Publication Type:
Book ChapterSource:
Geological Society of America, 2000 annual meeting, Geological Society of America (GSA), Boulder, CO, United States, Volume 32, p.313 (2000)ISBN:
0016-7592Keywords:
algae, Anthozoa, Arctic region, Asia, Atlantic Ocean, Baltic region, Baltica, calcium carbonate, Canada, carbon dioxide, carbonate platforms, carbonate rocks, Chlorophyta, Cnidaria, Coelenterata, Commonwealth of Independent States, Devonian, Estonia, Europe, greenland, highstands, Hudson Bay, Iapetus, Invertebrata, Laurentia, limestone, microfossils, middle Paleozoic, North America, North Atlantic, Nunavut, paleoclimatology, Paleozoic, Plantae, Porifera, Reefs, Rhodophyta, sea-level changes, Sedimentary rocks, Siberia, Silurian, transgression, uplifts, Urals, Uzbekistan, Western Canada Sedimentary BasinAbstract:
A new global database shows reefs reached two peaks for size and distribution during the mid-Paleozoic global greenhouse, with pCO2 at 12x to 16x above present day, no glaciation and maximal sealevel highstands. During the mid-Silurian (Wenlock), carbonate platform and reef development centered primarily around the Laurentia-Baltica-Siberia plates, straddling the equator: 7 reef belts longer than 1300 km are known, with the longest on the eastern flanks of Baltica (the Uralian belt, Novaya Zemlya-S Urals, ca. 3000km); E Laurentia from Iowa to Gaspe, ca. 2500 km; Nunavut-Greenland 2400 km, southern Baltica, UK-Estonia, ca. 2100 km. Others were the Hudson Bay belt, central Siberia, and Tuva. Reefs declined from Late Silurian through Early Devonian time, relative to closing of the Iapetus, provinciality, uplift and tectonism. Reefs resurged with transgressive system highstands in the 12-15 myr Eifel-mid Givet interval, reaching a global Phanerozoic peak. Largest Devonian reef belts were in (1) the western Canada sedimentary basin, ca. 3200 km, Manitoba-NWT; (2) the N Urals to Central Asia (Uzbekistan), <3000 km; (3) flanking the Old Red continent, Devon Poland, 2100 km; (4) the northern fringes of Gondwana (Algeria-Morocco-Spain, France-Carnic alps-Slovakia) reaching to 45 degrees S and 2500km+; (5) NE Russia (the Kolyma-Chukot belt at c. 2200km, up to 60 degrees N; (6) Canadian Arctic (Banks-Ellesmere, ca. 1600 km); (7) central Siberia (Norilsk-Altai Sayan) for ca. 1500 km, and (8) S China (ca. 1300 km). Equatorial mid-Paleozoic reefs were dominated by calcitic tabulate and rugose corals, aragonitic stromatoporoid sponges, aragonitic green algae, and calcitic red algae and calcimicrobes, except in high latitudes where mudmound reefs favoured calcimicrobes. To permit such paradoxic high rates of skeletal accretion, under a super greenhouse with SSTs well above Holocene interglacial norms, photosymbiosis and O2 output was either far more efficient in calcite oceans, or calcite skeletal accretion was buffered biologically for high CO2 (most Devonian reefs are associated with primary, organic-rich limestones and appear to have been hypoxia tolerant), or high rates of CaCO3 production presented major sinks for surplus CO2.
Notes:
GeoRef, Copyright 2018, American Geological Institute.<br/>2003-046538
