Paleocurrent
Encyclopedia
A paleocurrent or paleocurrent indicator is a geological feature (typically a sedimentary structure) that helps one determine the direction of flowing water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

 in the geologic past. This is an invaluable tool in the reconstruction of ancient depositional environments.

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
Rake (geology)
In structural geology rake is formally defined as "the angle between a line [or a feature] and the strike line of the plane in which it is found", measured on the plane. The three dimensional orientation of a line can be described with just a plunge and trend. The rake is a useful description of...

 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.

Below are a partial list of common paleocurrent indicators:

Unidirectional

  • Cross-bedding
    Cross-bedding
    In geology, the sedimentary structures known as cross-bedding refer to horizontal units that are internally composed of inclined layers. This is a case in geology in which the original depositional layering is tilted, and the tilting is not a result of post-depositional deformation...

     - the axis 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
    Sole markings
    Sole marks are sedimentary structures found on the bases of certain strata, that indicate small-scale grooves or irregularities. This usually occurs at the interface of two differing lithologies and/or grain sizes. They are commonly preserved as casts of these indents on the bottom of the...

    /flute casts - the short, steep side will point up steam, and the long, tapered side points down stream.

  • Imbrication
    Imbrication
    ' is the arrangement of planar bodies such that they stack in a consistent fashion - rather like a toppled run of dominoes.*In roofing, imbrication is employed in the Imbrex and tegula system.*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 lineation
    Parting lineation
    Parting lineation is a subtle sedimentary structure in which sand grains are aligned in parallel lines or grooves on the surface of a body of sand...

    s - flow is along the grains.
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