Paleocurrent: Difference between revisions
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*''Bidirectional'', which give a good linear direction, but it is unclear which direction along the linear trend the water flowed. |
*''Bidirectional'', which give a good linear direction, but it is unclear which direction along the linear trend the water flowed. |
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Paleocurrents are usually measured with an [[azimuth]], or as a [[Rake (geology)|rake]] on a bedding plane, and displayed with a [[Pie_chart#Polar_Area_Pie_Chart|Rose Diagram]] to show the dominant direction(s) of flow. This is needed because in some depositional environments, like [[meandering river]]s, the paleocurrent resulting from natural sinuosity has a natural variation of 180 degrees or more.<ref> |
Paleocurrents are usually measured with an [[azimuth]], or as a [[Rake (geology)|rake]] on a bedding plane, and displayed with a [[Pie_chart#Polar_Area_Pie_Chart|Rose Diagram]] to show the dominant direction(s) of flow. This is needed because in some depositional environments, like [[meandering river]]s, the paleocurrent resulting from natural sinuosity has a natural variation of 180 degrees or more.<ref>{{Cite journal | last = Miaoa | first = Xiaodong |
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| authorlink = | coauthors = Huayu Lua, Zhen Lid and Guangchao Caod | title = Paleocurrent and fabric analyses of the imbricated fluvial gravel deposits in Huangshui Valley, the northeastern Tibetan Plateau, China | journal = Geomorphology | volume = 99 | issue = 1-4 | pages = 433-442 | publisher = © 2007 Elsevier B.V. | location = | date = July 2008 | url = | issn = | doi = 10.1016/j.geomorph.2007.12.005 | id = | accessdate = 9 January 2009}}</ref> |
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Below are a partial list of common paleocurrent indicators: |
Below are a partial list of common paleocurrent indicators: |
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Revision as of 00:05, 10 January 2010
A paleocurrent or paleocurrent indicator is a geological feature (typically a sedimentary structure) that helps one determine the direction of flowing water in the geologic past. This is an invaluable tool in the reconstruction of ancient depositional environments.[1]
There are two main types of paleocurrent indicators:
- Unidirectional, which give a clear, single direction of flow
- Bidirectional, which give a good linear direction, but it is unclear which direction along the linear trend the water flowed.
Paleocurrents are usually measured with an azimuth, or as a rake on a bedding plane, and displayed with a Rose Diagram to show the dominant direction(s) of flow. This is needed because in some depositional environments, like meandering rivers, the paleocurrent resulting from natural sinuosity has a natural variation of 180 degrees or more.[2]
Below are a partial list of common paleocurrent indicators:
Unidirectional
- Cross-bedding - the axis of a trough of a trough cross bed or the down-dip direction of a tabular cross bed point the direction of paleo flow.
- Current ripple marks - will have the short side of the ripple pointing down stream.
- Sole markings/flute casts - the short, steep side will point up steam, and the long, tapered side points down stream.
- Imbrication - clasts line up in the direction of flow.
Bidirectional
- Symmetrical ripple marks - flow is perpendicular to the ridge crest.
- Tool mark - flow is along the mark.
- Parting lineations - flow is along the grains.
References
- ^ Prothero, D. R. and Schwab, F., 1996, Sedimentary Geology, pg. 48-51, ISBN 0-7167-2726-9
- ^ Miaoa, Xiaodong (July 2008). "Paleocurrent and fabric analyses of the imbricated fluvial gravel deposits in Huangshui Valley, the northeastern Tibetan Plateau, China". Geomorphology. 99 (1–4). © 2007 Elsevier B.V.: 433–442. doi:10.1016/j.geomorph.2007.12.005.
{{cite journal}}:|access-date=requires|url=(help); Unknown parameter|coauthors=ignored (|author=suggested) (help)
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