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Sauk Megasequence Deposition in Northeastern Washington, Northern Idaho, and Western Montana

By
John H. Bush
John H. Bush
Department of Geosciences, University of Idaho, Moscow, Idaho, U.S.A.
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Robert C. Thomas
Robert C. Thomas
Department of Environmental Sciences, The University of Montana Western, Dillon, Montana, U.S.A.
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Michael C. Pope
Michael C. Pope
Department of Geology and Geophysics, Texas A&M University, College Station, Texas, U.S.A.
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Published:
January 01, 2012

Abstract

Lower Cambrian–Lower Ordovician passive-margin sediments were deposited across northeastern Washington, northern Idaho, and western Montana. Lower Cambrian strata record the initial transgression onto Laurentia in northeastern Washington. Middle Cambrian–Lower Ordovician units were deposited across a much broader area and record the establishment of a western ooid-algal shoal complex that restricted water circulation in an intrashelf basin that formed between the shoal and craton. Long-standing topographic highs in the region include Montania, which may have controlled the location of the ooid-algal shoal complex, and the Lemhi arch, which served as a western source area for siliciclastic sediment input. The Sauk megasequence sediments were deposited in multiple grand cycles that are regionally correlative. Each grand cycle consists of a shale and sandstone base deposited as sea level transgressed onto the craton. The basal siliciclastic units are gradationally overlain by carbonate, which was deposited as sea level continued to rise and an extensive carbonate platform developed. Some of the boundaries between the grand cycles are unconformities, recording rapid changes in sea level. Meter-scale shallowing-upward cycles are common within grand cycles, but they have not yet been regionally correlated.

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Contents

Memoir

Great American Carbonate Bank: The Geology and Economic Resources of the Cambrian—Ordovician Sauk Megasequence of Laurentia

James Derby
James Derby
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Richard Fritz
Richard Fritz
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Susan Longacre
Susan Longacre
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William Morgan
William Morgan
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Charles Sternbach
Charles Sternbach
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American Association of Petroleum Geologists
Volume
98
ISBN electronic:
9781629810201
Publication date:
January 01, 2012

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