A Classification of Paleocurrent Models

A number of regional paleocurrent patterns occur repeatedly in time and space. A series of models are proposed in an attempt to clarify these. Each model is defined by three parameters: environment (i.e., depositional process), azimuthal paleocurrent pattern at outcrop (i.e., unimodal, bimodal, or polymodal), and the relationship between paleocurrents and paleoslope. One fanglomerate model is proposed, two fluviatile, one eolian, six shore-line, and two turbidite models. Fanglomerates are characterized by unimodal downslope-directed radiating paleocurrents. Both fluviatile models have unimodal downslope paleocurrents. In one case these are arranged radially, in the second centripetally. Eolian paleocurrents may be unimodal, bimodal, or polymodal, and are unrelated to paleoslope. One eolian model is definable by relating wind direction to high-pressure air cells. Shore lines are characterized by bimodal paleocurrents attributable to tidal currents, though unimodal and polymodal patterns are also known. These are all unrelated to paleoslope. Six shore-line models are proposed based on the presence or absence of fluviatile currents and on whether marine currents are dominantly onshore, offshore, or alongshore. The two turbidite models both have unimodal paleocurrents. These may be arranged in small-scale downslope radiating fans. On a larger scale, lateral and axial infilling is common in many marine troughs, though the role of turbidity currents has been questioned. All the models proposed are illustrated by reference to examples from ancient and recent sediments. The problems of deducing current directions from sedimentary structures are discussed, together with the relationship between paleocurrents and paleoslopes. Exceptions to the general rule that currents flow downslope are prevalent in eolian and shore-line sediments and may also be significant in flysch deposits.