greenstone intruded by gabbro and (Weber and others, 1992). This unit is diorite. Serpentinite is sheared and fo- mapped at the Sawtooth Mountain area liated to massive. Gabbros yield radiometric (T. 6-7 N., R. 8-11 W.). These rocks were ages from 643 to 518 Ma (Weber and mapped as unit |u by Chapman and others others, 1992). Rocks are generally green (1971), unit Pc by Frost and Stanley (1991), and dark green to black and are commonly and part of the Middle Devonian Cascaden overlain by barren to thinly vegetated soil Ridge unit of Weber (1989). [Chapman and rubble patches on upper slopes and and others, 1971; Frost and Stanley, 1991; hilltops. This unit is mapped at the Weber, 1989; Weber and others, 1992] Sawtooth Mountain area (T. 6-7 N., R. 8- Dc Cascaden Ridge unit (Middle Devonian)— 11 W.) and at Cascaden Ridge (T. 7 N., Informal unit of Weber and others (1992). R. 7 W.) and is spatially associated with Shale, siltstone, graywacke, conglomerate, unit SZa. These rocks were mapped as and minor limestone. Age based on unit Pzsp by Chapman and others (1971), abundant invertebrate fossils in the lime- unit _Zsp by Frost and Stanley (1992), and stone sections (Weber and others, 1992). as part of the mafic and ultramafic com- Thickness unknown; contacts not exposed. plex by Weber (1989). [Chapman and oth- This unit is mapped south of Cascaden ers, 1971; Frost and Stanley, 1991; Loney Ridge, which is just north of the map area and Himmelberg, 1987; Weber, 1989; (T. 7 N., R. 7 W.). These rocks were Weber and others, 1992] mapped as part of unit Dcl by Chapman and others (1971), unit Dcg by Frost and Stanley (1991), and part of the Cascaden Manley terrane Ridge unit of Weber (1989). [Chapman KJcs Clastic sedimentary rocks (Cretaceous and and others, 1971; Frost and Stanley, 1991; Late? Jurassic)—Graywacke, quartzose Weber, 1989; Weber and others, 1992] sandstone, quartzite, siltstone, shale, slate, SZa Amy Creek unit (Silurian? to Late Protero- argillite, and conglomerate. Sandstone beds zoic?)—Informal unit of Weber and oth- preserve sole marks and are commonly ers (1992). Siliceous dolomite, dolomitic normally graded. The entire unit is tightly mudstone, wackestone, and packstone, folded and faulted. Rare invertebrate and dolomite, chert, and argillite. Minor lime plant fossils indicate Late(?) Jurassic and mudstone that contains interbedded chert Cretaceous ages. Thickness poorly known; and basaltic greenstone and lenses of tuff, probably not less than 1,000 m and may tuffaceous siltstone, shale, and volcaniclastic be as much as 2,700 m. Unit KJcs crops graywacke. Basaltic flows and flow breccia out at T. 1-7 N., R. 3-19 W. and at T. are present locally in the argillaceous rocks 4 S., R. 22 W. Mapped as unit KJgs by at Amy Creek, just beyond the mapped Chapman and others (1975b), units KJs area (T. 8 N., R. 4 W.). Age range based and KJc by Chapman and others (1971), on sponge spicules in chert (Weber and and units Km, Kwcc, Kwcs, and KJw by others, 1992). At least 1,150 m thick. Weber and others (1992). [Chapman and This unit is mapped at the Sawtooth others, 1982, 1975a, 1975b, 1971; Weber Mountain area (T. 6-7 N., R. 10-12 W.). and others, 1992]

6 }|p Phyllite, schistose phyllite, quartzite, siltite, 1992, 1986; Jones and others, 1983, amphibolite, diorite, and greenstone 1982] (Mesozoic or Paleozoic)—Gray, pyritized ^bd Basalt, diabase, gabbro, and subordinate phyllite and schistose phyllite, quartzite, interbedded sedimentary rocks (Late and very finely layered siltite intruded by Triassic; Norian and Karnian)—Several- mafic rocks that include amphibolite, diorite, hundred- to several-thousand-meters-thick and greenstone. Amphibolite yielded a K- submarine sequence of mostly pillow basalts Ar age of 163.88± 21.1 Ma. (Weber and and gabbro and diabase sills and dikes that others, 1992). These rocks are limited also cut the underlying unit ^*s; subor- to two outcrops north of the Beaver Creek dinate interbedded sedimentary rocks are Fault at T. 5 N., R. 8 W. and T. 4 N., gray to green sandstones, siltstones, and R. 9 W. [Weber and others, 1992] argillites. This unit probably represents _Zsp Serpentinite and mafic rocks (Early Cam- a series of subaqueous basalt flows that brian and (or) Late Proterozoic)—Ser- contain minor intercalated clastic and pentinite, diabase, gabbro, and some pelagic sedimentary materials that were de- metadiorite and rodingite; includes some posited in a deep marine environment. thin layers of slaty to schistose rocks, Fossils are rare, but a bivalve of Late Triassic phyllite, and mafic volcaniclastic rocks. (Karnian and Norian) age and radiolarians Based on lithologic similarity, Loney and of Late Triassic (late Norian) age have been Himmelberg (1987) interpret these rocks identified. These rocks crop out in a nar- to be correlative with the Late Protero- row, discontinuous, fault-bounded, east-west- zoic to Cambrian ultramafic rocks of the trending belt between Panorama Mountain Livengood area (unit _Zum, Livengood (T. 16 S., R. 6 W.) and the Toklat River terrane) lying structurally above and pos- (T. 16 S., R. 13 W.). Metamorphic grade sibly in fault contact with unit KJcs in the is prehnite-pumpellyite. Depositionally Manley Hot Springs area (T. 3-4 N., R. overlies unit ^*s. These rocks were 15-18 W.). Chapman and others (1982) mapped as unit ^bd by Csejtey and oth- previously interpreted these rocks to in- ers (1992, 1986) and as unit ^bg by Jones trude the sedimentary rocks of unit KJcs and others (1983). [Csejtey and others, and assigned them a Late Cretaceous age. 1992, 1986; Jones and others, 1983, Unit _Zsp occurs along Serpentine Ridge 1982] (T. 3-4 N., R. 15-18 W.). These rocks ^cs Calcareous sedimentary rocks (Late Triassic; were mapped as unit Ksp by Chapman and Norian and Karnian)—Thin-bedded cal- others (1982) and Frost and Stanley (1991). careous marine shale, argillite, sandstone, [Chapman and others, 1982; Frost and siltstone, and argillaceous limestone, which Stanley, 1991; Loney and Himmelberg, include numerous dikes, sills, and small plugs 1987] of altered diabase and gabbro that are constrained by crosscutting relations to McKinley and Pingston terranes, undivided range in age from Jurassic to Early Cre- KJf