A paleocurrent or paleocurrent indicator is a

geological Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Eart ...

feature (typically a

sedimentary structure Sedimentary structures include all kinds of features in sediments and sedimentary rocks, formed at the time of deposition. Sediments and sedimentary rocks are characterized by bedding, which occurs when layers of sediment, with different partic ...

) that helps one determine the direction of flowing

water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...

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

depositional environment In geology, depositional environment or sedimentary environment describes the combination of physical, chemical, and biological processes associated with the deposition of a particular type of sediment and, therefore, the rock types that will be ...

s. 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 An azimuth (; from ar, اَلسُّمُوت, as-sumūt, the directions) is an angular measurement in a spherical coordinate system. More specifically, it is the horizontal angle from a cardinal direction, most commonly north. Mathematicall ...

, 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 river A meander is one of a series of regular sinuous curves in the channel of a river or other watercourse. It is produced as a watercourse erodes the sediments of an outer, concave bank (cut bank) and deposits sediments on an inner, convex bank ...

s, 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 In geology, cross-bedding, also known as cross-stratification, is layering within a stratum and at an angle to the main bedding plane. The sedimentary structures which result are roughly horizontal units composed of inclined layers. The origina ...

– 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 mark In geology, ripple marks are sedimentary structures (i.e., bedforms of the lower flow regime) and indicate agitation by water (current or waves) or wind. Defining ripple cross-laminae and asymmetric ripples * ''Current ripple marks'', ''unidi ...

s – will have the short side of the ripple pointing down stream. *

Sole markings Sole marks are sedimentary structures found on the bases of certain strata, that indicate small-scale (usually on the order of centimetres) grooves or irregularities. This usually occurs at the interface of two differing lithologies and/or gra ...

flute cast Sole marks are sedimentary structures found on the bases of certain strata, that indicate small-scale (usually on the order of centimetres) grooves or irregularities. This usually occurs at the interface of two differing lithologies and/or grai ...

s – the short, steep side will point up stream, and the long, tapered side points down stream. * Imbrication – clasts line up in the direction of flow.

Bidirectional

*Symmetrical

s – flow is perpendicular to the ridge crest. *

Tool mark A tool is an object that can extend an individual's ability to modify features of the surrounding environment or help them accomplish a particular task. Although many animals use simple tools, only human beings, whose use of stone tools dates ba ...

– flow is along the mark. *

Parting lineation Parting lineation (also known as current lineation or primary current 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 (or lithified as a sandstone). The ori ...

s – flow is along the grains.

References

Sedimentology {{petrology-stub