Abstract

Textural inversion occurs in a red bed horizon of the Lower Jurassic Ardon Formation at Makhtesh Ramon. This texture consists of highly spherical, well rounded very well-sorted, coarse quartz grains, dispersed within an argillaceous silty micrite. The former is indicative of high energy sedimentation while the latter is believed to represent a low energy environment of deposition. Negative skewness values (-0.172), together with low values of standard deviation, (0.345 phi ) suggest a beach environment for the dispersed quartz gram phase. Surface textural features of these grains, studied under the scanning electron microscope suggest the influence of aeolian activity in a previous cycle of sedimentation. Mixing of the two texturally differing quartz grain populations was demonstrated by the bimodality of grain size within the suspension sub-population occurring at 2.25 phi . A bimodility in grain shape, determined by electron microscopy in the 2.25 phi grain size fraction, further highlights the mixing of the two quartz populations. Mixing of barrier beach sediments by storm and high wave activity into free grained lagoonal sediments is postulated for the origin of the textural inversion.

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