The and () Systems in the - Alaska



Prepared in cooperation with the State of Alaska Depmhnent of Natural Resources, Diuinbn of Geologkal and Geophysical Smys

Historical review and summary of areal, stratigaphicJ structural, and ~onomicgeology of Mtistisippian and Pennsyluanian rocks in Ahka CONTENTS

Page Abstract ...... Introduction ...... Acknowldegrnents ...... History ...... Geologic setting ...... Lithostratigraphy ...... Environments of deposition ------Bi~stratigraph~...... Igneous and metamorphic rocks ...... Economic products ------References cited ......


Pape Pape FIGURE1. Map showing distribution of Carboniferous 4. Chart showing biostratigraphic zonations in rocks in Alaska ...... DD2 the Carboniferous of Alaska ------12 2. Regional stratigraphic correlation chart of 5. Isopach map of Lisburne Group in the sub- the Lisburne Group, northern Alaska --- 6 surface of the eastern Arctic Slope, 3. Index map of Arctic Alaska and adjacent Alaska ...... 13 showing locations of outcrops of 6. Reservoir data summary for the Lisburne Carboniferous rocks in Alaska and loca- Group in the subsurface of the eastern tions of sections including sections that Arctic Slope, Alaska ------14 contain the Lisburne Group ------10 THE MISSISSIPPIAN AND PENNSYLVANIAN (CARBONIFEROUS) SYSTEMS IN THE UNITED STATESALASKA

ABSTRACT low-water marine environments. Similar The Carboniferous rocks of Alaska are more widely dis- sections are also present at the western tip of the tributed than those of any other . The Lis- Seward Peninsula and on St. Lawrence Island in the burne Group of northern Alaska contains a great variety of Bering Sea. The Carboniferous of east-central carbonate facies, predominantly shallow-water deposits, but including some outer shelf and slope dewits. In east-central Alaska begins with deep-water dark chent and Alaska, the deep-water Ford Lake Shale is succeeded by the of the Ford Lake Shale ; the Ford Lake is overlain by Calico , which was probably deposited in a slope deposits of and shale, the Calico slope environment. Scattered throughout central and south- Bluff Formation, part of which is as young as Early western Alaska are remnants of deepwater laminated Pennsylvanian. Although the Carboniferous is and argillite deposits containing a few carbonate members that may be of shelf-gin or upper slope origin. In south- sparse1y represented in central, southern, and south- eastern Alaska, Carboniferous deposition began with deep- western Alaska, deep-water clasltic and volcaniclastic water chert and volcaniclastic rocks, but most of the sequence rocks are present in the Alaska Range, and bedded reflects upward-shoaling shallow-water carbonate deposition, chert and argillite are present in the Medfra quad- perhaps in an island archipelago. Correlations among the various sequences in Alaska and ad- rangle. Recently discovered terrestrial -bearing jacent amas are based mainly on the foraminiferal zonation conglomerates of Pennsylvanian age crop out on Mt. of B. L. Mamet and on other , among which the cephalo- Dall in the Talkeetna quadrangle, southwest of Mt. pods are most significant. , , , McKinley. This is the first positive evidence of non- and mollusks are regionally important guides in certain parts marine late Carboniferous deposits in Alaska. In of the section, and fusulinids are quite useful in the upper Carboryiferous deposits. , although minor elements southeastern Alaska, an essentially carbonate st+ of the total biota, are important in the Lower Mississippian quence of Mississippian and Lower Pennsylvanian clastic sequences and have provided a spectacular break- rocks is represented by the Iyoukeen Formation at through in the recognition of terrestrial Upper Pennsylvanian Freshwater Bay and by the Peratrovich and Klawak strata in the western Alaska Range. The most important economic factor in the Carboniferous Formations and the Ladrones Limestone in the deposits of the State is the ail and gas potential of the Lis- Prince of Island area. In addition, the Sagi- burne Group in the subsurface of northern Alaska The naw Bay Formation, which contains a lower volcanic abundance of carbonate rocks for potential industrial uses is member, a black chert member, a chert and lime- an untapped resource for possible future development. stone member, and an upper silty limestone member, is present in the northern part of Kuiu Island and INTRODUCTION on the Keku Islets. The Saginaw Bay Formation Rocks of Carboniferous age are w.idely distributed appears to include correIatives of the Peratrovich, in Alaska (fig. I), representing more outcrop area Ladrones, and Klawak. than those of any other Paleozoic system. Carbonate Most of the exposures in northern Alaska are rocks of the Lisburne Group compose most of the north of the line and, consequently, are mag- thrust sheets and folded structures in the central nificent. Except where covered by deposits of moun- and northern Brooks Range. This sequence in north- tain and recent talus cones and colluvium, ern Alaska was deposited by the sea onlapping older Carboniferous strata are tortally exposed, and oppor- terranes, the first rocks in the sequence are shore tunities for unravelling the stratigraphy, structure, and nearshore clastic rocks. The succeeding Missis- and geologic history of the region are unexcelled. sippian and Lower Pennsylvanian carbonate strata Much of the lowland region of central and southern were deposited in a complex of predominantly shal- Alaska is tree covered, and exposures are limited to DD2 THE MISSISSIPPIAN AND PENNSYLVANIAN SYSTEMS IN THE UNITED STATES

FIGURE1.-Map showing distribution of Carboniferous rocks (shaded areas) in Alaska. Modified from Armstrong (1975).

