Results 181 to 190 of about 29,816 (231)

Microbialite resurgence after the Late Ordovician extinction

Nature, 2004
Microbialites, including biogenic stromatolites, thrombolites and dendrolites, were formed by various microbial mats that trapped and bound sediments or formed the locus of mineral precipitation. Microbialites were common and diverse during the Proterozoic, but declined in abundance and morphological diversity when multicellular life diversified during
Peter M, Sheehan, Mark T, Harris
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Late Ordovician Tunnel Valleys

71st EAGE Conference and Exhibition - Workshops and Fieldtrips, 2009
Overdeepened incisions forming tunnel valleys are remarkable geomorphic elements, which provide valuable information on past subglacial hydrological regimes and may constitute attractive reservoir targets. Geometries and distribution of Quaternary tunnel valleys have been intensively illustrated based on geophysics, while the glacial record of pre ...
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Late Ordovician tunnel valleys in southern Jordan

Geological Society, London, Special Publications, 2012
Abstract The Upper Ordovician glacial record of southern Jordan (Ammar Fm.) essentially consists of palaeovalley infills and of a subordinate time-transgressive fluvial to shallow-marine succession overstepping both the palaeovalleys and interfluvial areas.
Douillet, G., Ghienne, Jean-François, Géraud, Yves, Abueladas, A., Diraison, Marc, Al-Zoubi, A.   +5 more
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Late Ordovician glaciation in southern Turkey

Terra Nova, 2003
ABSTRACT We present a new survey of several Palaeozoic sections in both the Taurus range and the Border Folds that documents typical glacial features including a glacial pavement and striated dropstones (Halevikdere Formation) and demonstrates the former presence of an ice sheet in southern and south‐eastern Turkey.
Monod, Olivier, Kozlu, H., Ghienne, J.-F., T. Dean, W., Günay, Y., Le Hérissé, Alain, Paris, Florentin, Robardet, M.   +7 more
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The Late Ordovician Mass Extinction

Annual Review of Earth and Planetary Sciences, 2001
▪ Abstract  Near the end of the Late Ordovician, in the first of five mass extinctions in the Phanerozoic, about 85% of marine species died. The cause was a brief glacial interval that produced two pulses of extinction. The first pulse was at the beginning of the glaciation, when sea-level decline drained epicontinental seaways, produced a harsh ...
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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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