Flysch (Early Cretaceous and Late Juras- taceous. These rocks are intensely and sic)—Monotonous, very thick (probably penetratively deformed and locally meta- several thousands of meters) turbidite morphosed to greenschist and amphibo- sequence that includes argillite, graywacke, lite facies. Unit ^cs is interpreted to conglomerate, a few thin interbeds of chert, represent a marine regressive sequence that and some thin beds of limestone. The entire has deep continental slope deposits at the sequence has been compressed into tight base that are overlain by progressively folds and complexly faulted, including thrust shallower slope deposits, then by outer shelf faults. These rocks unconformably over- deposits, and finally by inner shelf deposits. lie unit ^bd east of the Nenana River; The age range is based on conodonts and elsewhere the contact is tectonic or cov- pelecypods. Unit ^cs overlies unit Dy in ered by surficial deposits. Depositional slight angular unconformity as indicated age span is well established based on fossils; in a good exposure south of the Wood River age of metamorphism is about mid-Cre- (T. 14 S., R. 1-2 W.); the top of the se- taceous, but may span from Late Juras- quence is not exposed. Correlated with sic to early Tertiary based on K-Ar age unit ^cs (Nenana terrane) south of the determinations on mineral separates (Csejtey McKinley fault by Csejtey and others (1986). and others, 1992, 1986). Unit KJf crops Preserved thickness is uncertain, but it is out at T. 15-16 S., R. 1 E.-R. 14 W. These estimated to be several hundred meters. rocks were mapped as unit KJf by Csejtey These rocks crop out at T. 14-16 S., R. and others (1986) and as unit Ks by Jones 1 E.-R. 9 W. Mapped as unit ^s by Jones and others (1983). [Csejtey and others, and others (1983). [Csejtey and others,

7 1992, 1986; Jones and others, 1983, Ps Sedimentary rocks (Permian)—Shale, slaty 1982] and in part phyllitic, siltstone, argillite, ^*s Flysch-like sedimentary rocks (Late Trias- graywacke, pebble-to-granule conglomerate, sic to Pennsylvanian)—Conglomerate, and minor interbedded unfossiliferous chert. sandstone, siltstone, argillite, a few thin Graded bedding is common in sandstones; interbeds of limestone, and chert interca- siltstones are interbedded with shales and lated with argillite near the top. These phyllites. Sparsely fossiliferous clastic rocks are intensely folded, several hundred limestone crops out rarely in thin discon- meters thick, and massive to thin bedded. tinuous beds. Age is based on crinoid The depositional environment of this unit fragments and bryozoans in conglomerate. may have been slope to base-of-slope. Age Thickness unknown, but probably at least based on abundant fossils of marine 300 m in the Minook-Hoosier Creeks area macroinvertebrates, conodonts, and radi- (T. 6-7 N., R. 12-13 W.). Contact with olarians. Metamorphic grade is prehnite- unit KJcs (Manley terrane), which is litho- pumpellyite. Depositionally underlies unit logically similar, is a poorly exposed un- ^bd. Unit ^*s crops out at T. 16 S., R. conformity or possibly a fault. These rocks 7-13 W. [Csejtey and others, 1992, 1986; were mapped as unit Ps by Chapman and Jones and others, 1983, 1982] others (1982, 1975a), unit |c by Chapman Ps Dy Yanert Fork sequence (Late Devonian)— and others (1971), and unit by Weber Informal unit of Csejtey and others (1992, and others (1992). [Chapman and oth- 1986). Intensely deformed metasedimentary ers, 1982, 1975a, 1971; Patton and others, and metavolcanic rocks that consist of 1989; Weber and others, 1992] mudstone, argillite, shale, slate, phyllite, and quartzite. Also contains interbeds of Nenana terrane chert, metatuff, metabasalt, schistose ^sc Sedimentary calcareous rocks (Late Trias- metaconglomerate, and marble. Diabase sic)—Lithologically similar to unit ^cs and gabbro intrusions are present that are (McKinley and Pingston terranes, undivided) lithologically similar to those in units ^cs but occurs only south of the McKinley Fault (McKinley and Pingston terranes, undivided) (T. 16 S., R. 1-4 W.). Correlated by Csejtey and ^cs (Nenana terrane) and presumably and others (1986) with unit ^sc (McKinley of the same age (Jurassic to Early Creta- and Pingston terranes, undivided). [Csejtey ceous). Exposed mainly in the headwa- and others, 1992, 1986] ter region of Yanert Fork (T. 14-15 S., R. 2 E.-R. 5 W.). Overlain in slight angular Nixon Fork and Minchumina terranes, undivided unconformity by unit ^cs; basal contact Dls Limestone and siltstone (Late? Devonian)— is not exposed. Thickness unknown, but Dominantly gray limestone; forms promi- estimated to be at least 1,000 m. Meta- nent ridges; minor siltstone is gray, shaly morphic grade is lower greenschist facies; to phyllitic, and calcareous in part. Unit metamorphism probably occurred during Dls occurs at T. 1-2 S., R. 22 W. Fos- mid-Cretaceous time. Age span imperfectly sils from a locality 8 mi south of Redlands known, but conodont fossils present in a Lake, just west of mapped area (T. 3 S., marble interbed yielded a Late Devonian R. 24 W.), yielded an early Late Devonian (Famennian) age (Csejtey and others, 1992, (Frasnian) age. Thickness unknown; prob- 1986). Lithologies, depositional environ- ably at least 150 m. [Chapman and others, ment, metamorphic grade, age, and struc- 1975b] tural style are the same north and south DOc Chert (Early Devonian to Ordovician)—Gray, of the Hines Creek Fault. These rocks thin- to thick-bedded chert that has thin were mapped as unit |y by Csejtey and interbeds of siliceous siltstone, shaly to slaty others (1986). [Csejtey and others, 1992, mudstone, and shaly tuffaceous argillite. 1986; Jones and others, 1983, 1982] Overlies unit DOs; contact may be grada- tional. Radiolarians of early Paleozoic Minook terrane (Ordovician to Early Devonian) age are present in both chert and argillite; Ordovi- ^c Black shale and chert (Triassic)—Black shale and slate locally interlayered with light-olive- cian graptolites were found in thin shale gray, thinly to thickly bedded chert and beds at one site. May be correlative in light-greenish-gray tuff. Radiolarians in part with unit |cs (White Mountains ter- chert identified as Triassic in age (Karen rane, Wickersham terrane, and Yukon- Wheeler, oral commun., 1992). These Tanana terrane north of Tanana River, rocks crop out west of Sawtooth Moun- undivided) in the Dugan Hills area (T. 2 tain at T. 7 N., R. 11-12 W. [Weber and N.-T. 1 S., R. 11-13 W.). Correlated with others, 1992] the Livengood Dome Chert (unit Old,

