Overview of Lower Cambrian Mixed Carbonate-siliciclastic Deposition along the Western Laurentian Passive Margin
Michael C. Pope, John Stewart Hollingsworth, Kelly Dilliard, 2012. "Overview of Lower Cambrian Mixed Carbonate-siliciclastic Deposition along the Western Laurentian Passive Margin", 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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The Lower Cambrian (Waucoban Series; Fallotaspis–Olenellus Biozone) carbonate-siliciclastic units of western Laurentia outcrop from Sonora, Mexico, to western Nevada, and from northeastern Washington to east-central Alaska. The allochthonous Cassiar terrane in northwestern British Columbia was originally deposited between these two segments, forming a widespread large carbonate platform along this margin during the initial Paleozoic flooding (basal Sauk megasequence) of North America.
The Lower Cambrian carbonate-siliciclastic units of western Laurentia commonly are subdivided into two second-order or composite third-order depositional sequences. The lowstand systems tracts to these sequences commonly are marine siliciclastics that grade upward into transgressive systems tracts composed of interbedded shaly carbonates or carbonate-rich shales that grade upward into carbonate-dominated highstand systems tracts. The carbonates commonly record deposition on a gently sloping ramp; however, areas of localized syndepositional extensional faulting created locally faulted carbonate margins. Large allochthonous blocks of shallow-water carbonates and siliciclastics were deposited basinward of these active fault zones.
The facies of the western Laurentian Lower Cambrian carbonate ramps, arranged from land toward the basin, are fluvial nearshore siliciclastics, carbonate tidal flats, mixed carbonate-siliciclastic lagoons, high-energy ooid grainstone shoals containing or surrounded by algal-archaeocyathan mounds, downslope nodular facies, and interbedded calcisiltite and shale deposited below a fair-weather wave base. The algal-archaeocyathan mounds constructed small isolated biostromes (<90 m [<295 ft] thick), not large continuous reefs. The continuity of the ooid grainstone shoals along the western Laurentian margin indicates that they formed a barrier separating restricted facies to the east from open-marine facies to the west that stretched from present-day east-central Alaska to northwestern Mexico.
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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.
- biogenic structures
- British Columbia
- carbonate banks
- carbonate platforms
- carbonate rocks
- Lower Cambrian
- North America
- Northwest Territories
- passive margins
- plate tectonics
- Sauk Sequence
- sedimentary rocks
- sedimentary structures
- sequence stratigraphy
- Sonora Mexico
- United States
- Western Canada
- Yukon Territory
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