SHORT NOTES ON ALASKA GEOLOGY 1999 Edited by DeAnne S. Pinney and Paula K. Davis

Division of Geological & Geophysical Surveys Professional Report 119

Recent research on Alaska geology

Fairbanks, Alaska 2000

Front cover photo: lvlarine sedi111enta1y rocks of the N111:01i11 lvlountnin.~ sequence tblad strata in rhe foreground) in fault con/act with the Wnmge!lia composite le1rane in the N11t:o1i11 Mo11ntaim·. easran Alaska Range. While slrara in the midground i.s the Ni<in" Limes tune. Gray str'1to in the background ell the ridge crest is the Nikolai Greenstone. For scale. a person with a blue shirt can be seen on the ridgeline. View is 10 the north. {Photo by Jeffrey D. Manusrnk)

Back cover photo (top): Vie-w eastward along the weslfork q/Atig1111 River of prominent t111Licli11ol hinge in the upper Kanayut Conglomemte (loll'er Mississippian to Upper Devonian) within the Toyuk 1Jm1s1 :one. a major 1hrusl zone in the central B1·ooks Runge. See Chmil!fowski and otherr (this 1•olwne) . .. Dnplex s11·uc111re and Paleocene displacement of the Toyuk thrusl ::::011e near the Dn/10111-!ighway, north-central Brooks Range ... rPho10 by Reia i\!I. Chmielowski)

Back cover photo (bottom): Excavator and bul/do:er trench on lewis Ridge. Donlin Creek property. southwestern Alaska. Trench is approximate/)-' 1.300 feet long a11d pan of a 3. 7-mile 1re11chi11g program by Placer Dome faploration Inc. during the 1997 and 1998 field seasons. Light-colored rocks are igneous dikes and sills. ond darker rocks are Kuskokwim Croup shale and graJwacke. Nole the core drill rig in 1he backgrow1d to the right of center. (Phom by David J. Szumigala)

LA TE DEVONIAN (EARLY FRASNIAN) CONODONTS FROM DENALI NATIONAL PARK, ALASKA

Norman M. Savage, 1 Robert B. Blodgett,2 end Phil F. Brease3

INTRODUCTION

A brachiopod-bearing sample, collected in 1980 by Dr. Norman Silberling from dark gray. nodular argillaceous limestone beds in the upper part of an undated and unnamed shale unit in Denali National Park, was processed forconodonts by Savage but yielded only a few broken specimens of general Middle 10 Lale Devonian aspect. New samples were collected in I 994 by Csejrey (Csejtey and others, 1996; Dumoulin and others, l 998). and by Blodget1 and Brease from the sire (local ii)' 2 herein) and a nearby site (locality I herein) at the base of an overlying, unnamed massive limes.tone unit. These two localities. each yielding conodonts and brachiopods, are located on the north side or a promi­nent saddle in NE'/. NE'!. sec . 30, T.1 7 N .. R.12 W., Healy B-6 Quadrangle (fig. l ).

t..o<.:•' t<, ' •-. t liry :'

c

Al locality I. the overlying limestone unit is at lhe base of a prominen1, south-focing limesrone cliIT, about 18.3 m (60 ft) below the ridge crest. Conodonts from the upper limestone unit include P/(lyfordia a/T. P. prirnitiva

(Bischoffand Ziegler. 1957). Polygnathus cf. P robuslus Klapper and Lane, 1985. Polygnarhus ll'ebbi Stauffer, I 93l\, Ancyrode/la prislina Khalymbadzha and Chernyshcv:-i, 1970, Mesolaxis cf. M. falsiovolis Sandberg. Ziegler, and Bullynck, 1989, Jcriod11.t symmelricus Branson and Mehl. 1934. and lvleliiina sp. The interesting feature of the conodont fauna is the abundanct: of Playfordia aff P. primilivo, which is the mos1 common species present. The presence of this species. and Meso1axis cf. lvl. falsiovolis. indicates the (/'(.JJ1Sitm1s 10 p11nc101a Zones or Ziegler and Sandberg