8 Livengood terrane) by Chapman and others Wood River Buttes were mapped as unit (1981, p. B33; 1975b). These rocks occur Dmu by Péwé and others (1966). [Fos- at T. 4-9 S., R. 19-23 W., and were ter and others, 1987; Péwé and others, mapped as unit Oc by Chapman and others 1966] (1975b). [Chapman and Yeend, 1981; Chapman and others, 1981, 1975b] Tozitna terrane DOs Shaly rocks (Early Devonian to Ordovician)— ^Mms Mafic igneous rocks and sedimentary rocks Mudstone, argillite, grit, quartzite, calcareous (Triassic to Mississippian)—Volcanic, sedi- quartz-chert arenite, sandy limestone, and mentary, and ultramafic rocks that include minor amounts of chert and quartz-mica tuffs, greenstones, breccias, and basaltic, schist. Age range based on the presence diabasic, and rarely andesitic lavas; pyro- of Ordovician graptolites and a coral of clastic tuffaceous rocks apparently grade “probable Early or Middle Devonian” age into sedimentary tuffs and chert. Intru- in a lakeshore cobble (Chapman and others, sive rocks are fine- to coarse-grained 1981). Probably underlies unit DOc. These diabase-gabbro and some diorite that are rocks crop out at T. 7-13 S., R. 19-22 present as sills several meters to at least W. May be correlative in part with unit 90 m thick and commonly form prominent |ma at Mooseheart Mountain (T. 2-3 S., ridges, knobs, and bluffs. Serpentinized R. 17-18 W.) and the Bitzshtini Mountains ultramafic rocks have been reported at a (T. 5-6 S., R. 22-23 W.) and in part with few locations (Chapman and others, 1975a, unit _Zwa (White Mountains terrane, p. 6). Sedimentary rocks are argillite, chert, Wickersham terrane, and Yukon-Tanana graywacke, shale, and limestone. Referred terrane north of Tanana River, undivided) to as the Rampart Group by Chapman and in the Dugan Hills area (T. 2 N., R. 11- others (1975a), Jones and others (1984), 13 W.). [Chapman and others, 1981; Weber (1989), and Weber and others Chapman and Yeend, 1981] (1992). Age range of Mississippian to |ma Mudstone, argillite, grit, quartzite, calcareous Triassic is based on fossils (radiolarians in quartz-chert arenite, sandy limestone, chert and invertebrates in limestone) and and minor chert and quartz-mica schist a hornblende K-Ar age of 205± 6 Ma on (early Paleozoic?)—Lithologically similar a gabbroic intrusive body (Weber and others, to unit DOs. Lithology at Mooseheart 1992). Lower contact may be an uncon- Mountain (T. 1-2 S., R. 17-18 W.) com- formity, thrust fault, or both. Thickness prises brown slates and quartzites (Rich- unknown but probably at least 900 to 1,200 ard G. Stanley, field notes, 1986). Unit m. Unit ^Mms crops out north of the |ma crops out northwest of unit DOc in Bitzshtini Mountains at T. 2-3 S., R. 21- the Bitzshtini Mountains (T. 5-6 S., R. 22- 22 W., north of the Yukon River (T. 6- 23 W.). The same rocks were mapped 7 N., R. 20-22 W.), and north and south as units _qs and O_sl by Chapman and of Garnet Creek (T. 6-7 N., R. 12-15 W.). others (1975b) and as unit DOs by Chapman Part of this unit may be correlative with and others (1981). [Chapman and oth- unit Ps (Minook terrane). These rocks were ers, 1981, 1975b] mapped as units ^Pv and ^m by Chapman and others (1975a and 1975b, respectively) Seventymile terrane and units ^Mrv and ^Mrs by Weber and PMum Ultramafic and mafic rocks (Early Permi- others (1992). [Chapman and others, an? to Mississippian?)—Diorite and 1982, 1975a, 1975b; Jones and others, serpentinized peridotite; these rocks are 1984; Patton and others, 1989; Weber, present at Wood River Buttes (T. 5 S., R. 1989; Weber and others, 1992] 3 W.) and are lithologically similar to mafic White Mountains terrane, Wickersham terrane, and ultramafic rocks along the Salcha River and Yukon-Tanana terrane north of in the Big Delta quadrangle to the north- Tanana River, undivided east. An intense linear magnetic anomaly that extends from the Wood River Buttes ^m Mafic igneous rocks (Triassic)—Gabbro, to the Salcha River outcrops suggests that diorite, metadiorite, diabase, basalt, the mafic and ultramafic rocks in the two metabasalt, and greenstone. Intrudes unit areas are parts of a single belt (Péwé and Mg (White Mountains terrane). Unpublished others, 1966). In the Salcha River area radiometric data by J.K. Mortensen (Ca- and farther east, the mafic and ultrama- nadian Geological Survey) have identified fic rocks are associated with slightly re- a zircon as Triassic (232.1± 4.5 Ma) in age crystallized cherts that contain radiolarians (Weber and others, 1992). Unit ^m crops and conodonts of Early Permian age and out only south of the Beaver Creek Fault radiolarians of Mississippian age (Foster at T. 3-7 N., R. 2-10 W. Mapped as unit and others, 1987, p. 42). The rocks at |m by Chapman and others (1971) and

9 Frost and Stanley (1991) and as part of N., R. 1 W.). The southern boundary is the Globe unit of Weber (1989). [Chapman overthrust by unit _Zwa. True thickness and others, 1971; Frost and Stanley, 1991; is unknown, but it is at least 90 m thick Weber, 1989; Weber and others, 1992] (Weber and others, 1992). Beaver Bend Mg Globe unit (Mississippian)—Informal unit of unit of Weber and others (1992). Mapped Weber and others (1992). Vitreous quartz- as unit Dcl by Chapman and others (1971) ite, phyllite, and slate. Age is based on and unit Dc by Frost and Stanley (1991). lithologic similarity to the informally named [Chapman and others, 1971; Frost and Keno Hill quartzite of Tempelman-Kluit Stanley, 1991; Weber and others, 1992] (1970). These rocks crop out only south DSt Tolovana Limestone (Middle Devonian to of the Beaver Creek Fault along a narrow Early Silurian)—Thickly bedded to mas- band at T. 2-7 N., R. 2-13 W. Intruded sive, finely crystalline, gray limestone; in by unit ^m. Unit Mg is mapped as part places rich in peloids and ooids. Forms of the Globe unit of Weber (1989), unit prominent ridge near Dugan Hills (T. 2 |q by Frost and Stanley (1991), and unit N., R. 12-13 W.), COD Lake (T. 3 N., Oq by Chapman and others (1971). R. 6-7 W.), and at T. 6-7 N., R. 1-3 W. [Chapman and others, 1971; Frost and near the southern end of the White Stanley, 1991; Weber, 1989; Weber and Mountains, which are north of the map others, 1992] area (T. 8-10 N., R. 1-2 E.). Contains M_bh Birch Hill sequence (Mississippian to Cam- crushed zones recemented by white cal- brian)—Informal unit of Robinson and cite and quartz; chert is rare or absent. others (1990). Phyllite, micaceous calc- Fossils (conodonts, brachiopods, and corals) schist, calc-amphibolite, quartzite, and minor from the White Mountains have been iden- felsic tuff. Age based on evidence from tified as Silurian in age, and corals from Robinson and others (1990). Stratigraph- the Dugan Hills-COD Lake area have been ically overlies unit M_cr. According to identified as Middle Devonian in age Robinson and others (1990), these rocks (Blodgett and others, 1987; Oliver and are intruded by and are overlain by basalts others, 1975; Weber and others, 1992). that are part of unit Tv, Postaccretion Cover Unit DSt disconformably overlies unit Of; Deposits. Contains lower-greenschist-facies this contact is well exposed just off the mineral assemblages and may be correlative map area to the northeast (65°37’16” N, with the Keevy Peak Formation (unit |kp, 147°21’11” W) (Blodgett and others, 1987). Yukon-Tanana terrane south of Tanana Thickness exceeds 1,200 m in the White River) of the central Alaska Range. These Mountains area. Weber and others (1992) rocks crop out in a narrow belt northeast separate unit DSt into an upper subunit of Fairbanks near Fort Wainwright (T. 1 of Middle Devonian age that is exposed S., R. 1 E.). [Robinson and others, 1990] in the Dugan Hills-COD Lake area and is M_cr Chena River sequence (Mississippian to at least 457 m thick, and a lower main Cambrian)—Informal unit of Robinson and body of Silurian age exposed in the White others (1990). Banded amphibolite, tremo- Mountains. [Blodgett and others, 1987; lite marble, coarse-grained garnet-muscovite Chapman and others, 1971; Oliver and schist, biotite-rich schist, micaceous others, 1975; Péwé and others, 1966; calcschist, and pale-green metachert. Age Weber, 1989; Weber and others, 1992; based on evidence from Robinson and Wheeler and others, 1987] others (1990). Mineral assemblages and |cs Chert and siliceous shale (early Paleozoic)— textural maturity suggest these rocks were Thin- to thick-bedded chert and thin metamorphosed to lower-amphibolite-fa- interbeds of siliceous slaty shale. These cies grade. Structurally overlies the rocks crop out in the Dugan Hills area (T. Fairbanks schist unit (unit Zf). These rocks 1 S.-T. 2 N., R. 11-13 W.). Age is inferred crop out in a narrow belt north of the from lithologic similarity to unit DOc (Nixon Tanana River near Fairbanks (T. 2 S.-T. Fork and Minchumina terranes, undivided), 2 N., R. 1 E.-R. 2 W.). [Robinson and which contains Ordovician and Devonian others, 1990] fossils. These rocks are probably correlative Dcg Conglomerate, graywacke, and slate (De- with the sedimentary part of the Fossil vonian?)—Chert-pebble conglomerate; Creek Volcanics (unit Of, White Mountains graywacke has interbedded siltstone and terrane, Wickersham terrane, and Yukon- slate, which contain unidentifiable plant Tanana terrane north of Tanana River, un- fragments (Weber and others, 1992). Age divided) (F.R. Weber, written commun., based on fossils (Chapman and others, 1992). This unit was mapped as unit DOc 1971). These rocks occur south of the by Chapman and Yeend (1981), unit Oc Beaver Creek Fault near the confluence by Chapman and others (1982, 1975a), of Beaver and Wickersham Creeks (T. 7 and unit nc by Péwé and others (1966).

10 [Chapman and others, 1982, 1975a; Volcanics by Weber (1989). It is divided Chapman and Yeend, 1981; Péwé and into units Ofv and Ofs by Weber and others others, 1966] (1992). [Blodgett and others, 1987; |ch Chatanika unit (early Paleozoic)—Informal Chapman and others, 1975a, 1971; Frost unit of Weber and others (1992). and Stanley, 1991; Péwé and others, 1966; Allochthonous, garnet-bearing quartz-bi- Weber, 1989; Weber and others, 1992; otite-muscovite schist and quartzite. Wheeler and others, 1987] Primarily epidote-amphibolite facies, but _Zwa Wickersham unit (Early Cambrian and Late includes eclogitic rocks. These rocks struc- Proterozoic)—Informal unit of Weber and turally overlie unit Zf in fault contact. Age others (1992). Maroon and green argil- and origin are uncertain, but a Rb-Sr date lite, grit, quartzite, siltstone, graywacke, of 509 Ma on muscovite and K-Ar ages and phyllite. Includes thin beds of dark up to 470± 35 Ma on amphiboles were limestone. These rocks occur at T. 3-7 interpreted as an Ordovician metamorphic N., R. 1 E.-R. 4 W. southwest of the White event by Chapman and others (1971). (The Mountains, which are north of the map Rb-Sr date can be interpreted as Late area (T. 8-10 N., R. 1-2 E.), and at Cambrian to Early Ordovician in age based Sawtooth Mountain (T. 7 N., R. 9-11 W.). on the 1983 chronologic chart of the U.S. Intruded by gabbro (unit ^m, White Moun- Geological Survey, Geologic Names Com- tains terrane) at T. 6 N., R. 3 W. south- mittee.) Younger K-Ar ages (178 to 103 west of the White Mountains. Age is based Ma) and Rb-Sr ages (157± 8 Ma to 137± 8 on the occurrence of Oldhamia, a trace Ma) suggest that older rocks were over- fossil, near the top of this unit (Moore and printed during Mesozoic metamorphism Nokleberg, 1988), and a K-Ar age of (Weber and others, 1992). Weber (1989) 1.35± 40.6 Ga on white mica (Weber and mentions an Ordovician K-Ar age on others, 1992). The contact exposed along amphibolite in the eclogitic rocks and the Elliott Highway between units _Zwa assigns the entire sequence a Paleozoic(?) and Zwg (White Mountains terrane, age. Unit |ch crops out at T. 3 N., R. Wickersham terrane, and Yukon-Tanana 1 E.