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

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108 GEOLOGIC STUDIES IN ALASKA BY THE U.S. GEOLOGICAL SURVEY, 1992 Conglomerate = EXPLANATION Sigrnoidal macroforms 1-1 Channel Sandstone Mudstone, siltstone, Overbank and silty sandstone flood plain 2 Trough crossbeds 1- Ripple laminations - Coal, carbonaceous shale, and tonstein beds ?- } Mire )( Covered Fault-Arrows indicate relative horizontal displacement
EARLY CENOZOIC DEPOSITIONAL SYSTEMS, MATANUSKA COAL FIELD METERS O KILOMETERS 109 overthickened Midway coalbed, which abuts against a conglomeratic sandstone immediately to the east. This conglomeratic sandstone, in turn, merges upward with a conglomeratic sandstone that elsewhere overlies the Mid- way coalbed (fig. 7). This lateral-facies variation is re- corded where a left-lateral, oblique-slip fault is developed. The Premier coal zone contains six coalbeds interbedded with thin carbonaceous shale, mudstone, ironstone, and tonsteins. These coalbeds and coal-free interbeds are, in turn, separated by similar but thicker noncoaly intervals. In general, the lower four coalbeds contain more thick coal-free interbeds than the upper two coalbeds, which comprise more bone and bony coal interbeds (Barnes and Payne, 1956). Laterally, the six coalbeds of the Premier coal zone merge to the west. The thickness of intervening noncoaly interbeds is expanded by erosional-based, fining-upward sandstones and coarsening- upward sandstones (fig. 7). The eastward overthickening of the Premier coal zone and splitting of the coalbeds coin- cides with the occurrence of left-lateral, oblique-slip faults. In the erosional-based, fining-upward, conglomeratic sandstone above the Jonesville coal zone, the conglomeratic sandstone consists of an amalgamated, multistory, and multilateral architecture over the 800-m lateral extent shown in figure 8. However, the complex is interrupted by erosional-based bodies of interbedded mudstone, siltstone, and sandstone. The internal organization of the sigmoidal macroforms within this conglomeratic-sandstone also varies laterally. Sigmoidal macroforms, which are well developed in all the conglomeratic-sandstone bodies, generally show west-northwest dip orientation at the west end of the cross section and east-southeast dip orientation at the east end. Laterally to the west, the conglomeratic- sandstone complex grades into interbedded rooted mudstone and rippled siltstone and sandstone. The conglomeratic sandstone; kconformably overlie the Jonesville coal zone, which consists of four coalbeds interbedded with carbonaceous shale, mudstone, ironstone, and tonstein units (fig. 8). The lower- most coalbed and interbedded noncoaly units are separated from the upper three coalbeds by very thick (1.5 to 4.5 m) interbedded mudstones, siltstones, and sandstones that lo- cally thicken from east to west. However, in the section shown in figure 9 these clastic interbeds regionally thicken eastward in the direction of occurrence of the left-lateral, oblique-slip faults. The uppermost coalbed and thin noncoaly units (fig. 8) are separated from the middle coalbeds by thin to thick (15 cm to 1.5 m) mudstones and Figure 7. Lateral-facies architecture of interval from below Eska coal zone to Premier coal zone in the Chickaloon Formation. Architecture is restored from vertical component of movement of left-lateral, oblique-slip faults whose locations are shown in upper part of diagram.
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Geologic Studies in Alaska by the U
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CONTENTS Introduction Cynthia Dusel
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CONTENTS CONTRIBUTORS TO THIS BULLE
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GEOLOGIC STUDIES IN ALASKA BY THE U
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LATE HOLOCENE LONGITUDINAL AND PARA
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DEEP-WATER LITHOFACIES AND CONODONT
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Table 1. Locality register for key
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Table 1. Locality register for key
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LITHOFACIES AND CONODONTS OF CARBON
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LITHOFACES AND CONODONTS OF CARBONI
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Table 1. Conodont faunules and lith
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DEPOSITIONAL SEQUENCES IN ATIGUN SY
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Page 63 and 64: 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
Page 97 and 98: GOLD AND CINNABAR IN HEAVY-MINERAL
Page 107 and 108: EARLY CENOZOIC DEPOSITIONAL SYSTEMS
Page 111 and 112: EARLY CENOZOIC DEPOSITIONAL S YSTEM
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Page 125 and 126: RESERVOIR FRAMEWORK ARCHITECTURE, C
Page 137: GEOCHEMISTRY OF OPHIOLITIC ROCKS FR
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1 64 GEOLOGIC STUDlES IN ALASKA BY
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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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