A.G. FISCHER’S “CYCLOMANIA”: PHANEROZOIC LONG-PERIOD CYCLES

Alfred G. Fischer was a broad, innovative, original thinker—paleontologist, stratigrapher, sedimentologist. He is recognized for his important contributions to understanding global biotic diversity and paleobiogeography, carbonate buildups, patterns of coastal sedimentation and sea level variations, paleomagnetism in pelagic sedimentary rocks, and the record of cyclicity in ancient strata influenced by Earth’s orbital periodicity. His students benefitted from his broad view of the stratigraphic record and globally extensive fieldwork, including early experiences in industry and the Deep Sea Drilling Project, as well as from his inquisitive and speculative nature—always grounded in his knowledge of the literature, interactions with colleagues and international scientists, and his own experiences in the field. He provided sage guidance in research, but was quite willing to give us ample room to pursue our own research interests, providing critical insights.

One of Al Fischer’s more speculative and controversial ideas was a proposed 32-m.y. periodicity in Phanerozoic marine biotic diversity, climate, and ocean chemical/environmental changes. This idea was first outlined in a paper (with me as coauthor) in 1977, and was later explored in several published papers from 1981 through 1986. His thesis was that the 32-m.y. marine diversity cycles (also termed “greenhouse-icehouse" cycles in Al’s parlance) were superimposed over the two long Phanerozoic “super-cycles” and that all were forced by global climatic variations--perhaps the result of episodic volcanism. In this thinking, he was certainly influenced by his earlier reading of treatises by Umbgrove (1949) and Grabau (1940). However, the proposed 32 m.y. periodicity has so far not been supported by later work although other periodicities from 26 m.y. to 36 m.y., and even 62 m.y. have been proposed more recently.