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Book Chapter

The Sauk Megasequence in the Cratonic Interior of North America: Interplay between a Fully Developed Inner Detrital Belt and the Central Great American Carbonate Bank

By
Anthony C. Runkel
Anthony C. Runkel
Minnesota Geological Survey, St. Paul, Minnesota, U.S.A.
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Robert M. McKay
Robert M. McKay
Iowa Department of Natural Resources, Geological Survey Bureau, Iowa City, Iowa, U.S.A.
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Clinton A. Cowan
Clinton A. Cowan
Geology Department, Carleton College, Northfield, Minnesota, U.S.A.
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James F. Miller
James F. Miller
Department of Geography, Geology and Planning, Missouri State University, Springfield, Missouri, U.S.A.
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John F. Taylor
John F. Taylor
Geoscience Department, Indiana University of Pennsylvania, Indiana, Pennsylvania, U.S.A.
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Published:
January 01, 2012

Abstract

The Sauk megasequence in the far inboard region of the cratonic interior of North America (Minnesota, Wisconsin, and Iowa) is divisible into two packages that fundamentally differ from one another in facies and stratigraphic attributes. A lower Sauk succession package, Marjuman–early Skullrockian in age, is characterized by deposits of the traditional inner detrital belt (IDB) that interfinger hundreds of kilometers seaward with the middle carbonate belt or cratonward margin of the central mid-continent great American carbonate bank (GACB). The IDB contains a typical suite of nearshore siliciclastic facies containing features that document the importance of both wave- and tide-dominated currents in the depositional system. The transitional area between the IDB and the GACB in the Cambrian and earliest Ordovician was a moat, characterized by relatively deep-water deposition, which served as a catchment for mud that was winnowed from landward parts of the shelf and then deposited near the stormwave base. Mixed carbonate and siliciclastic facies in the moat are characterized by condensation features and other attributes indicative of suppressed carbonate productivity and starvation of siliciclastic sand. These facies contrast with shallower water facies that commonly filled available accommodation space in both seaward (central part of the GACB) and landward (cratonic shoreline) directions, the former dominated by typical stacks of oolitic, ribbon-rock, and microbialite lithofacies, and the latter by stacks of nearshore siliciclastic sand-dominated parasequences. Our chronostratigraphic framework provides temporal constraints that support the long-postulated hypothesis that these two depositional systems expanded and contracted in reciprocating fashion: substantial landward migration and expansion of the GACB occurred when siliciclastic input was diminished during the most rapid rates of transgression (marked by maximum flooding intervals in the IDB). Retreat and diminishment in the extent of the GACB corresponded to falls in sea level that led to major progradations of nearshore siliciclastics of the IDB and terrigenous poisoning of the carbonate factory.

An overlying upper Sauk succession package records the establishment of a fundamentally different depositional system in the far inboard regions of the cratonic interior beginning in the later Skullrockian. The Prairie du Chien Group and its equivalents represent a major landward migration and perhaps cratonwide distribution of the oolitic, ribbon-rock, and micro-bialite lithofacies that were previously restricted mostly to the GACB of Missouri and adjacent areas. This change was triggered by a pronounced continental-scale flooding event that led to onlap across much, or all, of the cratonic interior. The resultant burial of terrigenous source regions by carbonate strata is in part responsible for this fundamental change in de-positional conditions.

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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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