Article: The experimental formation of plant compression fossils

Despite the common occurrence of plant compression fossils, little experimental work has been done on the processes leading to their formation and their exposure by fracture. Models of the plant (in foam rubber) and the matrix (sawdust) systems have been subjected to deformation in an apparatus constructed so that the vertical plane can be kept under observation. The process of collapse and compression observed in vertical sections of plant fossils are more closely reproduced when the compression force acts through a number of free-moving pistons applied to the matrix than when a single larger piston is employed. The processes involved in the formation of compression fossils of Calamites, Lepidodendron, Stigmaria, and Sawdonia are explored and discussed. It is shown that the topography of a plant compression is governed not only by the structures revealed on the surface exposed, but by collapse of underlying plant tissue within the matrix. It is also demonstrated in lycopod leafy shoots that the fracture plane exposing the fossil is largely controlled by the angle between the bedding planes and the plant material.