
Geology Faculty Publications
Document Type
Article
Publication Date
2010
Publication Source
The Ordovician Earth System
Abstract
The Katian Age (early Late Ordovician) was a time of significant decline in marine biodiversity, but whether this decline was a real phenomenon or an artifact of the relatively few studies devoted to this interval requires further research. We examined the pattern of graptolite faunal changes across the boundary between the Climacograptus bicornis and Diplacanthograptus caudatus graptolite zones in North America and on several other continents.
A sharp decline in species diversity occurs in the Appalachian Basin. Scores for normalized diversity dropped from 20 in the C. bicornis Zone to 7 in the D. caudatus Zone. Only 11% of the species present in the C. bicornis Zone carry over into the D. caudatus Zone. A similar pattern occurs in central Oklahoma. Regions at higher paleolatitude, such as Wales and Baltoscandia, exhibit low graptolite diversity in lower Katian strata, and then diversity declines further in higher strata. In other regions at low paleolatitude, such as Australasia and Scotland, however, diversity is fairly constant across this interval (although the percentage of carryover taxa remains low).
We conclude that seawater temperature change or disruption of the oceanic density structure, which might accompany temperature change, provides explanations for the similarity between Laurentian and higher paleolatitude diversity patterns. Flooding of the Laurentian craton through the Sebree Trough by cool, subpolar Iapetus seawater may have adversely affected graptolite diversity there. Regions at high paleolatitudes likely underwent cooling associated with Katian climate deterioration. Thus seawater cooling, albeit driven by different mechanisms, may have produced similar diversity patterns at different paleolatitudes.
Inclusive pages
149-161
ISBN/ISSN
0072-1077
Document Version
Published Version
Copyright
Copyright © 2010, Geological Society of America. The document available for download is provided with the permission of the publisher.
Publisher
Geological Society of America
Volume
466
Peer Reviewed
yes
eCommons Citation
Goldman, Daniel and Wu, Shuang-Ye, "Paleogeographic, Paleoceanographic, and Tectonic Controls on Early Late Ordovician Graptolite Diversity Patterns" (2010). Geology Faculty Publications. 1.
https://ecommons.udayton.edu/geo_fac_pub/1
Included in
Geology Commons, Hydrology Commons, Oceanography and Atmospheric Sciences and Meteorology Commons, Other Earth Sciences Commons
Comments
Permission documentation is on file.
Source: The Ordovician Earth System, S.C. Finney and W.B.N. Berry eds. Geological Society of America Special Papers 466 (2010).