Geologic Studies in Alaska by the U.S. Geological Survey, 1992

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30 GEOLOGIC STUDIES IN ALASKA BY THE U.S. GEOLOGICAL SURVEY, 1992 Brooks Range and Arctic Slope, in Mull, C.G., and Adams, K.E., eds., Dalton Highway, Yukon River to Prudhoe Bay, Alaska: Alaska Division of Geological and Geophysical Surveys, Guidebook 7, v. 1, p. 31-46. Mull, C.G., Crowder, R.K., Adams, K.E., Siok, J.P., Bodnar, D.A., Hams, E.E., Alexander, R.A., and Solie, D.N., 1987, Stratigraphy and structural setting of the Picnic Creek Allochthon, Killik River quadrangle, central Brooks Range, Alaska: a summary, in Tailleur, I.L., and Weimer, Paul, eds., Alaskan North Slope Geology: Bakersfield, California, Pacific Section, Society of Economic Paleontologists and Mineralogists, Book 50, p. 649-662. Mull, C.G., Tailleur, I.L., Mayfield, C.F., Ellersieck, Inyo, and Curtis, S.M., 1982, New upper Paleozoic and lower Meso- zoic stratigraphic units, central and western Brooks Range, Alaska: American Association of Petroleum Geologists Bul- letin, v. 66, p. 348-362. Murchey, B.L., Jones, D.L., Holdsworth, B.K., and Wardlaw, B.R., 1988, Distribution patterns of facies, radiolarians, and conodonts in the Mississippian to Jurassic siliceous rocks of the northern Brooks Range, Alaska, in Gryc, George, ed., Geology and exploration of the National Petroleum Reserve in Alaska, 1974 to 1982: U.S. Geological Survey Profes- sional Paper 1399, p. 697-724. Sandberg, C.A., and Gutschick, R.C., 1984, Distribution, micro- fauna, and source-rock potential of Mississippian Delle Phosphatic Member of Woodman Formation and equiva- lents, Utah and adjacent States, in Woodward, Jane, and others, eds., Hydrocarbon source rocks of the Greater Rocky Mountain region: Denver, Rocky Mountain Asso- ciation of Geologists, p. 135-178. Reviewers: C. G. Mull and John E. Repetski
LITHOFACIES AND CONODONTS OF CARBONIFEROUS STRATA IN THE IVOTUK HILLS, WESTERN BROOKS RANGE, ALASKA ABSTRACT Carboniferous strata in the Ivotuk Hills, in the western Brooks Range fold and thrust belt, consist of about 45 m of dark-gray shale, mudstone, dolostone, and spiculitic chert (upper part of the Kayak Shale, Endicott Group) and at least 225 m of light- to dark-gray dolostone, chert, and minor shale (Lisburne Group). The Kayak Shale was deposited chiefly below wave base; subordinate beds of dolo- mitic bioclastic packstone probably formed as storm deposits. The Kayak contains conodonts of Early Missis- sippian (early Osagean) age. The Lisburne Group in the Ivotuk Hills can be divided into three subunits on the basis of bedding style and lithology. The lower and upper units are thin-bedded to laminated, consist chiefly of fine- grained dolostone and spiculite and subordinate dolo- mitized bioclastic packstone. The middle unit is massive and resistant and is made up mostly of crinoidal packstone and lesser bryozoan wackestone. The lower and middle units of the Lisburne Group yield conodonts of early Late Mississippian (late Meramecian) age; a sample from the upper unit produced latest Late Mississippian (late Chesterian) conodonts. The Kayak Shale in the Ivotuk Hills is in general similar to the Kayak elsewhere in the Brooks Range, but also has some lithologic and faunal similarities to the Kuna Formation of the Lisburne Group. The Kayak was probably deposited in a middle to outer platform or shelf setting in somewhat deeper water than that in which most of the Kayak accumulated, but under more oxygenated condi- tions than those typical of Kuna environments. Sedimentologic data and conodont biofacies indicate that the Lisburne Group in the Ivotuk Hills accumulated primarily in normal marine, middle to outer platform or shelf settings. The section correlates well in age and lithology with the Lisbume at Lisbume Ridge, about 40 km to the west. Repeated thrust panels of Carboniferous strata encountered in the Lisburne Test Well No. 1, drilled 1.5 km northeast of our study area in the Ivotuk Hills, corre- late biostratigraphically and lithologically with rocks exposed at the surface, but appear to have formed, at least in By Julie A. Dumoulin and Anita G. Harris part, in somewhat shallower water and more restricted depositional environments. INTRODUCTION Carboniferous carbonate rocks (Lisburne Group and carbonate layers in the underlying Kayak Shale) are