-R. 1 W. These rocks are part of the terrane north of Tanana River, undivided) Birch Creek Schist of former usage. Unit was interpreted as a thrust fault by |ch is mapped as unit eaf by Chapman Chapman and others (1971), Weber (1989), and others (1971), unit ec by Foster and and Weber and others (1992). Alterna- others (1987), unit |s by Frost and Stanley tively, according to Moore and Nokleberg (1991), and the Chatanika unit by Weber (1988), the contact in the vicinity of Cache (1989). [Chapman and others, 1971; Mountain (northeast of the map area) be- Foster and others, 1987; Frost and Stanley, tween units Zwg and _Zwa is conformable 1991; Nokleberg and others, 1989; Weber, and gradational with unit Zwg structurally 1989; Weber and others, 1992] and stratigraphically overlying unit _Zwa. Of Fossil Creek Volcanics (Late to Early There is still much controversy about which Ordovician)—Alkali basalt, agglomerate, of the two units is stratigraphically higher. volcaniclastic conglomerate, and minor Together units Zwg and _Zwa may be as limestone and sandstone; also, shale, chert, much as 7,000 m thick. In the Dugan Hills and limestone intruded by gabbro. Lower area (T. 1 S.-T. 2 N., R. 11-13 W.), these part is composed primarily of sedimentary rocks are lithologically similar to, and per- rocks; grades laterally and upward into a haps correlative with, unit DOs (Nixon Fork sequence of basalt, tuff, and agglomerate and Minchumina terranes, undivided), which that is generally capped by a thin layer contains Ordovician and Devonian(?) fossils. of volcanic-rich sedimentary rocks. Fos- The rocks of unit _Zwa were interpreted sil invertebrates (brachiopods, conodonts, by F.R. Weber (written commun., 1992) gastropods, and trilobites) indicate Early to be correlative with similar rocks farther to Late Ordovician ages. Disconformably to the northeast in the Wickersham Dome underlies unit DSt (this contact is well area (T. 4-5 N., R. 2-4 W.) and were exposed just northeast of the map area mapped as unit DOs by Chapman and at 65°37’16” N, 147°21’11” W) and Yeend (1981), unit _al by Chapman and unconformably overlies unit Zwg (Blodgett others (1982, 1975a), unit |sr by Frost and others, 1987). Thickness exceeds 610 and Stanley (1991), and unit ng by Péwé m. Unit Of crops out in a northeast- and others (1966). Elsewhere, unit _Zwa southwest-trending belt along the Beaver was mapped as unit _al by Chapman and Creek Fault (T. 2-7 N., R. 2-12 W.). This others (1971), unit _p_sl by Frost and unit is mapped as unit SOvs by Chapman Stanley (1991), and the maroon and green and others (1971), unit Ovs by Frost and slate subunit of the Wickersham unit by Stanley (1991), and the Fossil Creek Weber (1989). [Chapman and others,

11 1971; Frost and Stanley, 1991; Moore and Chapman and others, 1971; Foster and Nokleberg, 1988; Weber, 1989; Weber and others, 1987; Frost and Stanley, 1991; others, 1992] Nokleberg and others, 1989; Péwé and Zwg Grit (Late Proterozoic)—Grit, quartzite, others, 1966; Weber, 1989; Weber and graywacke, conglomerate, limestone, others, 1992] phyllite, slate, and argillite. Contact with the underlying unit Zf is gradational. Unit Zwg crops out in the Wickersham Dome Yukon-Tanana terrane south of Tanana River area (T. 2-6 N., R. 1 E.-R. 10 W.) and MDt Totatlanika Schist (Early Mississippian to in the Dugan Hills (T. 1 S.-T. 2 N., R. Middle Devonian)—Metavolcanic and 11-13 W.). F.R. Weber (written commun., metavolcaniclastic rocks (schist and gneiss), 1992) interpreted the rocks in the Dugan both felsic and mafic, and subordinate Hills area to be correlative with similar rocks amounts of intercalated metasedimentary farther to the northeast in the Wickersham rocks, such as black (carbonaceous) pelitic Dome area (T. 4-5 N., R. 2-4 W.). The schist and phyllite and, at one locality, a Dugan Hills rocks were mapped as unit thin interbed of fossiliferous marble. DOs by Chapman and Yeend (1981), unit Interpreted to represent continental margin _al by Chapman and others (1982, 1975a), deposits by Csejtey and others (1986). unit |sr by Frost and Stanley (1991), and Metamorphic mineral assemblages suggest unit ng by Péwé and others (1966). In recrystallization in the greenschist meta- the Wickersham Dome area, unit Zwg was morphic facies. Maximum preserved mapped as unit _gq by Chapman and others cumulative thickness is over 5,700 m, but, (1971), unit _p_g by Frost and Stanley in any one area, the thickness of the rocks (1991), and the basal grit subunit of the may be considerably less. Depositional age Wickersham unit by Weber (1989). span inadequately known because fossils [Chapman and others, 1971; Frost and were found only at one locality within a Stanley, 1991; Moore and Nokleberg, thin marble interbed; however, these fossils 1988; Weber, 1989; Weber and others, indicate a Middle Devonian to Early Mis- 1992] sissippian age. Unit MDt crops out at T. Zf Fairbanks schist unit (Late Proterozoic)— 8-16 S., R. 1 E.-R. 15 W. In the Kantishna Greenschist facies muscovite-chlorite schist, Hills (T. 12-16 S., R. 15-19 W.), unit MDt quartzite, and phyllite. Age based on may include rocks correlative with part of correlation with Windermere Supergroup unit |kp (Yukon-Tanana terrane south of in Canada and field relations (Weber and Tanana River). These rocks were mapped others, 1992). Nokleberg and others (1989) as unit |ts by Csejtey and others (1986) considered these rocks to be part of a and as unit DSt by Péwé and others (1966). metamorphosed Devonian to Mississippian [Bundtzen, 1981; Csejtey and others, 1992, igneous arc and associated metamorphosed 1986; Péwé and others, 1966] wall rocks. U-Pb geochronology of pri- Dms Metasedimentary rocks (Late or Middle mary zircon in metarhyolite from the Cleary Devonian)—Schist, phyllite, quartzite, subunit yields a Late Devonian age (369± 3 metachert, and marble; thin bedded with Ma, Aleinikoff and Nokleberg, 1989), while a well-developed foliation that parallels detrital zircons indicate an Early to Middle bedding. Metamorphic grade is lower Proterozoic or older age (2.3 to 2.1 Ga, greenschist facies; metamorphism probably Aleinikoff and Nokleberg, 1989; 3.3 to occurred during mid-Cretaceous time. Poorly 1.1 Ga, F.R. Weber and J.K. Mortensen, preserved fossils in marble interbeds indi- written commun., 1992). Unit Zf crops cate a Middle or Late Devonian age. These out at T. 6 N.-T. 4 S., R. 1 E.-R. 7 W. rocks are exposed in discontinuous outcrops These rocks are part of the Birch Creek just north of the Hines Creek Fault (T. 13 Schist of former usage. Unit Zf is mapped S., R. 1 E.