Further experimental investigations on the formation of plant compression fossils

Abstract

Experimental work has been conducted on the formation of plant compression fossils using a simple compression apparatus in which actual plant material was compressed in wet sediment. Pressure was applied through a single perforated piston which only allowed the passage of water upwards out of the compacting sediment. Several lines of investigation were followed to establish the principal factors that dictate the form of a plant compression fossil. It is demonstrated that these include the grain size and the compressibility of the sediment, the degree of sediment fill of hollow structures within the plant organ prior to the compression, and finally the rigidity or degree of decay of the plant tissues before the deformation. The results of this work indicate that the horizontal dimensions of the plant organ change during compression. This is directly related to the compressibility of the sediment the plant was buried in; stems buried in clay matrices increased in horizontal dimensions, whereas stems buried in sand matrices underwent reductions in horizontal dimensions. This is associated with the difference in the response of these sediments to the hydrostatic stress that exists within the system during the initial stages of compaction. The results of this experimental study are used to interpret the structure and form of some plant compression fossils.