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Neogene transpressional foreland basin development on the north side of the central Alaska Range, Usibelli Group and Nenana Gravel, Tanana basin

By
Kenneth D. Ridgway
Kenneth D. Ridgway
1
Dept. of Earth & Atmospheric Sciences, Purdue University, 550 Stadium Mall Drive, West Lafayette, Indiana 47907-2051, USA
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Evan E. Thoms
Evan E. Thoms
2
U.S. Geological Survey, 4200 University Drive, Anchorage, Alaska 99508-4667, USA, and Dept. of Geology and Geophysics, University of Alaska–Fairbanks, Natural Sciences Building, 900 Yukon Drive, PO Box 755780, Fairbanks, Alaska 99775-5780, USA
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Paul W. Layer
Paul W. Layer
3
Dept. of Geology and Geophysics, University of Alaska–Fairbanks, Natural Sciences Building, 900 Yukon Drive, PO Box 755780, Fairbanks, Alaska 99775-5780, USA
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Mark E. Lesh
Mark E. Lesh
4
Dept. of Earth & Atmospheric Sciences, Purdue University, 550 Stadium Mall Drive, West Lafayette, Indiana 47907-2051, USA, and A-Frame Maps & Illustrations, 4115 Riverside Avenue, Boulder, Colorado 80304, USA
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James M. White
James M. White
5
Geological Survey of Canada, Natural Resources Canada, 3303-33rd St. NW, Calgary, Alberta T2L 2A7, Canada
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Shane V. Smith
Shane V. Smith
6
Dept. of Earth & Atmospheric Sciences, Purdue University, 550 Stadium Mall Drive, West Lafayette, Indiana 47907-2051, USA, and Department of Geological and Environmental Sciences, Youngstown State University, One University Plaza, Youngstown, Ohio 44555, USA
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Published:
January 01, 2007

Neogene strata of the Tanana basin provide a long-term record of a northward-propagating, transpressional foreland-basin system related to regional shortening of the central Alaska Range and strike-slip displacement on the Denali fault system. These strata are ∼2 km thick and have been deformed and exhumed in thrust faults that form the foothills on the north side of the Alaska Range. The lower part of the sedimentary package, the Usibelli Group, consists of 800 m of mainly Miocene strata that were deposited in fluvial, lacustrine, and peat bog environments of the foredeep depozone of the foreland-basin system. Compositional data from conglomerate and sandstone, as well as recycled Upper Cretaceous palynomorphs, indicate that the Miocene foreland-basin system was supplied increasing amounts of sediment from lithologies currently exposed in thrust sheets located south of the basin. The upper part of the sedimentary package, the Nenana Gravel, consists of 1200 m of mainly Pliocene strata that were deposited in alluvial-fan and braidplain environments in the wedge-top depozone of the foreland-basin system. Compositional data from conglomerate and sandstone, as well as 40Ar/39Ar dating of detrital feldspars in sandstone and from granitic clasts in conglomerate, indicate that lithologies exposed in the central Alaska Range provided most of the detritus to the Pliocene foreland-basin system. 40Ar/39Ar dates from detrital feldspar grains also show that two main suites of plutons contributed sediment to the Nenana Gravel. Detrital feldspars with an average age of 56 Ma are interpreted to have been derived from the McKinley sequence of plutons located south of the Denali fault. Detrital feldspars with an average age of 34 Ma are interpreted to have been derived from plutons located north of the Denali fault. Plutons located south of the Denali fault provided detritus for the lower part of the Nenana Gravel, whereas plutons located north of the Denali fault began to contribute sediment during deposition of the upper part of the Nenana Gravel. This age distribution documented in detrital feldspars of the Nenana Gravel is interpreted as representing a progressive northward exhumation of plutons that were located south of the Pliocene Tanana basin. In contrast to previous studies, we interpret the Usibelli Group and Nenana Gravel to represent a continuum in the evolution of a transpressional foreland basin that began during Miocene time on the north side of the Alaska Range.

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GSA Special Papers

Tectonic Growth of a Collisional Continental Margin: Crustal Evolution of Southern Alaska

Kenneth D. Ridgway
Kenneth D. Ridgway
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Jeffrey M. Trop
Jeffrey M. Trop
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Jonathan M.G. Glen
Jonathan M.G. Glen
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J. Michael O'Neill
J. Michael O'Neill
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Geological Society of America
Volume
431
ISBN print:
9780813724317
Publication date:
January 01, 2007

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