The new chronostratigraphic classification of the Ordovician System and its relations to major regional series and stages and to δ13C chemostratigraphy
TL;DR: In this paper, a new global classification of the Ordovician System into three series and seven stages has been proposed, based on a variety of biostratigraphic data.
Abstract: The extensive work carried out during more than a decade by the International Subcommission on Ordovician Stratigraphy has resulted in a new global classification of the Ordovician System into three series and seven stages. Formal Global Boundary Stratotype Section and Points (GSSPs) for all stages have been selected and these and the new stage names have been ratified by the International Commission on Stratigraphy. Based on a variety of biostratigraphic data, these new units are correlated with chronostratigraphic series and stages in the standard regional classifications used in the UK, North America, Baltoscandia, Australia, China, Siberia and the Mediterranean-North Gondwana region. Furthermore, based mainly on graptolite and conodont zones, the Ordovician is subdivided into 20 stage slices (SS) that have potential for precise correlations in both carbonate and shale facies. The new chronostratigraphic scheme is also tied to a new composite δ13C curve through the entire Ordovician.
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TL;DR: The authors reviewed the relationships of the three major biotic events to chemical and physical processes occurring in the ocean and atmosphere during the Ordovician and Silurian, including sea-level changes, geochemical proxies (δ13C, δ18O, 87Sr/86Sr) of the ocean waters, and the evolution of the atmosphere (oxygen and carbon dioxide content).
315 citations
TL;DR: The "great Ordovician Biodiversification Event" (GOBE) as mentioned in this paper was a spectacular increase in marine biodiversity at all taxonomic levels largely within the phyla established much earlier during the so-called Cambrian Explosion.
276 citations
01 Jan 2012
TL;DR: A prolonged "hot-house" climate through Early Ordovician, cooling through Middle Ordovian and changing to ''ice-house'' conditions in Late Ordovicians, global glaciation, oceanic turnover and mass extinction at end of period, strong fluctuations in eustatic sea level, appearance and diversification of pandemic planktonic graptolites and conodonts important for correlation, moderate to strong benthic faunal provincialism, re-organization and rapid migration of tectonic plates surrounding the Iapetus Ocean and migration of
Abstract: Rapid and sustained biotic diversification reached its highest levels in the Paleozoic. A prolonged “hot-house” climate through Early Ordovician, cooling through Middle Ordovician and changing to “ice-house” conditions in Late Ordovician, global glaciation, oceanic turnover and mass extinction at end of period, strong fluctuations in eustatic sea level, appearance and diversification of pandemic planktonic graptolites and conodonts important for correlation, moderate to strong benthic faunal provincialism, re-organization and rapid migration of tectonic plates surrounding the Iapetus Ocean and migration of the South Pole from North Africa to central Africa all characterize the Ordovician Period. All seven Ordovician stages have formalized GSSPs.
232 citations
TL;DR: In this paper, Nitrogen isotope data show that the regions of oceanic anoxia were marked by intense water column denitrification in which cyanobacteria were the principal source of fixed N.
Abstract: The Late Ordovician (Katian-Hirnantian) through earliest Silurian (Rhuddanian) interval was a time of varying climate and sea level, marked by a peak glacial episode in the early-mid-Hirnantian. Synthesis of recently published data permits global correlation of at least two cycles of glacial advance and retreat with a distinct interglacial period that is recognizable in sequence-stratigraphic and chemostratigraphic records in many parts of the world. A period of warming and sea-level rise during the late Katian is marked by the widespread occurrences of oceanic anoxia in paleotropical and subtropical localities, mostly confined to regions of inferred upwelling and semirestricted marine basins. Nitrogen isotope data show that the regions of oceanic anoxia were marked by intense water-column denitrification in which cyanobacteria were the principal source of fixed N. In the overlying peak glacial interval of the Hirnantian, sedimentary successions from localities representing a wide range of water depths and paleolatitudes indicate that anoxia was restricted during the early-mid-Hirnantian. The shift to more positive N isotope values also suggests less intense water-column denitrification. In the overlying late Hirnantian and early Rhuddanian, the distribution of black shales reaches its greatest extent in the studied interval. Localities showing evidence of anoxia are globally spread over all paleolatitudes and water depths for which data are available, indicating a Rhuddanian ocean anoxic event comparable to examples from the Mesozoic. It is accompanied by a return to intensely denitrifying conditions within the water column, as indicated by the shift to negative N isotope values. The two phases of Hirnantian mass extinction coincide with rapid, climate-driven changes in oceanic anoxia. The first extinction occurred at the onset of glaciation and with the loss of anoxic conditions at the end of the Katian. The second extinction occurred at the demise of glaciation and coincided with the return of anoxic conditions during the late Hirnantian–early Rhuddanian. Integration of our N isotope data with graptolite biodiversity records suggests that the extinctions were profoundly influenced by changes occurring at the base of the marine food web, i.e., redox-driven changes in nutrient cycling and primary producer communities.
223 citations
TL;DR: In this article, the authors test the recent suggestion that OA leads not only to declining calcification of reef corals and reduced growth rates of reefs but may also have been a trigger of ancient reef crises and mass extinctions in the sea.
