William A. Morgan, 2012. "Sequence Stratigraphy of the Great American Carbonate Bank", Great American Carbonate Bank: The Geology and Economic Resources of the Cambrian—Ordovician Sauk Megasequence of Laurentia, James Derby, Richard Fritz, Susan Longacre, William Morgan, Charles Sternbach
Download citation file:
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 Tippe-canoe 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.
Figures & Tables
Great American Carbonate Bank: The Geology and Economic Resources of the Cambrian—Ordovician Sauk Megasequence of Laurentia
The Great American Carbonate Bank (GACB) comprises the carbonates (and related siliciclastics) of the Sauk megasequence, which were deposited on and around the Laurentian continent during Cambrian through earliest Middle Ordovician, forming one of the largest carbonate-dominated platforms of the Phanerozoic. The Sauk megasequence, which ranges upwards of several thousand meters thick along the Bank's margin, consists of distinctive Lithofacies and fauna that are widely recognized throughout Laurentia. A refined biostratigraphic zonation forms the chronostratigraphic framework for correlating disparate outcrops and subsurface data, providing the basis for interpreting depositional patterns and the evolution of the Bank. GACB hydrocarbon fields have produced 4 BBO and 21 TCFG, mostly from reservoirs near the Sauk-Tippecanoe unconformity. The GACB is also a source of economic minerals and construction material and, locally, serves as either an aquifer or repository for injection of waste material. This Memoir comprises works on biostratigraphy, ichnology, stratigraphy, depositional facies, diagenesis, and petroleum and mineral resources of the GACB. It is dedicated to James Lee Wilson who first conceived of this publication and who worked on many aspects of the GACB during his long and illustrious career.