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Author: Seth Allen Young
Publisher:
ISBN:
Category :
Languages : en
Pages : 236
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Author: Seth Allen Young
Publisher:
ISBN:
Category :
Languages : en
Pages : 236
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Author: Dennis R. Kolata
Publisher: Geological Society of America
ISBN: 0813723132
Category : Science
Languages : en
Pages : 94
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Author: Stanley Charles Finney
Publisher: Geological Society of America
ISBN: 081372466X
Category : Science
Languages : en
Pages : 204
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"The Ordovician period is a significant chapter in Earth's history that included the great Mid-Ordovician biodiversification event, the Hirnantian glaciation, and long-term greenhouse conditions. Ordovician rocks are widespread on most continents and the recent finalization of a modern chronostratigraphic classification of the Ordovician system now facilitates high-resolution correlations that allow for integrated multidisciplinary research. The diverse papers comprising this volume address orogenesis, paleogeography, climate modeling, sedimentation, biodiversity, and isotopic excursions; together they promote an integrated view of the Ordovician earth system."--Publisher's description.
Author: Seth Allen Young
Publisher:
ISBN:
Category : Carbon
Languages : en
Pages :
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Abstract: The latest Ordovician (444 million years ago) was a critical period in Earth history. This was a time of significant climatic global change with large-scale continental glaciation. Moreover, the end-Ordovician mass extinction is recognized as the secondmost devastating mass extinction to have affected the Earth. The anomalous Late Ordovician icehouse period has perplexed many researchers because all previous model and proxy climate evidence suggest high levels of atmospheric CO2 during the Late Ordovician glaciation. Also associated with this period is a large positive carbon isotope ([delta]13C) excursion (up to +7%) that represents a global perturbation of the carbon cycle. Additionally, a large decrease (0.001) in seawater 87Sr/ 86Sr occurs several million years prior (~460 million years ago); this could reflect an increase in atmospheric CO2 uptake due to weathering of volcanic rocks involved in uplift of the early Appalachian Mountains. To address these Ordovician anomalies, well-studied, thick, and continuous Late Ordovician limestone sequences from eastern West Virginia, south-central Oklahoma, central Nevada, Quebec (Canada), Estonia, and China have been sampled. Carbon and strontium isotopic ratios have been measured on samples from these localities of which Estonian and Chinese sample sites represent separate paleocontinents (Baltica and South China) and are compared with other data sets from North America. These data test previous interpretations that the well-documented latest Ordovician carbon isotope excursion coincides with maximum glaciation. They support a hypothesis that the large positive carbonate carbon isotope excursion was coincident with a warm interglacial (high CO2 levels) period that separated two major glacial advances (with lowered CO2 levels). There are clear parallels between the Late Ordovician and the Late Cenozoic (the most recent) greenhouse to icehouse transitions, with silicate weathering providing the initiator and positive feedback on changes in atmospheric CO2 levels. The results lead to a more complete understanding of climatic and biotic events of this critical interval, which will certainly help the understanding of the period of global climatic and biotic change affecting Earth today.
Author: Brian J. Witzke
Publisher: Geological Society of America
ISBN: 081372306X
Category : Science
Languages : en
Pages : 453
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Author: Stanley Charles Finney
Publisher:
ISBN: 9780813724669
Category : Science
Languages : en
Pages : 208
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"The Ordovician period is a significant chapter in Earth's history that included the great Mid-Ordovician biodiversification event, the Hirnantian glaciation, and long-term greenhouse conditions. Ordovician rocks are widespread on most continents and the recent finalization of a modern chronostratigraphic classification of the Ordovician system now facilitates high-resolution correlations that allow for integrated multidisciplinary research. The diverse papers comprising this volume address orogenesis, paleogeography, climate modeling, sedimentation, biodiversity, and isotopic excursions; together they promote an integrated view of the Ordovician earth system."--Publisher's description.
Author: Barry D. Webby
Publisher: Columbia University Press
ISBN: 0231501633
Category : Science
Languages : en
Pages : 497
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Book Description
Two of the greatest evolutionary events in the history of life on Earth occurred during Early Paleozoic time. The first was the Cambrian explosion of skeletonized marine animals about 540 million years ago. The second was the "Great Ordovician Biodiversification Event," which is the focus of this book. During the 46-million-year Ordovician Period (489–443 m.y.), a bewildering array of adaptive radiations of "Paleozoic- and Modern-type" biotas appeared in marine habitats, the first animals (arthropods) walked on land, and the first non-vascular bryophyte-like plants (based on their cryptospore record) colonized terrestrial areas with damp environments. This book represents a compilation by a large team of Ordovician specialists from around the world, who have enthusiastically cooperated to produce this first globally orientated, internationally sponsored IGCP (International Geological Correlation Program) project on Ordovician biotas. The major part is an assembly of genus- and species-level diversity data for the many Ordovician fossil groups. The book also presents an evaluation of how each group diversified through Ordovician time, with assessments of patterns of change and rates of origination and extinction. As such, it will become the standard work and data source for biotic studies on the Ordovician Period.
Author: James D. Miller
Publisher: Geological Society of America
ISBN: 0813700248
Category : Science
Languages : en
Pages : 593
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Author: Page Quinton
Publisher:
ISBN:
Category :
Languages : en
Pages : 164
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The Ordovician Period (483 -- 443 Ma) is an attractive interval to study for understanding the earth's climatic system because of the juxtaposition of climatic extremes. The Period is marked by major shifts in climatic conditions, increases in marine biodiversity (GOBE: Great Ordovician Biodiversification event), and the 2nd largest mass extinction event of the Phanerozoic. Uncertainty regarding the evolution of the Ordovician climate, however, complicates attempts to relate climatic and paleontological changes to various climatic forcing's (e.g. atmospheric CO2, tectonics, ocean circulation). This project was designed to test competing models for the evolution of Ordovician climate using stable oxygen and carbon isotopic measurements from North America and Australia. I measured carbon isotopic values from carbonates and trace organic matter to provide a record of fluctuations in the carbon cycle and used oxygen isotopic values measured from bioapatite (conodont elements and brachiopod shells) to infer trends in sea surface temperatures and test for climatic cooling during the Ordovician. Samples discussed come from seven sections in eastern North America and seven sections from New South Wales, Australia, coverage that allow for consideration of local, regional, and global influences on geochemical records. From these results I conclude that measured trends primarily reflect global to regional paleoenvironmental patterns. As such, these results improve knowledge of the evolution of the Ordovician climate. Carbon isotopic results are consistent with a drawdown of atmospheric CO2 during the early Late Ordovician; however, the lack of evidence for associated cooling at the same time suggests that any changes were not large enough to cause resolvable climatic cooling. Instead, oxygen isotopic results suggest that the climatic cooling and glaciation was confined to the last stage of the Ordovician (Hirnantian). Finally, inferred cooling in the Early to Middle Ordovician strengthens arguments that climate played an important role in the Great Ordovician Biodiversification event.
Author:
Publisher:
ISBN:
Category : Geology
Languages : en
Pages : 568
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