.~I·•' ( I

A

ALASKA

.c " I

B

Figure 1. Localiry maps.for !lie Tok/a/ River cnnodont samples. (A) Localirm of I-leafy J :250.VO(). scale quadrnng!e in so111hce111ral Alaska. (BJ location of pan oj Healy B-6 I 5-minute quadrangle. (C) Locmion ofsiles I and 2 near Tokla1 Rive1:

1 Depanmcnl of Cieologi1:al Sdences, I lni vcrsily "f Orcgnn, Eugene. On:gon 'l7403. Email for Nonn Savag<:: nmsn vngc'fl't>rcgon.uorcgon.t"du

~D.::pa11mcnt o fZ.o<>lngy. Oregon St~ic Uni\'crsi1y. -c-.m·ulfo. Oreg'"' '>7>~ I. .lDcn~li Nmio11al Park . P.O. Box 9. Den;il i Park. ;\la»ka 'l97)~ ,

85

86 SHORT Nom ON A.IASKA GEOLOGY 1999 SAVAGE ANO OTHERS

( l 990). and an early Frasnian age. Brachiopods include HJ •pothyridina sp., VMia1rypa (Radia1rypa) sp .. Spinmrypa (ExotrvpaJ sp., and El2111heroko111ma sp . Rugose corals are also common, and include bo1h colonial forms (notably phillipsas1reids and undetermined fasciculaie types). as well as solitary rugosans. Conodonts from locality 2 were recovered from nodular, argillaceous limes tone beds in the uppemlOSl parl of the under!) ing thick unnamed shale uni!. These limestone beds represent a thin transitional in1erval with tln~ overlying unit. Cl'nl•donb from 1hese beds include those listed above from the upper unit. Brachiopc1ds from these same beds include Schi::ophorl(I sp. E/(!Utherokomma sp. and Ladogioid.:s pux.

The massive limes1one unit and underl) r1lg.shalc unit :ire widespread in the area and share strong li1hologic similarities with similar Frnsnian sec1ions recognized near th.,; haw of the Mysiic sequence of west-central Alt1sh1, notably in 1he Shellabarger Pass area. Talkectna C-6 Qu;1dran~k, and in the Lime Hills D-4 Quadrangle (Bloclgen and Gi lbert, 1992). These close lithologic and f:111nal ties suggl·~t \ hai the rocks described hi.:n: fom1 an eastward extension of the Farewell terrane of Decker and others ( 1994). The areal i.:xt.:nt of the Farewell tcrranc is sho\111 in Blodg.en ( 1998, lig. 2). showing the co111po11L'llt subrerranes oft.he Farewell tcrrane as well as the location of Shellah:irger Pass.

Thi: Devonian fossils reported here are of significann• in providing badly needed timelin.:s within the weakly metamorphosed sediments exp0<>ed :.ilong the north ~idl· of th~ central Alaska Range within Denali National Park. Very few Paleozoic age fossil localities were kno·wn in th is area previl'Usly. It is of further interest in terms ofbio1ic diversity, since all Devonian collect ions from chis part of the Park he fore the 1990s consisted of poorly preserved corals . In addi1ion. the fossils reported here provide important e\ idence for more correct determinat ion of the stratigraphic framework for this reg.ion . The Frasni~m age determination and as~ociated brachiopod fauna provide evidence for correlation of these beds with the Mystic sequence (or "subtcrrane"} exposed furthe r to the soutlrn.cst in the McGrath, Talkeetna, and Lime Hilb: qua<lrangles . Prior to this study, rocks from 1his parl of the Park had been <1ssig.ned to the Dillinger terrnne by Jones and others ( 1981) and later to 1he Nixon Fork 1errane by Mullen and Cscjtey ( 1986) and Csejley and others ( 1992). On the basis of our recently acquired foss il data and regional lield studies conducted in I 994, WI!

now 1hink till' i\Ssignment of Dillinger "terranc" is incorrect (it is present and underlies the Mystic strata reported here), and that the ass ignment of Nixon Fork 1errane affinities is also incorrect (no ~hallow-water carbonale platfonn equivalent strata of Ordovician-early Middle Devonian age are recognized in the region).

