The Lower Cambrian to Lower Ordovician Carbonate Platform and Shelf Margin, Canadian Arctic Islands
Keith Dewing, Godfrey Nowlan, 2012. "The Lower Cambrian to Lower Ordovician Carbonate Platform and Shelf Margin, Canadian Arctic Islands", 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
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Five stratigraphic successions are recognized in the Sauk megasequence in the Canadian Arctic Islands. The Lower Cambrian succession was deposited on a distally steepened carbonate ramp that overlaid thick Lower Cambrian siliciclastics. The second Middle Cambrian succession is composed of oolitic grainstone, microbial boundstone, lime mudstone, and mixed carbonate-siliciclastic facies assemblages that developed on a platform. The second and third successions are separated by an unconformity that spanned most of the Steptoean. The third succession includes mixed carbonate-siliciclastic strata and spans the Sunwaptan Prosaukia Biozone to the Cordylodus proavus Biozone. This succession was terminated by the Cambrian–Ordovician unconformity. The shelf had a ramplike configuration during this time. The fourth succession starts above the Cambrian-Ordovician unconformity with a widespread shelf sandstone that spans the C. proavus to C. lindstromi Zones. This was followed by a rapid deepening in the earliest Ordovician (Iopetognathus fluctivagus Zone) marked by the deposition of open-marine carbonates. A progressive shallowing culminated in evaporite units in the Stairsian. A marked change in basin architecture occured during this fourth succession. Distinctive shelf-margin units appeared consisting of fenestral mudstone, shoal deposits, and common karst breccias. The shelf margin during this interval was very steep, and carbonate was not transported into the deep water. The platform also changed configuration during this time, with the development of an intraplat-formal basin. Evaporites accumulated in this silled basin. Strata in the intraplatformal basin are thicker than those at the shelf margin. The fifth succession (Tulean–Blackhillsian) consists of shallow subtidal carbonates.
The first two sequences in the Arctic Islands correspond closely to Sauk I and II elsewhere in Laurentia. Strata in the Arctic that are equivalent to the standard Sauk III supersequence contain three unconformity-bounded stratigraphic assemblages. This reflects local tectonic conditions that resulted from the change from a passive-margin setting in the Early Cambrian– earliest Ordovician to convergence later in the Early Ordovician. The downgoing slab, interpreted to be dipping below Laurentia, affected carbonate sedimentation along northwestern Laurentia during this time.
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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.