river bluffs and isolated hillltop outcro~s.Some Car- I ACKNOWLEDGMENTS boniferous strata crop out above the timberline in I am indebted to many people who by their the Alaska Range, and exPosures in southeastern tion, guidance, assistance, and forbearance have Alaska are superb along the island coastlines where made this paper possible. M~ firstwork on the ~i~- the great tidal range provides hectares of fine out- burne Group in 1949 was with A. L. Bowrsher, who crop from low tide to midtide. furnished a never-to-be-for~otten- introduction to The stratigraphic nomenclature used in this paper the subtleties of Carboniferous strata and fossils. has not been reviewed by the Geologic Names Com- Through the , I have had the good fortune to mittee of the U.S. Geological Survey. The nomen- be associated in Alaskan field projects with W. P. clature used here conforms with the current usage BrosggC, H. N. Reiser, R. L. Detterman, W. W. Pat- of the State of Alaska Department of Natural Re- ton, Jr., I. L. Tailleur, M. Churkin, Jr., E. G. Sable, sources, Division of Geological and Geophysical M. D. Mangus, D. H. Richter, R. M. Chapman, B. L. Surveys. Reed, C. L. Sainsbury, R. A. Loney, W. H. Condon, ALASKA DD3

M. C. Lachenbruch, A. H. Lachenbruch, and many cerning the distribution of Carboniferous rocks in others. All these men, through stimulating discus- Alaska. The Lisburne formation was named by F. C. sions about the geologic interpretation of innumera- Schrader (1902), who provisionally assigned it to ble puzzling field relationships, provided the con- the . By 1906, however, G. H. Girty and tinuing incentive to pursue my studies of the David White (in Collier, 1906) had correctly as- Paleozoic of Alaska. signed the Lisburne fossils to the early G. Arthur Cooper, Carl 0. Dunbar, James Skle Carboniferous. Williams, Helen M. Duncan, and Edwin M. Kirk, Carboniferous rocks were found during the geo- through their dedicated pursuit of taxonomic and logical reconnaissance conducted in conjunction with biostratigraphic problems, set a high standard which the w~orkof the International Boundary Survey in has guided my own paleont~ologicwork. 1911 and 1912. The part of the boundary between I am especially indebted to A. K. Armstrong, the Yukon and Porcupine Rivers was studied by the Bernard L. Mamet, Mackenzie Gordon, Jr., Ray- Geological Survey of Canada (Cairnes, 1914). The mond C. Douglass, I. G. Sohn, S. H. Mamay, and part from the Porcupine River no~thwardto the E. L. Yochelson for their expertise, freely shared, Arctic Coast was examined by the U.S. Geological on the groups of fossils that are their specialties. Survey (Maddren, 1912). Cairnes recognized three In alddition, the work of K. J. and C. F. Jor- major rock units-a shale group, a limestone-chert dan has been relied on, in large part, for the analy- group, and the Nation River Formation. Subsequent sis of the oil and gas potential of the Lisburne Group work has shown that the Nation River is Upper in northern Alaska. Devonian and that much of ;the shale group is lower Finally, I am grateful to a group of supervisors Paleozoic, but the limestone-chert group is pmbably who had the vision and faith in our work bo support what is now recognized as the Calico Bluff Forma- projects, at times rather esoteric, which permitted tion. G. H. Girty of the U.S. Geological Survey all of us to explore together the fascinating Car- identified many fossil collections and showed that boniferous gedogy of Alaska. These farsighted these rocks are, indeed, of Carbaoniferous age, al- chiefs include George Gryc, Preston E. Cloud, Jr., though many subsequent refinements in the ages and Wilmot H. Bradley, George L. Gates, Ralph L. Mil- correlations have been made. North of the Porcupine ler, Charles L. Anderson, and Thomas G. Ovenshine. River, Maddren (1912) found large areas of Car- boniferous limestone when he crossed the Brooks HISTORY Range. He reponted that these rocks stretch for nearly 64 km north of Ammerman Mountain and The first report of Carboniferous rocks from that they conttain Carboniferous fossils. Unfortu- Alaska is probably that of Capt. F. W. Beechey nately, Maddren's maps and complete report were (1831) who, along with other early coastal ex- never published, but much of the information has plorers, was awed by the spectacular cliff exposures been incorporated into later U.S. Geological Survey near Cape Lisburne. The first mention of Carbonif- maps and papers. erous fossils is by W. Buckland (1839, p. 171) who A flurry of activity in the 1920's rela~tedto the reported that fossils collected from Cape Lisburne exploration of Naval Petroleum Reserve (NPR) No. by the Beechey party are indistinguishable from 4 greatly increased the understanding of the geologic those of the Derbyshire Limestone and listed "pro- history of northern Alaska. Specific details of Car- ducts Martini, other p~oductae,lithostrotion, flustrae boniferous and an excellent summary of all and ." In the latkr half of the 19th century, earlier exploration were given by Smith and Mertie several other writers referred to the occurrence of (1930). During the same decade, detailed explora- Carboniferous fossils in Alaska, most of them rely- tion in southeastern Alaska resulted in the first re- ing on Buckland's earlier statement. By the end of gional geologic synthesis of the panhandle by - the century, scattered information on Paleonoic fos- dington and Chapin (1929). The Yukon-Tanana sils, including those of the Carboniferous, was sum- region, a third major area of Carboniferous mks, marized by Charles Schuchert, W. H. Dall, and F. H. was examined primarily by J. B. Mertie, Jr., in the Knowlton (in Dall, 1896, p. 864-865,876-906) in the 1920's and early 1930's. Mertie's oonclusions regard- 17th Annual Report of the U.S. Geological Survey. ing the stratigraphy, structure, and general geology During the first decade of this century, geologic of this vast region were presented in two major exploratilon related to the search for gdd and other papers (1930 and 1937). The general state of geo- mineral deposits added substantial knowledge con- logic knowledge of Alaska before World War I1 was DD4 THE MISSISSIPPIAN AND PENNSYLVANIAN SYSTEMS IN THE UNITED STATES

