The Sauk sequence was the earliest of the six

cratonic sequence A cratonic sequence in geology is a very large-scale lithostratigraphic sequence in the rock record that represents a complete cycle of marine transgression and regression on a craton (block of continental crust) over geologic time. Cratonic se ...

s that have occurred during the Phanerozoic in North America. It was followed by the Tippecanoe,

Kaskaskia The Kaskaskia were one of the indigenous peoples of the Northeastern Woodlands. They were one of about a dozen cognate tribes that made up the Illiniwek Confederation, also called the Illinois Confederation. Their longstanding homeland was in ...

, Absaroka, Zuñi, and Tejas sequences. The sequence dates from the late Proterozoic through the early

Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. T ...

periods, though the

marine transgression A marine transgression is a geologic event during which sea level rises relative to the land and the shoreline moves toward higher ground, which results in flooding. Transgressions can be caused by the land sinking or by the ocean basins filling ...

did not begin in earnest until the middle Cambrian.Monroe, JS, and R Wicander (1997) ''The Changing Earth: Exploring Geology and Evolution,'' 2nd ed. Belmont: West Publishing Company, 1997. pp. 533–534 It is one of the most striking cratonic sequences in the geological record, spreading sheets of

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...

across basement rock deep into the interiors of many continents. The transgression took place rapidly, advancing over across the Grand Canyon region in less than five million years. 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 Transcontinental Arch refers to the islands of North America which extended from New Mexico to Minnesota and the Great Lakes region. These islands were present during the Sauk sequence, the earliest cratonic sequence. As a result of the Sauk ...

. The stratigraphy of the Sauk sequence indicates shallow-water deposition, primarily consisting of well-sorted sandstones and clastic

carbonate A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate ...

s. A marine regression ended the Sauk sequence early in the Ordovician, to be followed by the

Tippecanoe sequence The Tippecanoe sequence was the cratonic sequence--that is, the marine transgression--that followed the Sauk sequence; it extended from roughly the Middle Ordovician to the Early Devonian. Sedimentary characteristics After the regression of the ...

later in the period. The transgression is attributed to thermal subsidence following the breakup of the supercontinent of Rodinia, combined with a rise in global sea level due to climate change or shifts in global tectonics.

References

Proterozoic geology Cambrian North America Ordovician North America Ediacaran United States Cambrian United States Ordovician United States Ediacaran stratigraphic units of North America {{US-geology-stub