Facies maps developed by William Krumbein, Lawrence Sloss, and Edward Dapples in the 1950s reflected areal lithologic change within stratigraphic units. From these maps it became obvious that stratigraphic intervals that contained major unconformities could not yield interpretable paleogeographic and tectonic patterns.

To understand regional patterns a new stratigraphic subdivision was required, and the term “sequence” was chosen. If regional patterns were to be understood, it became necessary to define stratigraphic intervals that did not include these unconformities. Sequences differed from the classic dual classification of rock and time-rock intervals, which included lithologic units of Group, Formation, and Member, and...

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