summarized by P. S. Smith (1939), who discussed A recent summary of the Carboniferous of most the Carboniferous deposits in each region and pre- I of Alaska, except the southeastern panhandle, was sented a very generalized clorrelation chart. prepared by Brosg6 and Dutro (1973). Biostrati- Until World War 11, practically all the paleonto- graphic studies emphasizing the calcareous micro- logic and biostratigraphic information on the Car- fossils have been an important part of all recent boniferous of Alaska was the result of the work of work in the Carbtoniferous. Microfaunal zonations G. H. Girty, who provided the extensive faunal lists, established by B. L. Mamet are used for general cor- age designations, and correlations that appeared in relations in Alaska as well as in most other parts of the reports of the U.S. Geological Survey during the (fig. 2). Papers documenting this first four decades of the century. zonation include those by Armstrong, Mamet, and Work in NPR No. 4 was renewed during the latter Dutro (1970, 1971) , Mamet and Armstrong (1972), years of World War 11. From 1944 to 1953, more and Armstrong and Mamet (1975, 1977). than 300 man-months of geologic fieldwork greatly increased the knowledge of the geology of Carbonif- GEOLOGIC SETTING erous deposits in about 54,390 kmz in northern Although in several areas no break in deposition Alaska and culminated in a of regional papers is apparent between Lower Mississippian rocks and and maps (Reed, 1958). uppermost Devonian strata, at most places the Car- Modern stratigraphic and paleontologic studies boniferous rocks lie unconformably on older rocks began with the work related to the exploration of (Churkin, 1973). In parts of the western and central NPR No. 4. New formational units were named, and Brooks Range, no structural break separates rocks a preliminary biostratigraphic zonation was estab- as old as Mamet's Zone 6 from the lished (Bowsher and Dutro, 1957). Several groups underlying marine Devonian beds of age. of fossils were described in some detail (Gordon, In the central Brooks Range, where the highest De- 1957 ; Yochelson and Dutro, 1960; Sohn, 1971). vonian unit is nonmarine, a Mississippian lit- In the early 1960's, major oil companies instituted toral lies disconformably on the upper massive regional studies and examined the possibil- Kanayut clastic sequence. In the eastern Brooks ity that the widespread Carboniferous carbonate Range, Mississippian strata are regionally uncon- rocks in northern Alaska would become oil and gas formable on rocks as old as . Broad producers. Detailed regional, stratigraphic, facies, anticlinoria characterize the eastern Brooks Range petrographic, and depositional analyses were made. and extend as far west as the Doonerak anticlino- A. K. Armstrong, now with the U.S. Geological Sur- rium in the northeastern Wiseman quadrangle, vey, contributed significant papers on bio- where the Carboniferous rests with angular uncon- stratigraphy, carbonate petrography, and environ- formity ton rocks as old as (Grybeck and mental reconstructions of the Lisburne rocks (1970a, others, 1977). In the extreme northeastern part of b, c ; 1972a, b ; 1975). the State, Mississippian beds were deposited across Major advances in understanding the Carbonifer- a varied older terrane that ranges in age from Pre- ous of southeastern Alaska resulted from detailed through early Middle Devonian (Reiser, mapping and stratigraphic work of U.S. Geological 1970). Survey parties during the past 20 years. The Perat- In east-central Alaska, where all the Upper Devo- rovich and Klawak Formations and the Ladrones nian and Carboniferous strata were deposited in rel- Limestone on Prince of Wales Island were described atively deep water, no depositional break is apparent by Eberlein and Churkin (1970) ; and the Iyoukeen at the boundary. In sloutheastern Alaska, the Missis- Formation of Freshwater Bay was named by Loney, sippian marine shale and carbonate rocks are dis- Condon and Dutro (1963). Fusulinids from the Lad- conformable on Upper Devonian marine volcanic rones and Klawak indicate that they are early Middle sequences, but the precise amount of time that is not Pennsylvanian (Douglass, 1971), Mississippian represented by mks is unknown. corals and of the Peratrovich were The geology of pre-Carboniferous rocks is bast described by Armstrong (1970~).Muffler (1967) shown in northern Alaska where Preambrian described the Saginaw Bay Formation in the Keku through lower Middle Devonian strata show the Islets and nearby northern Kuiu Island ; the Saginaw effects of at least three orogenic episodes. The older Bay Formation contains fossils of Mississippian and Precambrian is a sequence of quartz-mica schist Pennsylvanian ages. and relaM metamorphic rocks that is succeeded by ALASKA DD5 weakly metamorphosed marine deposits of late is a convenient