-R. 1 W. and T. 14-15 S., R. as unit gf by Chapman and others (1971), 11-13 W.). Unit Dms appears to be closely unit qq by Foster and others (1987), unit associated spatially with unit MDt; the contact MDqs by Frost and Stanley (1991), unit between the two units may be a thrust fault. bc by Péwé and others (1966), and the Along the Wood River (T. 13 S., R. 1 E.- Fairbanks schist unit by Weber (1989). R. 1 W.), unit Dms is very similar to unit Locally subdivided into the Cleary subunit Dy (McKinley and Pingston terranes, un- (mapped as unit Zfc by Weber and others, divided) in lithology, metamorphic grade 1992), which is a facies characterized by and level of recrystallization, deformation white felsic schist, micaceous quartzite, style, and apparent age and depositional chloritic or actinolitic greenschist, green- environment. These rocks were mapped stone, and marble. [Aleinikoff and oth- as unit |ms by Csejtey and others (1986). ers, 1984; Aleinikoff and Nokleberg, 1989; [Csejtey and others, 1992, 1986]

12 Dmg Metagabbro (Late Devonian?)—Dark greenish (T. 6 S., R. 1 E.), and at Clear Creek Butte gray; fine to medium grained and foliated; (T. 3 S., R. 1 W.). According to F.R. Weber greenschist facies metamorphism. Exposed (written commun., 1992), the rocks at Clear only as two small intrusive bodies within Creek Butte (T. 3 S., R. 1 W.) are prob- unit |p_s (T. 12 S., R. 1 W. and T. 13 ably part of the Fairbanks schist unit (unit S., R. 5 W.). Age is uncertain, but these Zf, White Mountains terrane, Wickersham rocks may be the intrusive equivalent of terrane, and Yukon-Tanana terrane north Late Devonian metabasalts and related of Tanana River, undivided). Robinson and metasedimentary rocks included in unit MDt. others (1990) map the rocks at Clear Creek Alternatively, they may correlate with Butte as part of the Birch Hill sequence Jurassic to Early Cretaceous gabbroic (unit M_bh, White Mountains terrane, intrusives north of the Hines Creek Fault Wickersham terrane, and Yukon-Tanana within units Dy and ^cs (McKinley and terrane north of Tanana River, undivided). Pingston terranes, undivided). These rocks Rocks of unit |p_s were mapped as unit were mapped as unit |mg by Csejtey and |p_p by Csejtey and others (1992), as unit others (1986). [Csejtey and others, 1992, pqs by Csejtey and others (1986), as unit 1986; Wahrhaftig, 1970b, 1970c] bc by Péwé and others (1966), and as unit |kp Keevy Peak Formation (early Paleozoic)— p_bc by Reed (1961). [Bundtzen, 1981; Sequence of quartz-sericite and (or) mus- Csejtey and others, 1992, 1986; Péwé and covite schist, black quartzite, black others, 1966; Reed, 1961] carbonaceous pelitic schist and phyllite, pebble conglomerate, greenish-gray and purple schist and slate, and a few thin marble interbeds. Rests unconformably on REFERENCES CITED unit |p_s and is overlain in fault contact Albanese, M.D., 1982, Two Holocene maars in the central by unit MDt. Thickness is unknown, but Alaska Range: Alaska Division of Geological and preserved section ranges from 700 to 1,200 Geophysical Surveys Geologic Report 73, p. 19-27. m in thickness. No fossils have been found; Albanese, M.D., and Turner, D.L., 1980, 40K-40Ar ages age is based on stratigraphic relations with from rhyolite of Sugar Loaf Mountain, central Alaska the underlying unit |p_s, which is early range: implications for offset along the Hines Creek Paleozoic in part (Csejtey and others, 1992). strand of the Denali fault system, in Short Notes on These rocks are exposed at T. 11-12 S., Alaskan Geology 1979-80: Alaska Division of R. 1 E.-R. 5 W. Mapped as unit |k by Geological and Geophysical Surveys Geologic Re- Csejtey and others (1992), as unit kp by port 63, p. 7-10. Csejtey and others (1986), and as part of Aleinikoff, J.N., Foster, H.L., Nokleberg, W.J., and Dusel- unit bc by Péwé and others (1966). [Csejtey Bacon, Cynthia, 1984, Isotopic evidence from detrital and others, 1992, 1986; Péwé and oth- zircons for Early Proterozoic crustal material, east- ers, 1966; Wahrhaftig, 1968] central Alaska, in Coonrad, W.L., and Elliott, R.L., |p_s Pelitic and quartzose schist (early Paleo- eds., The United States Geological Survey in Alaska: zoic and (or) Precambrian)—Pelitic schist, Accomplishments during 1981: U.S. Geological Survey quartzite, phyllite, and a few marble Circular 868, p. 43-45. interbeds; intensely deformed; lower green- Aleinikoff, J.N., and Nokleberg, W.J., 1989, Age of schist facies metamorphism. Contact with deposition and provenance of the Cleary sequence the overlying Keevy Peak Formation (unit of the Fairbanks schist unit, Yukon-Tanana terrane, |kp) is thought to be a depositional un- east-central Alaska, in Dover, J.H., and Galloway, conformity (Csejtey and others, 1992). J.P., eds., Geologic studies in Alaska by the U.S. Base is not exposed, therefore, thickness Geological Survey, 1988: U.S. Geological Survey is not known; however, thickness measured Bulletin 1903, p. 75-83. perpendicular to the axial plane of cleavage Barnes, D.F., 1961, Gravity low at Minto Flats, Alaska: is at least 3,000 m. Fossils from a marble U.S. Geological Survey Professional Paper 424-D, interbed indicate possibly an Ordovician p. D254-D257. or younger age (Csejtey and others, 1992, ———1972, Notes on the processing and presentation 1986, p. 82, no. 171); isotopic ages range of U.S. Geological Survey Alaskan gravity data: U.S. from 1,170 Ma to 120 Ma (Péwé and oth- Geological Survey Open-File Report 72-16, 25 p. ers, 1966), but are considered unreliable. ———1977, Bouguer gravity map of Alaska: U.S. Geo- Part of the Birch Creek Schist of former logical Survey Geophysical Investigations Map GP- usage. Unit |pes crops out in the Kantishna 913, scale 1:2,500,000, 1 sheet. Hills (T. 12-16 S., R. 15-19 W.) where ———1984, Digital elevation models improve processing it may, in part, include part of unit |kp of Alaskan gravity data, in Coonrad, W.L., and (Yukon-Tanana terrane south of Tanana Elliott, R.L., eds., United States Geological Sur- River), in the Alaska Range (T. 11-14 S., vey in Alaska: Accomplishments during 1981: U.S. R. 1 E.-R. 12 W.), east of Clear Creek Geological Survey Circular 868, p. 5-7.

