Figure 16. Transmitted reliefs and their effects on the preservation and appearance of sauropod footprints.

A, vertical section of thinly-layered substrate showing transmitted reliefs stacked beneath a sauropod footprint (natural mould). B, same example buried by influx of sediment which fills the footprint to form its natural cast. C, following lithification (transformation of soft wet sediments to hard dry rock), erosion to level of dotted line will produce the ‘onion-ring’ pattern which is characteristic of many sauropod footprints in the Broome Sandstone - a remnant of the natural cast encircled by the eroded edges of transmitted reliefs (Figures 3,15). D, the natural cast proves more durable than the surrounding rock, which is removed by erosion to leave a rock pillar - a stack of transmitted reliefs capped and protected by a remnant of the natural cast (Figures 5B,C and 21). Further erosion undercuts the upper part of the stack (red arrows). E, the upper part of the rock pillar breaks free and is rolled over by wave action, finally coming to rest on the beach as a ‘turtle-back’ boulder (Figures 18C,D).