expedient because lof the onlaming Precambrian, Cambrian, and Ordovician age. Middle nature of the depssi~tionfrom the Late Devonian into Devonian clastic rocks lie with angular unconform- the Middle Mississippian. ity on the Ordovician in the southwestern part of the In east-central Alaska, the Upper Devonian and Demarcation Point quadrangle. The onlapping Car- Lower Mississippian Ford Lake Shale apparently boniferous deposits cover all older structures. Gra- grades upward into the Calico Bluff Formation of nitic intrusive bodies in the Mt. Michelson-Jago Late Mississippian and Early Pennsylvanian age. River area are of two ages, 430 m.y. (million years) Throughout a broad belt in central and muthwest- and 360 m.y., and volcanic rocks of similar ages have ern Alaska, fragments of a deepwater argillite- been dated from the core of the Ikmnerak anticlino- chert-volcanic rock terrane have recently yielded rium (430 m.y. and 370 m.y.-380 m.y.). Equivalents radiolarians and of Carboniferous age. In of both the Taconic and Acadian mountain-building the past, some of these ou;tcrcups have been mapped episodes of eastern North America clearly are a part as Circle Volcanics, Rampart Group, or Livmgood of the early history of northern Alaska. Chert. Although the type Livengd Chert has sub- In most regions, Carbonifemus rocks are overlain sequently been shown to be of Ordovician and, unconformably by or younger sequences. perhaps,' age, some exposures in the Medfra, An exception is the east-central Alaska Range where Ruby, and Kantishna quadrangles have yielded Car- volcaniclastic rocks of the Pennsylvanian Slana Spur boniferous fossils (Patton and others, 1977). Formation grade upward into limestone and sandy volcaniclastic limestone of the Wolfcampian Eagle In the western Alaska Range (Talkeetna quad- Creek Formation. rangle), pods of limestone in deepwater graywacke- Carboniferous and early strata were sub- argillite sequences have yielded both Chesterian and sequently folded and faulked beginning in Late Atokan Foraminifera (Reed and others, 1978). In time. In northern Alaska, deformation is the east-central Alaska Range, the Rainbow Moun- most intense in the core of the Brooks Range where tain sequence is known to be of Middle or Late Penn- long-distance thrust faulting and imbricate thrust sylvanian age (Rowett, 1969). Further to the east, patterns are ubiquitous. Further north, as seen in Atokan and younger volcaniclastic strata containing the no*eastern part of the range, tectonic style thin limestone beds are included in the Slana Spur tends to more open folds and high-angle reverse Formation. This formation is underlain by the faulting. Broadly folded strata at the Arctic Tetelna Volcanics, a thick pile of marine flows and Coast near Barter Island indicate that tectonism associated volcanic rocks that may be of Early Penn- continued until relatively recent times. sylvanian or Mississippian age (Richter and Dutro, 1975 ; Richter, 1976). LITHOSTRATIGRAPHY Although Carboniferous rocks are found in only a few places in southeastern Alaska, they are very Most of the major stratigraphic units in the fossiliferous and are predominantly shallow-water Alaskan Carboniferous rocks have been examined in . The Peratrovich Formation, which is at least a broad reconnaissance way, and most units more than 300 m thick, includes relatively deep examined have been given formal names. water slope deposits of shale, chert, and volcanic In northern Alaska, the Lisburne Group is com- rocks at its base and grades upward through shelf posed of predominantly carbonate rocks of Mississip- to shoal-water carbonates near its top pian and Early Pennsylvanian age. Various forma- (Armstrong, 1970c). The Peratrovich is dliscon- tion and informal member names are applied to formably overlain by two formations, both proba+bly major mapped units, most of which reflect regional of Early or early Middle Pennsylvanian age. The facies variations (Bowsher and Dutro, 1957; Sable Klawak Formation is composed of 150-300 m of and Dutro, 1961). Figure 2 shows the correlation of calcareous sandstone and siltstone and minor beds of the Lisburne Group in sections whose locations are limestone and chert-pebble conglomerate. The Lad- shown on figure 3. rones Limestone, on the other hand, is nearly pure Lower Mississippian clastic rocks, including the massive-bedded lime mudstone containing some Kayak Shale, Kekiktuk Conglomerate, and Itkilya- dolomitic beds and is as much as 300 m thick. No riak Formation (Mull and Mangus, 1972), have been great time gap existed between depmition of the mapped on small- regional maps, together with Peratrovich and deposition of the overlying Pennsyl- Devonian clastic units, as the Endicott Group. This vanian strata as all Mamet's Foraminifera Zones DD6 THE MISSISSIPPIAN AND PENNSYLVANIAN SYSTEMS IN THE UNITED STATES