13 Barnes, D.F., Mariano, John, Morin, R.L., Roberts, quadrangles, Alaska: U.S. Geological Survey Open- C.W., and Jachens, R.C., 1994, Preliminary in- File Report 75-337, scale 1:250,000, 1 sheet. complete isostatic gravity map of Alaska (exclu- ———1982, Reconnaissance geologic map of the sive of the Aleutian and Bering Sea islands and Tanana quadrangle, Alaska: U.S. Geological Survey their adjacent continental shelves and seas), in Open-File Report 82-734, 17 p., scale 1:250,000, Plafker, George, and Berg, H.C., eds., The Cor- 1 sheet. dilleran Orogen, Alaska: Boulder, Colorado, Geo- Chapman, R.M., Yeend, W.E., and Patton, W.W., Jr., logical Society of America, The Geology of North 1975b, Preliminary reconnaissance geologic map America, v. G1, Plate 9, 1 sheet, scale 1:250,000. of the western half of Kantishna River quadrangle, Barnes, D.F., Nokleberg, W.J., and Brocher, T.M., 1991, Alaska: U.S. Geological Survey Open File Report Gravitational and seismic evidence for Tertiary 75-351, scale 1:250,000, 1 sheet. structural basins in the Alaska Range and Tanana Csejtey, Béla, Jr., Mullen, M.W., Cox, D.P., Gilbert, lowland [abs.]: Geological Society of America W.G., Yeend, W.E., Smith, T.E., Wahrhaftig, Clyde, Abstracts with Programs, v. 23, no. 2, p. 5. Craddock, C.C., Brewer, W.M., Sherwood, K.W., Blodgett, R.B., Wheeler, K.L., Rohr, D.M., Harris, A.G., Hickman, R.G., Stricker, G.D., St. Aubin, D.R., and Weber, F.R., 1987, A Late Ordovician age and Goerz, D.J., III, 1986, Geology and geochro- reappraisal for the upper Fossil Creek volcanics, nology of the Healy quadrangle, Alaska: U.S. Geo- and possible significance for glacio-eustasy, in logical Survey Open-File Report 86-396, 92 p., Hamilton, T.D., and Galloway, J.P., eds., Geologic scale 1:250,000, 4 sheets. studies in Alaska by the U.S. Geological Survey Csejtey, Béla, Jr., Mullen, M.W., Cox, D.P., and Stricker, during 1986: U.S. Geological Survey Circular 998, G.D., 1992, Geology and geochronology of the p. 54-58. Healy quadrangle, south-central Alaska: U.S. Geo- Buffler, R.T., and Triplehorn, D.M., 1976, Deposi- logical Survey Miscellaneous Investigations Series tional environments of the Tertiary coal-bearing Map I-1961, scale 1:250,000, 2 sheets, pamphlet. group, central Alaska, in Miller, T.P., ed., Recent Decker, J.E., and Gilbert, W.G., 1978, The Mount Galen and Ancient Sedimentary Environments in Alaska, Volcanics—a new middle Tertiary volcanic formation Proceedings of the Alaska Geological Society in the central Alaska Range: Alaska Division of Symposium held April 2-4, 1975, at Anchorage, Geological and Geophysical Surveys, Geologic Report Alaska: Alaska Geological Society, Anchorage, 59, 11 p. Alaska, p. H1-H10. Foster, H.L., Keith, T.E.C., and Menzie, W.D., 1987, Bundtzen, T.K., 1981, Geology and mineral deposits Geology of east-central Alaska: U.S. Geological of the Kantishna Hills, Mt. McKinley quadrangle, Survey Open-File Report 87-188, 59 p. Alaska: Fairbanks, Alaska, University of Alaska, Frost, G.M., and Stanley, R.G., 1991, Compiled geologic M.S. thesis, 238 p., scale 1:63,360, 4 plates. and Bouguer gravity map of the Nenana basin area, Chapman, R.M., Churkin, Michael, Jr., Carter, Claire, central Alaska: U.S. Geological Survey Open-File and Trexler, J.H., Jr., 1981, Ordovician grapto- Report 91-562, 30 p., scale 1:250,000, 2 sheets. lites and early Paleozoic radiolarians in the Lake Gilbert, W.G., Ferrell, V.M., and Turner, D.L., 1976, Minchumina area date a regional shale and chert The Teklanika formation—a new volcanic forma- belt, in Albert, N.R.D., and Hudson, Travis, eds., tion in the central Alaska Range: Alaska Division The United States Geological Survey in Alaska: of Geological and Geophysical Surveys, Geologic Accomplishments during 1979: Geological Sur- Report 47, 16 p. vey Circular 823-B, p. B32-B34. Grether, W.J., and Morgan, K.A., 1988, Exploration Chapman, R.M., Weber, F.R., Churkin, Michael, Jr., and hydrocarbon potential of interior basins, Alaska and Carter, Claire, 1980, The Livengood Dome [abs.]: American Association of Petroleum Geologists Chert, a new Ordovician formation in central Alaska, Bulletin, v. 72, no. 2, p. 191-192. and its relevance to displacement on the Tintina Hackett, S.W., 1981, Tabulated gravity field data, north Fault: U.S. Geological Survey Professional Paper flank of the Alaska Range, Alaska: Alaska Divi- 1126-F, p. F1-F13. sion of Geological and Geophysical Sciences Open- Chapman, R.M., Weber, F.R., and Taber, Bond, 1971, File Report 81-138, 6 p. Preliminary geologic map of the Livengood quad- Hite, D.M., and Nakayama, E.N., 1980, Present and rangle, Alaska: U.S. Geological Survey Open-File potential petroleum basins of Alaska, in Landwehr, Report, scale 1:250,000, 2 sheets. M.L., ed., Exploration and economics of the pe- Chapman, R.M., and Yeend, W.E., 1981, Geologic troleum industry: New ideas, new methods, new reconnaissance of the east half of Kantishna River developments: Dallas, Institute on Petroleum Ex- quadrangle and adjacent areas, in Albert, N.R.D., ploration and Economics, p. 511-554. and Hudson, Travis, eds., The United States Geo- Jachens, R.C., and Roberts, C.W., 1981, Documen- logical Survey in Alaska: Accomplishments during tation for a FORTRAN program, ‘isocomp,’ for 1979: U.S. Geological Survey Circular 823-B, p. computing isostatic residual gravity: U.S. Geological B30-B32. Survey Open-File Report 81-574, 26 p. Chapman, R.M., Yeend, W.E., Brosge, W.P., and Reiser, Jones, D.L., Silberling, N.J., Chapman, R.M., and Coney, H.N., 1975a, Preliminary geologic map of the P.J., 1984, New ages of radiolarian chert from Tanana and northeast part of the Kantishna River the Rampart district, east-central Alaska, in Coonrad,

