Silurian and Devonian Reefs: 80 Million Years of Global Greenhouse between two Ice Ages
Published:January 01, 2002
The Silurian-Devonian (mid-Paleozoic), a time of periodic, exceptional sea level highstands, vast epicontinental sea lanes, and global greenhouse climates well above Holocene norms, also identifies ihe ma ximal extent of Phanerozoic metazoan reef development and the acme of coral and sponge reef biodiversity Two peaks are identified for reef distribution, a mid-Silurian (Wenlock) maximum and a Mid- to Late Devonian (Eifel-Givet-middle Frasne) maximum, with reefs spread to latitudes as high as 45 lo 60 degrees, and major barrier-platform tropical reef belts stretched over more than 2000 km. Reef abundance broadly matched patterns of rise and fall in generic biodiversity for (he major cneiazoan reef builders (corals and stromatoporoids) and algae during this 80 million year episode. The mid-Paleosoic reef community originated in the Late Ordovician, taking over from the Cambro-Ordovician mud mound-dominated reef spectrum. It was only modestly affected by the glaciation-induced end-Ordovician(Hirnantian) mass extinction events Late Devonian reef extinction losses were initiated al the Givetian-Frasnian boundary by major declines in coral, stromatoporoid, and brachiopod bentliic components Reefs then experienced a second global expansion in the middle Frasnian, but with reduced faunal diversity. Catastrophic reef declines began in the late Frasnian rhenana conodont Zone and continued through the final lingurformis Zone, with events probably lasting ca.l Myr.Thecorat-stromatopofoid reef community was eliminated worldwide, with surviving patch reefs and reefalrnud mounds in ihe Famennian constructed by consortia of catcimicrobes, lifhisrid sponges, green and red algae, and foraminiferans. The surviving Famennian corals were primarily solitary, deep-water forms that played no major reef role. The last stramatoporoids died out within the Strunian praesuicata Zone, at the Devonian -Carboniferous boundary Widespread organic-rich carbonates of Civetian through Famennian age, normally taken as indicative of anoxia, do not show any correlation with local or global reef declines The Frasnian-Famennian extinction events foi reefs and reef faunas appear to have been second only to the end-Permian reef losses in terms of severity Metazoan reef extinction in the Late Devonian best parallels evidence for Famennian glaciarions, loss of reef accommodation space assealevels fell, 3nd increasing oxygenation of the atmosphere via the evolution of the first pteridophyte rainforests, forcing the terminal Famennian icehouse phases
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Phanerozoic Reef Patterns
Detecting patterns and processes of ecosystem evolution is among the main challenges of an integrated earth system science in the 21st century. The evolution of reefs reflects changes triggered by evolutionary innovations and variations in global and regional controls at different scales. The prime fossil record of Phanerozoic reefs offers the opportunity to trace these patterns through space and time. Phanerozoic Reef Patterns presents a comprehensive and up-to-date review on the history of reef building in the last 540 million years. A selection of internationally respected reef specialists presents a database on ancient reefs that is hardly available for any other ecosystem. The thoroughly documented patterns are analyzed with respect to global change, whose impact on living reefs is intensely discussed today. Phanerozoic Reef Patterns stands out from recent reviews on reef evolution by its careful qualitative and quantitative approach based on a comprehensive and multifaceted databank, by the strong focus on data, by a complete and unified coverage of the Phanerozoic from the Early Cambrian to the late Neogene, by emphasizing paleogeographic reef distributions presented on 32 newly developed color maps, and by a detailed index that makes the book a valuable research tool.