h a2 Shainin Lake Central Brooks Range

Dolomite member

FIGURE2.-Regional stratigraphic correlation chart of the Lisburne Group, northern Alaska and adjacent Canada. I ;;' ltkillik Lake * Wachsmuth Llmestone Alapah L~mestone r 2 5 rr rrY) 60C-1 to 72 I 2 Echooka River 8, Alapah Limestone Wahoo Limestone I 1 I 60E-601 to 690 I

lkiakpuk Creek Alapah Llmestona Wahoo Limestone 68A- 1

Western Sadlerochit Alapah Limestone Wahoo Limestone Mountains 69A- 1

D Alapah Limestone Wahoo L~mestone Sadlerochit Mountains 1 68A-3 Y5 a Alapah Limestone Wahoo L~mestone Sunset Pass * B 68A-4A. 40 D ", I cn5 Wahoo R Alapah L~mestone Old Man Creek 1 :;z-1 69A-4 + Egaksrak River i68A-5

Alapah Limestone West Trout Lake CANADA I ags 5a.g Alapah Limestone Trout Lake (0 3 a-.O_ CANADA 1 I z$ Alapah Limestone 3 2.8 Joe Mountain 8 5q CANADA

I I 1 WEST- VISEAN PHALIAN I DD8 THE MISSISSIPPIAN AND PENNSYLVANIAN SYSTEMS IN THE UNITED STATES are present, including Zone 19, which is the highest and the Meramecian-Osagean boundary is approxi- Mississippian zone in the Mamet classification. mately at the boundary between Zones 10 and 9. Beds of Zone 6 and pre-7 ages are equivalent to the ENVIRONMENTS OF DEPOSITION Kinderhookian, but the Kinderhookian-Osagean boundary has nlot been precisely set. The Carboniferous of northern Alaska was a time The first generalized sequence of megafossil zones of northward and eastward onlap across an older was discussed by Bowsher and Dutro (1957, p. 5-6) complex geological terrane. Initial deposits are now and was later slightly modified by Yochelson and littoral sandstone and shallow-water shale and shaly Dutro (1960, p. 114-115). These assemblage zones carbonate rock. Although many fluotuations are rep- are most useful for identifying informal subdivisions resented in the thick carbonate sequence, the general of the Wachsmuth and Alapah Limestones in the picture is one of regional shallow-water deposition central Brooks Range. throughout the Mississippian. In Meramecian time, from the Carboniferous of Alaska platform carbonates graded southward into deeper were described by Gordon (1957), who placed the water dark limestone and chert in some areas. In several occurrences of and in the northeast, nearly continuous deposition across the general zonal scheme that he had devised for the Mississippian-Pennsylvanian boundary extended North America. Correlatiaons with the worldwide the regionally shallowing pattern into the early zones were also shown. Middle Pennsylvanian rocks of Atokan age ( Gastropods were described by Yochelson and and Armstrong, 1975). Dutro (1960), and their relakimship to the mega- Throughout most of the rest of the State, the Mis- faunal zonation was indicated. The systematic de- sissippian deposits were laid down on the outer shelf scriptions of corals that have been published during or upper slope. In a few places, limestones probably the last decade by Armstrong (1970~;1972a, b) of shelf-edge origin contain shallow-water fossils were related by that author (1975) to the biostrati- that can be correlated with shallow-shelf deposits graphic scheme for the Lisburne Group, and a coral elsewhere. zonation was established. New ostracodes were de- Several of the deeper water Carboniferous de- scribed by Sohn (1971), and, although they appear posits have been interpreted recently as parts of an to be of limited biostratigraphic use, they provide extensive ophiolite terrane in the central and south- valuable paleontologic d~cumen~tationfor the Missis- western parts of the State (Patton and others, sippian fossil assemblages in Alaska. 1977). Although the mafic belts are thought to have Few Pennsylvanian megafossils have been de- been emplaced in the Jurassic, associated laminated scribed, but calcareous Foraminifera were described and volcaniclastic rocks have yielded Missis- by Armstrong and Mamet (1977), and Pennsylva- sippian, Pennsylvanian, and Permian fossils in at nian fusulinids of southeastern Alaska were de- least five places. scribed by Douglass (1971). The upward-shoaling sequence in southeastern Mississippian biostratigraphic zonations and oc- Alaska, because of its regional setting and local dis- currences of the several groups that tribution, may well represent carbonate deposition have been studied in more detail are shown on fig- in a volcanic archipelago (Churkin and Eberlein, ure 4. As a result of discussion with Mackenzie 1977). Gordon, Jr., and A. K. Armstrong (oral communs., 1978), positions of some of the and coral BIOSTRATIGRAPHY zones are adjusted slightly from those originally All oorrelations of the Carboniferous of Alaska published. are integrated by using the scheme of foraminifera1 Fossil plants are not abundant in the Carbonifer- zones proposed by B. L. Mamet (Mamet and Skipp, ous of Alaska, and no beds of any significance 1970; Sando and others, 1969). In this numbered are known. Nevertheless, plant fragments are pres- sequence of zones, 6 through 9 are Tournaisian, 10 ent in the dark near the base of the Mississip- through 16 are VisCan, 17 through 20 are Namurian, pian sequence throughout the Brooks Range. Many and 21 is early . The Mississippian- of these collections have been studied by S. H. Pennsylvanian boundary is about at the boundary Mamay during the past two decades. A combined list between Zones 19 and 20. In terms of midwntinent of this Mississippian floral assemblage includes stratigraphy, the Chesterian-Meramecian boundary Lepidodendropsis sp., sp., 'cf. S. lies at about the boundary between Zones 16,,, and 15, ficoides Sternberg, cf. L. veltheimii ALASKA DD9