widely exposed across northern Alaska in the Brooks Range fold and thrust belt. Lithofacies, biostratigraphy, and depositional environments of these units have been delineated at a reconnaissance scale in the eastern Brooks Range (Armstrong, 1974; Armstrong and Mamet, 1977), but are less well known to the west. Both shallow and deeper water Carboniferous facies occur in thrust sheets in the western Brooks Range; the structural, stratigraphic, and paleogeographic relationships of these facies remain con- troversial (Mayfield and others, 1988; Dumoulin and others, this volume). This paper describes the lithofacies and conodont biostratigraphy of Carboniferous strata in the Ivotuk Hills, western Killik River B-5 quadrangle (fig. 1). Although these strata constitute the type section of the Ivotuk Hills structural sequence of Martin (1970) and Mayfield and others (1988), no detailed sedimentologic or paleontologic studies of these rocks have previously been published. PREVIOUS WORK Carboniferous and younger rocks of the Ivotuk Hills area were first described by Martin (1970), who designated these strata, along with similar sections at Lisburne Ridge and Mount Bupto in the adjacent Howard Pass quadrangle (fig. I), as the Ivotuk Hills structural sequence. The Car- boniferous part of this sequence consists of about 300 m of dolomite and chert (Lisburne Group) overlying an indeter- minate thickness of dark-gray shale with subordinate iron- stone nodules and bioclastic limestone lenses (Kayak Shale) (Martin, 1970). In the tectonic reconstruction of Mayfield and others (1988), the Ivotuk Hills structural 3 1
Page 1 and 2: Geologic Studies in Alaska by the U
Page 3 and 4: CONTENTS Introduction Cynthia Dusel
Page 5 and 6: CONTENTS CONTRIBUTORS TO THIS BULLE
Page 7 and 8: GEOLOGIC STUDIES IN ALASKA BY THE U
Page 9 and 10: LATE HOLOCENE LONGITUDINAL AND PARA
Page 19 and 20: DEEP-WATER LITHOFACIES AND CONODONT
Page 25 and 26: Table 1. Locality register for key
Page 27 and 28: Table 1. Locality register for key
Page 35: DEEP-WATER LITHOFACIES AND CONODONT
Page 39 and 40: LITHOFACIES AND CONODONTS OF CARBON
Page 49 and 50: LITHOFACES AND CONODONTS OF CARBONI
Page 51 and 52: Table 1. Conodont faunules and lith
Page 55 and 56: DEPOSITIONAL SEQUENCES IN ATIGUN SY
Page 65 and 66: U-Pb AGES OF ZIRCON, MONAZITE, AND
Page 77 and 78: APPEAL FOR NONPROLIFERATION OF ESCA
Page 85 and 86: FAVORABLE AREAS FOR METALLIC MINERA
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FAVORABLE AREAS FOR METALLIC MINERA
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GOLD AND CINNABAR IN HEAVY-MINERAL
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EARLY CENOZOIC DEPOSITIONAL SYSTEMS
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EARLY CENOZOIC DEPOSITIONAL S YSTEM
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RESERVOIR FRAMEWORK ARCHITECTURE, C
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GEOCHEMISTRY OF OPHIOLITIC ROCKS FR
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Table 1. Isotopic ages of intrusive
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Table 1. Isotopic ages of intrusive
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GEOCHEMICAL EVALUATION OF STREAM-SE
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Table 3. Summary of geochemical sig
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GEOCHEMICAL CHARACTER OF UPPER PALE
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RECONNAISSANCE GEOCHEMISTRY OF BASA
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OSTRACODE ASSEMBLAGES FROM MODERN B
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RUBIDIUM-STRONTIUM ISOTOPIC SYSTEMA
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RUBIDIUM-STRONTIUM ISOTOPIC SYSTEMA
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US. GEOLOGICAL SURVEY REPORTS ON AL
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U.S. GEOLOGICAL SURVEY REPORTS ON A
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U.S. GEOLOGICAL SURVEY REPOR TS ON
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REPORTS ABOUT ALASKA IN NON-USGS PU
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REPORTS ABOUT ALASKA IN NON-USGS PU
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Geologic Studies in Alaska by the U.S. Geological Survey, 1992

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