File:Oncolitic limestone (Wirrapowie Limestone, Lower Cambrian; Mernmerna railroad bridge dry creek cut, South Australia) 3.jpg
![File:Oncolitic limestone (Wirrapowie Limestone, Lower Cambrian; Mernmerna railroad bridge dry creek cut, South Australia) 3.jpg](https://upload.wikimedia.org/wikipedia/commons/thumb/6/61/Oncolitic_limestone_%28Wirrapowie_Limestone%2C_Lower_Cambrian%3B_Mernmerna_railroad_bridge_dry_creek_cut%2C_South_Australia%29_3.jpg/800px-Oncolitic_limestone_%28Wirrapowie_Limestone%2C_Lower_Cambrian%3B_Mernmerna_railroad_bridge_dry_creek_cut%2C_South_Australia%29_3.jpg?20201027140048)
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[edit]DescriptionOncolitic limestone (Wirrapowie Limestone, Lower Cambrian; Mernmerna railroad bridge dry creek cut, South Australia) 3.jpg |
English: Oncolitic limestone in the Cambrian of South Australia.
Limestone is a biogenic sedimentary rock composed of the mineral calcite (CaCO3), which bubbles in acid. Many geologically young limestones are composed of aragonite (also CaCO3). Numerous varieties of limestone exist (e.g., fine-grained limestone/micritic limestone/lime mudstone, coquina, chalk, wackestone, packstone, grainstone, rudstone, rubblestone, coralstone, calcarenite, calcisiltite, calcilutite, calcirudite, floatstone, boundstone, framestone, oolitic limestone, oncolitic limestone, etc.). Most limestones represent deposition in ancient warm, shallow ocean environments. Oncolitic limestones have oncolites - macroscopic, concentrically layered, ~irregularly spheroidal masses of variable size. The oncolites are biogenic in origin - they grew in successive layers by the active or passive precipitation of calcium carbonate by cyanobacterial films (oncolites can be considered as mobile varieties of stromatolites). Oncolites are usually attributed to “algae”, and are often called “algal balls”. Referring to cyanobacteria as “algae” is a common error - they are frequently called “blue-green algae”. Cyanobacteria are photosynthetic, as algae are, but they are not algae. This oncolitic limestone is in a South Australian Lower Cambrian unit called the Wirrapowie Limestone. It consists of a fossiliferous limestone succession having archaeocyathans, trilobites, stromatolites, shell hash horizons, limestone conglomerates/intraclastic limestone breccias, and oncolitic limestones. Stratigraphy: Wirrapowie Limestone, Tommotian Stage to lower Atdabanian Stage, lower Lower Cambrian Locality of section: dry creek cut upstream from an abandoned railroad bridge at Mernmerna, South Australia (31° 34’ 25.30" South latitude, 138° 24’ 44.77" East longitude) |
Date | |
Source | https://www.flickr.com/photos/47445767@N05/49862253546/ |
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@N05/49862253546. It was reviewed on 27 October 2020 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
27 October 2020
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current | 14:00, 27 October 2020 | ![]() | 3,008 × 2,000 (4.63 MB) | Ser Amantio di Nicolao (talk | contribs) | Uploaded a work by James St. John from https://www.flickr.com/photos/47445767@N05/49862253546/ with UploadWizard |
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Camera manufacturer | NIKON CORPORATION |
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Date and time of data generation | 21:00, 18 August 2006 |
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Orientation | Normal |
Number of components | 3 |
Horizontal resolution | 300 dpi |
Vertical resolution | 300 dpi |
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File change date and time | 04:12, 6 May 2020 |
Y and C positioning | Co-sited |
Exposure Program | Not defined |
Exif version | 2.21 |
Date and time of digitizing | 21:00, 18 August 2006 |
Meaning of each component |
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APEX shutter speed | 7.643856 |
APEX aperture | 5.655638 |
APEX exposure bias | 0 |
Maximum land aperture | 4.3 APEX (f/4.44) |
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Sensing method | One-chip color area sensor |
File source | Digital still camera |
Scene type | A directly photographed image |
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White balance | Auto white balance |
Digital zoom ratio | 1 |
Focal length in 35 mm film | 105 mm |
Scene capture type | Standard |
Scene control | None |
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Lens used | 18.0-70.0 mm f/3.5-4.5 |
Date metadata was last modified | 00:12, 6 May 2020 |
Unique ID of original document | E153A99C15FB9F556BBE34D40A0AA345 |