Sternberg, Lepidophyllum sp., Lepidostrobus sp., tion are of Atokan age, the Tetelna must be Early Rhodea vespertina Read, and Triphyllopteris sp. Ac- Pennsylvanian or older. cording to Mamay (written commun., 1970), this In southeastern Alaska, both intrusive igneous assemblage represents Floral Zone 2 of Read and rocks and volcanic rocks are known. In the Kuiu- Mamay (1964). Kupreanof Islands area, Muffler (1967) reported Plants were collected years ago from carbonaceous basaltic to andesitic pyroclastic rocks and pillow shale in the exposures along the sea coast south of lavas, apparently of Early Mississippian age, in the Cape Lisburne (David White, in Collier, 1906, p. lower part of the Saginaw Bay Formation. On 22). In a review of these floras, Mamay (written Prince of Wales Island, granitic rocks about 280 commun., 1964) identified several forms among new m.y. old intrude the Klawak Formation of Early and collectio~that permitted him to recognize both Middle Pennsylvanian age (Eberlein and Churkin, Zones 2 and 3 of Read and Mamay (1964). The 1970). In the Nabesna quadrangle, the Ahtel pluton oldest marine fossils from beds lying above the is also of latest Pennsylvanian age. Richter (1976) plant-bearing strata are now known to be assignable reported its age to be about 280 m.y. With the ex- to Mamet's Microfaunal Assemblage Zone 13 (mid- ception of these very late Pennsylvanian intrusive dle Meramecian) ; thus, the Early Mississippian age rocks, no plutonic rocks of Carboniferous age are traditionally assigned to Floral Zones 1 and 2 of known in Alaska. Read and Mamay (1964) seems to be justified, and Metamorphic rocks of Carboniferous age are very Floral Zone 3 must begin as early as Meramecian. poorly known; the only possible candidate is the Until very recently, no known fossils of Pennsyl- Totatlanika Schist ~f the central Brooks Range. vanian plants had been reported from Alaska or, Wahrhaftig (1968) reported that fossils of probable for that matter, from any part of the western Cor- Mississippian age are found in this terrane which dillera north of Washington. In 1976, however, occupies a northeast-trending belt in which Permian Bruce Reed of the U.S. Geological Survey collected rocks lie unconformably on early Paleozoic or older an assemblage of plants that S. H. Mamay (written rocks. Significantly, this belt also includes the commun., 1977) reported to be "Middle Pennsylva- only known nonmarine Carboniferous plant-bearing nian, probably no lower than Alleghenian * * * pos- strata in the State. sibly Floral Zone 10 of Read and Mamay, 1964." The assemblage includes sp., ?Calamites sp., ECONOMIC PRODUCTS scheuchzeri Hoffman, cf. P. arborescens Schlotheim, and Pecopteris un:ta Brong- The major commodities in the Carboniferous of niart. These plants come from the upper half of the Alaska are oil and gas. The carbonate rocks of the Mt. Dall Conglomerate in the Talkeetna C-5 quad- Lisburne Gmup in the subsurface of northern rangle, about 5.23 km N. 76"E. from Mt. Dall (Reed Alaska provide one of the main reservoir zones for and others, 1978). storage of hydrocarbons. In the Prudhoe Bay field, porosity zones in the upper Lisburne are primary targets for drilling. Facies trends indicate that IGNEOUS AND METAMORPHIC ROCKS Chesterian (upper Alapah Formation) strata con- Igneous and metamorphic rocks of Carboniferous tain good to excellent dolomite porosities in a broad age are found in only a few places in Alaska. In band that extends generally west from the Prudhoe northern Alaska, mafic dikes and sills are found area to the northwestern Arctic Coast in the vicinity within the Lisburne Group in the northeastern part of Wainwright (Armstrong and Mamet, 1970). Un- of the Philip Smith Mountains quadrangle. Just to fortunately, most of the part of this band that is the north, in the southeastern Sagavanirktok quad- west of the Colville River is probably too deep for rangle, volcaniclastic rocks and associated andesitic exploratimon. However, in the region east of the Col- flows are present in about the same stratigraphic ville, from the foothills north to the coast, good pos- position. Fossils in the enclosing rocks suggest that sibilities exist for reaching the Lisburne in a number these volcanic rocks are Late Mississippian in age. of structural settings. In the east-central Alaska Range, the Mankomen An analysis of the discovery well in the Prudhoe Group is underlain by a predominantly mafic marine field, Prudhoe Bay State 1, by Armstrong and Mamet volcanic sequence, the Tetelna Volcanics of probable (1974) indicates that the Lisburne Group is 540 m Carboniferous age. As the oldest fossils in the over- thick and ranges in age from Mamet's Foraminifera lying dominantly volcaniclastic Slana Spur Forma- Zone 16,,,, to Zone 21. The Alapah Limestone is DDlO THE MISSISSIPPIAN AND PENNSYLVANIAN SYSTEMS IN THE UNITED STATES

50 100 lSOMlLES I 50 100 150 2 KILOMETERS

I I I I I I FIGURE3.-Index map of arctic Alaska and adjacent Canada showing locations of outcrops of Carboniferous rock in Alaska

320 m thick and is composed of arenaceous pack- a series of cycles composed of packstone and stone and wackestone, lime mudstone, and gypsifer- wackestone capped by lime mudstone and arenaceous ous microdolomite. The Alapah is entirely Ches- microdolomite. These deposits were interpreted by terian in age, ranging from Zone 16,.. through Zone Armstrong and Mamet (1974) to represent tidal- 18. The overlying Wahoo Limestone, 219 m thick, is flat lime muds directly above ooid tidal bars. The ALASKA DDll


------CIRCLE EXPLANATION 0 U.S. Gdogical Su~.eys.ction 0 union 0i1 section @ ~h.l~oi~~om~nysutb" G Outcrop o( ~artmniierousrock @ Chwron Stmdard Limited &on + ExpkrrRionoil~Isutb".

and locations of sections, some of which contain the Lisburne Group (fig.2). From Armstrong and Marnet (1977, fig. 1).

Wahoo Limestone is entirely Pennsylvanian (Foram- hand, the Wahoo Limestone is very similar to out. inifera Zones 20 and 21). The Alapah Limestune is crop sections in the Sadlerochits and represents a more arenaceous and dolomitic in the Prudhoe Bay similar depositional environment. State 1 well than are its outcrop equivalents in the The oil and gas potential of the Lisburne Lime- Franklin and Sadferochit Mountains. On the other stone in the subsurface of northern Alaska was re DD12 THE MISSISSIPPIAN AND PENNSYLVANIAN SYSTEMS IN THE UNITED STATES



Zone 2 (Read and

FIGURE4.-Bioatratigraphic zonations in the Carboniferous deposits of Alaska. cently analyzed by Bird and Jordan (1977) who re- a probable petroleum reservoir for many years, viewed the regional setting and reservoir potential these carbonate rocks were not penetrated by drill- of the Lisburne Gmp. According to Bird and ing until 1966. In that , both the Union Kookpuk Jordan, although the Lisburne had been considered No. 1 and the Sinclair Colville No. 1 reached the ALASKA DD13

