Results 181 to 190 of about 7,297 (224)

Late Ordovician Reefs and the Biological Crisis at the Ordovician–Silurian Boundary

Stratigraphy and Geological Correlation, 2018
Reef formation in the Late Ordovician was relatively widespread in the Sandbian and Katian times. In the late Katian, it gradually reduced and ended in the Hirnantian, before the end of the Ordovician. In parallel, reef-building skeleton frame-building biota disappeared and was replaced with algae and calcimicrobes.
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Late Ordovician Jordanian Tunnel Valleys

71st EAGE Conference and Exhibition - Workshops and Fieldtrips, 2009
The Hirnantian (latest Ordovician, ~ 444 Ma) glacial advance on the Gondwana shelf succession is documented throughout the Arabian and North African regions with resulting tunnel valleys described for instance in Mauritania (Ghienne et Deynoux 1998) or Libya (Le Heron et al., 2004). Following the work of Abed et al. (1993), Powell et al.
G. Douillet, J. -F. Ghienne
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Trace Fossil Evidence for Late Ordovician Animals on Land

Science, 1987
Fossil burrows within newly recognized buried soils in the Late Ordovician Juniata Formation, near Potters Mills in central Pennsylvania, represent the oldest reported nonmarine trace fossils. They are thought to have been an original part of the soil because their greater density toward the top of the paleosols corresponds with mineralogical ...
G J, Retallack, C R, Feakes
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Conodont provinces and biofacies of the Late Ordovician

1984
R- and Q-mode cluster analysis of data on the occurrence and distribution of 43 conodont species enables delineation in North America of warm-water Red River and Ohio Valley provinces during the Late Ordovician Velicuspis Chron, and suggests recognition of six major biofacies that represent a continuum from nearshore, shallow-water biotopes with ...
Walter C. Sweet, Stig M. Bergström
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Central Appalachian Late Ordovician Communities

Geological Society of America Bulletin, 1969
The fossiliferous beds at the top of the Reedsville and Martinsburg Formations (Upper Ordovician) in the central Appalachians, including the classic Orthorhynchula Zone, provide one of the earliest known examples of a prolific nearshore, clastic-facies fauna that contains species of distinctly modern aspect. A study of the faunal associations and their
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Anomalous geomagnetic field during the late Ordovician

Nature, 1976
MEASUREMENTS of the Lower Palaeozoic magnetic field in the British Isles1 show that it changed from around D=355°, I=−50° to D=20°, I=−54° (corresponding to an apparent shift of the south palaeomagnetic pole from 0° W to 35 °W along the present Equator) between Ordovician and Devonian times. Following unpublished work by W. E. Tremlett and J. C. Briden,
C. THOMAS, J. C. BRIDEN
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Late Ordovician global warming—The Boda event

Geology, 2005
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.
Richard A. Fortey, L. Robin M. Cocks
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Aplacophoran traits in the late Ordovician septemchitonid polyplacophorans

Journal of Morphology
Abstract A sample of phosphatized, originally calcareous, mollusk shells from the Katian age uppermost Mójcza Limestone at its type locality yielded a few hundred polyplacophoran plates. The chelodids are very rare among them. Three septemchitonid species dominate.
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"Rules of Assembly" for Two Late Ordovician Communities

PALAIOS, 1986
The logic that organic communities are little more than collections of species thrown together as accidents of space and time somehow seems less convincing when viewed over long spans of geologic time. We suggest that the apparent chaos of individualism results more from the intrinsic design of short-term ecological surveys, and that weak competitive ...
Peter W. Bretsky, Susan M. Klofak
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The Late Ordovician Biogeochemical Carbon Cycle

2014
The isotopic composition of the carbonate carbon (δ13Ccarb) is one of the best tools for understanding the biogeochemical carbon cycle through Earth history. δ13Ccarb is also used to chemostratigraphically correlate coeval strata. This dissertation has three main foci that all utilize δ13Ccarb as the common data type.
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