Middle Ordovician


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Middle Ordovician

[′mid·əl ‚ȯr·də′vish·ən]
(geology)
The geologic epoch occurring between the Upper and Lower Ordovician, beginning approximately 460,000,000 years ago.
References in periodicals archive ?
Both specimens of the genus Colpocoryphe were recently collected at two localities situated in the lower levels of the Middle Ordovician Sarka Formation (Darriwilian = Oretanian Regional Stage; see Fig.
The main source for the "Brown" or "Brady" sand is the Upper Cambrian Hickory Member of the Riley Formation in central Texas, Additional secondary frac sand sources include the Middle Ordovician Oil Creek Formation in Oklahoma, Sand deposits that are less suitable as frac sand, such as the Pliocene Bidahochi Formation in Arizona and the modern Loup River sands of Nebraska, are also being used in the proppant industry, As the demand for frac sand increases, new sources are being sought that may become economic with changes in technology and physical standards, despite their currently lower quality.
The term was coined in 1980 to indicate the system of carbonates and related shallow-water siliciclastics that were deposited on and around the Laurentian continent--the northern fragment as Pangaea broke up--during the Cambrian, Early Ordovician, and earliest Middle Ordovician nearly 500 million years ago.
The occurrence of kukersite interlayers within limestone deposits increases in the Middle Ordovician Uhaku Stage.
They point out that between the Early and Middle Ordovician, there was an unprecedented increase in marine life diversity (species, genus and family levels).
The target was composed of the stratified sedimentary cover comprising (from the top) bedded Upper and Middle Ordovician limestone (up to 20 m thick), Lower Ordovician Dictyonema shale (argillite with an admixture of organic matter, about 2 m thick), and an up to 200 m thick layer of Lower Ordovician to uppermost Vendian sand, silt, and some clay, which covered the Precambrian basement consisting of granites, gneisses, amphibolites, and other crystalline rocks.
Cumming noted that Orthambonites is Lower to Middle Ordovician.
Oxygen isotopic ratios in Middle Ordovician and Mississippian carbonates are within the range of secular variations in temperature reported in the literature for these age rocks.
Starting in late Precambrian time, this biological blast extended into the middle Ordovician period.
Over 52 named pay horizons ranging in age from the middle Ordovician to Pennsylvanian produce commercial quantities of oil.
Traditionally the Viru Series has been considered to be synonymous with Middle Ordovician [e.