Lisburne; both wells had porosity and oil shows. intergranular porosity, but, in addition, the presence The Arco-Humble Prudhoe Bay No. 1, discovery well of vugs and small vertical fractures enhances pri- for the Prudhoe field in 1968, also penetrated the mary porosity. The fractures, more importantly, also entire Carboniferous section. Records and samples provide increased permeability. Bird and Jordan from 46 wells reaching the Lisburne are now avail- (1977) suggested that an average po~osityof at able to the public and were used in the Bird and least 10 percent may be expected in the subsurface. Jordan study. Oolitic grainstones are common in the Lisburne, An isopach map of the Lisburne in the eastern and, although the open-framework packing has part of the Arctic Coastal Plain (fig. 5) shows that nearly always been found filled with secondary the thickest section is near the front of the Brooks calcite, this facies must be considered for its poten- Range where more than 1,200 m (4,000 ft) of strata tial contribution to the overall porosity of the car- are present. These carbonate deposits thin north- bonate deposits. westward to less than 150 m (500 ft) over a broad Although the extent of these strata is unknown, northwest-trending arch that is a major subsurface sandstone porosity may be important in offshore structural feature. To the northeast, near the mouth wells in the Beaufort Sea. The dolfomite thicknesses of the Canning River, the top of the Lisburne has and the possible distribution of sandstone in the been truncated below the ground surface, and the Lisburne Group are shown in figure 6. Carboniferous carbonate deposits are completely Hydrocarbons have been reported from the Lis- absent near the Arctic Coast. burne in three wells of the Prudhoe Bay field and Porosity in the Lisburne strata is of three kinds. from another well southeast of the field. Other wells Microdolomite has porosity values as high as 23 have yielded saltwater from the Lisburne part of percent from laboratory measurements and 27 per- the column. Oil and gas flow rates from the Lisburne cent as calculated from well logs. This is mostly have not been disclosed as yet; the saltwater flow

FIGURE5.-Isopach map of Lisburne Group in the subsurface of the eastern Arctic Slope, Alaska. Modified from Bird and Jordan (1977). DD14 THE MISSISSIPPIAN AND PENNSYLVANIAN SYSTEMS IN THE UNITED STATES 146" 152" 150" 148" 1 EXPLANATIONI Control point -200L/ Dolomite isopach . .. . LISBURNE TEST RESULTS ... POSSl9LE AREAL EXTENT OF 17Above dolomite zone 1-1 1-1 Within dolomite zone API=American Petroleum Institute


69" I I FIGURE6.-Reservoir data summary for the Lisburne Group in the subsurface of the eastern Arctic Slope, Alaska. Modified from Bird and Jordan (1977). rate from the dolomite in Mobil Mikkelson Bay No. 1 plunging anticlinal nose, faulted on bloth the north is 2,057 BPD (barrels per ) and from sandstone and south, and truncated and sealed by an uncon- in the same well is 1,470 BPD. forinity to the east. The Lisburne pool, presumably, Bird and Jordan (1977) suggested that, although is similarly trapped. the most likely source beds are Jurassic and Creta- Although nowhere commercially developed, the ceous shale, shale within the Lisburne Group and Carboniferous carbonate rocks of Alaska provide an the Kayak Shale are possible contributors as well. immense potential resource for various industrial They also indicated that coal in the basal Kekiktuk Uses of limestone. In northern Alaska alone, thou- Conglomerate may be a source for dry gas in the sands of cubic kilometers of limestone are exposed Lisburne. Various estimates indicate that, although in the ~~~k~ R~~~~,either at the surface or within this in the Prudhoe Bay area has not been a hundred meters of the surface. No detailed chemi- buried deep enough Or for a long enough period cal analyses have been made on these limestones, but generate gas, downdip correlatives to the south may the various carbonate facies that have been examined have generated gas. Several formations provide adequate sealing beds during field mapping and stratigraphic studies in- at the top of the Lisburne Group throughout the sub- dicate a full range of shelf-carbonate types, ranging surface area. Stratigraphic and structural traps and pure chemical-grade lime through combinations of both are present in northern Alaska. argillaceous and dolomitic l~me~toneto pure dolo- Along the Barrow arch, traps of the Prudhoe Bay mite. If industrial limestone is needed and if eco- type may be expected. In the Prudhoe Bay field, the nomic factors are favorable, the Carboniferous Sadlerochit pool was shown by Rickwood (1970) limestones of Alaska may become an invaluable and Morgridge and Smith (1972) to be on a west- asset. ALASKA DD15

