Article: The pre-depositional formation of some leaf impressions

Observations show that an inorganic sedimentary encrustation may be built up on plant leaves within a few weeks after entry into a depositional environment. Such an encrustation may be the basis of a detailed impression fossil. SEM examination and X-ray microanalysis of this encrustation on freeze-fractured, freeze-dried leaves reveals preferential deposition of fine-grained, iron-rich material that faithfully replicates the epidermal surface detail of the leaf. By analysis, fossil-leaf impressions from the Upper Cretaceous Dakota Sandstone of Kansas are shown to have a similar elemental composition. A possible biogenic origin for the surface encrustation is suggested.