14 W.L., and Elliott, R.L., eds., The United States Ridgway, K.D., Trop, J.M., and Sweet, A.R., 1994, Geological Survey in Alaska: Accomplishments during Depositional systems, age, and provenance of the 1981: U.S. Geological Survey Circular 868, p. Cantwell Formation, Cantwell basin, Alaska Range 39-43. [abs.]: Geological Society of America Abstracts with Jones, D.L., Silberling, N.J., and Coney, P.J., 1986, Programs, v. 26, no. 7, p. A-492. Collision tectonics in the Cordillera of western North Robinson, M.S., Smith, T.E., and Metz, P.A., 1990, America: examples from Alaska, in Coward, M.P. Bedrock geology of the Fairbanks mining district: and Ries, A.C., eds., Collision Tectonics: Geological Alaska Department of Natural Resources, Division Society Special Publication No. 19, p. 367-387. of Geological and Geophysical Surveys, Professional Jones, D.L., Silberling, N.J., Coney, P.J., and Plafker, Report 106, scale 1:63,360, 2 sheets. George, 1987, Lithotectonic terrane map of Alaska Silberling, N.J., and Jones, D.L., eds., 1984, Litho- (west of the 141st meridian): U.S. Geological Survey tectonic terrane maps of the North American Miscellaneous Field Studies Map MF-1874-A, scale Cordillera: U.S. Geological Survey Open-File Report 1:2,500,000, 1 sheet. 84-523, 104 pp., 4 sheets. Jones, D.L., Silberling, N.J., Gilbert, W., and Coney, Simpson, R.W., Jachens, R.C., Blakely, R.J., and Saltus, P.J., 1982, Character, distribution, and tectonic R.W., 1986, A new isostatic residual gravity map significance of accretionary terranes in the cen- of the conterminous United States with a discus- tral Alaska Range: Journal of Geophysical Research, sion of the significance of the isostatic residual 87(B5), May 10, 1982, p. 3,709-3,717. anomalies: Journal of Geophysical Research, V. ———1983, Interpretive bedrock geologic map of the 91, no. B8, p. 8,348-8,372. Mount McKinley region: U.S. Geological Survey Stanley, R.G., 1987a, Effects of weathering on pe- Open-File Report 83-11, scale 1:250,000, 2 sheets. troleum-source evaluation of coals from the Suntrana Kirschner, C.E., 1988, Map showing sedimentary basins Formation near Healy, Alaska, in Hamilton, T.D., of onshore and continental shelf areas, Alaska: U.S. and Galloway, J.P., eds., Geologic studies in Alaska Geological Survey Miscellaneous Investigations Map by the U.S. Geological Survey during 1986: U.S. I-1873, scale 1:5,000,000. Geological Survey Circular 998, p. 99-103. Loney, R.A., and Himmelberg, G.R., 1987, Ultramafic ———1987b, Thermal maturity and petroleum-source rocks of the Livengood terrane, in Galloway, J.P., potential of the Cantwell Formation (Paleocene), and Hamilton, T.D., eds., Geologic studies in Alaska Alaska Range, in Hamilton, T.D., and Galloway, by the U.S. Geological Survey during 1987: U.S. J.P., eds., Geologic studies in Alaska by the U.S. Geological Survey Circular 1016, p. 68-70. 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15 rangle, Alaska: U.S. Geological Survey Geologic International Geological Congress: American Geo- Quadrangle Map GQ-804, scale 1:63,360, 1 sheet. physical Union, Washington, D.C., p. 84-95. ———1970c, Geologic map of the Healy D-3 quad- Weber, F.R., Wheeler, K.L., Rinehart, C.D., Chapman, rangle, Alaska: U.S. Geological Survey Geologic R.M., and Blodgett, R.B., 1992, Geologic map of Quadrangle Map GQ-805, scale 1:63,360, 1 sheet. the Livengood quadrangle, Alaska: U.S. Geological ———1970d, Geologic map of the Healy D-4 quad- Survey Open-File Report 92-562, 20 p., scale rangle, Alaska: U.S. Geological Survey Geologic 1:250,000, 1 sheet. Quadrangle Map GQ-806, scale 1:63,360, 1 sheet. Wheeler, K.L., Forbes, R.B., Weber, F.R., and Rinehart, ———1987, The Cenozoic section at Suntrana, Alaska, C.D., 1987, Lithostratigraphy, petrology, and in Hill, M.L., ed., Geological Society of America, Cor- geochemistry of the Ordovician Fossil Creek vol- dilleran Section, Centennial Guide, v. 1, p. 445-450. canics, White Mountains, east-central Alaska, in Wahrhaftig, Clyde, Wolfe, J.A., Leopold, E.B., and Hamilton, T.D., and Galloway, J.P., eds., Geologic Lanphere, M.A., 1969, The coal-bearing group in studies in Alaska by the U.S. Geological Survey the Nenana coal field, Alaska: U.S. Geological during 1986: U.S. Geological Survey Circular 998, Survey Bulletin 1274-D, 30 p. p. 70-73. Weber, F.R., 1989, Geology between Fairbanks and Wolfe, J.A., and Wahrhaftig, Clyde, 1970, The Cantwell the Yukon River, in Alaskan Geological and Geo- Formation of the central Alaska Range: U.S. physical Transect, Field Trip Guidebook T104, 28th Geological Survey Bulletin 1294-A, p. A41-A55.

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