Experimental studies of strati ® cation in a granular Hele ± S haw cell

We show that, when a mixture of small and large grains is simply poured in a g̀ranular Hele± Shaw cell’ (two transparent slabs separated by a gap of about 5mm), the grains spontaneously stratify in alternating layers of small and large grains parallel to the surface of the pile. The spontaneous self-strati® cation occurs only when the large grains have a larger angle of repose than the small grains do. Conversely, we obtain only spontaneous self-segregation, that is the large grains are found preferentially near the bottom of the cell while the small grains are found near the top, when the large grains have a smaller angle of repose than the small grains. The observed strati® cation might be of relevance to explain similar strati® ed patterns observed in Aeolian rocks. §