Chapter 6: The cyclothemic concept in the Illinois Basin: A review
Ralph L. Langenheim, Jr., W. John Nelson, 1992. "Chapter 6: The cyclothemic concept in the Illinois Basin: A review", Eustasy: The Historical Ups and Downs of a Major Geological Concept, Robert H. Dott, Jr.
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Although earlier workers had noted Carboniferous sedimentary cycles in passing, the Illinois geologists J. A. Udden, J. Marvin Weller, and Harold Wanless in 1912 to 1932 were the First to explicitly describe and explain these cycles. They demonstrated that Pennsylvanian rocks of the North American craton are characterized by thin cyclically repeated sequences of both marine and nonmarine rock. To explain the phenomenon, Udden proposed periodic subsidence and basin-filling, Weller advocated diastrophic uplift and depression, and Wanless and Shepard advanced the notion of eustatic sea-level changes caused by waxing and waning of glaciers in Gondwanaland.
The cyclothemic concept in the Illinois Basin was established on outcrop data from the basin margins. The concept developed as abundant subsurface data from the deep basin became available. From the 1930s through the 1950s, cyclothems were widely mapped, and attempts were made to extend cyclothems into many other regions and facies.
Enthusiasm for cyclothems declined in the mid-1950s through the 1970s, as cyclothems were relegated to informal usage in stratigraphic codes, and viewed by some as purely local products of delta shifting. More recently, interest in cyclothems has revived. Their lateral continuity and contemporaneity with Gondwana glaciations now are widely, if not universally, accepted. After several decades of neglect, the idea of glacially driven eustasy has returned as a favored explanation for the cyclothemic phenomenon.