Coal in Alaska

Wahrhaftig, Clyde; Bartsch-Winkler, Susan; Stricker, Gary D.

doi:10.1130/dnag-gna-g1.937

Cited by 16 publications

(8 citation statements)

References 14 publications

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“…48-40 Ma; Fig. 11A; Calderwood and Fackler, 1972;Houston, 1994;Wahrhaftig et al, 1994;this study). Coarsegrained deposition along the arc margin continued through the late Eocene but was replaced by finer-grained alluvial fan-fluvial systems by late Oligocene or early Miocene time (ca.…”

Section: Influence Of Exhumation On Sediment Dispersal Patternsmentioning

confidence: 79%

“…This formation reaches a maximum thickness of 1259 m along the western margin of the basin but thins abruptly toward the center of the basin (Calderwood and Fackler, 1972;Houston, 1994). It consists of thick, conglomeratic strata deposited in alluvial fan and braided stream systems along the margin of the basin and nonmarine tuffaceous siltstone and claystone with minor coal and conglomerate in the subsurface near the basin axis (Calderwood and Fackler, 1972;Houston, 1994;Wahrhaftig et al, 1994).…”

Section: Cook Inlet Basin Stratigraphymentioning

confidence: 99%

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Provenance signature of changing plate boundary conditions along a convergent margin: Detrital record of spreading-ridge and flat-slab subduction processes, Cenozoic forearc basins, Alaska

2015

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Cenozoic strata from forearc basins in southern Alaska record deposition related to two different types of shallow subduction: Paleocene-Eocene spreading-ridge subduction and Oligocene-Recent oceanic plateau subduction. We use detrital zircon geochronology (n = 1368) and clast composition of conglomerate (n = 1068) to reconstruct the upper plate response to these two subduction events as recorded in forearc basin strata and modern river sediment. Following spreading-ridge subduction, the presence of Precambrian and Paleozoic detrital zircon ages in middle Eocene-lower Miocene arc-margin strata and Early Cretaceous ages in lower Miocene accretionary prism-margin strata indicates that sediment was transported to the basin from older terranes in interior Alaska and from the exhumed eastern part of the Cretaceous forearc system, respectively. By middle-late Miocene time, diminished abundances of these populations reflect shallow subduction of an oceanic plateau and associated exhumation that resulted in an overall contraction of the catchment area for the forearc depositional system.In the southern Alaska forearc basin system, upper plate processes associated with subduction of a spreading ridge resulted in an abrupt increase in the diversity of detrital zircon ages that reflect new sediment sources from far inboard regions. The detrital zircon signatures from strata deposited during oceanic plateau subduction record exhumation of the region above the flat slab, with the youngest detrital zircon population reflecting the last period of major arc activity prior to inser-tion of the flat slab. This study provides a foundation for new tectonic and provenance models of forearc basins that have been modified by shallow subduction processes, and may help to facilitate the use of U-Pb dating of detrital zircons to better understand basins that formed under changing geodynamic plate boundary conditions. ., 2015, Provenance signature of changing plate boundary conditions along a convergent margin: Detrital record of spreading-ridge and flat-slab subduction processes, Cenozoic forearc basins, Alaska: Geosphere, v. 11, no. 3,

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Section: Influence Of Exhumation On Sediment Dispersal Patternsmentioning

confidence: 79%

Section: Cook Inlet Basin Stratigraphymentioning

confidence: 99%

Provenance signature of changing plate boundary conditions along a convergent margin: Detrital record of spreading-ridge and flat-slab subduction processes, Cenozoic forearc basins, Alaska

2015

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“…Coal beds, for example, are up to 20 m thick in the Suntrana Formation, and lacustrine deposits of the Sanctuary and Grubstake Formations are tens of meters thick ( Fig. 6C; Wahrhaftig et al, 1969Wahrhaftig et al, , 1994. Paleocurrent measurements from the Usibelli Group are widely variable, but indicate a general west-southwestward regional paleodrainage ( Fig.…”

Section: Stratigraphy and Depositional Systemsmentioning

confidence: 98%

Mesozoic and Cenozoic tectonics of the eastern and central Alaska Range: Progressive basin development and deformation in a suture zone

Ridgway

Trop

Nokleberg

et al. 2002

Geological Society of America Bulletin

145

227

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Analysis of late Mesozoic and Cenozoic sedimentary basins, metamorphic rocks, and major faults in the eastern and central Alaska Range documents the progressive development of a suture zone that formed as a result of collision of an island-arc assemblage (the Wrangellia composite terrane) with the former North American continental margin. New basin-analysis, structural, and geochronologic data indicate the following stages in the development of the suture zone: (1) Deposition of 3-5 km of Upper Jurassic-Upper Cretaceous marine strata (the Kahiltna assemblage) recorded the initial collision of the island-arc assemblage with the continental margin. The Kahiltna assemblage exposed in the northern Talkeetna Mountains represents a Kimmeridgian-Valanginian backarc basin that was filled by northwestward-flowing submarine-fan systems that were transporting sediment derived from Mesozoic strata of the island-arc assemblage. The Kahiltna assemblage exposed in the southern Alaska Range represents a Valanginian-Cenomanian remnant ocean basin filled

