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Persistent oceanic anoxia and elevated extinction rates separate the Cambrian and Ordovician radiations

Matthew R. Saltzman, Cole T. Edwards, Jonathan M. Adrain and Stephen R. Westrop
Persistent oceanic anoxia and elevated extinction rates separate the Cambrian and Ordovician radiations
Geology (Boulder) (July 2015) 43 (9): 807-810

Abstract

Recurrent mass extinction events (at "biomere"-a biostratigraphic unit-boundaries) characterize the middle Cambrian to Early Ordovician (Tremadocian) time interval that is between the major Cambrian and Ordovician radiations of animal life. A role for anoxia in maintaining elevated extinction rates in the late Cambrian has been proposed based on coincidence of an extinction with positive excursions in delta (super 13) C (sub carb) and delta (super 34) S (sub CAS) (CAS-carbonate-associated sulfate). Here we examine an Early Ordovician extinction event at the base of the North American Stairsian Stage (upper Tremadocian), and demonstrate concurrent onset of positive excursions in delta (super 13) C and delta (super 34) S inferred to reflect enhanced organic matter burial under anoxic waters. Sea-level rise may have brought anoxic waters onto the shelf to initiate extinctions. The evidence for delta (super 13) C excursions and elevated extinction rates appears to wane in the Tremadocian, consistent with progressive oxygenation of the oceans reaching a threshold that helped facilitate initial stages of the Great Ordovician Biodiversification Event.


ISSN: 0091-7613
EISSN: 1943-2682
Coden: GLGYBA
Serial Title: Geology (Boulder)
Serial Volume: 43
Serial Issue: 9
Title: Persistent oceanic anoxia and elevated extinction rates separate the Cambrian and Ordovician radiations
Affiliation: Ohio State University, School of Earth Sciences, Columbus, OH, United States
Pages: 807-810
Published: 20150728
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 35
Accession Number: 2015-079077
Categories: Stratigraphy
Document Type: Serial
Bibliographic Level: Analytic
Annotation: GSA Data Repository item 2015274
Illustration Description: illus.
Secondary Affiliation: University of Iowa, USA, United StatesUniversity of Oklahoma, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2022, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201534
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