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The AAPG/Datapages Combined Publications Database
AAPG Special Volumes
Abstract
Morgan, William A.,
DOI:10.1306/13331489M981333
2012 by The American Association of Petroleum Geologists.
Sequence Stratigraphy of the Great American Carbonate Bank
William A. Morgan1
1ConocoPhillips, Houston, Texas, U.S.A.
ACKNOWLEDGMENTS
The author gratefully acknowledges the careful reviews of James R. Derby, Susan A. Longacre, and John E. Repetski, which greatly improved the manuscript. John Repetski's guidance on formation boundaries and biostratigraphic
zonation was especially helpful. The author also thanks ConocoPhillips for providing time to work on aspects of the manuscript. This paper is dedicated to James Lee Wilson, who first conceived of this volume and continued to strongly support its progress even in declining health. Jim's pioneering work, professionalism, and friendship have been continuing sources of inspiration. He will be greatly missed.
ABSTRACT
The Cambrian–Ordovician Sauk megasequence of the great American carbonate bank (GACB) comprises a succession of mixed lithologies, but dominantly carbonate rocks, whose thickness, stratigraphy, and lithofacies distribution reflect the presence of a complex of intrabank platforms and basins, aulacogens, and tectonically active margins that together make up the major part of the paleocontinent Laurentia. The stratigraphy of the Sauk megasequence can be subdivided and correlated across the GACB through the recognition of major unconformities, marine flooding events, and stratigraphic stacking patterns, documented within a robust biostratigraphic
framework.
The base of the Sauk megasequence is typically defined as the contact of Cambrian or sub-Tippecanoe-megasequence Ordovician rocks with Precambrian, mostly igneous, basement. The Sauk megasequence is overlain (commonly unconformably) by the Middle Ordovician Tippecanoe megasequence, the age
of which varies across the GACB. Where subsequent erosion has occurred, the Sauk megasequence may be overlain by rocks younger than the Tippecanoe megasequence. Palmer's (1981b) subdivision of the Sauk megasequence into Sauk I, II, and III subsequences (now referred to as supersequences) is widely, but not universally, recognized.
Across many areas of the GACB, the Sauk III supersequence of Palmer can be subdivided into two supersequences (defined as “Sauk IIIA” and “Sauk IIIB” in this chapter), based on an unconformity and/or biostratigraphic
changes near the Cambrian-Ordovician boundary. Additional significant unconformities and marine flooding events that can be correlated across much of the GACB are summarily described in this chapter.
The recognition of correlatable surfaces across the GACB has been challenging because of local syndepositional tectonics and paleotopography, and lithofacies heterogeneity. However, confidence in correlation
across the GACB has been greatly enhanced by an increasingly refined
biostratigraphic
framework.
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