Earliest known Carboniferous shallow-water reefs, Gudman Formation (Tn1b), Queensland, Australia: Implications for Late Devonian reef collapse and recovery

Abstract

The Phanerozoic history of reefs extensively has been considered a direct reflection of the history of skeletal reef-building organisms. However, such a relationship does not characterize global mid-Paleozoic reef history. The extinction of most reef-building stromatoporoids and corals at the Frasnian-Famennian boundary correlates with the collapse of North American and European stromatoporoid-dominated reefs, but Western Australian, Russian, and Chinese reefs were much less severely affected until the late Famennian, when algae, calcimicrobes, and nonskeletal microbialites (i.e., stromatolites, thrombolites) declined globally. Additionally, reef recovery was more rapid than previously thought. Small, early Tournaisian (Tn1b) shallow-water reefs in the Gudman Formation of eastern-central Queensland substantially reduce the duration of the “reefless lag time” following Late Devonian reef decline, essentially confining it to the Strunian. Gudman reefs are dominated by microbialite, but contain a diverse, although volumetrically insignificant, skeletal fauna and flora, including large colonial corals, bryozoans, crinoids, brachiopods, and calcareous algae. Hence, mid-Paleozoic reef collapse and recovery reflect an amalgam of more-or-less independent histories of skeletal organisms, calcimicrobes, and nonskeletal microbialites, in response to regional and global environmental parameters. A better understanding of mid-Paleozoic reef history will require detailed local- and regional-scale studies to isolate global from nonglobal signals.