Sauk sequence
The Sauk sequence was the earliest of the six cratonic sequences that have occurred during the Phanerozoic (followed by the Tippecanoe, Kaskaskia, Absaroka, Zuñi, and Tejas). It dates from the late Proterozoic through the early Ordovician, though the marine transgression did not begin in earnest until the middle Cambrian.[1]
At its peak, most of North America was covered by the shallow Sauk Sea, save for parts of the Canadian Shield and the islands of the Transcontinental Arch. The stratigraphy of the Sauk sequence indicates shallow-water deposition, primarily consisting of well-sorted sandstones and clastic carbonates. A marine regression ended the Sauk sequence early in the Ordovician, to be followed by the Tippecanoe sequence later in the period.[1]