Abstract: Anthropogenic rise in the carbon dioxide concentration in the atmosphere leads to global warming and acidification of the oceans. Ocean acidification (OA) is harmful to many organisms but especially to those that build massive skeletons of calcium carbonate, such as reef corals. Here, we test the recent suggestion that OA leads not only to declining calcification of reef corals and reduced growth rates of reefs but may also have been a trigger of ancient reef crises and mass extinctions in the sea. We analyse the fossil record of biogenic reefs and marine organisms to (1) assess the timing and intensity of ancient reef crises, (2) check which reef crises were concurrent with inferred pulses of carbon dioxide concentrations and (3) evaluate the correlation between reef crises and mass extinctions and their selectivity in terms of inferred physiological buffering. We conclude that four of five global metazoan reef crises in the last 500 Myr were probably at least partially governed by OA and rapid global warming. However, only two of the big five mass extinctions show geological evidence of OA.
212 citations
Cites background from "The new chronostratigraphic classif..."
...…of 6.5 Myr duration (see supporting information Table S1), whereas extinction rates had to be analysed on a somewhat coarser subset of 77 stages (7.0 Myr mean duration), mostly because the recent updates to the Ordovician time scale (Bergström et al., 2009) are not yet implemented in the PaleoDB....
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References
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TL;DR: In this article, an integrated δ13C and sequence stratigraphic analysis in Nevada is presented, showing that in the Late Ordovician Chatfieldian Stage (mid-Caradoc) a positive δ 13C excursion in the upper part of the Copenhagen Formation was closely followed by a regressive event evidenced within the prominent Eureka Quartzite.
Abstract: The timing and causes of the transition to an icehouse climate in the Late Ordovician are controversial. Results of an integrated δ13C and sequence stratigraphic analysis in Nevada show that in the Late Ordovician Chatfieldian Stage (mid-Caradoc) a positive δ13C excursion in the upper part of the Copenhagen Formation was closely followed by a regressive event evidenced within the prominent Eureka Quartzite. The Chatfieldian δ13C excursion is known globally and interpreted to record enhanced organic carbon burial, which lowered atmospheric p CO2 to levels near the threshold for ice buildup in the Ordovician greenhouse climate. The subsequent regressive event in central Nevada, previously interpreted as part of a regional tectonic adjustment, is here attributed in part to sea-level drawdown from the initiation of continental glaciation on Gondwana. This drop in sea level—which may have contributed to further cooling through a reduction in poleward heat transport and a lowering of p CO2 by suppressing shelf-carbonate production—signals the transition to a Late Ordovician icehouse climate ∼10 m.y. before the widespread Hirnantian glacial maximum at the end of the Ordovician.
297 citations
"The new chronostratigraphic classif..." refers background in this paper
...One example of this is the apparent absence in the Great Basin ( Saltzman & Young 2005 ) of the distinctive Mid-Darriwilian excursion recognized in Baltoscandia (Kaljo " # % 1 . 2007)....
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...More recently published ! 13C curves, which are based on extensive data sets and covering large parts of the Ordovician, have been published by Buggisch " # % 1 . (2003) and Saltzman & Young (2005) ....
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01 Jan 2012
TL;DR: A prolonged "hot-house" climate through Early Ordovician, cooling through Middle Ordovian and changing to ''ice-house'' conditions in Late Ordovicians, global glaciation, oceanic turnover and mass extinction at end of period, strong fluctuations in eustatic sea level, appearance and diversification of pandemic planktonic graptolites and conodonts important for correlation, moderate to strong benthic faunal provincialism, re-organization and rapid migration of tectonic plates surrounding the Iapetus Ocean and migration of
Abstract: Rapid and sustained biotic diversification reached its highest levels in the Paleozoic. A prolonged “hot-house” climate through Early Ordovician, cooling through Middle Ordovician and changing to “ice-house” conditions in Late Ordovician, global glaciation, oceanic turnover and mass extinction at end of period, strong fluctuations in eustatic sea level, appearance and diversification of pandemic planktonic graptolites and conodonts important for correlation, moderate to strong benthic faunal provincialism, re-organization and rapid migration of tectonic plates surrounding the Iapetus Ocean and migration of the South Pole from North Africa to central Africa all characterize the Ordovician Period. All seven Ordovician stages have formalized GSSPs.
232 citations
TL;DR: In this paper, a formal biozonation for the Ordovician chitinozoans of the Northern Gondwana Domain is proposed based on the study of several thousand assemblages recovered from closely spaced samples (both outcrop and subsurface material).
207 citations
"The new chronostratigraphic classif..." refers background in this paper
...The North Gondwanan chitinozoan zonation (Paris 1990) is useful for correlation with other regions, and sporadic occurrences of graptolites and shelly faunas of Baltic or Avalonian affinities (GutiérrezMarco et al ....
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TL;DR: There is substantial evidence for mid-Ashgillian global warming before the latest Ordovician Hirnantian glaciation, as shown by the movement of previously lower latitude benthic faunas such as trilobites and brachiopods to progressively higher latitudes and by an increase in endemic taxa at low latitudes.
Abstract: There is substantial evidence for mid-Ashgillian global warming before the latest Ordovician Hirnantian glaciation, as shown by the movement of previously lower latitude benthic faunas such as trilobites and brachiopods to progressively higher latitudes and by an increase in endemic faunas at low latitudes. This is shown by faunal dynamics on several paleocontinents and endorsed by published evidence of warmer-water sediments from Gondwana and elsewhere. We term this global warming the Boda event.
204 citations
"The new chronostratigraphic classif..." refers background in this paper
...A brief global amelioration, with a decrease of latitudinal temperature differences (the Boda Event of Fortey & Cocks 2005 ), resulted in the deposition of mudstones and conodont-bearing shelf limestones (Bergstrom & Massa 1992) in regions close to the South Pole....
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