Plate 39

Cross-bedding in pyroclastic deposits

A quarry wall in Lipari (Eolian Archipelago) shows the bedding style of a thick accumulation of pumice fragments (pebble-size particles of whitish, light and very porous volcanic glass) interbedded with some finer ash layers. The ash drapes some bed forms, which are cut oblique to the main flow. Two dunoids in a row are visible at half height, with internal cross-laminae following a sygmoidal pattern. Other isolated forms, above and below, are back-scoured and resemble chute-and-pools (see also inset).

Scale is absent in the picture: the approximate thickness of lensoid beds is 20 to 40 cm., as inferred from more accessible outcrops nearby.