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Secular changes in Cenozoic arc magmatism recorded by trends in forearc-basin sandstone composition, Cook Inlet, southern Alaska

By
Kenneth P. Helmold
Kenneth P. Helmold
Alaska Division of Oil & Gas, 550 W. 7th Avenue, Anchorage, Alaska 99501, USA
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Marwan A. Wartes
Marwan A. Wartes
Alaska Division of Geological & Geophysical Surveys, 3354 College Road, Fairbanks, Alaska 99709, USA
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Robert J. Gillis
Robert J. Gillis
Alaska Division of Geological & Geophysical Surveys, 3354 College Road, Fairbanks, Alaska 99709, USA
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David L. LePain
David L. LePain
Alaska Division of Geological & Geophysical Surveys, 3354 College Road, Fairbanks, Alaska 99709, USA
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Trystan M. Herriott
Trystan M. Herriott
Alaska Division of Geological & Geophysical Surveys, 3354 College Road, Fairbanks, Alaska 99709, USA
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Richard G. Stanley
Richard G. Stanley
U.S. Geological Survey, 345 Middlefield Road, MS 969, Menlo Park, California 94025, USA
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Michael D. Wilson
Michael D. Wilson
Wilson & Associates, 12255 W. 17th Avenue, Lakewood, Colorado 80215, USA
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Published:
December 28, 2018
Publication history
05 February 201819 November 2018

ABSTRACT

A robust set of modal composition data (238 samples) for Eocene to Pliocene sandstone from the Cook Inlet forearc basin of southern Alaska reveals strong temporal trends in composition, particularly in the abundance of volcanic lithic grains. Field and petrographic point-count data from the northwestern side of the basin indicate that the middle Eocene West Foreland Formation was strongly influenced by nearby volcanic activity. The middle Eocene to lower Miocene Hemlock Conglomerate and Oligocene to middle Miocene Tyonek Formation have a more mature quartzose composition with limited volcanic input. The middle to upper Miocene Beluga Formation includes abundant argillaceous sedimentary lithic grains and records an upward increase in volcanogenic material. The up-section increase in volcanic detritus continues into the upper Miocene to Pliocene Sterling Formation.

These first-order observations are interpreted to primarily reflect the waxing and waning of nearby arc magmatism. Available U-Pb detrital zircon geochronologic data indicate a dramatic reduction in zircon abundance during the early Eocene, and again during the Oligocene to Miocene, suggesting the arc was nearly dormant during these intervals. The reduced arc flux may record events such as subduction of slab windows or material that resisted subduction. The earlier hiatus in volcanism began ca. 56 Ma and coincided with a widely accepted model of ridge subduction beneath south-central Alaska. The later hiatus (ca. 25–8 Ma) coincided with insertion of the leading edge of the Yakutat terrane beneath the North American continental margin, resulting in an Oligocene to Miocene episode of flat-slab subduction that extended farther to the southwest than the modern seismically imaged flat-slab region. The younger tectonic event coincided with development of some of the best petroleum reservoirs in Cook Inlet.

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GSA Special Papers

Tectonics, Sedimentary Basins, and Provenance: A Celebration of the Career of William R. Dickinson
CONTAINS OPEN ACCESS

Raymond V. Ingersoll
Raymond V. Ingersoll
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Timothy F. Lawton
Timothy F. Lawton
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Stephan A. Graham
Stephan A. Graham
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Geological Society of America
Volume
540
ISBN electronic:
9780813795409
Publication date:
December 28, 2018

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