Interpretation of tectonically deformed fossils

Abstract

Taxonomic information can be recovered from tectonically deformed fossils by analysing the strain and then restoring the fossils to their original shapes. Trilobites and graptolites are used as examples of two kinds of fossils—the first with known original angles and the second with a known original dimension. The first kind enables the shape and orientation of the strain ellipse to be determined; three graphical methods are outlined. The second kind enables, in addition, the actual strains in the bedding plane to be determined, and a method using graptolite thecal spacing is described. Best results for determining actual strains are obtained when both angles and dimensions are used, and a new method using graptolites is described. Five methods of restoring the original shape of fossils are briefly outlined.

Keywords:

• deformed fossils
• graptolites
• restoration
• strain analysis
• tectonic strain