Flint (probably the Obryan Chert, Middle Pennsylvanian; Vinton County, Ohio, USA) 15 : 無料・フリー素材/写真
Flint (probably the Obryan Chert, Middle Pennsylvanian; Vinton County, Ohio, USA) 15 / James St. John
| ライセンス | クリエイティブ・コモンズ 表示 2.1 |
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| 説明 | Flint from the Pennsylvanian of Ohio, USA.Flint is the state gemstone of Ohio. "Flint" is sometimes used as a lithologic term by modern geologists, but it is a synonym for chert. Flint and chert are the same - they are cryptocrystalline, quartzose sedimentary rocks. Rockhounds often assert that flint is high-quality while chert is low-quality. Some geologists assert that "flint" implies a biogenic origin and "chert" implies a chemical origin.Many cherts do have a chemical origin - chert nodules are moderately common in some limestone units. The nodules form during diagenesis - pre-existing silica components in the carbonate sediments are dissolved, mobilized, and reprecipitated as chert masses. Some cherts do have a biogenic origin - for example, radiolarian cherts (rich in radiolarian microfossils) or spicular cherts (rich in siliceous sponge spicules). Some Pennsylvanian-aged cherts in eastern America are inferred to be recrystallized from quartzose eolian dust deposits (glacial loess?) on ancient seafloors.Stratigraphy: probably the Obryan Chert, Allegheny Group, Middle Pennsylvanian [Note: the photo of this sample was previously posted and identified as "Vanport Flint", an Allegheny Group unit in the Flint Ridge area of Ohio. In the early 20th century, an Allegheny Group limestone and accompanying chert / flint horizon in southern Ohio was identified as Vanport, or "southern Vanport". Correlation studies have since shown that "southern Vanport" is not the same as the Vanport Flint at Flint Ridge. "Southern Vanport" is now referred to as the Obryan Limestone and, when cherty or flinty, the Obryan Chert.]Locality: attributed to Vinton County, southeastern Ohio, USA-------------------------References on the Obryan:Rice et al. (1994) - Regional aspects of Pottsville and Allegheny stratigraphy and depositional environments, Ohio and Kentucky. United States Geological Survey Open-File Report 92-558. 67 pp. [The Obryan is mentioned on pp. 24 and 43.] (pubs.usgs.gov/of/1992/0558/report.pdf)Murphy (2009) - Obryan Chert: an overlooked and misunderstood lithic resource. Ohio Archaeologist 59(1): 28-31. (kb.osu.edu/server/api/core/bitstreams/616a675d-b519-5077-...) |
| 撮影日 | 2024-09-05 18:08:06 |
| 撮影者 | James St. John |
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