Determination of Paleocurrent Direction from Oblique Sections of Trough Cross-Stratification--A Precise Approach

Abstract

The study of paleoflow patterns is an essential part of basin analysis. Cross-stratification, both planar and trough, is the principal directional structure used for paleocurrent analysis. Trough cross-stratification is especially characteristic of fluvial deposits, where it is typically formed by the primary current and correlates strongly with the flow direction (Harms and Fahnestock 1965; Wermund 1965; Williams 1968; Barrett 1970; McGowen and Garner 1970; Dott 1973; Michelson and Dott 1973; High and Picard 1974). The only exception, reported by Meckel (1967), is an artifact of an erroneous sampling technique (High and Picard 1974). However, the paucity of three-dimensional exposures of trough cross-strata that are suitable for direct measurement of trough axis orientations quite often hinders the systematic collection of paleocurrent data. With a view to overcoming this problem, attempts have been made to estimate paleoflow directions from two-dimensional exposures of trough cross-strata (Slingerland and Williams 1979; DeCelles et al. 1983), because they are much more common. Slingerland and Williams (1979) proposed two specific ways of determining the orientations of trough axes from two-dimensional exposures. According to their first method, a single strike measured on a trough side can be corrected to give the trough axial azimuth, with reference to the plunge of the trough measured from a quasi-three-dimensional exposure (Slingerland and Williams 1979, p. 731). The plunge direction itself (after necessary tilt correction), however, indicates the flow direction, and if it can be measured beyond doubt no further measurement of any other part of the trough is required. This kind of exposure is also not qualitatively very different from a three-dimensional one. The second method proposed by Slingerland and Williams (1979) involves estimation of the trough axial azimuth by measuring, on perfectly two-dimensional vertical exposures, the face azimuths and two …