REFERENCES CITED Brosg6, W. P., and Dutro, J. T., Jr., 1973, Paleozoic rocks of northern and central Alaska, in Pitcher, M. G., ed., Arctic Armstrong, A. K., 1970a, Carbonate facies and the lithostro- geology: Am. Assoc. Petroleum Geol. Mem. 19, p. 361-375, tionid corals of the Mississippian Kogruk Formation, De- 15 figs. Long Mountains, northwestern Alaska: U.S. Geol. Survey Buckland, William, 1839, Geology, ill Beechey, F. W., and Prof. Paper 664, 38 p., 14 pls., 37 figs. others, The zoology of Captain Beechey's voyage ;': " " 1970b, Mississippian dolomites from Lisburne Group, 1825, 26, 27, 28: London, H. G. Bohn, p. 157-180. Killik River, Mount Bupto region, Brooks Range, Alaska: Buddington, A. F., and Chapin, Theodore, 1929, Gmlogy and Am. Assoc. Petroleum Geologists Bull., v. 54, no. 2, p. mineral deposits of southeastern Alaska: U.S. Geol. 251-264,lO figs. Survey Bull. 800, 398 p., 22 pls. 3 figs. 1970c, Mississippian rugose corals, Peratrovich Forma- Cairnes, D. 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Morgridge, D. L., and Smith, W. B., Jr., 1972, Geology and Richter, D. H., and Dutro, J. T., Jr., 1975, Revision of the discovery of Prudhoe Bay field, eastern Arctic Slope, type Mankomen Formation (Pennsylvanian and Permian), Alaska, in King, R. E., ed., Stratigraphic oil and gas Eagle Creek area, eastern Alaska Range, Alaska: U.S. fields; classification, exploration methods, and case his- Geol. Survey Bull. 1395-B, 25 p., 8 figs. tories: Am. Assoc. Petroleum Geologists Mem. 16, p. Rickwood, F. K., 1970, The Prudhoe Bay field, in Adkison, 489-501. W. L., and Brosg6, M. M., Proceedings of the geological Muffler, L. J. P., 1967, Stratigraphy of the Keku Islets and seminar on the North Slope of Alaska: Los Angeles, Am. neighboring parts of Kuiu and Kupreanof Islands, south- Assoc. Petroleum Geologists, Pacific Sec., p. L1-L11, 9 eastern Alaska: U.S. Geol. Survey Bull. 1241-C, 52 p., figs. 1 pl., 15 figs. Rowett, C. L., 1969, Upper Palaeozoic stratigraphy and corals Mull, C. G., and Mangus, M. D., 1972, Itkilyariak Formation; from the east-central Alaska Range, Alaska: Arctic Inst. New Mississippian Formation of Endicott Group, Arctic North America Tech. Paper 23, 120 p., 13 pls., 20 figs. Slope of Alaska: Am. Assoc. Petroleum Geologists Bull., Sable, E. G., and Dutro, J. T., Jr., 1961, New Devonian and v. 56, no. 8, p. 1364-1369, 6 figs. Mississippian Formations in DeLong Mountains, northern Patton, W. W., Jr., and Dutro, J. T., Jr., 1969, Preliminary Alaska: Am. Assoc. Petroleum Geologists Bull., v. 45, no. report on the Paleozoic and Mesozoic sedimentary sequence 5, p. 585-593, 4 figs. on St. Lawrence Island, Alaska: U.S. Geol. Survey Prof. Sando, W. J., Mamet, B. L., and Dutro, J. T., Jr., 1969, Car- Paper 650-D, p. D138-D143, 5 figs. boniferous megafaunal and microfaunal zonation in the Patton, W. W., Jr., Tailleur, I. L., Brosg6, W. P., and northern Cordillera of the United States: U.S. Geol. Lanphere, M. A., 1977, Preliminary report on the ophio- Survey Prof. Paper 613-E, 29 p., 1 pl., 7 figs. lites of northern and western Alaska, in Coleman, R. G., Schrader, F. C., 1902, Geological section of the Rocky Moun- and Irwin, W. P., eds., North American ophiolites: tains in northern Alaska: Geol. Soc. America Bull., v. 13, Oregon Dept. Geology and Mineral Industries Bull. 95, p. 233-252, pls. 40-43. p. 51-57. Smith, P. S., 1939, Areal : U.S. Geol. Survey Read, C. B., and Mamay, S. H., 1964, Upper Paleozoic floral Prof. Paper 192, 100 p., 18 pls. zones and floral provinces of the United States: U.S. Smith, P. S., and Mertie, J. B., Jr., 1930, Geology and min- Geol. Survey Prof. Paper 454-K, 35 p., 19 pls. eral resources of northwestern Alaska: U.S. Geol. Survey Reed, B. L., Nelson, S. W., Curtin, G. C., and Singer, D. A., Bull. 815, 351 p., 34 pls., 22 figs. 1978, Mineral resources map of the Talkeetna quad- Sohn, I. G., 1971, New Late Mississippian ostracode genera rangle, Alaska: U.S. Geol. Survey Misc. Field Studies and from northern Alaska: U.S. Geol. Survey Map MF-870-D, scale 1: 250,000. Prof. Paper 711-A, 24 p., 9 pls., 3 figs. Reed, J. C., 1958, Exploration of Naval Petroleum Reserve Steidtmann, Edward, and Cathcart, S. H., 1922, Geology of No. 4 and adjacent areas, northern Alaska, 1944-53. pt. 1, the York tin deposits, Alaska: U.S. Geol. Survey Bull. History of the exploration: U.S. Geol. Survey Prof. Paper 733, 130 p., 12 pls., 23 figs. 301, 192 p., 3 pls., 101 figs. Wahrhaftig, Clyde, 1968, Schists of the central Alaska Range: Reiser, H. N., 1970, Northeastern Brooks Range-A surface U.S. Geol. Survey Bull. 1254-E, 22 p., 5 figs. expression of the Prudhoe Bay section, in Adkison, W. L., Wood, G. V., and Armstrong, A. K., 1975, Diagenesis and and Brosg6, M. M., eds., Proceedings of the geological stratigraphy of the Lisburne Group limestones of the seminar on the North Slope of Alaska: Los Angeles, Am. Sadlerochit Mountains and adjacent areas, northeastern Assoc. Petroleum Geologists, Pacific Sec., p. K1-K14, 6 Alaska: U.S. Geol. Survey Prof. Paper 857, 47 p., 12 figs. pls., 25 figs. Richter, D. H., 1976, Geologic map of the Nabesna quad- Yochelson, E. L., and Dutro, J. T., Jr., 1960, Late Paleozoic rangle, Alaska: U.S. Geol. Survey Misc. Inv. Map 1-932, from northern Alaska: U.S. Geol. Survey Prof. scale 1: 250,000. Paper 334-D, p. Dlll-D147, 3 pls., 7 figs.

* V.S. GOVERNMENT PRINTING OFFICE: 1980 0- 31 1-34/88