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“…More than 5.4 ϫ 10 9 metric tons of low-sulfur coal reserves have been identified in the Healy Creek and Lignite Creek basins ( Fig. 2; Wahrhaftig et al 1994;Affolter et al 1995). The Neogene basins also have hydrocarbon potential judging from vitrinite reflectance and Rock-Eval pyrolysis data (Stanley et al 1990).…”

Section: Introductionmentioning

confidence: 97%

“…3; Wahrhaftig et al 1969;Wahrhaftig 1987). The Neogene basins are also of economic importance because coal mined from the Usibelli Group is a major component of industrial energy for Alaska and the countries bordering the northern Pacific Ocean (Merritt 1986;Wahrhaftig et al 1994). More than 5.4 ϫ 10 9 metric tons of low-sulfur coal reserves have been identified in the Healy Creek and Lignite Creek basins ( Fig.…”

Section: Introductionmentioning

confidence: 97%

Petrology and provenance of the Neogene Usibelli Group and Nenana Gravel; implications for the denudation history of the central Alaska Range

Ridgway

Trop

Jones

1999

Journal of Sedimentary Research

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Neogene basins exposed along the north-central flank of the Alaska Range record the geologic development of the highest mountain range in North America. Strata from these basins consist of the Miocene Usibelli Group (ϳ 600 m thick) and the Pliocene Nenana Gravel (ϳ 1000 m thick). Petrographic analyses of 54 sandstone thin sections and 36 conglomerate clast counts from one of these basins, the Healy Creek basin, delineate two distinct petrofacies. A stratigraphically older, quartz-rich petrofacies defines the Healy Creek, Suntrana, and Lignite Creek Formations of the Usibelli Group. A stratigraphically younger, lithic-rich petrofacies defines the Nenana Gravel. Sandstones of the lower petrofacies are characterized by a dominance of quartz (Q 60 F 27 L 12 ; Qm 33 F 28 Lt 39 ) and a high proportion of polycrystalline quartz (Qp 68 Lvm 21 Lsm 11 ). Schist and quartz clasts are common in conglomerates from this petrofacies. Imbricated conglomerate clasts and planar cross-stratification indicate southward to southwestward paleoflow for this quartz-rich petrofacies. Relative to the lower petrofacies, sandstones of the upper petrofacies are defined by a dominance of lithic fragments (Q 39 F 19 L 43 ; Qm 16 F 21 Lt 63 ), a lower proportion of polycrystalline quartz, and a higher proportion of volcanic lithic fragments (Qp 37 Lvm 55 Lsm 8 ). Conglomerate clast compositions in this petrofacies consist mainly of sedimentary and igneous clasts. This lithicrich petrofacies is dominated by northward paleocurrent indicators. The compositional and paleocurrent data of the Usibelli Group and Nenana Gravel suggest a regional paleodrainage reversal from southward-flowing fluvial systems transporting sediment from the quartzrich, metamorphic Yukon-Tanana terrane, to northward-flowing fluvial systems transporting sedimentary and igneous detritus from the growing Alaska Range.Superimposed on the first-order tectonic signal are second-order compositional differences. These differences may be related to a combination of factors but appear to be consistent with well documented changes in paleoclimate. For example, sandstones deposited during the warmest and wettest paleoclimates are characterized by a relative enrichment in quartz, especially polycrystalline quartz (Healy Creek Formation, Q 81 F 16 L 3 , Qp 93 Lvm 3 Lsm 4 ; Suntrana Formation, Q 61 F 25 L 14 , Qp 66 Lvm 25 Lsm 9 ). Sandstones deposited during cooler and drier climates, in contrast, have lower proportions of quartz and higher proportions of feldspar and lithic fragments (Lignite Creek Formation, Q 45 F 33 L 14 , Qp 56 Lvm 28 Lsm 17 ). Our analysis cannot account for all the possible influences on sandstone compositions during deposition of the Usibelli Group, but we contend that the apparent correlation between sandstone composition and changes in paleoclimate suggest that climatic modification of sandstone composition may have been significant.

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Coal in Alaska

Cited by 16 publications

References 14 publications

Provenance signature of changing plate boundary conditions along a convergent margin: Detrital record of spreading-ridge and flat-slab subduction processes, Cenozoic forearc basins, Alaska

Provenance signature of changing plate boundary conditions along a convergent margin: Detrital record of spreading-ridge and flat-slab subduction processes, Cenozoic forearc basins, Alaska

Mesozoic and Cenozoic tectonics of the eastern and central Alaska Range: Progressive basin development and deformation in a suture zone

Petrology and provenance of the Neogene Usibelli Group and Nenana Gravel; implications for the denudation history of the central Alaska Range

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