Abstract

The temporally extensive late Middle through Late Devonian biotic crisis involved at least three distinct peaks of elevated extinction intensity during an interval spanning ∼25 myr and resulted in the preferential elimination of certain shallow-marine, warm-water taxa, especially members of reef communities. By the end of the second peak, delimited by the Frasnian–Famennian (F–F) boundary, the stromatoporoids, members of the dominant constructor guild in mid-Paleozoic reefal ecosystems, had ceased building reefs in most parts of the world. The northern Dugway Range in west-central Utah, United States, however, represents one of the few locations globally where stromatoporoids continued reef building into the Famennian. Two measured sections there, which are constrained biostratigraphically using conodonts, indicate that the biohermal sequences occur within the middle Palmatolepis crepida biozone and are early Famennian in age. The post-F–F extinction Dugway reefal faunas are depauperate and dominated by labechiid and stylostromid stromatoporoids, as is characteristic of other early Famennian reefs. In this region, evidence for reefal development is episodic, with stromatoporoid-bearing units interbedded with peloidal and coated-grain carbonate units lacking evidence of reef construction. The stromatoporoid survivors, although fairly minor constituents of Frasnian reef communities, belong to long-ranging clades and may represent so-called extinction-resistant taxa that flourished, albeit locally in Laurentia, following the F–F mass extinction.

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