Date of Graduation

Spring 2017

Document Type

Honors Research Project

Degree Name

Bachelor of Science

Major

Geology

Research Sponsor

Dr. James Thomka

First Reader

Mr. John Beltz

Second Reader

Dr. Meagan Ankney

Abstract

Preservation of trace fossils (ichnofossils) in siliciclastic environments is often quite different from preservation in carbonate environments, representing an important source of variation that must be well understood in order to enhance interpretations of paleoenvironments and paleoecology. This study focuses on Conostichus, a relatively common burrow constructed by solitary sea anemones. These trace fossils are generally well-preserved (i.e., they display detailed external features) in siliciclastic rocks but are typically little more than conical masses in carbonate rocks. However, certain specimens recovered from the middle Silurian Massie Formation at the Napoleon quarry of southeastern Indiana are composed entirely out of carbonate mud but nevertheless preserve delicate features on the apical disk that have only been described previously from siliciclastic deposits. Specimens displaying typical carbonate-style preservation are also present in the same interval. This is interpreted as reflecting the fine grain size of sediment that passively infilled the well-preserved burrows, in contrast to the more poorly preserved burrows, which are filled with much coarser, skeletal grains. Further, specimens that are characterized by typical carbonate-style preservation contain a zoned infill, with coarser particles around the margin, preventing casting of delicate features. This indicates that grain size is a more important factor than sediment composition in preserving Conostichus at this locality. It is likely that other localities are also capable of producing siliciclastic-style preservation of trace fossils in carbonate environments.

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