The Mystic subterrane was originally defined by Jones and 01hers ( 1981) as a separace 1ectono­s1ra1igraphic entity of ful I terrane rank. More recently, Decker and others ( 1994) recogniz~d that the Mystic. as well as the Nixon Fork and Dillinger terranes, were genetically related and all were reduced in rank to subterranes or a larger terrane, termed the Farewel I 1erra11c. Gilbert and Bundtzen ( l 984) considered the Dilli11gc1· and Mystic terranes. each or whose type sections were close to one another, to represent a single stra1igraphil· succession of Paleozoic lo Triassic age, prefcrrin~ tll apply the tenn "sequence" to each. They cnnsidered lhe underlying Dillinger sequence 10 be a lamhrian to Lower Devonian deep-water succession that is followed depositionally by the Mystic sequence, wh ich consists of laterally variable Devonian to Triassic ('?)shallow-water to nonmarine sedimentary rocks and inlrusive and extrusive mafic and ultramalic rocks. 111e close slralig.raphic relationship between the Dillinger and Mystic ~c~1ut:nces (or sublerranes ) was supported by stral igraphic studies by Blodgett and Gilhert ( 1992) to tht: ,;outhwest in 1he lime Hills quadrangle.

SYSTEMATIC PALEONTOLOGY

Genus ANCYRODELLA Ulrich and Bassler, 1926 A1VCYRODELLA PRJSTINA Khalymbadzha and

Chernyshcva, 1970 Figure 2.7

Discussion. The sing,le specimen recovered has an asymmetrical platform outline and few but large nodes.

1\1t:11erial. I Pa element from locality I.

Genus iv/EHL/NA Youngquisc, 1945 MEHL/NA sp.

Figure 2.9 D1scu:.~·ion . These Pa specimens have the lateral profile

of O::Drkodi11a but lack the eharacteris1ic expanded platform margins and arc assigned 10 /vlehlina.

Ma1erial. 2 Pa elements from locality 2.

Genus POLYCNATl-IUS Hinde, 1879 POLYGNATHUS cf. P. ROBUSTUS Klapper and

Lane, 1985 Figures 2.5- 2.6

Disrnssw11. This specimen differs from 1ypical Pa elements of P. mb11st11s in having a convex inner plat form margin and smaller anterior dcnlicles on the l'ree blade. I I bears some resemblance to P ljasche11koi Kuzmin, 1995, but has a more convex inner platform margin than that species also.

Ma1erial. l Pa element from locality I.

LATE DEVONIAN (EARLY FAASN!AN) CONOOONTS FROM DENAU NATIONAi.. PARK, ALASKA 87

Figure 2. ( 1--4). Playfordia aff. P. primiliva (Bischoff and Zii:gle1; 195 7). (I) Upper view of USNM 481705 from locality J. (2) Upper view of USNM 481706/rom /ocafiry 2. (3) Upper l'iew of USNM 481707 from locality 2. (4) Lateral view of USN1\ll 48/ 708from locnlily I. ulf x 70. (5- 6) Polyg11athus off r. robustus Klapper and Lane. 1985. Upper and obliq11e-laterul views of Pa element USNM 471709 jivm lncaliry l, x 70. (7) Ancyrodella pristina Khalymbadzha and Chernysheva. 1970. Upper view of Pa elemem USNM 4 7 J 7 JO from locolity 1. x 70. (8) Mesota.xis ef. M. falsiovalis Sandberg. Ziegler and Bul(vnck. 1989. Upper vie11· of broken Pa element USN/vi 4 717 J /from locality 2. x 70. (9) Mehlina sp. /a1eral 1·ie11· of Pa element USNM 4717 I 2/rom /ocaliry 2. x 70. (JD­I I) lcriodus symmctricus Branson and iv/eh!. 1934. Upper views of Pa elements USNM 4 71 71 J-4 i / 714. both

fro111 /ocality I. x 70. (12-1 J) Possibly j11l'eni/es oj Jcriodus symmclricus Branson and Mehl. J 934. or mature specimens of!. praealtematus Scmdberg, Ziegler. and Dreesen. 1992. bo1h from locolity l. x 70. ( 14) Be lode Ila sp. USNM 4717 J 7 from locali1y 1. x 70

