File:Soft clay capping a flint meganodule (Vanport Flint, Middle Pennsylvanian; Nethers Flint Quarries, Flint Ridge, Ohio, USA) 1 (30419933454).jpg
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[edit]DescriptionSoft clay capping a flint meganodule (Vanport Flint, Middle Pennsylvanian; Nethers Flint Quarries, Flint Ridge, Ohio, USA) 1 (30419933454).jpg |
Clay capping a large chert nodule ("flint") in the Pennsylvanian of Ohio, USA. (geology hammer for scale) Flint is the "official" state gemstone of Ohio (actually, there's no such thing as "official" anything). "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). The most famous flint deposit in Ohio is Flint Ridge, in Licking County. At this locality, the Middle Pennsylvanian-aged Vanport Flint is exposed in several places. The geologic literature on the Vanport Flint is relatively sparse, with inaccurate, incomplete descriptions and characterizations. For example, the literature describes the Vanport as a sheet of flint at Flint Ridge - it's actually a meganodule horizon. Other descriptions refer to the chert as the remains of siliceous sponges. In reality, siliceous sponge spicules are quite scarce in Vanport samples. Two graduate student projects during the 2000s, conducted at two different universities, had very different conclusions & interpretations about the origin of the Vanport Flint. A 2003 study concluded that chert at Flint Ridge is biogenic in origin. A 2006 study concluded that the chert is chemical in origin. Studies done by geologists at Ohio State University at Newark indicate that the Vanport Flint has a relatively complex history, the details of which are still being worked out. Modern flint knappers value the Vanport Flint for being multicolored and high-quality (= very few impurities). With artificial heating, the flint is more easily knapped into arrowheads, spear points, and other objects. Prehistoric American Indians quarried the Vanport Flint at many specific sites on Flint Ridge. Old Indian flint pits can be examined along hiking trails in Flint Ridge State Park ("State Memorial"). Many authentic Indian artifacts found in Ohio (arrowheads & spearpoints - "projectile points") are composed of Vanport Flint. The gray material in the above photo is relatively soft clay that occurs atop a flint meganodule of Vanport Flint at Nethers Flint Quarries. Above that (not visible here) is a weathered sandstone. The clay contains some slender modern roots and also has slickensides, indicating that this is a paleosol, specifically a vertisol. Vertisols are rich in "swelling clays" (= montmorillonite) that expand when wet and contract when dry. This volume change explains the slickensides, which represent slight differential displacement along fractures within the clay. A clay mineralogy analysis is currently being conducted on this material. The clay paleosol likely started forming well into the pre-Pleistocene. Flint Ridge is at a relatively high elevation and it escaped glacial erosion during the Pleistocene Ice Age. Stratigraphy: clay horizon immediately above the Vanport Flint, Allegheny Group, upper Middle Pennsylvanian Locality: Nethers Flint Quarries - flint pit in the woods on the southwestern side of Flint Ridge Road, eastern Flint Ridge, far-western Muskingum County, east-central Ohio, USA (GPS: 40° 00.137’ North latitude, 82° 11.544’ West longitude) |
Date | |
Source | Soft clay capping a flint meganodule (Vanport Flint, Middle Pennsylvanian; Nethers Flint Quarries, Flint Ridge, Ohio, USA) 1 |
Author | James St. John |
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This image was originally posted to Flickr by James St. John at https://flickr.com/photos/47445767@N05/30419933454. It was reviewed on 12 October 2019 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
12 October 2019
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current | 06:24, 12 October 2019 | ![]() | 4,000 × 3,000 (5.74 MB) | Ser Amantio di Nicolao (talk | contribs) | Transferred from Flickr via #flickr2commons |
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Camera manufacturer | Canon |
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Date and time of data generation | 12:13, 24 September 2016 |
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Image title | |
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Horizontal resolution | 180 dpi |
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Software used | Adobe Photoshop Elements 13.0 (Macintosh) |
File change date and time | 18:30, 25 November 2016 |
Y and C positioning | Co-sited |
Exif version | 2.21 |
Date and time of digitizing | 12:13, 24 September 2016 |
Meaning of each component |
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File source | Digital still camera |
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Exposure mode | Manual exposure |
White balance | Auto white balance |
Digital zoom ratio | 1 |
Scene capture type | Landscape |
Lens used | 6.2-18.6 mm |
Date metadata was last modified | 11:30, 25 November 2016 |
Unique ID of original document | 017054E41A38F2FEF6A2172AC4618F83 |