Lawrence L. Sloss Cratonic Sequences
In the 1940's, Lawrence Sloss developed a stratigraphic model demonstrating a series of transgressions (rising sea level flooding the land) followed by regressions (falling sea level exposing land) that impacted North America. Transgressions were marked by a transgressive sedimentary sequence in which sandstones were overlain by marine shales and limestones. Regressions were marked by a return to terrestrial deposits and regional unconformities wherein sedimentary deposits were eroded away. Sloss designated names for each of the marine incursions. The Sauk sea invaded (flooding towards the center of the craon) North America in Early Cambrian and receded during the Late Cambrian and Early Ordovician (seas receded towards the margin of the craton). The Middle and Late Ordovician recorded the advance of the Tippecanoe seas.
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