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 ?
The gold produced at Blackridge was mostly hosted in basal conglomerates of Permian-aged sedimentary basins which include the mined coal measures that unconformably overlie the Anakie metamorphic rocks of Middle Ordovician age and older.
The specimens were probably derived from the late Middle Ordovician (Darriwilian Stage) of the east Baltic area, although their exact collection localities are not known.
This study offers significant implications towards the features associated to the sedimentation pattern in the shallow skeleton-deficient sea during Furongian before the metazoan radiation of the Middle Ordovician.
The Aroostook-Matapedia proximal facies on the western flank of the Miramichi terrane demonstrates that there was an emergent Miramichi highland after Middle Ordovician deformation and prior to deposition of the Late Ordovician to Silurian intermediate and distal facies (E and F in Table 2; Fig.
For the Tahe Oilfield, the current main oil-gas production layer is the Middle Ordovician Yijianfang Formation and the Early Middle Ordovician Ying-shan Formation, and considerable previous works have been done on these layers [12-17].
The trace element sampling layer is the Lower Middle Ordovician Yingshan Formation ([O.sub.1-2y]), from which a total of 37 rock-seam and karst cave infill pieces were collected including 12 pieces of seam-hole bedrock (limestone), 12 pieces of mechanical sand-shale infills, 8 pieces of chemical calcite infills, and 5 pieces of karst cave in karst breccia (limestone breccia).
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.
(2013), the Pochico Formation probably corresponds to the Dapingian sequence sensu lato in the southern part of the Central-Iberian Zone in Spain, being in this case the Middle Ordovician in age (Bergstrom et al., 2009).
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.