88 SHORT NOTES ON Al.AsKA GEOLOGY 199 9 SAVAGE AND OTHERS

Genus JCRJODUS Bran,;pn and Mehl, 1938 ICRIODUS SYMMt.TRICLS Branson and Mehl, 1934

Figures 2. l (}-2.13 Discm.sio11. These Denali specimens are more slender

than characteristic specimens of/. ~ ubf c:r11111111s Youngquist. 1945. and also differ in ha' ing :1 less expanded pos1crior plalform. They are unlike cypical specirnens of I. sv111111e1ric11s in h<1ving la1eral denticl~~ 1har almost alLt:rnate laterally with the median drn1icles, allhough Dr. Charles Sandberg (written cominun .. April 1999). believes that !he specimc·ns in F igs 2.1 0-11 are unquestionably /. gym11u:tric11s, and those in F igs .2.12-13 look like

juveniles of/. sym111etric11s or matur~ SPL'L·ime11:-; of/. praeo/tema111s Sandberg. Ziegler and Dreesen. I 992 .

. Mmerial. 8 Pa elements: 5 from localily I. and 3 from locality 2.

Genus ivf£SOT1/X/S Klap1'er and Philip, 1972 iv/ESOTAXJS cf. ,\/. l·.~l LS!O I AUS Sandberg. Ziegler

and Bullym:k, 1989

Figure 2.8 Disc11ssiv11. The only specimen is hn •ken but enough is

present to suggest the speci,·s }vfnutari/;.falsiowi/1.~. Ma1erial. I Pa element from locality~-

Genus PLA l'FORDIA Gk11i~ler and Klapper, 1966 PLAYFORD/A aff. P PR/.\JJT/VA (Bischoff and

Ziegler, 1957) Figures 2 .1-2.4

Discussion. The specimens of Noy/ordw :1ff P. primiflva

dif'tl.-r from typical member~ oflhe species in havin~ less projecting dc::micles at the posterior end. a~ poin1ed oul by Dr. Charles Sandberg. (written commun .. April I 999). The presence of this species. even in ils somewhat diffc:rc:nl form. helps considerably in detennining the age of the collections

bei.:ause it is known elsewhere only from the Late falsiova/is to 1ransi1am Lone s of Ziegler and Sandberg ( 1990). Dr. Sandberg has commented (wrinen C<'111mun ... \pril 1999) 1ha1 it has never been reported from thefalsiovalis Zones. However. lhe interpretation hy the senior author of ongoing work in the Timan Basin, Russia, i~ that P/ay/vrJia

primitfru •'l'.:urs there in the Lall' fa/s1oi:o/is Zone about 2 m (6.5 ft) below the first ui.;currence of Palmatolc:pis 1mnsi1ans.

Mo1erial. 23 Pa elemen1s; 9 from locality I. and 14 from locality 2.

Genus BELODFJIA l:.thi ngton, l 959 81-.UJUHLA sp.

Fig_ure 2.14 Discussion. The single spci:im..-n appear,:; to belong to a

Be!ude/lo apparatus. Devonian species of Be/ode/In

usually include apparalus elements that bear

numerous line demicles but our small collections do not include any of these elemenls .

Mmerial. 1 clcmcnl from locality } .

ACKNOWLEDGMENTS

We thank Barbara Savage for processing the samples and picking 1he conodonl residues. We also are grateful to Norman Silberling and Wyan G. Gilbert for bringing the 1980 discovery to our attention. Thanks are also 1:\tcnded to Paul Atkinson for his able assistance in the fi~ld. Charles Sandberg and Michael Orchard reviewed

the submi11ed manuscript ;:md provided valuable advice.

REFERENCES

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fossils indicate•) Siberian origin for lhc Farewell 1errane. i11 Clough, J.G. and Larson, Frank, eds.,

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LA.re D£VONIAN (EARLY FRASNlAN) coNoooNTS FROM DENALI NATIONAi. PARK, Al.AsKA 89

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