Plate 91

Clustered flute casts

A vertical bedding plane is a vantage point for observing sole marks and their areal distribution on Ancient bottoms. In contrast to plate 90, flute casts have here a larger size and a flatter shape (as can be measured, in relative terms, by the ratio between width and depth), with broad, blunted noses.

Moreover, flutes tend to cluster in bands or stripes parallel to the paleocurrent; the depth of scouring is greater in these bands than in intervening areas. This suggests a hierarchy of erosional forms, with the flutes forming minor features of larger scours; you can find a similar relation in tractive bed forms, with ripples printed on the back of dunes and dunes superposed to larger forms.

Marnoso-arenacea Formation, northern Apennines, Montedella Faggiola.